Arteries are blood vessels that carry blood away from the heart. They have thick walls composed of three layers: the tunica intima, tunica media, and tunica adventitia. The tunica intima is the innermost layer, consisting of a single layer of endothelial cells. The tunica media is the middle layer, rich in smooth muscle cells and elastic fibers, which allow arteries to withstand high pressure. The tunica adventitia is the outermost layer, composed mainly of connective tissue.
