Coronary Artery Structure and Histology 
 
The histological structure of the coronary arteries reflects the general structure of muscular (medium-sized) arteries, but with some distinctive features due to their critical role in supplying the myocardium and their exposure to pulsatile pressure. 

General Structure 
The coronary artery wall has three concentric layers: 

A. Tunica Intima (Inner Layer) 
Endothelium: A single layer of simple squamous endothelial cells lining the lumen. 
Subendothelial layer: Contains loose connective tissue, collagen, elastic fibres, and occasional smooth muscle cells. 
Internal elastic lamina (IEL): A well-defined, fenestrated elastic sheet that separates the intima from the media. 

B. Tunica Media (Middle Layer) 
Composed mainly of circularly arranged smooth muscle cells. 
Contains elastic fibres, collagen (type III), and proteoglycans. 
The amount of elastic tissue is less than in elastic arteries (like the aorta), but more than in small muscular arteries. 
Vasa vasorum (tiny blood vessels) may be present in the outer media and adventitia in larger coronary arteries.
 
C. Tunica Adventitia (Outer Layer) 
Made of loose connective tissue, collagen (type I), elastic fibres, and fibroblasts. 
Contains vasa vasorum and nerves (sympathetic fibers). 
Often blends with the surrounding epicardial adipose tissue. 
 
 
 
  Histological Appearance (Under Light Microscopy)
 
Endothelium lining a narrow lumen. 
Concentric smooth muscle layers in the media with elastic fibres visible under special stains (e.g., Verhoeff–Van Gieson or Weigert’s elastic stain). 
External elastic lamina may be visible at the border between media and adventitia. 
Vasa vasorum and nerve fibres in the adventitia.