Anatomy and Physiology II Practice Test 2026 - Free Anatomy Practice Questions and Study Guide

The innermost layer of tissue in an artery is called the tunica intima. This layer is composed of a thin lining of endothelial cells that provides a smooth surface to minimize friction as blood flows through the vessel. The primary function of the tunica intima is to facilitate the efficient flow of blood while also allowing for the exchange of substances between the bloodstream and surrounding tissues. This layer plays an important role in maintaining vascular health, as it also helps in regulating blood pressure and preventing clot formation by producing certain substances that inhibit platelet activation. In contrast, the tunica media, which is the middle layer, is made up of smooth muscle and elastic fibers that can constrict or dilate the artery, and the tunica externa, or adventitia, is the outer layer that provides structural support and protection to the artery. The endothelium is often considered part of the tunica intima, as it is the specific layer of cells that lines the inside of blood vessels.