The aorta like all large blood vessels, has a wall composed of three layers – the tunica intima, the tunica media, and the tunica adventitia. The innermost layer, the tunica intima, nearest the lumen of the vessel and is lined by a single layer of flattened endothelial cells. The endothelial cells are supported by a thin bed of subendothelial connective tissue that, in turn, rests upon a thick sheet of elastic tissue called the Internal Elastic Membrane. The Internal Elastic Membrane forms a boundary between the thin Tunica Intima and the middle layer, the thick Tunica Media.
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Virtual Microscopy thanks to NYU School of Medicine Histology
The aorta, is the largest blood vessel in the human body. It can deliver 12 gal of blood per minute to the general circulation during strenuous exercise. The aorta’s ability to handle that large volume of blood, forcefully pumped in pulsatile bursts from the left ventricle of the heart, is due to the great strength and resilience of its tunica media. The strength of the tunica media comes from its collagen fibers; the resilience, from large sheets of elastic fibers. These elastic sheets, are flat and perforated by holes like a slice of Swiss cheese, in this view they appear as black, wavy lines when viewed in cross section The dark fibers are elastin fibers. (adapted from visual histology)