179 Fun Facts About The Human Body

How many bones are in the adult human body?

206, far fewer than a newborn has, because many of a baby's bones fuse together as the body grows.

What is the largest organ in the human body?

Skin keeps water in and germs out, which is why burns over a large area bring dangerous fluid loss and infection.

Which type of blood cell is responsible for fighting infections?

White blood cells; the pus in an infected wound is largely made of ones that died fighting the infection.

What is the hardest substance in the human body?

Tooth enamel, which can't regrow once damaged, because the cells that made it die off around the time the tooth erupts.

Which chamber of the heart pumps blood to the entire body?

The left ventricle, whose walls are much thicker than the right ventricle's because it pushes blood round the whole body, not just the lungs.

An extra chromosome 21 causes which condition?

Down syndrome; its risk climbs with the mother's age, yet most babies with it are born to younger mothers.

What is the smallest bone in the human body?

The stapes, named for its stirrup shape, is the last link in the chain of tiny bones that carries sound into the inner ear.

Which organ is primarily responsible for filtering blood and producing urine?

The kidneys, which filter well over a hundred litres of fluid a day but turn only a litre or two of it into urine.

Which small brain region controls body temperature, hunger, thirst and circadian rhythms?

The hypothalamus, the body's thermostat; a fever is it turning the set point up in response to an infection.

What pigment gives human blood its red color?

Hemoglobin, an iron-containing protein; when iron runs short the body can't make enough of it, and people turn noticeably pale.

What is the longest bone in the human body?

The femur (thighbone) is the longest, heaviest, and strongest bone in the human body, making up about a quarter of a person's total height.

Approximately how many taste buds does the average human tongue have?

About 2,000 to 8,000, and the taste cells inside them are replaced every week or two.

What is the primary job of platelets?

Platelets stop bleeding by clumping into a plug; aspirin disables them for their whole 8 to 9 day life, which is why it raises bleeding risk.

Which vitamin does the body make for itself when sunlight falls on the body's outer surface?

Vitamin D; with enough summer sunshine most people can make all they need, so unlike other vitamins it is only conditionally essential in the diet.

How many liters of blood does an average adult human body contain?

The average adult body contains about 5 liters (roughly 1.3 gallons) of blood, which makes up about 7% of total body weight.

What is the tough fibrous protein that forms hair and nails?

Keratin, the same protein that builds feathers, claws, hooves and even rhinoceros horn.

Which part of the digestive system absorbs most of the nutrients from food?

The small intestine, called small for its narrow width even though it is the longest part of the gut.

What is the medical term for a resting heart rate below 60 beats per minute?

Bradycardia, which is common in trained athletes, whose efficient hearts can pump enough blood with fewer beats.

Which organ produces bile?

The liver, which can regrow after much of it is removed, so a living donor can give more than half of theirs to a patient.

Stepping into bright sunlight makes up to a third of people do what?

Sneeze: the photic sneeze reflex, nicknamed ACHOO syndrome, affects roughly 18 to 35% of people and runs in families.

What is the name of the thin membrane that covers the outside of bones?

The periosteum is a dense layer of connective tissue that covers the outer surface of most bones. It contains nerves and blood vessels that nourish the bone.

Which hormone lowers blood sugar levels?

Insulin; a 13-year-old Toronto boy dying of diabetes became the first person ever treated with an injection of it.

Approximately how many neurons are in the human brain?

About 86 billion, joined by a roughly equal number of non-neuronal cells.

What type of joint is the knee?

The knee is classified as a modified hinge joint (ginglymus). While it primarily allows flexion and extension, it also permits slight rotation when the knee is bent.

What is the medical term for swelling caused by fluid trapped in the body's tissues?

Edema; pressing a swollen spot can leave a dent that lingers after you let go, a sign doctors call pitting edema.

Which tiny hair-like structures sweep mucus up and out of the airways?

Cilia, about 200 on each airway cell; cigarette smoke can shorten them, leaving coughing as the backup way to clear mucus.

