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Human Anatomy

As the basis for careers in either medicine or nursing, human anatomy is one of the required building-blocks of your education. Make use of the following animations, videos, and multiple-choice practice tests to prepare for anatomy exams.

The Basics
Terminology
Anatomical Position
Body Planes
Terms of Movement
Terms of Location
Embryology Terms


Histology
Bone
Skeletal Muscle
Blood Vessels
Nerves
Lymphatics
Skin


Skeletal System
Skull
Bony Orbit
Sphenoid Bone
Ethmoid Bone
Temporal Bone
Mandible
Nasal Skeleton
Cranial Foramina
Cervical Spine
Hyoid Bone
Ribs
Sternum
Thoracic Spine
Vertebral Column
Scapula
Clavicle
Humerus
Ulna
Radius
The Hand
Lumbar Spine
Hip Bone
Pelvic Girdle
Sacrum
Coccyx
Femur
Patella
Tibia
Fibula
The Foot


Joints
Classification
Synovial Joint
Joint Stability
Acromioclavicular Joint
Sternoclavicular Joint
Shoulder Joint
Elbow Joint
Radioulnar Joints
Wrist Joint
Hip Joint
Knee Joint
Tibiofibular Joints
Ankle Joint
Subtalar Joint


Muscles
The Tongue
Facial Expression
Extraocular
Mastication
Suboccipital
Suprahyoids
Infrahyoids
Scalenes
Thoracic Cage
Diaphragm
Superficial Back Muscles
Intermediate Layer
Deep back Muscles
Pectorals
Shoulder Muscles
Upper Arm Muscles
Anterior Forearm
Posterior Forearm
Hand Muscles
Fascia Lata
Anterolateral Abdominal Wall
Posterior Abdominal Wall
Pelvic Floor
Gluteal Region
Thigh Muscles
Leg
Foot Muscles


Brainstem
Midbrain
Pons
Medulla Oblongata
Basal Ganglia
Cerebrum
Cerebellum
Spinal Cord (Grey Matter)
Ascending Tracts
Descending Tracts
Visual Pathway
Auditory Pathway


Nervous System
Spinal Cord
Cubital Fossa
Ulnar Tunnel
Ulnar Canal
Carpal Tunnel
Brachial Plexus
Axillary Nerve
Musculocutaneous Nerve
Median Nerve
Radial Nerve
Ulnar Nerve
Lumbar Plexus
Sacral Plexus
Femoral Nerve
Obturator Nerve
Sciatic Nerve
Tibial Nerve
Common Fibular Nerve
Superficial Fibular Nerve
Deep Fibular Nerve


Cardiovascular System
Neck Arteries
Neck Veins
Lymphatics
Nueral Arterial Supply
Neural Venous Drainage
Cavernous Sinus
Ventricles


Organs
Pineal Gland
Pituitary Gland
The Ear
The Eye
Nose and Sinuses
Salivary Glands
Oral Cavity
Pharynx
Larynx
Oesophagus
Thyroid Gland
Parathyroid Glands
Thymus Gland
Mammary Glands
Heart
Lungs
Tracheobronchial Tree
Pleurae
Liver
Gallbladder
Pancreas
Spleen
Adrenal Glands
Kidneys
Mesentery
Ureter
Urinary Bladder
Urethra
Endocrine System
Gastrointestinal System
Respiratory System


Intestinal Tract
Oesophagus
Stomach
Small Intestine
Appendix
Cecum
Colon
Rectum
Anal Canal


Male Reproduction
Penis
Testes and Epididymis
Scrotum
Spermatic Cord
Prostate Gland
Bulbourethral Glands
Seminal Vesicles
Male Pelvis


Female Reproduction
Female Reproductive Tract
Vulva
Vagina
Cervix
Uterus
Fallopian (Uterine) Tubes
Ovaries
Female Pelvis
Supporting Ligaments


Embryology
Weeks 1-3
Dermatomes
Myotomes
The Limbs
Head and Neck
Cardiovascular System
Respiratory System
Urinary System
Reproductive System
Central Nervous System


The Heart

The heart has four valves, namely the mitral, aortic, tricuspid, and pulmonary, that regulate the flow of blood through the heart's four chambers. Each valve consists of a flap, or leaflet, that regulates the blood flow to adjacent chambers, then snaps shut to prevent blood from flowing backwards. As in an automobile engine, valves can experience leakage, a situation in which valves do not close completely, allowing blood to flow in reverse. A second valve disorder is stenosis, in which the malfunctioning valve limits the volume of blood flow.

