<Ul> <Li> Tunica intima (the thinnest layer): a single layer of simple squamous endothelial cells glued by a polysaccharide intercellular matrix, surrounded by a thin layer of subendothelial connective tissue interlaced with a number of circularly arranged elastic bands called the internal elastic lamina . </Li> <Li> Tunica media (the thickest layer in arteries): circularly arranged elastic fiber, connective tissue, polysaccharide substances, the second and third layer are separated by another thick elastic band called external elastic lamina . The tunica media may (especially in arteries) be rich in vascular smooth muscle, which controls the caliber of the vessel . Veins don't have the external elastic lamina, but only an internal one . </Li> <Li> Tunica adventitia: (the thickest layer in veins) entirely made of connective tissue . It also contains nerves that supply the vessel as well as nutrient capillaries (vasa vasorum) in the larger blood vessels . </Li> </Ul> <Li> Tunica intima (the thinnest layer): a single layer of simple squamous endothelial cells glued by a polysaccharide intercellular matrix, surrounded by a thin layer of subendothelial connective tissue interlaced with a number of circularly arranged elastic bands called the internal elastic lamina . </Li> <Li> Tunica media (the thickest layer in arteries): circularly arranged elastic fiber, connective tissue, polysaccharide substances, the second and third layer are separated by another thick elastic band called external elastic lamina . The tunica media may (especially in arteries) be rich in vascular smooth muscle, which controls the caliber of the vessel . Veins don't have the external elastic lamina, but only an internal one . </Li> <Li> Tunica adventitia: (the thickest layer in veins) entirely made of connective tissue . It also contains nerves that supply the vessel as well as nutrient capillaries (vasa vasorum) in the larger blood vessels . </Li>

Explain the different blood vessels in the body and their function