veins, arteries, capillaries

• Arteries


  Carry very high pressure blood from the heart to the organs in the body
• Arteries


  • Have very thick muscular walls to withstand the very high pressure of the blood
  • Contain elastic fibers that stretch when the surge of blood passes through and then recoil in between the surges to keep the blood moving
• Capillaries


  Where substances such as glucose and oxygen diffuse from the blood to the cells, and carbon dioxide diffuses from the cells back to the blood
• Capillaries


  • Have very thin walls so the diffusion pathway is very short, allowing substances to diffuse rapidly between the blood and the body cells
• Veins


  Carry blood back to the heart
• Veins


  • Have thin walls because the blood pressure is low
  • Contain valves that stop blood flow backwards when the blood is flowing in the correct direction
• Blood travels through the arteries and surges every time the heart beats, which can be felt as a pulse in the wrist
• Once the blood has passed through the organs, it makes its way back to the heart through the veins
• The blood travels slowly under low pressure in the veins, which means it could stop or even go backwards