Veins and venules:
have a large radii, and thus low resistance to blood flow. Capacitance vessels. Serve both as a passage way to the heart and as blood reservoir. Less smooth muscle than arteries, more collagen fibers. Have little elasticity and thus no recoil, coalesce in to larger veins as they approach the heart and as the corss sectional area decreases, the blood flow increases as veins approach the heart? Contain valves to prevent back flow. has little myogenic tone, richly supplied by sympathetic nerve fibres causing vaso constriction and increases in pressure which decreases the capacity but resistance is affected insignificantly because the diameter is still large.