192 Fun Facts About Anatomy

Which bone is the longest in the human body?

The femur, or thigh bone, is the longest and strongest bone in the body; it is so sturdy that in a healthy adult it usually takes a car crash or similar force to break it.

Which organ is both the heaviest internal organ and the largest gland in the human body?

The liver weighs about 1.5 kg and can regrow lost tissue, which is why a living donor can give away part of theirs: both portions grow back to normal size.

Which bone is the largest sesamoid bone in the human body, meaning it sits embedded within a tendon?

The patella, or kneecap, grows inside a tendon and works like a pulley: by holding the tendon away from the joint it adds leverage, so the knee straightens with less effort.

What is the primary function of red blood cells in the human body?

Transport oxygen is the job: red cells are packed with iron-rich haemoglobin that binds oxygen in the lungs and releases it as the cells squeeze through capillaries.

What is the outermost layer of the human skin called?

The epidermis has no blood vessels of its own, and its surface is a layer of dead, flattened cells that flake away constantly and are replaced from below.

What is the microscopic structural and functional unit of the kidney?

The nephron comes about a million to each kidney, more working tissue than the body strictly needs, which is why most people can live healthily with only one kidney.

Which of the twelve pairs of cranial nerves carries the sense of smell?

Olfactory nerve fibres reach the brain through a sieve of tiny holes in the skull above the nose, so a head injury can damage them and leave a person permanently unable to smell.

What is the tough, fibrous outer layer of the eye that is commonly known as the 'white of the eye'?

The sclera is the tough white coat that holds the eyeball's shape; the six muscles that turn the eye are anchored to its surface, so it is what they pull on to shift your gaze.

Which structure, known as the voice box, houses the vocal cords?

The larynx grows under testosterone at puberty: the vocal folds inside it lengthen and thicken, which is why male voices usually settle at a deeper pitch.

Which small gland, hanging by a stalk from the base of the brain, controls many of the body's other hormone glands?

The pituitary gland also makes growth hormone, which sets how tall we grow: too much of it in childhood causes gigantism.

What type of tissue primarily connects muscle to bone?

Tendons transmit the pull of muscle contraction to bone; ligaments, the usual mix-up, join bone to bone.

Which horseshoe-shaped neck bone is the only human bone not connected to another bone?

The hyoid hangs from muscles and ligaments alone, anchoring the tongue; it is so well shielded that in an adult a fractured hyoid is a classic sign of strangulation.

Which glands make the natural oil that keeps skin and hair supple and can clog pores into acne?

Sebaceous glands empty into hair follicles; the hormone changes of puberty can make them overproduce, and when excess oil and dead cells plug a follicle the result is acne.

How many bones are typically found in the adult human skeleton?

206 is the usual adult count; a newborn has many more separate bones, which fuse together through childhood and adolescence.

Which part of the brain is primarily responsible for balance and coordination?

The cerebellum, the 'little brain' at the back of the head, does not initiate movement but fine-tunes its coordination, precision and timing.

What type of muscle tissue is found in the walls of internal organs like the stomach and intestines?

Smooth muscle is named for lacking the stripes of skeletal muscle; nerves and hormones outside conscious control drive it, so digestion carries on without your having to think about it.

Which is the smallest bone in the human body?

The stapes is the last in a chain of three tiny bones that carry sound inward; its flat footplate sits in a small window and passes the vibration on to the inner ear.

Which organ is primarily responsible for filtering waste products from the blood and producing urine?

Kidneys strain far more fluid out of the blood than they get rid of: almost all of it is taken straight back, and only the small remainder leaves as urine.

Which type of blood vessel carries deoxygenated blood back to the heart?

Veins return blood to the heart, and most carry blood low in oxygen; the pulmonary veins are the exception, bringing freshly oxygenated blood back from the lungs.

What is the brain's wrinkled outer layer, the seat of thought and language, called?

The cerebral cortex is a thin sheet of grey matter; it is folded into ridges and grooves because folding packs far more surface into the limited space inside the skull.

Which transparent structure behind the pupil changes shape to focus light on the retina?

The lens changes shape as the ring of muscle around it tightens or relaxes; it stiffens with age, which is why most people need reading glasses from middle age.

Which blood type is the universal recipient for red cell transfusions?

AB+ already carries A and B antigens plus the Rh factor, so the immune system has nothing new to attack; O- is the universal donor.

What are the three protective membranes that surround the brain and spinal cord collectively called?

Meninges come in three layers, the tough dura, the web-like arachnoid and the delicate pia mater; when an infection inflames them, the result is meningitis.

Which heart chambers pump blood out to the lungs and body?

Ventricles are the lower pair of chambers; the left one has the thicker wall because it must drive blood round the whole body, while the right only supplies the lungs next door.

Which arteries supply the heart's own muscle with blood, causing a heart attack when one is blocked?

Coronary arteries run over the surface of the heart; unusually, they fill mainly between beats, because each contraction squeezes the branches buried in the heart wall.

