Veins are also known as:

• A. Capacitance vessels.
• B. Resistance vessels.
• C. Exchange vessels.
• D. Arterial vessels

Answer: (A)

Veins are best described as capacitance vessels. Their thin walls and large lumens give them high compliance, meaning they can stretch and hold a large volume of blood with only a small increase in pressure. Because the venous system contains most of the circulating blood, it acts as a reservoir that can be mobilized to maintain venous return to the heart when needed. This is in contrast to resistance vessels (arteries and arterioles), which regulate blood pressure by changing their diameter; exchange vessels (capillaries) are where diffusion of gases and nutrients occurs; arterial vessels (arteries) are high‑pressure conduits that carry blood away from the heart. Venous tone can be adjusted by the sympathetic nervous system, shifting blood from the venous reservoir into the circulation when demand rises. This storage and rapid mobilization capability is why veins are called capacitance vessels.