What is the outer layer of blood vessels made of?

The outer layer of blood vessels, known as the tunica adventitia, provides structural support and protection to the vessel. This layer is primarily composed of connective tissue, including collagen and elastic fibers, which help to anchor the blood vessels to surrounding tissues. The tunica adventitia also contains larger blood vessels, known as vasa vasorum, that supply the blood vessel walls with oxygen and nutrients.

The other layers of blood vessels serve different functions. The endothelium is the innermost layer, playing a crucial role in regulating blood flow and maintaining vascular health. The tunica media is the middle layer, primarily composed of smooth muscle, which regulates vessel diameter and blood pressure. The subendothelial layer lies between the endothelium and the tunica media, providing additional support for the endothelium. Understanding the roles of these various layers is important for comprehending how blood vessels function within the circulatory system.