Arterial Tunics & Their Functions

• Arteries are made up of three layers, or tunics.virtual artery image by Yali Shi from Fotolia.com
  
  All blood vessels, except some of the smallest capillaries, are made up of three tunics, or layers, according to Vanderbilt University Medical Center. The arterial tunics are the tunica intima, tunica media and tunica adventitia. The make-up of arterial tunics varies according to the blood vessel's function.
  
  Arterial arteries are either elastic or muscular, explains North Seattle Community College. Elastic arteries have a high level of elastin because they must stretch to absorb the pressure from blood leaving the heart; muscular arteries supply the organs with blood and have the thickest tunica media and most muscular fiber of all blood vessels.
  
  

Tunica Intima

• The smooth layer helps prevents blood from clotting.cells 4 image by chrisharvey from Fotolia.com
  
  The tunica intima is the innermost layer of the blood vessel. It is made up of endothelial cells, connective tissue and an elastic membrane. The cells form a slick surface that reduces friction, explains Augusta Technical College.
  
  

Tunica Media

• Elastic arteries stretch to smooth out blood pressure force leaving the heart.heart beat medical image by Nicemonkey from Fotolia.com
  
  The tunica media is the thickest layer of arterial tunics and is made up of collagen, elastin and smooth muscle. In muscular arteries, the muscle cells are in a spiral formation to help them contract or dilate to maintain blood pressure. In elastic arteries, there is a high degree of elastin. This, says Vanderbilt University, smooths out the pressure wave of blood leaving the heart.
  
  

Tunica Adventitia

• All blood vessels except the smallest capillaries have three tunics.virtual vein image by Yali Shi from Fotolia.com
  
  The tunica adventitia is the outermost layer of the arterial tunics. It is made up of small blood vessels, nerves, collagen, elastin and connective tissue. The function of this thin layer is to anchor and protect the blood vessel and supply the blood vessel itself with blood. Nerve fibers in the tunica adventitia innervate the smooth muscle of the blood vessel.