Your circulatory system is made up of your heart and blood vessels. Blood vessels are flexible, hollow tubes. Your heart pumps blood through blood vessels. It sends blood to your lungs to pick up oxygen. It pumps blood out to all parts of your body.
Arteries are blood vessels that carry oxygen-rich blood out to your body. Veins are blood vessels that carry blood back to your heart. The blood vessels near your heart are thick. Farther from your heart, the blood vessels are smaller.
The tiniest blood vessels are called capillaries. Capillaries go all through your body. They give up oxygen and nutrients that your body needs. They carry away waste products.