Both conditions can significantly reduce the heart's ability to pump blood. In many cases, heart disease progresses slowly, as the heart compensates for irregularities in blood flow, so symptoms may not seem severe. One may appear symptom-free, yet have serious heart valve disease, requiring immediate hospitalization. In general, irregular valve activity creates abnormal heart sounds, such as murmurs and clicks, that can be heard with a stethoscope. Finally, an echocardiogram may be called for in order to confirm the diagnosis. Further diagnostics can be performed, such as CT-angiography and cardiac MRI.

Anatomy of the Lungs

The lungs have miles of tiny passages, easily clogged by pollutants such as smoke, and other microscopic irritants. Asthma is a chronic lung disease that narrows the airways. In the US, more than 25 million people are known to have asthma, and new research indicates that a chemical compound found in many air fresheners, bathroom cleaners, and deodorizing products, may be harmful to the lungs.

Air first enters your body through your nose or mouth, which wets and warms the air. Conversely, cold, dry air can irritate your lungs. The air then travels through your voice box and down your windpipe, which splits into two bronchial tubes entering the lungs. A thin flap of tissue called the epiglottis covers your windpipe when you swallow, preventing food and drink from entering the air passage.

Except for the mouth and some parts of the nose, all of the airways are covered by cilia, which contain a sticky, mucus coating. The cilia trap germs and other foreign particles that enter your airways when you breathe in. Fine hairs then sweep the particles up to the nose or mouth. From there, they're swallowed, coughed, or sneezed out of the body.

Your lungs and associated blood vessels deliver oxygen to your body and remove carbon dioxide. Interestingly, the left lung is slightly smaller than the right lung, allowing additional room for your heart. Within the lungs, individual bronchi branch into thousands of thinner tubes called bronchioles. These tubes end in bunches of tiny round air sacs, the alveoli. Each air sac is covered by a mesh of tiny capillaries. The pulmonary artery delivers blood rich in carbon dioxide (lacking in oxygen) to the capillaries that surround the air sacs. Inside, carbon dioxide migrates from the blood back into the air. At the same time, oxygen is absorbed. The oxygen-rich blood then travels to the heart through the pulmonary vein, completing respiration.

The Digestive System

The digestive system is made up of the alimentary canal (also called the digestive tract) and other organs, such as the liver and pancreas. The alimentary canal is the long tube of organs including the esophagus, stomach, and intestine. An adult's digestive tract is about 30 feet (about 9 meters) long.

As the teeth tear and chop the food, spit moistens it for easy swallowing. A digestive enzyme in saliva called amylase (pronounced: AH-meh-lace) starts to break down some of the carbohydrates (starches and sugars) in the food even before it leaves the mouth.

Swallowing, done by muscle movements in the tongue and mouth, moves the food into the throat, or pharynx (pronounced: FAIR-inks). The pharynx is a passageway for food and air. A soft flap of tissue called the epiglottis closes over the windpipe when we swallow to prevent choking.

From the throat, food travels down a muscular tube in the chest called the esophagus. Waves of muscle contractions called peristalsis force food down through the esophagus to the stomach. A person normally isn't aware of the movements of the esophagus, stomach, and intestine that take place as food passes through the digestive tract.

At the end of the esophagus, a muscular ring allows food to enter the stomach and then squeezes shut to keep food or fluid from flowing back up into the esophagus. The stomach muscles churn and mix the food with digestive juices that have acids and enzymes, breaking it into much smaller, digestible pieces. An acidic environment is needed for the digestion that takes place in the stomach.

