The tunica externa (New Latin "outer coat") — also known as the tunica adventitia (New Latin "additional coat"), 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.
Section of a medium-sized artery.
|Part of||Wall of blood vessels|
|Latin||Tunica externa, tunica adventitia|
A common pathological disorder concerning the tunica externa is scurvy, also known as vitamin C deficiency. Scurvy occurs because vitamin C is essential for the synthesis of collagen, and without it, the faulty collagen cannot maintain the vein walls and rupture, leading to a multitude of problems.
- Anatomy photo: Circulatory/vessels/vessels7/vessels4 - Comparative Organology at University of California, Davis - "Bird, vessels (LM, High)"
- Image at About.com