Which component nourishes the outer layers of the arterial wall?

• A. Elastin fibers
• B. Smooth muscle cells
• C. Nerves and vasa vasorum
• D. Endothelial cells

Answer: (C)

The outer layers of large arteries are nourished by tiny blood vessels called the vasa vasorum. These microvessels run in the adventitia and sometimes penetrate into the outer part of the media to supply oxygen and nutrients directly to the cells there. Diffusion from the lumen isn’t enough to reach the outer layers, so the vasa vasorum provide the essential blood supply that keeps the outer tunics viable.

Elastin fibers give the vessel its elasticity; smooth muscle cells in the middle layer provide contractile strength; endothelial cells line the inner surface. Nerves carry signals but don’t supply nutrients. That’s why the nourishing component is the vasa vasorum.