164 Fun Facts About Anatomy

Which bone is the longest in the human body?

The femur, or thigh bone, is the longest, strongest and heaviest bone in the body, and the only bone in the upper leg.

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

The liver weighs about 1.5 kg in an adult and is the only internal organ that can regenerate much of its own tissue.

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

The patella, or kneecap, is the largest sesamoid bone in the body; it is embedded in the quadriceps tendon and shields the front of the knee joint.

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

Transport oxygen is the job: erythrocytes 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 is the thin, tough, outermost layer of the skin that provides a waterproof barrier and protects the body from the environment.

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

The nephron is the minute structural and functional unit of the kidney, responsible for filtering blood and producing urine.

How many pairs of cranial nerves are typically found in the human body?

They are numbered I to XII, and a thirteenth, the terminal nerve (numbered 0), has more recently been recognised.

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

The sclera is the opaque, fibrous outer coat, mostly collagen, that keeps the eye's shape; the clear cornea at the front is continuous with it.

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

The larynx holds the vocal folds, whose slit, the rima glottidis, is its narrowest part; the pharynx sits above it.

Which pea-sized 'master gland' hangs off the base of the brain?

The pituitary gland, about the size of a pea, hangs by a stalk from the base of the brain and controls many other endocrine glands, earning it the name 'master gland'.

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 and helping with swallowing.

What is the largest organ of the human body?

Skin makes up roughly 16% of body mass; the heaviest internal organ is a different one.

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

206 in an adult, down from around 270 at birth, as bones fuse during growth.

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 involuntary and has no striations; the same tissue lines blood vessels as vascular smooth muscle.

Which bone, tucked in the middle ear, is the smallest in the human body?

The stapes, about 3 mm long, is the smallest and lightest bone in the body, one of the three ossicles that carry vibrations across the middle ear.

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

Kidneys filter about a fifth of the blood that enters them at the glomerulus, and the resulting urine drains down the ureters to the bladder.

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

Veins are blood vessels that carry deoxygenated blood from the body's tissues back to the heart. The main exceptions are the pulmonary veins, which carry oxygenated blood from the lungs to the heart.

What is the outermost layer of the cerebrum called?

The cerebral cortex is the brain's outer sheet of grey matter, folded into ridges (gyri) and grooves (sulci); it is only about 2 to 4 mm thick.

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

The lens is a flexible, transparent disc behind the iris; the ciliary muscle alters its curvature, a process called accommodation, to focus light from near or far objects onto the retina.

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 are three layers: the tough dura mater, the web-like arachnoid and the delicate pia mater.

How many chambers does the human heart possess?

The human heart is a double pump with four chambers: two upper atria (right and left) and two lower ventricles (right and left).

Which muscular organ pumps blood through the body's blood vessels?

The heart, a muscular pump about the size of a closed fist, sits between the lungs in the middle of the chest and drives blood through the body's vessels.

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

The humerus is the long bone of the upper arm, running from the shoulder to the elbow; bumping the ulnar nerve near its lower end gives the 'funny bone' tingle.

Which bone is commonly known as the collarbone?

The clavicle, or collarbone, is a slender S-shaped bone about 15 centimetres long that acts as a strut between the shoulder blade and the breastbone.

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

Alveoli, from the Latin for 'little cavity', are the tiny air sacs at the ends of the bronchioles; oxygen crosses their thin walls into the blood while carbon dioxide passes out.

Which coloured, ring-shaped part of the eye controls the size of the pupil?

The iris is the coloured ring of muscle around the pupil; like a camera diaphragm it widens or narrows the pupil to control how much light enters the eye.

What is the medical name for the windpipe?

The trachea, or windpipe, is a tube about 10 to 12 cm long held open by C-shaped cartilage rings, running from the larynx down to the two main bronchi.

Which is the single largest muscle in the human body?

The gluteus maximus, the big buttock muscle, is the largest single muscle by volume; it keeps the trunk upright and powers standing up, climbing and running.

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, about 2.5 cm wide at its root, rises from the left ventricle, arches over and runs down into the abdomen before splitting into the two common iliac arteries.

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

The esophagus is a muscular tube about 25 centimetres long that squeezes food from the pharynx to the stomach with wave-like peristaltic contractions, so you could swallow upside down.

