Artery
From Encyclopædia
An artery is any blood vessel that carries blood from the HEART toward the CAPILLARIES, in contrast to a VEIN, which carries blood from the capillaries toward the heart. The largest artery is the AORTA, which receives blood from the left ventricle of the heart. Several main arteries branch from the aorta and successively branch into vessels of smaller diameter, culminating in tiny arteries called arterioles. These deliver blood to the capillaries, the network of microscopic blood vessels that brings blood close to all the
cells of the body. The capillaries collect into venules, which are the beginning of the venous system for return of blood to the heart.Arteries have three concentric layers of tissue. The innermost consists of a smooth endothelial lining, connective tissue, and a few muscle
cells. The middle layer comprises primarily muscle
cells and elastic fibers for expansion during a pulse of blood set in motion by heart contraction. The outer layer is mainly fibrous connective tissue that prevents overexpansion during the pulse (see
PULSE, BIOLOGY). Large arteries near the heart have a large amount of elastic tissue but little muscle. This elasticity allows them to resist the high
pressures that occur during heart contraction; between heart contractions, the elastic recoil in the arteries keeps the blood moving. Smaller arteries and arterioles have a thick muscular layer, which can
contract or relax under
Control of the
nervous system to vary the artery's internal diameter. This variation helps regulate BLOOD
pressure and blood distribution in various regions of the body.Peter L. PetrakisBibliography: Bunce, Donald F., Atlas of Arterial Histology, 2d ed. (1975); Harcus, Alfred, and Adamson, Leslie, Arteries and Veins (1975); O'Rourke,
Michael F., Arterial Function in Health and Disease (1982).See also:
ANEURYSM;
CIRCULATORY SYSTEM;
CORONARY ARTERY.Picture Caption[s]The artery wall is composed of three layers of tissue. The tunica intima, which is the innermost layer, comprises a sheet of endothelial
cells and a sheet of connective tissue and some muscle
cells. The tunica media comprises two layers of elastic tissue, with a layer of smooth muscle and some connective tissue in between. The tunica adventitia is a thick outer layer of connective tissue.