The humerus is a long bone found in which part of the body?

The humerus is the bone of the upper arm; a nerve runs just under the skin behind its lower end, and knocking it there sets off the tingling 'funny bone' feeling.

Which bone is commonly known as the collarbone?

The clavicle, or collarbone, is the most commonly broken bone in the body: the force of a fall onto an outstretched arm or the point of the shoulder runs along it until it gives way.

What are the millions of tiny air sacs in the lungs, where oxygen enters the blood, called?

Alveoli stay open thanks to surfactant, a film that lowers the surface tension of their moist lining; babies born very early have not yet made enough of it and struggle to breathe.

Which part of the eye widens or narrows the pupil to control how much light gets in?

The iris is the coloured ring of the eye; its muscle shrinks the pupil in bright light and opens it in the dark, and its pattern is distinctive enough to identify a person by scan.

What is the medical name for the windpipe?

The trachea is kept from collapsing by C-shaped rings of cartilage; a band of muscle bridges the open back of each ring and tightens during a cough, narrowing the tube to force the air out.

Which muscle is the largest in the human body?

The gluteus maximus forms the bulk of each buttock; it is the main muscle that straightens the hip, driving the body upward when you climb, run or stand up from a stoop.

Which organ, located behind the stomach, secretes the hormone insulin?

The pancreas, lying behind the stomach, works double duty: its islet cells release insulin and glucagon into the blood while its acinar cells send digestive enzymes into the small intestine.

What is the main and largest artery in the human body?

The aorta has an elastic wall that stretches with each surge from the heart and springs back between beats, which keeps pressure up and blood moving while the heart refills.

Food travels from the throat to the stomach through which muscular tube?

The esophagus moves food by peristalsis: its muscle squeezes shut behind each mouthful in a wave that travels down the tube and pushes the food into the stomach.

How many permanent (adult) teeth does a human usually have?

Adults usually have 32 permanent teeth; the last four, the wisdom teeth, come through in the late teens or early twenties, often into a jaw with no room left, which is why so many are removed.

Which is the longest and widest single nerve in the human body?

The sciatic nerve runs from the lower back down each leg to the foot; when something presses on it, most often a slipped disc, the pain called sciatica follows the same route.

Which leaf-shaped flap in the throat closes over the airway when you swallow?

The epiglottis is a leaf-shaped flap of elastic cartilage that folds down over the airway when you swallow; if it closes too late, food 'goes down the wrong way' and sets off a cough.

Which small, pear-shaped organ stores and concentrates bile?

The gallbladder, a pear-shaped sac tucked beneath the liver, stores and concentrates bile between meals; it can be removed entirely and people live normally without it.

What is the medical name for the lower jawbone?

The mandible is the largest and strongest bone of the face; it starts out as two halves, which fuse at the chin during a baby's first year.

What type of joint is the shoulder, allowing the arm to swing in almost any direction?

The shoulder is a ball-and-socket joint with an unusually shallow socket: that gives the arm its great range of movement but also makes the joint easy to dislocate.

Which two tubes branch from the windpipe, one into each lung?

Bronchi are not a matched pair: the right one is wider and more upright, so a crumb or small object breathed in by accident usually ends up on that side.

Which thick, slippery fluid fills joints such as the hip and shoulder and keeps the bone ends gliding?

Synovial fluid has the consistency of egg white; besides cutting friction, it carries nutrients to the cartilage capping the bone ends, which has no blood vessels of its own.

Which air-filled hollows in the skull around the nose can block painfully after a cold?

Sinuses are lined with the same mucus-making membrane as the nose and drain into it; when a cold swells that lining, the mucus cannot escape and the pressure causes the ache.

Which muscle forms the 'six-pack' on a lean torso?

Rectus abdominis is one long muscle on each side of the midline; three bands of tough tissue cross it and tie it down, so the muscle bulges between them into the familiar blocks.

Where is the smallest skeletal muscle in the human body found?

The middle ear holds this tiny muscle; it tightens when a loud noise arrives, damping the vibration of the ear bones before it reaches the inner ear.

The sartorius, the body's longest muscle, takes its name from the Latin for which profession?

Tailor is sartor in Latin; the muscle helps fold the legs into the cross-legged position that tailors are said to have worked in, though other explanations of the name exist.

Which term correctly describes the muscle of the heart wall?

Cardiac muscle is involuntary: it is striated like skeletal muscle, but its branched cells, joined by intercalated discs, beat under the heart's own pacemaker rather than conscious command.

Which muscle contracts and flattens to enlarge the chest cavity every time you breathe in?

The diaphragm is a dome of muscle beneath the lungs; quiet breathing out takes no effort, because it simply relaxes, and a sudden spasm of it is what starts a hiccup.

The masseter, one of the strongest muscles of chewing, does what when both sides contract?

