Vessel that carries blood from the heart to other parts of the body (see cardiovascular system). Arterial blood carries oxygen and nourishment to tissues; the one exception is the pulmonary artery, which conveys oxygen-depleted blood from the heart to the lungs for oxygenation and removal of excess carbon dioxide. Arteries are muscular, elastic tubes that transport blood under the pressure of the heart's pumping action, which can be felt as the pulse. Large arteries branch off from the aorta and give rise to smaller arteries, down to the threadlike arterioles, which branch into capillaries. An artery wall's inner layer (tunica intima) consists of an endothelial (cellular) lining, a fine connective tissue network, and a layer of elastic fibres. The middle layer (tunica media) is mostly smooth muscle cells. The outer layer (tunica externa) contains supportive collagen fibres. See also capillary; vein.
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