Veins are described as capacitance vessels. Which statement best reflects this role?

Veins are described as capacitance vessels. Which statement best reflects this role?

• A. They store a large portion of blood and can expand at low pressure
• B. They generate most cardiac output
• C. They are the site of gas exchange
• D. They contain the majority of smooth muscle in the vascular wall

Answer: (A)

Veins are capacitance vessels, meaning their walls are highly compliant and can accommodate a large blood volume with only a small rise in pressure. This makes the venous system a flexible reservoir that stores most of the blood at low pressure and can expand or constrict to adjust venous return to the heart as needed. This reservoir function is exactly captured by saying they store a large portion of blood and expand at low pressure. In contrast, the heart generates the majority of cardiac output, gas exchange occurs in the capillaries, and the majority of the vascular smooth muscle is in arteries and arterioles, not veins.

Veins are capacitance vessels, meaning their walls are highly compliant and can accommodate a large blood volume with only a small rise in pressure. This makes the venous system a flexible reservoir that stores most of the blood at low pressure and can expand or constrict to adjust venous return to the heart as needed. This reservoir function is exactly captured by saying they store a large portion of blood and expand at low pressure. In contrast, the heart generates the majority of cardiac output, gas exchange occurs in the capillaries, and the majority of the vascular smooth muscle is in arteries and arterioles, not veins.