The masseter raises the lower jaw, pressing the teeth together for biting and chewing; anchored to the cheekbone above and the jaw below, it pulls the two together each time you bite.

Which cartilage layers near the ends of a child's long bones turn to bone by adulthood?

Growth plates lay down new bone all through childhood; during puberty rising hormone levels close them, the cartilage turns to bone, and the person stops getting taller.

The axial skeleton is skull, spine and what else?

The rib cage, skull and spine make up the axial skeleton; the collarbones, shoulder blades and hip bones count as appendicular because their job is to hang the limbs onto that central axis.

Each of the 12 pairs of ribs attaches at the back to which set of vertebrae?

Thoracic vertebrae, twelve of them, each carry a pair of ribs; only the first seven pairs join the sternum directly, and the last two end free at the front, hence 'floating ribs'.

What is the lowest of the three parts of the sternum called?

The xiphoid process takes its name from the Greek for 'sword-shaped'; it is still cartilage in a young adult and only hardens into bone in middle age.

Which bone do surgeons divide down the middle to reach the heart in open-heart surgery?

The breastbone, or sternum, is cut lengthwise to open the chest; afterwards the two halves are fastened back together with metal wires, which usually stay in the body for good.

What is the anatomical name for the armpit?

The axilla is the hollow beneath the shoulder; most of the lymph from the breast drains to nodes there, which is why they are checked when breast cancer is suspected.

Which four muscles make up the rotator cuff?

Subscapularis, supraspinatus, infraspinatus, teres minor: remembered as SITS, the four keep the shoulder joint steady through its wide range of movement, and tears in them are a common cause of shoulder pain.

Which forearm bone lies on the same side as the little finger?

The ulna sits on the little-finger side and stays put when the hand turns over; the other forearm bone swings across it.

The olecranon, a hook of bone at the top of the ulna, forms the bony point of which joint?

The elbow's bony tip is the olecranon, the hooked upper end of a forearm bone; when the arm straightens, it slots into a matching hollow in the back of the bone above.

The word radius, for the forearm bone, is Latin for what?

Ray, or the spoke of a wheel, is what radius meant in Latin; geometry uses the same word for a line running from a circle's centre to its edge, like a spoke.

Which two movements at the radioulnar joints turn the palm to face up or down?

Supination and pronation turn the palm up and down; in pronation one forearm bone swings across the other, so the two lie crossed in an X.

In Latin, the word 'tibia' named both the shinbone and which musical instrument?

A flute, or reed pipe, shared the name tibia with the shinbone in Latin; such pipes are said to have been made of bone at first, and scholars are unsure which meaning came first.

Which is the second-largest bone in the human body?

The tibia, or shinbone, is the main weight-bearing bone of the lower leg; its inner face lies directly under the skin, which is the hard ridge you can feel down your shin.

The fibula gets its name from a Latin word for what object?

A clasp or brooch for fastening clothes was a fibula to the Romans; the slim leg bone that took the name bears almost none of the body's weight, and its lower end is the bony knob on the outside of the ankle.

The eight small carpal bones make up which part of the body?

The wrist's carpal bones form an arch roofed by a band of ligament, the carpal tunnel; when the nerve running through it is squeezed, the fingers tingle and go numb.

What is the topmost vertebra, the one that carries the skull, called?

Atlas is named after the Titan of Greek myth condemned to hold up the sky; the ring-shaped bone has no solid body of its own and lets the head nod on top of it.

What is the largest bone in the tarsus, bearing weight in the heel?

The calcaneus, or heel bone, is most often broken in a fall from a height or a car crash, when the heel is crushed under the weight of the body.

What are the bones of the fingers and toes called?

Phalanges share their name with the phalanx, the close-ranked battle line of ancient Greek infantry; the bones lie side by side in rows, much like the soldiers.

Which digit of the hand has only two bones?

The thumb has two bones where each finger has three; its reach comes instead from a specially shaped joint at its base, which lets it swing across the palm to meet the fingertips.

Which organ filters the blood and removes worn-out red cells?

The spleen filters the blood and helps fight germs in it; people can live without one, but they are left more open to certain infections.

What does 'vermiform', as in vermiform appendix, mean?

Worm-shaped is the literal meaning; the appendix is a narrow tube rich in immune tissue, yet it has no vital job, which is why it can be removed without lasting harm.

The appendix connects to which pouch-like part of the large intestine?

The cecum is the blind pouch where the large intestine begins, low on the right side of the abdomen, which is why the pain of appendicitis usually settles there.

Which lymphocytes mature in the thymus?

T cells take their name from the thymus, where they mature; the gland is at its busiest early in life and shrinks with age, its tissue gradually replaced by fat.

Where are the glands that produce cortisol and aldosterone located?

Above the kidneys sit the two adrenal glands, like small caps; besides cortisol they release adrenaline, the hormone that readies the body to respond to sudden stress.

The hormone aldosterone raises blood pressure by making the body retain which mineral?

