50 Fun Facts About Human Body Trivia for Seniors

How many bones does an adult human normally have?

About 206. A baby is born with dozens more, somewhere between 270 and 300, because many bones start out as separate pieces that fuse together as the child grows.

Which is the longest bone in the human body?

The thigh (femur). It makes up about a quarter of a person's height, which is why forensic scientists can estimate how tall someone was from a single thigh bone.

Where in the body is its smallest bone, which is shaped like a stirrup?

In the ear. Called the stapes, Latin for stirrup, it is the last in a chain of three tiny bones that carry sound vibrations from the eardrum to the inner ear.

Which is the only bone in the body that is joined to no other bone?

The hyoid, in the throat. This U-shaped bone hangs from muscles and ligaments alone, and it anchors the tongue, which is what lets us swallow and speak.

Roughly how big is the human heart usually said to be?

The size of a closed fist. It sits slightly left of centre, which is why the left lung is the smaller of the two, with a notch in it to make room.

A resting adult heart beats 60 to 100 times a minute; whose normally beats just 40 to 60?

Athletes. Years of training enlarge and strengthen the heart, so it shifts more blood with every beat and can get by on far fewer of them.

Which heart chamber pumps blood around the body?

Left ventricle. Its wall is about three times as thick as the right ventricle's, which only has to push blood the short distance to the lungs and back.

Which is the largest artery in the body, carrying blood out of the heart?

The aorta. Its elastic wall stretches with every heartbeat and springs back between beats, which keeps blood moving even while the heart is refilling.

Which iron-containing protein carries oxygen in red blood cells and gives blood its colour?

Haemoglobin. It is bright red when loaded with oxygen and dark red without it, never blue, whatever the colour of the veins on the back of your hand.

Roughly how long does a red blood cell live before the body recycles it?

About four months. A red cell has no nucleus, so it cannot repair itself, and after roughly 120 days of squeezing through tiny vessels it is filtered out and broken down in the spleen.

Which 1901 discovery by Austrian doctor Karl Landsteiner finally made blood transfusions safe?

Blood groups. Landsteiner noticed that mixing blood from two people often made the red cells clump together, worked out why, and won a Nobel Prize for it in 1930.

Which is the largest organ of the human body?

The skin. As well as keeping water in and germs out, it works as a chemical factory, making vitamin D whenever sunlight falls on it.

Which pigment gives skin its colour and helps protect it from the sun's ultraviolet rays?

Melanin. A suntan is this defence in action: when sunlight starts to damage them, cells called melanocytes make extra pigment and the skin darkens.

Which is the heaviest internal organ and the body's largest gland?

The liver. It can regrow lost tissue, which is why a living donor can give part of a liver to someone else and have the rest grow back.

What fluid does the body's largest gland make to help digest fats?

Bile. It works like a detergent, breaking fat into tiny droplets that digestive juices can attack, and it waits in the pear-shaped gallbladder until a meal arrives.

The kidneys are often described as being shaped like which food?

A bean. The kidney bean is in fact named after the organ, not the other way round, and each kidney packs in about a million tiny filters called nephrons.

What releases the 'fight or flight' hormone when we are frightened?

The adrenals. These two small glands sit on top of the kidneys, and their name says so: 'adrenal' is built from the Latin for 'near the kidneys'.

Which hormone, made in the pancreas, controls the level of sugar in the blood?

Insulin. Its name comes from the Latin for island, because it is made in little islands of cells scattered through the pancreas.

Which butterfly-shaped gland in the neck controls how fast the body burns energy?

The thyroid. It needs iodine to make its hormones, and without enough it swells into a goitre, which is why iodine is added to table salt.

The small intestine is the longest part of the gut, so what does the 'small' in its name describe?

Its width. The tube is only two or three centimetres across, yet it runs for several metres and takes in most of the nutrients we get from food.

Which is the last part of the digestive tract, where water is absorbed and waste is stored?

The large intestine. It is also home to vast numbers of bacteria, which feed on what we cannot digest and make vitamin K for us in return.

How many adult teeth does a person usually have, wisdom teeth included?

32. A child gets by with only 20 baby teeth, and the extra adult ones replace nothing: they grow in at the back as the jaw gets longer.

Which type of teeth do the cutting at the front of the mouth?

Incisors. Standing at the very front, the upper middle pair are also the teeth most often chipped or knocked out in accidents.

What is the hardest substance in the human body?

Tooth enamel. It is 96 percent mineral, yet acids from food and drink can still wear it away, and because it contains no living cells it never grows back.

Wisdom teeth are the last to arrive; at about what age do they usually come through?

Around 20. They turn up so long after the other teeth, when a person has reached adulthood, that they were named for wisdom.