What is the name of the structure that connects muscle to bone?

A tendon; tennis elbow is overuse damage to the one that anchors a forearm muscle at the outer elbow.

In adults, where are the body's new oxygen-carrying blood cells made?

Bone marrow, mostly in the pelvis, sternum, skull and vertebrae.

Into which part of the body do the tear ducts drain excess tears?

The nose: the ducts empty into the nasal cavity, which is why crying or watery allergy eyes make your nose run.

What is the colored part of the eye called?

The iris, whose muscles resize the pupil; its fine patterns differ even between a person's own two eyes, so scanners can identify people by it.

What is the name of the valve between the two chambers on the left side of the heart?

The mitral valve, named for its likeness to a bishop's mitre; its two flaps contrast with the three of the tricuspid valve on the right.

Which painful rash comes from the chickenpox virus reawakening in nerve cells, often decades later?

Shingles; the rash usually forms a stripe on just one side of the body, following the nerve where the virus lay dormant.

Which gland is often called the "master gland" because it controls other endocrine glands?

The pituitary gland; Robert Wadlow, the tallest man on record at 2.72 metres, kept growing because an enlarged one flooded him with growth hormone.

What is the medical term for the collarbone?

The clavicle, the S-shaped strut between shoulder blade and breastbone, and the most commonly broken bone in the body.

Which structure connecting the cerebrum to the spinal cord controls breathing and heart rate?

The brainstem; doctors confirm brain death partly by checking that the reflexes it controls, such as pupils reacting to light, are gone.

Which two proteins slide past each other to make a muscle contract?

Actin and myosin; myosin needs ATP to let go of actin, so when ATP runs out after death the muscles lock in rigor mortis.

During which stage of sleep do most vivid dreams happen while the body is almost paralysed?

REM sleep; when that paralysis fails, people act out their dreams, kicking, punching or even jumping out of bed.

What is the function of the epiglottis?

Its job is to keep food out of the airway by folding back over the entrance to the windpipe as you swallow.

Which part of the eye is responsible for detecting light and sending signals to the brain?

The retina; where the optic nerve leaves it there are no light-sensing cells, which gives every eye a blind spot.

What is the largest single muscle in the human body?

The gluteus maximus is the largest muscle in the human body. It makes up the bulk of the buttocks and is essential for maintaining an upright posture and climbing stairs.

What is the name of the process by which cells divide to produce two identical daughter cells?

Mitosis; meiosis, by contrast, halves the chromosome number to make egg and sperm cells.

Which small organ stores and concentrates bile until fat arrives in the gut?

The gallbladder, which the body can do without: removing it, often because of gallstones, is one of the most common operations.

What is the technical name for the kneecap?

The patella, the body's largest sesamoid bone; babies are born with a cartilage kneecap that only starts turning to bone at about age three.

What is the Broca's area of the brain primarily responsible for?

Broca's area, located in the left frontal lobe, is crucial for speech production and language processing. Damage to it causes Broca's aphasia, where a person understands language but struggles to speak fluently.

Approximately how many cells are in the human body?

37 trillion by one widely cited count, and the bacteria living in and on the body number about the same.

A sprained ankle is an injury to which kind of tissue?

A ligament, usually on the outer side of the ankle, stretched or torn when the foot rolls inward.

What is the medical term for low blood sugar?

Hypoglycemia; starved of sugar, the brain can leave a person shaky and confused, and severe cases can cause seizures.

Which spiral of the inner ear turns sound vibrations into nerve signals?

The cochlea, named from the Latin and Greek for snail shell; cochlear implants can give deaf people a sense of sound by stimulating its nerve directly.

Which type of blood vessel carries blood away from the heart?

Arteries, though not all carry oxygen-rich blood: the pulmonary arteries take oxygen-poor blood to the lungs.

Which salivary enzyme starts breaking down starch before you've even swallowed?

