Anatomy and Physiology II Practice Test

The tunica media, which is the middle layer of the artery, plays a crucial role in maintaining blood pressure. This layer is composed primarily of smooth muscle fibers and elastic tissue, allowing it to contract and relax. When the smooth muscle contracts, it narrows the lumen of the artery, a process known as vasoconstriction, which increases blood pressure. Conversely, when the smooth muscle relaxes, the luminal diameter increases through vasodilation, which can reduce blood pressure.

The ability of the tunica media to change the diameter of the artery is essential for regulating blood flow and pressure throughout the circulatory system, particularly in response to different physiological demands such as exercise, stress, or changes in body position. This layer's muscular and elastic properties are what primarily enable arteries to withstand and manage the high pressure of blood as it is pumped from the heart.