Sodium is held back on aldosterone's signal, and water follows the salt, so blood volume and pressure rise; the same hormone makes the body shed potassium.

What is the thin band of tissue connecting the two lobes of the thyroid called?

The isthmus borrows the geographer's word for a narrow strip joining two larger parts; it crosses the front of the windpipe and gives the thyroid its butterfly shape.

Besides T3 and T4, which peptide hormone does the thyroid secrete?

Calcitonin comes from the thyroid's parafollicular (C) cells, scattered between the follicles that make T3 and T4; it acts on bone, slowing the cells that break it down.

The parathyroid glands control the blood level of which mineral?

Calcium is their main concern: when its level in the blood dips, the glands release a hormone that frees more of it from bone.

Which tiny finger-like projections line the small intestine and absorb nutrients?

Villi, together with the folds they stand on, greatly enlarge the small intestine's absorbing surface, and each holds tiny blood vessels that carry the nutrients away.

Which is the shortest of the three regions of the small intestine?

The duodenum is so short that its name records its length: medieval Latin for 'twelve', as in twelve finger-widths, roughly 25 cm.

Which nutrient is chiefly absorbed in the ileum, the last part of the small intestine?

Vitamin B12 can be absorbed only at the far end of the ileum, and only when bound to a carrier protein made in the stomach; lose either, and B12-deficiency anaemia follows.

What does the large intestine mainly absorb from the waste passing through it?

Water: the waste arrives as a liquid, and the large intestine slowly draws the water back out of it, so that what is left firms up into solid stool.

What is the name of the valve between the small and large intestines?

The ileocecal valve stays mostly shut, opens to let digested food through, then closes again so that the contents of the colon cannot flow back into the small intestine.

Which ring of muscle controls the passage of partly digested food out of the stomach?

The pyloric sphincter opens to let only a little of the stomach's contents through at a time, since a larger rush would overwhelm the small intestine.

In which quadrant of the abdomen does the stomach lie?

Left upper is one of the four quadrants doctors use to map the abdomen: because each holds different organs, where a pain or lump sits narrows down what might be causing it.

A stroke in the left half of the brain usually weakens which part of the body?

The right side: most of the nerve fibres carrying movement commands cross over at the base of the brainstem, so each half of the brain controls the opposite side of the body.

Which lobe of the brain is dedicated to vision?

The occipital lobe, at the back of the head, receives the signals from the eyes; damage to it can leave a person blind even though both eyes are perfectly healthy.

In which lobe is Broca's area, responsible for speech, located?

Frontal: in 1861 the French surgeon Paul Broca examined the brains of two patients who had lost the power of speech and found damage at the same spot, low in the left frontal lobe.

Roughly how many neurons does the human brain contain?

About 86 billion: a 2009 count led by Suzana Herculano-Houzel replaced the round 100 billion long quoted in textbooks, and found the brain's other cells about equal in number rather than ten times as many.

Which brain structure consolidates short-term memory into long-term memory?

The hippocampus, a curved structure in each temporal lobe, converts short-term memories into long-term ones; it is among the first regions damaged in Alzheimer's disease.

Which almond-shaped brain structure processes fear, anxiety and aggression?

The amygdala takes its name from the Greek for almond; a woman known as S.M., whose amygdalae were destroyed by a rare genetic disease, has been studied for decades because she feels almost no fear.

Which brain region links the nervous system to the endocrine system and acts as the body's thermostat?

The hypothalamus triggers sweating and extra blood flow to the skin when the body overheats and shivering when it cools; it also regulates hunger, thirst and sleep.

Which part of the brain contains the centers that control heartbeat and breathing?

The medulla oblongata, the lowest part of the brainstem, regulates heartbeat, breathing and blood pressure and triggers reflexes such as coughing, sneezing and vomiting.

What is the largest white-matter structure in the human brain, connecting the two hemispheres?

The corpus callosum is sometimes cut to stop severe epilepsy spreading; Roger Sperry's studies of such 'split-brain' patients, whose two hemispheres then work independently, won him a share of the 1981 Nobel Prize.

Which fatty substance insulates nerve fibres and gives the brain's white matter its colour?

Myelin wraps nerve fibres like the plastic around a wire, speeding up their signals; in multiple sclerosis the immune system attacks it, slowing or blocking the messages.

The coiled cochlea of the inner ear is named after which animal's shell?

Snail: cochlea is Latin for a snail shell. Hair cells near its wide base pick up high-pitched sounds and those deeper in the coil pick up low ones, so each pitch has its own place along the spiral.

What is the sensory structure for hearing inside the cochlea called?

The organ of Corti holds the hair cells that turn sound vibrations into nerve signals; unlike those of birds, human hair cells never grow back, which is why noise damage to hearing is permanent.

Which retinal cells function mainly in dim light and give monochromatic vision?

Rods work in dim light and give only monochromatic vision, which is why colours fade at night; cones handle colour and high-acuity vision in bright light.

