Circulatory system - Blood Vessels

• There are three different types of blood vessel:

  1. Arteries - they carry blood away rom the heart.
  2. Capillaries - they are involved in exchanging materials at the tissues.
  3. Veins - they carry blood to the heart
• Features of an artery:

  • They have strong and elastic walls.
  • Thick walls.
  • Walls have thick layers of muscle.
• Why do arteries have strong and elastic walls?


  The blood is very high pressure, and needs to withstand the force the blood is moving at.
• Why do the arteries have layers of muscle and have elastic fibres?


  To make them strong, and allow them to stretch and spring back.
• Features of capillaries:

  • One call thick walls
  • Permeable walls
  • Very small lumen
• What is the function of a capillary?


  To deliver food and oxygen, and take away waste like $CO_2$.
• Why do they have thin walls?

  To increase the rate of diffusion by decreasing the distance in which it covers.
• Features of veins:

  • Large lumen
  • Elastic fibres and smooth muscle in the walls
  • Valves
• The veins carry low pressure blood and therefore don't need thick walls like arteries.
• They have a bigger lumen to help the blood flow despite lower pressure.
• Why do veins have valves?


  To keep blood flowing in the right direction.
• Rate of blood flow = volume of blood $\div$number of minutes
• 1464ml of blood passed through an artery in 4.5 minutes. calculate the rate of blood flow in ml/min.


  1464 $\div$ 4.5 = 325 ml/min