AnimationPlayer
This animation shows the passage of allergens (pollen) into the nasal cavity. The body response includes the release of histamine, a chemical that produces allergy symptoms in the body.  Launch animation
AnimationPlayer
This animation shows the brain and the changes that occur to it from Alzheimer's disease.  Launch animation
AnimationPlayer
This animation illustrates and compares the severity of an ankle sprain (Type I, II, III).  Launch animation
AnimationPlayer
This animation shows the cardiac conduction system and the arrhythmias of a fast and slow beating heart.  Launch animation
AnimationPlayer
This animation illustrates the location of basal ganglia in the brain. Injury to the basal ganglia may result in athetosis (constant writhing movements of the body).  Launch animation
AnimationPlayer
This animation shows the use of balloon angioplasty to open a narrowed coronary artery lumen caused by deposits of plaque.  Launch animation
AnimationPlayer
This animation shows the neurological control of normal bladder function.  Launch animation
AnimationPlayer
This animation shows the eye’s response to invading foreign substances, resulting in blinking and the lacrimal gland’s production of tears which then pass into the nose through tear ducts.  Launch animation
AnimationPlayer
This animation depicts the process of blood clotting in an enlarged view of a small artery. Cells shown include red blood cells, platelets, fibrin, and clotting factors.  Launch animation
AnimationPlayer
This animation shows the cycle of blood circulation through the heart, arteries, veins, and lungs within the body.  Launch animation
AnimationPlayer
This animation defines normal blood pressure and the measurement of systole and diastole. Structures shown include a front-view of the heart beating, a cut-view of the heart beating, and blood flowing through a small artery.  Launch animation
AnimationPlayer
This animation shows one method in which a severe wrist fracture is treated by inserting a bone graft from the hip followed by fixation with a metal plate and screws.  Launch animation
AnimationPlayer
This interactive animation takes you on a 3-D journey to explore the anatomy of the brain. Rotate the brain or pick from a list of terms to identify various structures.  Launch animation
AnimationPlayer
This animation highlights the major sections of the brain and explains their primary functions.  Launch animation
AnimationPlayer
This animation shows a breast reduction (lift) procedure.  Launch animation
AnimationPlayer
This animation illustrates the major structures of the respiratory system and shows the mechanism of breathing (respiration).  Launch animation
AnimationPlayer
This animation shows the formation of a bunion.  Launch animation
AnimationPlayer
From a top view of the voice box (larynx) and vocal cords, this animation shows the formation of a malignant tumor on the right vocal cord.  Launch animation
AnimationPlayer
This animation illustrates the cardiac conduction system, a group of specialized muscle cells that signal the rest of the heart to contract. An ECG tracing is shown in tandem with a normal heart beat.  Launch animation
AnimationPlayer
This animation shows a catheter being inserted into the heart where alcohol is injected causing the swollen ventricle wall to shrink.  Launch animation
AnimationPlayer
This animation displays a normal heart beating. Also shown are red blood cells traveling through an enlarged cut-section of a small artery and the percentage of the blood’s components.  Launch animation
AnimationPlayer
This animations depicts how a cataract is seen in the eye.  Launch animation
AnimationPlayer
This animation traces the growth and migration of a fertilized egg cell through the fallopian tubes to the uterine lining. Enlarged views show the action of cilia in the fallopian tube transporting the egg and its implantation into the uterine lining.  Launch animation
AnimationPlayer
This animation shows a cerebral aneurysm growing and rupturing filling the brain with blood.  Launch animation
AnimationPlayer
This interactive animation shows the process of cervical dilation during labor.  Launch animation
AnimationPlayer
This animation describes and depicts the common reasons for having a cesarean section delivery. The location of an epideral application is shown in a side view followed by a Cesarean section delivery illustrated in both side and front views.  Launch animation
AnimationPlayer
This animation shows an enlarged view of a section of skin, highlighting its layers and various structures.  Launch animation
AnimationPlayer
This animation shows the process of conception in which a sperm unites with an egg cell to form a fertilized egg.  Launch animation
AnimationPlayer
This interactive animation takes you on a journey through the female reproductive system to see the processes of ovulation, fertilization and implantation of a fertilized egg (zygote).  Launch animation
AnimationPlayer
This animation shows the process in which an egg cell is fertilized by a sperm cell to form a fertilized egg (zygote).  Launch animation
AnimationPlayer
In a microscopic view, this animations shows the conception of identical (maternal) twins.  Launch animation
AnimationPlayer
This animations shows the head receiving two impacts. One on the front, and one on the side from a boxing glove.  Launch animation
AnimationPlayer
This animation shows corneal infections resulting from corneal injury.  Launch animation
AnimationPlayer
This animation shows a coronary artery bypass graft (CABG) procedure in which a portion of vein is grafted on the heart to reroute blood from a blocked section of a coronary artery.  Launch animation
AnimationPlayer
Shown in an enlarged view of a damaged coronary artery is the build-up of plaque and restriction of blood flow, progressing to complete arterial blockage and heart muscle ischemia (heart attack). Anteriorly, a normal heart beating is also illustrated.  Launch animation
AnimationPlayer
This animation describes a series of cosmetic surgeries, including forehead lift, eyelid lift, and facelift.  Launch animation
AnimationPlayer
This animation shows the mechanism of coughing caused by an irritant entering the windpipe (larynx), resulting in its dislodgement. The steps of the coughing reflex are shown from a side view of the body in tandem with a top view of the vocal cords.  Launch animation
AnimationPlayer
This animations depicts changes to the retina resulting from diabetes mellitus.  Launch animation
AnimationPlayer
This animation highlights the major parts of the digestive system and follows the breakdown of celery from consumption to excretion.  Launch animation
AnimationPlayer
This animation shows a Directional Coronary Atherectomy (DCA) procedure performed to remove the blockage from the coronary arteries by a tiny spinning cutter that slices away plaque lesions and stores them to be withdrawn.  Launch animation
AnimationPlayer
This interactive animation takes you on a 3-D journey to explore the anatomy of the ear. Rotate the ear or pick from a list of terms to identify various structures.  Launch animation
AnimationPlayer
This animation shows the signs of the first phase of labor (early labor).  Launch animation
AnimationPlayer
This animation depicts the maturation of egg cells within ovary and illustrates the role of hormones in menstruation and egg cell fertilization and implantation.  Launch animation
AnimationPlayer
This animation illustrates the development cycle of an egg in an ovary and the sequence of events to fertilization of the egg or not.  Launch animation
AnimationPlayer
An electrocardiogram (ECG) enables the rhythm of the heart to be viewed in waveform. This interactive animation shows the ECG waveforms for normal sinus rhythm and various conditions of the heart.  Launch animation
AnimationPlayer
This animation illustrates the glands of the endocrine system, specifically enlarging the pituitary gland, thyroid gland, parathyroid glands, thymus, adrenal glands, and pancreas. A communication path within the neuroendocrine system is also shown.  Launch animation
AnimationPlayer
This animation illustrates the prostate gland and its surrounding structures and shows the effects of benign prostatic hypertrophy (BPH).  Launch animation
AnimationPlayer
This animation illustrates the prostate gland and its surrounding structures and shows the effects of benign prostatic hypertrophy (BPH).  Launch animation
AnimationPlayer
This animation shows the release of epinephrine and its effect of the heart.  Launch animation
AnimationPlayer
This animation gives a general comparison between anaerobic exercise (lifting weights) and aerobic exercise (jogging).  Launch animation
AnimationPlayer
This interactive animation takes you on a 3-D journey to explore the anatomy of the eye. Rotate the eye or pick from a list of terms to identify various structures.  Launch animation
AnimationPlayer
This animation shows the body’s response to a bee sting on the nose, giving a general description of the communication between the peripheral nervous system detecting the pain and the central nervous system issuing a reactive response.  Launch animation
AnimationPlayer
This interactive animation takes you on a 3-D journey to explore the anatomy of the female reproductive system. Rotate to or pick from a list of terms to identify various structures of the system.  Launch animation
AnimationPlayer
Creating a new life is nothing short of a miracle. With the fetal development interactive tool, you can get an insider's view of a baby in the making - from conception to term. You can watch the entire development, specify portions of the pregnancy, or freeze the frame on a specific week by dragging the slider bars back and forth.  Launch animation
AnimationPlayer
This animation illustrates the development of a baby’s outer ear from its embryonic origins. Structures of a baby’s middle and inner ear are also shown from the front view.  Launch animation
AnimationPlayer
This animation shows the differences between the development of a single baby, identical twins, and non-identical twins.  Launch animation
AnimationPlayer
This animation illustrates the passage of air and exchange of oxygen and carbon dioxide within the lungs on both a gross and microscopic level.  Launch animation
AnimationPlayer
This animation shows the affects of untreated glaucoma.  Launch animation
AnimationPlayer
This animation shows uric acid crystals moving to the big toe joint causing pain.  Launch animation
AnimationPlayer
Through a series of magnifications of the ear, this animation depicts the movement, amplification, translation, and interpretation of sound waves traveling through the ear’s three regions, ultimately becoming neural messages sent to the brain.  Launch animation
AnimationPlayer
This animation shows the various structures of the ear and the process of hearing.  Launch animation
AnimationPlayer
This interactive animation takes you on a 3-D journey to explore the anatomy of the heart. Rotate the heart, view in transparent mode, or pick from a list of terms to take you to various structures.  Launch animation
AnimationPlayer
This animation shows the procedure of a heart bypass surgery.  Launch animation
AnimationPlayer
This animation shows the development of the fetal heart from day 18 to day 57. A functional comparison is made between a fetal and newborn heart.  Launch animation
AnimationPlayer
This animation follows the passage of blood through the heart’s chambers and valves.  Launch animation
AnimationPlayer
This animation depicts how certain ingested foods can cause regurgitation of the stomach’s contents back into the esophagus resulting in the sensation of heartburn. The relationship between the location of the esophagus and heart is shown in a front view of the body.  Launch animation
AnimationPlayer
This animation shows displacement of an intervertebral disk (disk between the vertebrae).  Launch animation
AnimationPlayer
This animation depicts the process of maintaining homeostasis in the body through hormonal negative feedback mechanisms. An analogy is made between thermostat temperature regulation in a home to the hormonal control of sugar levels within the bloodstream.  Launch animation
AnimationPlayer
This animation shows the formation of a fetal face during the early weeks of development.  Launch animation
AnimationPlayer
This animation shows the effects of hypertension on a cerebral artery.  Launch animation
AnimationPlayer
This animation shows an enlarged view of femoral bone marrow containing immature specialized white blood cells (lymphocytes) and depicts their maturation and migration into either B cell or T cell lymphocytes.  Launch animation
AnimationPlayer
This animations shows the process of Intracytoplasmic sperm injection (ICSI), a procedure used to fertilize an egg cell outside of the body.  Launch animation
AnimationPlayer
This animation begins with an front view of the urinary tract and continues with the formation of kidney stones shown in a cut-section of the kidney. Severities of kidney stones are depicted, demonstrating various degrees of urine obstruction.  Launch animation
AnimationPlayer
This animation gives a cartooned comical view of birth through a vaginal delivery.  Launch animation
AnimationPlayer
Illustrated for a child’s perspective, this animation depicts the growth of a baby within a uterus from the first month to the ninth month of pregnancy.  Launch animation
AnimationPlayer
Illustrated for a child’s perspective, this cartooned animation explains the sperm’s role in determining if a baby will be a girl or a boy.  Launch animation
AnimationPlayer
Illustrated for a child’s perspective, this cartooned animation explains how food and air are supplied from the mother to the baby through it's umbilical cord.  Launch animation
AnimationPlayer
Created for a child’s perspective, this cartooned animation illustrates the appearance and origin of a sperm cell and egg cell as well as the development of a baby within the uterus.  Launch animation
AnimationPlayer
A vibrating suction cannula is shown removing abdominal fat.  Launch animation
AnimationPlayer
This interactive animation takes you on a 3-D journey to explore the anatomy of the lungs. Rotate the lungs view in transparent mode, or pick from a list of terms to take you to various structures of the lungs.  Launch animation
AnimationPlayer
This animation shows an enlarged view of one lymph node filtering out micro-organisms from the fluid passing through.  Launch animation
AnimationPlayer
This animation discusses and depicts several aspects of the lymphatic system including a microscopic view of lymph formation, edema, breast lymphatics and the spread of breast cancer.  Launch animation
AnimationPlayer
This animation shows the process of macular degeneration in the eye.  Launch animation
AnimationPlayer
This interactive animation takes you on a 3-D journey to explore the anatomy of the male reproductive system. Rotate to or pick from a list of terms to identify various structures of the system.  Launch animation
AnimationPlayer
This interactive animation shows the changes that occur during the menstrual cycle to hormone levels, body temperature, an ovary, and lining of the uterus.  Launch animation
AnimationPlayer
This animation discusses the four functions of muscle and displays the three different types of muscle tissue in external and microscopic views.  Launch animation
AnimationPlayer
This animation provides a general overview of the nervous system and shows the process in which nerve impulses are transmitted.  Launch animation
AnimationPlayer
This animation shows the early formation of the nervous system.  Launch animation
AnimationPlayer
This animation shows an enlargement of a blood capillary with red blood cells traversing through it. A section of the artery is enlarged further to display the exchange of oxygen and carbon dioxide between a capillary and its surrounding tissue.  Launch animation
AnimationPlayer
This animation compares the a normal adult knee joint and a knee joint affected by osteoarthritis.  Launch animation
AnimationPlayer
This animation begins by showing a hip fracture due to osteoporosis (fracture in neck of the femur, anterior view). The bone then dissolves into a frontal section to compare the bony interior of a normal femur to that of an osteoporotic femur.  Launch animation
AnimationPlayer
This animations shows the process of ovulation (the release a single egg cell from an ovary).  Launch animation
AnimationPlayer
This animations shows sporatic brain activity and a twitching hand that occur with Parkinson's disease, followed by treatment with dopamine stimulation.  Launch animation
AnimationPlayer
This animation shows a Percutaneous Transluminal Coronary Angioplasty (PTCA) procedure to open up blocked coronary arteries by inflating a tiny balloon to compress the plaque against the walls of the artery, flattening it out so that blood can once again flow through the blood vessel freely.  Launch animation
AnimationPlayer
This animation follows the processing of food through the digestive tract, focusing on the intestinal peristaltic movement (a series of wave-like muscle contractions that moves the food mixture down the digestive tract).  Launch animation
AnimationPlayer
This animation shows the process of a macrophage ingesting a foreign substance.  Launch animation
AnimationPlayer
This animation describes the regulation of the pituitary gland and the hormones it releases to regulate various organs and processes in the body.  Launch animation
AnimationPlayer
This animation illustrates the delivery of the placenta by strong uterine contractions and gentle abdominal pressure applied by a physician.  Launch animation
AnimationPlayer
This animation illustrate the formation of the placenta and blood barrier and their role in providing the embryo with nutrients and oxygen, removing waste products, and preventing harmful substance from entering in.  Launch animation
AnimationPlayer
This animation depicts hypertension caused by pre-eclampsia that adversely affects the fetus by causing constriction of the placental arteries.  Launch animation
AnimationPlayer
This animation illustrates the development cycle of an egg in an ovary and the sequence of events to fertilization of the egg or not.  Launch animation
AnimationPlayer
This animation shows the process of red blood cell formation and the components that comprise blood.  Launch animation
AnimationPlayer
This animation shows the body’s reflex response to a hot substance landing on the hand.  Launch animation
AnimationPlayer
This animation shows the process in which light is transformed by the retina as electical impulses that travel to the brain through the optic nerve.  Launch animation
AnimationPlayer
This animation shows a retinal detachment injury.  Launch animation
AnimationPlayer
In a side view of the body with the baby in utero, the mucous plug (bloody show) is illustrated followed by the rupturing of the amniotic sac (water breaking), indicating the onset of labor.  Launch animation
AnimationPlayer
This animation illustrates the various structures of the eye and how the shape of the eye affects vision (nearsightedness and farsightedness).  Launch animation
AnimationPlayer
This animation illustrates the development of the external sex organs in a female and male fetus.  Launch animation
AnimationPlayer
This animation shows a dislocation of the shoulder joint.  Launch animation
AnimationPlayer
This animation details the components of the fetal skeletal system and illustrates the process of bone development through ossification of the membranes and cartilage.  Launch animation
AnimationPlayer
This animation illustrates the organization of skeletal muscle, enlarging from a muscle belly up to its myofibrils. Simultaneously in side and front views, the actions of a leg muscle and its myofibrils are shown while performing leg extension exercises.  Launch animation
AnimationPlayer
This animation highlights the individual bones and groups of bones that comprise the skeletal system.  Launch animation
AnimationPlayer
This animation illustrates some common skin conditions such as moles, birthmarks, age spots, and warts.  Launch animation
AnimationPlayer
This interactive animation takes you on a 3-D journey to explore the anatomy of the skull. Rotate the skull, see it in an exploded view, or pick from a list of terms to identify its various structures.  Launch animation
AnimationPlayer
This animation depicts the inhalation of air and scent molecules from a rose into an enlarged sagittal view of the nasal cavity. The smell receptors are magnified further to show their action of relaying a neural message of “scent” to the brain.  Launch animation
AnimationPlayer
Normal, healthy lungs are compared to the lungs of a long-term smoker.  Launch animation
AnimationPlayer
From a side view of the head and neck, this animation shows the structures involved in snoring. The common causes for snoring are also discussed  Launch animation
AnimationPlayer
This animation highlights the structures of the male reproductive system and the pathway of ejaculate. A testicle is sectioned and enlarged to depict its internal anatomy, including a microscopic view of individual sperm.  Launch animation
AnimationPlayer
This animation highlights from a mid-sagittal view the structures of the male reproductive system and the pathway of ejaculate. A testicle is sectioned and enlarged to depict its internal anatomy, including a microscopic view of individual sperm.  Launch animation
AnimationPlayer
This animation shows a stomach ulcer forming and then reducing in size as it heals.  Launch animation
AnimationPlayer
This animation shows a stroke resulting by an embolism traveling from an internal carotid artery and lodging within a cerebral artery in the brain  Launch animation
AnimationPlayer
This animations shows a piece of clot breaking away from the heart, travelling to the brain, resulting in a stroke.  Launch animation
AnimationPlayer
This animation enlarges a section of skin to illustrate melanocytes producing melanin in response to sun exposure. Also depicted on this enlarged section is sunburn and skin cancer.  Launch animation
AnimationPlayer
From a side view of the head, this animation shows the step-by-step process and mechanism of chewing and swallowing a piece of celery.  Launch animation
AnimationPlayer
This animation shows an enlargement of a section of skin to highlight an individual sweat gland. The gland then expels sweat onto the surface of skin.  Launch animation
AnimationPlayer
This animation shows a heart with tachycardia.  Launch animation
AnimationPlayer
This animation begins with a top view of the tongue then magnifies and shows two individual taste buds detecting taste molecules. The various taste centers (bitter, sour, sweet, and salty) are highlighted on the tongue.  Launch animation
AnimationPlayer
This animation discusses and depicts the role and function of the amniotic fluid surrounding a fetus.  Launch animation
AnimationPlayer
This animation shows the difference between a smoker's and non-smoker's artery  Launch animation
AnimationPlayer
This animation depicts Twin to Twin Transfusion Syndrome (TTTS) and the use of laser surgery to correct the condition.  Launch animation
AnimationPlayer
From an front view of the stomach, this animation shows the development of an ulcer in the stomach lining.  Launch animation
AnimationPlayer
This animation demonstrates how an ultrasound identifies the solid and hollow areas of structures within a fetus.  Launch animation
AnimationPlayer
This interactive animation enables you to visualize how a fetus may appear at 17, 19, and 30 weeks by enabling you to toggling a flat ultrasound image with an illustration of the baby's actual position.  Launch animation
AnimationPlayer
In a general overview, the formation and passage of urine through the various components of the urinary system is shown. Enlarged areas include the kidney, sectioned kidney, nephrons, renal corpuscle, and passage of particles and red blood cells within.  Launch animation
AnimationPlayer
In an enlarged view of a cut section of a small artery, this animation shows a vaccine injection and follows the path of its antigens, initiating the body's development of antibodies.  Launch animation
AnimationPlayer
This animation shows the process of a normal vaginal delivery.  Launch animation
AnimationPlayer
This animation shows a vasectomy procedure.  Launch animation
AnimationPlayer
Allergens like pollen are nothing more than foreign plant antigens. The stimulus for sneezing gets triggered when allergens first enter the nasal tissue. Pollen allergens encounter the plasma cells in the nose, which respond by producing antibodies. These antibodies attach to mast cells, which are white blood cells containing the chemical histamine. As more antibodies are produced, they cause the mast cells to release histamine. Histamine then produces allergy symptoms. A stuffy and runny nose, sneezing and watery eyes help to remove the invading pollen. Medications called antihistamines may be used to help alleviate severe allergy symptoms. In a person with Alzheimer's Disease, neurofibrillary tangles and plaques develop causing both structural and chemical problems in the brain. Alzheimer's disease appears to disconnect areas of the brain that normally work together.

An ankle sprain occurs when the joint’s ligament is stretched or torn. Ligaments are bands or sheets of regular, tough fibrous tissue that connect bones together. Symptoms of an ankle sprain include swelling and discoloration near the affected area. Ankle sprains may be classified as follows:

• Type I sprain – ligaments stretched

• Type II sprain – ligaments slightly torn

• Type III sprain – ligaments completely torn

Treatment for a Type I sprain should include rest, ice, compression and immobilization, and elevation of the affected area. This is easy to remember if you think of the acronym RICE. If you suspect a ligament is torn or completely severed, see your medical care professional for treatment.

A change in the heart's normal electrical conduction system can result in an arrhythmia or irregular heartbeat. An arrhythmia can be an abnormally slow heartbeat, or an abnormally fast heartbeat. In some cases, it can be fatal. Athetosis, or constant writhing movements, is often caused by injury to deeply situated structures with the brain called basal ganglia. Angioplasty is a procedure to open narrowed or blocked arteries caused by deposits of plaque. If the blockage is not major, the problem may be corrected by inflating the balloon several times to compact the plaque against the arterial wall, widening the passage for the blood to flow through. Typically, a device called a stent is placed within the coronary artery to keep the vessel open. When the bladder fills with urine, sensory nerves send impulses to the brain indicating that the bladder is full. The sensory nerves connect with other nerves in the spinal cord to relay this information. In turn, the brain sends impulses back to the bladder instructing the bladder to empty its contents.

The nervous system enables a person to blink to prevent harmful substances from getting in the eyes. During the normal course of a day, a person blinks an average of 15 times a minute to keep the eyes healthy. The lacrimal gland provides lubricating fluid for the eyes. The eyelid moves fluid from the lacrimal gland and across the eye. Blinking also provides the eyes with protection from foreign objects.

When the eye becomes irritated, the lacrimal gland produces extra tears to wash out impurities. Excess fluid drains through the tear ducts and into the nasal cavity. An abundance of tears draining through the nasal cavity may cause the nose to run and a person to sniffle.

The body contains a natural process to stop bleeding from minor cuts in a matter of several minutes. When a small artery is cut, the collagen fibers in its tissue are exposed, which signals clotting process to begin. As platelets begin to adhere to the cut edges, they release chemicals to attract even more platelets. Eventually a platelet plug is formed, and the external bleeding stops. Clotting factors in the blood cause strands of blood-borne material, called fibrin, to stick together and seal the inside of the wound. Eventually, the cut blood vessel heals, and the blood clot dissolves after several days. As the heart pumps, the arteries carry oxygen-rich blood (shown in red) away from the heart and toward the body’s tissues and vital organs. These include the brain, liver, kidneys, stomach, and muscles, including the heart muscle itself. At the same time, the veins carry oxygen-poor blood (shown in blue) from the tissues back toward the heart. From there, it passes to the lungs to receive more oxygen. This cycle repeats itself when oxygen-rich blood returns to the heart from the lungs, which pumps it throughout the body. Normal blood pressure is important for proper blood flow to the body’s organs and tissues. Blood pressure moves from high pressure near the heart to low pressure away from the heart. The force of the blood on the walls of the arteries is called blood pressure. Blood pressure is measured both as the heart contracts, which is called systole, and as it relaxes, which is called diastole. Normal blood pressure is considered to be a systolic blood pressure of 115 millimeters of mercury a diastolic pressure of 70 millimeters of mercury (stated as "115 over 70"). If an individual were to have a consistent blood pressure reading of 140 over 90, he would be evaluated for having high blood pressure. If left untreated, high blood pressure can damage important organs, such as the brain and kidneys as well as lead to a stroke. If a bone fracture is severe, a bone graft may be used to help speed the healing process. In this example, a metal plate is also used and fixated with screws. The plate and screws will be removed after the bone has healed.

After the animation loads, click and drag the model to rotate it in any direction. Select a term from the structure list to travel to its location.

Click the "pin" button to hide or show the identification pin.

Click the "light bulb" button to view in highlight or full color mode.

Click the "double box" button to see and rotate the model in transparent mode.

The brain is composed of more than a thousand million neurons. Specific groups of them, working in concert, provide us with the capacity to reason, to experience feelings, and to understand the world. They also give us the capacity to remember numerous pieces of information.

The 3 major components of the brain are the cerebrum, cerebellum, and brain stem.

The cerebrum is divided into is left and right hemispheres, each composed of a frontal, temporal, parietal, and occipital lobes. The cerebral cortex (gray matter) is the outside portion of the cerebrum and provides us with functions associated with conscious thought. The grooves and folds increase the cerebrum’s surface area, allowing us to have a tremendous amount of gray matter inside of the skull. Deep to the gray matter is the cerebral "white matter". The white matter provides for the communication between the cortex and lower central nervous system centers.

The cerebellum is located near the base of the head. It creates automatic programs so we can make complex movements without thinking.

The brain stem connects the brain with the spinal cord and is composed of 3 structures: the midbrain, pons, and medulla oblongata. The brain stem provides us with automatic functions that are necessary for survival.

In a breast lift or breast reduction procedure, incisions are made to accommodate a higher position for the areola and nipple, as well as to remove excess skin and breast tissue. Stitches usually follow the circumference of the areola, the natural lower crease of the breast, and a vertical line extending between the areola and lower crease.

The two lungs are the primary organs of the respiratory system. Other components of the respiratory system conduct air to the lungs, such as the trachea (windpipe) which branches into smaller structures called bronchi.

The process of breathing (respiration) is divided into two distinct phases, inspiration (inhalation) and expiration (exhalation). During inspiration, the diaphragm contracts and pulls downward while the muscles between the ribs contract and pull upward. This increases the size of the thoracic cavity and decreases the pressure inside. As a result, air rushes in and fills the lungs.

During expiration, the diaphragm relaxes, and the volume of the thoracic cavity decreases, while the pressure within it increases. As a result, the lungs contract and air is forced out.

Bunions are usually caused by prolonged pressure put on the feet that compresses the big toe and pushes it toward the second toe. Over time, the condition may become painful as extra bone grows where the base of the big toe meets the foot. Malignant tumors of the vocal cords are typically caused by tobacco use. The cardiac conduction system is a group of specialized cardiac muscle cells in the walls of the heart that send signals to the heart muscle causing it to contract. The main components of the cardiac conduction system are the SA node, AV node, bundle of HIS, bundle branches, and Purkinje fibers. The SA node (anatomical pacemaker) starts the sequence by causing the atrial muscles to contract. From there, the signal travels to the AV node, through the bundle of HIS, down the bundle branches, and through the Purkinje fibers, causing the ventricles to contract. This signal creates an electrical current that can be seen on a graph called an Electrocardiogram (EKG or ECG). Doctors use an EKG to monitor the cardiac conduction system’s electrical activity in the heart. In this case of cardiomyopathy, part of the septum dividing the ventricles, is interfering with the normal emptying of the left ventricle. This is one variety of the condition called hypertrophic obstructive cardiomyopathy (HOCM). A catheter is introduced into the heart and through it, concentrated alcohol is applied to the abnormal area, shrinking it, allowing the heart to function normally. The cardiovascular system is composed of the heart and the network of arteries, veins, and capillaries that transport blood throughout the body. The average adult male has between 5 to 6 liters of blood or blood volume, while the average adult female has between 4 to 5 liters. The blood carries oxygen and essential nutrients to all of the living cells in the body, and also carries waste products from the tissues to the systems of the body through which they are eliminated.

Most of the blood is made up of a watery, protein-laden fluid called plasma. A little less than half of this blood volume is composed of red and white blood cells, and other solid elements called platelets. Cataracts may develop with advancing age or in response to diseases such as diabetes. A cataract appears as a cloudy area in the lens. During the first 12 hours after conception, the fertilized egg cell remains a single cell. After approximately 30 hours, it divides from 1 cell into 2 and 15 hours later, the 2 cells divide into 4. And at the end of 3 days, the fertilized egg cell has become a berry-like structure made up of 16 cells. This structure is called a morula, which is Latin for mulberry.

The cells continue to divide 8 or 9 days following conception into a blastocyst. Although it is only the size of a pinhead, the blastocyst is composed of hundreds of cells. The blastocyst is slowly carried by tiny hair-like projections in the fallopian tube called cilia toward the uterus. During the critically important process of implantation, it must attach itself to the uterine lining where it will be able to get nourishment from the mother’s blood supply. If the blastocyst is unable to attach, the pregnancy will fail to survive. The tissue of the brain is supplied by a network of cerebral arteries. If the wall of a cerebral artery becomes weakened, a portion of the wall may balloon out forming an aneurysm. A cerebral aneurysm may enlarge until is bursts, sending blood throughout the spaces in or surrounding the brain. Click and drag the slider bar to see the various stages of cervical dilation between 0 and 10 cm. Although Cesarean (C-sections) are relatively safe surgical procedures, they should only be performed in appropriate medical circumstances. Some of the most common reasons for a Cesarean are:

· If the baby is in a feet first (breech) position · If the baby is in a shoulder first (transverse) position · If the baby’s head is too large to fit through the birth canal · If labor is prolonged and the mother’s cervix will not dilate to 10 centimeters · If the mother has placenta previa, where the placenta is blocking the birth canal · If there are signs of fetal distress which is when the fetus is in danger because of decreased oxygen flow to the fetus

Some common causes of fetal distress are: · Compression of the umbilical cord · Compression of major blood vessels in the mother’s abdomen because of her birthing position · Maternal illness due to hypertension, anemia, or heart disease

Like many surgical procedures, Cesarean sections require anesthesia. Usually, the mother is given an epidural or a spinal block. Both of these will numb the lower body, but the mother will remain awake. If the baby has to be delivered quickly, as in an emergency, the mother may be given a general anesthetic, which will make her fall asleep.

During the surgery, an incision is made in the lower abdomen followed by an incision made in the uterus. There is no pain associated with either of these incisions because of the anesthesia. Once the uterus is open, the doctor will let the amniotic fluid drain from the amniotic sac. Then the baby is carefully eased through the incision and out into the world. The procedure usually lasts about ten minutes.

Afterward, the physician delivers the placenta and stitches up the incisions in the uterus and abdominal wall. Usually, the mother is allowed to leave the hospital within a week, barring complications. Skin is the body’s largest organ. About six pounds of skin cover eighteen square feet on an average adult.

The top layer of skin is called the epidermis. It protects the underlying skin layers from the outside environment and contains cells that make keratin, a substance that waterproofs and strengthens the skin. The epidermis also has cells that contain melanin, the dark pigment that gives skin its color. Other cells in the epidermis allow us to feel the sensation of touch and provide the body with immunity against foreign invaders like germs and bacteria.

The very bottom layer of the skin is the hypodermis. It contains the fat cells, or adipose tissue, that insulate the body and help it conserve heat. The layer between the epidermis and the hypodermis is the dermis. It contains the cells that give skin strength, support, and flexibility. As a person ages, the cells in the dermis lose their strength and flexibility, causing the skin to lose its youthful appearance.

Located in the dermis are sensory receptors. They allow the body to receive stimulation from the outside environment and experience pressure, pain, and temperature. Small blood vessels provide the skin with nutrients, and remove its waste products.

Sebaceous glands produce the oil in the skin, which keeps it from drying out. The oil from the sebaceous glands also helps to soften hair and kill bacteria that get in the skin’s pores. These oil glands are all over the body, except on the palms of the hands and the soles of the feet.

During intercourse, sperm are released into the vagina near the cervix, swim through the uterus and travel up the fallopian tubes. Sperm are composed of 3 parts: a head, a middle section, and a tail. The tail propels the sperm, which is powered by energy cells stored in the middle section. The head of the sperm contains the man’s genetic material and an enzyme-filled acrosomal cap needed to help the sperm penetrate through the outer membrane of the egg.

As an egg released by an ovary travels through a fallopian tube, it may encounter hundreds of sperm that have survived to reach this point in their journey. Eventually, one sperm may succeed in breaking through the egg’s outer membrane.

After penetrating the egg’s outer membrane, the sperm releases its nucleus, which unites with the nucleus from the egg. Fertilization or conception occurs when the sperm fuses with the egg to form a fertilized egg (zygote).

Click a circle in the "Navigation" box to travel to a particular section of the female reproductive system. At each section, select the "Click here to play animation" to see an action occur that leads to the successful conception of a fertilized egg. During sexual intercourse, sperm are released into the vagina near the cervix, which is the entrance to the uterus. The sperm travel through the cervix, into uterus and up the fallopian tubes.

After being release from an ovary, the egg cell moves through the fallopian tube by tiny cilia that line the tube’s walls. The egg cell only survives for approximately 24 hours after ovulation. Of the millions of sperm that are released into the naturally acid environment of the woman’s reproductive tract, relatively few will survive to encounter the egg cell.

When one of the sperm cells finally succeeds in breaking through the egg cell's outer membrane, the egg cell forms a protective barrier preventing other sperm cells from entering. This ensures that only one sperm cell fertilizes the egg cell.

Next, the sperm cell releases its nucleus containing the man’s chromosomes. After several hours, it unites with the nucleus of the egg cell, which contains the woman’s chromosomes. When the two nuclei fuse, their genetic material combines together to create a fertilized egg cell which is called a zygote. Millions of sperm are released during a single ejaculation. Their tails propel on their journey to encounter the single egg cell. Of the millions of sperm, only a few will survive to reach the egg and just one will penetrate the egg cell’s wall to combine it’s genetic material with that of the egg in the process called fertilization. If during the first week of cell division, the fertilized egg cell, or zygote, divides into 2 zygotes, identical twins will form. Each developing embryo contains the same genetic material as the other. In a severe impact to the head, the brain moves and hits the skull causing injury. During a boxing match, the brain moves from side to side after the impact of a punch. Following a concussion head injury, confusion and disorientation due to temporary distortion of the brain may result. Injury or infection of the cornea, the transparent front window of the eye, can lead to serious visual impairment.

Coronary artery bypass graft surgery (CABG) is an invasive procedure that involves taking a section of vein from the leg and grafting it onto a location on the heart, which allows blood to bypass the blocked portion of the coronary artery.

The procedure begins with the surgeon making a cut in the leg and removing a section of vein. Both ends of the vein are tied-off in the leg and cut is closed. The chest is opened and the blood is rerouted through a heart-lung machine. The heart is then stopped.

The surgeon locates the blocked coronary artery and attaches the section of vein taken from the leg to the aorta and to the coronary artery below the blocked segment of the artery. The surgeon may do as many bypasses on as many blocked coronary arteries as the patient needs.

Once each bypass graft is placed, it is checked for leaks. Following this, the heart is restarted. Once the heart is beating again, the surgeon will remove its attachments to the heart-lung machine and sew the openings closed. Following this the chest is closed. A pacemaker may be inserted during the procedure to help control any heart rhythm problems the patient may have.

The coronary arteries supply blood to the heart muscle itself. Damage to or blockage of a coronary artery can result in injury to the heart. Normally, blood flows through a coronary artery unimpeded. However, if the inner wall of a coronary artery becomes damaged, cholesterol plaque can build-up, progressively narrowing the available pathway through which blood can flow.

Clotted blood attempting to traverse the blood vessel may find it tortuous and too narrow for passage, and the artery may become completely constricted or blocked-off. The blocked artery results in a lack of oxygen, or ischemia, to the part of the heart muscle that the artery supplies. The result is a heart attack. Facial cosmetic surgery may include a forehead lift. In this procedure, a hairline incision is made, the forehead skin is pulled-up and excess skin tissue is removed. In an eyelid lift (blepharoplasty), creases and wrinkles around the eyes can be minimized by removing excess fat and skin from the upper and lower eyelids. A facelift usually consists of an incision along or above the hairline and in front of the ears. Excess fat and skin is removed and facial muscles may be tightened.

Coughing is a sudden expulsion of air from the lungs through the epiglottis at an amazingly fast speed (estimated at 100 miles per hour). With such a strong force of air, coughing is the body’s mechanism for clearing the breathing passageways of unwanted irritants.

In order for a cough to occur, several events need to take place in sequence. First, the vocal cords open widely, allowing additional air to pass through into the lungs. Then the epiglottis closes off the windpipe (larynx), and simultaneously, the abdominal and rib muscles contract, increasing the pressure behind the epiglottis. With the increased pressure, the air is forcefully expelled, and creates a rushing sound as it moves very quickly past the vocal cords. The rushing air dislodges the irritant, making it possible to breathe comfortably again.

Diabetes may affect the retina by causing the formation of whitish patches called exudates. Other indications may include tiny enlargements of the blood vessels resulting in microaneurysms and hemorrhages.

Digestion is the process in which food is broken down into nutrients used by the body. Food passes from the mouth through the esophagus to the stomach. The stomach churns the food and breaks it down further with its contents of hydrochloric acid and an enzyme called pepsin.

The process of breaking food down in the stomach takes a few hours. From there, it goes to the duodenum where it is broken down further by digestive bile produced by the liver and stored in the gallbladder along with enzymes from the pancreas. Enzymes are chemicals that speed up the digestion of specific types of food. For example, the enzyme trypsin breaks down the protein in steak, lipase helps to break down fat, and lactase breaks down the sugar in milk.

Once everything is broken down, the small intestine absorbs the nutrients the body needs. From there the nutrients go into the bloodstream and to the liver, where poisons are removed. Undigested food and water continue through the small intestine and go into the large intestine, where water is reabsorbed. Finally, feces are eliminated through the rectum and anus.

Directional Coronary Atherectomy (DCA) is a minimally invasive procedure to remove the blockage from the coronary arteries and allow more blood to flow to the heart muscle and ease the pain caused by blockages.

