Elastic arteries are large vessels that convey blood from the heart to systemic and pulmonary circulations. During the contraction phase of the cardiac cycle (systole), the higher pressure causes their walls to distend. During the relaxation phase of the cardiac cycle (diastole), the lower pressure causes their walls to deflate. This helps the movement of blood through the arteries.
This pumping action is possible because of the elastic tissue in the arterial wall. Although unstained by H&E, elastin stains dark purple with aldehyde fuchsin.
Tunica Intima - inner layer composed of the endothelium and subendothelial connective tissue. This is the thinnest of the three layers in elastic arteries. The nuclei of endothelial cells bulge into the lumen. The internal elastic membrane is the innermost layer of elastic tissue (dark purple) in the arterial wall.
Tunica Media - middle layer composed of alternating layers of circumferentially arranged smooth muscle (unstained) and sheets of elastic tissue (dark purple). This is the thickest of the three layers in elastic arteries. The number of elastic lamellae is linked to blood pressure in the artery.
Tunica Adventitia - outer layer of dense irregular connective tissue. This layer is usually less than half the thickness of the tunica media in elastic arteries.