arterial wall, the fibrous and muscular wall of vessels that carry oxygenated blood from the heart to structures throughout the body, and of the pulmonary arteries that carry deoxygenated blood from the heart to the lungs. The wall of an artery has three layers: the tunica intima, the inner layer; the tunica media, the middle layer; and the tunica adventitia, the outer layer. Nerves from the autonomic nervous system constrict or dilate the vessel and thus control the flow of blood into the areas served by the artery. The middle layer in smaller arteries is almost entirely muscular and in larger arteries is more elastic. The thickness of the outer layer varies with the location of the artery. In protected areas, such as the abdominal and cranial cavities, the outer layer of associated arteries is very thin, but in more exposed locations, as in the limbs, it is much thicker. See also tunica intima, tunica adventitia, tunica media.