The word retina comes from the Latin for what?

Net: retina comes from the Latin rete, probably after the net-like web of blood vessels across it; its light-sensing cells turn the image into electrical signals that travel down the optic nerve to the brain.

What is the common name for the point on the retina where the optic nerve leaves the eye?

The blind spot has no light receptors because it is where the retina's nerve fibres bundle together and pass out of the eye as the optic nerve; anything whose image falls there goes unseen.

Why does the healthy cornea contain no blood vessels?

Transparency is essential, so the cornea has no blood vessels; it is, however, packed with nerve endings, which is why the lightest touch or speck of grit makes the eye blink shut.

Which prefix in medical terms refers to the cornea?

Kerat- is Greek for 'horn', and cornea itself comes from the Latin for 'horny' tissue; that is why the K in LASIK, the laser surgery that reshapes the cornea, stands for keratomileusis.

Which tiny bone is attached directly to the eardrum?

The malleus is fixed to the inside of the eardrum; with the two bones linked to it, it forms a lever chain that strengthens the vibrations on their way to the inner ear.

What are the English names of the three ossicles?

Hammer, anvil and stirrup are named for their shapes; the hammer and anvil evolved from two bones that formed the jaw joint in the ancestors of mammals.

What is the medical name for the eardrum?

The tympanic membrane, or eardrum, vibrates when sound strikes it; if it is torn, it usually heals by itself within a couple of months.

Which structures in the ear sense the turning of the head and help keep balance?

The semicircular canals are three fluid-filled loops set at right angles; when the head turns, the fluid lags behind and bends sensory hairs, telling the brain which way it is rotating.

What are the two layers of the dermis called?

The dermis has a thin papillary layer on top, ridged with the loops that give fingerprints, and a thick reticular layer of dense collagen beneath; it holds hair follicles, sweat glands, vessels and touch receptors.

Which specialized cells produce the pigment that colours skin and hair?

Melanocytes make melanin and hand it to neighbouring skin cells, where it shields their DNA from ultraviolet light; sunshine makes them step up production, which is what a tan is.

Which hair colour comes mostly from pheomelanin rather than the eumelanin that makes hair black or brown?

Red hair is mostly pheomelanin with only a little eumelanin; it arises when a receptor called MC1R on the pigment cells is not switched on, so they make pheomelanin instead.

What is the hardest substance in the human body?

Tooth enamel is the most highly mineralised tissue in the body, yet acids made by mouth bacteria can dissolve those minerals away, which is how a cavity begins.

What is the primary mineral in the hard outer covering of teeth?

Hydroxyapatite, a calcium phosphate crystal, also hardens bone; fluoride from toothpaste slots into the crystal in place of its hydroxyl groups, which strengthens the enamel against decay.

What is the technical name for baby teeth?

Deciduous, the word for trees that shed their leaves each year, fits: the 20 baby teeth are shed too, from about the age of six, as the permanent teeth come through to replace them.

Which type of tooth is designed for tearing food?

Canines, named after the fangs of dogs, grip and tear food; the upper pair are also called eye teeth, perhaps because they sit directly below the eyes.

Fingernails and hair are both made mostly of which protein?

Alpha-keratin is packed into cells that die and harden as they are pushed outward, so the hair and nails you can see are dead tissue with no nerves, which is why cutting them is painless.

What is the pale crescent at the base of a fingernail called?

The lunula, Latin for 'little moon', looks pale because a thick layer of cells over the nail's growth zone hides the blood vessels that tint the rest of the nail bed pink.

Which muscle on the front of the thigh straightens the knee?

The quadriceps femoris is four muscles working as one; a tap just below the kneecap makes them twitch and the leg kick, the reflex doctors test with a rubber hammer.

Which muscle is principally responsible for straightening the elbow?

Triceps brachii, the 'three-headed' muscle on the back of the arm, is the antagonist of the biceps: when one of the pair contracts to move the elbow, the other has to relax and lengthen.

Which two bones form the back of the pelvic skeleton?

The sacrum and coccyx form the back wall of the pelvis; each starts out as separate vertebrae, five in the sacrum and about four in the tailbone, which begin to fuse only in adulthood.

What are the fibrous joints that lock the bones of the skull together called?

Sutures are rigid in adults, but in a baby they are still flexible seams, so the head can squeeze through the birth canal and the skull can expand as the brain grows.

Which organ is reshaped by four pairs of intrinsic muscles lying within it?

The tongue's intrinsic muscles lie within the tongue itself, running lengthwise, crosswise and vertically, so they can curl, flatten or narrow it, while four extrinsic pairs anchored outside it move it about.

What is the vertical band of fibrous tissue dividing the tongue's left and right sides?

The lingual septum marks the seam where the two swellings that built the front of the tongue fused in the embryo; on the surface it shows as the tongue's central groove.

Which basic taste is missing from the debunked classroom map that gave each taste its own zone?