Which is the coloured part of the eye that controls the amount of light getting in?

The iris. One ring of muscle in it tightens the pupil in bright light, and a second set, arranged like the spokes of a wheel, pulls it wide in the dark.

Which cells in the eye let us see colour in good light?

Cones. Rods take over in dim light but play little part in telling colours apart, which is why the world fades towards grey at dusk.

Besides hearing, what else does the human ear look after?

Balance. Three fluid-filled loops in the inner ear work as motion sensors: whenever the head turns, the fluid sloshes and tells the brain which way it moved.

Which spiral part of the inner ear does the actual hearing?

The cochlea. Its name is Latin for snail shell, and the thousands of tiny sensory cells inside it never grow back once loud noise has killed them.

Which is the fifth basic taste, alongside sweet, sour, salty and bitter?

Umami (savoury). Japanese chemist Kikunae Ikeda pinned it down in 1908 while asking what made seaweed broth so tasty, then turned his answer into the seasoning MSG.

Muscles can only pull, never push, so how are most arranged?

In pairs. When the biceps pulls the elbow bent, the triceps on the other side of the arm relaxes, then takes its turn and pulls the arm straight again.

Where in the body is its largest single muscle?

The buttock. The gluteus maximus is the main muscle for straightening the hip, which makes it the engine of running and of lifting heavy weights.

The masseter, one of the strongest muscles for its size, is used for what?

Chewing. Clench your teeth and you can feel it bulge at the back of each cheek; it is especially powerful in animals that grind plants all day.

Which part of the brain, whose name is Latin for 'little brain', fine-tunes movement and coordination?

The cerebellum. It takes up only about a tenth of the brain's volume, yet its tiny, densely packed cells outnumber the neurons in all the rest put together.

Roughly how much does an adult human brain weigh?

About 1,300 grams. That is only around 2 percent of body weight, yet the brain uses about a fifth of all the energy the body burns.

Which cranial nerve, Latin for 'wandering', reaches the heart and gut?

The vagus. True to its name it wanders through the chest and abdomen, carrying the 'rest and digest' signals that slow the heartbeat and set the gut to work.

Which is the longest and widest nerve in the body, running from the hip to the foot?

The sciatic. Pressure on it, often from a slipped disc in the lower back, is what causes the shooting leg pain known as sciatica.

Body temperature rises and falls over each day; when is it usually at its lowest?

Before dawn. It bottoms out about two hours before a person normally wakes and climbs again through the day, so the famous 37 °C (98.6 °F) is only an average.

A hiccup is a sudden contraction of which muscle?

The diaphragm. A split second after it jerks, the vocal cords snap shut on the incoming breath, and that sudden stop is what makes the 'hic'.

Goose bumps are caused by tiny muscles pulling on what?

Body hairs. In furry animals the same reflex fluffs up the coat to trap warm air, or to look bigger when threatened; on us it only raises bumps.

A fingerprint is the impression left by what?

The friction ridges on the fingertip. They form in the womb and last for life, and even identical twins, who share their genes, end up with different prints.

Fingernails, toenails and hair are all made mainly of which tough protein?

Keratin. The part of a hair you can see is dead keratin with no nerve endings in it, which is why a haircut doesn't hurt.

Which part of the cell is nicknamed 'the powerhouse' because it makes the cell's energy?

The mitochondrion. It is thought to have begun as a free-living bacterium swallowed by a larger cell, which is why it still carries its own DNA, passed down from the mother.

In the dreaming stage of sleep known as REM, what do the three letters stand for?

Rapid eye movement. The eyes dart about behind closed lids while the arms and legs lie temporarily paralysed, which stops us acting out our dreams.

Drinking far too much water too fast can kill by leaving the blood short of which mineral?

Sodium. With too little of it in the blood, water floods into the body's cells and swells them, and the pressure that builds in the brain can be fatal.

What is the outer, waterproof layer of the skin called?

The epidermis. It never stops renewing itself: new cells form at its base, are pushed up to the surface as they die, and flake away to be replaced.

What causes the natural blind spot in each of our eyes?

The optic nerve. Where it leaves the back of the eye there are no light-detecting cells at all, but the brain fills in the gap so smoothly that we never notice.

How much urine can a healthy adult bladder comfortably hold?

About 400 ml. That is a little under two cups: the bladder is a muscular bag that stretches like a balloon as it fills, then squeezes itself empty.

Which part of the eye turns cloudy when a person develops a cataract?

The lens. Its proteins break down and clump together with age, fogging the view, and surgeons cure it by swapping in a clear artificial lens.

What fills the inside of many bones and makes the body's new blood cells?

Marrow. It makes every red cell, white cell and platelet in the blood, which is why a marrow transplant can rebuild a patient's whole blood supply.