Salivary amylase (also called ptyalin) begins breaking down starches into simpler sugars as soon as food enters the mouth. This is why bread tastes slightly sweet if chewed for a long time.

What is the outermost of the body's main integumentary layers called?

The epidermis, which has no blood vessels of its own and takes in much of its oxygen straight from the air.

Which mineral, the most abundant metal in the human body, is stored mostly in the bones?

Calcium; when blood levels fall, bone-dissolving cells release some of the skeleton's store back into the blood.

Which blood type is considered the 'universal donor'?

O-negative; with no A, B or RhD antigens on its cells, it can be given in an emergency before a patient's blood type is known.

Which part of the brain, tucked low at the back of the skull, fine-tunes movement and balance?

The cerebellum holds more than half of all the brain's neurons in about a tenth of its volume, and alcohol disrupts it, hence the drunken stagger.

Which dome-shaped muscle does most of the work of breathing?

The diaphragm flattens as it contracts, pulling air in; a hiccup is a spasm of it followed by the vocal cords snapping shut.

Which part of the digestive system mainly absorbs water and turns what is left of food into stool?

The large intestine is also home to most of your gut bacteria, which ferment whatever you could not digest.

Which gland behind the stomach produces the hormones that regulate blood sugar?

The pancreas: in 1889, when two doctors removed one from a dog, the dog developed diabetes.

The hammer, anvil and stirrup of the middle ear are known collectively as what?

The ossicles, a tiny lever system that boosts the eardrum's vibrations so sound can pass from air into the fluid of the inner ear.

Which organelle, the cell's 'powerhouse', generates most of its ATP?

Mitochondria, descended from free-living bacteria that another cell engulfed in the distant past.

What is the small fleshy tab that hangs at the back of the mouth called?

The uvula, which rises with the soft palate as you swallow to stop food going the wrong way, and can vibrate when you snore.

Which protein lets artery walls and lungs snap back after stretching?

Elastin, the stretchy core of elastic fibres, which are built on a scaffold of fibrillin rather than collagen.

Sweat cools the body mainly through which process?

Evaporation, which is why humid days feel so much hotter: when the air is already moist, sweat evaporates less and cools you less.

What is the largest artery in the body?

The aorta arches up from the heart, runs down the abdomen and splits in two at the pelvis.

Which fatty sheath insulates nerve fibres and speeds their electrical impulses?

Myelin; in multiple sclerosis the immune system attacks it, so nerves struggle to carry their signals.

Which bone is better known as the shinbone?

The tibia takes most of the body's weight below the knee; the slender fibula beside it mostly anchors muscles.

Which acid does the stomach lining secrete, strong enough to kill most of the bacteria you swallow?

Hydrochloric acid gives stomach juice a pH of around 1 to 2; a layer of mucus stops it from digesting the stomach itself.

Which hormone is most closely associated with the 'fight or flight' response?

Adrenaline, also called epinephrine, is the drug in an EpiPen; in a fright it boosts heart output, dilates the pupils and raises blood sugar.

Which small pit at the back of the eye gives the sharp central vision needed for reading and driving?

The fovea gives the sharpest sight, and many birds of prey go one better, with a second fovea in each eye.

Which cells in the circulation are primarily responsible for transporting oxygen throughout the body?

Erythrocytes, better known as red blood cells, are packed with an iron-containing protein that picks up oxygen in the lungs and releases it in the tissues.

How many chambers does the human heart have?

Four, which makes the human heart two pumps side by side, one for the lungs and one for the body; a fish's heart is a single pump with two chambers.

Which long bone of the upper arm ends at the elbow?

The humerus narrows just below its rounded head into a 'surgical neck', the most common spot for fractures at the top of the bone.

Which horseshoe-shaped neck bone is held in place by muscles rather than jointed to any other bone?

The hyoid anchors the tongue, and in adults a fractured hyoid strongly suggests strangulation, so forensic examiners check it closely.

Slipped discs happen most often in which part of the spine?

