Which structural layer is primarily responsible for regulating the diameter of arteries?

Which structural layer is primarily responsible for regulating the diameter of arteries?

• A. Endothelium
• B. Tunica adventitia
• C. Tunica media
• D. Internal elastic lamina

Answer: (C)

The tunica media is responsible because it contains the vascular smooth muscle that can contract or relax to change the radius of the artery. This smooth muscle tone directly controls lumen diameter, with sympathetic nerves and local mediators (like nitric oxide, endothelin, and calcium-dependent signaling) adjusting constriction or dilation. The endothelium influences diameter indirectly by releasing these signaling molecules, but the actual structural control comes from the smooth muscle in the tunica media. The internal elastic lamina mainly provides elasticity between layers, and the tunica adventitia is mainly supportive connective tissue rather than a regulator of diameter.

The tunica media is responsible because it contains the vascular smooth muscle that can contract or relax to change the radius of the artery. This smooth muscle tone directly controls lumen diameter, with sympathetic nerves and local mediators (like nitric oxide, endothelin, and calcium-dependent signaling) adjusting constriction or dilation. The endothelium influences diameter indirectly by releasing these signaling molecules, but the actual structural control comes from the smooth muscle in the tunica media. The internal elastic lamina mainly provides elasticity between layers, and the tunica adventitia is mainly supportive connective tissue rather than a regulator of diameter.