Human Anatomy Explorer

206 bones that hold you up, protect organs, make blood cells and store calcium.

• Skull (cranium): Bony case around the brain plus the bones of the face. Protects the brain and holds the eyes, nose and mouth.
• Mandible: The U-shaped lower jaw, the only skull bone that moves. Chewing and speaking. The tongue attaches to it.
• Cervical spine: Seven small vertebrae in the neck. C1 (atlas) holds the skull; C2 (axis) lets the head rotate. Supports the head and protects the spinal cord in the neck.
• Clavicle: S-shaped bone from the top of the sternum to the shoulder. Props the shoulder out to the side and connects the arm to the trunk.
• Scapula: Flat triangular bone on the upper back (drawn faded because it sits behind the ribs). Anchors the shoulder muscles and forms the shoulder socket.
• Sternum: Flat bone down the middle of the chest. Top = manubrium, middle = body, tip = xiphoid process. Anchors the ribs and protects the heart.
• Ribs: 12 pairs. Ribs 1 to 7 attach straight to the sternum (true ribs). Ribs 8 to 12 are false ribs: 8 to 10 join through shared cartilage and 11 and 12 float free. Protect the heart, lungs, liver and spleen and move with each breath.
• Thoracic spine: 12 vertebrae in the upper back, one for each pair of ribs. Protects the spinal cord and anchors the ribs.
• Lumbar spine: Five large vertebrae in the lower back that carry most of the body's weight. Supports the upper body and allows bending.
• Sacrum & coccyx: Five fused vertebrae (sacrum) plus the small tailbone (coccyx) at the back of the pelvis. Connects the spine to the pelvis.
• Pelvis: Ring of bone made of two hip bones (ilium, ischium and pubis fused together) and the sacrum. Carries body weight to the legs and protects the bladder, rectum and reproductive organs.
• Humerus: The single bone of the upper arm, from shoulder to elbow. Lever for the shoulder and elbow.
• Radius: Forearm bone on the thumb side (lateral in anatomical position). Rotates around the ulna so you can turn your palm up and down.
• Ulna: Forearm bone on the pinky side. Its tip at the elbow is the olecranon. Forms the hinge of the elbow.
• Hand & wrist bones: 8 carpals (wrist), 5 metacarpals (palm) and 14 phalanges (fingers). Fine movement and grip.
• Femur: The longest and strongest bone, from hip to knee. Carries body weight and anchors the strongest muscles.
• Patella: Small bone in the front of the knee, inside the quadriceps tendon. Gives the quadriceps leverage to straighten the knee.
• Tibia: The large, weight-bearing bone on the inside of the lower leg. Carries body weight from the knee to the ankle.
• Fibula: Thin bone on the outside of the lower leg. Attachment for muscles and forms the outer ankle bump (lateral malleolus).
• Foot & ankle bones: 7 tarsals including the heel (calcaneus), 5 metatarsals and 14 phalanges. Supports and balances the body.

Skeletal muscle moves you, holds posture, protects the abdomen and makes body heat.

• Sternocleidomastoid: Strap muscle on each side of the neck, from behind the ear to the sternum and clavicle. Turns and tilts the head and helps lift the chest during hard breathing.
• Trapezius: Large diamond-shaped muscle across the upper back and top of the shoulders. Shrugs and steadies the shoulders.
• Deltoid: Rounded cap of muscle over the shoulder. Lifts the arm out to the side.
• Pectoralis major: Fan-shaped chest muscle from the sternum and clavicle to the upper humerus. Pulls the arm across the body. Helps lift the chest during hard breathing.
• Biceps brachii: Muscle on the front of the upper arm. Bends the elbow and turns the palm up.
• Forearm muscles: Muscle groups on the front (flexors) and back (extensors) of the forearm, wrapped in tight fascia. Move the wrist and fingers.
• Rectus abdominis: Two vertical strap muscles down the front of the abdomen, split by tendon bands into the six-pack. Flex the trunk and protect the abdominal organs. Help push air out during forced exhalation.
• Obliques: Layered muscles on the sides of the abdomen. Twist and bend the trunk and compress the abdomen.
• Quadriceps: Four muscles on the front of the thigh. The vastus lateralis is the outer one. Straighten the knee.
• Tibialis anterior: Muscle beside the shin in the anterior compartment of the lower leg. Lifts the foot (dorsiflexion).

