Vasa vasorum

The vasa vasorum is a network of small arterioles, capillaries and venules that supply the outer tissues of large blood vessels like the aorta. Most cells need to be within a few cell-widths of a capillary to stay alive, and the cells that make up the outer walls of a blood vessel are no exception. The vasa vasorum penetrate the tunica adventitia, as well as the deeper tunica media of larger vessels such as the aorta.

The exact makeup of the vasa vasorum depends on the vessel. They provide the vessel wall that they penetrate with metabolites which they would otherwise not receive due to the thickness of the layers making up the wall. The vasa vasorum are considered to be present more frequently in arteries than in veins. However, several books hypothesize that vasa vasorum would be more abundant in large veins, as partial oxygen pressure is lower than in arteries as well as osmotic pressure.Fact|date=April 2008 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.

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