Histological layers within a vessel: easy discussion

  Vessel (artery, vein) : vessels are tube like structure. 

Histologically there are three district layers within outward.

1. Tunica intima : the inner most layer. it is the combination of three layer

• endothelium : simple squamous epithelium
• subendothelial connective tissue: a very thin connective tissue layer occasionally contain smooth muscle cells 
• internal elastic lamina : a membrane like structure which is formed by elastic fibres

  2.Tunica media :it is formed by

• smooth muscle cells : number of cell layer vary in large, medium and small sized artery and vein 

• elastic and collagen fibres 

3. Tunica adventitia : this layer is formed by connective tissue rich in collagen fibers. The thickness of this layer also vary in artery and vein

some time external elastic lamina separate tunica media from tunica adventitia