The heart pumps blood through arteries to the tissues and veins bring it back.

• Heart: Fist-sized muscle in the middle of the chest behind the sternum, tipped to the left. The apex points to about the 5th intercostal space, left midclavicular line. Right side pumps blood to the lungs; left side pumps it to the body. The SA node sets the rate.
• Aorta: Leaves the left ventricle, arches over the heart, then runs down in front of the spine and splits into the iliac arteries near the umbilicus. Carries oxygenated blood to the whole body.
• Vena cavae: The two largest veins. The superior drains the head and arms; the inferior runs up beside the spine and drains everything below the diaphragm. Both empty into the right atrium. Return blood to the heart.
• Carotid arteries: Run up both sides of the neck beside the trachea. Supply the brain, face and scalp.
• Jugular veins: The internal jugular runs deep beside the carotid; the external jugular is visible on the side of the neck over the sternocleidomastoid. Drain blood from the head back toward the heart.
• Subclavian vessels: Artery and vein that run under the clavicle into the arm. Carry blood to and from the arms. The thoracic duct empties into the left subclavian vein.
• Brachial artery: Runs down the inside of the upper arm in the groove beside the biceps. Main blood supply to the arm.
• Radial & ulnar arteries: The radial artery runs on the thumb side of the forearm to the wrist; the ulnar on the pinky side. Supply the forearm and hand.
• Antecubital veins: Veins in the crook of the elbow and along the forearm. Return blood from the arm.
• Femoral artery & vein: Enter the thigh at the groin, midway between the hip bone and pubic bone. The vein is medial to the artery. Main supply and drainage for the leg.
• Popliteal artery: Runs behind the knee (drawn dashed because it is on the back side). Supplies the lower leg.
• Lower leg pulses: Posterior tibial pulse: behind the inner ankle bone. Dorsalis pedis: top of the foot. Supply the foot.

Moves air in and out so oxygen gets into the blood and carbon dioxide gets out.

• Nasal cavity & sinuses: Air passage behind the nose, lined with turbinates. Air-filled sinuses sit in the bones around it. Warms, humidifies and filters air.
• Pharynx & tongue: The throat, from behind the nose (nasopharynx) past the mouth (oropharynx) down to the larynx and esophagus (hypopharynx). Shared path for air and food.
• Epiglottis: Flap at the base of the tongue that folds over the larynx when you swallow. Keeps food and liquid out of the trachea.
• Larynx & vocal cords: Box of cartilage at the top of the trachea. The thyroid cartilage (Adam's apple) is its front. The vocal cords inside form the glottic opening. Makes voice and protects the airway.
• Cricothyroid membrane: Soft spot between the thyroid cartilage (above) and the ring-shaped cricoid cartilage (below). Shown in yellow. Connects the cartilages.
• Trachea: Tube of C-shaped cartilage rings from the larynx to the carina in the chest. Carries air to the lungs.
• Bronchi & carina: The trachea splits at the carina into the right and left mainstem bronchi, which keep branching inside the lungs. Carry air into each lung.
• Right lung: Three lobes (upper, middle, lower). Slightly larger than the left. Gas exchange in millions of alveoli.
• Left lung: Two lobes (upper and lower) with a notch for the heart. Gas exchange.
• Pleura: Two thin membranes around each lung. The thin space between them normally holds a little fluid and negative pressure. Lets the lungs glide and keeps them stuck to the chest wall.
• Diaphragm: Dome-shaped muscle separating the chest from the abdomen. The right side sits a little higher because of the liver. Contracts and flattens to pull air in. Does most of the work of quiet breathing.

