A Histology Art for Circulatory System Body Tissues!

Except for capillary vessels, all blood vessels are made up of these three layers:

Tunica adventitia
In this case, this is the outermost covering. It is often made up of simple squamous epithelium, a basement membrane, connective tissue, blood vessels, and smooth muscle cells.

This layer is very thick, so it needs its blood supply because it’s so big and heavy. The vessels that supply blood to the tunica adventitia are called “vasa vasorum” (vessels of the vessels).

Tunica media
This is made up of layers of smooth muscle fibers and elastin. Some small blood vessels don’t have muscle fibers or elastin.

Tunica intima
This is the most inner covering. The simple, squamous cells (epithelium) line the inside of blood vessels that make up the endothelium. The tunica intima comprises the endothelium and the basement membrane below it. Some blood vessels have a small amount of subendothelial connective tissue and an internal elastic layer (lamina), but not all of them do.