Anatomy & Physiology I and II

Anatomy & Physiology Study Guide than their tunica media. The tunica externa’s connective tissue fibers blend into those of adjacent tissues, stabilizing and anchoring the blood vessel. Their layered walls give arteries and veins substantial strength. The muscular and elastic components also allow controlled alterations in diameter as blood pressure or blood volume changes. However, the walls of arteries and veins are too thick to allow diffusion between the bloodstream and surrounding tissues, or even between the blood and the tissues of the vessel itself. For this reason, the walls of large vessels contain small arteries and veins that supply the smooth muscle cells and fibrocytes of the tunica media and tunica externa. These blood vessels are called the vasa vasorum .

©2018 Achieve Test Prep Page 255 of 367 20.2 Arteries Arteries are contractile and elastic with relatively thick, muscular walls. Elasticity permits passive changes in vessel diameter in response to changes in blood pressure. The contractility of the arterial walls enables them to change in diameter actively. Arterial smooth muscles contract when