The procedure begins with the doctor injecting some local anesthesia into the groin area and putting a needle into the femoral artery, the blood vessel that runs down the leg. A guide wire is placed through the needle and the needle is removed. An introducer is then placed over the guide wire, after which the wire is removed. A different sized guide wire is put in its place.
 
Next, a long narrow tube called a diagnostic catheter is advanced through the introducer over the guide wire, into the blood vessel. This catheter is then guided to the aorta and the guide wire is removed. Once the catheter is placed in the opening or ostium of one the coronary arteries, the doctor injects dye and takes an x-ray.

If a treatable blockage is noted, the first catheter is exchanged for a guiding catheter. Once the guiding catheter is in place, a guide wire is advanced across the blockage, then a catheter designed for lesion cutting is advanced across the blockage site. A low-pressure balloon, which is attached to the catheter adjacent to the cutter, is inflated such that the lesion material is exposed to the cutter.

The cutter spins, cutting away pieces of the blockage. These lesion pieces are stored in a section of the catheter called a nosecone, and removed after the intervention is complete. Together with rotation of the catheter, the balloon can be deflated and re-inflated to cut the blockage in any direction, allowing for uniform debulking.

A device called a stent may be placed within the coronary artery to keep the vessel open. After the intervention is completed the doctor injects contrast media and takes an x-ray to check for any change in the arteries. Following this, the catheter is removed and the procedure is completed.

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After the membranes rupture and the water breaks, a woman may begin to experience the first phase of labor (early labor). The average time of early labor is extremely variable, lasting anywhere from 2 to 6 hours. In rare cases, it can last up to 24 hours.

During this time, the pressure of repeated regular contractions causes the cervix, which had been closed when labor began, to open up to a diameter of 3 centimeters while becoming much thinner.

Various techniques can be used to help alleviate the discomfort a woman may experience during the first phase of labor such as back-rubs and breathing exercises. All of the immature egg cells (oocytes) a woman will ever produce are stored in the ovaries by the time she is born. The average age that girls begin to menstruate is 12 years old. Each menstrual cycle occurs approximately every 28 days. During each cycle, hormonal messages from the brain cause the ovaries to develop a single mature egg cell for potential fertilization, even as other hormones instruct the uterine lining to thicken in preparation for nourishing the fertilized egg cell.

The cycle starts when a follicle grows within one of the ovaries. A follicle is composed of the developing egg cell and the support cells that surround and nourish it. On day 1 of the cycle, a small structure in the brain, the pituitary gland, releases two hormones, FSH and LH, both of which cause the follicle to begin growing.

Over the next 13 days, the growing follicle releases estrogen, a hormone that prepares the lining of the uterus to receive a fertilized egg cell. Meanwhile, the estrogen in the bloodstream causes the brain to release a surge of LH. In response to the LH surge, the follicle enlarges rapidly. On day 14, it ruptures and releases the egg cell in a process known as ovulation.

The ruptured follicle begins secreting the hormone progesterone, which also helps to prepare the uterine lining for a fertilized egg cell. The egg cell is swept into the fallopian tube entrance by its waving structures called fimbriae.

Once the egg cell is within the fallopian tube, it will either be fertilized by a sperm cell, or fertilization will fail to take place. If the egg cell is not fertilized within 24 hours after its release from the ovary, it will stop developing and will dissolve before reaching the uterus. The absence of a fertilized egg cell gradually causes a woman’s body to stop releasing the hormones that would otherwise prepare the uterus for the developing egg cell. In response, the uterus sheds its lining on days 24 through 28 during menstruation.

If a sperm does fertilize the egg cell, tiny hair-like cells called cilia will transport it towards the uterus. The fertilized egg now called a blastocyst, lodges in the uterine wall in a process called implantation to receive nourishment from the uterine lining. The remaining cells of the ruptured follicle in the ovary produce progesterone so that the uterine lining will stay rich in blood vessels, and the fertilized egg cell will survive.

A woman is born with all of the egg cells she will release throughout her lifetime. Starting at about age 12 through menopause, a woman’s reproductive cycle releases an egg about once a month.

Hormonal messages from the brain instruct the ovaries to develop several follicles in which a single dominant follicle in one of the ovaries will release an egg for fertilization. During this time, other hormones instruct the uterine lining to thicken in preparation for nourishing a fertilized egg.

There are several hormones that regulate the reproductive cycle. Follicle stimulating hormone (FSH) stimulates preparation of the egg for fertilization by instructing a follicle to begin dividing it’s genetic material (chromosomes).

The follicle then releases estrogen, the hormone that prepares the lining of the uterus to receive a fertilized egg. Increased levels of estrogen in the bloodstream cause a small structure in the brain, the pituitary gland, to stop releasing the hormone FSH, and to start releasing luteinizing hormone (LH).

LH causes the follicle to enlarge rapidly and to release its egg in a process known as ovulation. Once the egg is out of the follicle, the follicle begins secreting the hormone progesterone, which also helps to prepare the uterine lining for the fertilized egg. The remaining cells of the follicle shrink into a hormone producing mass of cells called a corpus luteum.

The egg is swept into the fallopian tube by its waving structures called fimbriae. Fertilization of the egg usually occurs in the fallopian tube. From there, it is transported to the uterus and implants itself in the uterine wall, where it is nourished by the uterine lining. In the ovary, the corpus luteum produces progesterone so that the egg can develop into a fetus.

If the egg is not fertilized within 24 hours after its release from the ovary, it stops developing and dissolves before reaching the uterus. The absence of a fertilized egg causes the body to stop releasing the hormones that prepare the uterus for implantation. In response, the uterus sheds its lining over a period of four to five days in a process known as menstruation.

Click the waveform pull-down list to view various waveforms showing normal and pathological conditions of the heart. The endocrine system is primarily composed of glands that produce chemical messengers called hormones. Glands of the endocrine system include the pituitary gland, the thyroid gland, the parathyroid glands, the thymus, and the adrenal glands. Other glands are also included within the endocrine system since they contain endocrine tissue that secretes hormones such as the pancreas, ovaries and testes.

The endocrine and nervous systems work very closely together. The brain continuously sends instructions to the endocrine system, and in return receives feedback from the endocrine glands. Because of this intimate relationship, the nervous and endocrine systems are referred to as the neuroendocrine system.

The hypothalamus is known as the master switchboard because it’s the part of the brain that controls the endocrine system. The pituitary gland, which hangs by a thin stalk from the hypothalamus, is called the master gland of the body because it regulates the activity of the endocrine glands.

The hypothalamus detects the rising level of the target organ’s hormones then sends either hormonal or electrical messages to the pituitary gland. In response, the pituitary gland releases hormones, which travel through the bloodstream to a target endocrine gland, instructing it to stop producing its hormones.

The endocrine system constantly adjusts hormone levels so that the body can function normally. This process is called homeostasis. The prostate gland is located underneath the bladder and is about the size of a chestnut. Part of the urethra is encased within the prostate gland. As a man ages, the prostate typically enlarges in size in a process called benign hypertrophy (non-cancerous enlargement).

The enlarged prostate crowds its surrounding structures and may cause the urethra to narrow. The narrowed urethra results in several of the symptoms of benign prostatic hypertrophy (BPH). Symptoms may include a slowed or delayed start in urination, the need to urinate frequently during the night, difficulty in emptying the bladder, a strong, sudden urge to urinate, and incontinence. Less than half of all men with BPH have symptoms of the disease, or their symptoms are minor and do not restrict their life style.

BPH is a normal physiological process of aging and treatment options are available. The choice of the appropriate treatment is based on the severity of the symptoms, the extent to which they effect lifestyle, and the presence of other medical conditions. Men with BPH should consult with their physician yearly to monitor the progression of the symptoms and decide the best course of treatment as needed. The prostate gland is located underneath the bladder and is about the size of a chestnut. Part of the urethra is encased within the prostate gland. As a man ages, the prostate typically enlarges in size in a process called benign hypertrophy (non-cancerous enlargement).
The enlarged prostate crowds its surrounding structures and may cause the urethra to narrow. The narrowed urethra results in several of the symptoms of benign prostatic hypertrophy (BPH). Symptoms may include a slowed or delayed start in urination, the need to urinate frequently during the night, difficulty in emptying the bladder, a strong, sudden urge to urinate, and incontinence. Less than half of all men with BPH have symptoms of the disease, or their symptoms are minor and do not restrict their life style.
BPH is a normal physiological process of aging and treatment options are available. The choice of the appropriate treatment is based on the severity of the symptoms, the extent to which they effect lifestyle, and the presence of other medical conditions. Men with BPH should consult with their physician yearly to monitor the progression of the symptoms and decide the best course of treatment as needed. During periods of stress, such as preparing to run in a race, the brain signals the adrenal glands to produce epinephrine or "adrenaline". Epinephrine increases the rate in which the heart beats. The increased cardiac output supplies more oxygen to the muscles, putting the body a heightened state to react. As a longer term response to stress, cortisol is secreted by the adrenal glands, promoting the release of energy. Weight lifting is a form of anaerobic exercise. It is very demanding, requiring a great deal of energy, which quickly depletes the body’s oxygen reserves. Sprinting and push-ups are other examples of anaerobic activities. They each create a situation called oxygen debt, which requires us to breathe deeply and rapidly in order to restore a proper oxygen level to the muscle cells.

If oxygen reserves become depleted while exercising, muscles convert a starch, called glycogen, into energy. This conversion process creates a waste product called lactic acid, which can be partly responsible for muscle soreness the next day.

Jogging is a form of aerobic exercise. Exercising over a long duration requires a steady level of energy for the body. If properly conditioned, the body will be able to supply adequate oxygen to meet its energy requirements during aerobic exercise and much less lactic acid will be formed in the muscles.

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Pain provides the body with a protective mechanism, alerting it to potential or actual damage to the body’s tissues. In the example of a bee sting, the pain receptors in the skin detect tissue damage from the bee sting. Then, the peripheral nerves send a pain signal to the brain. The brain analyzes the pain signal. In turn, the brain delivers a message back to the muscles of the arm to react.

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Click and drag a slider bar underneath an image window to see the process of embryonic and fetal development.

The ears begin their development during the fifth week of pregnancy. Ear formation starts from a few small bulges called branchial arches. Portions of the branchial arches form into structures called auricular hillocks. The auricular hillocks grow and join together to form the outer ears.

During the fifth month, the inner and middle parts of the ear develop, but won’t be completely finished until birth.

Twins occur in about 1% of all pregnancies in which 30% are identical (maternal, monozygotic) twins and 70% are non-identical (fraternal, dizygotic) twins.

A single baby is formed when an egg cell is fertilized by a single sperm cell to form a zygote. The zygote divides to form a structure composed of hundreds of cells called a blastocyst. The blastocyst implants into the uterine lining and will grow into a single baby.

Identical twins start out from a single fertilized egg cell (zygote). Unlike a single baby, the fertilized egg cell will split into two separate embryos during the two-cell stage (day 2), early blastocyst stage (day 4), or late blastocyst stage (day 6).

The stage at which the egg cell splits determines how the twins will implant in the uterine lining, and whether or not they share an amnion, chorion, and placenta. The earlier the splitting occurs, the more independently the twins will develop in the uterus. Twins that split during the late blastocyst stage will share an amnion, chorion, and amniotic sac.

Non-identical twins develop from two fertilized egg cells (zygotes). During ovulation, two egg cells are released and fertilized by two different sperm cells. Non-identical twin embryos develop separately each having their own chorion, amnion, and placenta.

Air first enters the body through the mouth or nose, quickly moves to the pharynx (throat), passes through the larynx (voice box), enters the trachea, which branches into a left and right bronchus within the lungs and further divides into smaller and smaller branches called bronchioles. The smallest bronchioles end in tiny air sacs, called alveoli, which inflate during inhalation, and deflate during exhalation.

Gas exchange is the delivery of oxygen from the lungs to the bloodstream, and the elimination of carbon dioxide from the bloodstream to the lungs. It occurs in the lungs between the alveoli and a network of tiny blood vessels called capillaries, which are located in the walls of the alveoli.

The walls of the alveoli actually share a membrane with the capillaries in which oxygen and carbon dioxide to move freely between the respiratory system and the bloodstream. Oxygen molecules attach to red blood cells, which travel back to the heart. At the same time, the carbon dioxide molecules in the alveoli are blown out of the body with the next exhalation.

Glaucoma is the development of increased pressure within the eye. If left untreated, glaucoma may damage the optic nerve, resulting in visual impairment and eventually blindness. Gout is caused by increased production of uric acid. Uric acid crystals travel and accumulate in the joints, especially in the feet and legs, causing great pain and swelling.

The ear is divided into three regions: the outer ear, middle ear and inner ear.

When sound waves enter the ear canal, they cause the eardrum to vibrate. The vibration moves the three bones in the middle ear, called the ossicles. The ossicles are also known as the hammer (malleus), anvil (incus), and stirrup (stapes). These tiny bones transfer and amplify sound waves to the oval window, which is located behind the stirrup.

When the oval window vibrates, it moves fluid across a membrane inside the cochlea. The fluid causes the membrane to move. Specialized hair cells translate this movement into nerve impulses, which are sent to the brain through the vestibulocochlear nerve. The brain interprets the impulses as sound.

As sound waves entering the ear, they travel through the outer ear, the external auditory canal, and strike the eardrum causing it to vibrate. The central part of the eardrum is connected to a small bone of the middle ear called the malleus (hammer). As the malleus vibrates, it transmits the sound vibrations to the other two small bones or ossicles of the middle ear, the incus and stapes. As the stapes moves, it pushes a structure called the oval window in and out. This action is passed onto the cochlea, which is a fluid-filled snail-like structure that contains the receptor organ for hearing. The cochlea contains the spiral organ of Corti, which is the receptor organ for hearing. It consists of tiny hair cells that translate the fluid vibration of sounds from its surrounding ducts into electrical impulses that are carried to the brain by sensory nerves. As the stapes rocks back and forth against the oval window, it transmi ts pressure waves of sound through the fluid of the cochlea, sending the organ of Corti in the cochlear duct into motion. The fibers near the cochlear apex resonate to lower frequency sound while fibers near the oval window response to higher frequency sound.

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Heart bypass surgery begins with an incision made in the chest, with the breastbone cut exposing the heart. Next, a portion of the saphenous vein is harvested from the inside of the leg. Pieces of this great vein will be used to bypass the blocked arteries in the heart. The venous graft is sewn to the aorta and to the affected coronary artery past the blocked site. The internal mammary artery from the chest may also be used to bypass a clogged artery. Several arteries may be bypassed depending on the condition of the heart. The embryo’s heart is the first organ that forms. It is derived from two primitive heart tubes. Between days 18 to 30, the primitive heart tubes fuse together, bend and twist to form a simple version of the heart. About half way through this process, the heart starts to beat.

At 2 months, the heart bears a close resemblance to what it will look like after the baby’s born. The resemblance is only superficial since the inside of the heart is different in both form and function.

In a newborn’s heart, oxygen-poor blood from the body enters the right atrium, goes to the right ventricle where it is pumped to the lungs to become rich with oxygen. From the lungs, the blood flows back to the heart filling the left atrium then enters the left ventricle. The left ventricle pumps the oxygen rich blood through the aorta, which carries it to the rest of the newborn’s body.

The fetal heart has the same basic components as the newborn heart, but there are a couple important differences. Because the placenta is providing all of the oxygen the fetus requires, its lungs are not needed to perform this task. Much of the fetus’ blood is detoured away from the lungs through two openings or connections: the foramen ovale, which connects the right and left atria, and the ductus arteriosus, which connects the aorta and the pulmonary artery. These two important connections will remain open up until the time of birth.

Within thirty minutes after the baby’s first breath, the ductus arteriosus will completely close, and the flap of the foramen ovale will shut off like a valve. This happens because of an increase in pressure on the left side of the heart, and a decrease on the right side. These changes in the heart anatomy cause the blood to flow to the lungs, which will take over their lifelong job of supplying oxygen to the body. The heart is a four-chambered organ with four main vessels, which either bring blood to or carry blood away from the heart. The four chambers of the heart are the right atrium, right ventricle, left atrium, and left ventricle.

The great vessels of the heart include: • Superior and inferior vena cava (brings blood from the body to the right atrium) • Pulmonary artery (transports blood from the right ventricle to the lungs) • Aorta (the body’s largest artery, which transports oxygen-rich blood from the left ventricle to the rest of the body)

A series of one-way valves keep the blood flowing in one direction with every heartbeat. Blood first enters the heart into the right atrium then passes from the right atrium through the tricuspid valve and into the right ventricle. When the right ventricle contracts, the muscular force pushes blood through the pulmonary semilunar valve into the pulmonary artery.

Blood then travels to the lungs, where it receives oxygen. Next, it drains out of the lungs via the pulmonary veins, and travels to the left atrium. From the left atrium, the blood is forced through the bicuspid valve into the left ventricle. The left ventricle is the major muscular pump that sends the blood out to the body systems. When the left ventricle contracts, it forces the blood through the aortic semilunar valves and into the aorta. The aorta and its branches carry blood to all the tissues of the body. Heartburn is pain felt in the chest by a burning sensation in the esophagus, which is located close to where the heart is. At junction between the stomach and esophagus is the cardiac sphincter. This muscular sphincter acts as a valve that normally keeps food and stomach acid in the stomach and prevents the stomach’s contents from regurgitating back into the esophagus.

However, certain foods may affect the cardiac sphincter, making it less effective. The stomach produces hydrochloric acid to digest food. The stomach has a mucous lining that protects it from hydrochloric acid, but the esophagus does not. When food and stomach acid regurgitate back into the esophagus, a burning sensation is felt near the heart resulting in heartburn. Antacids may be used to relieve heartburn by making stomach juices less acidic, therefore reducing the burning feeling felt in the esophagus. If heartburn becomes frequent or prolonged, medical intervention may be necessary to correct the problem. The disks between the vertebrae are liable to displacement when put under strain. Heavy lifting may produce forces which cause a lumbar intervertebral disk to move out of place ("slipped disk"). Homeostasis is a state of balance inside the body, where the body systems work together to keep it functioning normally. The endocrine system keeps this internal balancing act going by releasing chemicals called hormones. The release of the hormones is controlled by negative feedback mechanisms.

A negative feedback mechanism works something like a thermostat in your home. A thermostat helps maintain a constant temperature, called the normal range. When the temperature rises beyond the normal range, the thermostat turns on the air conditioner. Eventually the air conditioner restores the temperature to the normal range. This process is called negative feedback. It starts with a normal range, goes beyond the normal range, and then back to normal again.

An example of how negative feedback works in the body can be demonstrated by the endocrine system’s controls over the amount of sugar in the bloodstream. Insulin is a hormone secreted by the pancreas that maintains a normal amount of sugar in the bloodstream. Shortly after eating a candy bar, tiny sugar molecules enter the bloodstream raising the blood sugar levels. In response, the pancreas secretes the insulin into the bloodstream. Now, the sugar molecules move out of the bloodstream and into the cells of the skeletal muscles, fat and liver. In turn, the blood sugar levels return to normal. The human face starts as a series of paired tissue mounds called branchial arches. During embryotic development, the face forms from the first branchial arch along with the area just above it.

At 28 days of development, the lower jaw has fused together from the branchial arches. The nostrils start to form by day 21 and the eyes appear on each side of the head. 2 days later, the nostrils move toward the center of the face and the ears begin to form.

At 35 days, the nostrils are closer together and more of the eyes can be seen. At 40 days, the eyelids have developed and the nose begins to take its form. At 48 days, the nasal swellings have joined in the center of the face and the eyes have moved to the front of the head.

3 weeks later, the fetal face takes on its human appearance. The face continues to develop more typical proportions right up until the time of birth. If left untreated, hypertension can lead to the thickening of arterial walls causing its lumen, or blood passage way, to narrow in diameter. As a result, the heart must work harder to pump blood through the narrowed arterial openings. In addition, people with hypertension may be more susceptible to stroke. The immune system is comprised of specialized white blood cells, called lymphocytes that adapt themselves to fight specific foreign invaders. These cells develop into two groups in the bone marrow.

From the bone marrow, one group of lymphocytes migrates to a gland called the thymus and become T lymphocytes or T cells. Within the thymus, the T cells mature under the influence of several hormones.

The T cells mature into several different types, including helper, killer and suppressor cells. When matured, the T cell types are ready to work together to directly attack foreign invaders, providing what physicians call cell-mediated immunity. This type of immunity can become deficient in persons with HIV, the virus that causes AIDS, because HIV attacks and destroys helper T cells.

The other group of lymphocytes, B lymphocytes or B cells, mature and develop within the bone marrow itself. In that process, they achieve the ability to recognize specific foreign invaders. From the bone marrow, B cells migrate through the body fluids to the lymph nodes, spleen and blood. B lymphocytes provide the body with humoral immunity as they circulate in the fluids in search of specific foreign invaders to destroy. Intracytoplasmic sperm injection, or ICSI, is a form of in vitro fertilization in which fertilization occurs outside of the body. First, egg cells are harvested and transferred to a special media in a laboratory dish. Within a few hours, a single sperm is injected through a fine needle into the center of an egg cell to aid in the process of fertilization. If successful, the cell will divide and form the beginning stages of an embryo. If necessary, the DNA of a single cell from an embryo may be checked to ensure that various genetic disorders are not present. Typically, several egg cells are harvested and fertilized at the same time then inserted back into the uterus to increase the chances that one will implant and develop into a successful pregnancy.

The urinary tract includes the kidneys, ureters, bladder and urethra. Within each kidney, urine flows from the outer cortex to the inner medulla. The renal pelvis is the funnel through which urine exits the kidney and enters the ureter.

As urine can become very concentrated as it passes through the kidneys. When the urine becomes too concentrated, calcium, uric acid salts and other chemicals dissolved in the urine can crystallize, forming a kidney stone (renal calculus).

Usually the calculus is the size of a small pebble. But ureters are very sensitive to being stretched, and when stones form and distend it, the stretching can be very painful. Often, people may not know they have kidney stones until they feel the painful symptoms resulting from a stone being stuck anywhere along the urinary tract. Fortunately, small stones typically passed out of the kidneys and through the ureters on their own without causing any problems.

However, stones can become more problematic when they block the flow of urine. A staghorn kidney stone may obstruct the entire kidney. Fortunately, these stones are the exception rather than the rule.

When a baby is ready to be born, the mother starts to feel labor contractions. That means that her uterus starts squeezing and pushing so the baby can come out. It’s a tight fit, but it doesn’t hurt the baby during delivery.

At 1 month, the baby growing inside the mother’s uterus is very small. The baby is so small she could fit in the palm of your hand and is about the size of your thumbnail.

Over the next 9 months, the baby will grow more inside the uterus until she is ready to be born.

To make a baby, a man’s sperm meets and joins with a woman’s egg cell inside her body. Inside the man’s sperm are a set of instructions that tell the baby to be a boy or a girl.

The instructions in the man’s sperm cell can either carry the letter "X" or the letter "Y". If the letter is an "X", it means the baby will be a girl. If the letter is a "Y", the baby will be a boy.

When the baby is in the mother’s uterus, it can’t eat or breathe on its own, so it needs some help. The baby has a little tube that goes to its middle called the umbilical cord. The umbilical cord goes to the placenta, which connects to the mother’s uterus.

Here’s how it works. First, the food that the mother eats and air that she breathes get into her bloodstream as very tiny pieces called molecules.

These molecules, or tiny pieces of food and air, travel through the mother’s bloodstream to her placenta. From there, they go to the umbilical cord and into the baby’s body. That’s how the baby eats and breathes inside the uterus.

After a baby is born, the umbilical cord goes away. Guess what’s left? You’re belly button.

Two things are needed to make a baby: a sperm cell and an egg cell. A man makes the sperm cell inside his body and a woman makes the egg cell inside her body.

Both the sperm cell and egg cell are very small. You would need a microscope to see them in real life. A microscope is like a magnifying glass, only much stronger.

When the sperm cell and the egg cell meet each other, they make a tiny baby that’s smaller than a grain of salt. The baby will grow inside a special place in woman’s body called the uterus. After about nine months, the baby will come out as a little boy or girl.

A vibrating suction cannula, or flexible tube, is used in a liposuction procedure. The cannula is inserted through a small hole into the abdominal fat tissue to remove excess fat deposits.

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The lymphatic system is a complex network of thin vessels, valves, ducts, nodes, and organs. It helps to protect and maintain the fluid environment of the body by producing, filtering, and conveying lymph and by producing various blood cells.

Lymph nodes play an important part in the body’s defense against infection. The most common cause of swollen lymph nodes is infection, which might occur even if the infection is trivial or not. Afferent lymph vessels bring unfiltered fluids into the lymph node to be filtered while efferent vessels carry clean fluids away from the lymph node and to the cardiovascular system where it helps form the plasma in the blood.

Overall, lymph nodes work like a biological filtering system. When the body is invaded by foreign organisms, the painful swelling sometimes felt in the neck, armpits, groin, or tonsils comes from the microorganisms being trapped inside collections of lymph cells or nodes. Eventually, these organisms are destroyed and eliminated by cells that line the walls of the lymph nodes and the swelling and pain subside. The lymphatic system is often referred to as the body’s "secondary circulatory system". The lymphatic system collects excess fluid in the body’s tissues and returns it to the bloodstream.

Lymph formation occurs at the microscopic level. During the exchange of fluid and molecules between the blood circulation and body tissues, blood capillaries may not reabsorb all of the fluid. Surrounding lymphatic capillaries absorb the excess fluid. The fluid is then filtered and transported back by the lymphatic system into large veins near the heart.

The lymphatic system can play a very worrisome role in the spread of breast cancer. Components of the lymphatic system called lymph nodes are distributed at specific locations throughout the body. There is also an extensive network of lymphatic vessels in every woman’s breast tissue, which is important in regulating the local fluid balance as well as in filtering out harmful substances.

The lymph vessels in the breast may inadvertently supply cancerous cells with access to a highway along which the cancerous cells can move to other parts of the body. This process is called metastasis and may result in the formation of a secondary cancer mass in a different location of the body. Regular breast self examinations can help to detect tumors earlier in their growth, hopefully before they spread quickly or metastasize. The macula is the part of the retina that distinguishes fine details at the center of the field of vision. Macular degeneration results from a partial breakdown of the insulating layer between the retina and the choroid layer of blood vessels behind the retina. Macular degeneration results in the loss of central vision only.

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Click and drag the slider bar to see changes that occur during a normal 28 day menstrual cycle.

Muscles perform four important body functions: maintain body posture, stabilize the joints, provide mobility, and generate heat that the body requires.

The body contains three types of muscle to perform these functions:
• Smooth muscle - involuntary muscle found in the walls of body organs; functions without conscious control
• Cardiac muscle - involuntary muscle found only in the walls of the heart; functions without conscious control
• Skeletal muscle - attaches to and covers the bony skeleton to provide movement of the body; the only type of muscle under voluntary or conscious control

The nervous system is composed of two divisions, the central nervous system (CNS) and peripheral nervous system (PNS). The CNS contains the brain and the spinal cord and the PNS consists of thousands of nerves that connect the spinal cord to muscles and sensory receptors.

A peripheral nerve is composed of nerve bundles (fascicles) that contain hundreds of individual nerve fibers (neurons). Neurons consist of dendrites, axon, and cell body. The dendrites are the tree-like structures that receive signals from other neurons and from special sensory cells that sense the body’s surrounding environment. The cell body is the headquarters of the neuron and contains its genetic information in the form of DNA. The axon transmits signals away from the cell body to other neurons.

Many neurons are insulated like pieces of electrical wire. This insulation protects them and also allows their signals to move faster along the axon. Without this insulation, signals from the brain might never reach the outlying muscle groups in the limbs.

The operation of the nervous system depends on the flow of communication between neurons. For an electrical signal to travel between two neurons, it must first be converted to a chemical signal, which then crosses a space of about a millionth of an inch wide. The space is called a synapse, and the chemical signal is called a neurotransmitter.

Neurotransmitters allow the billions of neurons in the nervous system to communicate with one another, making the nervous system the master communication system of the body.

The most critical stage of development for the embryo’s nervous system is the third and fourth weeks of pregnancy.

On day 14, the embryo looks like a little disc. The first part of the nervous system that forms is an indentation called the neural groove. Over the next 7 days, the groove deepens as the cells around it form ridges called neural folds.

By day 27, the neural folds wrap around the neural groove and form the neural tube. The neural tube will further develop into the brain and spinal cord. Structures called somites form the vertebral column, or backbone. They also help form the ribs and the muscles of the neck, arms, and legs.

The embryo’s nervous system is particularly vulnerable during the early stage of development, so an expectant mother should be careful about avoiding any substances that could potentially harm it. Nutrient exchange is a continuous cycle, constantly supplying the body with oxygen and nutrients while removing carbon dioxide and metabolic waste.

Red blood cells are the cells in the blood that carry oxygen from the lungs to the body tissues through blood pumped by the heart. As they travel away from the heart, they traverse smaller and smaller arteries, finally arriving at the collections of microscopic blood vessels called capillaries. Capillaries contain a high concentration of oxygen and nutrients, while the surrounding tissues contain a lower concentration. Through a process called diffusion, these particles leave the capillaries and enter the body’s tissues.

Conversely, the body’s tissues contain high concentrations of carbon dioxide and metabolic waste, while the capillaries contain a lower concentration. Waste products diffuse from the tissues into the capillaries and from there are carried by the venous system back toward the heart. The waste products are eventually eliminated from the bloodstream through the urinary and respiratory systems.

Osteoarthritis is the most common form of arthritis and is associated with the aging process. Osteoarthritis is a chronic disease causing the deterioration of the cartilage within a joint.

For most people, the cause of osteoarthritis is unknown, but metabolic, genetic, chemical, and mechanical factors play a role in its development. Symptoms of osteoarthritis include loss of flexibility, limited movement, and pain and swelling within the joint. The condition results from injury to the cartilage, which normally absorbs stress and covers the bones, so they can move smoothly.

The cartilage of the affected joint is roughened and becomes worn down. As the disease progresses, the cartilage becomes completely worn down and the bone rubs on bone. Bony spurs usually develop around the margins of the joint.
Part of the pain results from these bone spurs, which can restrict the joint’s movement as well.

Osteoporosis is a condition that leads to loss of bone mass. From the outside, osteoporotic bone is shaped like normal bone. However, the inside of the bones becomes more porous during the again process due to the loss of calcium and phosphate. The loss of these minerals makes the bones more prone to fracture even during routine activities, like walking, standing, or bathing. Often, a person will sustain a fracture before becoming aware of the presence of the disease.

Prevention is the best measure for treating osteoporosis by eating a recommended balanced diet including foods with sufficient amounts of calcium, phosphorous, and vitamin D. In addition, maintaining a regular exercise program as approved by your health care provider will help to keep the bones strong.

Various medications can be used as part of the treatment for osteoporosis and should be discussed thoroughly with your health care provider. Ovulation occurs though a sequence of hormonal responses. Located deep within the brain, the pituitary gland releases the hormones FSH and LH, which travel through the blood stream to the ovaries. These hormones signal the development and release a single egg cell from one of the ovaries. The sweeping motion of the fimbriae draws the egg cell through a very small space in the open body cavity into the uterine, or fallopian, tube. The egg cell will either be fertilized by sperm or will dissolve if fertilization does not take place. In Parkinson's disease, dopamine production becomes irregular and inadequate and nerve cells cannot properly transmit messages. This results in the loss of muscle function. By providing an even, adequate supply of medication that the body converts into dopamine, neurons are able to transmit messages and tremors improve.

Percutaneous Transluminal Coronary Angioplasty (PTCA) is a minimally invasive procedure to open up blocked coronary arteries, allowing blood to circulate unobstructed to the heart muscle.

The procedure begins with the doctor injecting some local anesthesia into the groin area and putting a needle into the femoral artery, the blood vessel that runs down the leg. A guide wire is placed through the needle and the needle is removed. An introducer is then placed over the guide wire, after which the wire is removed. A different sized guide wire is put in its place.

Next, a long narrow tube called a diagnostic catheter is advanced through the introducer over the guide wire, into the blood vessel. This catheter is then guided to the aorta and the guide wire is removed. Once the catheter is placed in the opening or ostium of one the coronary arteries, the doctor injects dye and takes an x-ray.

If a treatable blockage is noted, the first catheter is exchanged for a guiding catheter. Once the guiding catheter is in place, a guide wire is advanced across the blockage, then a balloon catheter is advanced to the blockage site. The balloon is inflated for a few seconds to compress the blockage against the artery wall. Then the balloon is deflated.

The doctor may repeat this a few times, each time pumping up the balloon a little more to widen the passage for the blood to flow through. This treatment may be repeated at each blocked site in the coronary arteries. A device called a stent may be placed within the coronary artery to keep the vessel open. Once the compression has been performed, contrast media is injected and an x-ray is taken to check for any change in the arteries. Following this, the catheter is removed and the procedure is completed.

Peristalsis is a series of wave-like muscle contractions that moves food to different processing stations in the digestive tract. The process of peristalsis begins in the esophagus when a bolus of food is swallowed. The strong wave-like motions of the smooth muscle in the esophagus carry the food to the stomach, where it is churned into a liquid mixture called chyme.

Next, peristalsis continues in the small intestine where it mixes and shifts the chyme back and forth, allowing nutrients to be absorbed into the bloodstream through the small intestine walls.

Peristalsis concludes in the large intestine where water from the undigested food material is absorbed into the bloodstream. Finally, the remaining waste products are excreted from the body through the rectum and anus. Macrophages are scavenger cells that can ingest dead tissue and foreign cells. Macrophages form tentacles called pseudopods to surround an invader. Once inside the macrophage, the invader is walled off and then digested and destroyed by a bag of digestive chemicals, or enzymes. The pituitary gland is often referred to as the "master gland" of the body, since it regulates many activities of other endocrine glands. Located above the pituitary gland is the hypothalamus. The hypothalamus decides which hormones the pituitary should release by sending it either hormonal or electrical messages.

In response to hormonal messages from the hypothalamus, the pituitary gland releases the following hormones: • GH (growth hormone) – increases size of muscle and bone • THS (thyroid stimulating hormone) – stimulates the thyroid gland to release T3 and T4 to stimulate metabolism in other cells throughout the body • FSH (follicle stimulating hormone) – stimulates ovarian follicle production in women; stimulates sperm production in men • LH (luteinizing hormone) – stimulates ovaries to produce estrogen in women; stimulates sperm production in men • Prolactin – stimulates breast tissue in nursing mothers to produce milk • ACTH (adrenocorticotropic hormone) - causes the adrenal glands to produce important substances that have properties similar to steroids

In response to electrical messages from the hypothalamus, the pituitary gland releases the following hormones: • ADH (antidiuretic hormone) - stimulates the kidneys to reabsorb fluid and produce less urine • Oxytocin – initiates labor, uterine contractions and milk ejection in mothers The placenta provides the baby with nutrients and oxygen from the mother and carries away fetal waste. Following delivery, the uterus naturally contracts to push the placenta out of the uterus. In addition, the delivering practitioner will assist by gently pressing the abdomen to work the placenta free of the uterus.

Delivery of the placenta is typically painless and takes approximately 15 minutes.

Once the placenta is delivered, it is examined to see if the placental tissue is healthy and in one piece. At times, the placenta can break off and cause bleeding in the uterus. The placenta is commonly referred to as the afterbirth. Its successful delivery signals the end of the final stage of childbirth.

The growing embryo requires nutrition and oxygen, and a disposal system for the waste products of its own metabolism. All of this is accomplished by the placenta, which allows the growing embryo to eat and breathe while in the mother’s uterus.

Following implantation of the fertilized egg into the uterine lining, the outer layer of the embryo develops spaces called lacunae. The lacunae filled up with blood from the mother’s uterine lining. Small projections from the embryo’s chorionic layer reached out into the uterine lining. The chorionic layer is one of the membranes that surround the embryo and help it implant. Blood vessels begin to form beneath this chorionic layer.

Around day 21, the embryo’s bloodstream and the mother’s bloodstream are in such close contact that nutrients and oxygen can cross from mother to embryo. The two bloodstreams are separated by a thin collection of tissues in the placenta called the blood barrier. This barrier permits small particles like nutrients and oxygen to pass from the mother to the embryo and allows waste products to pass from the embryo back to the mother.

The blood barrier also prevents many large or potentially harmful particles from entering the embryo’s bloodstream. The red blood cells do not cross from the mother’s bloodstream to the embryo’s bloodstream.

It’s important to keep the two bloodstreams separate since the blood type of the mother and embryo could be different. If the mother’s blood type is positive, and her embryo’s blood type is negative, then the mother’s blood cells would treat the embryo as an invading foreign organism, and try to destroy it.

The placenta and its blood barrier are important for supplying the growing embryo with nutrition and oxygen, removing its waste products, and preventing harmful substances from getting into the embryo’s bloodstream.

Hypertension caused by pre-eclampsia can adversely affect the fetus by causing constriction of the placental arteries. Arterial constriction may result in severe reduction in the blood flow to areas of the placenta. If the blood flow remains constricted, areas of the placenta may "die", putting the baby in distress.

A woman is born with all of the egg cells she will release throughout her lifetime. Starting at about age 12 through menopause, a woman’s reproductive cycle releases an egg about once a month.

Hormonal messages from the brain instruct the ovaries to develop several follicles in which a single dominant follicle in one of the ovaries will release an egg for fertilization. During this time, other hormones instruct the uterine lining to thicken in preparation for nourishing a fertilized egg.

There are several hormones that regulate the reproductive cycle. Follicle stimulating hormone (FSH) stimulates preparation of the egg for fertilization by instructing a follicle to begin dividing it’s genetic material (chromosomes).

The follicle then releases estrogen, the hormone that prepares the lining of the uterus to receive a fertilized egg. Increased levels of estrogen in the bloodstream cause a small structure in the brain, the pituitary gland, to stop releasing the hormone FSH, and to start releasing luteinizing hormone (LH).

LH causes the follicle to enlarge rapidly and to release its egg in a process known as ovulation. Once the egg is out of the follicle, the follicle begins secreting the hormone progesterone, which also helps to prepare the uterine lining for the fertilized egg. The remaining cells of the follicle shrink into a hormone producing mass of cells called a corpus luteum.

The egg is swept into the fallopian tube by its waving structures called fimbriae. Fertilization of the egg usually occurs in the fallopian tube. From there, it is transported to the uterus and implants itself in the uterine wall, where it is nourished by the uterine lining. In the ovary, the corpus luteum produces progesterone so that the egg can develop into a fetus.

