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Tubular channels for blood transport, of which there are three principal types: arteries, capillaries, and veins. Only the larger arteries and veins in the body bear distinct names. Arteries carry blood away from the heart through a system of successively smaller vessels. Capillaries are the smallest but most extensive blood vessels, forming a network everywhere in the body tissues. Veins carry blood from the capillary beds back to the heart through increasingly larger vessels. In certain locations blood vessels are modified for particular functions, as the sinusoids of the liver and the spleen and the choroid plexuses of the brain ventricles. See Lymphatic system
in animals and man, vessels through which blood moves from the heart or central pulsating organ to the tissues (the arteries, arterioles, and arterial capillaries) and from the tissues to the heart (the venous capillaries, venules, and veins). The blood vessels and the heart together form a single cardiovascular system.