Blood vessels transport blood around the entire body. Blood is made up of red blood cells (carrying oxygen and nutrients to feed the body), water, hormones, proteins, salts, platelets, and white blood cells (to defend against germs and disease). Early doctors and scientists knew about blood vessels. An ancient Egyptian document called the Ebers Papyrus written 3,400 years ago talked about them. The blood system is much older than that though. It probably evolved over 600 million years ago.
The heart pumps blood into blood vessels, which spread throughout the body. Blood travels to every part of your body to drop off oxygen, nutrients, and white blood cells where they are needed and to pick up carbon dioxide and other waste so they can be disposed of. The heart even has its own blood vessels.

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