If the egg is not fertilized within 24 hours after its release from the ovary, it stops developing and dissolves before reaching the uterus. The absence of a fertilized egg causes the body to stop releasing the hormones that prepare the uterus for implantation. In response, the uterus sheds its lining over a period of four to five days in a process known as menstruation.

Blood carries various substances that must be brought to one part of the body or another. Red blood cells are an important element of blood. Their job is to transport oxygen to the body’s tissues in exchange for carbon dioxide, which is carried to and eliminated by the lungs.

Red blood cells are formed in the red bone marrow of bones. Stem cells in the red bone marrow called hemocytoblasts give rise to all of the formed elements in blood. If a hemocytoblast commits to becoming a cell called a proerythroblast, it will develop into a new red blood cell.

The formation of a red blood cell from hemocytoblast takes about 2 days. The body makes about two million red blood cells every second.

Blood is made up of both cellular and liquid components. If a sample of blood is spun in a centrifuge, the formed elements and fluid matrix of blood can be separated from each other. Blood consists of 45% red blood cells, less than 1% white blood cells and platelets, and 55% plasma.

The skeletal muscles are under voluntary (conscious) control most of the time. However, skeletal muscle movement can also by induced by involuntary reflexes.

Reflexes are involuntary reactions to a stimulus such as the burning of the hand. As soon as a hot substance contacts the hand, pain receptors in the skin send a signal to the spinal cord. In turn, the spinal cord sends a signal back to the arm muscles that instruct the hand to pull away. The arm flexed as it withdrew, which is known as a flexor (withdrawal) reflex. There are many other reflexes that protect the body as well.

If the body did not have the reflexes to withdraw quickly from a painful stimulus, we would be at risk for serious injury.

As light enters the eye, it strikes the cells receptor cells of the retina called the rods and cones. A chemical reaction results in the formation of electric impulses, which then travel to the brain through the optic nerve. Retinal detachments are associated with a tear or hole in the retina through which the internal fluids of the eye may leak, causing separation of the retina from underlying tissues. One of the first signs of labor starting is the appearance of a mucus plug, or what is sometimes called a "bloody show." The bloody show is the discharge of a small amount of pinkish mucus that formed the barrier between the uterus and vagina during pregnancy.

Shortly after the bloody show, the amniotic sac ruptures and amniotic fluid begins to trickle out of the uterus and vagina. For some women, it can actually gush out in a stream. The rupturing of the amniotic sac, which surrounds and protects the baby, is commonly referred to as the "water breaking."

The combination of contractions, the bloody show, and water breaking indicates the start of the first phase of labor.

The eye is the organ of sight and is shaped as a slightly irregular hollow sphere. Various structures in the eye enable it to translate light into recognizable images. Among these are the cornea, the lens, and the retina.

Light first passes through the cornea, a clear dome-like structure covering the iris, or colored part, of the eye. The cornea bends, or refracts, the light onto the lens. The light is then refracted a second time while passing through the lens, finally focusing on the retina. The retina is the light sensitive part of the eye. Impulses travel down the optic nerve to the occipital lobe of the brain, which then interprets the image in the correct perspective.

The shape of the eye is very important in keeping the things we see in focus. If the shape of the eye changes, it affects a person’s vision.

Normally, light is precisely focused onto the retina at a location called the focal point. A nearsighted eye is longer from front to back than a normal eye causing light to be focused in front of the retina instead of directly onto it. This makes it difficult to see objects that are far away. Glasses with concave lenses are used to correct nearsightedness. The concave lens focuses light back onto the focal point of the retina.

Farsightedness occurs when the length of the eye is too short. Light is focused at a point behind the retina, making it difficult to see objects that are up close. A convex lens is used to correct farsightedness because it directs the focal point back onto the retina.

A baby's sex is determined at the time of conception. When a baby is conceived, the X or Y chromosome carried by the sperm cell fuses with the X chromosome in the egg cell. The chromosome combination determines whether the baby will be female or male. An XX combination means the baby will be a girl and XY means it will be a boy.

Even though gender is determined at conception, the fetus doesn’t develop its external sexual organs until the fourth month of pregnancy. At seven weeks after conception, the front of the fetus appears to be sexually indifferent, looking neither like a female or a male.

Over the next five weeks, the fetus begins producing hormones that cause its sex organs to grow into either female or male organs. This process is called sexual differentiation. If the fetus is female, it will produce hormones called estrogens. If the fetus is a male, it will produce hormones called androgens.

Hormones will instruct a common structure called the genital tubercle to either form the clitoris in the female or the penis in the male. The clitoris and penis are called sexual analogs because they originate from the same structure.

A shoulder dislocation usually occurs as a result of force to the joint. The bone is pushed out of the socket, which may cause damage to the surrounding ligaments, tendons, and nerves.

A baby's skeleton begins as fragile membranes and cartilage. As the fetus develops, the membranes and cartilage turn into bone in a process called ossification.

During the third month of development, the membranes on the side and back of the fetus’ skull start to ossify. Bone tissue slowly grows over the area where the membranes once existed. Eventually, these bone plates will grow together forming the cranial cavity which protects the brain.

Close to birth, the bones of the skull still have gaps between them called fontanelles. The fontanelles allow room for the baby's brain to grow and enable the head to be compressed during delivery.

Most of the bones of the skeleton start off as cartilage, such as the arms, legs, ribs, fingers, and backbone. From the second month until the end of the third month, the cartilage in the middle of the bones begins to ossify outward. Bones continue to grow in this manner until adulthood, allowing them to increase in their length and width.

Skeletal muscle is well-organized body tissue, composed in a complex array of smaller and smaller structures. Each skeletal muscle is composed of many units called muscle fascicles. The fascicles are bound together by a type of connective tissue called fascia.

Fascicles are composed of smaller organizational units called muscle fibers.

Smaller strands called myofibrils organize muscle fibers. The myofibrils move as skeletal muscle contracts. It is the interaction of the myofibrils as they slide and pull along side each other that gives skeletal muscle its functional ability to do work and move things.

Putting it all back together, myofibrils compose muscle fibers, muscle fibers make-up muscle fascicles, and muscle fascicles are bound together by fascia to compose skeletal muscle.

The skeletal system consists of approximately 206 bones, providing the body with structure and support.

The skull has 8 cranial bones that protect the brain. The facial skeleton has 14 bones that provide a framework for the eye sockets, jaws, and teeth. The facial bones provide the framework for the various structures of the face including the overlying muscles, fat and skin.

The vertebral column is composed of 24 individual vertebrae, along with two sets of fused bones called the sacrum and coccyx. The vertebral column protects the spinal cord and provides support for the trunk of the body. 12 pairs of ribs form a protective cage for the heart, lungs, and other internal organs.

The shoulder joint is the most movable joint in the body and includes the shoulder blade (scapula) and collar bone (clavicle). The bones of the upper limb include the humerus, which connects the shoulder with the elbow, the ulna, the radius, the wrist bones or carpals, the hand bones or metacarpals, and the finger bones or phalanges.

A pair of hip bones forms the pelvic girdle. Each hip bone is comprised of 3 fused bones, the ilium, ischium, and pubis. The pelvic girdle connects with the thigh bone (femur) at the hip joint. The femur is the longest bone in the body and is important for bearing the body’s weight while standing.

The femur articulates with the shin bone (tibia) at the knee. The fibula does not bear weight, but several muscles attach to it. The kneecap (patella) is suspended within muscle tendons and glides over the femur and tibia when the knee bends. The foot bones, which include the tarsals, metatarsals, and phalanges, are organized into a series of arches that allow the feet to support the body’s weight. A few common skin conditions include moles, birthmarks, age spots, and warts.

Moles are colored spots on the skin, formed by cells containing the dark pigment, melanin. While generally harmless, some moles can change shape and color, or start bleeding and require immediate evaluation.

Some birthmarks are simply moles that are present at birth, called a pigmented birthmark. Others result from the rapid growth of blood vessels in a localized area, called red birthmarks.

When a person becomes older, they may develop age spots. Age spots are patches of increased pigmentation on the skin’s surface, like freckles.

Warts are benign, or non-cancerous, growths of skin caused by a virus.

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As a person inhales, air and scent molecules move past the smell receptors in the nose. In turn, the smell receptors relay a signal to the brain. Smells can trigger memories and emotional responses.

The lungs are the primary respiratory organs. They act as filters for the air the body breathes in and normally are a healthy pink color.

Filtering smoke from the air breathed in can do damage to the lung tissue as seen in a smoker’s lung. Over time, carbon molecules from inhaled smoke deposit in the lung tissue, giving it a blackened appearance.

Smoking can eventually lead to the formation of tumors and other serious lung diseases. Smoking has also been linked to diseases that affect the cardiovascular system, such as atherosclerosis, which can lead to a heart attack or stroke.

Snoring affects many of people during their sleep when the airway become partially blocked, forcing the lungs to inhale harder to compensate for the lack of air entering the body. The snoring sound results from the vibration the soft palate and the uvula.

Several factors are thought to cause snoring, including poor muscle tone, too much alcohol, heavy smoking, colds or allergies, obesity, and obstruction by enlarged adenoids and tonsils.

Usually, snoring is not an indication of an underlying disorder. However, people who snore and have quiet periods lasting more than 10 seconds may have some degree of sleep apnea.

Sperm are produced, stored, and delivered by the male reproductive system. The male reproductive system includes the testes, urethra, vas deferens, prostate gland, seminal vesicle, and penis.

The testes contain coiled structures called seminiferous tubules, which are the sites of sperm production. They produce over 12 billion sperm per month. The epididymis lies on top of the seminiferous tubules. Immature sperm migrate from the seminiferous tubules to the epididymis to mature and be stored. The migration process usually takes about 20 days. Before intercourse, the penis fills with blood and becomes erect. With sufficient stimulation, the ejaculatory process begins.

The mature sperm travel from the epididymis through the vas deferens. The vas deferens is a narrow, muscular tube about 18 inches long. Its smooth muscle contractions propel the sperm forward. They arrive first at the ampulla, the widest part of the vas deferens, and then pass into the ejaculatory ducts. In the ejaculatory ducts, a liquid secretion from the seminal vesicles mixes with the sperm. Seminal fluid contains fructose sugar, which the sperm use as fuel as well as alkalines, which help to counteract the naturally acidic environment of the vagina and uterus providing the sperm a better chance for survival.

The liquid mixture is propelled forward through the ejaculatory ducts toward the urethra, passing first through the prostate gland, where milky prostatic fluid is added, forming the substance we call semen. The prostatic fluid helps the sperm swim faster, which is important for getting to the egg cell.

Finally, about a teaspoon of semen is ejected out (ejaculated) through the far end of the urethra at the end of the penis. From the time the sperm leave the man’s body, they have between 12 and 48 hours to find and fertilize the egg cell, assuming an egg is available. Of the 300 million sperm ejaculated, only about 200 or so will survive to reach the egg cell and only one will succeed in fertilizing it.

The key male reproductive organs include the testes, epididymis, urethra, vas deferens, prostate gland, seminal vesicle, and penis.

The testes are composed of coiled structures called seminiferous tubules, which are the sites of sperm production. The structure on top of the seminiferous tubules in the testes is the epididymis. The sperm migrate from of the seminiferous tubules to the epididymis. Within the epididymis, the sperm mature while they are stored in this structure.

The ejaculation process begins as the penis fills with blood and becomes erect. With sufficient stimulation, mature sperm travel from the epididymis through the vas deferens, a muscular tube, which propels sperm forward through smooth muscle contractions. The sperm arrive first at the ampulla, where secretions from the seminal vesicle are added.

From the ampulla, seminal fluid is propelled forward through the ejaculatory ducts toward the urethra, passing first by the prostate gland, where a milky fluid is added to form semen. Finally, the semen is ejaculated through the far end of the urethra.

A stomach ulcer is caused by an imbalance between acid and pepsin secretion and the defenses of the stomach mucosal lining. Ulcers can be treated through dietary changes and medication. A stroke may occur if an embolism travels from another part of the body and lodges within an artery in the brain. When an internal arterial wall becomes damaged, various types of emboli can form, such as one derived from platlets, thrombotic, cholesterol, or mixed. In this example, an embolism is formed in the internal carotid artery, breaks loose, travels towards the brain and lodges in a cerebral artery. The blocked artery deprives the brain of oxygen, damaging the surrounding brain tissue. The result is a stroke. A blood clot, or embolus, can form and break-off from the heart. The clot travels through the bloodstream where it can lodge in an artery of the brain, blocking the flow of blood. The lack of oxygen results in damage, destruction, or even tissue death of the brain beyond the affected area. The result is a stroke. The skin uses sunlight to help manufacture vitamin D, which is important for normal bone formation. But sometimes its ultraviolet light can be very detrimental.

Within the skin’s epidermal (outer) layer are cells that contain the pigment melanin. Melanin protects skin from the sun’s ultraviolet rays, which can burn the skin, and over time, could reduce its elasticity and cause a person to age prematurely. Suntanning occurs because exposure to sunlight causes the skin to produce more melanin and to darken. The tan fades as these cells move toward the surface and are sloughed off.

Too much exposure to ultraviolet or UV rays can cause sunburn. UV rays penetrate the outer skin layers and pass into the deeper layers, where they can damage or kill skin cells. People who do not have much melanin and sun burn easily should protect themselves by covering up sensitive areas, wearing sun block, limiting their total exposure time, and limiting their sun exposure between the hours of 10 a.m. and 2 p.m.

Frequent and prolonged exposure to ultraviolet rays over many years is the chief cause of skin cancer. Examine skin regularly for development of suspicious growths or changes in an existing skin lesion. Early detection and treatment are key in increasing the cure rate for skin cancer. The structures involved with the process of swallowing include the tongue, teeth, epiglottis, and esophagus.

The teeth are used to grind and chop up food into tiny pieces, while the glands in the mouth moisten the food with saliva. In the first stage of swallowing, the tongue pushes the food into the throat. In the second stage of swallowing, an important small flap of tissue called the epiglottis, folds over the voice box (larynx) at the entrance to the windpipe (trachea), preventing food from going down the wrong way. In the final stage, the esophagus contracts and moves food toward the stomach. There are more than two and a half million eccrine sweat glands all over the body. They lie deep in the skin and are connected to the surface by coiled tubes called ducts. Sweat (perspiration) is a liquid mixture made up of 99% water and 1% salt and fat. Up to a quart of liquid a day can evaporate through the sweat glands.

As the body becomes overheated, a person sweats, which evaporates and cools the body. When a person becomes frightened or nervous, like being pinned under heavy weights, the body begins to sweat on the palms and forehead, as well as the soles of the feet and in the armpits. These are the sites where sweat glands are most abundant. Tachycardia is a condition in which the heart beats at an abnormally fast rate of more than 100 beats per minute. This type of arrhythmia is caused by an abnormality in the heart’s electrical system. Tachycardia can be treated surgically or with medication.

The tongue has about 10,000 taste buds. The taste buds are linked to the brain by nerve fibers. Food particles are detected by the taste buds, which send nerve signals to the brain.

Certain areas of the tongue are more sensitive to certain tastes, like bitter, sour, sweet, or salty. Often, taste sensations are a mixture of these qualities.

Inside a pregnant woman’s uterus is an amniotic sac, which contains amniotic fluid and the growing fetus. The amniotic fluid is important for several reasons:

Amniotic fluid is 98% water and 2% salts and cells from the baby. Until the fetal kidneys started working during month four, the mother’s body makes amniotic fluid. But after month 4, the baby makes a contribution to the amniotic fluid by urinating into it. The urine in the amniotic sac is completely harmless to the baby.

The baby swallows amniotic fluid, which then passes through the digestive system, into the kidneys, and returns to the amniotic sac as urine. In this way, the baby can practice using the digestive and urinary systems prior to birth. Shown here is a comparison of an artery affected with plaque in a non-smoker and smoker. The artery of the smoker is at greater risk for developing complications since smoking constrict arteries, predisposing them to clotting by altering platelet function and coagulability of blood. The result is blockage of the artery. Twin to Twin Transfusion Syndrome, or TTTS, is a disease of the placenta. This condition affects twins or other multiples that share a single placenta containing blood vessels going from one baby to the other. Blood from the smaller "donor" twin is transferred to the larger "recipient" twin through interconnecting vessels causing an unequal exchange of blood. The recipient twin is at risk for heart failure receiving too much blood from both the placenta and donor twin, forcing its heart to work harder, while the donor twin is at risk for loss of blood. Laser surgery may be performed to correct the problem. A laser is endoscopically inserted into the womb to burn and seal the interconnecting blood vessels, restoring the normal flow of blood. Following treatment, the babies are regularly monitored. The stomach is the organ of the digestive system in which food travels from the esophagus and is further broken down before its nutrients are absorbed in the small intestine. It produces acid and various enzymes that break down food into simple substances. The inside wall of the stomach is protected from the acid and enzymes by a mucous lining.

Ulcers are caused when there is an imbalance between the digestive juices produced by the stomach and the various factors that protect the lining of the stomach. Symptoms of ulcers may include bleeding. On rare occasions, an ulcer may completely erode the stomach wall.

A major cause of stomach ulcers is the bacteria called Helicobacter pylori. Treatment regimens for ulcers caused this bacterium usually include medications to suppress the stomach acid as well as antibiotics to eradicate the infection.

Ultrasound is a useful procedure for monitoring the baby’s development in the uterus. Ultrasound uses inaudible sound waves to produce a two-dimensional image of the baby while inside the mother’s uterus. The sound waves bounce off solid structures in the body and are transformed into an image on a monitor screen.

Solid structures, such as bones and muscles, reflect sound waves and appear as light gray or white. Soft or hollow areas, like the chambers of the heart, don’t reflect sound waves and appear dark or black.

An ultrasound can supply vital information about a mother’s pregnancy and her baby's health. Even though there are no known risks for ultrasound at present, it is highly recommended that pregnant women consult their physician before undergoing this procedure.

Select a week by clicking one of the three buttons. Next, click and drag the slider bar to see an illustration of the baby's position gradually appear. With the cursor, roll-over the image to identify the various structures of the fetus.

The urinary system has four main components: the kidneys, ureters, urinary bladder, and urethra. Urine, a liquid waste product, is formed in the kidneys. From there it moves through the ureters and into the bladder, where it is stored. When the bladder gets full, urine is emptied from the body through the urethra in a process called urination.

The creation of urine is a complex process. The kidneys filter waste from the blood that passes through them, and reabsorb substances that the body requires, even though those requirements may change from moment to moment.

Each of the kidneys is composed of approximately one million subunits called nephrons. Each nephron consists of a microscopic ball of blood vessels called a glomerulus, which is connected to a twisting length of tube called the renal tubule. Because the blood vessels in the glomeruli are porous, they act as filters, removing most of the water, salt, and waste from the blood that passes through them.

As filters, the glomeruli have physical properties that prevent large cells, like red blood cells, from passing into the renal tubules. On the other hand, smaller particles, like sugar and salt, can pass easily through the glomerulus. Within the renal tubules, waste products are passed into the urine. Simultaneously, substances the body needs, such as water and salt, are reabsorbed back into the bloodstream.

The path of urine formation, reabsorption, and excretion begins at the glomerulus, continues through the renal tubules, and proceeds through a ureter into the bladder. The unique, expandable cells in the wall of the bladder stretch and become thinner as it fills. Finally, urine is excreted through the urethra.

Vaccinations are injections of antigens into the body. Once the antigens enter the blood, they circulate along with other cells, such B and T cells. B and T cells are white blood cells that help the body defend itself against foreign invaders.

As the antigens invade the body’s tissues, they attract the attention of macrophages. Macrophages are non-specific scavengers, which in this case, engulf the antigens. The macrophages then signal the T cells that antigens are invading. The killer-type of T cells respond by attacking the invading antigen. Finally, the suppressor T cells stop the attack.

After a vaccination, the body will have a memory of an encounter with a potentially dangerous invader for a period of time, and hopefully have a better ability to fight it off if ever exposed to it again in greater numbers. When the cervix dilates to 10 centimeters, the pushing and delivery phase of childbirth begins. During this phase, the baby starts the journey down the birth canal. As the baby’s head rotates , it may become distorted while slowing coming down the narrow opening. The baby’s skull bones have gaps called fontanelles that allow the head to elongate and fit within the birth canal.

As the baby’s head is delivered, it will naturally turn to one side. The baby’s head and shoulders are supported and the rest of the baby’s body generally comes out fairly quickly. A vasectomy is a procedure to cause permanently sterility in a man by preventing the transport of sperm out of the testes. A small incision is made in the scrotum and each vas deferens is tied off and cut apart preventing sperm from being released within the ejaculate. The small skin incision is stitched closed and the surgery does not affect a man's sexual function.
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This animation shows the passage of allergens (pollen) into the nasal cavity. The body response includes the release of histamine, a chemical that produces allergy symptoms in the body.  Launch animation
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This animation shows the brain and the changes that occur to it from Alzheimer's disease.  Launch animation
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This animation illustrates and compares the severity of an ankle sprain (Type I, II, III).  Launch animation
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This animation shows the cardiac conduction system and the arrhythmias of a fast and slow beating heart.  Launch animation
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This animation illustrates the location of basal ganglia in the brain. Injury to the basal ganglia may result in athetosis (constant writhing movements of the body).  Launch animation
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This animation shows the use of balloon angioplasty to open a narrowed coronary artery lumen caused by deposits of plaque.  Launch animation
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This animation shows the neurological control of normal bladder function.  Launch animation
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This animation shows the eye’s response to invading foreign substances, resulting in blinking and the lacrimal gland’s production of tears which then pass into the nose through tear ducts.  Launch animation
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This animation depicts the process of blood clotting in an enlarged view of a small artery. Cells shown include red blood cells, platelets, fibrin, and clotting factors.  Launch animation
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This animation shows the cycle of blood circulation through the heart, arteries, veins, and lungs within the body.  Launch animation
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This animation defines normal blood pressure and the measurement of systole and diastole. Structures shown include a front-view of the heart beating, a cut-view of the heart beating, and blood flowing through a small artery.  Launch animation
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This animation shows one method in which a severe wrist fracture is treated by inserting a bone graft from the hip followed by fixation with a metal plate and screws.  Launch animation
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This interactive animation takes you on a 3-D journey to explore the anatomy of the brain. Rotate the brain or pick from a list of terms to identify various structures.  Launch animation
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This animation highlights the major sections of the brain and explains their primary functions.  Launch animation
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This animation shows a breast reduction (lift) procedure.  Launch animation
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This animation illustrates the major structures of the respiratory system and shows the mechanism of breathing (respiration).  Launch animation
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This animation shows the formation of a bunion.  Launch animation
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From a top view of the voice box (larynx) and vocal cords, this animation shows the formation of a malignant tumor on the right vocal cord.  Launch animation
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This animation illustrates the cardiac conduction system, a group of specialized muscle cells that signal the rest of the heart to contract. An ECG tracing is shown in tandem with a normal heart beat.  Launch animation
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This animation shows a catheter being inserted into the heart where alcohol is injected causing the swollen ventricle wall to shrink.  Launch animation
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This animation displays a normal heart beating. Also shown are red blood cells traveling through an enlarged cut-section of a small artery and the percentage of the blood’s components.  Launch animation
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This animations depicts how a cataract is seen in the eye.  Launch animation
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This animation traces the growth and migration of a fertilized egg cell through the fallopian tubes to the uterine lining. Enlarged views show the action of cilia in the fallopian tube transporting the egg and its implantation into the uterine lining.  Launch animation
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This animation shows a cerebral aneurysm growing and rupturing filling the brain with blood.  Launch animation
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This interactive animation shows the process of cervical dilation during labor.  Launch animation
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This animation describes and depicts the common reasons for having a cesarean section delivery. The location of an epideral application is shown in a side view followed by a Cesarean section delivery illustrated in both side and front views.  Launch animation
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This animation shows an enlarged view of a section of skin, highlighting its layers and various structures.  Launch animation
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This animation shows the process of conception in which a sperm unites with an egg cell to form a fertilized egg.  Launch animation
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This interactive animation takes you on a journey through the female reproductive system to see the processes of ovulation, fertilization and implantation of a fertilized egg (zygote).  Launch animation
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This animation shows the process in which an egg cell is fertilized by a sperm cell to form a fertilized egg (zygote).  Launch animation
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In a microscopic view, this animations shows the conception of identical (maternal) twins.  Launch animation
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This animations shows the head receiving two impacts. One on the front, and one on the side from a boxing glove.  Launch animation
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This animation shows corneal infections resulting from corneal injury.  Launch animation
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This animation shows a coronary artery bypass graft (CABG) procedure in which a portion of vein is grafted on the heart to reroute blood from a blocked section of a coronary artery.  Launch animation
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Shown in an enlarged view of a damaged coronary artery is the build-up of plaque and restriction of blood flow, progressing to complete arterial blockage and heart muscle ischemia (heart attack). Anteriorly, a normal heart beating is also illustrated.  Launch animation
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This animation describes a series of cosmetic surgeries, including forehead lift, eyelid lift, and facelift.  Launch animation
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This animation shows the mechanism of coughing caused by an irritant entering the windpipe (larynx), resulting in its dislodgement. The steps of the coughing reflex are shown from a side view of the body in tandem with a top view of the vocal cords.  Launch animation
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This animations depicts changes to the retina resulting from diabetes mellitus.  Launch animation
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This animation highlights the major parts of the digestive system and follows the breakdown of celery from consumption to excretion.  Launch animation
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This animation shows a Directional Coronary Atherectomy (DCA) procedure performed to remove the blockage from the coronary arteries by a tiny spinning cutter that slices away plaque lesions and stores them to be withdrawn.  Launch animation
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This interactive animation takes you on a 3-D journey to explore the anatomy of the ear. Rotate the ear or pick from a list of terms to identify various structures.  Launch animation
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This animation shows the signs of the first phase of labor (early labor).  Launch animation
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This animation depicts the maturation of egg cells within ovary and illustrates the role of hormones in menstruation and egg cell fertilization and implantation.  Launch animation
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This animation illustrates the development cycle of an egg in an ovary and the sequence of events to fertilization of the egg or not.  Launch animation
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An electrocardiogram (ECG) enables the rhythm of the heart to be viewed in waveform. This interactive animation shows the ECG waveforms for normal sinus rhythm and various conditions of the heart.  Launch animation
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This animation illustrates the glands of the endocrine system, specifically enlarging the pituitary gland, thyroid gland, parathyroid glands, thymus, adrenal glands, and pancreas. A communication path within the neuroendocrine system is also shown.  Launch animation
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This animation illustrates the prostate gland and its surrounding structures and shows the effects of benign prostatic hypertrophy (BPH).  Launch animation
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This animation illustrates the prostate gland and its surrounding structures and shows the effects of benign prostatic hypertrophy (BPH).  Launch animation
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This animation shows the release of epinephrine and its effect of the heart.  Launch animation
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This animation gives a general comparison between anaerobic exercise (lifting weights) and aerobic exercise (jogging).  Launch animation
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This interactive animation takes you on a 3-D journey to explore the anatomy of the eye. Rotate the eye or pick from a list of terms to identify various structures.  Launch animation
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This animation shows the body’s response to a bee sting on the nose, giving a general description of the communication between the peripheral nervous system detecting the pain and the central nervous system issuing a reactive response.  Launch animation
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This interactive animation takes you on a 3-D journey to explore the anatomy of the female reproductive system. Rotate to or pick from a list of terms to identify various structures of the system.  Launch animation
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Creating a new life is nothing short of a miracle. With the fetal development interactive tool, you can get an insider's view of a baby in the making - from conception to term. You can watch the entire development, specify portions of the pregnancy, or freeze the frame on a specific week by dragging the slider bars back and forth.  Launch animation
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This animation illustrates the development of a baby’s outer ear from its embryonic origins. Structures of a baby’s middle and inner ear are also shown from the front view.  Launch animation
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This animation shows the differences between the development of a single baby, identical twins, and non-identical twins.  Launch animation
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This animation illustrates the passage of air and exchange of oxygen and carbon dioxide within the lungs on both a gross and microscopic level.  Launch animation
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This animation shows the affects of untreated glaucoma.  Launch animation
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This animation shows uric acid crystals moving to the big toe joint causing pain.  Launch animation
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Through a series of magnifications of the ear, this animation depicts the movement, amplification, translation, and interpretation of sound waves traveling through the ear’s three regions, ultimately becoming neural messages sent to the brain.  Launch animation
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This animation shows the various structures of the ear and the process of hearing.  Launch animation
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This interactive animation takes you on a 3-D journey to explore the anatomy of the heart. Rotate the heart, view in transparent mode, or pick from a list of terms to take you to various structures.  Launch animation
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This animation shows the procedure of a heart bypass surgery.  Launch animation
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This animation shows the development of the fetal heart from day 18 to day 57. A functional comparison is made between a fetal and newborn heart.  Launch animation
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This animation follows the passage of blood through the heart’s chambers and valves.  Launch animation
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This animation depicts how certain ingested foods can cause regurgitation of the stomach’s contents back into the esophagus resulting in the sensation of heartburn. The relationship between the location of the esophagus and heart is shown in a front view of the body.  Launch animation
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This animation shows displacement of an intervertebral disk (disk between the vertebrae).  Launch animation
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This animation depicts the process of maintaining homeostasis in the body through hormonal negative feedback mechanisms. An analogy is made between thermostat temperature regulation in a home to the hormonal control of sugar levels within the bloodstream.  Launch animation
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This animation shows the formation of a fetal face during the early weeks of development.  Launch animation
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This animation shows the effects of hypertension on a cerebral artery.  Launch animation
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This animation shows an enlarged view of femoral bone marrow containing immature specialized white blood cells (lymphocytes) and depicts their maturation and migration into either B cell or T cell lymphocytes.  Launch animation
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This animations shows the process of Intracytoplasmic sperm injection (ICSI), a procedure used to fertilize an egg cell outside of the body.  Launch animation
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This animation begins with an front view of the urinary tract and continues with the formation of kidney stones shown in a cut-section of the kidney. Severities of kidney stones are depicted, demonstrating various degrees of urine obstruction.  Launch animation
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This animation gives a cartooned comical view of birth through a vaginal delivery.  Launch animation
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Illustrated for a child’s perspective, this animation depicts the growth of a baby within a uterus from the first month to the ninth month of pregnancy.  Launch animation
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Illustrated for a child’s perspective, this cartooned animation explains the sperm’s role in determining if a baby will be a girl or a boy.  Launch animation
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Illustrated for a child’s perspective, this cartooned animation explains how food and air are supplied from the mother to the baby through it's umbilical cord.  Launch animation
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Created for a child’s perspective, this cartooned animation illustrates the appearance and origin of a sperm cell and egg cell as well as the development of a baby within the uterus.  Launch animation
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A vibrating suction cannula is shown removing abdominal fat.  Launch animation
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This interactive animation takes you on a 3-D journey to explore the anatomy of the lungs. Rotate the lungs view in transparent mode, or pick from a list of terms to take you to various structures of the lungs.  Launch animation
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This animation shows an enlarged view of one lymph node filtering out micro-organisms from the fluid passing through.  Launch animation
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This animation discusses and depicts several aspects of the lymphatic system including a microscopic view of lymph formation, edema, breast lymphatics and the spread of breast cancer.  Launch animation
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This animation shows the process of macular degeneration in the eye.  Launch animation
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This interactive animation takes you on a 3-D journey to explore the anatomy of the male reproductive system. Rotate to or pick from a list of terms to identify various structures of the system.  Launch animation
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This interactive animation shows the changes that occur during the menstrual cycle to hormone levels, body temperature, an ovary, and lining of the uterus.  Launch animation
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This animation discusses the four functions of muscle and displays the three different types of muscle tissue in external and microscopic views.  Launch animation
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This animation provides a general overview of the nervous system and shows the process in which nerve impulses are transmitted.  Launch animation
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This animation shows the early formation of the nervous system.  Launch animation
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This animation shows an enlargement of a blood capillary with red blood cells traversing through it. A section of the artery is enlarged further to display the exchange of oxygen and carbon dioxide between a capillary and its surrounding tissue.  Launch animation
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This animation compares the a normal adult knee joint and a knee joint affected by osteoarthritis.  Launch animation
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This animation begins by showing a hip fracture due to osteoporosis (fracture in neck of the femur, anterior view). The bone then dissolves into a frontal section to compare the bony interior of a normal femur to that of an osteoporotic femur.  Launch animation
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This animations shows the process of ovulation (the release a single egg cell from an ovary).  Launch animation
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This animations shows sporatic brain activity and a twitching hand that occur with Parkinson's disease, followed by treatment with dopamine stimulation.  Launch animation
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This animation shows a Percutaneous Transluminal Coronary Angioplasty (PTCA) procedure to open up blocked coronary arteries by inflating a tiny balloon to compress the plaque against the walls of the artery, flattening it out so that blood can once again flow through the blood vessel freely.  Launch animation
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This animation follows the processing of food through the digestive tract, focusing on the intestinal peristaltic movement (a series of wave-like muscle contractions that moves the food mixture down the digestive tract).  Launch animation
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This animation shows the process of a macrophage ingesting a foreign substance.  Launch animation
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This animation describes the regulation of the pituitary gland and the hormones it releases to regulate various organs and processes in the body.  Launch animation
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This animation illustrates the delivery of the placenta by strong uterine contractions and gentle abdominal pressure applied by a physician.  Launch animation
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This animation illustrate the formation of the placenta and blood barrier and their role in providing the embryo with nutrients and oxygen, removing waste products, and preventing harmful substance from entering in.  Launch animation
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This animation depicts hypertension caused by pre-eclampsia that adversely affects the fetus by causing constriction of the placental arteries.  Launch animation
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This animation illustrates the development cycle of an egg in an ovary and the sequence of events to fertilization of the egg or not.  Launch animation
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This animation shows the process of red blood cell formation and the components that comprise blood.  Launch animation
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This animation shows the body’s reflex response to a hot substance landing on the hand.  Launch animation
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This animation shows the process in which light is transformed by the retina as electical impulses that travel to the brain through the optic nerve.  Launch animation
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This animation shows a retinal detachment injury.  Launch animation
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In a side view of the body with the baby in utero, the mucous plug (bloody show) is illustrated followed by the rupturing of the amniotic sac (water breaking), indicating the onset of labor.  Launch animation
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This animation illustrates the various structures of the eye and how the shape of the eye affects vision (nearsightedness and farsightedness).  Launch animation
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This animation illustrates the development of the external sex organs in a female and male fetus.  Launch animation
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This animation shows a dislocation of the shoulder joint.  Launch animation
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This animation details the components of the fetal skeletal system and illustrates the process of bone development through ossification of the membranes and cartilage.  Launch animation
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This animation illustrates the organization of skeletal muscle, enlarging from a muscle belly up to its myofibrils. Simultaneously in side and front views, the actions of a leg muscle and its myofibrils are shown while performing leg extension exercises.  Launch animation
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This animation highlights the individual bones and groups of bones that comprise the skeletal system.  Launch animation
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This animation illustrates some common skin conditions such as moles, birthmarks, age spots, and warts.  Launch animation
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This interactive animation takes you on a 3-D journey to explore the anatomy of the skull. Rotate the skull, see it in an exploded view, or pick from a list of terms to identify its various structures.  Launch animation
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This animation depicts the inhalation of air and scent molecules from a rose into an enlarged sagittal view of the nasal cavity. The smell receptors are magnified further to show their action of relaying a neural message of “scent” to the brain.  Launch animation
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Normal, healthy lungs are compared to the lungs of a long-term smoker.  Launch animation
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From a side view of the head and neck, this animation shows the structures involved in snoring. The common causes for snoring are also discussed  Launch animation
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This animation highlights the structures of the male reproductive system and the pathway of ejaculate. A testicle is sectioned and enlarged to depict its internal anatomy, including a microscopic view of individual sperm.  Launch animation
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This animation highlights from a mid-sagittal view the structures of the male reproductive system and the pathway of ejaculate. A testicle is sectioned and enlarged to depict its internal anatomy, including a microscopic view of individual sperm.  Launch animation
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This animation shows a stomach ulcer forming and then reducing in size as it heals.  Launch animation
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This animation shows a stroke resulting by an embolism traveling from an internal carotid artery and lodging within a cerebral artery in the brain  Launch animation
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This animations shows a piece of clot breaking away from the heart, travelling to the brain, resulting in a stroke.  Launch animation
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This animation enlarges a section of skin to illustrate melanocytes producing melanin in response to sun exposure. Also depicted on this enlarged section is sunburn and skin cancer.  Launch animation
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From a side view of the head, this animation shows the step-by-step process and mechanism of chewing and swallowing a piece of celery.  Launch animation
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This animation shows an enlargement of a section of skin to highlight an individual sweat gland. The gland then expels sweat onto the surface of skin.  Launch animation
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This animation shows a heart with tachycardia.  Launch animation
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This animation begins with a top view of the tongue then magnifies and shows two individual taste buds detecting taste molecules. The various taste centers (bitter, sour, sweet, and salty) are highlighted on the tongue.  Launch animation
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This animation discusses and depicts the role and function of the amniotic fluid surrounding a fetus.  Launch animation
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This animation shows the difference between a smoker's and non-smoker's artery  Launch animation
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This animation depicts Twin to Twin Transfusion Syndrome (TTTS) and the use of laser surgery to correct the condition.  Launch animation
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From an front view of the stomach, this animation shows the development of an ulcer in the stomach lining.  Launch animation
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This animation demonstrates how an ultrasound identifies the solid and hollow areas of structures within a fetus.  Launch animation
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This interactive animation enables you to visualize how a fetus may appear at 17, 19, and 30 weeks by enabling you to toggling a flat ultrasound image with an illustration of the baby's actual position.  Launch animation
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In a general overview, the formation and passage of urine through the various components of the urinary system is shown. Enlarged areas include the kidney, sectioned kidney, nephrons, renal corpuscle, and passage of particles and red blood cells within.  Launch animation
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In an enlarged view of a cut section of a small artery, this animation shows a vaccine injection and follows the path of its antigens, initiating the body's development of antibodies.  Launch animation
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This animation shows the process of a normal vaginal delivery.  Launch animation
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This animation shows a vasectomy procedure.  Launch animation
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Allergens like pollen are nothing more than foreign plant antigens. The stimulus for sneezing gets triggered when allergens first enter the nasal tissue. Pollen allergens encounter the plasma cells in the nose, which respond by producing antibodies. These antibodies attach to mast cells, which are white blood cells containing the chemical histamine. As more antibodies are produced, they cause the mast cells to release histamine. Histamine then produces allergy symptoms. A stuffy and runny nose, sneezing and watery eyes help to remove the invading pollen. Medications called antihistamines may be used to help alleviate severe allergy symptoms. In a person with Alzheimer's Disease, neurofibrillary tangles and plaques develop causing both structural and chemical problems in the brain. Alzheimer's disease appears to disconnect areas of the brain that normally work together.

