Blood Vessels

• • The blood passes around the body in blood vessels 
  • The body contains 3 different types of blood vessel
  • Arteries 
  • Veins 
  • Capillaries
• Function and structure of Arteries

  • Arteries take blood from your heart to your organs
  • Arteries have thick muscular walls made from elastic fibres - this allows them to withstand the very high blood pressure of the heart 

  
• Why do arteries have elastic fibres in their walls

  • Blood travels through the heart in surges every time the heart beats (This surge can be felt in the wrist as your pulse) 
  • Elastic fibres stretch when the surge of blood passes through, and then recoil in between surges which keeps the blood moving
• Capillaries

  • When blood passes through the capillaries, the capillaries allow substances needed by the cells (e.g. glucose and oxygen) to diffuse into them from the blood 
  • They allow substances they don’t need (e.g. carbon dioxide) to diffuse out of them into the blood  
  • Capillaries have very thin walls , so the diffusion path is very short - this allows substances to diffuse rapidly between the blood and the body cells 
  • Capillaries are also very narrow

  
• Function and structure of Veins

  • Veins take blood from your organs to your heart 
  • Veins have a thin wall - this is because the blood pressure is low so the wall does not need to be thick 
  • Veins contain valves to stop blood flowing backwards (backflow)

  
• Describe what valves do depending on the direction that blood flows

  • When blood is flowing in the correct direction, the valves open to allow blood to flow through 
  • When the blood starts to flow backwards, the valves close