What is the vasa vasorum?

• A. Small vessels supplying the walls of large arteries and veins
• B. Nerve fibers that regulate capillary flow
• C. Lymphatic vessels draining tissue fluid
• D. The inner lining of the heart chambers

Answer: (A)

Vasa vasorum are small vessels that nourish the walls of large arteries and veins. In thick-walled vessels, the outer layers are too far from the lumen to receive enough oxygen and nutrients by diffusion alone, so these tiny vessels supply the vessel wall directly. They run in the adventitia and outer media, and in some cases from the lumen into the inner layers. This microcirculation keeps the vessel walls healthy and prevents ischemia. The other options describe different structures—a nerve network that can influence flow, lymphatic vessels that drain tissue fluid, and the inner lining of heart chambers—none of which are the vasa vasorum.