The common pattern is the presence of three layers – the tunica intima, tunica media and the tunica adventitia from inside out. The tunica intima is the innermost layer, towards the luminal side of the blood vessel and is composed of simple, squamous endothelial cells and the supporting connective tissue. It is separated from the tunica media by the inner elastic lamina. The tunica media is composed of circular smooth muscle interspersed with connective tissue and is separated from the outermost layer by the outer elastic lamina. The tunica adventitia is made up entirely of connective tissue. The walls of the arteries are much thicker than those of the veins as they have to carry the blood pumped by the heart to distant organs which is usually at a higher pressure. The arteries therefore comprise of more elastic tissue in the tunica intima. The medium arteries are more muscular than elastic and the internal elastic membrane is more prominent. The spiral smooth muscle cells of the tunica media assist in the propulsion of blood as well as the maintenance of the blood pressure. The tunica adventitia is composed of collagen as well as elastic fibers and the innermost portion has an external elastic membrane. More elastic and muscular tissue in the arteries serves to sustain the vigorous systolic pressure of the blood and the maintenance of its pressure. The veins, on the other hand have thinner walls. Although they possess the basic histological structure associated with all blood vessels, the three layers are not well demarcated and blend into each other. They have lesser elastic tissue and the tunica adventitia is the thickest layer made up of collagen fibers and longitudinally oriented smooth muscle cells. The tunica intima is modified into loose folds which form pockets or valves to resist the back flow of blood along its journey to the heart.
2. The integument fulfills several roles, including that