Table of Contents
- adventitia, the outermost layer, which is primarily connective tissue that gives the artery its FLEXIBILITY
- media, the middle layer, which is mostly smooth MUSCLEtissue that gives the artery the ability to contract and relax
- intima, the inner layer, which is epithelial tissue that provides a smooth surface to facilitate the flow of blood
The adventitia is more prominent in larger arteries such as the AORTA and the carotid arteries, encasing the artery in a weblike fashion without clear direction to its fibers. In smaller arteries, the media often dominates the artery’s structure. The muscle fibers of the media encircle the artery, helping strengthen and stabilize the artery’s walls. The delicate intima contains two structural levels, the basement or foundation membrane and the subepithelial layer, both of which run lengthwise. Each may be only a cell’s thickness in small arteries, indistinguishable without magnification.
The intima’s two-level structure gives the artery its ability to carry blood cells without having them stick to its inner walls. However, it also makes the artery vulnerable to ATHEROSCLEROSIS, which develops between the intima’s two levels. The tiniest of the body’s arteries, about the thickness of a hair, are arterioles. The body’s largest artery is the aorta, which carries blood from the heart to the network of arteries that then carry the blood throughout the body.
Fibrous sheaths enclose most of the body’s arteries, usually along with the companion VEIN and NERVE. These sheaths often parallel skeletal structures for protection and stability, or run deep within the body. Arteries also receive blood themselves from other arteries, which deliver oxygen and other nutrients to the layers of the artery, and contain nerves that deliver the signals to constrict or dilate. The walls of the arteries constrict and dilate in wavelike contractions that coordinate with the heartbeat to help push blood through the body. These pulsations are detectable as the PULSE at points where the artery is near the surface of the skin, such as at the wrist and the groin.
For further discussion of the artery within the context of cardiovascular structure and function, please see the overview section “The Cardiovascular System.”