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

Adults usually have 32 permanent teeth: eight incisors, four canines, eight premolars and twelve molars, with the four wisdom teeth arriving last, typically in the late teens or early twenties.

How many cervical (neck) vertebrae do humans have?

Giraffes have exactly the same number, just enormously elongated.

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

The sciatic nerve, about as thick as a thumb where it leaves the pelvis, runs from the lower back down the back of each leg; irritation of it, sciatica, is felt all the way down.

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 over the larynx during swallowing; when it fails to close in time, food 'goes down the wrong way' and triggers coughing.

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, or lower jaw, is the largest and strongest bone of the face and the only skull bone that moves freely, hinging at the two temporomandibular joints.

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

The shoulder is a ball-and-socket joint: the round head of the humerus sits in the shallow glenoid cavity of the scapula, giving great freedom but making it the most often dislocated joint.

How many lobes does the human right lung have?

The right lung has three lobes (upper, middle and lower); the left has only two because it shares chest space with the heart.

Which is the largest joint in the human body?

The knee is the largest joint in the body, a modified hinge between femur and tibia that also allows slight rotation, which is one reason it is so often injured in sport.

How many bones is the adult human skull generally considered to have?

That breaks down into eight cranial bones around the brain and fourteen bones of the face.

Roughly how many skeletal muscles does the human body contain?

The body has more than 600 skeletal muscles, roughly 35 to 40% of body weight; each fibre is packed with sarcomeres, where actin and myosin filaments slide past each other to contract.

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

The stapedius, just over a millimetre long, sits in the middle ear, where it steadies the stapes and dampens its vibration during loud sounds as part of the acoustic reflex.

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

It runs diagonally down the thigh and helps you sit cross-legged, the posture tailors once worked in. Sartor is Latin for tailor.

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-shaped sheet of skeletal muscle between the chest and abdomen; it contracts and flattens on every inhalation, and when it relaxes, elastic recoil pushes the air back out.

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

The masseter raises the lower jaw, clamping the teeth together; you can feel it bulge at the angle of the jaw when you clench, and it is especially powerful in grazing herbivores.

Bone makes up roughly what share of total body weight?

Bone makes up about 14% of body weight, roughly 10 kg in a 70-kg adult, while skeletal muscle accounts for about 35 to 40%.

How many bones make up the axial skeleton?

The appendicular skeleton of limbs and girdles adds the other 126.

How many pairs of ribs does a typical human thoracic cage have?

12 pairs, articulating with the 12 thoracic vertebrae and joined to the sternum via costal cartilage.

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

The xiphoid process is the small, pointed lowest part of the sternum; above it sit the body (also called the gladiolus) and, at the top, the manubrium.

The sternum is roughly the shape of which item of clothing?

The sternum is roughly necktie-shaped, broad at the top and tapering to a point at the bottom, about 17 cm long in adults; its name comes from the Greek sternon, meaning chest.

What is the anatomical name for the armpit?

The axilla is the anatomical name for the armpit, the pyramid-shaped hollow beneath the shoulder joint through which the axillary artery, vein and the nerves of the brachial plexus pass into the arm.

Which four muscles make up the rotator cuff?

The rotator cuff is the subscapularis, supraspinatus, infraspinatus and teres minor, remembered as SITS; all four run from the scapula to the head of the humerus and hold it in its socket.

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

The ulna runs along the little-finger side of the forearm; it is slightly longer than the radius, which lies on the thumb side and is the thicker of the two.

What is the hook-like bony process of the ulna that forms the point of the elbow?

The olecranon is the large hook-like process at the upper end of the ulna; it locks into the olecranon fossa of the humerus when the arm straightens, preventing hyperextension.

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

Radius is Latin for 'ray'; the bone runs to the thumb side of the wrist, is thicker but slightly shorter than the ulna, and rotates around it when the hand turns over.

Which two movements does the radioulnar joint allow?

The proximal and distal radioulnar joints are pivot joints that let the radius rotate around the ulna, producing supination and pronation, the movements that turn the palm up or down.

The tibia is named after which musical instrument?

It is the second largest bone in the body after the femur.

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

The tibia, or shinbone, is the second-largest bone after the femur; it runs from the knee to the ankle on the inner side of the lower leg and carries most of the weight below the knee.

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

It resembles a clasp like a modern safety pin and is the most slender long bone in proportion to its length.

