Final answer:
The tunica media is the blood vessel layer made of smooth muscles and elastic fibers, and it is thicker in arteries than in veins. This layer is essential for regulating blood pressure and flow through adjustments in vessel diameter.
Step-by-step explanation:
The Tunica Media Layer in Blood Vessels
The layer of blood vessels that is made of smooth muscles and elastic fibers, and is notably thicker in arteries, is called the tunica media. This layer is crucial for maintaining blood pressure and controlling the flow of blood through vasoconstriction and vasodilation. In arteries, the tunica media is thick to accommodate the higher pressure from the heart. It consists of elastic fibers arranged in circular sheets and smooth muscle cells. The proportions of these components vary with distance from the heart, with more elastic fibers near the heart in what are called elastic arteries and more smooth muscle cells in the muscular arteries farther from the heart.
The tunica media in larger arteries contains an internal elastic membrane at its boundary, which provides structure and allows for stretching of the vessel. This structure differs from veins, which have thinner walls and valves to prevent backflow of blood.
Overall, the tunica media is where smooth muscle and elastic fibers predominantly exist, serving crucial functions in blood circulation by adjusting the vessel diameter in response to various physiological demands.