The heart and blood vessels

• Arteries?

  • Carry blood from heart to every tissue in the body
  • thick elastic wall that can expand during systole and can recoil during diastole to even out pulsating blood
  • more collagen in smooth muscle to provide strength and prevent damage
• Veins?

  • Carry blood from tissue to heart
  • blood has lost almost all its pressure so it moves slowly
  • veins don’t have thick walls and have a large lumen to reduce flow resistance
  • they have semi-lunar valves to prevent back flow
  • blood that is difficult to flow e.g up the legs, is helped with contractions of leg muscle which the body relies on for the blood to return to the heart
• Capilaries?

  • Where transported substances enter/leave the blood
  • they are narrow and thin walled
  • many for a large surface area to volume ratio to aid rapid diffusion of substances between blood and cells
  • arranged in capillary bed feeding a group of cells
  • no cell is more than 2 cells away from a capillary
• Tissue fluid?

  • Watery liquid that contains glucose, amino acids, fatty acids, salts and oxygen
  • supplies tissue with these substances and receives waste material
  • these substances are exchanged between the blood and the cell
  • first they diffuse into tissue fluid then to cells