Tunica_externa
Tunica externa
Outer layer of blood vessel
The tunica externa (Neo-Latin "outer coat"), also known as the tunica adventitia (Neo-Latin "additional coat"),[1][2] is the outermost tunica (layer) of a blood vessel, surrounding the tunica media. It is mainly composed of collagen and, in arteries, is supported by external elastic lamina. The collagen serves to anchor the blood vessel to nearby organs, giving it stability.
The three layers of the blood vessels are: an inner tunica intima, a middle tunica media, and an outer tunica externa.