An ankle sprain occurs when the joint’s ligament is stretched or torn. Ligaments are bands or sheets of regular, tough fibrous tissue that connect bones together. Symptoms of an ankle sprain include swelling and discoloration near the affected area. Ankle sprains may be classified as follows:

• Type I sprain – ligaments stretched

• Type II sprain – ligaments slightly torn

• Type III sprain – ligaments completely torn

Treatment for a Type I sprain should include rest, ice, compression and immobilization, and elevation of the affected area. This is easy to remember if you think of the acronym RICE. If you suspect a ligament is torn or completely severed, see your medical care professional for treatment.

A change in the heart's normal electrical conduction system can result in an arrhythmia or irregular heartbeat. An arrhythmia can be an abnormally slow heartbeat, or an abnormally fast heartbeat. In some cases, it can be fatal. Athetosis, or constant writhing movements, is often caused by injury to deeply situated structures with the brain called basal ganglia. Angioplasty is a procedure to open narrowed or blocked arteries caused by deposits of plaque. If the blockage is not major, the problem may be corrected by inflating the balloon several times to compact the plaque against the arterial wall, widening the passage for the blood to flow through. Typically, a device called a stent is placed within the coronary artery to keep the vessel open. When the bladder fills with urine, sensory nerves send impulses to the brain indicating that the bladder is full. The sensory nerves connect with other nerves in the spinal cord to relay this information. In turn, the brain sends impulses back to the bladder instructing the bladder to empty its contents.

The nervous system enables a person to blink to prevent harmful substances from getting in the eyes. During the normal course of a day, a person blinks an average of 15 times a minute to keep the eyes healthy. The lacrimal gland provides lubricating fluid for the eyes. The eyelid moves fluid from the lacrimal gland and across the eye. Blinking also provides the eyes with protection from foreign objects.

When the eye becomes irritated, the lacrimal gland produces extra tears to wash out impurities. Excess fluid drains through the tear ducts and into the nasal cavity. An abundance of tears draining through the nasal cavity may cause the nose to run and a person to sniffle.

The body contains a natural process to stop bleeding from minor cuts in a matter of several minutes. When a small artery is cut, the collagen fibers in its tissue are exposed, which signals clotting process to begin. As platelets begin to adhere to the cut edges, they release chemicals to attract even more platelets. Eventually a platelet plug is formed, and the external bleeding stops. Clotting factors in the blood cause strands of blood-borne material, called fibrin, to stick together and seal the inside of the wound. Eventually, the cut blood vessel heals, and the blood clot dissolves after several days. As the heart pumps, the arteries carry oxygen-rich blood (shown in red) away from the heart and toward the body’s tissues and vital organs. These include the brain, liver, kidneys, stomach, and muscles, including the heart muscle itself. At the same time, the veins carry oxygen-poor blood (shown in blue) from the tissues back toward the heart. From there, it passes to the lungs to receive more oxygen. This cycle repeats itself when oxygen-rich blood returns to the heart from the lungs, which pumps it throughout the body. Normal blood pressure is important for proper blood flow to the body’s organs and tissues. Blood pressure moves from high pressure near the heart to low pressure away from the heart. The force of the blood on the walls of the arteries is called blood pressure. Blood pressure is measured both as the heart contracts, which is called systole, and as it relaxes, which is called diastole. Normal blood pressure is considered to be a systolic blood pressure of 115 millimeters of mercury a diastolic pressure of 70 millimeters of mercury (stated as "115 over 70"). If an individual were to have a consistent blood pressure reading of 140 over 90, he would be evaluated for having high blood pressure. If left untreated, high blood pressure can damage important organs, such as the brain and kidneys as well as lead to a stroke. If a bone fracture is severe, a bone graft may be used to help speed the healing process. In this example, a metal plate is also used and fixated with screws. The plate and screws will be removed after the bone has healed.

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The brain is composed of more than a thousand million neurons. Specific groups of them, working in concert, provide us with the capacity to reason, to experience feelings, and to understand the world. They also give us the capacity to remember numerous pieces of information.

The 3 major components of the brain are the cerebrum, cerebellum, and brain stem.

The cerebrum is divided into is left and right hemispheres, each composed of a frontal, temporal, parietal, and occipital lobes. The cerebral cortex (gray matter) is the outside portion of the cerebrum and provides us with functions associated with conscious thought. The grooves and folds increase the cerebrum’s surface area, allowing us to have a tremendous amount of gray matter inside of the skull. Deep to the gray matter is the cerebral "white matter". The white matter provides for the communication between the cortex and lower central nervous system centers.

The cerebellum is located near the base of the head. It creates automatic programs so we can make complex movements without thinking.

The brain stem connects the brain with the spinal cord and is composed of 3 structures: the midbrain, pons, and medulla oblongata. The brain stem provides us with automatic functions that are necessary for survival.

In a breast lift or breast reduction procedure, incisions are made to accommodate a higher position for the areola and nipple, as well as to remove excess skin and breast tissue. Stitches usually follow the circumference of the areola, the natural lower crease of the breast, and a vertical line extending between the areola and lower crease.

The two lungs are the primary organs of the respiratory system. Other components of the respiratory system conduct air to the lungs, such as the trachea (windpipe) which branches into smaller structures called bronchi.

The process of breathing (respiration) is divided into two distinct phases, inspiration (inhalation) and expiration (exhalation). During inspiration, the diaphragm contracts and pulls downward while the muscles between the ribs contract and pull upward. This increases the size of the thoracic cavity and decreases the pressure inside. As a result, air rushes in and fills the lungs.

During expiration, the diaphragm relaxes, and the volume of the thoracic cavity decreases, while the pressure within it increases. As a result, the lungs contract and air is forced out.

Bunions are usually caused by prolonged pressure put on the feet that compresses the big toe and pushes it toward the second toe. Over time, the condition may become painful as extra bone grows where the base of the big toe meets the foot. Malignant tumors of the vocal cords are typically caused by tobacco use. The cardiac conduction system is a group of specialized cardiac muscle cells in the walls of the heart that send signals to the heart muscle causing it to contract. The main components of the cardiac conduction system are the SA node, AV node, bundle of HIS, bundle branches, and Purkinje fibers. The SA node (anatomical pacemaker) starts the sequence by causing the atrial muscles to contract. From there, the signal travels to the AV node, through the bundle of HIS, down the bundle branches, and through the Purkinje fibers, causing the ventricles to contract. This signal creates an electrical current that can be seen on a graph called an Electrocardiogram (EKG or ECG). Doctors use an EKG to monitor the cardiac conduction system’s electrical activity in the heart. In this case of cardiomyopathy, part of the septum dividing the ventricles, is interfering with the normal emptying of the left ventricle. This is one variety of the condition called hypertrophic obstructive cardiomyopathy (HOCM). A catheter is introduced into the heart and through it, concentrated alcohol is applied to the abnormal area, shrinking it, allowing the heart to function normally. The cardiovascular system is composed of the heart and the network of arteries, veins, and capillaries that transport blood throughout the body. The average adult male has between 5 to 6 liters of blood or blood volume, while the average adult female has between 4 to 5 liters. The blood carries oxygen and essential nutrients to all of the living cells in the body, and also carries waste products from the tissues to the systems of the body through which they are eliminated.

Most of the blood is made up of a watery, protein-laden fluid called plasma. A little less than half of this blood volume is composed of red and white blood cells, and other solid elements called platelets. Cataracts may develop with advancing age or in response to diseases such as diabetes. A cataract appears as a cloudy area in the lens. During the first 12 hours after conception, the fertilized egg cell remains a single cell. After approximately 30 hours, it divides from 1 cell into 2 and 15 hours later, the 2 cells divide into 4. And at the end of 3 days, the fertilized egg cell has become a berry-like structure made up of 16 cells. This structure is called a morula, which is Latin for mulberry.

The cells continue to divide 8 or 9 days following conception into a blastocyst. Although it is only the size of a pinhead, the blastocyst is composed of hundreds of cells. The blastocyst is slowly carried by tiny hair-like projections in the fallopian tube called cilia toward the uterus. During the critically important process of implantation, it must attach itself to the uterine lining where it will be able to get nourishment from the mother’s blood supply. If the blastocyst is unable to attach, the pregnancy will fail to survive. The tissue of the brain is supplied by a network of cerebral arteries. If the wall of a cerebral artery becomes weakened, a portion of the wall may balloon out forming an aneurysm. A cerebral aneurysm may enlarge until is bursts, sending blood throughout the spaces in or surrounding the brain. Click and drag the slider bar to see the various stages of cervical dilation between 0 and 10 cm. Although Cesarean (C-sections) are relatively safe surgical procedures, they should only be performed in appropriate medical circumstances. Some of the most common reasons for a Cesarean are:

· If the baby is in a feet first (breech) position · If the baby is in a shoulder first (transverse) position · If the baby’s head is too large to fit through the birth canal · If labor is prolonged and the mother’s cervix will not dilate to 10 centimeters · If the mother has placenta previa, where the placenta is blocking the birth canal · If there are signs of fetal distress which is when the fetus is in danger because of decreased oxygen flow to the fetus

Some common causes of fetal distress are: · Compression of the umbilical cord · Compression of major blood vessels in the mother’s abdomen because of her birthing position · Maternal illness due to hypertension, anemia, or heart disease

Like many surgical procedures, Cesarean sections require anesthesia. Usually, the mother is given an epidural or a spinal block. Both of these will numb the lower body, but the mother will remain awake. If the baby has to be delivered quickly, as in an emergency, the mother may be given a general anesthetic, which will make her fall asleep.

During the surgery, an incision is made in the lower abdomen followed by an incision made in the uterus. There is no pain associated with either of these incisions because of the anesthesia. Once the uterus is open, the doctor will let the amniotic fluid drain from the amniotic sac. Then the baby is carefully eased through the incision and out into the world. The procedure usually lasts about ten minutes.

Afterward, the physician delivers the placenta and stitches up the incisions in the uterus and abdominal wall. Usually, the mother is allowed to leave the hospital within a week, barring complications. Skin is the body’s largest organ. About six pounds of skin cover eighteen square feet on an average adult.

The top layer of skin is called the epidermis. It protects the underlying skin layers from the outside environment and contains cells that make keratin, a substance that waterproofs and strengthens the skin. The epidermis also has cells that contain melanin, the dark pigment that gives skin its color. Other cells in the epidermis allow us to feel the sensation of touch and provide the body with immunity against foreign invaders like germs and bacteria.

The very bottom layer of the skin is the hypodermis. It contains the fat cells, or adipose tissue, that insulate the body and help it conserve heat. The layer between the epidermis and the hypodermis is the dermis. It contains the cells that give skin strength, support, and flexibility. As a person ages, the cells in the dermis lose their strength and flexibility, causing the skin to lose its youthful appearance.

Located in the dermis are sensory receptors. They allow the body to receive stimulation from the outside environment and experience pressure, pain, and temperature. Small blood vessels provide the skin with nutrients, and remove its waste products.

Sebaceous glands produce the oil in the skin, which keeps it from drying out. The oil from the sebaceous glands also helps to soften hair and kill bacteria that get in the skin’s pores. These oil glands are all over the body, except on the palms of the hands and the soles of the feet.

During intercourse, sperm are released into the vagina near the cervix, swim through the uterus and travel up the fallopian tubes. Sperm are composed of 3 parts: a head, a middle section, and a tail. The tail propels the sperm, which is powered by energy cells stored in the middle section. The head of the sperm contains the man’s genetic material and an enzyme-filled acrosomal cap needed to help the sperm penetrate through the outer membrane of the egg.

As an egg released by an ovary travels through a fallopian tube, it may encounter hundreds of sperm that have survived to reach this point in their journey. Eventually, one sperm may succeed in breaking through the egg’s outer membrane.

After penetrating the egg’s outer membrane, the sperm releases its nucleus, which unites with the nucleus from the egg. Fertilization or conception occurs when the sperm fuses with the egg to form a fertilized egg (zygote).

Click a circle in the "Navigation" box to travel to a particular section of the female reproductive system. At each section, select the "Click here to play animation" to see an action occur that leads to the successful conception of a fertilized egg. During sexual intercourse, sperm are released into the vagina near the cervix, which is the entrance to the uterus. The sperm travel through the cervix, into uterus and up the fallopian tubes.

After being release from an ovary, the egg cell moves through the fallopian tube by tiny cilia that line the tube’s walls. The egg cell only survives for approximately 24 hours after ovulation. Of the millions of sperm that are released into the naturally acid environment of the woman’s reproductive tract, relatively few will survive to encounter the egg cell.

When one of the sperm cells finally succeeds in breaking through the egg cell's outer membrane, the egg cell forms a protective barrier preventing other sperm cells from entering. This ensures that only one sperm cell fertilizes the egg cell.

Next, the sperm cell releases its nucleus containing the man’s chromosomes. After several hours, it unites with the nucleus of the egg cell, which contains the woman’s chromosomes. When the two nuclei fuse, their genetic material combines together to create a fertilized egg cell which is called a zygote. Millions of sperm are released during a single ejaculation. Their tails propel on their journey to encounter the single egg cell. Of the millions of sperm, only a few will survive to reach the egg and just one will penetrate the egg cell’s wall to combine it’s genetic material with that of the egg in the process called fertilization. If during the first week of cell division, the fertilized egg cell, or zygote, divides into 2 zygotes, identical twins will form. Each developing embryo contains the same genetic material as the other. In a severe impact to the head, the brain moves and hits the skull causing injury. During a boxing match, the brain moves from side to side after the impact of a punch. Following a concussion head injury, confusion and disorientation due to temporary distortion of the brain may result. Injury or infection of the cornea, the transparent front window of the eye, can lead to serious visual impairment.

Coronary artery bypass graft surgery (CABG) is an invasive procedure that involves taking a section of vein from the leg and grafting it onto a location on the heart, which allows blood to bypass the blocked portion of the coronary artery.

The procedure begins with the surgeon making a cut in the leg and removing a section of vein. Both ends of the vein are tied-off in the leg and cut is closed. The chest is opened and the blood is rerouted through a heart-lung machine. The heart is then stopped.

The surgeon locates the blocked coronary artery and attaches the section of vein taken from the leg to the aorta and to the coronary artery below the blocked segment of the artery. The surgeon may do as many bypasses on as many blocked coronary arteries as the patient needs.

Once each bypass graft is placed, it is checked for leaks. Following this, the heart is restarted. Once the heart is beating again, the surgeon will remove its attachments to the heart-lung machine and sew the openings closed. Following this the chest is closed. A pacemaker may be inserted during the procedure to help control any heart rhythm problems the patient may have.

The coronary arteries supply blood to the heart muscle itself. Damage to or blockage of a coronary artery can result in injury to the heart. Normally, blood flows through a coronary artery unimpeded. However, if the inner wall of a coronary artery becomes damaged, cholesterol plaque can build-up, progressively narrowing the available pathway through which blood can flow.

Clotted blood attempting to traverse the blood vessel may find it tortuous and too narrow for passage, and the artery may become completely constricted or blocked-off. The blocked artery results in a lack of oxygen, or ischemia, to the part of the heart muscle that the artery supplies. The result is a heart attack. Facial cosmetic surgery may include a forehead lift. In this procedure, a hairline incision is made, the forehead skin is pulled-up and excess skin tissue is removed. In an eyelid lift (blepharoplasty), creases and wrinkles around the eyes can be minimized by removing excess fat and skin from the upper and lower eyelids. A facelift usually consists of an incision along or above the hairline and in front of the ears. Excess fat and skin is removed and facial muscles may be tightened.

Coughing is a sudden expulsion of air from the lungs through the epiglottis at an amazingly fast speed (estimated at 100 miles per hour). With such a strong force of air, coughing is the body’s mechanism for clearing the breathing passageways of unwanted irritants.

In order for a cough to occur, several events need to take place in sequence. First, the vocal cords open widely, allowing additional air to pass through into the lungs. Then the epiglottis closes off the windpipe (larynx), and simultaneously, the abdominal and rib muscles contract, increasing the pressure behind the epiglottis. With the increased pressure, the air is forcefully expelled, and creates a rushing sound as it moves very quickly past the vocal cords. The rushing air dislodges the irritant, making it possible to breathe comfortably again.

Diabetes may affect the retina by causing the formation of whitish patches called exudates. Other indications may include tiny enlargements of the blood vessels resulting in microaneurysms and hemorrhages.

Digestion is the process in which food is broken down into nutrients used by the body. Food passes from the mouth through the esophagus to the stomach. The stomach churns the food and breaks it down further with its contents of hydrochloric acid and an enzyme called pepsin.

The process of breaking food down in the stomach takes a few hours. From there, it goes to the duodenum where it is broken down further by digestive bile produced by the liver and stored in the gallbladder along with enzymes from the pancreas. Enzymes are chemicals that speed up the digestion of specific types of food. For example, the enzyme trypsin breaks down the protein in steak, lipase helps to break down fat, and lactase breaks down the sugar in milk.

Once everything is broken down, the small intestine absorbs the nutrients the body needs. From there the nutrients go into the bloodstream and to the liver, where poisons are removed. Undigested food and water continue through the small intestine and go into the large intestine, where water is reabsorbed. Finally, feces are eliminated through the rectum and anus.

Directional Coronary Atherectomy (DCA) is a minimally invasive procedure to remove the blockage from the coronary arteries and allow more blood to flow to the heart muscle and ease the pain caused by blockages.

The procedure begins with the doctor injecting some local anesthesia into the groin area and putting a needle into the femoral artery, the blood vessel that runs down the leg. A guide wire is placed through the needle and the needle is removed. An introducer is then placed over the guide wire, after which the wire is removed. A different sized guide wire is put in its place.
 
Next, a long narrow tube called a diagnostic catheter is advanced through the introducer over the guide wire, into the blood vessel. This catheter is then guided to the aorta and the guide wire is removed. Once the catheter is placed in the opening or ostium of one the coronary arteries, the doctor injects dye and takes an x-ray.

If a treatable blockage is noted, the first catheter is exchanged for a guiding catheter. Once the guiding catheter is in place, a guide wire is advanced across the blockage, then a catheter designed for lesion cutting is advanced across the blockage site. A low-pressure balloon, which is attached to the catheter adjacent to the cutter, is inflated such that the lesion material is exposed to the cutter.

The cutter spins, cutting away pieces of the blockage. These lesion pieces are stored in a section of the catheter called a nosecone, and removed after the intervention is complete. Together with rotation of the catheter, the balloon can be deflated and re-inflated to cut the blockage in any direction, allowing for uniform debulking.

A device called a stent may be placed within the coronary artery to keep the vessel open. After the intervention is completed the doctor injects contrast media and takes an x-ray to check for any change in the arteries. Following this, the catheter is removed and the procedure is completed.

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After the membranes rupture and the water breaks, a woman may begin to experience the first phase of labor (early labor). The average time of early labor is extremely variable, lasting anywhere from 2 to 6 hours. In rare cases, it can last up to 24 hours.

During this time, the pressure of repeated regular contractions causes the cervix, which had been closed when labor began, to open up to a diameter of 3 centimeters while becoming much thinner.

Various techniques can be used to help alleviate the discomfort a woman may experience during the first phase of labor such as back-rubs and breathing exercises. All of the immature egg cells (oocytes) a woman will ever produce are stored in the ovaries by the time she is born. The average age that girls begin to menstruate is 12 years old. Each menstrual cycle occurs approximately every 28 days. During each cycle, hormonal messages from the brain cause the ovaries to develop a single mature egg cell for potential fertilization, even as other hormones instruct the uterine lining to thicken in preparation for nourishing the fertilized egg cell.

The cycle starts when a follicle grows within one of the ovaries. A follicle is composed of the developing egg cell and the support cells that surround and nourish it. On day 1 of the cycle, a small structure in the brain, the pituitary gland, releases two hormones, FSH and LH, both of which cause the follicle to begin growing.

Over the next 13 days, the growing follicle releases estrogen, a hormone that prepares the lining of the uterus to receive a fertilized egg cell. Meanwhile, the estrogen in the bloodstream causes the brain to release a surge of LH. In response to the LH surge, the follicle enlarges rapidly. On day 14, it ruptures and releases the egg cell in a process known as ovulation.

The ruptured follicle begins secreting the hormone progesterone, which also helps to prepare the uterine lining for a fertilized egg cell. The egg cell is swept into the fallopian tube entrance by its waving structures called fimbriae.

Once the egg cell is within the fallopian tube, it will either be fertilized by a sperm cell, or fertilization will fail to take place. If the egg cell is not fertilized within 24 hours after its release from the ovary, it will stop developing and will dissolve before reaching the uterus. The absence of a fertilized egg cell gradually causes a woman’s body to stop releasing the hormones that would otherwise prepare the uterus for the developing egg cell. In response, the uterus sheds its lining on days 24 through 28 during menstruation.

If a sperm does fertilize the egg cell, tiny hair-like cells called cilia will transport it towards the uterus. The fertilized egg now called a blastocyst, lodges in the uterine wall in a process called implantation to receive nourishment from the uterine lining. The remaining cells of the ruptured follicle in the ovary produce progesterone so that the uterine lining will stay rich in blood vessels, and the fertilized egg cell will survive.

A woman is born with all of the egg cells she will release throughout her lifetime. Starting at about age 12 through menopause, a woman’s reproductive cycle releases an egg about once a month.

Hormonal messages from the brain instruct the ovaries to develop several follicles in which a single dominant follicle in one of the ovaries will release an egg for fertilization. During this time, other hormones instruct the uterine lining to thicken in preparation for nourishing a fertilized egg.

There are several hormones that regulate the reproductive cycle. Follicle stimulating hormone (FSH) stimulates preparation of the egg for fertilization by instructing a follicle to begin dividing it’s genetic material (chromosomes).

The follicle then releases estrogen, the hormone that prepares the lining of the uterus to receive a fertilized egg. Increased levels of estrogen in the bloodstream cause a small structure in the brain, the pituitary gland, to stop releasing the hormone FSH, and to start releasing luteinizing hormone (LH).

LH causes the follicle to enlarge rapidly and to release its egg in a process known as ovulation. Once the egg is out of the follicle, the follicle begins secreting the hormone progesterone, which also helps to prepare the uterine lining for the fertilized egg. The remaining cells of the follicle shrink into a hormone producing mass of cells called a corpus luteum.

The egg is swept into the fallopian tube by its waving structures called fimbriae. Fertilization of the egg usually occurs in the fallopian tube. From there, it is transported to the uterus and implants itself in the uterine wall, where it is nourished by the uterine lining. In the ovary, the corpus luteum produces progesterone so that the egg can develop into a fetus.

If the egg is not fertilized within 24 hours after its release from the ovary, it stops developing and dissolves before reaching the uterus. The absence of a fertilized egg causes the body to stop releasing the hormones that prepare the uterus for implantation. In response, the uterus sheds its lining over a period of four to five days in a process known as menstruation.

Click the waveform pull-down list to view various waveforms showing normal and pathological conditions of the heart. The endocrine system is primarily composed of glands that produce chemical messengers called hormones. Glands of the endocrine system include the pituitary gland, the thyroid gland, the parathyroid glands, the thymus, and the adrenal glands. Other glands are also included within the endocrine system since they contain endocrine tissue that secretes hormones such as the pancreas, ovaries and testes.

The endocrine and nervous systems work very closely together. The brain continuously sends instructions to the endocrine system, and in return receives feedback from the endocrine glands. Because of this intimate relationship, the nervous and endocrine systems are referred to as the neuroendocrine system.

The hypothalamus is known as the master switchboard because it’s the part of the brain that controls the endocrine system. The pituitary gland, which hangs by a thin stalk from the hypothalamus, is called the master gland of the body because it regulates the activity of the endocrine glands.

The hypothalamus detects the rising level of the target organ’s hormones then sends either hormonal or electrical messages to the pituitary gland. In response, the pituitary gland releases hormones, which travel through the bloodstream to a target endocrine gland, instructing it to stop producing its hormones.

The endocrine system constantly adjusts hormone levels so that the body can function normally. This process is called homeostasis. The prostate gland is located underneath the bladder and is about the size of a chestnut. Part of the urethra is encased within the prostate gland. As a man ages, the prostate typically enlarges in size in a process called benign hypertrophy (non-cancerous enlargement).

The enlarged prostate crowds its surrounding structures and may cause the urethra to narrow. The narrowed urethra results in several of the symptoms of benign prostatic hypertrophy (BPH). Symptoms may include a slowed or delayed start in urination, the need to urinate frequently during the night, difficulty in emptying the bladder, a strong, sudden urge to urinate, and incontinence. Less than half of all men with BPH have symptoms of the disease, or their symptoms are minor and do not restrict their life style.

BPH is a normal physiological process of aging and treatment options are available. The choice of the appropriate treatment is based on the severity of the symptoms, the extent to which they effect lifestyle, and the presence of other medical conditions. Men with BPH should consult with their physician yearly to monitor the progression of the symptoms and decide the best course of treatment as needed. The prostate gland is located underneath the bladder and is about the size of a chestnut. Part of the urethra is encased within the prostate gland. As a man ages, the prostate typically enlarges in size in a process called benign hypertrophy (non-cancerous enlargement).
The enlarged prostate crowds its surrounding structures and may cause the urethra to narrow. The narrowed urethra results in several of the symptoms of benign prostatic hypertrophy (BPH). Symptoms may include a slowed or delayed start in urination, the need to urinate frequently during the night, difficulty in emptying the bladder, a strong, sudden urge to urinate, and incontinence. Less than half of all men with BPH have symptoms of the disease, or their symptoms are minor and do not restrict their life style.
BPH is a normal physiological process of aging and treatment options are available. The choice of the appropriate treatment is based on the severity of the symptoms, the extent to which they effect lifestyle, and the presence of other medical conditions. Men with BPH should consult with their physician yearly to monitor the progression of the symptoms and decide the best course of treatment as needed. During periods of stress, such as preparing to run in a race, the brain signals the adrenal glands to produce epinephrine or "adrenaline". Epinephrine increases the rate in which the heart beats. The increased cardiac output supplies more oxygen to the muscles, putting the body a heightened state to react. As a longer term response to stress, cortisol is secreted by the adrenal glands, promoting the release of energy. Weight lifting is a form of anaerobic exercise. It is very demanding, requiring a great deal of energy, which quickly depletes the body’s oxygen reserves. Sprinting and push-ups are other examples of anaerobic activities. They each create a situation called oxygen debt, which requires us to breathe deeply and rapidly in order to restore a proper oxygen level to the muscle cells.

If oxygen reserves become depleted while exercising, muscles convert a starch, called glycogen, into energy. This conversion process creates a waste product called lactic acid, which can be partly responsible for muscle soreness the next day.

Jogging is a form of aerobic exercise. Exercising over a long duration requires a steady level of energy for the body. If properly conditioned, the body will be able to supply adequate oxygen to meet its energy requirements during aerobic exercise and much less lactic acid will be formed in the muscles.

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Pain provides the body with a protective mechanism, alerting it to potential or actual damage to the body’s tissues. In the example of a bee sting, the pain receptors in the skin detect tissue damage from the bee sting. Then, the peripheral nerves send a pain signal to the brain. The brain analyzes the pain signal. In turn, the brain delivers a message back to the muscles of the arm to react.

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Click and drag a slider bar underneath an image window to see the process of embryonic and fetal development.

The ears begin their development during the fifth week of pregnancy. Ear formation starts from a few small bulges called branchial arches. Portions of the branchial arches form into structures called auricular hillocks. The auricular hillocks grow and join together to form the outer ears.

During the fifth month, the inner and middle parts of the ear develop, but won’t be completely finished until birth.

Twins occur in about 1% of all pregnancies in which 30% are identical (maternal, monozygotic) twins and 70% are non-identical (fraternal, dizygotic) twins.

A single baby is formed when an egg cell is fertilized by a single sperm cell to form a zygote. The zygote divides to form a structure composed of hundreds of cells called a blastocyst. The blastocyst implants into the uterine lining and will grow into a single baby.

Identical twins start out from a single fertilized egg cell (zygote). Unlike a single baby, the fertilized egg cell will split into two separate embryos during the two-cell stage (day 2), early blastocyst stage (day 4), or late blastocyst stage (day 6).

The stage at which the egg cell splits determines how the twins will implant in the uterine lining, and whether or not they share an amnion, chorion, and placenta. The earlier the splitting occurs, the more independently the twins will develop in the uterus. Twins that split during the late blastocyst stage will share an amnion, chorion, and amniotic sac.

Non-identical twins develop from two fertilized egg cells (zygotes). During ovulation, two egg cells are released and fertilized by two different sperm cells. Non-identical twin embryos develop separately each having their own chorion, amnion, and placenta.

Air first enters the body through the mouth or nose, quickly moves to the pharynx (throat), passes through the larynx (voice box), enters the trachea, which branches into a left and right bronchus within the lungs and further divides into smaller and smaller branches called bronchioles. The smallest bronchioles end in tiny air sacs, called alveoli, which inflate during inhalation, and deflate during exhalation.

Gas exchange is the delivery of oxygen from the lungs to the bloodstream, and the elimination of carbon dioxide from the bloodstream to the lungs. It occurs in the lungs between the alveoli and a network of tiny blood vessels called capillaries, which are located in the walls of the alveoli.

The walls of the alveoli actually share a membrane with the capillaries in which oxygen and carbon dioxide to move freely between the respiratory system and the bloodstream. Oxygen molecules attach to red blood cells, which travel back to the heart. At the same time, the carbon dioxide molecules in the alveoli are blown out of the body with the next exhalation.

Glaucoma is the development of increased pressure within the eye. If left untreated, glaucoma may damage the optic nerve, resulting in visual impairment and eventually blindness. Gout is caused by increased production of uric acid. Uric acid crystals travel and accumulate in the joints, especially in the feet and legs, causing great pain and swelling.

The ear is divided into three regions: the outer ear, middle ear and inner ear.

When sound waves enter the ear canal, they cause the eardrum to vibrate. The vibration moves the three bones in the middle ear, called the ossicles. The ossicles are also known as the hammer (malleus), anvil (incus), and stirrup (stapes). These tiny bones transfer and amplify sound waves to the oval window, which is located behind the stirrup.

When the oval window vibrates, it moves fluid across a membrane inside the cochlea. The fluid causes the membrane to move. Specialized hair cells translate this movement into nerve impulses, which are sent to the brain through the vestibulocochlear nerve. The brain interprets the impulses as sound.

As sound waves entering the ear, they travel through the outer ear, the external auditory canal, and strike the eardrum causing it to vibrate. The central part of the eardrum is connected to a small bone of the middle ear called the malleus (hammer). As the malleus vibrates, it transmits the sound vibrations to the other two small bones or ossicles of the middle ear, the incus and stapes. As the stapes moves, it pushes a structure called the oval window in and out. This action is passed onto the cochlea, which is a fluid-filled snail-like structure that contains the receptor organ for hearing. The cochlea contains the spiral organ of Corti, which is the receptor organ for hearing. It consists of tiny hair cells that translate the fluid vibration of sounds from its surrounding ducts into electrical impulses that are carried to the brain by sensory nerves. As the stapes rocks back and forth against the oval window, it transmi ts pressure waves of sound through the fluid of the cochlea, sending the organ of Corti in the cochlear duct into motion. The fibers near the cochlear apex resonate to lower frequency sound while fibers near the oval window response to higher frequency sound.

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Heart bypass surgery begins with an incision made in the chest, with the breastbone cut exposing the heart. Next, a portion of the saphenous vein is harvested from the inside of the leg. Pieces of this great vein will be used to bypass the blocked arteries in the heart. The venous graft is sewn to the aorta and to the affected coronary artery past the blocked site. The internal mammary artery from the chest may also be used to bypass a clogged artery. Several arteries may be bypassed depending on the condition of the heart. The embryo’s heart is the first organ that forms. It is derived from two primitive heart tubes. Between days 18 to 30, the primitive heart tubes fuse together, bend and twist to form a simple version of the heart. About half way through this process, the heart starts to beat.

At 2 months, the heart bears a close resemblance to what it will look like after the baby’s born. The resemblance is only superficial since the inside of the heart is different in both form and function.

In a newborn’s heart, oxygen-poor blood from the body enters the right atrium, goes to the right ventricle where it is pumped to the lungs to become rich with oxygen. From the lungs, the blood flows back to the heart filling the left atrium then enters the left ventricle. The left ventricle pumps the oxygen rich blood through the aorta, which carries it to the rest of the newborn’s body.

The fetal heart has the same basic components as the newborn heart, but there are a couple important differences. Because the placenta is providing all of the oxygen the fetus requires, its lungs are not needed to perform this task. Much of the fetus’ blood is detoured away from the lungs through two openings or connections: the foramen ovale, which connects the right and left atria, and the ductus arteriosus, which connects the aorta and the pulmonary artery. These two important connections will remain open up until the time of birth.

Within thirty minutes after the baby’s first breath, the ductus arteriosus will completely close, and the flap of the foramen ovale will shut off like a valve. This happens because of an increase in pressure on the left side of the heart, and a decrease on the right side. These changes in the heart anatomy cause the blood to flow to the lungs, which will take over their lifelong job of supplying oxygen to the body. The heart is a four-chambered organ with four main vessels, which either bring blood to or carry blood away from the heart. The four chambers of the heart are the right atrium, right ventricle, left atrium, and left ventricle.

The great vessels of the heart include: • Superior and inferior vena cava (brings blood from the body to the right atrium) • Pulmonary artery (transports blood from the right ventricle to the lungs) • Aorta (the body’s largest artery, which transports oxygen-rich blood from the left ventricle to the rest of the body)

A series of one-way valves keep the blood flowing in one direction with every heartbeat. Blood first enters the heart into the right atrium then passes from the right atrium through the tricuspid valve and into the right ventricle. When the right ventricle contracts, the muscular force pushes blood through the pulmonary semilunar valve into the pulmonary artery.

Blood then travels to the lungs, where it receives oxygen. Next, it drains out of the lungs via the pulmonary veins, and travels to the left atrium. From the left atrium, the blood is forced through the bicuspid valve into the left ventricle. The left ventricle is the major muscular pump that sends the blood out to the body systems. When the left ventricle contracts, it forces the blood through the aortic semilunar valves and into the aorta. The aorta and its branches carry blood to all the tissues of the body. Heartburn is pain felt in the chest by a burning sensation in the esophagus, which is located close to where the heart is. At junction between the stomach and esophagus is the cardiac sphincter. This muscular sphincter acts as a valve that normally keeps food and stomach acid in the stomach and prevents the stomach’s contents from regurgitating back into the esophagus.

However, certain foods may affect the cardiac sphincter, making it less effective. The stomach produces hydrochloric acid to digest food. The stomach has a mucous lining that protects it from hydrochloric acid, but the esophagus does not. When food and stomach acid regurgitate back into the esophagus, a burning sensation is felt near the heart resulting in heartburn. Antacids may be used to relieve heartburn by making stomach juices less acidic, therefore reducing the burning feeling felt in the esophagus. If heartburn becomes frequent or prolonged, medical intervention may be necessary to correct the problem. The disks between the vertebrae are liable to displacement when put under strain. Heavy lifting may produce forces which cause a lumbar intervertebral disk to move out of place ("slipped disk"). Homeostasis is a state of balance inside the body, where the body systems work together to keep it functioning normally. The endocrine system keeps this internal balancing act going by releasing chemicals called hormones. The release of the hormones is controlled by negative feedback mechanisms.

A negative feedback mechanism works something like a thermostat in your home. A thermostat helps maintain a constant temperature, called the normal range. When the temperature rises beyond the normal range, the thermostat turns on the air conditioner. Eventually the air conditioner restores the temperature to the normal range. This process is called negative feedback. It starts with a normal range, goes beyond the normal range, and then back to normal again.

An example of how negative feedback works in the body can be demonstrated by the endocrine system’s controls over the amount of sugar in the bloodstream. Insulin is a hormone secreted by the pancreas that maintains a normal amount of sugar in the bloodstream. Shortly after eating a candy bar, tiny sugar molecules enter the bloodstream raising the blood sugar levels. In response, the pancreas secretes the insulin into the bloodstream. Now, the sugar molecules move out of the bloodstream and into the cells of the skeletal muscles, fat and liver. In turn, the blood sugar levels return to normal. The human face starts as a series of paired tissue mounds called branchial arches. During embryotic development, the face forms from the first branchial arch along with the area just above it.

At 28 days of development, the lower jaw has fused together from the branchial arches. The nostrils start to form by day 21 and the eyes appear on each side of the head. 2 days later, the nostrils move toward the center of the face and the ears begin to form.

At 35 days, the nostrils are closer together and more of the eyes can be seen. At 40 days, the eyelids have developed and the nose begins to take its form. At 48 days, the nasal swellings have joined in the center of the face and the eyes have moved to the front of the head.

3 weeks later, the fetal face takes on its human appearance. The face continues to develop more typical proportions right up until the time of birth. If left untreated, hypertension can lead to the thickening of arterial walls causing its lumen, or blood passage way, to narrow in diameter. As a result, the heart must work harder to pump blood through the narrowed arterial openings. In addition, people with hypertension may be more susceptible to stroke. The immune system is comprised of specialized white blood cells, called lymphocytes that adapt themselves to fight specific foreign invaders. These cells develop into two groups in the bone marrow.

From the bone marrow, one group of lymphocytes migrates to a gland called the thymus and become T lymphocytes or T cells. Within the thymus, the T cells mature under the influence of several hormones.

The T cells mature into several different types, including helper, killer and suppressor cells. When matured, the T cell types are ready to work together to directly attack foreign invaders, providing what physicians call cell-mediated immunity. This type of immunity can become deficient in persons with HIV, the virus that causes AIDS, because HIV attacks and destroys helper T cells.

