Final answer:
The tunica media is made up of layers of smooth muscle and connective tissue that include a high amount of elastic fibers. It's primarily responsible for regulating blood vessel diameter through contraction and relaxation, influencing blood pressure and flow, with a more pronounced role in arteries than in veins.
Step-by-step explanation:
The Composition of the Tunica Media in Vasculature
The tunica media is the middle layer of the vessel wall and is especially prominent in arteries. It consists primarily of smooth muscle supported by connective tissue, which contains high amounts of elastic fibers arranged largely in circular sheets. In arteries, the tunica media is generally the thickest layer, as it needs to withstand and regulate the pressure of the blood pumped by the heart. The smooth muscle layers are essential for the processes of vasoconstriction and vasodilation, whereby they contract or relax to change the diameter of the blood vessel, thus regulating blood flow and pressure. Contraction leads to a narrower lumen and increased blood pressure, while relaxation allows the vessel to widen and reduce pressure. The autonomic nervous system, through sympathetic fibers in the nervi vasorum, and various hormones and chemicals, control these critical actions. Whereas in veins, the tunica media is less pronounced as veins operate at lower pressures compared to arteries.
In larger arteries, the tunica media boundary may also feature the external elastic membrane that helps maintain vessel integrity and flexibility. The strong cooperation between the different elements of the tunica media underpins the dynamic regulation of vascular function crucial for overall circulatory health.