Slipped discs strike the lower back far more than anywhere else, and most people feel better within weeks or months without surgery.

Which soft spots between a newborn's skull bones let the head change shape during birth?

Fontanelles let the head squeeze through the birth canal and leave room for the brain to grow; the largest, on top, usually closes before age two.

Where are over half your bones?

The hands and feet hold more than half of the adult skeleton's bones; each wrist alone is made of eight small carpal bones arranged in two rows.

Gout most often attacks which joint?

The big toe: too much uric acid in the blood forms needle-like crystals in a joint, bringing sudden, severe pain.

Which is the longest muscle in the human body?

The sartorius takes its name from the Latin for tailor, after the cross-legged position tailors once sat in to sew.

Cardiac muscle is described as which two things?

Cardiac muscle is involuntary and striated, and its cells barely renew, so muscle killed in a heart attack is replaced by scar tissue that cannot contract.

Which organ acts primarily as a blood filter and resembles a large lymph node?

The spleen filters out old and damaged blood cells, and people can live without one, though they stay more vulnerable to serious infections for life.

Which type of immune cell matures within the thymus?

T cells take their name from the thymus, which is largest and most active in childhood and starts shrinking in the early teens.

A lack of which element in the diet causes most cases of goitre, a swelling in the neck?

Iodine is why table salt is iodised: Switzerland began adding it in 1922 and cut the goitre that had been widespread across the country.

Appendicitis pain often starts near the belly button, then moves to which part of the abdomen?

Lower right: that is where the appendix sits, and the pain usually shifts there within a few hours and gets worse.

Which gland produces melatonin, the hormone that modulates sleep patterns?

In some amphibians and reptiles, the pineal gland is linked to a light-sensing 'parietal eye' on top of the head.

Roughly how many alveoli does a typical pair of human lungs contain?

Those 480 million or so alveoli give the lungs a gas-exchange surface of around 70 square metres.

The windpipe splits into which two tubes, one per lung?

Of the two bronchi, the right is wider and steeper, so in adults inhaled food or small objects more often lodge on the right.

The trachea is reinforced by 16–20 rings of what?

The hyaline cartilage rings are C-shaped, open at the back of the windpipe, where a band of muscle bridges the gap between their ends.

Which straw-coloured liquid carries the blood cells and makes up over half of blood's volume?

Plasma is over 90% water, and frozen donated plasma is on the World Health Organization's list of essential medicines.

Breaking down old red blood cells produces which yellow pigment, the cause of jaundice?

Bilirubin build-up is why babies with newborn jaundice are placed under blue-green light, a treatment called phototherapy.

Who distinguished the main ABO blood groups in 1901?

Karl Landsteiner's blood groups made safe transfusions possible and won him a Nobel Prize, and World Blood Donor Day falls on his birthday, 14 June.

Which region of the right atrium acts as the heart's natural pacemaker?

The sinoatrial node fires by itself, which is why a transplanted heart, cut off from its nerves, keeps beating, just at a higher resting rate.

What is the double-walled, fluid-filled sac that contains the heart called?

If fluid builds up fast inside the pericardium it can squeeze the heart, a medical emergency called cardiac tamponade.

Bell's palsy affects which nerve?

Bell's palsy is thought to come from swelling that squeezes the facial nerve inside its narrow bony canal, and most people recover within months.

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

The sciatic nerve gives sciatica its name: when it is irritated or compressed, pain can shoot down the back of the leg into the foot.

Which structure connects the left and right cerebral hemispheres?

Cutting the corpus callosum can calm severe epilepsy, and these 'split-brain' patients showed that each hemisphere can perceive and act on its own.

Which brain region consolidates short-term memories into long-term ones?

Surgeons removed much of the hippocampus on both sides in patient H.M. to treat his epilepsy; afterwards he could no longer form new memories of events or facts, yet could still learn motor skills.

Which almond-shaped brain structure plays a key role in processing fear?

The amygdala is named for the Greek word for almond, and a woman known as S.M., whose amygdalae were destroyed by disease, showed no fear handling snakes.