The other group of lymphocytes, B lymphocytes or B cells, mature and develop within the bone marrow itself. In that process, they achieve the ability to recognize specific foreign invaders. From the bone marrow, B cells migrate through the body fluids to the lymph nodes, spleen and blood. B lymphocytes provide the body with humoral immunity as they circulate in the fluids in search of specific foreign invaders to destroy. Intracytoplasmic sperm injection, or ICSI, is a form of in vitro fertilization in which fertilization occurs outside of the body. First, egg cells are harvested and transferred to a special media in a laboratory dish. Within a few hours, a single sperm is injected through a fine needle into the center of an egg cell to aid in the process of fertilization. If successful, the cell will divide and form the beginning stages of an embryo. If necessary, the DNA of a single cell from an embryo may be checked to ensure that various genetic disorders are not present. Typically, several egg cells are harvested and fertilized at the same time then inserted back into the uterus to increase the chances that one will implant and develop into a successful pregnancy.

The urinary tract includes the kidneys, ureters, bladder and urethra. Within each kidney, urine flows from the outer cortex to the inner medulla. The renal pelvis is the funnel through which urine exits the kidney and enters the ureter.

As urine can become very concentrated as it passes through the kidneys. When the urine becomes too concentrated, calcium, uric acid salts and other chemicals dissolved in the urine can crystallize, forming a kidney stone (renal calculus).

Usually the calculus is the size of a small pebble. But ureters are very sensitive to being stretched, and when stones form and distend it, the stretching can be very painful. Often, people may not know they have kidney stones until they feel the painful symptoms resulting from a stone being stuck anywhere along the urinary tract. Fortunately, small stones typically passed out of the kidneys and through the ureters on their own without causing any problems.

However, stones can become more problematic when they block the flow of urine. A staghorn kidney stone may obstruct the entire kidney. Fortunately, these stones are the exception rather than the rule.

When a baby is ready to be born, the mother starts to feel labor contractions. That means that her uterus starts squeezing and pushing so the baby can come out. It’s a tight fit, but it doesn’t hurt the baby during delivery.

At 1 month, the baby growing inside the mother’s uterus is very small. The baby is so small she could fit in the palm of your hand and is about the size of your thumbnail.

Over the next 9 months, the baby will grow more inside the uterus until she is ready to be born.

To make a baby, a man’s sperm meets and joins with a woman’s egg cell inside her body. Inside the man’s sperm are a set of instructions that tell the baby to be a boy or a girl.

The instructions in the man’s sperm cell can either carry the letter "X" or the letter "Y". If the letter is an "X", it means the baby will be a girl. If the letter is a "Y", the baby will be a boy.

When the baby is in the mother’s uterus, it can’t eat or breathe on its own, so it needs some help. The baby has a little tube that goes to its middle called the umbilical cord. The umbilical cord goes to the placenta, which connects to the mother’s uterus.

Here’s how it works. First, the food that the mother eats and air that she breathes get into her bloodstream as very tiny pieces called molecules.

These molecules, or tiny pieces of food and air, travel through the mother’s bloodstream to her placenta. From there, they go to the umbilical cord and into the baby’s body. That’s how the baby eats and breathes inside the uterus.

After a baby is born, the umbilical cord goes away. Guess what’s left? You’re belly button.

Two things are needed to make a baby: a sperm cell and an egg cell. A man makes the sperm cell inside his body and a woman makes the egg cell inside her body.

Both the sperm cell and egg cell are very small. You would need a microscope to see them in real life. A microscope is like a magnifying glass, only much stronger.

When the sperm cell and the egg cell meet each other, they make a tiny baby that’s smaller than a grain of salt. The baby will grow inside a special place in woman’s body called the uterus. After about nine months, the baby will come out as a little boy or girl.

A vibrating suction cannula, or flexible tube, is used in a liposuction procedure. The cannula is inserted through a small hole into the abdominal fat tissue to remove excess fat deposits.

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The lymphatic system is a complex network of thin vessels, valves, ducts, nodes, and organs. It helps to protect and maintain the fluid environment of the body by producing, filtering, and conveying lymph and by producing various blood cells.

Lymph nodes play an important part in the body’s defense against infection. The most common cause of swollen lymph nodes is infection, which might occur even if the infection is trivial or not. Afferent lymph vessels bring unfiltered fluids into the lymph node to be filtered while efferent vessels carry clean fluids away from the lymph node and to the cardiovascular system where it helps form the plasma in the blood.

Overall, lymph nodes work like a biological filtering system. When the body is invaded by foreign organisms, the painful swelling sometimes felt in the neck, armpits, groin, or tonsils comes from the microorganisms being trapped inside collections of lymph cells or nodes. Eventually, these organisms are destroyed and eliminated by cells that line the walls of the lymph nodes and the swelling and pain subside. The lymphatic system is often referred to as the body’s "secondary circulatory system". The lymphatic system collects excess fluid in the body’s tissues and returns it to the bloodstream.

Lymph formation occurs at the microscopic level. During the exchange of fluid and molecules between the blood circulation and body tissues, blood capillaries may not reabsorb all of the fluid. Surrounding lymphatic capillaries absorb the excess fluid. The fluid is then filtered and transported back by the lymphatic system into large veins near the heart.

The lymphatic system can play a very worrisome role in the spread of breast cancer. Components of the lymphatic system called lymph nodes are distributed at specific locations throughout the body. There is also an extensive network of lymphatic vessels in every woman’s breast tissue, which is important in regulating the local fluid balance as well as in filtering out harmful substances.

The lymph vessels in the breast may inadvertently supply cancerous cells with access to a highway along which the cancerous cells can move to other parts of the body. This process is called metastasis and may result in the formation of a secondary cancer mass in a different location of the body. Regular breast self examinations can help to detect tumors earlier in their growth, hopefully before they spread quickly or metastasize. The macula is the part of the retina that distinguishes fine details at the center of the field of vision. Macular degeneration results from a partial breakdown of the insulating layer between the retina and the choroid layer of blood vessels behind the retina. Macular degeneration results in the loss of central vision only.

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Click and drag the slider bar to see changes that occur during a normal 28 day menstrual cycle.

Muscles perform four important body functions: maintain body posture, stabilize the joints, provide mobility, and generate heat that the body requires.

The body contains three types of muscle to perform these functions:
• Smooth muscle - involuntary muscle found in the walls of body organs; functions without conscious control
• Cardiac muscle - involuntary muscle found only in the walls of the heart; functions without conscious control
• Skeletal muscle - attaches to and covers the bony skeleton to provide movement of the body; the only type of muscle under voluntary or conscious control

The nervous system is composed of two divisions, the central nervous system (CNS) and peripheral nervous system (PNS). The CNS contains the brain and the spinal cord and the PNS consists of thousands of nerves that connect the spinal cord to muscles and sensory receptors.

A peripheral nerve is composed of nerve bundles (fascicles) that contain hundreds of individual nerve fibers (neurons). Neurons consist of dendrites, axon, and cell body. The dendrites are the tree-like structures that receive signals from other neurons and from special sensory cells that sense the body’s surrounding environment. The cell body is the headquarters of the neuron and contains its genetic information in the form of DNA. The axon transmits signals away from the cell body to other neurons.

Many neurons are insulated like pieces of electrical wire. This insulation protects them and also allows their signals to move faster along the axon. Without this insulation, signals from the brain might never reach the outlying muscle groups in the limbs.

The operation of the nervous system depends on the flow of communication between neurons. For an electrical signal to travel between two neurons, it must first be converted to a chemical signal, which then crosses a space of about a millionth of an inch wide. The space is called a synapse, and the chemical signal is called a neurotransmitter.

Neurotransmitters allow the billions of neurons in the nervous system to communicate with one another, making the nervous system the master communication system of the body.

The most critical stage of development for the embryo’s nervous system is the third and fourth weeks of pregnancy.

On day 14, the embryo looks like a little disc. The first part of the nervous system that forms is an indentation called the neural groove. Over the next 7 days, the groove deepens as the cells around it form ridges called neural folds.

By day 27, the neural folds wrap around the neural groove and form the neural tube. The neural tube will further develop into the brain and spinal cord. Structures called somites form the vertebral column, or backbone. They also help form the ribs and the muscles of the neck, arms, and legs.

The embryo’s nervous system is particularly vulnerable during the early stage of development, so an expectant mother should be careful about avoiding any substances that could potentially harm it. Nutrient exchange is a continuous cycle, constantly supplying the body with oxygen and nutrients while removing carbon dioxide and metabolic waste.

Red blood cells are the cells in the blood that carry oxygen from the lungs to the body tissues through blood pumped by the heart. As they travel away from the heart, they traverse smaller and smaller arteries, finally arriving at the collections of microscopic blood vessels called capillaries. Capillaries contain a high concentration of oxygen and nutrients, while the surrounding tissues contain a lower concentration. Through a process called diffusion, these particles leave the capillaries and enter the body’s tissues.

Conversely, the body’s tissues contain high concentrations of carbon dioxide and metabolic waste, while the capillaries contain a lower concentration. Waste products diffuse from the tissues into the capillaries and from there are carried by the venous system back toward the heart. The waste products are eventually eliminated from the bloodstream through the urinary and respiratory systems.

Osteoarthritis is the most common form of arthritis and is associated with the aging process. Osteoarthritis is a chronic disease causing the deterioration of the cartilage within a joint.

For most people, the cause of osteoarthritis is unknown, but metabolic, genetic, chemical, and mechanical factors play a role in its development. Symptoms of osteoarthritis include loss of flexibility, limited movement, and pain and swelling within the joint. The condition results from injury to the cartilage, which normally absorbs stress and covers the bones, so they can move smoothly.

The cartilage of the affected joint is roughened and becomes worn down. As the disease progresses, the cartilage becomes completely worn down and the bone rubs on bone. Bony spurs usually develop around the margins of the joint.
Part of the pain results from these bone spurs, which can restrict the joint’s movement as well.

Osteoporosis is a condition that leads to loss of bone mass. From the outside, osteoporotic bone is shaped like normal bone. However, the inside of the bones becomes more porous during the again process due to the loss of calcium and phosphate. The loss of these minerals makes the bones more prone to fracture even during routine activities, like walking, standing, or bathing. Often, a person will sustain a fracture before becoming aware of the presence of the disease.

Prevention is the best measure for treating osteoporosis by eating a recommended balanced diet including foods with sufficient amounts of calcium, phosphorous, and vitamin D. In addition, maintaining a regular exercise program as approved by your health care provider will help to keep the bones strong.

Various medications can be used as part of the treatment for osteoporosis and should be discussed thoroughly with your health care provider. Ovulation occurs though a sequence of hormonal responses. Located deep within the brain, the pituitary gland releases the hormones FSH and LH, which travel through the blood stream to the ovaries. These hormones signal the development and release a single egg cell from one of the ovaries. The sweeping motion of the fimbriae draws the egg cell through a very small space in the open body cavity into the uterine, or fallopian, tube. The egg cell will either be fertilized by sperm or will dissolve if fertilization does not take place. In Parkinson's disease, dopamine production becomes irregular and inadequate and nerve cells cannot properly transmit messages. This results in the loss of muscle function. By providing an even, adequate supply of medication that the body converts into dopamine, neurons are able to transmit messages and tremors improve.

Percutaneous Transluminal Coronary Angioplasty (PTCA) is a minimally invasive procedure to open up blocked coronary arteries, allowing blood to circulate unobstructed to the heart muscle.

The procedure begins with the doctor injecting some local anesthesia into the groin area and putting a needle into the femoral artery, the blood vessel that runs down the leg. A guide wire is placed through the needle and the needle is removed. An introducer is then placed over the guide wire, after which the wire is removed. A different sized guide wire is put in its place.

Next, a long narrow tube called a diagnostic catheter is advanced through the introducer over the guide wire, into the blood vessel. This catheter is then guided to the aorta and the guide wire is removed. Once the catheter is placed in the opening or ostium of one the coronary arteries, the doctor injects dye and takes an x-ray.

If a treatable blockage is noted, the first catheter is exchanged for a guiding catheter. Once the guiding catheter is in place, a guide wire is advanced across the blockage, then a balloon catheter is advanced to the blockage site. The balloon is inflated for a few seconds to compress the blockage against the artery wall. Then the balloon is deflated.

The doctor may repeat this a few times, each time pumping up the balloon a little more to widen the passage for the blood to flow through. This treatment may be repeated at each blocked site in the coronary arteries. A device called a stent may be placed within the coronary artery to keep the vessel open. Once the compression has been performed, contrast media is injected and an x-ray is taken to check for any change in the arteries. Following this, the catheter is removed and the procedure is completed.

Peristalsis is a series of wave-like muscle contractions that moves food to different processing stations in the digestive tract. The process of peristalsis begins in the esophagus when a bolus of food is swallowed. The strong wave-like motions of the smooth muscle in the esophagus carry the food to the stomach, where it is churned into a liquid mixture called chyme.

Next, peristalsis continues in the small intestine where it mixes and shifts the chyme back and forth, allowing nutrients to be absorbed into the bloodstream through the small intestine walls.

Peristalsis concludes in the large intestine where water from the undigested food material is absorbed into the bloodstream. Finally, the remaining waste products are excreted from the body through the rectum and anus. Macrophages are scavenger cells that can ingest dead tissue and foreign cells. Macrophages form tentacles called pseudopods to surround an invader. Once inside the macrophage, the invader is walled off and then digested and destroyed by a bag of digestive chemicals, or enzymes. The pituitary gland is often referred to as the "master gland" of the body, since it regulates many activities of other endocrine glands. Located above the pituitary gland is the hypothalamus. The hypothalamus decides which hormones the pituitary should release by sending it either hormonal or electrical messages.

In response to hormonal messages from the hypothalamus, the pituitary gland releases the following hormones: • GH (growth hormone) – increases size of muscle and bone • THS (thyroid stimulating hormone) – stimulates the thyroid gland to release T3 and T4 to stimulate metabolism in other cells throughout the body • FSH (follicle stimulating hormone) – stimulates ovarian follicle production in women; stimulates sperm production in men • LH (luteinizing hormone) – stimulates ovaries to produce estrogen in women; stimulates sperm production in men • Prolactin – stimulates breast tissue in nursing mothers to produce milk • ACTH (adrenocorticotropic hormone) - causes the adrenal glands to produce important substances that have properties similar to steroids

In response to electrical messages from the hypothalamus, the pituitary gland releases the following hormones: • ADH (antidiuretic hormone) - stimulates the kidneys to reabsorb fluid and produce less urine • Oxytocin – initiates labor, uterine contractions and milk ejection in mothers The placenta provides the baby with nutrients and oxygen from the mother and carries away fetal waste. Following delivery, the uterus naturally contracts to push the placenta out of the uterus. In addition, the delivering practitioner will assist by gently pressing the abdomen to work the placenta free of the uterus.

Delivery of the placenta is typically painless and takes approximately 15 minutes.

Once the placenta is delivered, it is examined to see if the placental tissue is healthy and in one piece. At times, the placenta can break off and cause bleeding in the uterus. The placenta is commonly referred to as the afterbirth. Its successful delivery signals the end of the final stage of childbirth.

The growing embryo requires nutrition and oxygen, and a disposal system for the waste products of its own metabolism. All of this is accomplished by the placenta, which allows the growing embryo to eat and breathe while in the mother’s uterus.

Following implantation of the fertilized egg into the uterine lining, the outer layer of the embryo develops spaces called lacunae. The lacunae filled up with blood from the mother’s uterine lining. Small projections from the embryo’s chorionic layer reached out into the uterine lining. The chorionic layer is one of the membranes that surround the embryo and help it implant. Blood vessels begin to form beneath this chorionic layer.

Around day 21, the embryo’s bloodstream and the mother’s bloodstream are in such close contact that nutrients and oxygen can cross from mother to embryo. The two bloodstreams are separated by a thin collection of tissues in the placenta called the blood barrier. This barrier permits small particles like nutrients and oxygen to pass from the mother to the embryo and allows waste products to pass from the embryo back to the mother.

The blood barrier also prevents many large or potentially harmful particles from entering the embryo’s bloodstream. The red blood cells do not cross from the mother’s bloodstream to the embryo’s bloodstream.

It’s important to keep the two bloodstreams separate since the blood type of the mother and embryo could be different. If the mother’s blood type is positive, and her embryo’s blood type is negative, then the mother’s blood cells would treat the embryo as an invading foreign organism, and try to destroy it.

The placenta and its blood barrier are important for supplying the growing embryo with nutrition and oxygen, removing its waste products, and preventing harmful substances from getting into the embryo’s bloodstream.

Hypertension caused by pre-eclampsia can adversely affect the fetus by causing constriction of the placental arteries. Arterial constriction may result in severe reduction in the blood flow to areas of the placenta. If the blood flow remains constricted, areas of the placenta may "die", putting the baby in distress.

A woman is born with all of the egg cells she will release throughout her lifetime. Starting at about age 12 through menopause, a woman’s reproductive cycle releases an egg about once a month.

Hormonal messages from the brain instruct the ovaries to develop several follicles in which a single dominant follicle in one of the ovaries will release an egg for fertilization. During this time, other hormones instruct the uterine lining to thicken in preparation for nourishing a fertilized egg.

There are several hormones that regulate the reproductive cycle. Follicle stimulating hormone (FSH) stimulates preparation of the egg for fertilization by instructing a follicle to begin dividing it’s genetic material (chromosomes).

The follicle then releases estrogen, the hormone that prepares the lining of the uterus to receive a fertilized egg. Increased levels of estrogen in the bloodstream cause a small structure in the brain, the pituitary gland, to stop releasing the hormone FSH, and to start releasing luteinizing hormone (LH).

LH causes the follicle to enlarge rapidly and to release its egg in a process known as ovulation. Once the egg is out of the follicle, the follicle begins secreting the hormone progesterone, which also helps to prepare the uterine lining for the fertilized egg. The remaining cells of the follicle shrink into a hormone producing mass of cells called a corpus luteum.

The egg is swept into the fallopian tube by its waving structures called fimbriae. Fertilization of the egg usually occurs in the fallopian tube. From there, it is transported to the uterus and implants itself in the uterine wall, where it is nourished by the uterine lining. In the ovary, the corpus luteum produces progesterone so that the egg can develop into a fetus.

If the egg is not fertilized within 24 hours after its release from the ovary, it stops developing and dissolves before reaching the uterus. The absence of a fertilized egg causes the body to stop releasing the hormones that prepare the uterus for implantation. In response, the uterus sheds its lining over a period of four to five days in a process known as menstruation.

Blood carries various substances that must be brought to one part of the body or another. Red blood cells are an important element of blood. Their job is to transport oxygen to the body’s tissues in exchange for carbon dioxide, which is carried to and eliminated by the lungs.

Red blood cells are formed in the red bone marrow of bones. Stem cells in the red bone marrow called hemocytoblasts give rise to all of the formed elements in blood. If a hemocytoblast commits to becoming a cell called a proerythroblast, it will develop into a new red blood cell.

The formation of a red blood cell from hemocytoblast takes about 2 days. The body makes about two million red blood cells every second.

Blood is made up of both cellular and liquid components. If a sample of blood is spun in a centrifuge, the formed elements and fluid matrix of blood can be separated from each other. Blood consists of 45% red blood cells, less than 1% white blood cells and platelets, and 55% plasma.

The skeletal muscles are under voluntary (conscious) control most of the time. However, skeletal muscle movement can also by induced by involuntary reflexes.

Reflexes are involuntary reactions to a stimulus such as the burning of the hand. As soon as a hot substance contacts the hand, pain receptors in the skin send a signal to the spinal cord. In turn, the spinal cord sends a signal back to the arm muscles that instruct the hand to pull away. The arm flexed as it withdrew, which is known as a flexor (withdrawal) reflex. There are many other reflexes that protect the body as well.

If the body did not have the reflexes to withdraw quickly from a painful stimulus, we would be at risk for serious injury.

As light enters the eye, it strikes the cells receptor cells of the retina called the rods and cones. A chemical reaction results in the formation of electric impulses, which then travel to the brain through the optic nerve. Retinal detachments are associated with a tear or hole in the retina through which the internal fluids of the eye may leak, causing separation of the retina from underlying tissues. One of the first signs of labor starting is the appearance of a mucus plug, or what is sometimes called a "bloody show." The bloody show is the discharge of a small amount of pinkish mucus that formed the barrier between the uterus and vagina during pregnancy.

Shortly after the bloody show, the amniotic sac ruptures and amniotic fluid begins to trickle out of the uterus and vagina. For some women, it can actually gush out in a stream. The rupturing of the amniotic sac, which surrounds and protects the baby, is commonly referred to as the "water breaking."

The combination of contractions, the bloody show, and water breaking indicates the start of the first phase of labor.

The eye is the organ of sight and is shaped as a slightly irregular hollow sphere. Various structures in the eye enable it to translate light into recognizable images. Among these are the cornea, the lens, and the retina.

Light first passes through the cornea, a clear dome-like structure covering the iris, or colored part, of the eye. The cornea bends, or refracts, the light onto the lens. The light is then refracted a second time while passing through the lens, finally focusing on the retina. The retina is the light sensitive part of the eye. Impulses travel down the optic nerve to the occipital lobe of the brain, which then interprets the image in the correct perspective.

The shape of the eye is very important in keeping the things we see in focus. If the shape of the eye changes, it affects a person’s vision.

Normally, light is precisely focused onto the retina at a location called the focal point. A nearsighted eye is longer from front to back than a normal eye causing light to be focused in front of the retina instead of directly onto it. This makes it difficult to see objects that are far away. Glasses with concave lenses are used to correct nearsightedness. The concave lens focuses light back onto the focal point of the retina.

Farsightedness occurs when the length of the eye is too short. Light is focused at a point behind the retina, making it difficult to see objects that are up close. A convex lens is used to correct farsightedness because it directs the focal point back onto the retina.

A baby's sex is determined at the time of conception. When a baby is conceived, the X or Y chromosome carried by the sperm cell fuses with the X chromosome in the egg cell. The chromosome combination determines whether the baby will be female or male. An XX combination means the baby will be a girl and XY means it will be a boy.

Even though gender is determined at conception, the fetus doesn’t develop its external sexual organs until the fourth month of pregnancy. At seven weeks after conception, the front of the fetus appears to be sexually indifferent, looking neither like a female or a male.

Over the next five weeks, the fetus begins producing hormones that cause its sex organs to grow into either female or male organs. This process is called sexual differentiation. If the fetus is female, it will produce hormones called estrogens. If the fetus is a male, it will produce hormones called androgens.

Hormones will instruct a common structure called the genital tubercle to either form the clitoris in the female or the penis in the male. The clitoris and penis are called sexual analogs because they originate from the same structure.

A shoulder dislocation usually occurs as a result of force to the joint. The bone is pushed out of the socket, which may cause damage to the surrounding ligaments, tendons, and nerves.

A baby's skeleton begins as fragile membranes and cartilage. As the fetus develops, the membranes and cartilage turn into bone in a process called ossification.

During the third month of development, the membranes on the side and back of the fetus’ skull start to ossify. Bone tissue slowly grows over the area where the membranes once existed. Eventually, these bone plates will grow together forming the cranial cavity which protects the brain.

Close to birth, the bones of the skull still have gaps between them called fontanelles. The fontanelles allow room for the baby's brain to grow and enable the head to be compressed during delivery.

Most of the bones of the skeleton start off as cartilage, such as the arms, legs, ribs, fingers, and backbone. From the second month until the end of the third month, the cartilage in the middle of the bones begins to ossify outward. Bones continue to grow in this manner until adulthood, allowing them to increase in their length and width.

Skeletal muscle is well-organized body tissue, composed in a complex array of smaller and smaller structures. Each skeletal muscle is composed of many units called muscle fascicles. The fascicles are bound together by a type of connective tissue called fascia.

Fascicles are composed of smaller organizational units called muscle fibers.

Smaller strands called myofibrils organize muscle fibers. The myofibrils move as skeletal muscle contracts. It is the interaction of the myofibrils as they slide and pull along side each other that gives skeletal muscle its functional ability to do work and move things.

Putting it all back together, myofibrils compose muscle fibers, muscle fibers make-up muscle fascicles, and muscle fascicles are bound together by fascia to compose skeletal muscle.

The skeletal system consists of approximately 206 bones, providing the body with structure and support.

The skull has 8 cranial bones that protect the brain. The facial skeleton has 14 bones that provide a framework for the eye sockets, jaws, and teeth. The facial bones provide the framework for the various structures of the face including the overlying muscles, fat and skin.

The vertebral column is composed of 24 individual vertebrae, along with two sets of fused bones called the sacrum and coccyx. The vertebral column protects the spinal cord and provides support for the trunk of the body. 12 pairs of ribs form a protective cage for the heart, lungs, and other internal organs.

The shoulder joint is the most movable joint in the body and includes the shoulder blade (scapula) and collar bone (clavicle). The bones of the upper limb include the humerus, which connects the shoulder with the elbow, the ulna, the radius, the wrist bones or carpals, the hand bones or metacarpals, and the finger bones or phalanges.

A pair of hip bones forms the pelvic girdle. Each hip bone is comprised of 3 fused bones, the ilium, ischium, and pubis. The pelvic girdle connects with the thigh bone (femur) at the hip joint. The femur is the longest bone in the body and is important for bearing the body’s weight while standing.

The femur articulates with the shin bone (tibia) at the knee. The fibula does not bear weight, but several muscles attach to it. The kneecap (patella) is suspended within muscle tendons and glides over the femur and tibia when the knee bends. The foot bones, which include the tarsals, metatarsals, and phalanges, are organized into a series of arches that allow the feet to support the body’s weight. A few common skin conditions include moles, birthmarks, age spots, and warts.

Moles are colored spots on the skin, formed by cells containing the dark pigment, melanin. While generally harmless, some moles can change shape and color, or start bleeding and require immediate evaluation.

Some birthmarks are simply moles that are present at birth, called a pigmented birthmark. Others result from the rapid growth of blood vessels in a localized area, called red birthmarks.

When a person becomes older, they may develop age spots. Age spots are patches of increased pigmentation on the skin’s surface, like freckles.

Warts are benign, or non-cancerous, growths of skin caused by a virus.

After the animation loads, click and drag the model to rotate it in any direction. Select a term from the structure list to travel to its location.

Click the "pin" button to hide or show the identification pin.

Click the "light bulb" button to view in highlight or full color mode.

As a person inhales, air and scent molecules move past the smell receptors in the nose. In turn, the smell receptors relay a signal to the brain. Smells can trigger memories and emotional responses.

The lungs are the primary respiratory organs. They act as filters for the air the body breathes in and normally are a healthy pink color.

Filtering smoke from the air breathed in can do damage to the lung tissue as seen in a smoker’s lung. Over time, carbon molecules from inhaled smoke deposit in the lung tissue, giving it a blackened appearance.

Smoking can eventually lead to the formation of tumors and other serious lung diseases. Smoking has also been linked to diseases that affect the cardiovascular system, such as atherosclerosis, which can lead to a heart attack or stroke.

Snoring affects many of people during their sleep when the airway become partially blocked, forcing the lungs to inhale harder to compensate for the lack of air entering the body. The snoring sound results from the vibration the soft palate and the uvula.

Several factors are thought to cause snoring, including poor muscle tone, too much alcohol, heavy smoking, colds or allergies, obesity, and obstruction by enlarged adenoids and tonsils.

Usually, snoring is not an indication of an underlying disorder. However, people who snore and have quiet periods lasting more than 10 seconds may have some degree of sleep apnea.

Sperm are produced, stored, and delivered by the male reproductive system. The male reproductive system includes the testes, urethra, vas deferens, prostate gland, seminal vesicle, and penis.

The testes contain coiled structures called seminiferous tubules, which are the sites of sperm production. They produce over 12 billion sperm per month. The epididymis lies on top of the seminiferous tubules. Immature sperm migrate from the seminiferous tubules to the epididymis to mature and be stored. The migration process usually takes about 20 days. Before intercourse, the penis fills with blood and becomes erect. With sufficient stimulation, the ejaculatory process begins.

The mature sperm travel from the epididymis through the vas deferens. The vas deferens is a narrow, muscular tube about 18 inches long. Its smooth muscle contractions propel the sperm forward. They arrive first at the ampulla, the widest part of the vas deferens, and then pass into the ejaculatory ducts. In the ejaculatory ducts, a liquid secretion from the seminal vesicles mixes with the sperm. Seminal fluid contains fructose sugar, which the sperm use as fuel as well as alkalines, which help to counteract the naturally acidic environment of the vagina and uterus providing the sperm a better chance for survival.

The liquid mixture is propelled forward through the ejaculatory ducts toward the urethra, passing first through the prostate gland, where milky prostatic fluid is added, forming the substance we call semen. The prostatic fluid helps the sperm swim faster, which is important for getting to the egg cell.

Finally, about a teaspoon of semen is ejected out (ejaculated) through the far end of the urethra at the end of the penis. From the time the sperm leave the man’s body, they have between 12 and 48 hours to find and fertilize the egg cell, assuming an egg is available. Of the 300 million sperm ejaculated, only about 200 or so will survive to reach the egg cell and only one will succeed in fertilizing it.

The key male reproductive organs include the testes, epididymis, urethra, vas deferens, prostate gland, seminal vesicle, and penis.

The testes are composed of coiled structures called seminiferous tubules, which are the sites of sperm production. The structure on top of the seminiferous tubules in the testes is the epididymis. The sperm migrate from of the seminiferous tubules to the epididymis. Within the epididymis, the sperm mature while they are stored in this structure.

The ejaculation process begins as the penis fills with blood and becomes erect. With sufficient stimulation, mature sperm travel from the epididymis through the vas deferens, a muscular tube, which propels sperm forward through smooth muscle contractions. The sperm arrive first at the ampulla, where secretions from the seminal vesicle are added.

From the ampulla, seminal fluid is propelled forward through the ejaculatory ducts toward the urethra, passing first by the prostate gland, where a milky fluid is added to form semen. Finally, the semen is ejaculated through the far end of the urethra.

A stomach ulcer is caused by an imbalance between acid and pepsin secretion and the defenses of the stomach mucosal lining. Ulcers can be treated through dietary changes and medication. A stroke may occur if an embolism travels from another part of the body and lodges within an artery in the brain. When an internal arterial wall becomes damaged, various types of emboli can form, such as one derived from platlets, thrombotic, cholesterol, or mixed. In this example, an embolism is formed in the internal carotid artery, breaks loose, travels towards the brain and lodges in a cerebral artery. The blocked artery deprives the brain of oxygen, damaging the surrounding brain tissue. The result is a stroke. A blood clot, or embolus, can form and break-off from the heart. The clot travels through the bloodstream where it can lodge in an artery of the brain, blocking the flow of blood. The lack of oxygen results in damage, destruction, or even tissue death of the brain beyond the affected area. The result is a stroke. The skin uses sunlight to help manufacture vitamin D, which is important for normal bone formation. But sometimes its ultraviolet light can be very detrimental.

Within the skin’s epidermal (outer) layer are cells that contain the pigment melanin. Melanin protects skin from the sun’s ultraviolet rays, which can burn the skin, and over time, could reduce its elasticity and cause a person to age prematurely. Suntanning occurs because exposure to sunlight causes the skin to produce more melanin and to darken. The tan fades as these cells move toward the surface and are sloughed off.

Too much exposure to ultraviolet or UV rays can cause sunburn. UV rays penetrate the outer skin layers and pass into the deeper layers, where they can damage or kill skin cells. People who do not have much melanin and sun burn easily should protect themselves by covering up sensitive areas, wearing sun block, limiting their total exposure time, and limiting their sun exposure between the hours of 10 a.m. and 2 p.m.

Frequent and prolonged exposure to ultraviolet rays over many years is the chief cause of skin cancer. Examine skin regularly for development of suspicious growths or changes in an existing skin lesion. Early detection and treatment are key in increasing the cure rate for skin cancer. The structures involved with the process of swallowing include the tongue, teeth, epiglottis, and esophagus.

The teeth are used to grind and chop up food into tiny pieces, while the glands in the mouth moisten the food with saliva. In the first stage of swallowing, the tongue pushes the food into the throat. In the second stage of swallowing, an important small flap of tissue called the epiglottis, folds over the voice box (larynx) at the entrance to the windpipe (trachea), preventing food from going down the wrong way. In the final stage, the esophagus contracts and moves food toward the stomach. There are more than two and a half million eccrine sweat glands all over the body. They lie deep in the skin and are connected to the surface by coiled tubes called ducts. Sweat (perspiration) is a liquid mixture made up of 99% water and 1% salt and fat. Up to a quart of liquid a day can evaporate through the sweat glands.

As the body becomes overheated, a person sweats, which evaporates and cools the body. When a person becomes frightened or nervous, like being pinned under heavy weights, the body begins to sweat on the palms and forehead, as well as the soles of the feet and in the armpits. These are the sites where sweat glands are most abundant. Tachycardia is a condition in which the heart beats at an abnormally fast rate of more than 100 beats per minute. This type of arrhythmia is caused by an abnormality in the heart’s electrical system. Tachycardia can be treated surgically or with medication.

The tongue has about 10,000 taste buds. The taste buds are linked to the brain by nerve fibers. Food particles are detected by the taste buds, which send nerve signals to the brain.

Certain areas of the tongue are more sensitive to certain tastes, like bitter, sour, sweet, or salty. Often, taste sensations are a mixture of these qualities.

Inside a pregnant woman’s uterus is an amniotic sac, which contains amniotic fluid and the growing fetus. The amniotic fluid is important for several reasons:

Amniotic fluid is 98% water and 2% salts and cells from the baby. Until the fetal kidneys started working during month four, the mother’s body makes amniotic fluid. But after month 4, the baby makes a contribution to the amniotic fluid by urinating into it. The urine in the amniotic sac is completely harmless to the baby.

The baby swallows amniotic fluid, which then passes through the digestive system, into the kidneys, and returns to the amniotic sac as urine. In this way, the baby can practice using the digestive and urinary systems prior to birth. Shown here is a comparison of an artery affected with plaque in a non-smoker and smoker. The artery of the smoker is at greater risk for developing complications since smoking constrict arteries, predisposing them to clotting by altering platelet function and coagulability of blood. The result is blockage of the artery. Twin to Twin Transfusion Syndrome, or TTTS, is a disease of the placenta. This condition affects twins or other multiples that share a single placenta containing blood vessels going from one baby to the other. Blood from the smaller "donor" twin is transferred to the larger "recipient" twin through interconnecting vessels causing an unequal exchange of blood. The recipient twin is at risk for heart failure receiving too much blood from both the placenta and donor twin, forcing its heart to work harder, while the donor twin is at risk for loss of blood. Laser surgery may be performed to correct the problem. A laser is endoscopically inserted into the womb to burn and seal the interconnecting blood vessels, restoring the normal flow of blood. Following treatment, the babies are regularly monitored. The stomach is the organ of the digestive system in which food travels from the esophagus and is further broken down before its nutrients are absorbed in the small intestine. It produces acid and various enzymes that break down food into simple substances. The inside wall of the stomach is protected from the acid and enzymes by a mucous lining.

Ulcers are caused when there is an imbalance between the digestive juices produced by the stomach and the various factors that protect the lining of the stomach. Symptoms of ulcers may include bleeding. On rare occasions, an ulcer may completely erode the stomach wall.

A major cause of stomach ulcers is the bacteria called Helicobacter pylori. Treatment regimens for ulcers caused this bacterium usually include medications to suppress the stomach acid as well as antibiotics to eradicate the infection.

Ultrasound is a useful procedure for monitoring the baby’s development in the uterus. Ultrasound uses inaudible sound waves to produce a two-dimensional image of the baby while inside the mother’s uterus. The sound waves bounce off solid structures in the body and are transformed into an image on a monitor screen.

Solid structures, such as bones and muscles, reflect sound waves and appear as light gray or white. Soft or hollow areas, like the chambers of the heart, don’t reflect sound waves and appear dark or black.

An ultrasound can supply vital information about a mother’s pregnancy and her baby's health. Even though there are no known risks for ultrasound at present, it is highly recommended that pregnant women consult their physician before undergoing this procedure.

Select a week by clicking one of the three buttons. Next, click and drag the slider bar to see an illustration of the baby's position gradually appear. With the cursor, roll-over the image to identify the various structures of the fetus.

The urinary system has four main components: the kidneys, ureters, urinary bladder, and urethra. Urine, a liquid waste product, is formed in the kidneys. From there it moves through the ureters and into the bladder, where it is stored. When the bladder gets full, urine is emptied from the body through the urethra in a process called urination.

The creation of urine is a complex process. The kidneys filter waste from the blood that passes through them, and reabsorb substances that the body requires, even though those requirements may change from moment to moment.

Each of the kidneys is composed of approximately one million subunits called nephrons. Each nephron consists of a microscopic ball of blood vessels called a glomerulus, which is connected to a twisting length of tube called the renal tubule. Because the blood vessels in the glomeruli are porous, they act as filters, removing most of the water, salt, and waste from the blood that passes through them.

As filters, the glomeruli have physical properties that prevent large cells, like red blood cells, from passing into the renal tubules. On the other hand, smaller particles, like sugar and salt, can pass easily through the glomerulus. Within the renal tubules, waste products are passed into the urine. Simultaneously, substances the body needs, such as water and salt, are reabsorbed back into the bloodstream.

The path of urine formation, reabsorption, and excretion begins at the glomerulus, continues through the renal tubules, and proceeds through a ureter into the bladder. The unique, expandable cells in the wall of the bladder stretch and become thinner as it fills. Finally, urine is excreted through the urethra.

Vaccinations are injections of antigens into the body. Once the antigens enter the blood, they circulate along with other cells, such B and T cells. B and T cells are white blood cells that help the body defend itself against foreign invaders.

As the antigens invade the body’s tissues, they attract the attention of macrophages. Macrophages are non-specific scavengers, which in this case, engulf the antigens. The macrophages then signal the T cells that antigens are invading. The killer-type of T cells respond by attacking the invading antigen. Finally, the suppressor T cells stop the attack.

After a vaccination, the body will have a memory of an encounter with a potentially dangerous invader for a period of time, and hopefully have a better ability to fight it off if ever exposed to it again in greater numbers. When the cervix dilates to 10 centimeters, the pushing and delivery phase of childbirth begins. During this phase, the baby starts the journey down the birth canal. As the baby’s head rotates , it may become distorted while slowing coming down the narrow opening. The baby’s skull bones have gaps called fontanelles that allow the head to elongate and fit within the birth canal.

