Arteries,veins and capillaries

• What do arteries do ?

  they carry very high pressure blood from the heart to the organs
• Structure of an artery

  • very thick muscular walls allowing to withstand the high pressure of the blood
  • blood travels through the arteries in surges every time heart beats
• What do elastic fibres do when the surge of blood is released?

  they stretch and recoil in between surges ,keeps the blood moving
• What are capillaries ?

  Tiny blood vessels.
• What do capillaries do ?

  blood passes through,e.g. glucose and oxygen

  carbon dioxide diffuses from the cells back to thee blood
• Structure of capillaries

  • very thin walls (diffusion path is very short ),allows substances to diffuse rapidly
• What are veins for?

  the blood travelling slowly and at low pressure meaning that it could stop or even go backwards
• Structure of veins

  • thin walls (blood pressure is low )
  • contains valves (to stop backflow)
• How do valves work ?

  when the blood is flowing the correct direction the valves open to let the blood to flow through, but when it starts to flow backwards the valves shut