Capillaries are the smallest and thinnest blood vessels having one-cell thick wall. They are meant to exchange materials between the blood and surrounding body tissues and fluid.\xa0
Blood capillaries are very fine blood vessels which penetrate into the tissues and supply them with blood. They have very small diameter and have very thin walls through which material can easily move. Their main function is to supply the tissues with nutrients, oxygen, hormones, etc and to take up the wastes from them.