How the Body Works: The Continuous Circuit

In an adult's body about ten pints of blood are continuously being pumped by the heart through sixty thousand miles of blood vessels. Blood, which has acquired oxygen in the lungs, leaves the heart through the aorta, an inch-wide tube. The aorta branches into large arteries, which take the blood to the neck, head and arms. It then passes down the middle of the body carrying blood to the kidneys, liver, intestines and legs. The large arteries further divide into smaller arterioles and, then finally, into minute capillaries, which surround the body cells. Blood then passes into venules, small veins, and then into larger veins, which feed into the superior vena cava and the inferior vena cava, which return the deoxygenated blood to the heart and then to the lung, where the blood gives up carbon dioxide and acquires a fresh supply of oxygen.