Which neurotransmitter is central to the brain's reward-motivated behaviour?

Dopamine-making neurons die off in Parkinson's disease, so its most widely used treatment, levodopa, is a chemical precursor of dopamine.

Which cranial nerve, the tenth, is the longest of the autonomic nervous system?

The vagus nerve's name is Latin for 'wandering', and it roams from the base of the brain through the neck, chest and abdomen as far as the colon.

Which light-sensing cells in the eye work best in dim light and give black-and-white vision?

Rods vastly outnumber cones but play little part in colour vision, which is the main reason colours fade in dim light.

A sudden loss of which sense proved to be one of the most telling signs of COVID-19?

Loss of smell, called anosmia, was sometimes the only symptom, and one large survey found it predicted COVID-19 better than fever or cough.

What is the medical name for the eardrum?

A burst tympanic membrane usually heals by itself within weeks, and hearing returns to normal.

Which condition makes the spine curve sideways?

Scoliosis most often starts in the growth spurt before puberty, and the skeleton of King Richard III, dug up under a Leicester car park, shows he had it too.

Which specialised cells make the pigment that gives a suntan its colour?

People of every complexion have similar numbers of melanocytes; the difference lies in how much and what kind of melanin those cells produce.

Which type of sweat gland is largely limited to the armpits and perineal area?

Apocrine sweat is odourless when it leaves the gland; body odour appears only once bacteria break it down.

What is the wave of muscle contractions that pushes food along the gut, even if you eat upside down?

Peristalsis is why swallowing works in any position: smooth muscle squeezes in sequence behind each ball of food.

Barry Marshall drank which bacterium, expecting it to give him an ulcer?

Helicobacter pylori gave Barry Marshall gastritis rather than an ulcer, but linking the bacterium to ulcers still won him and Robin Warren a Nobel Prize.

Which clear front part of the eye has no blood vessels and gets its oxygen from air dissolved in tears?

With no blood vessels, the cornea is less prone to rejection, and most corneal transplants improve sight for many years.

Cortisol belongs to which class of steroid hormones?

Glucocorticoids are named for their role in glucose regulation, and as drugs such as hydrocortisone they are used to calm inflammation.

Which hormone is released during childbirth and is linked to social bonding?

Oxytocin triggers the contractions of labour, and as the drug Pitocin it is given to start labour or speed it up.

Antibodies are also known by what name?

Immunoglobulins are Y-shaped, and one type, IgG, crosses the placenta, giving a newborn borrowed protection that can last for months.

Wisdom teeth are formally known as what?

Third molars usually come through in the late teens or early twenties, long after the other teeth, when people were presumed to be wiser.

What is the medical term for a dangerous drop in core body temperature?

Hypothermia sets in below 35 °C, and in severe cases some victims strip off their clothes as they feel falsely overheated, a response called paradoxical undressing.

Approximately how many base pairs does the human genome contain?

Of those 3.1 billion base pairs, only about 1 to 2% actually code for proteins.

Which two joints are the classic examples of ball-and-socket joints?

The hip and shoulder both swivel in many directions, and the shoulder is so mobile that it is the body's most commonly dislocated joint.

What are the specialised cells that make up cartilage called?

Chondrocytes are fed only by diffusion, because cartilage has no blood vessels, which is part of why damaged cartilage repairs so slowly.

Which organ is commonly called the voice box?

The larynx grows at puberty, far more in boys, and its vocal cords lengthen and thicken, which is what makes the voice drop and deepen.

The Adam's apple is formed by the angle of which cartilage?

The thyroid cartilage grows during puberty, more so in men, and its jutting angle helps shield the vocal cords behind it.

Hitting your 'funny bone' actually strikes which nerve?

The ulnar nerve is the body's largest nerve unprotected by muscle or bone, so a knock at the elbow sends a jolt toward the little finger.

Being short-sighted, so that distant things look blurry, is known medically as what?

