Circulatory system

• Functions of the circulatory system

  • transports oxygen and blood around the body
  • protects red blood cells
  • regulates body temperature
• Veins

  • thin outer walls
  • large lumen
  • have valves to prevent backflow of blood
• Capillaries 


  1 cell thick

  small lumen

  allows substances to diffuse through
• Vasoconstriction 


  Reducing the diameter of the arteries to reduce blood flow
• Vasodilation

  Increasing the diameter of the arteries to increase blood flow
• Adaptations of alveoli

  • large surface area
  • huge capillary network nearby
  • thin walls
  • moist walls