The blood vessels are the part of the circulatory system that transports blood throughout the human body. There are three major types of blood vessels: the arteries, which carry the blood away from the heart; the capillaries, which enable the actual exchange of water and chemicals between the blood and the tissues; and the veins, which carry blood from the capillaries back toward the heart.
Large vessels: arteries and veins
Structural differences between (A) Artery and a (V) vein
Capillary structure: endothelial cells form its tunica intima (inner layer), and pericytes form its tunica adventitia (outer layer)
Pericytes (Peri- around) are cells that lie close to the endothelial cells of blood capillaries and small venules into which the capillaries drain. They are a potential source of new fibroblasts and smooth muscle cells, and help to repair damage.