Which cartilage of the larynx is the only complete ring in the airway?

The cricoid cartilage, shaped like a signet ring, is the only complete cartilage ring in the airway; the tracheal rings below it are C-shaped and open at the back.

How many carpal bones are in each human wrist?

Each wrist has eight carpal bones arranged in two rows of four; with a ligament across the front they form the carpal tunnel, through which the median nerve passes into the hand.

How many tarsal bones are in each human foot?

Each foot has seven tarsal bones between the lower leg and the metatarsals; the uppermost, the talus, forms the ankle joint with the tibia and fibula.

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

The calcaneus, or heel bone, is the largest tarsal bone and takes the body's weight at the heel; the talus sits on top of it and forms the ankle joint with the tibia and fibula.

How many phalanges are there in the human body?

The body has 56 phalanges, 14 in each hand and 14 in each foot, arranged in proximal, middle and distal rows; the distal ones carry the nails.

How many phalanges, or finger bones, does a human thumb have?

Two, while every other finger and toe has three; the big toe shares the thumb's shortfall.

Which organ removes old red blood cells and holds a reserve of blood?

The spleen filters the blood, breaking down worn-out red cells, recycling their iron and holding a reserve of blood; it also works like a large lymph node.

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

Vermiform means worm-shaped, from the Latin vermis, 'worm'; the appendix is a narrow, blind-ended tube about 9 cm long on average, though its length varies widely.

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

The appendix opens off the cecum, the blind pouch at the start of the large intestine in the lower right abdomen; its surface marking is McBurney's point.

Which lymphocytes mature in the thymus?

T cells take their name from the thymus, where they mature; the gland sits behind the sternum and shrinks after adolescence, replaced by fat.

Where are the glands that produce cortisol and aldosterone located?

The adrenal glands sit above the kidneys like small caps; their cortex makes steroid hormones such as cortisol and aldosterone, and their medulla makes adrenaline.

Which zone of the adrenal cortex produces aldosterone?

Aldosterone comes from the zona glomerulosa, the outermost layer of the adrenal cortex; cortisol comes from the zona fasciculata and androgens from the zona reticularis.

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

The isthmus is the narrow band of thyroid tissue crossing the front of the trachea to join the gland's two lobes, giving the butterfly shape just below the Adam's apple.

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

Calcitonin, made by the thyroid's parafollicular (C) cells, lowers blood calcium by slowing bone breakdown; it is a 32-amino-acid peptide, unlike the iodine-based T3 and T4.

How many parathyroid glands do humans usually have?

They sit on the back of the thyroid and secrete parathyroid hormone when blood calcium is low.

Roughly how long is the human small intestine?

The small intestine is about 6.5 metres long when relaxed, coiled into the abdomen; it is called 'small' because it is narrower, not shorter, than the large intestine.

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

The duodenum, about 25 cm long, is the shortest of the three; it receives bile and pancreatic juice, and is followed by the much longer jejunum and ileum.

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

Vitamin B12, bound to intrinsic factor from the stomach, is absorbed in the terminal ileum, which also reclaims about 95% of the bile salts for reuse by the liver.

Roughly how long is the human large intestine?

The large intestine is about 1.5 metres long, running from the cecum through the colon to the rectum, a fraction of the small intestine's length but much wider.

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

The ileocecal valve is the sphincter-like fold where the ileum, the last part of the small intestine, opens into the cecum of the large intestine in the right lower abdomen.

Which ring of muscle controls the passage of chyme out of the stomach?

The pyloric sphincter is the ring of smooth muscle at the stomach's outlet; it opens briefly to release chyme into the duodenum a few millilitres at a time.

In which quadrant of the abdomen does the stomach lie?

The stomach lies mainly in the left upper quadrant, tucked under the diaphragm and the left ribs, while the liver fills most of the right upper quadrant.

How many neuronal layers does the neocortex have?

The neocortex has six neuronal layers, numbered I (outermost) to VI; the evolutionarily older allocortex has only three or four.

Which lobe of the brain is dedicated to vision?

The occipital lobe at the back of the brain houses the primary visual cortex, where signals from the retinas arrive via the optic radiations.

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

Broca's area lies in the frontal lobe, in the inferior frontal gyrus, usually of the left hemisphere, just in front of the motor cortex that controls the mouth and tongue.

