MICROSCOPIC ANATOMY OF BLOOD VESSELS

• 3 layers (tunics) in blood vessels (except capillaries) (superficial to deep):

  • Tunica externa - fibrous connective tissue
  • Tunica media - smooth muscle and elastic tissue
  • Tunica intima - endothelium, reduces friction
• Structural differences in arteries, veins, and capillaries:

  • Arteries - heavier, stronger tunica media to withstand pressure changes
  • Veins - thinner tunica media to operate under low pressure; has valves to prevent backflow
  • Capillaries - only have tunica intima; blood flow through capillary beds is called microcirculation
  • True capillaries - branch off a terminal arteriole and empty into a postcapillary venule