Circulatory system - blood vessels

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  • Circulatory system - blood vessels
    • Arteries carry blood under pressure
      • Carry blood away from the heart
      • Heart pumps blood out at high pressure
      • Artery walls are strong and elastic
      • Have thick layers of muscle to make them strong
      • Have elastic fibres to allow them to stretch and spring back
      • Thick walls compared to the size of the hole down the middle -  'lumen'
    • Capillaries are really small
      • Arteries branch into capillaries
      • Carry blood really close to every cell in the body to exchange substances with them
      • Have gaps in their walls so substances can diffuse in and out
      • Supply food and oxygen and take away CO2
      • Walls are usually one cell thick - diffuse very fast because there is only a short distance for molecules to travel
      • Very small lumen
    • Veins take blood back to the heart
      • Join up to form veins
      • Blood is at a lower pressure in the veins - walls don't need to be as thick as artery walls
      • Veins have a bigger lumen than artieries which helps the blood flow despite a lower pressure
      • Also have valves - help to keep the blood flowing in the right direction
    • Calculating the rate of blood flow
      • Rate of blood flow = volume of blood / number of minutes


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