structure and function

• blood vessels: delivery system that ends and starts with the heart

  • works with the lymphatic system to circulate fluids
• arteries: oxygenated blood away from the heart except in the pulmonary and circulation and umbilical vessels of fetus
• veins: carry deoxygenated blood to the heart except for pulmonary circulation and umbilical vessels of fetus
• capillaries: have intimate with tissues and deliver cellular needs
• lumen: All vessels have this blood containing space surrounded by a wall
• • Walls of all vessels, except capillaries, have three layers, or tunics:

  1.  Tunica intima
  2.  Tunica media
  3. Tunica externa
• Capillaries have Endothelium with sparse basal lamina
• Tunica intima: innermost layer made of simple squamous epithelium that is in contact with blood

  • continuous with endocardium
  • slick surface reduces friction
  • additional found in vessels larger than 1 mm is the subendothelial layer a connective tissue basement membrane
• Tunica Media: middle layer made of mostly smooth muscles and elastin

  • innervated by sympathetic vasomotor fibers controlling vasoconstriction and dilation
  • bulkiest layer responsible for maintaining blood flow and blood pressure
• tunica externa (tunica adventitia): outermost layer

  • composed of loose collagen fibers that protect and reinforce wall and anchor to surroundings
  • infiltrated with nerve fibers, lymphatic vessels
  • larger veins also contain elastic fibers
• • Vasa vasorum: system of tiny blood vessels found in larger vessels 
  • Function to nourish outermost layer
• Artery, vein, capillaries

  A) endothelium

  B) internal elastic membrane

  C) external elastic membrane

  D) vasa vasorum

  E) lumen

  F) artery

  G) vein

  H) capillary