By the time food is ready to leave the stomach, it has been processed into a thick liquid called chyme. A walnut-sized muscular valve at the outlet of the stomach called the pylorus keeps chyme in the stomach until it reaches the right consistency to pass into the small intestine. Chyme is then squirted down into the small intestine, where digestion of food continues so the body can absorb the nutrients into the bloodstream.

The Small Intestine

The inner wall of the small intestine is covered with millions of microscopic, finger-like projections called villi (pronounced: VIH-lie). The villi are the vehicles through which nutrients can be absorbed into the blood. The blood then brings these nutrients to the rest of the body. The small intestine is composed of three parts:

  1. The duodenum, the C-shaped first part
  2. The jejunum, the coiled midsection
  3. The ileum, the final section that leads into the large intestine

The liver (under the ribcage in the right upper part of the abdomen), the gallbladder (hidden just below the liver), and the pancreas (beneath the stomach) are not part of the alimentary canal, but these organs are essential to digestion.

The liver makes bile, which helps the body absorb fat. Bile is stored in the gallbladder until it is needed. The pancreas makes enzymes that help digest proteins, fats, and carbs. It also makes a substance that neutralizes stomach acid. These enzymes and bile travel through special pathways (called ducts) into the small intestine, where they help to break down food. The liver also helps process nutrients in the bloodstream.

From the small intestine, undigested food (and some water) travels to the large intestine through a muscular ring or valve that prevents food from returning to the small intestine.

Lumbar Disc Disease


Lower back pain may result from a variety of causes, including degenerative diseases of lumbar discs.

Heart and Blood Vessels


3D anatomy tutorial on the heart and some of the major vessels in the thorax that lead to and from the heart using the BioDigital Human browser. This is a good basic tutorial to watch if you want to learn some simple but important anatomy of the cardiovascular system.

Eyeball Anatomy


The eye sits in a protective bony socket called the orbit. Six extraocular muscles in the orbit are attached to the eye. These muscles move the eye up and down, side to side, and rotate the eye. The extraocular muscles are attached to the white part of the eye called the sclera. This is a strong layer of tissue that covers nearly the entire surface of the eyeball.

Parts of the Brain


This video covers the basic structure of the human brain, looking at the brainstem (pons, medulla, midbrain), cerebellum, basal ganglia, thalami, ventricular system, and the cortex.

Muscles of the Thigh


The muscular anatomy of the thigh and the gluteal region. We take a look at the gluteal muscles: gluteus maximus, medius and minimus, tensor fascia, lateral rotators, and the greater and lesser sciatic foramen.

ANATOMY OF THE EYE

The eye sits in a protective bony socket called the orbit. Six extraocular muscles in the orbit are attached to the eye. These muscles move the eye up and down, side to side, and rotate the eye. The extraocular muscles are attached to the white part of the eye called the sclera. This is a strong layer of tissue that covers nearly the entire surface of the eyeball.

The surface of the eye and the inner surface of the eyelids are covered with a clear membrane called the conjunctiva. Tears lubricate the eye and are made up of three layers. These three layers together are called the tear film. The mucous layer is made by the conjunctiva. The watery part of the tears is made by the lacrimal gland. The eye’s lacrimal gland sits under the outside edge of the eyebrow (away from the nose) in the orbit. The meibomian gland makes the oil that becomes another part of the tear film. Tears drain from the eye through the tear duct.

Light is focused into the eye through the clear, dome-shaped front portion of the eye called the cornea. Behind the cornea is a fluid-filled space called the anterior chamber. The fluid is called aqueous humor. The eye is always producing aqueous humor. To maintain a constant eye pressure, aqueous humor also drains from the eye in an area called the drainage angle. Behind the anterior chamber is the eye’s iris (the colored part of the eye) and the dark hole in the middle called the pupil. Muscles in the iris dilate (widen) or constrict (narrow) the pupil to control the amount of light reaching the back of the eye.

