Why are vasa vasorum necessary in the walls of large arteries but not large veins?
Most authorities say that the vasa vasorum is present more frequently in arteries than veins, because arteries are thicker.But some authorities hypothesize that the vasa vasorum would be more abundant in large veins, as partial oxygen pressure and osmotic pressure is lower in veins. This would lead to more vasa vasorum needed to supply the vessels sufficiently. The converse argument is that generally artery walls are thicker and more muscular than veins as the blood passing through is of a higher pressure. This means that it would take longer for any oxygen to diffuse through to the cells in the tunica adventitia and the tunica media, causing them to need a more extensive vasa vasorum. An interesting point of fact is that, in the human descending aorta, vasa vasorum cease to supply the arterial walls with oxygenated blood at the level of the renal arteries. Thus, below this point, the aorta is dependent on diffusion for its metabolic needs, and is necessarily markedly thinner. This lea
