cap·il·lar·y / ˈkapəˌlerē/ • n. 1. Anat. any of the fine branching blood vessels that form a network between the arterioles and venules.2. (also capillary tube) a tube that has an internal diameter of hairlike thinness.• adj. of or relating to capillaries or capillarity.

capillary (blood capillary) The narrowest type of blood vessel in the vertebrate circulatory system. Capillaries conduct blood from arterioles to all living cells: their walls are only one cell layer thick, so that oxygen and nutrients can pass through them into the surrounding tissues. Capillaries also transport waste material (e.g. urea and carbon dioxide) to venules for ultimate excretion. Capillaries can be constricted or dilated, according to local tissue requirements. See microcirculation.

capillary Smallest of blood vessels, connecting arteries and veins. They are about 0.1mm (0.004in) in diameter. Capillary walls consist of only a single layer of cells, so that water containing dissolved oxygen and other nutrients (as well as carbon dioxide and other wastes) can pass easily between the blood and surrounding tissues.

capillary (kă-pil-er-i) n. an extremely narrow blood vessel. Capillaries form networks in most tissues; they are supplied with blood by arterioles and drained by venules. The vessel wall is only one cell thick, which enables exchange of oxygen, carbon dioxide, water, salts, etc., between the blood and the tissues.

capillary of hair, hair-like. XVII. — L. capillāris, f. capillus hair; after F. capillaire; see -ARY.