50 Fun Facts About Human Body Trivia for Seniors

How many bones does an adult human normally have?

Babies start with around 270; many fuse together as we grow, especially in the skull and spine.

Which is the longest in the human skeleton?

It is also the largest and thickest, and the only bone in the upper leg.

The smallest bone in the body is shaped like a stirrup. Where is it?

It is called the stapes and passes sound vibrations to the inner ear. It is one of three tiny bones there.

Which is the only bone in the body not connected to any other bone?

It sits above the voice box, held by muscles, and helps anchor the tongue for swallowing and speech.

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

It sits between the lungs, slightly to the left, with the atria on top and the ventricles below.

Roughly how many times a minute does a healthy adult heart beat at rest?

The American Heart Association counts anything from 60 to 100 as normal. Ultra-trained athletes can be down in the high 30s.

How many chambers does the human heart have?

Blood comes back to the right side, goes to the lungs for oxygen, returns to the left side and is pumped out to the body.

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

It rises from the left ventricle, arches over and runs down to the abdomen, where it splits into the two iliac arteries for the legs.

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

Blood is bright red when it is loaded with oxygen and dark red when it has given the oxygen up.

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

They are made in the bone marrow, at a rate of about 2.4 million a second, and the spleen clears out the old ones.

Which Austrian doctor discovered blood groups A, B and O in 1901?

He first called the third group C. Matching ABO and Rh types made blood transfusion safe.

Which is the largest organ of the human body?

It makes up roughly 16 percent of body weight and covers 1.5 to 2 square metres on an adult.

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

It is made by cells called melanocytes and absorbs some of the harmful UV radiation.

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

It is dark reddish-brown with two unequal lobes, and it can regrow lost tissue better than any other organ.

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

It is stored and concentrated in the pear-shaped gallbladder until a meal arrives.

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

Each one contains around a million tiny filters called nephrons that clean the blood.

Which small organs sit on top of the kidneys and produce adrenaline?

They also make the steroid hormones cortisol and aldosterone. Their other name, suprarenal, just means 'above the kidney'.

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

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

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

It sits just below the Adam's apple. The commonest cause of an underactive one worldwide is too little iodine.

Roughly how long is the small intestine, folded up inside the abdomen?

Despite the name, it is much longer than the colon, just narrower. It has three parts: duodenum, jejunum and ileum.

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

Its colon runs up, across and down the abdomen before reaching the rectum.

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

Children have 20 baby teeth, which usually start appearing at about six months old.

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

Canines tear food, and the molars and premolars at the back crush it.

What is the hardest substance in the human body?

It is 96 percent mineral, but acids from food and drink can still wear it away, and it does not grow back.

Wisdom teeth are the last to come through. When does that usually happen?

If there is no room they can get stuck, or impacted, which is why so many are removed.

Which is the coloured part of the eye that controls how much light gets in?

The pupil is the opening in its middle. The white part is called the sclera.

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

Rods handle dim light and give only grey, low-detail vision, which is why colours fade at dusk.

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

Fluid-filled canals in the inner ear tell the brain which way the head is moving.

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

Its name is Latin for snail shell. The semicircular canals sit next to it.

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

The tongue has 2,000 to 8,000 taste buds, and each one is replaced about every ten days.

Roughly how many muscles are in the human body?

In healthy young adults they make up about 40 percent of body weight.

Which is the largest muscle in the body?

It is the outermost of the three gluteal muscles and gives the hips their shape.

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

It runs from the cheekbone to the jaw. It is especially powerful in plant-eating animals that chew all day.

What are the three main parts of the brain?

The cerebellum, Latin for 'little brain', fine-tunes coordination and timing rather than starting movements.

Roughly how much does an adult brain weigh?

That is about 2 percent of body weight, yet it holds more than 86 billion nerve cells.

How many pairs of cranial nerves run directly from the brain?

They are numbered with Roman numerals I to XII, from the nerves of smell and sight down to the wandering vagus nerve.

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

Pressure on it is what causes the shooting leg pain known as sciatica.

What is the average human body temperature usually said to be?

That figure was set in the 1800s; the normal range is really 36.5 to 37.5. Temperature is lowest about two hours before you normally wake.

A hiccup is a sudden contraction of which muscle?

The 'hic' sound comes when the vocal cords snap shut about 35 milliseconds later. Its medical name is singultus.

Goose bumps are caused by tiny muscles pulling on what?

They appear when we are cold, tickled or feeling strong emotion. Some scientists think the reflex is a leftover from furrier ancestors.

A fingerprint is the impression left by what?

Ink transferred from the peaks of the ridges onto paper gives the classic print used for identification.

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

The same protein makes up the claws, hooves and horns of other animals. Nails grow from living tissue called the matrix.

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

The nickname was popularised by a 1957 Scientific American article. Its inner membrane is folded to make more energy.

Sleep alternates between two main modes. What does REM stand for?

During REM sleep the body is virtually paralysed, which stops us acting out our dreams.

Roughly what share of an adult man's body is water?

That is some 42 litres, most of it inside the cells rather than in the blood.

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

It contains no blood vessels of its own; the deeper dermis beneath it holds the sweat glands and hair roots.

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

It sits about 15 degrees to the outside of centre, and the brain fills in the gap so we never notice it.

How much can a normal bladder comfortably hold?

Urine trickles in from the kidneys every 10 to 15 seconds, and a full bladder signals the brain when it is time to go.

By about what age has the human eyeball reached its full adult size?

It grows from around 16 mm across at birth to about 24 mm, and left and right eyes end up the same size.

Roughly what share of a person's total body weight is bone?

That is around 10 to 11 kilograms for an average adult, with bone mass peaking between the ages of 25 and 30.