Blood vessels

• Arteries

  • carry blood away from the heart
  • thick muscular walls to make them strong
  • small lumen (internal holes)
  • carry blood under high pressure
  • strong and elastic (elastic fibres to allow them to stretch
• Veins

  • carry blood to the heart
  • thin walls
  • large lumen to help blood flow
  • carry blood under low pressure
  • have valves to keep blood flowing in right direction
• capillaries

  • connect arteries and veins
  • carry blood close to cells to exchange substances
  • one cell thick
  • permeable walls (substances can diffuse)
  • carry blood under under very low pressure
  • take away waste like CO2 to supply food and oxygen