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The Human Body: fun facts and quiz
The essentials in 7 ideas, with fun facts, an illustrated story and a quiz to see how much you know.
The essentials
Bones
An adult skeleton has 206 bones. Babies are born with around 300, but many of them fuse together as they grow.
Key fact
The smallest bone, the stirrup, is deep inside your ear.
The Heart
Your heart is a muscle about the size of a fist. It pumps blood around your body, beating around 100,000 times a day.
Key fact
A resting adult heart beats about 60 to 100 times a minute.
Breathing
Your lungs take in oxygen and get rid of carbon dioxide. At rest you breathe about 12 to 20 times a minute, over 20,000 times a day.
Key fact
The left lung is smaller, leaving room for the heart.
The Brain
Your brain has about 86 billion nerve cells. It’s only about 2% of your body weight, but it uses around 20% of your energy.
Key fact
Your brain is about three-quarters water.
Blood
Blood carries oxygen, food and heat around the body. Red cells carry oxygen, white cells fight germs, and platelets help it clot.
Key fact
An adult has about 5 litres of blood.
Digestion
Digestion breaks food into pieces small enough to absorb. It starts in the mouth, carries on in the stomach, and most nutrients are absorbed in the small intestine.
Key fact
The small intestine is around 6 metres long.
Skin
Skin is your largest organ. It keeps germs out, holds water in, and helps control your temperature by sweating.
Key fact
You shed millions of skin cells every day.
Fun facts
More than half of your bones are in your hands and feet.
Your heart has its own electrical pacemaker, so it can keep beating for a while even outside the body.
Your lungs hold hundreds of millions of tiny air sacs, with a total surface of around 70 square metres.
The brain itself feels no pain, which is why some brain surgery is done while patients are awake.
Octopuses have blue blood: it carries oxygen using copper instead of iron.
Your stomach lining renews itself every few days, so its own acid doesn’t wear it away.
Your thinnest skin is on your eyelids; the thickest is on the soles of your feet.
Story: The Doctor Who Tested Himself
The Doctor Who Tested Himself
1929, Germany. Young doctor Werner Forssmann believes a thin tube could reach the heart through a vein. His boss forbids it.
So he tries it on himself: he slides a tube up a vein in his arm, then walks to the X-ray room to photograph it.
It had reached his heart. He lost his job over it, but in 1956 he shared the Nobel Prize in Medicine.
True or false?
Tap your answer to see if you got it, and why.
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Question 1 of 10
Babies have more bones than adults.
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True. About 300 at birth; many fuse to leave 206.
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Question 2 of 10
The heart is a muscle.
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True. A very tireless one: it never takes a day off.
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Question 3 of 10
The left lung is a little smaller than the right.
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True. It has a notch where the heart sits.
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Question 4 of 10
The brain uses about a fifth of the body’s energy.
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True. Around 20%, for only about 2% of your weight.
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Question 5 of 10
White blood cells help fight infections.
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True. They hunt down germs and help the body remember them.
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Question 6 of 10
Most nutrients are absorbed in the small intestine.
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True. Its folded lining gives a huge surface for absorbing food.
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Question 7 of 10
Skin is the body’s largest organ.
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True. It covers about 2 square metres on an adult.
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Question 8 of 10
The thigh bone is the smallest bone in the body.
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False. It’s the longest. The smallest is the stirrup, in the ear.
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Question 9 of 10
Blood leaves the heart through veins.
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False. Arteries carry blood away; veins bring it back.
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Question 10 of 10
The air we breathe out is mostly carbon dioxide.
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False. It’s still mostly nitrogen, with only about 4% carbon dioxide.
Keep going in the app
KnowSoda learns what you know and brings back what you’re about to forget. The Human Body has 6 more ideas at the Advanced and Expert levels.
Sources
- NHS — Health A to Z, how the body works
- NIH MedlinePlus — Anatomy
- American Heart Association — Heart rate
- Herculano-Houzel (2009), “The human brain in numbers”
- Encyclopaedia Britannica — human skeleton, digestion, skin
- NHS — How the kidneys work; the nervous system
- U.S. National Library of Medicine, MedlinePlus — Endocrine glands; muscles
