blood vessels

• arteries

  carry blood away from the heart
• capillaries

  involved in the exchange of materials at the tissues
• veins

  carry blood into the heart
• arteries

  • thick muscular walls to withstand the high pressure
  • elastic fibres so they can stretch under pressure then recoil to push blood along
  • narrow lumen to maintain a high pressure
• capillaries

  • very thin walls so substances diffuse over a short distance improving the rate of diffusion
  • they have permeable walls that let substances in and out
• veins

  • valves to stop backflow
  • large lumen to allow blood to flow easily