What is the function of capillaries?

Capillaries are called exchange vessels. The task of the capillaries is the exchange of substances between the bloodstream and tissues. Not all capillaries function at the same time. In some capillaries, the blood flow occurs continuously, and in some it is intermittent, intermittent. The capillaries are smaller than the veins and arteries. In the walls of the capillaries through the pores, there is an exchange of nutrients and water, as well as gas exchange.