Myopia usually begins in childhood, and time spent outdoors appears to lower children's risk of it.

Newborn babies can barely shiver, so to make heat they mainly burn which special tissue?

Brown adipose tissue makes up about 5% of a newborn's body mass, mostly along the upper back, and burns energy purely to release heat.

Which anatomist discovered the hormone-making islets, now named after him, in 1869?

Paul Langerhans described the islets in his doctoral research without knowing what they did, and they were later named in his honour.

Which hormone signals the body to release stored sugar when blood sugar drops too low?

Glucagon is also an emergency medicine: an injection can raise blood sugar in someone who is unconscious and cannot swallow sugar.

Veins often look blue, but what colour is the blood inside them?

Dark red: blood low in oxygen is darker than oxygen-rich blood, and veins look blue because of the way light scatters in the body.

Which digit of the hand has only two phalanges?

The thumb has just two phalanges, but a saddle-shaped joint at its base lets it swing round to touch the other fingertips.

Scurvy, which makes gums bleed and old wounds reopen, is caused by a lack of which vitamin?

Vitamin C is needed to build collagen, the protein that holds gums, blood vessels and healing wounds together, so without it they start to break down.

Which germ-eating cells are the most common type of immune cell in human blood?

Neutrophils are among the first cells to rush to an infection, and the whitish-yellow pus of an infected wound is mostly dead neutrophils.

Which of these differs even between identical twins, who share nearly all their DNA?

Fingerprints form in the womb as each fetus touches different parts of its surroundings, so even identical twins end up with different patterns.

Which are the smallest blood vessels in the body?

Capillaries are only 5 to 10 micrometres wide, barely wider than a blood cell, and they are where oxygen passes from the blood into the tissues.

Which newborn reflex makes a startled baby fling its arms wide?

The Moro reflex normally fades by about six months, and a lopsided one can point to a nerve injury from birth.

The topmost bone of the spine, which holds up the skull, is named after which Greek mythological figure?

Atlas held up the heavens in myth, just as the atlas vertebra carries the head. The joint it forms with the skull is what lets you nod 'yes'.

Humans and giraffes have the same number of vertebrae in the neck: how many is that?

The 7 neck vertebrae are a rule nearly all mammals share. A giraffe's are simply stretched, each one over 28 cm long.

When you hold your breath, the urge to breathe comes from a build-up of which gas?

Carbon dioxide, not a shortage of oxygen, sets off the alarm. Divers who over-breathe before a dive flush it out and can black out with no warning.

Tiny muscles pulling each body hair upright when you are cold or frightened produce which familiar effect?

Goosebumps once did a job: in furry animals the raised hairs trap a layer of insulating air. Porcupines use the same reflex to lift their quills.

The human navel is a scar marking the spot where which structure was attached before birth?

Umbilical cord scars are one of a kind. Because the navel is a scar, every belly button is unique to its owner.

The 'lub-dub' of a heartbeat heard through a stethoscope is the sound of what happening?

Valves snapping shut make both sounds. 'Lub' is the pair between the upper and lower chambers closing; 'dub' is the pair at the exits.

Which metal lets red blood cells carry oxygen, with one atom binding each oxygen molecule picked up?

Iron does the gripping. Each oxygen-carrying molecule in a red blood cell holds four iron atoms, so it ferries four oxygen molecules at a time.

Injections given in the upper arm usually go into which thick, triangular muscle?

Deltoid comes from the muscle's shape, like the Greek capital letter delta. It is the prime mover when you raise your arm out to the side.

The point where the optic nerve leaves each eye has no light-detecting cells, creating what?

Blind spot is the name, and you never notice yours because the brain fills the gap using surrounding detail and the view from the other eye.

Which protein, the most abundant in mammals including humans, takes its name from the Greek for glue?

Collagen was named for the old practice of boiling animal hides and sinews to make glue. It makes up 25 to 35% of the protein in a mammal's body.

