Which vessel layer is the middle layer composed of smooth muscle cells, elastic fibers and connective tissues?

• A. Tunica Media
• B. Tunica Adventitia
• C. Tunica Intima
• D. Endothelium

Answer: (A)

The middle layer of a blood vessel wall is the tunica media. This layer is rich in smooth muscle cells arranged in concentric layers, with elastic fibers and supportive connective tissue. The smooth muscle allows the vessel to constrict or dilate, regulating blood flow and pressure, while the elastic fibers give the wall the ability to recoil after being stretched by the pulse.

By contrast, the innermost layer is the tunica intima, which is the endothelial lining (plus a subendothelial layer). The outermost layer is the tunica adventitia, made mostly of connective tissue and containing vessels and nerves that supply the vessel. The endothelium refers specifically to the single-cell lining of the intima, not the middle layer.