Blood vessels

Blood vessels

  • 3 types of blood vessels:
    1. Arteries –carry blood away from the heart
    2. Capillaries – are involved in the exchange of materials
    3. Veins –carry the blood to the heart


  • The heart pumps the blood out at high pressure so the artery walls are strong and elastic.
  • The walls are thick compared to its lumen. They contain thick layers of muscles to make them strong.


  • Arteries branch into capillaries.
  • Very small with very thin walls to allow substances to diffuse in and out of the blood.
  • Carry blood close to cells to exchange substances with them.
  • One-cell thick walls.


  • Capillaries join up to form veins.
  • The blood is at lower pressure so the walls don’t need to be as thick as artery walls.
  • Bigger lumen to help the blood flow despite lower pressure.

Valves to help keep the blood flowing in the right direction.