Which small bone at the very base of the spine is the remnant of a tail?

Coccyx comes from the Greek for cuckoo, because its last few fused segments look like the bird's beak when seen from the side.

Rescuers giving CPR press down on the lower half of which flat bone in the chest?

Sternum is the breastbone, and good compressions push it down 5 to 6 cm in an adult, hard enough that ribs sometimes break.

Which bone, the largest and strongest in the skull, is the only one you can move at will?

Mandible is the anatomical name for the lower jaw, which hinges on the temporal bones at either side of the head so you can chew and talk.

Eight small bones called carpals, arranged in two rows, make up which part of the body?

Wrist is what the Greek word karpos means, hence carpals. The boat-shaped scaphoid is the one of the eight most often fractured.

What is the smooth patch between the eyebrows called, from the Latin for 'hairless'?

Glabella pinching is a quick bedside check for dehydration: doctors gently lift the flesh there to see how readily it springs back.

What are the fairly rigid, fibrous joints between the bony plates of the skull called?

Sutures are held together mainly by tiny fibres that grow out of each bone into the one next to it, stitching the plates edge to edge.

Which pair of lymphoid organs at either side of the back of the throat is often surgically removed?

Tonsils are part of the immune system's front line, but surgeons take them out when they keep getting infected or swell enough to hinder swallowing.

A boy's voice deepens during puberty because which structures in the throat grow longer and thicker?

Vocal cords are a pair of folds that vibrate as air from the lungs is pushed between them. Sex hormones drive the change at puberty.

Which transparent part of the eye changes shape to focus and turns cloudy when cataracts form?

Lens focusing fades with age too, which is why reading glasses become necessary: the eye gradually loses its ability to focus on nearby objects.

Which group of three muscles at the back of the thigh bends the knee and is often strained by sprinters?

Hamstrings take their name from the Old English 'ham', the bend of the knee, plus the string-like cords you can feel on either side behind it.

What is the junction where one neuron passes a signal to the next, across a gap of about 20 nanometres?

Synapse entered science in 1897, when the physiologist Charles Sherrington needed a word for a union between two separate elements.

Phineas Gage's personality reportedly changed after a metal bar was blasted through which part of his brain?

Frontal lobe damage left the railroad foreman, in his friends' words, 'no longer Gage'. He survived the 1848 accident by 12 years.

Which natural painkillers, made in the brain, are released during vigorous exercise and lift feelings of well-being?

Endorphins take their name from a contraction of 'endogenous morphine', meaning morphine made inside the body. They work by blocking the perception of pain.

About 90% of which mood-linked chemical messenger is made in the gut, not the brain?

Serotonin made in the gut wall has a humbler job than its famous role in mood: it regulates the movements of the bowel.

Which itch-causing chemical, released by mast cells in allergic reactions, do many allergy tablets block?

Histamine is a central trigger of itching. The first tablets made to block it also slipped into the brain, which is why they cause drowsiness.

Which waxy substance, carried in the blood as 'good' HDL and 'bad' LDL, builds up in plaques in vessel walls?

Cholesterol is not all bad: every animal cell makes its own, and it is an essential building block of cell membranes.

Around 65% of adults worldwide have trouble absorbing which sugar found in milk?

Lactose is split by an enzyme that dwindles in most people as they grow up. As few as 5% of northern Europeans are affected, but up to 90% of adults in parts of Asia.

Coeliac disease is an abnormal immune reaction to which protein found in wheat, barley and rye?

Gluten sets off inflammation that damages the lining of the gut in people with the condition, so the only treatment is cutting it out for life.

Which nutrient, which the body can make from the beta-carotene in carrots, is needed to see in dim light?

Vitamin A shortage first shows as trouble seeing at night, and left untreated it can progress to blindness in children.

Most human cells carry how many chromosomes, half inherited from each parent?

46 was only confirmed in 1956. For three decades before that the accepted count was 48, after an early microscope miscount was copied by others.

