Tunica media of vessel

The tunica media is the middle layer of the vessel wall and is generally its thickest portion. It consists primarily of smooth muscle fibers, collagen, and varying amounts of elastic tissue. The relative proportion of these components differs among vessel types, forming the structural basis for their functional distinctions.

This layer plays a vital role in strengthening the vessel wall and enabling it to withstand internal blood pressure. Through the coordinated contraction and relaxation of its smooth muscle fibers, the tunica media regulates the vessel’s diameter — processes known respectively as vasoconstriction (narrowing) and vasodilation (widening). These mechanisms are essential for controlling blood flow and maintaining vascular resistance within the circulatory system.