Roughly how many neurons does the human brain contain?

The brain has about 86 billion neurons, a figure from Suzana Herculano-Houzel's cell-counting studies, plus a roughly equal number of non-neuronal glial cells.

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, named from the Greek for almond and first described by Karl Friedrich Burdach in 1822, lies deep in each temporal lobe and processes fear, anxiety and aggression.

Which brain region links the nervous system to the endocrine system via the pituitary?

The hypothalamus, about the size of an almond, sits just above the pituitary and controls it through releasing hormones, while also regulating body temperature, hunger, thirst and sleep.

Which part of the brainstem contains the cardiovascular and respiratory centers?

The medulla oblongata, the lowest part of the brainstem, houses the cardiovascular and respiratory centres and controls involuntary functions from breathing and heart rate to vomiting and sneezing.

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

The corpus callosum is about 10 cm long and carries some 200 million axons between the two hemispheres; it is found only in placental mammals.

What does the Latin name of the brain's great commissure, literally translated, mean?

Corpus callosum is Latin for 'tough body' (callosus means hard or callous); its parts are the rostrum, genu, body and splenium.

How many turns does the human cochlea make around its axis?

The cochlea coils about 2.75 turns around its central bony axis, the modiolus; its name comes from the Latin for snail shell.

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

The organ of Corti, named for Alfonso Corti who described it in 1851, runs along the cochlea's basilar membrane; its hair cells turn vibrations into nerve signals.

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?

Retina comes from the Latin rete, 'net', after the net-like web of blood vessels seen across its surface; it works much like the film or sensor in a camera.

Roughly what fraction of the eye's total optical power does the cornea provide?

The cornea provides about two-thirds of the eye's roughly 60 dioptres of focusing power, a fixed 43 dioptres or so; the lens adds the rest and does the fine focusing.

Why does the healthy cornea contain no blood vessels?

Transparency is essential: blood vessels would scatter light, so the cornea stays avascular and takes oxygen dissolved in tears and nutrients from the aqueous humour.

Which prefix in medical terms refers to the cornea?

Kerat- comes from the Greek keras, 'horn', and refers to the cornea: keratitis is inflammation of the cornea and keratoconus is its cone-shaped bulging.

Which ossicle is attached directly to the eardrum?

The malleus is fixed to the inner surface of the eardrum and passes its vibrations to the incus and then the stapes.

What are the English names of the three ossicles?

The hammer (malleus), anvil (incus) and stirrup (stapes) are named for their shapes; together they carry vibrations from the eardrum to the inner ear.

What is the medical name for the eardrum?

The tympanic membrane, or eardrum, is a thin cone-shaped membrane about 9 to 10 mm across separating the outer ear canal from the middle ear; it vibrates with sound.

Which structures of the inner ear enable balance and eye tracking while moving?

The three semicircular canals, set at right angles to each other, sense rotation of the head and drive the reflex that keeps the eyes steady while moving; the utricle and saccule sense tilt and linear motion.

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, found in the basal layer of the epidermis, make melanin from the amino acid tyrosine and pass it to the surrounding keratinocytes.

Which form of melanin gives red or yellow tints to skin and hair?

Pheomelanin, a sulfur-containing form of melanin, gives red and yellow tints and is abundant in red hair; eumelanin, the brown-black form, dominates where photoprotection matters.

What is the hardest substance in the human body?

Tooth enamel is about 96 percent mineral by weight and contains no cells, nerves or blood vessels, which is why it cannot heal itself.

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

Hydroxyapatite, a crystalline calcium phosphate, makes up about 96% of tooth enamel by weight and is also the main mineral of bone.

How many teeth are in a full set of primary 'baby' teeth?

A full primary set has 20 teeth, ten in each jaw; humans are diphyodont, growing two sets, and the first primary teeth erupt at around six months.

Which type of tooth is designed for tearing food?

Canines, the pointed teeth beside the incisors, grip and tear food; incisors cut, and the premolars and molars crush and grind.

Fingernails and hair are both made mostly of which protein?

Alpha-keratin, a tough fibrous protein rich in the amino acid cysteine, forms fingernails and hair; the same protein family builds claws, hooves and horns in other vertebrates.

Roughly how fast does a fingernail grow each month?

Fingernails grow about 3.5 mm a month on average, roughly twice the rate of toenails; growth slows with age and is fastest on the middle finger.

