The adventitia of arteries contains which components?

• A. Smooth muscle and elastic fibers
• B. Endothelium and basal lamina
• C. Nerves and vasa vasorum only
• D. Connective tissue with collagen, nerves, and vasa vasorum

Answer: (D)

Arterial walls have three layers, and the adventitia is the outermost one. It is primarily connective tissue that provides structural support and anchoring to surrounding structures. In larger arteries, this layer contains the vasa vasorum, the small vessels that feed the vessel wall, and the nervi vasorum, the nerve fibers that regulate tone. The connective tissue here also includes collagen fibers (and sometimes elastic fibers) and fibroblasts. That combination—the connective tissue with collagen, nerves, and vasa vasorum—is what defines the adventitia. By contrast, smooth muscle and elastic fibers are mainly in the middle layer (the tunica media), and the inner layer contains the endothelium plus its basal lamina (the tunica intima). So the full, correct description of the adventitia is connective tissue with collagen, nerves, and vasa vasorum.