The function of the capillaries in the circulatory system is to allow diffusion of wastes, oxygen, and nutrients to the tissues. The rest of the circulatory system is designed to move the blood to the capillaries so they can perform this function.
The blood vessels, which include the capillaries, function to distribute nutrients such as glucose and oxygen to the body tissues and to carry wastes such as carbon dioxide and urea away from the tissues to be excreted.
The function of blood capillaries is to provide cellular, or tissue, respiration, provide nutrients and remove waste products. They are the tiny blood vessels that are between the venules and arterioles and the interstitial space between cells.