Your body has lots of organs — special parts, each doing a job. Here are six of the most important ones, all working right now while you read this.
Right now, your heart is squeezing — about 100 times a minute when you're a kid. Each squeeze sends blood with food and oxygen everywhere it's needed.
If you sit very still and put your fingers on the side of your neck, you can feel each beat — like a tiny tap-tap-tap-tap.
Your body grows mostly when you sleep. While you're asleep, the brain sorts out everything you saw during the day, the bones get longer, scrapes heal, and tired muscles fix themselves.
That's why kids need 10–12 hours of sleep, but grown-ups only need 7–8. You're building a person.
Every part of you — skin, bone, brain, blood — is made of tiny pieces called cells. You have 37 trillion of them. (That's 37 followed by twelve zeros.)
Most cells live a few days, then die and are replaced. So in a real sense, the "you" of seven years ago is mostly gone. But your brain is still you, your memories are still yours, and so is the smile.