Directly behind the pupil sits the lens. The lens focuses light toward the back of the eye. The lens changes shape to help the eye focus on objects up close. Small fibers called zonules are attached to the capsule holding the lens, suspending it from the eye wall. The lens is surrounded by the lens capsule, which is left in place when the lens is removed during cataract surgery. Some types of replacement intraocular lenses go inside the capsule, where the natural lens was. By helping to focus light as it enters the eye, the cornea and the lens both play important roles in giving us clear vision. In fact, 70% of the eye's focusing power comes from the cornea and 30% from the lens.

The vitreous cavity lies between the lens and the back of the eye. A jellylike substance called vitreous humor fills the cavity. Light that is focused into the eye by the cornea and lens passes through the vitreous onto the retina, the light-sensitive tissue lining the back of the eye. A tiny but very specialized area of the retina called the macula is responsible for giving us our detailed, central vision. The other part of the retina, the peripheral retina, provides us with our peripheral (side) vision.

The retina has special cells called photoreceptors. These cells change light into energy that is transmitted to the brain. There are two types of photoreceptors: rods and cones. Rods perceive black and white, and enable night vision. Cones perceive color, and provide central (detail) vision. The retina sends light as electrical impulses through the optic nerve to the brain. The optic nerve is made up of millions of nerve fibers that transmit these impulses to the visual cortex, the part of the brain responsible for our sight.

Disorders of the Ear

The ear depends on coordinated events that transform sound waves into electrical impulses. The auditory nerve transmits these signals to the brain. Initially, sound waves enter the outer ear and traverse the outer ear canal, leading to the eardrum. The eardrum vibrates from the incoming sound waves and sends vibrations to three tiny bones in the middle ear.

These bones couple the sound waves from the air to fluid vibrations in the cochlea of the inner ear. Hair-like sensory cells perched on top of the basilar membrane ride the ripple of fluid thus created. As the hair cells move up and down, microscopic stereocilia sitting on top of the hair cells bump against an overlying structure and bend, which causes pore-like channels at the tips of the stereocilia to open. When that happens, chemicals rush into the cell, sparking an electrical signal. The auditory nerve then carries this signal to the brain, which translates it into a sound that we can recognize and understand.

When exposed to loud noises over an extended period, hearing losses may occur. Over time, sounds become distorted, and it may be difficult to understand other people when they talk. Sometimes exposure to continuous noise causes a temporary hearing loss, but there also may be residual long-term damage. Loud noise exposure also may be responsible for tinnitus, which is perceived as a ringing in the ears or cranium.

Auditory Neuropathy
Auditory Processing Disorder
Ear Infections in Children
Enlarged Vestibular Aqueducts (EVA)
Hearing Loss/Deafness, Sudden
Hearing Loss and Older Adults
Hearing Loss, Noise Induced
Hearing Loss, Ten Ways to Recognize
Ménière's Disease
Otosclerosis
Pendred Syndrome
Presbycusis
Tinnitus
Usher Syndrome
Vestibular Schwannoma and Neurofibromatosis


Common noise levels (in decibels):

Humming of a refrigerator = 45 decibels
Normal conversation = 60 decibels
Heavy city traffic = 85 decibels
Motorcyle engine = 95 decibels
An MP3 player at maximum volume = 105 decibels
Police siren = 120 decibels
Firecrackers = 150 decibels

Advances in ear replacement surgery:

Biological scientists used 3-D printing of cartilage cells and nano-sized materials to create functional ears that receive radio signals. The experiments demonstrated that it may be possible to create bionic tissues and organs. Scientists used 3-D printing to merge living tissue with an antenna that is able to receive radio signals. In tissue engineering, cells and other biological materials are used to augment or replace deteriorating muscle matter, bone and cartilage. Currently, it’s difficult to create 3-D structures for use in the body, especially organs with complex geometry such as the ear.

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