What is the primary function of capillaries?

The primary function of capillaries is to facilitate the exchange of nutrients, gases, and waste materials between the blood and the tissues of the body. Capillaries are the smallest blood vessels and serve as the connecting point between the arterial and venous systems. Their thin walls allow for the diffusion of oxygen and carbon dioxide, as well as nutrients such as glucose and waste products like carbon dioxide and urea, to move in and out of the bloodstream efficiently. This exchange is crucial for maintaining homeostasis and ensuring that tissues receive the necessary substances for metabolism while removing byproducts of cellular activity.

The other functions listed in the options are not characteristic of capillaries. Transporting blood away from the heart is primarily the role of arteries. Storing oxygen and carbon dioxide mainly occurs in red blood cells, not capillaries. While capillaries can indirectly influence body temperature through blood flow, regulating body temperature itself is not a primary function associated with them. Thus, the main role of capillaries revolves around their ability to allow for crucial exchanges necessary for life.