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

The quadriceps femoris, the four-part muscle on the front of the thigh, pulls on the kneecap and tibia through the patellar tendon to straighten the knee; the hamstrings at the back bend it.

Which muscle is principally responsible for straightening the elbow?

Triceps brachii, 'three-headed', has medial, lateral and long heads; the biceps on the other side bends the elbow.

Which two bones form the back of the pelvic skeleton?

The sacrum and coccyx, the fused lower end of the spine, form the back wall of the bony pelvis; the two hip bones complete the ring at the front and sides.

What are the firm fibrous junctions between cranial bones called?

Sutures are the immovable fibrous joints between the skull bones; in infants they have not yet closed, leaving the soft spots called fontanelles.

How many intrinsic muscles alter the shape of the tongue?

They are not attached to bone; four paired extrinsic muscles move it.

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

The lingual septum is a vertical sheet of fibrous tissue dividing the tongue into left and right halves; it shows on the surface as the groove called the median sulcus.

Which three cranial nerves carry taste information to the brain?

Taste travels on the seventh, ninth and tenth cranial nerves, serving the front two-thirds of the tongue, the back third and the epiglottis respectively; the five basic tastes can be detected anywhere on the tongue.

Roughly how many blood cells does human bone marrow produce each day?

Bone marrow turns out about 500 billion blood cells a day, mostly red cells and platelets, from a tissue that makes up roughly 4 to 5 percent of body mass.

What is the tough fibrous membrane covering cartilage called?

The perichondrium is the dense fibrous membrane wrapping most cartilage, the counterpart of the periosteum around bone; articular cartilage at joint surfaces lacks one.

What is the study of ligaments known as?

Desmology, from the Greek desmos, 'band', is the study of ligaments; osteology covers bones, myology muscles and arthrology joints.

Which sweat glands, found mostly in the armpits, are not significant for cooling humans?

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.

How much urine does a typical adult bladder hold before the urge to urinate?

A typical adult bladder holds 300 to 500 ml before the urge to empty becomes pressing, though it can stretch to hold considerably more; its Latin name, vesica urinaria, gives the prefix vesico-.

What is the medical term for knock-knee, where the femurs converge until the knees touch?

Genu valgum is knock-knee, the knees angling inward to touch while the ankles stay apart; bow-leggedness, with the knees apart, is the opposite condition, genu varum.

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

Fascicles are bundles of muscle fibres wrapped in a sheath called the perimysium; each fibre is itself packed with myofibrils made of repeating sarcomeres.

Which bone cells resorb bone tissue?

Osteoclasts are large multinucleated cells that dissolve and resorb bone tissue, while osteoblasts build new bone and osteocytes maintain it; the balance remodels the skeleton continuously.

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

The cardiac notch is the indentation in the front edge of the left lung that makes room for the heart; it is also why the left lung has only two lobes.

Roughly how long is an adult human kidney?

An adult kidney is about 12 centimetres long, 6 cm wide and 3 cm thick, roughly fist-sized; the bean-shaped organs sit in the retroperitoneal space on either side of the spine.

Which medical prefix comes from the Greek word for liver?

Hepat- comes from the Greek hepar, 'liver', as in hepatitis (inflammation of the liver); the liver sits in the right upper quadrant under the lower right ribs.

Blood accounts for roughly what share of human body weight?

The average adult carries about five litres.

Plasma makes up about what percentage of blood?

Plasma makes up about 55% of blood volume; the remaining 45% is mostly red cells, a share measured as the haematocrit. Plasma itself is about 92 percent water.

Roughly how many hemoglobin molecules does one human red blood cell contain?

Each red blood cell packs about 270 million haemoglobin molecules, each able to bind four oxygen molecules; mature red cells are biconcave discs with no nucleus.

How long do healthy human red blood cells circulate before being recycled?

Red cells circulate for about 100 to 120 days before macrophages in the spleen and liver break them down and recycle the iron; newborns' cells last only about 80 to 90 days.

Platelets are fragments of cytoplasm shed by which bone-marrow cells?

Platelets bud off from megakaryocytes, giant bone-marrow cells that each shed thousands of fragments; the platelets lack a nucleus, and true platelets occur only in mammals.

What is the scientific name for white blood cells?

