A characteristic of capacitance vessels is that they:

• A. They stretch and hold more blood with volume increases.
• B. They have thick muscular walls
• C. They do not stretch
• D. They are the primary site of gas exchange

Answer: (A)

Capacitance vessels are veins, and their defining feature is high compliance: they stretch easily as blood volume increases, allowing the venous system to hold more blood without a large rise in pressure. This venous reservoir helps regulate venous return to the heart and buffers fluctuations in blood volume. The other statements don’t fit because veins have relatively thin walls and large lumens, not thick muscular walls; they do stretch to accommodate more blood, not stay rigid; and gas exchange occurs in the lungs (in the alveolar-capillary membranes), not in capacitance vessels.