Big numbers
37 trillioncells in an adult body, about
100,000heartbeats a day
60,000miles of blood vessels
206bones in an adult
Babies are born with nearly 300 bones; many fuse together as we grow.
Parts that rebuild
| Part | How often it renews | Note |
|---|---|---|
| Stomach lining | Every few days | Protects against its own acid |
| Outer skin | About every month | Much household dust is old skin |
| Red blood cells | About every 4 months | Millions made every second |
| Skeleton | About every 10 years | Bone is living tissue |
These are rough averages and vary by person and age.
Surprising facts
You're half microbe
Bacteria in your body roughly match your own cells in number
Your brain is hungry
About 2% of body weight, 20% of the energy
Your eyes adjust fast
Pupils react in a fraction of a second
You're taller in the morning
Spine discs compress during the day
Remember
Your body is quietly rebuilding itself every day.
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Answer key
- About how many times does your heart beat each day?100,000Roughly 100,000 beats a day.
- How many bones are in an adult body?206Babies start with nearly 300; many fuse.
- About how long are all your blood vessels end to end?60,000 milesAbout 60,000 miles, more than twice around the Earth.
- How much of your energy does your brain use?About 20%About 20%, though it's only about 2% of body weight.
- Why are you taller in the morning?Spine discs decompress while lying downDiscs compress during the day and recover at night.