The brain and spinal cord (central nervous system) plus the nerves (peripheral nervous system) run every other system.

• Cerebrum: The two hemispheres that make up most of the brain, divided into frontal, parietal, temporal and occipital lobes. Thinking, personality, speech, vision, movement and sensation. Each side controls the opposite side of the body.
• Cerebellum: Sits at the back of the skull under the cerebrum (faded here because it is behind). Balance, coordination and smooth movement.
• Brainstem: Connects the brain to the spinal cord. Controls breathing, heart rate, blood pressure and consciousness.
• Spinal cord: Runs down the spinal canal from the brainstem and ends around L1 to L2. Below that, nerve roots continue as the cauda equina. Carries messages between the brain and body and handles reflexes.
• Brachial plexus & arm nerves: Network of nerves from C5 to T1 that passes under the clavicle and splits into the median, ulnar and radial nerves. Movement and feeling in the arm and hand.
• Phrenic nerve: Leaves the neck at C3 to C5 and runs down through the chest to the diaphragm. Makes the diaphragm contract.
• Vagus nerve: Long cranial nerve from the brainstem down the neck beside the carotid to the heart, lungs and gut. Main parasympathetic nerve: slows the heart and drives digestion.
• Sciatic & femoral nerves: The femoral nerve runs down the front of the thigh. The sciatic nerve, the body's largest, runs down the back of the leg (dashed). Movement and feeling in the leg.
• Eye: The globe sits in the bony orbit. Light passes through the cornea and pupil to the retina; the optic nerve carries it to the brain. Vision. Pupils show brainstem and drug effects.
• Ear: Outer ear and canal, middle ear (eardrum and tiny bones) and inner ear (hearing and balance). Hearing and balance.

Breaks food down, absorbs nutrients and water, and gets rid of waste. The liver also filters blood and makes clotting factors.

• Esophagus: Muscular tube behind the trachea, from the pharynx through the diaphragm to the stomach. Moves food to the stomach.
• Stomach: J-shaped organ in the left upper quadrant under the diaphragm. Stores food and starts digestion with acid.
• Liver: Large solid organ in the right upper quadrant, tucked under the right ribs. Filters blood, makes clotting factors and bile, stores sugar and breaks down drugs.
• Gallbladder: Small sac under the liver in the right upper quadrant. Stores bile to digest fat.
• Pancreas: Lies across the back of the upper abdomen behind the stomach (retroperitoneal). Makes digestive enzymes and the hormones insulin and glucagon.
• Small intestine: About 6 meters of coiled tube filling the middle of the abdomen. Absorbs most nutrients.
• Large intestine: Frames the small intestine: ascending (right), transverse, descending (left) and sigmoid colon. Absorbs water and stores stool.
• Appendix: Small finger-shaped pouch off the cecum in the right lower quadrant. Has a minor immune role.
• Rectum & anus: Last part of the large intestine, inside the pelvis. Stores and passes stool.

Kidneys filter blood, make urine and control fluid, electrolytes, acid-base and blood pressure.

• Kidneys: Bean-shaped organs against the back muscles at T12 to L3. The right sits a little lower because of the liver. Filter blood, make urine and control fluid, electrolytes, acid-base balance and blood pressure.
• Ureters: Thin tubes from each kidney down to the bladder. Carry urine to the bladder.
• Bladder: Muscular sac behind the pubic bone. Stores urine.
• Urethra: Tube from the bladder to the outside. Much shorter in women. Carries urine out.

Glands that release hormones into the blood to control metabolism, growth, stress response and blood sugar.

