Which statement best describes capillary function?

• A. They return blood to the heart from the body.
• B. They store most of the blood volume.
• C. They allow nutrient and gas exchange between blood and tissues.
• D. They regulate arterial blood pressure.

Answer: (C)

Capillaries are the sites where exchange happens. Their walls are extremely thin, just a single cell layer, and they form vast networks with a large surface area. This design lets oxygen and nutrients move from the blood into surrounding tissues, while carbon dioxide and other wastes move from tissues into the blood to be carried away. The slow, meandering flow through these tiny vessels gives enough time for diffusion to occur at the cellular level, making capillaries ideal for this exchange process. While capillaries participate in local regulation of flow, the broader control of arterial blood pressure comes from arteries and arterioles (and the venous system handles most blood storage).