As the baby’s head is delivered, it will naturally turn to one side. The baby’s head and shoulders are supported and the rest of the baby’s body generally comes out fairly quickly. A vasectomy is a procedure to cause permanently sterility in a man by preventing the transport of sperm out of the testes. A small incision is made in the scrotum and each vas deferens is tied off and cut apart preventing sperm from being released within the ejaculate. The small skin incision is stitched closed and the surgery does not affect a man's sexual function.
Allergies
This animation shows the passage of allergens (pollen) into the nasal cavity. The body response includes the release of histamine, a chemical that produces allergy symptoms in the body.  Launch animation
Allergies
Allergens like pollen are nothing more than foreign plant antigens. The stimulus for sneezing gets triggered when allergens first enter the nasal tissue. Pollen allergens encounter the plasma cells in the nose, which respond by producing antibodies. These antibodies attach to mast cells, which are white blood cells containing the chemical histamine. As more antibodies are produced, they cause the mast cells to release histamine. Histamine then produces allergy symptoms. A stuffy and runny nose, sneezing and watery eyes help to remove the invading pollen. Medications called antihistamines may be used to help alleviate severe allergy symptoms.
Alzheimer's disease
This animation shows the brain and the changes that occur to it from Alzheimer's disease.  Launch animation
Alzheimer's disease

In a person with Alzheimer's disease, neurofibrillary tangles and plaques develop causing both structural and chemical problems in the brain. Alzheimer's disease appears to disconnect areas of the brain that normally work together.

Ankle ligament injury
This animation illustrates and compares the severity of an ankle sprain (Type I, II, III).  Launch animation
Ankle ligament injury

While playing basketball, this player sprained his ankle. Probably not a good idea to play without shoes! Symptoms of a sprain include swelling and discoloration near the affected area.

A sprain occurs when a ligament is inflamed or torn. Ligaments, such as those of the ankle, are bands or sheets of regular, tough fibrous tissue that connect bones together.

Here is the normal state of the ankle and its ligaments. Depending on the severity of the injury, the ligaments may be mildly injured and inflamed as in a Type One ankle sprain; partially torn, classified as a Type Two sprain; or completely torn, making it a Type Three sprain.

Treatment for a Type One sprain should include Rest, Ice, Compression and immobilization, and Elevation of the affected area. This is easy to remember if you think of the acronym RICE. If you suspect a ligament is torn or completely severed, see your health care provider for treatment.

Arrhythmias
This animation shows the cardiac conduction system and the arrhythmias of a fast and slow beating heart.  Launch animation
Arrhythmias
A change in the heart's normal electrical conduction system can result in an arrhythmia or irregular heartbeat. An arrhythmia can be an abnormally slow heartbeat, or an abnormally fast heartbeat. In some cases, it can be fatal.
Atherosclerosis
This animation shows Atherosclerosis  Launch animation
Atherosclerosis

Normally, the walls of an artery are smooth, allowing blood to flow unimpeded. Atherosclerosis is when harmful material collects on the wall of an artery. This material includes fat, cholesterol, and other substances.

Eventually, the material builds up and a plaque is formed, narrowing the artery. When the build-up is severe, a clot could block the vessel completely.

Athetosis resulting from basal ganglia injury
This animation illustrates the location of basal ganglia in the brain. Injury to the basal ganglia may result in athetosis (constant writhing movements of the body).  Launch animation
Athetosis resulting from basal ganglia injury
Athetosis, or constant writhing movements, is often caused by injury to deeply situated structures within the brain called the basal ganglia.
Balloon angioplasty - short segment
This animation shows the use of balloon angioplasty to open a narrowed coronary artery lumen caused by deposits of plaque.  Launch animation
Balloon angioplasty - short segment

Angioplasty is a procedure to open narrowed or blocked arteries caused by deposits of plaque. If the blockage is not major, the problem may be corrected by inflating the balloon several times to compact the plaque against the arterial wall, widening the passage for the blood to flow through. Typically, a device called a stent is placed within the coronary artery to keep the vessel open.

Bladder function - neurological control
This animation shows the neurological control of normal bladder function.  Launch animation
Bladder function - neurological control

When the bladder fills with urine, sensory nerves send impulses to the brain indicating that the bladder is full. The sensory nerves connect with other nerves in the spinal cord to relay this information. In turn, the brain sends impulses back to the bladder instructing the bladder to empty its contents.

Blinking
This animation shows the eye’s response to invading foreign substances, resulting in blinking and the lacrimal gland’s production of tears which then pass into the nose through tear ducts.  Launch animation
Blinking

The nervous system enables a person to blink to prevent harmful substances from getting in the eyes. During the normal course of a day, a person blinks an average of 15 times a minute to keep the eyes healthy. The lacrimal gland provides lubricating fluid for the eyes. The eyelid moves fluid from the lacrimal gland and across the eye. Blinking also provides the eyes with protection from foreign objects.

When the eye becomes irritated, the lacrimal gland produces extra tears to wash out impurities. Excess fluid drains through the tear ducts and into the nasal cavity. An abundance of tears draining through the nasal cavity may cause the nose to run and a person to sniffle.

Blood clotting
This animation depicts the process of blood clotting in an enlarged view of a small artery. Cells shown include red blood cells, platelets, fibrin, and clotting factors.  Launch animation
Blood clotting
The body contains a natural process to stop bleeding from minor cuts in a matter of several minutes. When a small artery is cut, the collagen fibers in its tissue are exposed, which signals the clotting process to begin. As platelets begin to adhere to the cut edges, they release chemicals to attract even more platelets. Eventually a platelet plug is formed, and the external bleeding stops. Clotting factors in the blood cause strands of blood-borne material, called fibrin, to stick together and seal the inside of the wound. Eventually, the cut blood vessel heals, and the blood clot dissolves after several days.
Blood flow
This animation shows the cycle of blood circulation through the heart, arteries, veins, and lungs within the body.  Launch animation
Blood flow
As the heart pumps, the arteries carry oxygen-rich blood (shown in red) away from the heart and toward the body’s tissues and vital organs. These include the brain, liver, kidneys, stomach, and muscles, including the heart muscle itself. At the same time, the veins carry oxygen-poor blood (shown in blue) from the tissues back toward the heart. From there, it passes to the lungs to receive more oxygen. This cycle repeats itself when oxygen-rich blood returns to the heart from the lungs, which pumps it throughout the body.
Blood pressure
This animation defines normal blood pressure and the measurement of systole and diastole. Structures shown include a front-view of the heart beating, a cut-view of the heart beating, and blood flowing through a small artery.  Launch animation
Blood pressure

Normal blood pressure is important for proper blood flow to the body’s organs and tissues. The force of the blood on the walls of the arteries is called blood pressure. Blood pressure is measured both as the heart contracts, which is called systole, and as it relaxes, which is called diastole. Normal blood pressure is considered to be a systolic blood pressure of 115 millimeters of mercury a diastolic pressure of 70 millimeters of mercury (stated as "115 over 70"). If an individual were to have a consistent blood pressure reading of 140 over 90, he would be evaluated for having high blood pressure. If left untreated, high blood pressure can damage important organs, such as the brain and kidneys, as well as lead to a stroke.

Bone fracture repair
This animation shows one method in which a severe wrist fracture is treated by inserting a bone graft from the hip followed by fixation with a metal plate and screws.  Launch animation
Bone fracture repair

If a bone fracture is severe, a bone graft may be used to help speed the healing process. In this example, a metal plate is also used and secured with screws.

Brain - interactive tool
This interactive animation takes you on a 3-D journey to explore the anatomy of the brain. Rotate the brain or pick from a list of terms to identify various structures.  Launch animation
Brain - interactive tool

After the animation loads, click and drag the model to rotate it in any direction. Select a term from the structure list to travel to its location.

Click the "pin" button to hide or show the identification pin.

Click the "light bulb" button to view in highlight or full color mode.

Click the "double box" button to see and rotate the model in transparent mode.

Brain components
This animation highlights the major sections of the brain and explains their primary functions.  Launch animation
Brain components

The brain is composed of more than a thousand billion neurons. Specific groups of them, working in concert, provide us with the capacity to reason, to experience feelings, and to understand the world. They also give us the capacity to remember numerous pieces of information.

The 3 major components of the brain are the cerebrum, cerebellum, and brain stem.

The cerebrum is divided into left and right hemispheres, each composed of a frontal, temporal, parietal, and occipital lobe. The cerebral cortex (gray matter) is the outside portion of the cerebrum and provides us with functions associated with conscious thought. The grooves and folds increase the cerebrum’s surface area, allowing us to have a tremendous amount of gray matter inside of the skull. Deep to the gray matter is the cerebral "white matter." The white matter provides for the communication between the cortex and lower central nervous system centers.

The cerebellum is located near the base of the head. It creates automatic programs so we can make complex movements without thinking.

The brain stem connects the brain with the spinal cord and is composed of 3 structures: the midbrain, pons, and medulla oblongata. The brain stem provides us with automatic functions that are necessary for survival.

Breast lift
This animation shows a breast reduction (lift) procedure.  Launch animation
Breast lift
In a breast lift or breast reduction procedure, incisions are made to accommodate a higher position for the areola and nipple, as well as to remove excess skin and breast tissue. Stitches usually follow the circumference of the areola, the natural lower crease of the breast, and a vertical line extending between the areola and lower crease.
Breathing
This animation illustrates the major structures of the respiratory system and shows the mechanism of breathing (respiration).  Launch animation
Breathing

The two lungs are the primary organs of the respiratory system. Other components of the respiratory system conduct air to the lungs, such as the trachea (windpipe) which branches into smaller structures called bronchi.

The process of breathing (respiration) is divided into two distinct phases, inspiration (inhalation) and expiration (exhalation). During inspiration, the diaphragm contracts and pulls downward while the muscles between the ribs contract and pull upward. This increases the size of the thoracic cavity and decreases the pressure inside. As a result, air rushes in and fills the lungs.

During expiration, the diaphragm relaxes, and the volume of the thoracic cavity decreases, while the pressure within it increases. As a result, the lungs contract and air is forced out.

Bunion
This animation shows the formation of a bunion.  Launch animation
Bunion
Bunions are usually caused by prolonged pressure put on the feet that compresses the big toe and pushes it toward the second toe. Over time, the condition may become painful as extra bone grows where the base of the big toe meets the foot.
Cancer of the throat or larynx
From a top view of the voice box (larynx) and vocal cords, this animation shows the formation of a malignant tumor on the right vocal cord.  Launch animation
Cancer of the throat or larynx
Malignant tumors of the vocal cords are typically caused by tobacco use.
Cardiac conduction system
This animation illustrates the cardiac conduction system, a group of specialized muscle cells that signal the rest of the heart to contract. An ECG tracing is shown in tandem with a normal heart beat.  Launch animation
Cardiac conduction system

The cardiac conduction system is a group of specialized cardiac muscle cells in the walls of the heart that send signals to the heart muscle causing it to contract. The main components of the cardiac conduction system are the SA node, AV node, bundle of His, bundle branches, and Purkinje fibers. The SA node (anatomical pacemaker) starts the sequence by causing the atrial muscles to contract. From there, the signal travels to the AV node, through the bundle of His, down the bundle branches, and through the Purkinje fibers, causing the ventricles to contract. This signal creates an electrical current that can be seen on a graph called an Electrocardiogram (EKG or ECG). Doctors use an EKG to monitor the cardiac conduction system’s electrical activity in the heart.

Cardiomyopathy
This animation shows a catheter being inserted into the heart where alcohol is injected causing the swollen ventricle wall to shrink.  Launch animation
Cardiomyopathy
In this case of cardiomyopathy, part of the septum dividing the ventricles is interfering with the normal emptying of the left ventricle. This is one variety of the condition called hypertrophic obstructive cardiomyopathy (HOCM). A catheter is introduced into the heart and through it, concentrated alcohol is applied to the abnormal area, shrinking it, allowing the heart to function normally.
Cardiovascular system
This animation displays a normal heart beating. Also shown are red blood cells traveling through an enlarged cut-section of a small artery and the percentage of the blood’s components.  Launch animation
Cardiovascular system

The cardiovascular system is composed of the heart and the network of arteries, veins, and capillaries that transport blood throughout the body. The average adult male has between 5 to 6 liters of blood or blood volume, while the average adult female has between 4 to 5 liters. The blood carries oxygen and essential nutrients to all of the living cells in the body, and also carries waste products from the tissues to the systems of the body through which they are eliminated.

Most of the blood is made up of a watery, protein-laden fluid called plasma. A little less than half of this blood volume is composed of red and white blood cells, and other solid elements called platelets.

Cataract
This animations depicts how a cataract is seen in the eye.  Launch animation
Cataract
Cataracts may develop with advancing age or in response to diseases such as diabetes. A cataract appears as a cloudy area in the lens.
Cell division
This animation traces the growth and migration of a fertilized egg cell through the fallopian tubes to the uterine lining. Enlarged views show the action of cilia in the fallopian tube transporting the egg and its implantation into the uterine lining.  Launch animation
Cell division
During the first 12 hours after conception, the fertilized egg cell remains a single cell. After approximately 30 hours, it divides from 1 cell into 2 and 15 hours later, the 2 cells divide into 4. And at the end of 3 days, the fertilized egg cell has become a berry-like structure made up of 16 cells. This structure is called a morula, which is Latin for mulberry.

The cells continue to divide 8 or 9 days following conception into a blastocyst. Although it is only the size of a pinhead, the blastocyst is composed of hundreds of cells. The blastocyst is slowly carried by tiny hair-like projections in the fallopian tube called cilia toward the uterus. During the critically important process of implantation, it must attach itself to the uterine lining where it will be able to get nourishment from the mother’s blood supply. If the blastocyst is unable to attach, the pregnancy will fail to survive.
Cerebral aneurysm
This animation shows a cerebral aneurysm growing and rupturing filling the brain with blood.  Launch animation
Cerebral aneurysm

The tissue of the brain is supplied by a network of cerebral arteries. If the wall of a cerebral artery becomes weakened, a portion of the wall may balloon out forming an aneurysm. A cerebral aneurysm may enlarge until it bursts, sending blood throughout the spaces in or surrounding the brain.

Cervical dilation - interactive tool
This interactive animation shows the process of cervical dilation during labor.  Launch animation
Cervical dilation - interactive tool

Click and drag the slider bar to view cervical dilation.

If you have previously delivered a child, your cervix looks slot-shaped at 0 centimeters, not round.

During early labor your cervix dilates from 0 to 4 centimeters. Mild contractions, about 60 to 90 seconds in length, occur every 2 to 5 minutes.

You’ve entered the active phase of labor, which means your cervix is dilating from 4 to 10 centimeters, contractions have grown stronger. They’re occurring once every 1 and half to 3 minutes or so, and are lasting about 45 seconds long. If desired, you may get an epidural at this point.

Near the active phase of labor you arrive at the transition phase; your cervix dilates from 8 to 10 centimeters.

At 10 centimeters, your cervix is fully dilated and you are ready to start pushing with every contraction.

Cesarean section
This animation describes and depicts the common reasons for having a cesarean section delivery. The location of an epideral application is shown in a side view followed by a Cesarean section delivery illustrated in both side and front views.  Launch animation
Cesarean section

Although cesarean (C-sections) are relatively safe surgical procedures, they should only be performed in appropriate medical circumstances. Some of the most common reasons for a cesarean are:

Some common causes of fetal distress are:

Like many surgical procedures, cesarean sections require anesthesia. Usually, the mother is given an epidural or a spinal block. Both of these will numb the lower body, but the mother will remain awake. If the baby has to be delivered quickly, as in an emergency, the mother may be given a general anesthetic, which will make her fall asleep.

During the surgery, an incision is made in the lower abdomen followed by an incision made in the uterus. There is no pain associated with either of these incisions because of the anesthesia. The doctor will open the uterus and the amniotic sac. Then the baby is carefully eased through the incision and out into the world. The procedure usually lasts about 20 minutes.

Afterward, the physician delivers the placenta and stitches up the incisions in the uterus and abdominal wall. Usually, the mother is allowed to leave the hospital within a few days, barring complications like wound infections.

One concern that many women have is whether they’ll be able to have a normal delivery after having a cesarean. The answer depends on what the reasons were for having the c-section in the first place. If it was because of a one-time problem, like umbilical cord compression or breech position, then the mother may be able to have a normal birth.

Therefore, as long as the mother has had one or two previous cesarean deliveries with a low-transverse uterine incision, and there are no other indications for a cesarean, she is a candidate for vaginal birth after cesarean, also called VBAC (say as "vee-back").

Cesarean sections are safe, and can even save the lives of both mother and baby during emergency deliveries. Expectant mothers should be prepared for the possibility of having one. Keep in mind, in childbirth, it’s not only the delivery method that matters, but the end result: a healthy mother and baby.

Components of skin
This animation shows an enlarged view of a section of skin, highlighting its layers and various structures.  Launch animation
Components of skin
Skin is the body’s largest organ. About six pounds of skin cover eighteen square feet on an average adult.

The top layer of skin is called the epidermis. It protects the underlying skin layers from the outside environment and contains cells that make keratin, a substance that waterproofs and strengthens the skin. The epidermis also has cells that contain melanin, the dark pigment that gives skin its color. Other cells in the epidermis allow us to feel the sensation of touch and provide the body with immunity against foreign invaders like germs and bacteria.

The very bottom layer of the skin is the hypodermis. It contains the fat cells, or adipose tissue, that insulate the body and help it conserve heat. The layer between the epidermis and the hypodermis is the dermis. It contains the cells that give skin strength, support, and flexibility. As a person ages, the cells in the dermis lose their strength and flexibility, causing the skin to lose its youthful appearance.

Located in the dermis are sensory receptors. They allow the body to receive stimulation from the outside environment and experience pressure, pain, and temperature. Small blood vessels provide the skin with nutrients, and remove its waste products.

Sebaceous glands produce the oil in the skin, which keeps it from drying out. The oil from the sebaceous glands also helps to soften hair and kill bacteria that get in the skin’s pores. These oil glands are all over the body, except on the palms of the hands and the soles of the feet.
Conception - general
This animation shows the process of conception in which a sperm unites with an egg cell to form a fertilized egg.  Launch animation
Conception - general

During intercourse, sperm are released into the vagina near the cervix, swim through the uterus and travel up the fallopian tubes. Sperm are composed of 3 parts: a head, a middle section, and a tail. The tail propels the sperm, which is powered by energy cells stored in the middle section. The head of the sperm contains the man’s genetic material and an enzyme-filled cap needed to help the sperm penetrate through the outer membrane of the egg.

As an egg released by an ovary travels through a fallopian tube, it may encounter hundreds of sperm that have survived to reach this point in their journey. Eventually, one sperm may succeed in breaking through the egg’s outer membrane.

After penetrating the egg’s outer membrane, the sperm releases its nucleus, which unites with the nucleus from the egg. Fertilization or conception occurs when the sperm fuses with the egg to form a fertilized egg (zygote).

Conception - interactive tool
This interactive animation takes you on a journey through the female reproductive system to see the processes of ovulation, fertilization and implantation of a fertilized egg (zygote).  Launch animation
Conception - interactive tool
Click a circle in the "Navigation" box to travel to a particular section of the female reproductive system. At each section, select the "Click here to play animation" to see an action occur that leads to the successful conception of a fertilized egg.
Conception - pregnancy
This animation shows the process in which an egg cell is fertilized by a sperm cell to form a fertilized egg (zygote).  Launch animation
Conception - pregnancy
During sexual intercourse, sperm are released into the vagina near the cervix, which is the entrance to the uterus. The sperm travel through the cervix, into uterus and up the fallopian tubes.

After being release from an ovary, the egg cell moves through the fallopian tube by tiny cilia that line the tube’s walls. The egg cell only survives for approximately 24 hours after ovulation. Of the millions of sperm that are released into the naturally acid environment of the woman’s reproductive tract, relatively few will survive to encounter the egg cell.

When one of the sperm cells finally succeeds in breaking through the egg cell's outer membrane, the egg cell forms a protective barrier preventing other sperm cells from entering. This ensures that only one sperm cell fertilizes the egg cell.

Next, the sperm cell releases its nucleus containing the man’s chromosomes. After several hours, it unites with the nucleus of the egg cell, which contains the woman’s chromosomes. When the two nuclei fuse, their genetic material combines together to create a fertilized egg cell which is called a zygote.
Conception of identical twins
In a microscopic view, this animations shows the conception of identical (maternal) twins.  Launch animation
Conception of identical twins

Millions of sperm are released during a single ejaculation. Their tails propel on their journey to encounter the single egg cell. Of the millions of sperm, only a few will survive to reach the egg and just one will penetrate the egg cell’s wall to combine it’s genetic material with that of the egg in the process called fertilization. If during the first 13 days of cell division, the fertilized egg cell, or zygote, divides into 2 zygotes, identical twins will form. Each developing embryo contains the same genetic material as the other.

Concussion
This animations shows the head receiving two impacts. One on the front, and one on the side from a boxing glove.  Launch animation
Concussion
In a severe impact to the head, the brain moves and hits the skull causing injury. During a boxing match, the brain moves from side to side after the impact of a punch. Following a concussion head injury, confusion and disorientation due to temporary distortion of the brain may result.
Corneal injury
This animation shows corneal infections resulting from corneal injury.  Launch animation
Corneal injury
Injury or infection of the cornea, the transparent front window of the eye, can lead to serious visual impairment.
Coronary artery bypass graft (CABG)
This animation shows a coronary artery bypass graft (CABG) procedure in which a portion of vein is grafted on the heart to reroute blood from a blocked section of a coronary artery.  Launch animation
Coronary artery bypass graft (CABG)

One option to treat the blocked coronary artery is a surgical procedure called coronary artery bypass grafting surgery. The procedure involves taking a section of blood vessel from elsewhere in the body, such as the leg, and grafting it onto a location on the heart, which allows blood to bypass the blocked portion of the coronary artery.

The procedure begins with the surgeon making a cut in the leg and removing a section of vein. Both ends of the vein are tied-off in the leg and cut is closed. The chest is opened and the blood is rerouted through a heart-lung machine. The heart is then stopped.

The surgeon will then divide the sternum, the bone that runs down the middle of the chest, exposing the chest cavity. The heart is then usually connected to a heart-lung machine, which takes over the work of the heart and lungs during the treatment. Once this is competed, the heart is stopped. The surgeon then locates the blocked coronary artery and attaches the section of vein taken from the leg to the aorta and to the coronary artery below the blocked segment of the artery. The surgeon may do as many bypasses on as many blocked coronary arteries as the patient needs.

Once each bypass graft is placed, it is checked for leaks. Following this, the heart is restarted. Once the heart is beating again, the surgeon will remove its attachments to the heart-lung machine and sew the openings closed. Following this the chest is closed. A pacemaker may be inserted during the procedure to help control any heart rhythm problems the patient may have.

Coronary artery disease
Shown in an enlarged view of a damaged coronary artery is the build-up of plaque and restriction of blood flow, progressing to complete arterial blockage and heart muscle ischemia (heart attack). Anteriorly, a normal heart beating is also illustrated.  Launch animation
Coronary artery disease
The coronary arteries supply blood to the heart muscle itself. Damage to or blockage of a coronary artery can result in injury to the heart. Normally, blood flows through a coronary artery unimpeded. However, if the inner wall of a coronary artery becomes damaged, cholesterol plaque can build-up, progressively narrowing the available pathway through which blood can flow.

Clotted blood attempting to traverse the blood vessel may find it tortuous and too narrow for passage, and the artery may become completely constricted or blocked-off. The blocked artery results in a lack of oxygen, or ischemia, to the part of the heart muscle that the artery supplies. The result is a heart attack.
Cosmetic surgery of the face
This animation describes a series of cosmetic surgeries, including forehead lift, eyelid lift, and facelift.  Launch animation
Cosmetic surgery of the face
Facial cosmetic surgery may include a forehead lift. In this procedure, a hairline incision is made, the forehead skin is pulled-up and excess skin tissue is removed. In an eyelid lift (blepharoplasty), creases and wrinkles around the eyes can be minimized by removing excess fat and skin from the upper and lower eyelids. A facelift usually consists of an incision along or above the hairline and in front of the ears. Excess fat and skin is removed and facial muscles may be tightened.
Coughing
This animation shows the mechanism of coughing caused by an irritant entering the windpipe (larynx), resulting in its dislodgement. The steps of the coughing reflex are shown from a side view of the body in tandem with a top view of the vocal cords.  Launch animation
Coughing

Coughing is a sudden expulsion of air from the lungs through the epiglottis at an amazingly fast speed (estimated at 100 miles per hour). With such a strong force of air, coughing is the body’s mechanism for clearing the breathing passageways of unwanted irritants.

In order for a cough to occur, several events need to take place in sequence. First, the vocal cords open widely, allowing additional air to pass through into the lungs. Then the epiglottis closes off the windpipe (larynx), and simultaneously, the abdominal and rib muscles contract, increasing the pressure behind the epiglottis. With the increased pressure, the air is forcefully expelled, and creates a rushing sound as it moves very quickly past the vocal cords. The rushing air dislodges the irritant, making it possible to breathe comfortably again.

Diabetes - retinal conditions
This animations depicts changes to the retina resulting from diabetes mellitus.  Launch animation
Diabetes - retinal conditions
Diabetes may affect the retina by causing the formation of whitish patches called exudates. Other indications may include tiny enlargements of the blood vessels resulting in microaneurysms and hemorrhages.
Digestion
This animation highlights the major parts of the digestive system and follows the breakdown of celery from consumption to excretion.  Launch animation
Digestion

Digestion is the process in which food is broken down into nutrients used by the body. Food passes from the mouth through the esophagus to the stomach. The stomach churns the food and breaks it down further with its contents of hydrochloric acid and an enzyme called pepsin.

The process of breaking food down in the stomach takes a few hours. From there, it goes to the duodenum where it is broken down further by digestive bile produced by the liver and stored in the gallbladder along with enzymes from the pancreas. Enzymes are chemicals that speed up the digestion of specific types of food. For example, the enzyme trypsin breaks down the protein in steak, lipase helps to break down fat, and lactase breaks down the sugar in milk.

Once everything is broken down, the small intestine absorbs the nutrients the body needs. From there the nutrients go into the bloodstream and to the liver, where poisons are removed. Undigested food and water continue through the small intestine and go into the large intestine, where water is reabsorbed. Finally, feces are eliminated through the rectum and anus.

Directional coronary atherectomy (DCA)
This animation shows a Directional Coronary Atherectomy (DCA) procedure performed to remove the blockage from the coronary arteries by a tiny spinning cutter that slices away plaque lesions and stores them to be withdrawn.  Launch animation
Directional coronary atherectomy (DCA)

Directional Coronary Atherectomy (DCA) is a minimally invasive procedure to remove the blockage from the coronary arteries and allow more blood to flow to the heart muscle and ease the pain caused by blockages.

The procedure begins with the doctor injecting some local anesthesia into the groin area and putting a needle into the femoral artery, the blood vessel that runs down the leg. A guide wire is placed through the needle and the needle is removed. An introducer is then placed over the guide wire, after which the wire is removed. A different sized guide wire is put in its place.

Next, a long narrow tube called a diagnostic catheter is advanced through the introducer over the guide wire, into the blood vessel. This catheter is then guided to the aorta and the guide wire is removed. Once the catheter is placed in the opening or ostium of one of the coronary arteries, the doctor injects dye and takes an x-ray.

If a treatable blockage is noted, the first catheter is exchanged for a guiding catheter. Once the guiding catheter is in place, a guide wire is advanced across the blockage, then a catheter designed for lesion cutting is advanced across the blockage site. A low-pressure balloon, which is attached to the catheter adjacent to the cutter, is inflated such that the lesion material is exposed to the cutter.

The cutter spins, cutting away pieces of the blockage. These lesion pieces are stored in a section of the catheter called a nosecone, and removed after the intervention is complete. Together with rotation of the catheter, the balloon can be deflated and re-inflated to cut the blockage in any direction, allowing for uniform debulking.

A device called a stent may be placed within the coronary artery to keep the vessel open. After the intervention is completed the doctor injects contrast media and takes an x-ray to check for any change in the arteries. Following this, the catheter is removed and the procedure is completed.

Ear - interactive tool
This interactive animation takes you on a 3-D journey to explore the anatomy of the ear. Rotate the ear or pick from a list of terms to identify various structures.  Launch animation
Ear - interactive tool

After the animation loads, click and drag the model to rotate it in any direction. Select a term from the structure list to travel to its location.

Click the "pin" button to hide or show the identification pin.

Click the "light bulb" button to view in highlight or full color mode.

Click the "double box" button to see and rotate the model in transparent mode.

Early labor
This animation shows the signs of the first phase of labor (early labor).  Launch animation
Early labor

After the membranes rupture and the water breaks, a woman may begin to experience the first phase of labor (early labor). The average time of early labor is extremely variable, lasting from hours to days. It is more common for the first phase of labor to begin before the membranes rupture.

During this time, the pressure of repeated regular contractions causes the cervix, which may have been closed when labor began, to open up to a diameter of 4 centimeters while becoming much thinner.

Various techniques can be used to help alleviate the discomfort a woman may experience during the first phase of labor such as back-rubs and breathing exercises.

Egg cell production
This animation depicts the maturation of egg cells within ovary and illustrates the role of hormones in menstruation and egg cell fertilization and implantation.  Launch animation
Egg cell production

For conception to take place, a mature egg cell, or ovum, must be at the right place at the right time. Conception takes place when a sperm penetrates the egg cell and fertilizes it, and the two cells combine to form a new life.

Let's take a quick look at some of a woman’s key reproductive organs and see how they function during menstruation and ovulation, two processes that are critical in preparing her for conception.

Here are the uterus, ovaries, fallopian tubes, and vagina.

You can see a cut-away view of one of the ovaries on the right. The purple structures inside the ovary are immature egg cells, or oocytes. All of the 400,000 egg cells a woman will ever produce are already present in her ovaries when she is born, although the eggs are in an undeveloped form.

The average age that girls begin to menstruate is 12 years old. Each menstrual cycle occurs approximately every twenty-eight days. During each cycle, hormonal messages from the brain cause the ovaries to develop a single mature egg cell for potential fertilization, even as other hormones instruct the uterine lining to thicken in preparation for nourishing the fertilized egg cell.

As you may know, hormones are chemicals released into the blood stream by organs or glands. In general, their job is to regulate body functions by either stimulating or inhibiting other cells or organs. The ovaries are just one of the many organs in the body regulated by hormones.

The cycle starts when a follicle grows within one of the ovaries. A follicle is composed of the developing egg cell and the support cells that surround and nourish it.

Throughout the first portion of the cycle, a small structure in the brain, the pituitary, releases hormones, mostly FSH. This causes follicles to begin growing.

One of the follicles becomes dominant and releases estrogen, a hormone that prepares the lining of the uterus to receive a fertilized egg cell. Meanwhile, the estrogen in the blood stream causes the brain to release a surge of LH. In response to the LH surge, the follicle enlarges rapidly. About 24 to 36 hours after the LH surge, the follicle ruptures and releases the egg cell in a process known as ovulation.

The ruptured follicle begins secreting the hormone progesterone, which also helps to prepare the uterine lining for a fertilized egg cell.

The large structure on the right is the entrance to the fallopian tube. The smaller, waving structures at its opening are called fimbriae. They're moving a lot because it's their job to sweep the egg cell into the fallopian tube's entrance and toward the uterus.

Once the egg cell is within the fallopian tube, one of two things will happen to it: it will either be fertilized by a sperm cell, or fertilization will fail to take place.

If the egg cell is NOT fertilized within 12 to 24 hours after its release from the ovary, it will stop developing and will dissolve before reaching the uterus.

The absence of a fertilized egg cell gradually causes a woman’s body to stop releasing the hormones that would otherwise prepare the uterus for the developing egg cell. In response, the uterus sheds its lining. Menstruation signifies the start of the next menstrual cycle and lasts from 2 to 7 days.

If the egg cell DOES become fertilized by a sperm, it will be transported by tiny hair-like cells called cilia to the uterus. There, it lodges in the uterine wall in a process called implantation, and receives nourishment from the uterine lining.

Meanwhile, back in the ovary, the remaining cells of the ruptured follicle produce progesterone so that the uterine lining will stay rich in blood vessels, and the fertilized egg cell will survive.

As you can see, the hormones, which control the reproductive system, maintain a delicate balance over the life cycle of the egg cell.

Egg production
This animation illustrates the development cycle of an egg in an ovary and the sequence of events to fertilization of the egg or not.  Launch animation
Egg production

A woman is born with all of the egg cells she will release throughout her lifetime. Starting at about age 12 through menopause, a woman’s reproductive cycle releases an egg about once a month.

Hormonal messages from the brain instruct the ovaries to develop several follicles in which a single dominant follicle in one of the ovaries will release an egg for fertilization. During this time, other hormones instruct the uterine lining to thicken in preparation for nourishing a fertilized egg.

There are several hormones that regulate the reproductive cycle. Follicle stimulating hormone (FSH) stimulates preparation of the egg for fertilization by instructing a follicle to begin dividing it’s genetic material (chromosomes).

The follicle then releases estrogen, the hormone that prepares the lining of the uterus to receive a fertilized egg. Increased levels of estrogen in the bloodstream cause a small structure in the brain, the pituitary gland to start releasing luteinizing hormone (LH).

LH causes the follicle to enlarge rapidly and to release its egg in a process known as ovulation. Once the egg is out of the follicle, the follicle begins secreting the hormone progesterone, which also helps to prepare the uterine lining for the fertilized egg. The remaining cells of the follicle shrink into a hormone producing mass of cells called a corpus luteum.

The egg is swept into the fallopian tube by its waving structures called fimbriae. Fertilization of the egg usually occurs in the fallopian tube. From there, it is transported to the uterus and implants itself in the uterine wall, where it is nourished by the uterine lining. In the ovary, the corpus luteum produces progesterone so that the egg can develop into a fetus.

If the egg is not fertilized within 24 hours after its release from the ovary, it stops developing and dissolves before reaching the uterus. The absence of a fertilized egg causes the body to stop releasing the hormones that prepare the uterus for implantation. In response, the uterus sheds its lining over a period of four to five days in a process known as menstruation.

Electrocardiogram (ECG) - interactive tool
An electrocardiogram (ECG) enables the rhythm of the heart to be viewed in waveform. This interactive animation shows the ECG waveforms for normal sinus rhythm and various conditions of the heart.  Launch animation
Electrocardiogram (ECG) - interactive tool
Click the waveform pull-down list to view various waveforms showing normal and pathological conditions of the heart.
Endocrine glands
This animation illustrates the glands of the endocrine system, specifically enlarging the pituitary gland, thyroid gland, parathyroid glands, thymus, adrenal glands, and pancreas. A communication path within the neuroendocrine system is also shown.  Launch animation
Endocrine glands

The endocrine system is primarily composed of glands that produce chemical messengers called hormones. Glands of the endocrine system include the pituitary gland, the thyroid gland, the parathyroid glands, the thymus, and the adrenal glands.

Other glands are also included within the endocrine system since they contain endocrine tissue that secretes hormones. These include the pancreas, ovaries and testes.

The endocrine and nervous systems work very closely together. The brain continuously sends instructions to the endocrine system, and in return receives feedback from the endocrine glands. Because of this intimate relationship, the nervous and endocrine systems are referred to as the neuroendocrine system.

The hypothalamus is known as the master switchboard because it’s the part of the brain that controls the endocrine system. The pituitary gland, which hangs by a thin stalk from the hypothalamus, is called the master gland of the body because it regulates the activity of the endocrine glands.

The hypothalamus detects the rising level of the target organ’s hormones then sends either hormonal or electrical messages to the pituitary gland. In response, the pituitary gland releases hormones, which travel through the bloodstream to a target endocrine gland, instructing it to stop producing its hormones.

Here’s how the endocrine system keeps itself in check: eventually, the hypothalamus detects the rising level of the target organ’s hormones, and sends a message to the pituitary gland. The pituitary gland then stops releasing certain hormones, causing the target organ to stop producing its hormones.

The endocrine system constantly adjusts hormone levels so that the body can function normally. This process is called homeostasis.

Enlarged prostate
This animation illustrates the prostate gland and its surrounding structures and shows the effects of benign prostatic hypertrophy (BPH).  Launch animation
Enlarged prostate
The prostate gland is located underneath the bladder and is about the size of a chestnut. Part of the urethra is encased within the prostate gland. As a man ages, the prostate typically enlarges in size in a process called benign hypertrophy (non-cancerous enlargement).

The enlarged prostate crowds its surrounding structures and may cause the urethra to narrow. The narrowed urethra results in several of the symptoms of benign prostatic hypertrophy (BPH). Symptoms may include a slowed or delayed start in urination, the need to urinate frequently during the night, difficulty in emptying the bladder, a strong, sudden urge to urinate, and incontinence. Less than half of all men with BPH have symptoms of the disease, or their symptoms are minor and do not restrict their life style.

BPH is a normal physiological process of aging and treatment options are available. The choice of the appropriate treatment is based on the severity of the symptoms, the extent to which they effect lifestyle, and the presence of other medical conditions. Men with BPH should consult with their physician yearly to monitor the progression of the symptoms and decide the best course of treatment as needed.
Enlarged prostate gland
This animation illustrates the prostate gland and its surrounding structures and shows the effects of benign prostatic hypertrophy (BPH).  Launch animation
Enlarged prostate gland

The prostate gland is located underneath the bladder and is about the size of a chestnut.

In this cut section, you can see that part of the urethra is encased within the prostate gland. As a man ages, the prostate typically enlarges in size in a process called benign hypertrophy, which means that the gland got larger without becoming cancerous.

The enlarged prostate crowds its anatomical neighbors, particularly the urethra, causing it to narrow. The narrowed urethra results in several of the symptoms of benign prostatic hypertrophy, or BPH. Symptoms may include a slowed or delayed start in urination, the need to urinate frequently during the night, difficulty in emptying the bladder, a strong, sudden urge to urinate, and incontinence. Less than half of all men with BPH have symptoms of the disease, or their symptoms are minor and do not restrict their life style.

BPH is a normal physiological process of aging and treatment options are available. The choice of the appropriate treatment is based on the severity of the symptoms, the extent to which they affect lifestyle, and the presence of other medical conditions. Men with BPH should consult with their physician yearly to monitor the progression of the symptoms and decide the best course of treatment as needed.

