Question

Describe histological structure of artery.

Answer 1

Arteries are composed of endothelial cells, smooth muscle cells and extracellular matrix (including collagen and elastin). These are arranged into three concentric layers : intima, media and adventitia. The walls of arteries are thicker than that of veins to withstand pulsatile flow and higher blood pressures. As arteries become smaller, wall thickness gradually decreases but the ratio of wall thickness to lumen diameter increases

1. The Intima (or tunica intima)

• inner layer abutting the vessel lumen, and the thinnest layer
  
• composed of a single layer of endothelial cells and a small amount of sub endothelial connective tissue
  

o is separated from the media by a dense elastic membrane called the internal elastic lamina

2. the media (or tunica media)

• sandwiched between the intima and adventitia, and the thickest layer
  
• provides structural support, vasoreactivity and elasticity
  
• composed of smooth muscle cells, elastic fibres and connective tissue, which vary in amount depending on the type of vessel
  
• smooth muscle cells contract (vasoconstriction) or relax (vasodilatation), which is controlled by autonomic nerves and local metabolic factors
  
• elastic fibres allow the vessel to expand with systole and contract with diastole, thereby propelling blood forward
  
• the media is separated from the adventitia by a dense elastic membrane called the external elastic lamina
  

3. the adventitia (or tunica adventitia)

• outer layer abutting the perivascular soft tissue
  
• composed of connective tissue, nutrient vessels and autonomic nerves
  

The intima and inner part of the media are nourished by diffusion of oxygen and nutrients from blood in the lumen, and the adventitia and outer part of the media are nourished by vasa vasorum.