Umami, the savoury taste identified in Japan in 1908, was absent from the map, which grew out of a 1942 misreading of a 1901 German study; in fact every taste can be sensed wherever there are taste buds.

Which soft tissue turns out billions of new blood cells every day?

Bone marrow has to work nonstop because blood cells wear out fast: platelets last little more than a week. In adults the blood-making red marrow lies mainly in the ribs, breastbone, spine and hip bones.

What is the tough fibrous membrane covering cartilage called?

The perichondrium wraps most cartilage, a tissue with no blood vessels of its own; nutrients have to seep in through its matrix, which is why damaged cartilage is so slow to heal.

What is the study of ligaments known as?

Desmology is the study of ligaments; when one is overstretched or torn the injury is called a sprain, most often at the ankle, knee or wrist.

Which sweat glands, clustered in the armpits, do little to cool the body?

Apocrine sweat glands, concentrated in the armpits and groin, release a thick secretion that skin bacteria turn into body odour; eccrine glands, densest on the palms and soles, do the cooling.

Through which tube does urine leave the bladder and the body?

The urethra carries urine out of the body; the two ureters that feed the bladder do not simply drain into it but squeeze the urine along with waves of muscle contraction.

What is the medical term for knock-knee?

Genu valgum is a normal phase of growing up: most children turn knock-kneed at around three and straighten out again as they grow, whereas bow legs are the opposite bend, genu varum.

What are the bundles of muscle fibers within a skeletal muscle called?

Fascicles, from the Latin for 'little bundles', are wrapped in a sheath called the perimysium; how they are arranged shapes both the force a muscle can produce and how far it can move.

Which bone cells break down old bone tissue?

Osteoclasts dissolve old bone while osteoblasts lay down new, so the skeleton is constantly renewed; when the breakdown outpaces the rebuilding, bones thin and osteoporosis sets in.

What is the indentation on the front edge of the left lung called?

The cardiac notch is a hollow in the left lung that makes room for the heart, which shares that side of the chest; for the same reason the left lung is the smaller of the two.

An adult human kidney is roughly the size of which of these?

A fist: each bean-shaped kidney is only about 12 cm long, yet one is enough to live on, which is why a healthy person can donate the other.

Which medical prefix comes from the Greek word for liver?

Hepat- comes from the Greek hepar, 'liver', as in hepatitis; the blood thinner heparin got its name because it was first isolated from liver cells, taken from dogs.

Roughly how much blood does an average adult's body contain?

About 5 litres, which is why a standard donation of nearly half a litre takes roughly a tenth of your blood; US donors must then wait eight weeks before giving whole blood again.

What colour is blood plasma?

Pale yellow: plasma is a straw-coloured fluid that makes up roughly 55% of blood; rich in vital proteins, it is given to burn, shock and trauma patients.

A mature red blood cell lacks which structure, found in almost every other cell of the body?

A nucleus: the maturing red cell ejects it to make room for hemoglobin, packing in some 270 to 300 million molecules and becoming little more than a flexible bag of the pigment.

Roughly how long does a human red blood cell circulate before it is broken down and recycled?

About 4 months: a red cell lasts up to 120 days. It cannot make new proteins to repair itself, so it simply wears out, and scavenger cells then engulf it and recycle its iron.

Platelets are fragments of cytoplasm shed by which giant cells?

Megakaryocytes push long extensions through the walls of tiny blood vessels and shed thousands of platelets from them into the bloodstream.

What is the scientific name for white blood cells?

Leukocytes, unlike red cells, do most of their work outside the blood: they squeeze out through the walls of the smallest vessels to hunt microbes in the tissues.

Which body system returns fluid that has leaked out of the blood capillaries back to the bloodstream?

The lymphatic system has no pump of its own: body movement, breathing and one-way valves keep the fluid moving, and when its vessels are blocked the tissues swell, a condition called lymphoedema.

Which hormone does the pineal gland produce?

The pineal gland, named for its pine-cone shape and sitting near the centre of the brain, secretes melatonin in darkness, helping to set the sleep-wake cycle.

Which philosopher claimed the pineal gland was the principal seat of the soul?

René Descartes argued that this one small gland at the centre of the brain was where the soul met the body and steered it; later science found it to be an ordinary hormone gland.

Who wrote De Humani Corporis Fabrica, the 1543 book that founded modern anatomy?

Andreas Vesalius broke with custom by doing his dissections himself instead of leaving the cutting to an assistant, and so saw that Galen's anatomy, long taken on trust, had been based on animals such as apes.

At which university did the author of the 1543 anatomy book De Humani Corporis Fabrica hold the chair of surgery?

Padua offered him its chair of surgery and anatomy as soon as he took his doctorate there in 1537; the dissections he staged for his students became the basis of the book.

The 1543 anatomy book De Humani Corporis Fabrica was dedicated to which emperor?

