what is the importance of capillaries in the circulatory system?

They connect branches of artries and veins.Endotheliun of artries allow the exchange of materials like nutrients, respiratiry gases, waste materials, hormones etc.between blood and body cells through the tissue fluid, e.g. passage of nutrients & oxygen from blood into body cells, and passage of nitrogenous wastes and carbondioxide from body cells into blood.