The arteries are the tubes that carry blood from your heart to all parts of your body. (The tubes that carry blood back to your heart are called veins.) The complete story of how the blood circulates through your body is told in the article on blood . The name artery comes from the Greek language, in which arteria means "an air-keeper." The Greeks, thousands of years ago, believed that the arteries carried air, not blood. They thought the air a person breathed in was sent through the body in the arteries.

Now we know the arteries carry blood, not air. The arteries are round hollow rubes, much like macaroni or rubber tubing. The walls of an artery have three layers. The outer layer is elastic, as rubber is. The middle layer is a muscle. The inner layer is smooth and transparent. When your heart beats it pumps blood into the arteries. The main artery leading from the heart is called the aorta. Blood flows from the aorta into many other arteries. The arteries branch off into smaller and smaller arteries as they carry the blood through the body.

The middle layer regulates the size of the artery, and how much blood can flow through. When you feel your pulse, you are feeling the force of your heartbeat in the artery in your wrist. The blue blood vessels you see under the surface of your skin are veins. Your arteries are buried deeper inside your body. When a vein is cut, the blood usually flows out slowly. When an artery is cut, the blood gushes out in spurts. A cut artery is very dangerous. The article on f i r s t a i d tells what to do. Arteries, like other parts of the human body, may become diseased. Such diseases are almost always found in very old people. The most common form of arterial disease is called arteriosclerosis. This means "hardening of the arteries." They lose their elasticity and are apt to break and crack.