Leukocytes, the white blood cells, include neutrophils, lymphocytes and monocytes; unlike red cells and platelets, all of them have nuclei.

How much fluid does the lymphatic system return to the blood each day?

The lymphatic system returns about 3 litres of fluid to the blood each day: capillaries filter roughly 20 litres into the tissues daily and reabsorb about 17 directly.

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 archaic vertebrates lack a pineal gland entirely?

Hagfish, jawless and nearly blind, lack a pineal gland; lampreys, the other living jawless fish, have one, and in some reptiles it links to a light-sensing 'third eye'.

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

Andreas Vesalius, born in Brussels, published the seven-book Fabrica in Basel in 1543 and later served as physician to Emperor Charles V.

At which university did Vesalius hold the chair of surgery and anatomy from 1537?

Vesalius took the chair of surgery and anatomy at Padua in December 1537, straight after graduating there; his public dissections in Padua supplied the material for the Fabrica.

How old was Vesalius when the first edition of the Fabrica was published?

Vesalius was 28: born on 31 December 1514, he saw the first edition of the Fabrica, in seven books, appear in June 1543 and overturn many of Galen's long-dominant teachings.

In which ancient city, now Bergama in Turkey, was the physician Galen born?

Galen was born in Pergamon in AD 129, a Greek city in Asia Minor famed for its library and its temple of Asclepius; the site is modern Bergama.

Which Roman emperor did Galen serve as court physician?

Galen became court physician to Marcus Aurelius in Rome around AD 169 and later treated his son Commodus; he wrote in Greek, and his works dominated medicine for more than a thousand years.

Which four humors underpinned Galen's understanding of medicine?

Galen built on the Hippocratic theory of four humors: black bile, yellow bile, blood and phlegm, set out in the treatise On the Nature of Man; health meant keeping them in balance.

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

Gray and Carter dissected unclaimed bodies for 18 months to produce the book.

At which London hospital's medical school did Henry Gray lecture on anatomy?

Henry Gray spent his whole career at St George's Hospital in London, entering as a student in 1845 and rising to lecturer on anatomy; he was elected a Fellow of the Royal Society at 25.

Which disease killed Henry Gray in 1861 at age 34?

He was struck by confluent smallpox, the deadliest form.

Which prefix, from the Greek for shoulder, refers to the shoulder blade in medical terms?

Omo- comes from the Greek omos, 'shoulder', as in the omohyoid muscle and omoplate, an old name for the shoulder blade; the Greek word is cognate with the Latin humerus.

How many bones make up the appendicular skeleton?

The appendicular skeleton has 126 bones: the two pectoral girdles (4), the upper limbs (60), the pelvic girdle (2) and the lower limbs (60).

What is the large opening in the base of the skull for the spinal cord called?

The foramen magnum, Latin for 'great hole', is the opening in the occipital bone at the base of the skull through which the brainstem continues into the spinal cord.

Which two structures make up the human skull?

The facial skeleton evolved from the first pharyngeal arch.

Which two bones does the scapula connect?

The scapula connects the humerus and the clavicle: its glenoid cavity holds the head of the humerus, and its acromion meets the clavicle at the acromioclavicular joint.

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

The Achilles, or calcaneal, tendon is the thickest and strongest tendon in the body; it anchors the gastrocnemius, soleus and plantaris muscles to the heel bone and bears several times body weight when running.

Which type of joint is the elbow?

The elbow is a hinge joint: the trochlea of the humerus fits the ulna's notch so the forearm can only flex and extend, while turning the palm comes from the separate radioulnar joints.

The vagus nerve is which numbered cranial nerve?

The vagus is the tenth cranial nerve, CN X; it wanders from the brainstem to the heart, lungs and gut, supplying most of the parasympathetic output that slows heart rate and drives 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, bounded by the hamstring and calf muscles, through which the popliteal artery and vein and the tibial nerve pass.

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

Ūva is Latin for grape, and a swollen uvula was itself once called an ūva; its other name is staphyle.

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

The sinoatrial node sits in the wall of the right atrium near the opening of the superior vena cava; this 15-mm strip of specialised muscle, also called the Keith-Flack node, fires each heartbeat.

Who discovered the hormone-producing islets of the pancreas in 1869?

The German pathological anatomist gave his name to the islets, which make up only 1-2% of the pancreas but take 10-15% of its blood flow.