What is the primary function of capillaries in the cardiovascular system?

The primary function of capillaries in the cardiovascular system is to facilitate the exchange of materials between blood and tissues. Capillaries are the smallest blood vessels, connecting arterioles and venules, and their thin walls are composed of just a single layer of endothelial cells. This structure allows for efficient diffusion of oxygen, carbon dioxide, nutrients, and waste products between the blood and surrounding tissues.

The exchange occurs due to concentration gradients; for example, oxygen and nutrients move from the blood in the capillaries into the tissues that need them, while carbon dioxide and metabolic waste products move from the tissues into the blood for removal. This crucial exchange is fundamental to maintaining homeostasis and ensuring that cells receive the necessary substances to function while also removing harmful byproducts.