Which tunica is the inner layer of a blood vessel?

• A. Tunica Intima
• B. Tunica Media
• C. Tunica Adventitia
• D. Subendothelial layer

Answer: (A)

The inner lining of a blood vessel is the tunica intima. This layer directly contacts blood and is made up of endothelial cells that line the lumen, supported by a basement membrane and, in larger vessels, a subendothelial connective tissue layer and sometimes an internal elastic lamina. These features allow the intima to regulate permeability, prevent thrombosis, and modulate vessel tone through endothelial signaling. The middle layer, tunica media, consists of smooth muscle and elastic fibers that control diameter, while the outer layer, tunica adventitia, provides structural support and anchors the vessel to surrounding tissues. The subendothelial layer is not a separate tunic; it’s part of the intima, contributing to its structure.