Arteries veins and capillaries

• Arteties have very thick muscular walls . This allows them to withstand very high pressure of the blood

  
• Arteries contain elastic fibres which stretch when the surge of blood passes through
• Blood travels to the organs in arteries
• When the blood is in the organs it passes through capillaries

  
• When blood passes through capillaries substances such as glucose and oxygen diffuse from the blood to the cells and carbon dioxide diffuses from the cells back into the blood
• Capillaries have thin walls so the diffusion path is very short
• capillaries thin walls allows substances to diffuse rapidly between the blood and the body cells
• Veins have a thin wall as the blood pressure is low so the wall doesn’t need to be thick
• Many veins contain valves to stop blood flowing backwards