Blood vessels

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  • Blood vessels
    • arteries
      • carry blood away from the heart
        • so artery walls are very strong and elastic
      • heart pumps out blood at high pressure
      • walls are thick compared to the size of the lumen
        • lumen is the inside of the artery
      • have elastic fibres to allow them to stretch and spring back
      • contain thick layers of muscle to make them strong
    • capillaries
      • involved in the exchange of materials at the tissues
      • arteries branch into capillaries
      • they are tiny- too small to see
      • carry blood really close to every cell in the body to exchange substances with them
      • have permeable walls
        • so substances can diffuse in and out
      • supply food and oxygen
        • and take away waste like carbon dioxide
      • walls are only one cell thick
        • increases the rate of diffusion
          • decreases the distance over which it occurs
    • veins
      • carry blood to the heart
      • capillaries join up to form veins
      • carry low pressure blood
        • thin artery walls
      • bigger lumen to blood flow despite it being low pressure
      • have valves to make sure blood flows in the right direction
        • prevent backflow

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