What is the primary function of capillaries?

The primary function of capillaries is to facilitate nutrient exchange between blood and tissues. Capillaries are the smallest and most numerous blood vessels in the body, and they form an extensive network throughout various tissues. Their walls are extremely thin—typically one cell layer thick—which allows for the efficient diffusion of gases, nutrients, and waste products between the bloodstream and surrounding tissues.

As blood flows through the capillaries, oxygen and nutrients such as glucose pass from the blood into the tissues, where they are used for cellular processes. Conversely, carbon dioxide and other metabolic wastes move from the tissues into the blood. This exchange is crucial for maintaining homeostasis, as it ensures that cells receive the necessary substances to function properly while removing waste products that could be harmful in high concentrations.

The other options describe functions associated with other types of blood vessels or processes but do not capture the essential role of capillaries in nutrient exchange. Thus, understanding the unique structure and function of capillaries is critical for recognizing their importance in the circulatory system.