The FAST checklist of a drooping face, a weak arm and slurred speech helps people spot which medical emergency?

Stroke comes in two kinds, a blocked blood supply to part of the brain or a burst vessel. The T in FAST stands for time to call emergency services.

Which condition, commonest in women after menopause, thins the bones until they fracture easily?

Osteoporosis speeds up after menopause because levels of oestrogen fall. It is the most common reason for a broken bone among the elderly.

Which inherited clotting disorder, 'the royal disease', did Queen Victoria pass to royal families across Europe?

Hemophilia reached the Russian throne this way: Tsarevich Alexei inherited it through his mother Alexandra, one of Victoria's granddaughters.

Which sense of body position and movement lets you clap with your eyes closed?

Proprioception is what a roadside sobriety test probes: alcohol blunts it, so drinkers struggle to touch their own nose with their eyes shut.

Between 50% and 80% of amputees feel pain in an arm or leg that is no longer there: what is this called?

Phantom limb pain is generated by the brain itself, which goes on perceiving a body part after it has been surgically removed.

Which temporary organ grows during pregnancy to nourish the fetus and is expelled shortly after the birth?

Placenta is Latin for a kind of flat cake, a nod to its round, flat shape. Delivering it is known as the third stage of labour.

Which basin-shaped ring of bones is wider in women, a shape that evolved for childbirth?

Pelvis shape is often explained as a compromise between two demands, a wide birth canal and efficient walking, an idea known as the obstetrical dilemma.

Swallowing makes your ears 'pop' on a plane by opening which passage to the middle ear?

Eustachian tube walls normally stay collapsed; swallowing opens them so middle-ear pressure can match the cabin's. The name honours the anatomist Bartolomeo Eustachi.

Which slender bone runs down the outer side of the lower leg yet carries almost none of the body's weight?

Fibula is, for its length, the most slender of all the long bones. Its thicker neighbour, the shinbone, does the load-bearing.

Which veins in the neck carry blood from the head back towards the heart?

Jugular veins come in two sets, internal and external, and doctors watch the pulse in them for clues to heart and lung disease.

Which English physician showed in a 1628 treatise that the heart pumps blood around the body in a circuit?

William Harvey published it in Frankfurt, home of an annual book fair that he knew would spread his 72-page work quickly.

Which anatomist's 1543 book 'On the Fabric of the Human Body' earned him the title founder of modern anatomy?

Andreas Vesalius broke the long dominance of the ancient physician Galen, and dedicated the seven-book work to Emperor Charles V.

Which 'hunger hormone', produced mainly in the stomach, increases the drive to eat?

Ghrelin levels in the blood peak just before a meal, when you feel hungriest, and fall back once you have eaten.

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

Lunula tissue is not actually white: it only looks pale because a thickened layer beneath the nail hides the blood vessels below.

What is the vertical groove in the middle of the upper lip, named from the Greek for 'love charm'?

Philtrum grooves do real work in most mammals, carrying dissolved odours from the wet snout to a sensing organ inside the mouth.

Which everyday reflex, known to doctors as singultus, afflicted American Charles Osborne for 68 years?

Hiccups struck Osborne from 1922 to 1990, an estimated 430 million of them, which put him in Guinness World Records.

Which stomach enzyme, named from the Greek for digestion, starts breaking proteins into smaller pieces?

Pepsin was one of the first enzymes ever discovered, found in 1836 by Theodor Schwann, who also gave it its name.

Which tiny finger-like projections line the gut wall, multiplying its surface area for absorbing nutrients?

Villi are each about a millimetre long and are themselves carpeted with microvilli around 1,000 times shorter still.

Which term, coined by Walter Cannon in 1926, means the body keeping its internal conditions stable?

Homeostasis built on the work of Claude Bernard, the French physiologist who first described the body regulating its internal environment.

Which three fluid-filled tubes in the inner ear detect the rotation of the head?

Semicircular canals sit at right angles to one another, so that between them they can pick up a turn of the head in any direction.