• Hypothalamus: Small area at the base of the brain, above the pituitary. Links the nervous and endocrine systems. Controls temperature, thirst, hunger and the pituitary.
• Pituitary gland: Pea-sized gland under the brain, behind the eyes. Releases hormones that control the thyroid, adrenals, growth, water balance (ADH) and labor (oxytocin).
• Thyroid gland: Butterfly-shaped gland on the front of the trachea, just below the larynx. Tiny parathyroid glands sit behind it. Thyroid hormone sets metabolic rate. Parathyroids control calcium.
• Thymus: Gland behind the upper sternum, large in children and shrinking in adults. Trains T cells for the immune system.
• Adrenal glands: Small caps on top of each kidney. Make epinephrine and norepinephrine (fight or flight) and cortisol (stress hormone, keeps BP and sugar up).
• Pancreatic islets: Clusters of hormone cells scattered through the pancreas. Beta cells make insulin (lowers sugar); alpha cells make glucagon (raises it).
• Ovaries & testes (hormones): Ovaries in the pelvis; testes in the scrotum. Make sex hormones (estrogen, progesterone, testosterone) and eggs or sperm.

Returns leaked fluid to the blood, filters it through lymph nodes and helps fight infection.

• Spleen: Fist-sized organ in the left upper quadrant, tucked under ribs 9 to 11. Filters old blood cells and germs, stores blood and platelets.
• Tonsils: Lymph tissue on both sides of the back of the throat. First line of defense against swallowed and inhaled germs.
• Cervical lymph nodes: Chains of nodes along both sides of the neck. Filter lymph from the head and throat.
• Axillary lymph nodes: Nodes in the armpit. Filter lymph from the arm and chest wall.
• Inguinal lymph nodes: Nodes in the groin crease. Filter lymph from the legs and lower abdomen.
• Lymph vessels: Thin vessels that run beside veins throughout the body. Collect fluid leaked from capillaries and return it to the blood through the nodes.
• Thoracic duct: Main lymph vessel, running up in front of the spine to the left subclavian vein. Drains lymph from most of the body into the blood.

Female reproductive organs shown (uterus, tubes, ovaries, vagina). Male organs are testes, epididymis, vas deferens, prostate and penis.

• Uterus: Pear-shaped muscular organ behind the bladder. The cervix is its lower end. Holds and grows the fetus, then contracts to deliver it.
• Fallopian tubes: Thin tubes from the top corners of the uterus toward each ovary. Carry the egg to the uterus. Fertilization happens here.
• Ovaries: Almond-sized organs on each side of the uterus. Release eggs and make estrogen and progesterone.
• Vagina & cervix: Muscular canal from the cervix to the outside. Birth canal.

The largest organ. Keeps fluid in and germs out, controls temperature and senses touch, pain and heat.

• Epidermis: Thin outer layer with no blood vessels. Waterproof barrier and protection from germs.
• Dermis: Thick layer with blood vessels, nerves, sweat glands and hair follicles. Strength, feeling, sweating and temperature control.
• Subcutaneous tissue: Fat and connective tissue under the dermis, above the muscle. Insulation, energy storage and padding.

Divide the abdomen with two lines through the umbilicus to describe where pain is and guess which organ is involved.

• Right upper quadrant: Patient's right side, above the umbilicus. Contains the liver, gallbladder, part of the colon, duodenum and the right kidney (behind).
• Left upper quadrant: Patient's left side, above the umbilicus. Contains the stomach, spleen, pancreas tail, part of the colon and the left kidney (behind).
• Right lower quadrant: Patient's right side, below the umbilicus. Contains the appendix, cecum, right ovary and tube, right ureter.
• Left lower quadrant: Patient's left side, below the umbilicus. Contains the sigmoid colon, left ovary and tube, left ureter.
• Epigastric region: Upper middle abdomen, just below the xiphoid. Over the stomach, part of the liver and pancreas.
• Periumbilical region: Around the belly button. Over the small intestine and aorta.

Quick estimate of burned body surface area (TBSA) in adults. Count only partial- and full-thickness burns. The patient's palm, including fingers, is about 1%.

• Head & neck: 9%: Whole head and neck. Adult: 9%. Infant: 18% because a baby's head is much larger.
• Each arm: 9%: Whole arm including the hand. Adult and child: 9% each.
• Front of trunk: 18%: Chest and abdomen. The back of the trunk is another 18%. Adult and child: 18% front, 18% back.
• Each leg: 18%: Whole leg including the foot. Adult: 18% each. Infant: about 14% each.
• Genitals/perineum: 1%: Groin area. 1% in every age group.