Epinephrine and exercise
This animation shows the release of epinephrine and its effect of the heart.  Launch animation
Epinephrine and exercise
During periods of stress, such as preparing to run in a race, the brain signals the adrenal glands to produce epinephrine or "adrenaline". Epinephrine increases the rate in which the heart beats. The increased cardiac output supplies more oxygen to the muscles, putting the body in a heightened state to react. As a longer term response to stress, cortisol is secreted by the adrenal glands, promoting the release of energy.
Exercise
This animation gives a general comparison between anaerobic exercise (lifting weights) and aerobic exercise (jogging).  Launch animation
Exercise

Weight lifting is a form of anaerobic exercise. It is very demanding, requiring a great deal of energy, which quickly depletes the body’s oxygen reserves. Sprinting and push-ups are other examples of anaerobic activities. They each create a situation called oxygen debt, which requires us to breathe deeply and rapidly in order to restore a proper oxygen level to the muscle cells.

If oxygen reserves become depleted while exercising, muscles convert a starch, called glycogen, into energy. This conversion process creates a waste product called lactic acid.

Jogging is a form of aerobic exercise. Exercising over a long duration requires a steady level of energy for the body. If properly conditioned, the body will be able to supply adequate oxygen to meet its energy requirements during aerobic exercise and much less lactic acid will be formed in the muscles.

Eye - interactive tool
This interactive animation takes you on a 3-D journey to explore the anatomy of the eye. Rotate the eye or pick from a list of terms to identify various structures.  Launch animation
Eye - interactive tool

After the animation loads, click and drag the model to rotate it in any direction. Select a term from the structure list to travel to its location.

Click the "pin" button to hide or show the identification pin.

Click the "light bulb" button to view in highlight or full color mode.

Feeling pain
This animation shows the body’s response to a bee sting on the nose, giving a general description of the communication between the peripheral nervous system detecting the pain and the central nervous system issuing a reactive response.  Launch animation
Feeling pain
Pain provides the body with a protective mechanism, alerting it to potential or actual damage to the body’s tissues. In the example of a bee sting, the pain receptors in the skin detect tissue damage from the bee sting. Then, the peripheral nerves send a pain signal to the brain. The brain analyzes the pain signal. In turn, the brain delivers a message back to the muscles of the arm to react.
Female reproductive system - interactive tool
This interactive animation takes you on a 3-D journey to explore the anatomy of the female reproductive system. Rotate to or pick from a list of terms to identify various structures of the system.  Launch animation
Female reproductive system - interactive tool

After the animation loads, click and drag the model to rotate it in any direction. Select a term from the structure list to travel to its location.

Click the "pin" button to hide or show the identification pin.

Click the "light bulb" button to view in highlight or full color mode.

Fetal development - interactive tool
Creating a new life is nothing short of a miracle. With the fetal development interactive tool, you can get an insider's view of a baby in the making - from conception to term. You can watch the entire development, specify portions of the pregnancy, or freeze the frame on a specific week by dragging the slider bars back and forth.  Launch animation
Fetal development - interactive tool
Click and drag a slider bar underneath an image window to see the process of embryonic and fetal development.
Fetal ear development
This animation illustrates the development of a baby’s outer ear from its embryonic origins. Structures of a baby’s middle and inner ear are also shown from the front view.  Launch animation
Fetal ear development

The ears begin their development during the fifth week of pregnancy. Ear formation starts from a few small bulges called branchial arches. Portions of the branchial arches form into structures called auricular hillocks. The auricular hillocks grow and join together to form the outer ears.

During the fifth month, the inner and middle parts of the ear develop, but won’t be completely finished until birth.

Formation of twins
This animation shows the differences between the development of a single baby, identical twins, and non-identical twins.  Launch animation
Formation of twins

Twins are rare and special, occurring in about 2% of all pregnancies. Of that number, 30% are identical twins. The other 70% are non-identical, or fraternal twins.

This animation will show you the differences between the development of a single baby, identical twins, and fraternal twins.

Starting with the single baby, let's go back to the beginning, when fertilization occurs. Here you see that the egg cell is fertilized by a single sperm cell to form a zygote. Over the next few days, the fertilized egg cell divides over and over to form a structure composed of hundreds of cells called a blastocyst.

During the first week after fertilization, we can look inside the blastocyst and see the mass of cells that will form the embryo. Right there. The blastocyst will continue traveling toward the uterus where it will implant in the uterine lining, and grow into a single baby.

Now let's watch the development of identical twins. Identical twins start out from a single fertilized egg cell, or zygote, which is why they're also called monozygotic twins. Like the single baby we just saw, the egg is fertilized by a single sperm cell.

Unlike the single baby, this fertilized egg cell will split into two separate embryos, and grow into identical twins. This remarkable event takes place during the first week after fertilization, and can happen at several different times:

The stage at which the egg cell splits determines how the twins will implant in the uterine lining, and whether or not they share an amnion, chorion, and placenta. Basically, the earlier the splitting occurs, the more independently the twins will develop in the uterus. So, a pair of identical twins that split during the two-cell stage will each develop its own amnion, chorion, and placenta.

Twins that split during the late blastocyst stage will share an amnion, chorion, and placenta.

A common misconception about the conception of identical twins is that the trait for having them is passed on to future generations through the mother's genes. But the truth is science doesn't know the reason why identical twins occur. At this time, we can just say that they're examples of a nine-month double miracle.

Now let's take a look at the second type of twins. Non-identical, or fraternal, twins develop from two fertilized egg cells, or zygotes. Which is why they're also called dizygotic twins. Unlike identical twins, however, fraternal twins are definitely influenced by the mother's genes. Here's why:

When the mother of fraternal twins ovulates, sometimes her ovaries release two egg cells for fertilization. Typically, only one egg cell is released during ovulation.

During conception, both of these egg cells become fertilized by two different sperm cells, which is why fraternal twins don't look exactly alike. Sometimes they're not even the same sex.

Here in the uterus, you can see that the twin embryos develop separately each having his or her own chorion, amnion, and placenta.

Gas exchange
This animation illustrates the passage of air and exchange of oxygen and carbon dioxide within the lungs on both a gross and microscopic level.  Launch animation
Gas exchange

Air first enters the body through the mouth or nose, quickly moves to the pharynx (throat), passes through the larynx (voice box), enters the trachea, which branches into a left and right bronchus within the lungs and further divides into smaller and smaller branches called bronchioles. The smallest bronchioles end in tiny air sacs, called alveoli, which inflate during inhalation, and deflate during exhalation.

Gas exchange is the delivery of oxygen from the lungs to the bloodstream, and the elimination of carbon dioxide from the bloodstream to the lungs. It occurs in the lungs between the alveoli and a network of tiny blood vessels called capillaries, which are located in the walls of the alveoli.

The walls of the alveoli actually share a membrane with the capillaries in which oxygen and carbon dioxide move freely between the respiratory system and the bloodstream. Oxygen molecules attach to red blood cells, which travel back to the heart. At the same time, the carbon dioxide molecules in the alveoli are blown out of the body with the next exhalation.

Glaucoma
This animation shows the affects of untreated glaucoma.  Launch animation
Glaucoma
Glaucoma is the development of increased pressure within the eye. If left untreated, glaucoma may damage the optic nerve, resulting in visual impairment and eventually blindness.
Gout
This animation shows uric acid crystals moving to the big toe joint causing pain.  Launch animation
Gout
Gout is caused by increased production of uric acid. Uric acid crystals travel and accumulate in the joints, especially in the feet and legs, causing great pain and swelling.
Hearing
Through a series of magnifications of the ear, this animation depicts the movement, amplification, translation, and interpretation of sound waves traveling through the ear’s three regions, ultimately becoming neural messages sent to the brain.  Launch animation
Hearing

The ear is divided into three regions: the outer ear, middle ear and inner ear.

When sound waves enter the ear canal, they cause the eardrum to vibrate. The vibration moves the three bones in the middle ear, called the ossicles. The ossicles are also known as the hammer (malleus), anvil (incus), and stirrup (stapes). These tiny bones transfer and amplify sound waves to the oval window, which is located behind the stirrup.

When the oval window vibrates, it moves fluid across a membrane inside the cochlea. The fluid causes the membrane to move. Specialized hair cells translate this movement into nerve impulses, which are sent to the brain through the vestibulocochlear nerve. The brain interprets the impulses as sound.

Hearing and the cochlea
This animation shows the various structures of the ear and the process of hearing.  Launch animation
Hearing and the cochlea

As sound waves enter the ear, they travel through the outer ear, the external auditory canal, and strike the eardrum causing it to vibrate.

The central part of the eardrum is connected to a small bone of the middle ear called the malleus (hammer). As the malleus vibrates, it transmits the sound vibrations to the other two small bones or ossicles of the middle ear, the incus and stapes.

As the stapes moves, it pushes a structure called the oval window in and out. This action is passed onto the cochlea, which is a fluid-filled snail-like structure that contains the receptor organ for hearing.

The cochlea contains the spiral organ of Corti, which is the receptor organ for hearing. It consists of tiny hair cells that translate the fluid vibration of sounds from its surrounding ducts into electrical impulses that are carried to the brain by sensory nerves.

As the stapes rocks back and forth against the oval window, it transmits pressure waves of sound through the fluid of the cochlea, sending the organ of Corti in the cochlear duct into motion. The fibers near the cochlear apex resonate to lower frequency sound while fibers near the oval window respond to higher frequency sound.

Heart - interactive tool
This interactive animation takes you on a 3-D journey to explore the anatomy of the heart. Rotate the heart, view in transparent mode, or pick from a list of terms to take you to various structures.  Launch animation
Heart - interactive tool

After the animation loads, click and drag the model to rotate it in any direction. Select a term from the structure list to travel to its location.

Click the "pin" button to hide or show the identification pin.

Click the "light bulb" button to view in highlight or full color mode.

Heart bypass surgery
This animation shows the procedure of a heart bypass surgery.  Launch animation
Heart bypass surgery
Heart bypass surgery begins with an incision made in the chest, with the breastbone cut exposing the heart. Next, a portion of the saphenous vein is harvested from the inside of the leg. Pieces of this great vein will be used to bypass the blocked arteries in the heart. The venous graft is sewn to the aorta and to the affected coronary artery past the blocked site. The internal mammary artery from the chest may also be used to bypass a clogged artery. Several arteries may be bypassed depending on the condition of the heart.
Heart formation
This animation shows the development of the fetal heart from day 18 to day 57. A functional comparison is made between a fetal and newborn heart.  Launch animation
Heart formation
The embryo’s heart is the first organ that forms. It is derived from two primitive heart tubes. Between days 18 to 30, the primitive heart tubes fuse together, bend and twist to form a simple version of the heart. About half way through this process, the heart starts to beat.

At 2 months, the heart bears a close resemblance to what it will look like after the baby’s born. The resemblance is only superficial since the inside of the heart is different in both form and function.

In a newborn’s heart, oxygen-poor blood from the body enters the right atrium, goes to the right ventricle where it is pumped to the lungs to become rich with oxygen. From the lungs, the blood flows back to the heart filling the left atrium then enters the left ventricle. The left ventricle pumps the oxygen rich blood through the aorta, which carries it to the rest of the newborn’s body.

The fetal heart has the same basic components as the newborn heart, but there are a couple important differences. Because the placenta is providing all of the oxygen the fetus requires, its lungs are not needed to perform this task. Much of the fetus’ blood is detoured away from the lungs through two openings or connections: the foramen ovale, which connects the right and left atria, and the ductus arteriosus, which connects the aorta and the pulmonary artery. These two important connections will remain open up until the time of birth.

Within thirty minutes after the baby’s first breath, the ductus arteriosus will completely close, and the flap of the foramen ovale will shut off like a valve. This happens because of an increase in pressure on the left side of the heart, and a decrease on the right side. These changes in the heart anatomy cause the blood to flow to the lungs, which will take over their lifelong job of supplying oxygen to the body.
Heartbeat
This animation follows the passage of blood through the heart’s chambers and valves.  Launch animation
Heartbeat

The heart is a four-chambered organ with four main vessels, which either bring blood to or carry blood away from the heart. The four chambers of the heart are the right atrium, the right ventricle, the left atrium, and the left ventricle.

The great vessels of the heart include the superior and inferior vena cava, which bring blood from the body to the right atrium; the pulmonary artery, which transports blood from the right ventricle to the lungs; and the aorta, the body’s largest artery, which transports oxygen-rich blood from the left ventricle to the rest of the body.

If we remove some of the tough fibrous coating of the heart and great vessels, you can get a better look at the heart beating. If you look carefully, you can see a series of one-way valves that keep the blood flowing in one direction. If we inject dye into the superior vena cava, you can watch it pass through the heart as it goes through the cardiac cycle.

The blood first enters the heart into the right atrium. Blood passes from the right atrium through the tricuspid valve and into the right ventricle. When the right ventricle contracts, the muscular force pushes blood through the pulmonary semilunar valve into the pulmonary artery.

The blood then travels to the lungs, where it receives oxygen. Next, it drains out of the lungs via the pulmonary veins, and travels to the left atrium. From the left atrium, the blood is forced through the mitral valve into the critically important left ventricle. The left ventricle is the major muscular pump that sends the blood out to the body systems. When the left ventricle contracts, it forces the blood through the aortic semilunar valves and into the aorta. From here, the aorta and its branches carry blood to all the tissues of the body.

Heartburn
This animation depicts how certain ingested foods can cause regurgitation of the stomach’s contents back into the esophagus resulting in the sensation of heartburn. The relationship between the location of the esophagus and heart is shown in a front view of the body.  Launch animation
Heartburn

Eating spicy foods, such as pizza, may cause a person to feel heartburn. Although the name may imply the heart, heartburn has nothing to do with the heart itself. Heartburn is pain felt in the chest by a burning sensation in the esophagus, which is located close to where the heart is.

Here you can see the pizza passing from the mouth to the esophagus and on to the stomach. At junction between the stomach and esophagus is the lower esophageal sphincter. This muscular sphincter acts as a valve that normally keeps food and stomach acid in the stomach and prevents the stomach’s contents from regurgitating back into the esophagus.

However, certain foods may affect the lower esophageal sphincter, making it less effective. That’s how heartburn begins. The stomach produces hydrochloric acid to digest food. The stomach has a mucous lining that protects it from hydrochloric acid, but the esophagus does not.

So, when food and stomach acid regurgitate back into the esophagus, a burning feeling is felt near the heart. This feeling is known as heartburn. Antacids may be used to relieve heartburn by making stomach juices less acidic, therefore reducing the burning feeling felt in the esophagus. If heartburn becomes frequent or prolonged, medical intervention may be necessary to correct the problem.

Herniated nucleus pulposus (slipped disk)
This animation shows displacement of an intervertebral disk (disk between the vertebrae).  Launch animation
Herniated nucleus pulposus (slipped disk)
The disks between the vertebrae are liable to displacement when put under strain. Heavy lifting may produce forces which cause a lumbar intervertebral disk to move out of place ("slipped disk").
Homeostasis
This animation depicts the process of maintaining homeostasis in the body through hormonal negative feedback mechanisms. An analogy is made between thermostat temperature regulation in a home to the hormonal control of sugar levels within the bloodstream.  Launch animation
Homeostasis
Homeostasis is a state of balance inside the body, where the body systems work together to keep it functioning normally. The endocrine system keeps this internal balancing act going by releasing chemicals called hormones. The release of the hormones is controlled by negative feedback mechanisms.

A negative feedback mechanism works something like a thermostat in your home. A thermostat helps maintain a constant temperature, called the normal range. When the temperature rises beyond the normal range, the thermostat turns on the air conditioner. Eventually the air conditioner restores the temperature to the normal range. This process is called negative feedback. It starts with a normal range, goes beyond the normal range, and then back to normal again.

An example of how negative feedback works in the body can be demonstrated by the endocrine system’s controls over the amount of sugar in the bloodstream. Insulin is a hormone secreted by the pancreas that maintains a normal amount of sugar in the bloodstream. Shortly after eating a candy bar, tiny sugar molecules enter the bloodstream raising the blood sugar levels. In response, the pancreas secretes the insulin into the bloodstream. Now, the sugar molecules move out of the bloodstream and into the cells of the skeletal muscles, fat and liver. In turn, the blood sugar levels return to normal.
Human face formation
This animation shows the formation of a fetal face during the early weeks of development.  Launch animation
Human face formation

You might not be aware of this, but during its early development a fetus looks remarkably like something from the dawn of time.

Its face starts as a serious of paired tissue mounds called branchial arches.

There’s a human fetus’s head during the first month of development, when it was still an embryo. Its face starts as a series of paired tissue mounds called branchial arches.

Let’s take a look from the front. The embryo’s face actually forms from the first and second branchial arches, along with the area just above it.

The forehead and nose form from this area. (pause) These areas will form the cheekbones, and these lower areas will form the lower jaw. And this area will form the mouth.

At 28 days of development, you can see the lower jaw, which has fused together from the branchial arches. The thickenings you see here will eventually form the nostrils.

By day 31, you can see the nostrils have started to form. And, quite remarkably, the eyes have now appeared on each side of the head.

Two days later, the nostrils have moved toward the center of the face. You can also see that as the ears begin to form, they are positioned in a pretty odd location. But don’t worry, they will move.

At 35 days, the nostrils are even closer together, and we can see more of the eyes.

At 40 days, the baby has developed eyelids, and the nose looks much more developed.

Here he is at 48 days and he’s looking pretty darn good. The nasal swellings have joined in the center of the face, and the eyes have moved to the front of the head.

Three weeks later, the fetus looks more human than ever. After that, its face continues to develop more typical proportions right up until the time of its birth. Let’s look at the entire process again...

As you can see, the development of the face is a fascinating process that has some very dramatic changes taking place in a relatively short amount of time.

Hypertension - overview
This animation shows the effects of hypertension on a cerebral artery.  Launch animation
Hypertension - overview
If left untreated, hypertension can lead to the thickening of arterial walls causing its lumen, or blood passage way, to narrow in diameter. As a result, the heart must work harder to pump blood through the narrowed arterial openings. In addition, people with hypertension may be more susceptible to stroke.
Immune response
This animation shows an enlarged view of femoral bone marrow containing immature specialized white blood cells (lymphocytes) and depicts their maturation and migration into either B cell or T cell lymphocytes.  Launch animation
Immune response

The immune system includes specialized white blood cells, called lymphocytes that adapt themselves to fight specific foreign invaders. These cells develop into two groups in the bone marrow.

From the bone marrow, one group of lymphocytes migrates to a gland called the thymus and become T lymphocytes or T cells. Within the thymus, the T cells mature under the influence of several hormones.

The T cells mature into several different types, including helper, killer and suppressor cells. T cells are responsible for cell-mediated immunity. This type of immunity becomes deficient in persons with HIV, the virus that causes AIDS, because HIV attacks and destroys helper T cells.

The other group of lymphocytes, B lymphocytes or B cells, mature and develop within the bone marrow itself. In that process, they achieve the ability to recognize specific foreign invaders. From the bone marrow, B cells migrate through the body fluids to the lymph nodes, spleen and blood. B lymphocytes provide the body with humoral immunity as they circulate in the fluids in search of specific foreign invaders to destroy.

Kidney stones
This animation begins with an front view of the urinary tract and continues with the formation of kidney stones shown in a cut-section of the kidney. Severities of kidney stones are depicted, demonstrating various degrees of urine obstruction.  Launch animation
Kidney stones

The urinary tract includes the kidneys, ureters, bladder and urethra. Within each kidney, urine flows from the outer cortex to the inner medulla. The renal pelvis is the funnel through which urine exits the kidney and enters the ureter.

As urine can become very concentrated as it passes through the kidneys. When the urine becomes too concentrated, calcium, uric acid salts and other chemicals dissolved in the urine can crystallize, forming a kidney stone (renal calculus).

Usually the calculus is the size of a small pebble. But ureters are very sensitive to being stretched, and when stones form and distend it, the stretching can be very painful. Often, people may not know they have kidney stones until they feel the painful symptoms resulting from a stone being stuck anywhere along the urinary tract. Fortunately, small stones typically pass out of the kidneys and through the ureters on their own without causing any problems.

However, stones can become more problematic when they block the flow of urine. A staghorn kidney stone may obstruct the entire kidney. Fortunately, these stones are the exception rather than the rule.

Kids-How does the baby come out?
This animation gives a cartooned comical view of birth through a vaginal delivery.  Launch animation
Kids-How does the baby come out?
When a baby is ready to be born, the mother starts to feel labor contractions. That means that her uterus starts squeezing and pushing so the baby can come out. It’s a tight fit, but it doesn’t hurt the baby during delivery.
Kids-How big is the baby?
Illustrated for a child’s perspective, this animation depicts the growth of a baby within a uterus from the first month to the ninth month of pregnancy.  Launch animation
Kids-How big is the baby?

At 1 month, the baby growing inside the mother’s uterus is very small. The baby is so small she could fit in the palm of your hand and is about the size of your thumbnail.

Over the next 9 months, the baby will grow more inside the uterus until she is ready to be born.

Kids-Is it a girl or boy?
Illustrated for a child’s perspective, this cartooned animation explains the sperm’s role in determining if a baby will be a girl or a boy.  Launch animation
Kids-Is it a girl or boy?

To make a baby, a man’s sperm meets and joins with a woman’s egg cell inside her body. Inside the man’s sperm are a set of instructions that tell the baby to be a boy or a girl.

The instructions in the man’s sperm cell can either carry the letter "X" or the letter "Y". If the letter is an "X", it means the baby will be a girl. If the letter is a "Y", the baby will be a boy.

Kids-Umbilical cord
Illustrated for a child’s perspective, this cartooned animation explains how food and air are supplied from the mother to the baby through it's umbilical cord.  Launch animation
Kids-Umbilical cord

When the baby is in the mother’s uterus, it can’t eat or breathe on its own, so it needs some help. The baby has a little tube that goes to its middle called the umbilical cord. The umbilical cord goes to the placenta, which connects to the mother’s uterus.

Here’s how it works. First, the food that the mother eats and air that she breathes get into her bloodstream as very tiny pieces called molecules.

These molecules, or tiny pieces of food and air, travel through the mother’s bloodstream to her placenta. From there, they go to the umbilical cord and into the baby’s body. That’s how the baby eats and breathes inside the uterus.

After a baby is born, the umbilical cord goes away. Guess what’s left? Your belly button.

Kids-Where do babies come from?
Created for a child’s perspective, this cartooned animation illustrates the appearance and origin of a sperm cell and egg cell as well as the development of a baby within the uterus.  Launch animation
Kids-Where do babies come from?

Two things are needed to make a baby: a sperm cell and an egg cell. A man makes the sperm cell inside his body and a woman makes the egg cell inside her body.

Both the sperm cell and egg cell are very small. You would need a microscope to see them in real life. A microscope is like a magnifying glass, only much stronger.

When the sperm cell and the egg cell meet each other, they make a tiny baby that’s smaller than a grain of salt. The baby will grow inside a special place in woman’s body called the uterus. After about nine months, the baby will come out as a little boy or girl.

Liposuction
A vibrating suction cannula is shown removing abdominal fat.  Launch animation
Liposuction
A vibrating suction cannula, or flexible tube, is used in a liposuction procedure. The cannula is inserted through a small hole into the abdominal fat tissue to remove excess fat deposits.
Lungs - interactive tool
This interactive animation takes you on a 3-D journey to explore the anatomy of the lungs. Rotate the lungs view in transparent mode, or pick from a list of terms to take you to various structures of the lungs.  Launch animation
Lungs - interactive tool

After the animation loads, click and drag the model to rotate it in any direction. Select a term from the structure list to travel to its location.

Click the "pin" button to hide or show the identification pin.

Click the "light bulb" button to view in highlight or full color mode.

Click the "double box" button to see and rotate the model in transparent mode.

Lymph nodes
This animation shows an enlarged view of one lymph node filtering out micro-organisms from the fluid passing through.  Launch animation
Lymph nodes
The lymphatic system is a complex network of thin vessels, valves, ducts, nodes, and organs. It helps to protect and maintain the fluid environment of the body by producing, filtering, and conveying lymph and by producing various blood cells.

Lymph nodes play an important part in the body’s defense against infection. The most common cause of swollen lymph nodes is infection, which might occur even if the infection is trivial or not. Afferent lymph vessels bring unfiltered fluids into the lymph node to be filtered while efferent vessels carry clean fluids away from the lymph node and to the cardiovascular system where it helps form the plasma in the blood.

Overall, lymph nodes work like a biological filtering system. When the body is invaded by foreign organisms, the painful swelling sometimes felt in the neck, armpits, groin, or tonsils comes from the microorganisms being trapped inside collections of lymph cells or nodes. Eventually, these organisms are destroyed and eliminated by cells that line the walls of the lymph nodes and the swelling and pain subside.
Lymphatics and the breast
This animation discusses and depicts several aspects of the lymphatic system including a microscopic view of lymph formation, edema, breast lymphatics and the spread of breast cancer.  Launch animation
Lymphatics and the breast
The lymphatic system is often referred to as the body’s "secondary circulatory system". The lymphatic system collects excess fluid in the body’s tissues and returns it to the bloodstream.

Lymph formation occurs at the microscopic level. During the exchange of fluid and molecules between the blood circulation and body tissues, blood capillaries may not reabsorb all of the fluid. Surrounding lymphatic capillaries absorb the excess fluid. The fluid is then filtered and transported back by the lymphatic system into large veins near the heart.

The lymphatic system can play a very worrisome role in the spread of breast cancer. Components of the lymphatic system called lymph nodes are distributed at specific locations throughout the body. There is also an extensive network of lymphatic vessels in every woman’s breast tissue, which is important in regulating the local fluid balance as well as in filtering out harmful substances.

The lymph vessels in the breast may inadvertently supply cancerous cells with access to a highway along which the cancerous cells can move to other parts of the body. This process is called metastasis and may result in the formation of a secondary cancer mass in a different location of the body. Regular breast self examinations can help to detect tumors earlier in their growth, hopefully before they spread quickly or metastasize.
Macular degeneration
This animation shows the process of macular degeneration in the eye.  Launch animation
Macular degeneration
The macula is the part of the retina that distinguishes fine details at the center of the field of vision. Macular degeneration results from a partial breakdown of the insulating layer between the retina and the choroid layer of blood vessels behind the retina. Macular degeneration results in the loss of central vision only.
Male reproductive system - interactive tool
This interactive animation takes you on a 3-D journey to explore the anatomy of the male reproductive system. Rotate to or pick from a list of terms to identify various structures of the system.  Launch animation
Male reproductive system - interactive tool

After the animation loads, click and drag the model to rotate it in any direction. Select a term from the structure list to travel to its location.

Click the "pin" button to hide or show the identification pin.

Click the "light bulb" button to view in highlight or full color mode.

Menstrual cycle - interactive tool
This interactive animation shows the changes that occur during the menstrual cycle to hormone levels, body temperature, an ovary, and lining of the uterus.  Launch animation
Menstrual cycle - interactive tool
Click and drag the slider bar to see changes that occur during a normal 28 day menstrual cycle.
Muscle types
This animation discusses the four functions of muscle and displays the three different types of muscle tissue in external and microscopic views.  Launch animation
Muscle types

Muscles perform four important body functions: maintain body posture, stabilize the joints, provide mobility, and generate heat that the body requires.

The body contains three types of muscle to perform these functions:
• Smooth muscle - involuntary muscle found in the walls of body organs; functions without conscious control
• Cardiac muscle - involuntary muscle found only in the walls of the heart; functions without conscious control
• Skeletal muscle - attaches to and covers the bony skeleton to provide movement of the body; the only type of muscle under voluntary or conscious control

Nerve conduction
This animation provides a general overview of the nervous system and shows the process in which nerve impulses are transmitted.  Launch animation
Nerve conduction

The nervous system is composed of two divisions, the central nervous system (CNS) and peripheral nervous system (PNS). The CNS contains the brain and the spinal cord and the PNS consists of thousands of nerves that connect the spinal cord to muscles and sensory receptors.

A peripheral nerve is composed of nerve bundles (fascicles) that contain hundreds of individual nerve fibers (neurons). Neurons consist of dendrites, axon, and cell body. The dendrites are the tree-like structures that receive signals from other neurons and from special sensory cells that sense the body’s surrounding environment. The cell body is the headquarters of the neuron and contains its genetic information in the form of DNA. The axon transmits signals away from the cell body to other neurons.

Many neurons are insulated like pieces of electrical wire. This insulation protects them and also allows their signals to move faster along the axon. Without this insulation, signals from the brain might never reach the outlying muscle groups in the limbs.

The operation of the nervous system depends on the flow of communication between neurons. For an electrical signal to travel between two neurons, it must first be converted to a chemical signal, which then crosses a space of about a millionth of an inch wide. The space is called a synapse, and the chemical signal is called a neurotransmitter.

Neurotransmitters allow the billions of neurons in the nervous system to communicate with one another, making the nervous system the master communication system of the body.

Nervous system formation
This animation shows the early formation of the nervous system.  Launch animation
Nervous system formation
The most critical stage of development for the embryo’s nervous system is the third and fourth weeks of pregnancy.

On day 14, the embryo looks like a little disc. The first part of the nervous system that forms is an indentation called the neural groove. Over the next 7 days, the groove deepens as the cells around it form ridges called neural folds.

By day 27, the neural folds wrap around the neural groove and form the neural tube. The neural tube will further develop into the brain and spinal cord. Structures called somites form the vertebral column, or backbone. They also help form the ribs and the muscles of the neck, arms, and legs.

The embryo’s nervous system is particularly vulnerable during the early stage of development, so an expectant mother should be careful about avoiding any substances that could potentially harm it.
Nutrient exchange
This animation shows an enlargement of a blood capillary with red blood cells traversing through it. A section of the artery is enlarged further to display the exchange of oxygen and carbon dioxide between a capillary and its surrounding tissue.  Launch animation
Nutrient exchange

Nutrient exchange is a continuous cycle, constantly supplying the body with oxygen and nutrients while removing carbon dioxide and metabolic waste.

Red blood cells are the cells in the blood that carry oxygen from the lungs to the body tissues through blood pumped by the heart. As they travel away from the heart, they traverse smaller and smaller arteries, finally arriving at the collections of microscopic blood vessels called capillaries.

Capillaries contain a high concentration of oxygen and nutrients, while the surrounding tissues contain a lower concentration. Through a process called diffusion, these particles leave the capillaries and enter the body’s tissues.

Conversely, the body’s tissues contain high concentrations of carbon dioxide and metabolic waste, while the capillaries contain a lower concentration. Waste products diffuse from the tissues into the capillaries and from there are carried by the venous system back toward the heart.

The waste products are eventually eliminated from the bloodstream by the liver, kidneys, and lungs.

Osteoarthritis
This animation compares a normal adult knee joint and a knee joint affected by osteoarthritis.  Launch animation
Osteoarthritis

Osteoarthritis is the most common form of arthritis and is associated with the aging process. Osteoarthritis is a chronic disease causing the deterioration of the cartilage within a joint.

For most people, the cause of osteoarthritis is unknown, but metabolic, genetic, chemical, and mechanical factors play a role in its development. Symptoms of osteoarthritis include loss of flexibility, limited movement, and pain and swelling within the joint. The condition results from injury to the cartilage, which normally absorbs stress and covers the bones, so they can move smoothly.

The cartilage of the affected joint is roughened and becomes worn down. As the disease progresses, the cartilage becomes completely worn down and the bone rubs on bone. Bony spurs usually develop around the margins of the joint.

Part of the pain results from these bone spurs, which can restrict the joint’s movement as well.

Osteoporosis
This animation begins by showing a hip fracture due to osteoporosis (fracture in neck of the femur, anterior view). The bone then dissolves into a frontal section to compare the bony interior of a normal femur to that of an osteoporotic femur.  Launch animation
Osteoporosis
Osteoporosis is a condition that leads to loss of bone mass. From the outside, osteoporotic bone is shaped like normal bone. However, the inside of the bones becomes more porous during the again process due to the loss of calcium and phosphate. The loss of these minerals makes the bones more prone to fracture even during routine activities, like walking, standing, or bathing. Often, a person will sustain a fracture before becoming aware of the presence of the disease.

Prevention is the best measure for treating osteoporosis by eating a recommended balanced diet including foods with sufficient amounts of calcium, phosphorous, and vitamin D. In addition, maintaining a regular exercise program as approved by your health care provider will help to keep the bones strong.

Various medications can be used as part of the treatment for osteoporosis and should be discussed thoroughly with your health care provider.
Ovulation
This animations shows the process of ovulation (the release a single egg cell from an ovary).  Launch animation
Ovulation
Ovulation occurs though a sequence of hormonal responses. Located deep within the brain, the pituitary gland releases the hormones FSH and LH, which travel through the blood stream to the ovaries. These hormones signal the development and release a single egg cell from one of the ovaries. The sweeping motion of the fimbriae draws the egg cell through a very small space in the open body cavity into the uterine, or fallopian, tube. The egg cell will either be fertilized by sperm or will dissolve if fertilization does not take place.
Parkinson's disease
This animations shows sporatic brain activity and a twitching hand that occur with Parkinson's disease, followed by treatment with dopamine stimulation.  Launch animation
Parkinson's disease
In Parkinson's disease, dopamine production becomes irregular and inadequate and nerve cells cannot properly transmit messages. This results in the loss of muscle function. By providing an even, adequate supply of medication that the body converts into dopamine, neurons are able to transmit messages and tremors improve.
Percutaneous transluminal coronary angioplasty (PTCA)
This animation shows a Percutaneous Transluminal Coronary Angioplasty (PTCA) procedure to open up blocked coronary arteries by inflating a tiny balloon to compress the plaque against the walls of the artery, flattening it out so that blood can once again flow through the blood vessel freely.  Launch animation
Percutaneous transluminal coronary angioplasty (PTCA)

Percutaneous transluminal coronary angioplasty (PTCA) is a minimally invasive procedure to open up blocked coronary arteries, allowing blood to circulate unobstructed to the heart muscle.

The procedure begins with the doctor injecting some local anesthesia into the groin area and putting a needle into the femoral artery, the blood vessel that runs down the leg. A guide wire is placed through the needle and the needle is removed. An introducer is then placed over the guide wire, after which the wire is removed. A different sized guide wire is put in its place.

Next, a long narrow tube called a diagnostic catheter is advanced through the introducer over the guide wire, into the blood vessel. This catheter is then guided to the aorta and the guide wire is removed. Once the catheter is placed in the opening or ostium of one the coronary arteries, the doctor injects dye and takes an x-ray.

If a treatable blockage is noted, the first catheter is exchanged for a guiding catheter. Once the guiding catheter is in place, a guide wire is advanced across the blockage, then a balloon catheter is advanced to the blockage site. The balloon is inflated for a few seconds to compress the blockage against the artery wall. Then the balloon is deflated.

The doctor may repeat this a few times, each time pumping up the balloon a little more to widen the passage for the blood to flow through. This treatment may be repeated at each blocked site in the coronary arteries. A device called a stent may be placed within the coronary artery to keep the vessel open. Once the compression has been performed, contrast media is injected and an x-ray is taken to check for any change in the arteries. Following this, the catheter is removed and the procedure is completed.

Peristalsis
This animation follows the processing of food through the digestive tract, focusing on the intestinal peristaltic movement (a series of wave-like muscle contractions that moves the food mixture down the digestive tract).  Launch animation
Peristalsis
Peristalsis is a series of wave-like muscle contractions that moves food to different processing stations in the digestive tract. The process of peristalsis begins in the esophagus when a bolus of food is swallowed. The strong wave-like motions of the smooth muscle in the esophagus carry the food to the stomach, where it is churned into a liquid mixture called chyme.

Next, peristalsis continues in the small intestine where it mixes and shifts the chyme back and forth, allowing nutrients to be absorbed into the bloodstream through the small intestine walls.

Peristalsis concludes in the large intestine where water from the undigested food material is absorbed into the bloodstream. Finally, the remaining waste products are excreted from the body through the rectum and anus.
Phagocytosis
This animation shows the process of a macrophage ingesting a foreign substance.  Launch animation
Phagocytosis
Macrophages are scavenger cells that can ingest dead tissue and foreign cells. Macrophages form tentacles called pseudopods to surround an invader. Once inside the macrophage, the invader is walled off and then digested and destroyed by a bag of digestive chemicals, or enzymes.
Pituitary gland
This animation describes the regulation of the pituitary gland and the hormones it releases to regulate various organs and processes in the body.  Launch animation
Pituitary gland

The pituitary gland is often referred to as the "master gland" of the body, since it regulates many activities of other endocrine glands. Located above the pituitary gland is the hypothalamus. The hypothalamus decides which hormones the pituitary should release by sending it either hormonal or electrical messages.

In response to hormonal messages from the hypothalamus, the pituitary gland releases the following hormones:

In response to electrical messages from the hypothalamus, the pituitary gland releases the following hormones:

Placenta delivery
This animation illustrates the delivery of the placenta by strong uterine contractions and gentle abdominal pressure applied by a physician.  Launch animation
Placenta delivery
The placenta provides the baby with nutrients and oxygen from the mother and carries away fetal waste. Following delivery, the uterus naturally contracts to push the placenta out of the uterus. In addition, the delivering practitioner will assist by gently pressing the abdomen to work the placenta free of the uterus.

Delivery of the placenta is typically painless and takes approximately 15 minutes.

Once the placenta is delivered, it is examined to see if the placental tissue is healthy and in one piece. At times, the placenta can break off and cause bleeding in the uterus. The placenta is commonly referred to as the afterbirth. Its successful delivery signals the end of the final stage of childbirth.
Placenta formation
This animation illustrate the formation of the placenta and blood barrier and their role in providing the embryo with nutrients and oxygen, removing waste products, and preventing harmful substance from entering in.  Launch animation
Placenta formation

Many people have mistaken ideas about how a growing embryo eats and breathes in the uterus.

From the earliest stages of its development, the growing embryo requires nutrition and oxygen, and a disposal system for the waste products of its own metabolism. All of this is accomplished by the placenta, which allows the growing embryo to eat and breathe while in the mother’s uterus.

To get some perspective on how the placenta began, let’s go back to Day 8. This hollow ball of cells moving through the uterus is the blastocyst, searching for an implantation site. Here you see its outer layer beginning to extend out and implant in the uterine lining, searching for the uterine blood vessels that would nourish it throughout the pregnancy.

As it went deeper, a single layer of cells from the mother’s uterine lining surrounded it, so that it would be protected from harm. On Day 9, as it grew larger and more complex, the blastocyst became an embryo. Here it’s about the size of a pinhead.

Also on Day 9, the outer layer of the embryo developed spaces called lacunae. The lacunae filled up with blood from the mother’s uterine lining.

On Day 13, small projections from the embryo’s chorionic layer reached out into the uterine lining. The chorionic layer is one of the membranes that surround the embryo and help it implant.

