Structure and function in arteries veins and capillries

• arteries - very thick wall - to withstand high blood pressure

  capillaries - very thin wall, just one cell thick - allow rapid exchange between blood and tissues

  veins - relatively thin wall - blood under low pressure
• arteries - narrow lumen - low friction surface to ease blood flow

  capillaries - small lumen - link arteries and veins

  veins - wide lumen - large volume acts as blood reservoir
• arteries - no valves

  veins - valves - valves stop backflow, ensuring a one-way flow of blood towards the heart