Charles V, to whom the 28-year-old author dedicated the book, took him on that same year as a physician to the imperial household; the anatomist later served Charles's son, Philip II of Spain.

In which ancient city, famed for a library second only to Alexandria's, was the physician Galen born?

Pergamon, now Bergama in Turkey, is also where Galen began his career as physician to the city's gladiators, whose wounds taught him much about treating injuries.

Which second-century Roman emperor did Galen serve as a physician?

Marcus Aurelius took Galen on as a physician, and Galen went on to treat the emperor's son Commodus as well; his writings then dominated European medicine for well over a thousand years.

Which four humors underpinned Galen's understanding of medicine?

Black bile, yellow bile, blood and phlegm had to stay in balance for good health, so doctors bled patients to drain an excess; the theory survives in the word melancholy, Greek for 'black bile'.

Who illustrated the first edition of Gray's Anatomy in 1858?

Henry Vandyke Carter, himself medically trained, made the drawings for the book's 363 illustrations directly from fresh dissections that he and Gray carried out together.

Which English physician showed in 1628 that blood circulates around the body?

William Harvey argued from the sheer quantity of blood passing from the veins to the arteries that it could not be made fresh each time, as Galen had taught, but must travel round in a circuit.

Which disease, caught while nursing a sick nephew, killed anatomist Henry Gray in his mid-thirties?

Smallpox killed Gray in June 1861, only three years after his textbook first appeared; other editors took it over and carried it on through many further editions.

Which muscle forms the rounded cap of the shoulder?

Deltoid means 'delta-shaped', after the triangular Greek letter; this thick muscle is the one that raises the arm out to the side.

With each step, the arches of the foot act like which device?

Spring: the arches flatten a little as weight comes onto the foot, storing some of the energy, then rebound as it lifts, which cushions each step and puts bounce into the next.

What is the opening in the base of the skull through which the spinal cord passes called?

The foramen magnum, Latin for 'large opening', sits further forward under the skull in species that walk upright, so fossil hunters use its position to tell whether an ancient relative walked on two legs.

Which two structures make up the human skull?

The neurocranium and the facial skeleton are the braincase and the bones of the face; of all the skull's bones only the lower jaw can move, the rest being locked into one rigid unit that shields the brain.

Which two bones does the scapula connect?

The humerus and the clavicle are the scapula's only bony links: it has no joint with the ribcage and is held against the back by muscles alone, which lets it glide freely as the arm moves.

Which is the thickest and strongest tendon in the human body?

The Achilles tendon is the body's thickest and strongest, yet it is named, ironically, after the one weak spot of the hero Achilles in Greek legend: his heel.

Which type of joint is the elbow?

Hinge joint: the elbow swings one way like a door; in small children it is loosely held, so a sharp tug on the hand can slip a bone out of place, the injury called nursemaid's elbow.

Which cranial nerve, the tenth, runs down into the chest and abdomen?

Vagus is Latin for 'wandering': unlike the other cranial nerves, which mostly serve the head and neck, it roams down to the organs of the chest and belly, helping to regulate heart rate and digestion.

What is the anatomical name for the hollow at the back of the knee?

The popliteal fossa is the diamond-shaped hollow behind the knee through which the leg's main vessels and nerves pass; fluid from a troubled knee joint can bulge into it as a Baker's cyst.

The uvula hanging at the back of the throat takes its name from the Latin for 'little' what?

Grape: uvula is a diminutive of the Latin uva, a grape or bunch of grapes. When you swallow, it lifts with the soft palate to stop food and drink going up into the nose.

The sinoatrial node, the heart's natural pacemaker, sits in the wall of which chamber?

Right atrium: the node sits high in its wall and sets the heartbeat; if it fails, a backup node lower down takes over at a slower rate, one reason artificial pacemakers are fitted.

Which German pathologist gave his name to the hormone-producing 'islets' he discovered as a student in 1869?

Paul Langerhans described the cell clusters in his doctoral thesis; the hormone they make was later named insulin, from the Latin insula, 'island', after them.

Which body fluid is classed as a connective tissue because its cells float in a liquid matrix?

Blood qualifies because, like bone and cartilage, it is cells scattered through a matrix; here the matrix is liquid plasma. Lymph is classed the same way.

Collagen, the body's most abundant protein, is named from the Greek word for which sticky substance?

Glue was once made by boiling animal skins and sinews, and the word collagen literally means 'glue producer'.

Which ingredient that sets gummy sweets is made from the collagen in animal skin and bones?

Gelatin is collagen partly broken down, brittle when dry and rubbery when moist. It also turns up in marshmallows, ice cream and medicine capsules.

Scurvy struck sailors on long voyages because collagen cannot be built without which nutrient?

Vitamin C is needed by the enzymes that lock collagen's strands together, so without it the gums bleed and wounds heal poorly.

Which heat-producing tissue is especially abundant in newborn babies and hibernating mammals?

Brown fat owes its colour to iron-rich mitochondria that burn fuel to make heat, with no shivering required.