On Days 15 through 21, blood vessels began to form beneath this chorionic layer.

Around Day 21, the embryo’s blood stream and the mother’s blood stream were in such close contact that nutrients and oxygen could cross from mother to embryo. This was how the embryo first got its food and air from the mother, and technically this is when the placenta began to function.

Let’s magnify this area so you can see what we’re talking about. Here you see a vein and an artery from the embryo in close contact with the blood in the mother’s uterine lining. Inside the blood vessels, you can also see red blood cells, which carry oxygen.

The two blood streams are separated by a thin collection of tissues in the placenta called the blood barrier. This barrier permits small particles like nutrients and oxygen to pass from the mother to the embryo, (pause) and allows waste products to pass from the embryo back to the mother. The blood barrier also prevents many large or potentially harmful particles from entering the embryo’s blood stream. Notice that the red blood cells do not cross from the mother’s blood stream to the embryo’s.

You may be wondering how a mother’s blood cells could be harmful to her growing baby, and why it’s important to keep the two blood streams separate. If the mother’s blood type is RH negative, and her embryo’s blood type is RH positive, then the mother’s antibodies would treat the embryo as an invading foreign organism, and try to destroy it.

Now you can see why the placenta and its blood barrier are important for supplying the growing embryo with nutrition and oxygen, removing its waste products, and preventing harmful substances from getting into its blood stream.

Preeclampsia
This animation depicts hypertension caused by pre-eclampsia that adversely affects the fetus by causing constriction of the placental arteries.  Launch animation
Preeclampsia

Hypertension caused by preeclampsia can adversely affect the fetus by causing constriction of the placental arteries. Arterial constriction may result in severe reduction in the blood flow to areas of the placenta. If the blood flow remains constricted, areas of the placenta may "die", putting the baby in distress.

Pregnancy
This animation illustrates the development cycle of an egg in an ovary and the sequence of events to fertilization of the egg or not.  Launch animation
Pregnancy

The first trimester consists of the first 14 weeks of the 40-week pregnancy. During this time, a woman may experience various emotions due to the hormonal changes in her body. The breasts became enlarged and tender, and she may experience “morning sickness” at any time during the day or night.

During the first trimester, nearly all of the fetus’ internal organs form. The fetus is approximately the size of a fist and can even begin to move a little.

During the second trimester, weeks 15 through 27, a woman may experience symptoms of heartburn and indigestion. The baby’s growth in the abdominal area becomes noticeable, and stretch marks may develop as the skin of the abdomen expands.

The developing fetus grows very rapidly during the second trimester, and the fetus’ arms and legs become well developed and strong. The expectant mother may begin to feel the baby moving inside. Although the fetus is almost fully formed, the lungs need to develop further while the fetus puts on more fat and weight.

During the third trimester, weeks 28 through 40, the baby continues to grow and the lungs develop further. It can be difficult for a woman at this stage to find a comfortable position either awake or asleep.

The baby’s growing body within the uterus pushes the abdominal organs up under the diaphragm and compresses the bladder and colon. Near the end of the 40-week cycle, the baby drops down into the pelvic cavity, which is nature’s way of saying, “It’s time to give birth”.

Red blood cell production
This animation shows the process of red blood cell formation and the components that comprise blood.  Launch animation
Red blood cell production

Blood carries various substances that must be brought to one part of the body or another. Red blood cells are an important element of blood. Their job is to transport oxygen to the body’s tissues in exchange for carbon dioxide, which is carried to and eliminated by the lungs.

Red blood cells are formed in the red bone marrow of bones. Stem cells in the red bone marrow called hemocytoblasts give rise to all of the formed elements in blood. If a hemocytoblast commits to becoming a cell called a proerythroblast, it will develop into a new red blood cell.

The formation of a red blood cell from hemocytoblast takes about 2 days. The body makes about two million red blood cells every second.

Blood is made up of both cellular and liquid components. If a sample of blood is spun in a centrifuge, the formed elements and fluid matrix of blood can be separated from each other. Blood consists of 45% red blood cells, less than 1% white blood cells and platelets, and 55% plasma.

Reflex response
This animation shows the body’s reflex response to a hot substance landing on the hand.  Launch animation
Reflex response

The skeletal muscles are under voluntary (conscious) control most of the time. However, skeletal muscle movement can also by induced by involuntary reflexes.

Reflexes are involuntary reactions to a stimulus such as the burning of the hand. As soon as a hot substance contacts the hand, pain receptors in the skin send a signal to the spinal cord. In turn, the spinal cord sends a signal back to the arm muscles that instruct the hand to pull away. The arm flexed as it withdrew, which is known as a flexor (withdrawal) reflex.

If the body did not have the reflexes to withdraw quickly from a painful stimulus, we would be at risk for serious injury.

Retina
This animation shows the process in which light is transformed by the retina as electical impulses that travel to the brain through the optic nerve.  Launch animation
Retina
As light enters the eye, it strikes the receptor cells of the retina called the rods and cones. A chemical reaction results in the formation of electric impulses, which then travel to the brain through the optic nerve.
Retinal detachment
This animation shows a retinal detachment injury.  Launch animation
Retinal detachment
Retinal detachments are associated with a tear or hole in the retina through which the internal fluids of the eye may leak, causing separation of the retina from underlying tissues.
Rupturing membranes
In a side view of the body with the baby in utero, the mucous plug (bloody show) is illustrated followed by the rupturing of the amniotic sac (water breaking), indicating the onset of labor.  Launch animation
Rupturing membranes

When the amniotic sac ruptures the amniotic fluid begins to trickle out of the uterus and vagina. For some women, it can actually gush out in a stream.

The rupturing of the amniotic sac, which surrounds and protects the baby, is commonly referred to as the "water breaking."

The combination of regular contractions and cervical change indicates the first phase of labor is starting.

Seeing
This animation illustrates the various structures of the eye and how the shape of the eye affects vision (nearsightedness and farsightedness).  Launch animation
Seeing

The eye is the organ of sight and is shaped as a slightly irregular hollow sphere. Various structures in the eye enable it to translate light into recognizable images. Among these are the cornea, the lens, and the retina.

Light first passes through the cornea, a clear dome-like structure covering the iris, or colored part, of the eye. The cornea bends, or refracts, the light onto the lens. The light is then refracted a second time while passing through the lens, finally focusing on the retina. The retina is the light sensitive part of the eye. Impulses travel down the optic nerve to the occipital lobe of the brain, which then interprets the image in the correct perspective.

The shape of the eye is very important in keeping the things we see in focus. If the shape of the eye changes, it affects a person’s vision.

Normally, light is precisely focused onto the retina at a location called the focal point. A nearsighted eye is longer from front to back than a normal eye causing light to be focused in front of the retina instead of directly onto it. This makes it difficult to see objects that are far away. Glasses with concave lenses are used to correct nearsightedness. The concave lens focuses light back onto the focal point of the retina.

Farsightedness occurs when the length of the eye is too short. Light is focused at a point behind the retina, making it difficult to see objects that are up close. A convex lens is used to correct farsightedness because it directs the focal point back onto the retina.

Sexual differentiation
This animation illustrates the development of the external sex organs in a female and male fetus.  Launch animation
Sexual differentiation

A baby’s sex is determined at the time of conception. When the baby is conceived, a chromosome from the sperm cell, either X or Y, fuses with the X chromosome in the egg cell, determining whether the baby will be female or male. Two X’s means the baby will be a girl, and XY means it will be a boy.

But even though gender is determined at conception, the fetus doesn’t develop its external sexual organs until the fourth month of pregnancy.

Let’s go to seven weeks after conception. You can see from the front that the fetus appears to be sexually indifferent, looking neither like a male or a female.

Over the next five weeks, the fetus begins producing hormones that cause its sex organs to grow into either male or female organs. This process is called sexual differentiation.

We don’t know what sex this fetus is yet, so we’ll have to be hypothetical here.... Now, if the fetus is a male, it will produce hormones called androgens, which will cause his sexual organs to form like this...

On the other hand, a female fetus would not produce androgens; she would produce estrogens… so her sex organs would form like this...

Now let’s take a look at something you may have missed. At seven weeks, the sex organs of a male and female look identical. Let’s add some color to see what happens during sexual differentiation. Keep your eye on the genital tubercle.

See that? The genital tubercle formed the penis in the male, (pause) and the clitoris in the female.

The penis and clitoris are called sexual analogs (pause) because they originate from the same structure.

Shoulder joint dislocation
This animation shows a dislocation of the shoulder joint.  Launch animation
Shoulder joint dislocation

A shoulder dislocation usually occurs as a result of force to a joint. The bone is pushed out of the socket, which may cause damage to the surrounding ligaments, tendons, and nerves.

Skeletal formation
This animation details the components of the fetal skeletal system and illustrates the process of bone development through ossification of the membranes and cartilage.  Launch animation
Skeletal formation

A baby’s skeleton begins as fragile membranes and cartilage, (pause) but after three months, the membranes and cartilage start turning into bone, providing protection for the internal organs, and a solid framework for the muscles.

Late in the second month of fetal development, a fetus’ skeleton is made up of thin membranes, which are about the thickness of paper tissue, (pause) and soft, flexible cartilage, like the kind you find in your ear. Over time, both types of tissue will turn into bone in a process called ossification.

Ossification occurs in two ways...the first is when membranes turn into bone.

If we look at a fetus during the third month, we can see that the membranes on the side and back of the skull are starting to ossify. That means that the bone tissue is slowly growing over the area where the membranes once existed. Eventually, these bone plates will grow together forming the cranial cavity which protects the brain.

As the baby’s development is close to birth, you can see the bones of the skull still have gaps between them. These gaps, called fontanelles, allow room for the baby’s brain to grow, (pause) and also enable the head to be compressed during delivery.

The fontanelles will remain open until the end of the second year. And even though they’re commonly known as the baby’s soft spot, the fontanelles are actually about the thickness and strength of a piece of canvas. Which kind of makes them a soft, but tough, spot.

The bones of the skull won’t stop growing until a child reaches adulthood. That’s when the joints between the bones, called the sutures, will fuse together.

Now let’s go back once again and watch the second type of ossification when cartilage turns into bone.

This time we’ll look at the hand. Most of the bones of the skeleton, like the arms, legs, ribs, fingers, and backbone, start off as cartilage.

We can get a good idea of how cartilage turns into bone by looking at this portion of the hand. Here’s what it looks like on the inside…

From the second month until the end of the third month, remarkable changes take place. Watch the middle of the cartilage: both the inside and the outside turn into bone, or ossifies.

This is how the bones will continue to grow until adulthood---from the middle of the bone outward. That way they can continue to increase in their length and width.

Skeletal muscle
This animation illustrates the organization of skeletal muscle, enlarging from a muscle belly up to its myofibrils. Simultaneously in side and front views, the actions of a leg muscle and its myofibrils are shown while performing leg extension exercises.  Launch animation
Skeletal muscle

Skeletal muscle is well-organized body tissue, composed in a complex array of smaller and smaller structures. Each skeletal muscle is composed of many units called muscle fascicles. The fascicles are bound together by a type of connective tissue called fascia.

Fascicles are composed of smaller organizational units called muscle fibers.

Smaller strands called myofibrils organize muscle fibers. The myofibrils move as skeletal muscle contracts. It is the interaction of the myofibrils as they slide and pull along side each other that gives skeletal muscle its functional ability to do work and move things.

Putting it all back together, myofibrils compose muscle fibers, muscle fibers make-up muscle fascicles, and muscle fascicles are bound together by fascia to compose skeletal muscle.

Skeletal system components
This animation highlights the individual bones and groups of bones that comprise the skeletal system.  Launch animation
Skeletal system components

The skeletal system consists of approximately 206 bones, providing the body with structure and support. Let’s take a tour of various components that form the skeletal system.

Here’s the skull. It has 8 cranial bones that protect the brain. The facial skeleton has 14 bones that provide a framework for the eye sockets, jaws, and teeth. The facial bones provide the framework for the various structures of the face including the overlying muscles, fat and skin.

The vertebral column is composed of 24 individual vertebrae, along with two sets of fused bones called the sacrum and coccyx. In addition to providing support for the trunk of the body, the vertebral column protects the spinal cord. All together, there are 7 cervical, or neck vertebrae; 12 thoracic, or upper back, vertebrae; and 5 lumbar, or lower back, vertebrae.

The sacrum is composed of 5 fused bones, while the coccyx, or tailbone, is typically made up of 3 to 5 bones.

Twelve pairs of ribs form a protective cage for the heart, lungs, and other internal organs.

The first 7 ribs are called true ribs because they attach to the breastbone, or sternum. Ribs 8 through 12 are called false ribs, because they either attach indirectly, or, as is the case with ribs 11 and 12, float and don’t attach to the sternum at all.

Now let’s take a look at the pair of shoulder blades, or scapulae, and the collar bones, or clavicles. It is very important for the scapulae to be mobile, because they connect to the shoulder joint, which is the most movable joint in the body.

The bones of the upper limb include the humerus, which connects the shoulder with the elbow, the ulna, the radius, the wrist bones or carpals, the hand bones or metacarpals, and the finger bones or phalanges.

To complete our tour, let’s take a look at the pelvic girdle, knee, and foot.

The pelvic girdle is formed by a pair of hip bones. Each hip bone is comprised of 3 fused bones, the ilium, ischium, and pubis.

The pelvic girdle connects with the femur or thigh bone at the hip joint.

The femur is the longest bone in the body and is important for bearing the body’s weight while standing.

At the knee, the femur articulates with the tibia or shin bone. The tibia bone bears about 85% of the weight through the leg. The fibula does not bear weight, but several muscles attach to it. The patella, or kneecap, is suspended within muscle tendons and glides through a notch at the end of the femur when the knee bends.

And last, but certainly not the least, are the feet. The foot bones, which include the tarsals, metatarsals, and phalanges, are organized into a series of arches that allow the feet to support the body’s weight.

Skin conditions
This animation illustrates some common skin conditions such as moles, birthmarks, age spots, and warts.  Launch animation
Skin conditions
A few common skin conditions include moles, birthmarks, age spots, and warts.

Moles are colored spots on the skin, formed by cells containing the dark pigment, melanin. While generally harmless, some moles can change shape and color, or start bleeding and require immediate evaluation.

Some birthmarks are simply moles that are present at birth, called a pigmented birthmark. Others result from the rapid growth of blood vessels in a localized area, called red birthmarks.

When a person becomes older, they may develop age spots. Age spots are patches of increased pigmentation on the skin’s surface, like freckles.

Warts are benign, or non-cancerous, growths of skin caused by a virus.
Skull - interactive tool
This interactive animation takes you on a 3-D journey to explore the anatomy of the skull. Rotate the skull, see it in an exploded view, or pick from a list of terms to identify its various structures.  Launch animation
Skull - interactive tool

After the animation loads, click and drag the model to rotate it in any direction. Select a term from the structure list to travel to its location.

Click the "pin" button to hide or show the identification pin.

Click the "light bulb" button to view in highlight or full color mode.

Smelling
This animation depicts the inhalation of air and scent molecules from a rose into an enlarged sagittal view of the nasal cavity. The smell receptors are magnified further to show their action of relaying a neural message of “scent” to the brain.  Launch animation
Smelling
As a person inhales, air and scent molecules move past the smell receptors in the nose. In turn, the smell receptors relay a signal to the brain. Smells can trigger memories and emotional responses.
Smoking
Normal, healthy lungs are compared to the lungs of a long-term smoker.  Launch animation
Smoking

The lungs are the primary respiratory organs. They act as filters for the air the body breathes in and normally are a healthy pink color.

Inhaling smoke from cigarettes can damage the lung tissue as seen in a smoker’s lung. Over time, carbon molecules from inhaled smoke deposit in the lung tissue, giving it a blackened appearance.

Smoking is the main risk factor for emphysema (also called COPD) and greatly increase the likelihood of lung cancer.

Smoking has also been linked to diseases that affect the cardiovascular system, such as atherosclerosis, which can lead to a heart attack or stroke.

The best advice is if you't smoke, don't start. If you do smoke, it's never too late to quit.

Snoring
From a side view of the head and neck, this animation shows the structures involved in snoring. The common causes for snoring are also discussed  Launch animation
Snoring

Snoring affects many of people during their sleep. Often, people do not even realize they are snoring. Let’s turn on the lights and see where the snoring is coming from.

Snoring occurs when the airway become partially blocked, forcing the lungs to inhale harder to compensate for the lack of air entering the body.

The snoring sound results from the vibration of these two structures, the soft palate and the uvula.

Several factors contribute to snoring, including excessive alcohol intake, nasal congestion, obesity, and enlarged tonsils and adenoids

Snoring by itself is not necessarily dangerous, but some snorers have such severe airflow blockage that it prevents them from getting quality sleep. This condition, called sleep apnea, is common but dangerous if left untreated.

Sperm production
This animation highlights the structures of the male reproductive system and the pathway of ejaculate. A testicle is sectioned and enlarged to depict its internal anatomy, including a microscopic view of individual sperm.  Launch animation
Sperm production

Sperm are produced, stored, and delivered by the male reproductive system. The male reproductive system includes the testes, urethra, vas deferens, prostate gland, seminal vesicle, and penis.

The testes contain coiled structures called seminiferous tubules, which are the sites of sperm production. They produce over 12 billion sperm per month. The epididymis lies on top of the seminiferous tubules. Immature sperm migrate from the seminiferous tubules to the epididymis to mature and be stored.

Before intercourse, the penis fills with blood and becomes erect. With sufficient stimulation, the ejaculatory process begins.

The mature sperm travel from the epididymis through the vas deferens. The vas deferens is a narrow, muscular tube about 18 inches long. Its smooth muscle contractions propel the sperm forward. They arrive first at the ampulla, the widest part of the vas deferens, and then pass into the ejaculatory ducts. In the ejaculatory ducts, a liquid secretion from the seminal vesicles mixes with the sperm. Seminal fluid contains fructose sugar, which the sperm use as fuel as well as alkalines, which help to counteract the naturally acidic environment of the vagina and uterus providing the sperm a better chance for survival.

The liquid mixture is propelled forward through the ejaculatory ducts toward the urethra, passing first through the prostate gland, where milky prostatic fluid is added, forming the substance we call semen. The prostatic fluid helps the sperm swim faster, which is important for getting to the egg cell.

Finally, about a teaspoon of semen is ejected out (ejaculated) through the far end of the urethra at the end of the penis. From the time the sperm leave the man’s body, they have between 12 and 48 hours to find and fertilize the egg cell, assuming an egg is available. Of the 300 million sperm ejaculated, only about 200 or so will survive to reach the egg cell and only one will succeed in fertilizing it.

Sperm release pathway
This animation highlights from a mid-sagittal view the structures of the male reproductive system and the pathway of ejaculate. A testicle is sectioned and enlarged to depict its internal anatomy, including a microscopic view of individual sperm.  Launch animation
Sperm release pathway

The key male reproductive organs include the testes, epididymis, urethra, vas deferens, prostate gland, seminal vesicle, and penis.

The testes are composed of coiled structures called seminiferous tubules, which are the sites of sperm production. The structure on top of the seminiferous tubules in the testes is the epididymis. The sperm migrate from of the seminiferous tubules to the epididymis. Within the epididymis, the sperm mature while they are stored in this structure.

The ejaculation process begins as the penis fills with blood and becomes erect. With sufficient stimulation, mature sperm travel from the epididymis through the vas deferens, a muscular tube, which propels sperm forward through smooth muscle contractions. The sperm arrive first at the ampulla, where secretions from the seminal vesicle are added.

From the ampulla, seminal fluid is propelled forward through the ejaculatory ducts toward the urethra, passing first by the prostate gland, where a milky fluid is added to form semen. Finally, the semen is ejaculated through the far end of the urethra.

Stomach ulcer
This animation shows a stomach ulcer forming and then reducing in size as it heals.  Launch animation
Stomach ulcer
A stomach ulcer is caused by an imbalance between acid and pepsin secretion and the defenses of the stomach mucosal lining. Ulcers can be treated through dietary changes and medication.
Stroke
This animation shows a stroke resulting by an embolism traveling from an internal carotid artery and lodging within a cerebral artery in the brain  Launch animation
Stroke
A stroke may occur if an embolism travels from another part of the body and lodges within an artery in the brain. When an internal arterial wall becomes damaged, various types of emboli can form, such as one derived from platlets, thrombotic, cholesterol, or mixed. In this example, an embolism is formed in the internal carotid artery, breaks loose, travels towards the brain and lodges in a cerebral artery. The blocked artery deprives the brain of oxygen, damaging the surrounding brain tissue. The result is a stroke.
Stroke - secondary to cardiogenic embolism
This animations shows a piece of clot breaking away from the heart, travelling to the brain, resulting in a stroke.  Launch animation
Stroke - secondary to cardiogenic embolism
A blood clot, or embolus, can form and break-off from the heart. The clot travels through the bloodstream where it can lodge in an artery of the brain, blocking the flow of oxygen-rich blood. The lack of oxygen results in damage, destruction, or even tissue death of the brain beyond the affected area. The result is a stroke.
Sun’s effect on skin
This animation enlarges a section of skin to illustrate melanocytes producing melanin in response to sun exposure. Also depicted on this enlarged section is sunburn and skin cancer.  Launch animation
Sun’s effect on skin

The skin uses sunlight to help manufacture vitamin D, which is important for normal bone formation. But sometimes its ultraviolet light can be very detrimental.

Within the skin’s epidermal (outer) layer are cells that contain the pigment melanin. Melanin protects skin from the sun’s ultraviolet rays, which can burn the skin, and over time, could reduce its elasticity and cause a person to age prematurely. Suntanning occurs because exposure to sunlight causes the skin to produce more melanin and to darken. The tan fades as these cells move toward the surface and are sloughed off.

Too much exposure to ultraviolet or UV rays can cause sunburn. UV rays penetrate the outer skin layers and pass into the deeper layers, where they can damage or kill skin cells. People who do not have much melanin and sun burn easily should protect themselves by covering up sensitive areas, wearing sun block, limiting their total exposure time, and limiting their sun exposure between the hours of 10 a.m. and 2 p.m.

Frequent and prolonged exposure to ultraviolet rays over many years is the chief cause of skin cancer. Examine skin regularly for development of suspicious growths or changes in an existing skin lesion. Early detection and treatment are key in increasing the cure rate for skin cancer.

Swallowing
From a side view of the head, this animation shows the step-by-step process and mechanism of chewing and swallowing a piece of celery.  Launch animation
Swallowing

The structures involved with the process of swallowing include the tongue, teeth, epiglottis, and esophagus.

The teeth are used to grind and chop up food into tiny pieces, while the glands in the mouth moisten the food with saliva. In the first stage of swallowing, the tongue pushes the food into the throat. In the second stage of swallowing, an important small flap of tissue called the epiglottis, folds over the voice box (larynx) at the entrance to the windpipe (trachea), preventing food from going down the wrong way. In the final stage, the esophagus contracts and moves food toward the stomach.

Sweating
This animation shows an enlargement of a section of skin to highlight an individual sweat gland. The gland then expels sweat onto the surface of skin.  Launch animation
Sweating
There are more than two and a half million eccrine sweat glands all over the body. They lie deep in the skin and are connected to the surface by coiled tubes called ducts. Sweat (perspiration) is a liquid mixture made up of 99% water and 1% salt and fat. Up to a quart of liquid a day can evaporate through the sweat glands.

As the body becomes overheated, a person sweats, which evaporates and cools the body. When a person becomes frightened or nervous, like being pinned under heavy weights, the body begins to sweat on the palms and forehead, as well as the soles of the feet and in the armpits. These are the sites where sweat glands are most abundant.
Tachycardia
This animation shows a heart with tachycardia.  Launch animation
Tachycardia
Tachycardia is a condition in which the heart beats at an abnormally fast rate of more than 100 beats per minute. This type of arrhythmia is caused by an abnormality in the heart’s electrical system. Tachycardia can be treated surgically or with medication.
Tasting
This animation begins with a top view of the tongue then magnifies and shows two individual taste buds detecting taste molecules. The various taste centers (bitter, sour, sweet, and salty) are highlighted on the tongue.  Launch animation
Tasting

The tongue has about 10,000 taste buds. The taste buds are linked to the brain by nerve fibers. Food particles are detected by the taste buds, which send nerve signals to the brain.

Certain areas of the tongue are more sensitive to certain tastes, like bitter, sour, sweet, or salty. Often, taste sensations are a mixture of these qualities.

The role of amniotic fluid
This animation discusses and depicts the role and function of the amniotic fluid surrounding a fetus.  Launch animation
The role of amniotic fluid

Inside a pregnant woman’s uterus is an amniotic sac, which contains amniotic fluid and the growing fetus.

The amniotic fluid is important for several reasons -- it helps keep the baby warm, and because his body parts are growing so fast, the fluid provides lubrication that keeps them from growing together. In some cases, fingers and toes can become webbed as a result of not enough amniotic fluid circulating in the uterus. Amniotic fluid also helps the baby's lungs develop.

The amniotic fluid also lets the baby move easily so he can exercise his muscles and strengthen his bones before he’s born.

In addition, it acts like a liquid shock absorber for the baby by distributing any force that may push on the mother’s uterus. Even sex won’t hurt the baby.

Amniotic fluid is 98% water and 2% salts and cells from the baby. Until the fetal kidneys started working during month four, amniotic fluid is made by the mother’s body. But after month 4, the little guy started to make his contribution to the amniotic fluid by urinating into it.

You heard right. It may not sound appealing to us, but the urine in the amniotic sac is completely harmless to the baby.

The baby swallows amniotic fluid, which then passes through his digestive system, into his kidneys, and back out again to the amniotic sac as urine. In this way, he can practice using his digestive and urinary systems before he’s even born. In fact, doctors can tell by the amount of amniotic fluid whether the baby has difficulty with his swallowing reflex.

By the time he’s born, he will consume up to 15 ounces of amniotic fluid a day.

Tobacco use - effects on arteries
This animation shows the difference between a smoker's and non-smoker's artery  Launch animation
Tobacco use - effects on arteries
Shown here is a comparison of an artery affected with plaque in a non-smoker and smoker. The artery of the smoker is at greater risk for developing complications since smoking constrict arteries, predisposing them to clotting by altering platelet function and coagulability of blood. The result is blockage of the artery.
Twin-to-twin transfusion syndrome
This animation depicts Twin to Twin Transfusion Syndrome (TTTS) and the use of laser surgery to correct the condition.  Launch animation
Twin-to-twin transfusion syndrome

Twin to Twin Transfusion Syndrome, or TTTS, is a disease of the placenta. This condition affects twins or other multiples that share a single placenta containing blood vessels going from one baby to the other.

Blood from the smaller "donor" twin is transferred to the larger "recipient" twin through interconnecting vessels causing an unequal exchange of blood.

The recipient twin is at risk for heart failure receiving too much blood from both the placenta and donor twin, forcing its heart to work harder, while the donor twin is at risk for loss of blood.

Laser surgery may be performed to correct the problem. A laser is endoscopically inserted into the womb to burn and seal the interconnecting blood vessels, restoring the normal flow of blood. Following treatment, the babies are regularly monitored.

Stomach ulcer
From an front view of the stomach, this animation shows the development of an ulcer in the stomach lining.  Launch animation
Stomach ulcer
The stomach is the organ of the digestive system in which food travels from the esophagus and is further broken down before its nutrients are absorbed in the small intestine. It produces acid and various enzymes that break down food into simple substances. The inside wall of the stomach is protected from the acid and enzymes by a mucous lining.

Ulcers are caused when there is an imbalance between the digestive juices produced by the stomach and the various factors that protect the lining of the stomach. Symptoms of ulcers may include bleeding. On rare occasions, an ulcer may completely erode the stomach wall.

A major cause of stomach ulcers is the bacteria called Helicobacter pylori. Treatment regimens for ulcers caused this bacterium usually include medications to suppress the stomach acid as well as antibiotics to eradicate the infection.
Ultrasound
This animation demonstrates how an ultrasound identifies the solid and hollow areas of structures within a fetus.  Launch animation
Ultrasound

Ultrasound is a useful procedure for monitoring the baby’s development in the uterus. Ultrasound uses inaudible sound waves to produce a two-dimensional image of the baby while inside the mother’s uterus. The sound waves bounce off solid structures in the body and are transformed into an image on a monitor screen.

Solid structures, such as bones and muscles, reflect sound waves and appear as light gray or white. Soft or hollow areas, like the chambers of the heart, don’t reflect sound waves and appear dark or black.

An ultrasound can supply vital information about a mother’s pregnancy and her baby's health. Even though there are no known risks for ultrasound at present, it is highly recommended that pregnant women consult their physician before undergoing this procedure.

Ultrasound - interactive tool
This interactive animation enables you to visualize how a fetus may appear at 17, 19, and 30 weeks by enabling you to toggling a flat ultrasound image with an illustration of the baby's actual position.  Launch animation
Ultrasound - interactive tool
Select a week by clicking one of the three buttons. Next, click and drag the slider bar to see an illustration of the baby's position gradually appear. With the cursor, roll-over the image to identify the various structures of the fetus.
Urination
In a general overview, the formation and passage of urine through the various components of the urinary system is shown. Enlarged areas include the kidney, sectioned kidney, nephrons, renal corpuscle, and passage of particles and red blood cells within.  Launch animation
Urination

The urinary system has four main components: the kidneys, ureters, urinary bladder, and urethra. Urine, a liquid waste product, is formed in the kidneys. From there it moves through the ureters and into the bladder, where it is stored. When the bladder gets full, urine is emptied from the body through the urethra in a process called urination.

The creation of urine is a complex process. The kidneys filter waste from the blood that passes through them, and reabsorb substances that the body requires, even though those requirements may change from moment to moment.

Each of the kidneys is composed of approximately one million subunits called nephrons. Each nephron consists of a microscopic ball of blood vessels called a glomerulus, which is connected to a twisting length of tube called the renal tubule. Because the blood vessels in the glomeruli are porous, they act as filters, removing most of the water, salt, and waste from the blood that passes through them.

As filters, the glomeruli have physical properties that prevent large cells, like red blood cells, from passing into the renal tubules. On the other hand, smaller particles, like sugar and salt, can pass easily through the glomerulus. Within the renal tubules, waste products are passed into the urine. Simultaneously, substances the body needs, such as water and salt, are reabsorbed back into the bloodstream.

The path of urine formation, reabsorption, and excretion begins at the glomerulus, continues through the renal tubules, and proceeds through a ureter into the bladder. The unique, expandable cells in the wall of the bladder stretch and become thinner as it fills. Finally, urine is excreted through the urethra.

Vaccines
In an enlarged view of a cut section of a small artery, this animation shows a vaccine injection and follows the path of its antigens, initiating the body's development of antibodies.  Launch animation
Vaccines
Vaccinations are injections of antigens into the body. Once the antigens enter the blood, they circulate along with other cells, such B and T cells. B and T cells are white blood cells that help the body defend itself against foreign invaders.

As the antigens invade the body’s tissues, they attract the attention of macrophages. Macrophages are non-specific scavengers, which in this case, engulf the antigens. The macrophages then signal the T cells that antigens are invading. The killer-type of T cells respond by attacking the invading antigen. Finally, the suppressor T cells stop the attack.

After a vaccination, the body will have a memory of an encounter with a potentially dangerous invader for a period of time, and hopefully have a better ability to fight it off if ever exposed to it again in greater numbers.
Vaginal delivery
This animation shows the process of a normal vaginal delivery.  Launch animation
Vaginal delivery
When the cervix dilates to 10 centimeters, the pushing and delivery phase of childbirth begins. During this phase, the baby starts the journey down the birth canal. As the baby’s head rotates , it may become distorted while slowing coming down the narrow opening. The baby’s skull bones have gaps called fontanelles that allow the head to elongate and fit within the birth canal.

As the baby’s head is delivered, it will naturally turn to one side. The baby’s head and shoulders are supported and the rest of the baby’s body generally comes out fairly quickly.
Ankle ligament injuryBone fracture repairBunionHerniated nucleus pulposus (slipped disk)OsteoarthritisOsteoporosisRed blood cell productionShoulder joint dislocationSkeletal formationSkull - interactive tool
Alzheimers diseaseAthetosis resulting from basal ganglia injuryBlinkingBrain - interactive toolBrain componentsCataractConcussionCorneal injuryDiabetes mellitus - retinal conditionsEar - interactive toolEye - interactive toolFeeling painGlaucomaHearingHearing and the CochleaMacular degenerationNerve conductionNervous system formationParkinson's diseaseReflex responseRetinaRetinal detachmentSeeingSmellingTasting
DigestionHeartburnPeristalsisStomach ulcerSwallowingUlcers
ArrhythmiasAtherosclerosisBalloon angioplasty - short segmentBlood clottingBlood flowBlood pressureCardiac Conduction SystemCardiomyopathyCardiovascular SystemCerebral aneurysmCoronary artery bypass graft (CABG)Coronary Artery DiseaseDirectional coronary atherectomy (DCA)Electrocardiogram (ECG) - interactive toolEpinephrine and exerciseGas exchangeHeart - interactive toolHeart Bypass SurgeryHeart formationHeartbeatHypertension - overviewNutrient ExchangePercutaneous transluminal coronary angioplasty (PTCA)Red blood cell productionStrokeStroke - secondary to cardiogenic embolismTachycardiaTobacco use - effects on arteries
Endocrine GlandsHomeostasisPituitary Gland
AllergiesImmune ResponsePhagocytosisVaccines
BreathingCancer of the throat or larynxCoughingGas exchangeLungs - interactive toolSmokingSnoring
Lymph nodesLymphatics and the Breast
ExerciseMuscle typesSkeletal muscle
Breast liftCell divisionCervical dilation - interactive toolCesarean sectionConception - generalConception - interactive toolConception - pregnancyConception of Identical TwinsEarly laborEgg cell productionEgg productionEnlarged prostate glandFemale reproductive system - interactive toolFetal development - interactive toolFetal ear developmentFormation of twinsKids-BirthKids-How big is the baby?Kids-Is it a girl or boy?Kids-Umbilical cordKids-Where Babies Come From?Male reproductive system - interactive toolMenstrual cycle - interactive toolOvulationPlacenta deliveryPlacenta FormationPre-eclampsiaPregnancyRupturing membranesSexual differentiationSperm productionSperm release pathwayThe role of amniotic fluidTwin-to-twin transfusion syndromeUltrasoundUltrasound - interactive toolVaginal delivery
Breast liftComponents of SkinCosmetic surgery of the faceHuman face formationLiposuctionSkin ConditionsSun’s Effect on SkinSweating
Bladder function - neurological controlEnlarged prostateEnlarged prostate glandGoutKidney stonesUrination
AllergiesBreathingCoughingLungs - interactive tool
Cancer of the throat or larynxLymphatics and the BreastSmokingSun’s Effect on Skin
ArrhythmiasBalloon angioplasty - short segmentBlood clottingBlood flowBlood pressureCardiac Conduction SystemCardiomyopathyCardiovascular SystemCerebral aneurysmCoronary artery bypass graft (CABG)Coronary Artery DiseaseDirectional coronary atherectomy (DCA)Electrocardiogram (ECG) - interactive toolEpinephrine and exerciseExerciseGas exchangeHeart - interactive toolHeart Bypass SurgeryHeart formationHeartbeatHypertension - overviewMuscle typesNutrient ExchangePercutaneous transluminal coronary angioplasty (PTCA)Red blood cell productionSmokingStrokeStroke - secondary to cardiogenic embolismTachycardiaTobacco use - effects on arteries
Components of SkinSkin ConditionsSun’s Effect on SkinSweating
Ovulation
BreathingCoughingEar - interactive toolFetal ear developmentHearingHearing and the CochleaLungs - interactive toolSmellingSmokingSnoringSwallowingTasting
Fetal development - interactive toolHuman face formationNervous system formationSkeletal formationUltrasound - interactive tool
Endocrine GlandsHomeostasisPituitary Gland
BlinkingCataractCorneal injuryDiabetes mellitus - retinal conditionsGlaucomaMacular degenerationRetinaRetinal detachmentSeeing
Electrocardiogram (ECG) - interactive toolExerciseMuscle typesSkeletal muscle
DigestionHeartburnPeristalsisStomach ulcerUlcers
Enlarged prostate gland
Immune ResponseLymph nodesLymphatics and the BreastPhagocytosisVaccines
Alzheimers diseaseAthetosis resulting from basal ganglia injuryBladder function - neurological controlBrain - interactive toolBrain componentsConcussionElectrocardiogram (ECG) - interactive toolFeeling painNerve conductionNervous system formationParkinson's diseaseReflex responseSkull - interactive tool
Cell divisionCervical dilation - interactive toolCesarean sectionConception - generalConception - interactive toolConception - pregnancyConception of Identical TwinsEarly laborEgg cell productionEgg productionFemale reproductive system - interactive toolFetal development - interactive toolFormation of twinsKids-BirthKids-How big is the baby?Kids-Is it a girl or boy?Kids-Umbilical cordKids-Where Babies Come From?Menstrual cycle - interactive toolOvulationPlacenta deliveryPlacenta FormationPre-eclampsiaPregnancyRupturing membranesThe role of amniotic fluidTwin-to-twin transfusion syndromeUltrasoundUltrasound - interactive toolVaginal delivery
Ankle ligament injuryBone fracture repairBunionHerniated nucleus pulposus (slipped disk)OsteoarthritisOsteoporosisRed blood cell productionShoulder joint dislocationSkeletal muscleSkeletal system components
Cell divisionCesarean sectionConception - interactive toolConception - pregnancyEarly laborEgg cell productionFetal development - interactive toolFetal ear developmentFormation of twinsHeart formationKids-BirthKids-How big is the baby?Kids-Is it a girl or boy?Kids-Umbilical cordKids-Where Babies Come From?PregnancySexual differentiationSkeletal formationThe role of amniotic fluidUltrasound - interactive toolVaginal delivery
Breast liftCesarean sectionCoronary artery bypass graft (CABG)Cosmetic surgery of the faceDirectional coronary atherectomy (DCA)LiposuctionPercutaneous transluminal coronary angioplasty (PTCA)
Bladder function - neurological controlConception - generalEnlarged prostateEnlarged prostate glandGoutKidney stonesMale reproductive system - interactive toolSperm productionUrination
BlinkingCataractCorneal injuryDiabetes mellitus - retinal conditionsGlaucomaMacular degenerationRetinaRetinal detachmentSeeing
   
 
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