2.65 describe the structure of arteries, veins and capillaries and understand their roles



  • Arteries carry oxygenated blood to supply the body with blood
  • Arteries carry blood away from the heart
  • Walls are strong, elastic and thick as the heart pumps blood out at high pressures
  • Arteries contain thick muscle layers, making the arteries strong and helps them to retain shape
  • Exception: Pulmonary artery in the heart carries deoxygenated blood to the lungs
  • Note: The largest artery is the aorta, oxygenated blood from left ventricle


  • Capillaries supply cells with nutrition and oxygen and remove waste and carbon dioxide from the cells by diffusion, therefore they have thin cell walls
  • Capillaries branch off arteries
  • Involved with a change of substances through diffusion, they carry blood very close to the cell in order for the cell to exchange substances – therefore in order to make this diffusion fast, capillaries only have 1 cell wall thick cell walls (Very permeable)
  • This makes it faster as it decreases diffusion distance


  • Veins carry deoxygenated blood back into the heart by low pressure of a large lumen
  • Capillaries join to form veins
  • Veins take the blood back into the heart. Blood is not at a high pressure therefore the walls of veins do not have to be thick
  • Veins have valves which stops the backflow of blood and has a large lumen
  • Exception: Pulmonary vein brings oxygenated blood from the lungs to the left atrium
  • Note: Largest vein is the vena cava



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