Spaces that hold the organs. Injuries and bleeding behave differently in each one.

• Cranial cavity: Inside the skull. Holds the brain, its coverings and fluid.
• Spinal canal: Tunnel through the vertebrae. Holds the spinal cord.
• Thoracic cavity: Inside the rib cage, above the diaphragm. Two pleural cavities (lungs) and the mediastinum in the middle (heart, great vessels, trachea, esophagus). Holds the heart and lungs.
• Abdominal cavity: From the diaphragm down to the pelvis. Holds the digestive organs. The kidneys, pancreas and aorta are behind it (retroperitoneal).
• Pelvic cavity: Inside the bony pelvis. Holds the bladder, rectum and reproductive organs.

The words used to describe location in a report. Always from the patient's point of view in anatomical position: standing, facing you, palms forward.

• Superior / inferior: Superior = toward the head. Inferior = toward the feet. The nose is superior to the mouth.
• Medial / lateral: Medial = closer to the midline. Lateral = farther from it. The thumb is lateral in anatomical position (palms forward).
• Proximal / distal: For limbs: proximal = closer to the trunk, distal = farther away. The elbow is proximal to the wrist.
• Midline & sagittal plane: The midline runs down the center. A sagittal plane divides the body into left and right. The midclavicular and axillary lines run parallel to it.
• Transverse plane: Horizontal plane dividing upper and lower body. CT scans are transverse slices.
• Patient's right & left: Right and left are always the patient's, not yours. When facing a patient, their right is on your left. This diagram faces you, so the patient's right is on your left.

Where to feel pulses, start IVs and IOs, and decompress a chest.

• Carotid pulse: Beside the trachea, in the groove next to the neck muscle. Central pulse.
• Brachial pulse: Inside the upper arm between the biceps and triceps. Pulse check in infants.
• Radial pulse: Thumb side of the inner wrist. Peripheral pulse.
• Femoral pulse: In the groin crease, midway between the hip bone and pubic bone. Central pulse.
• Popliteal pulse: Behind the knee (shown from the front). Lower leg perfusion.
• Posterior tibial pulse: Behind the inner ankle bone. Foot perfusion.
• Dorsalis pedis pulse: Top of the foot, between the big and second toe tendons. Foot perfusion.
• IV: antecubital: Large veins in the inner elbow. Best site for large-bore IVs.
• IV: dorsal hand & forearm: Veins on the back of the hand and forearm. Smaller catheters.
• IV: external jugular: Vein crossing the sternocleidomastoid. Backup adult IV site.
• IO: proximal tibia: Flat part of the tibia, about 1 to 2 cm below and medial to the tibial tuberosity. Gets fluid and drugs into the marrow when veins can't be found.
• IO: proximal humerus: Greater tubercle of the humerus, with the hand on the belly. Fast flow to the central circulation.
• Needle decompression: 2nd ICS: 2nd intercostal space at the midclavicular line, on the affected side. Releases a tension pneumothorax.
• Needle decompression: 4th/5th ICS: 4th or 5th intercostal space at the anterior or mid-axillary line. Alternate site with a thinner chest wall in many adults.

Where the electrodes and defibrillation pads go.

• V1: 4th intercostal space, right sternal border. Looks at the septum.
• V2: 4th intercostal space, left sternal border. Looks at the septum.
• V3: Halfway between V2 and V4. Looks at the anterior wall.
• V4: 5th intercostal space, left midclavicular line. Looks at the anterior wall.
• V5: Same level as V4, left anterior axillary line. Looks at the lateral wall.
• V6: Same level as V4, left midaxillary line. Looks at the lateral wall.
• Limb leads: On the arms and legs or on the torso close to the limbs. Make leads I, II, III, aVR, aVL and aVF.
• Defibrillation pads: One pad below the right clavicle, the other on the left side below the armpit at the apex. Lets current pass through the heart.