A sprain, unlike a strain of muscle, is by definition a stretch or tear of which structure?

A ligament is a tough band of collagen tying bone to bone, so a joint forced past its normal range can overstretch it.

Which skin layer, just beneath the surface, is made mostly of dense irregular connective tissue?

Dermis fibers are woven in every direction, which lets skin resist tearing whichever way it is pulled.

What are the body's fat-storing cells, each swollen by one large droplet of lipid, properly called?

Adipocytes hold so much fat that the nucleus is flattened and pushed to the very edge of the cell.

Which bendy part of the head keeps its shape thanks to a framework of elastic cartilage?

The outer ear springs back after being folded because its cartilage is threaded with stretchy fibers; the nose is stiffened by a firmer kind.

Which connective tissue residents release histamine, raising the red bump after a mosquito bite?

Mast cells sit packed with granules of histamine, ready to burst within seconds of meeting an allergen. They are best known for allergy and anaphylaxis.

Which cells, the most common in connective tissue, produce its collagen and help to heal wounds?

Fibroblasts are spindle-shaped builders: besides collagen they make elastic fibers and the framework that other cells live in.

Which wandering cells of connective tissue develop from monocytes and engulf microbes and debris?

Macrophages go by local names around the body, such as Kupffer cells in the liver and microglia in the brain, but all swallow and digest what does not belong.

Which cells, the only kind found in healthy cartilage, produce and maintain the cartilage matrix?

Chondrocytes live walled inside the matrix they make, and because cartilage has no vessels of its own, their food has to seep in from outside.

Which cells build new bone by laying down osteoid, a soft matrix that later hardens with mineral?

Osteoblasts work in connected teams, and any that end up buried in their own matrix change into a different, longer-lived kind of cell.

Which tough form of cartilage makes up the discs between the vertebrae and the menisci of the knee?

Fibrocartilage mixes cartilage with dense fibrous tissue, which lets each spinal disc work as a shock absorber.

Hyaline cartilage, the smooth cap on bones at joints, is named from the Greek for which material?

Glass is what fresh hyaline cartilage looks like: smooth and translucent. The same tissue shapes the nose and holds the windpipe open.

Which loose connective tissue, the body's most widespread, underlies nearly every epithelium?

Areolar tissue is mostly open, fluid-filled space, so defensive cells can roam through it and meet invaders that slip past the surface lining.

Which fine, branching fibers form the supporting mesh inside lymph nodes, the liver and bone marrow?

Reticular fibers are a thin kind of collagen that links into a soft scaffold, holding an organ's working cells in place.

How are the collagen fibers arranged inside a tendon?

In parallel bundles the fibers act like the strands of a rope, resisting a pull along one line, so a tendon counts as dense regular connective tissue. Few vessels reach it, so it is slow to heal.

What name is given to the gel that fills the space between a connective tissue's cells and fibers?

Ground substance is mostly water trapped by long sugar chains, which is what gives it a gel-like texture and keeps the collagen fibers lubricated.

Which embryonic germ layer, also the source of muscle, gives rise to most connective tissue?

Mesoderm, the middle layer, first forms a loose embryonic tissue called mesenchyme, which can mature into every kind of connective tissue.

Which inherited connective tissue disorder typically gives a tall, thin build with very long limbs?

Marfan syndrome stems from a fault in the gene for fibrillin, and its gravest risk is hidden: the wall of the body's main artery can weaken and bulge.

Which genetic condition of connective tissue causes very loose joints and stretchy, velvety skin?

Ehlers–Danlos syndrome is really a family of related conditions, most caused by faults in how collagen is built or processed.

Collagen owes its rope-like strength to protein chains wound together into which molecular shape?

Triple helix is the signature of collagen: three chains twist into a unit called tropocollagen, the building block of every collagen fiber.

Which numbered form of collagen, found in bone and tendon, makes up about 90% of the body's total?

Type I collagen is so plentiful that it is also the single most abundant protein in the body. Cartilage relies on type II instead.

Which sheets of connective tissue wrap each muscle and include the plantar band beneath the foot?

Fascia also walls the limbs into compartments, each holding a group of muscles together with their nerves.

Wharton's jelly, a soft mucous connective tissue, cushions the vessels of which structure?

The umbilical cord carries two arteries and one vein, and the jelly packed around them protects and insulates all three.

Which water-binding molecule of connective tissue is also injected as a filler for wrinkles?

Hyaluronic acid swells with water to form a gel, and it is also a major ingredient of the slippery fluid inside joints.

The mature cells of cartilage and bone sit in small matrix cavities known by which Latin name?

Lacunae in bone each hold a single cell, and hair-fine channels run between them so the walled-in cells can trade nutrients.

What is a tendon called when it is flattened into a broad sheet, as across the front of the abdomen?

An aponeurosis stores energy like a spring when it is stretched and returns it on the recoil; thick ones also lie in the lower back.