blood vessels

• arteries


  endothelium- one cell thick, smooth to reduce friction, folded to expland under high pressure

  smooth muscle- thick, withstand pressure, allows contriction to decrease blood flow

  elastic tissue- maintain blood pressure, stretch +recoil to do this

  collagen- protects blood vessels from damage by over stretching

  narrow lumen- maintain high BP

  pulse- stretch to accommadate an increase volume of blood with heart beat
• veins

  • smooth muscular wall and elastic layer- thinner as dont have to withstand high bp
  • lumen- larger, ensure blood returns to heart at adequate speed, reduces friction
  • valves- prevents backflow of blood
• capillaries

  • one cell thick walls- permeable, substances leave blood and into tissue and reduces diffusion distance between blood and tissues
  • small lumen-RBCs travel single file, forcing blood to move slowly allowing sufficient time for diffusion
  • pores in cell wall- blood plasma leaks out