Artery

An artery is a blood vessel that carries blood away from the heart to other parts of the body. Almost all arteries carry blood with a lot of oxygen in it. The only arteries that do not carry oxygen-rich blood are the pulmonary artery, and (in a fetus) the umbilical artery.^[1]

Every artery has three layers. The outer layer is a thick covering made of stretchy tissue. The middle layer is made of muscle, so the artery can get wider or get smaller when the body needs it to. The inner lining is made of the same cells that line the heart.^[2]

Arteries are deep under the skin. They do not have valves to prevent blood from flowing backwards. Instead, every time the heart beats, the arteries stretch out so the blood has room to go through. Once the walls have completely stretched out, the muscles in the arteries make them shrink back to their normal size. This pushes the blood through.^[1]

Arteries split down into small vessels called arterioles.

1. ↑ ^{1.0 1.1} "Artery: Anatomy". Britannica.com. Encyclopædia Britannica. January 14, 2016. Retrieved January 29, 2016.
2. ↑ "Anatomy of the Aorta and Heart". Cedars-Sinai Heart Institute – Aortic Program. Cedars-Sinai. 2016. Archived from the original on February 11, 2016. Retrieved January 29, 2016.