What is the primary role of capillaries in the circulatory system?

The primary role of capillaries in the circulatory system is to exchange materials between blood and cells. Capillaries are the smallest blood vessels in the body, and they connect arterioles (which carry blood away from the heart) to venules (which return blood to the heart). Their walls are extremely thin—just one cell layer thick—allowing for the efficient transfer of oxygen, carbon dioxide, nutrients, and waste products between the blood and the surrounding tissues. This exchange is critical for maintaining homeostasis and ensuring that cells receive the necessary substances for metabolism while removing wastes effectively. The unique structure of capillaries facilitates these exchanges, making them essential for the function of the entire circulatory system.