Your body is amazing. Did you know you have more than 200 bones and 600 muscles? Your nerves carry messages from your brain to make those muscles cooperate so you can stand up and move around. Your blood vessels could stretch all the way around the planet! White blood cells stand guard like soldiers waiting to attack any invader. Your heart, lungs, stomach, and other organs are at work 24 hours a day for your entire life. There are too many parts inside you to count, but they all work together to keep you alive. No machine is as complex as you are.
The many parts of your body are grouped into systems. Each system has a job to do in your body. The systems work together to keep you alive and healthy.