B2 - Blood vessels

• Arteries


  Carry blood away from the heart
• Capillaries


  Exchange nutrients and oxygen with the tissues
• Veins


  Carry the blood back to the heart
• Arteries


  • Have a thick layer of muscle tissue to keep them strong
  • Have a thick layer of elastic tissue so they can stretch and recoil
• Capillaries


  • Have walls that are only a single cell thick
  • Are permeable, allowing substances to easily diffuse through them
  • Have a total cross-sectional area that is much higher than arteries, allowing lower blood pressure and slower flow
• Veins


  • Have relatively large lumens
  • Have relatively thin walls with only small layers of elastic fibers and smooth muscle
  • Have valves to prevent backward flow of blood
• Calculating rate of blood flow

  Divide the volume of blood by the time taken