Arteries, veins and capillaries

• 1. Arteries carry blood away from the heart
  2. capillaries are involved in the exchange of materials at the tissue
  3. veins carry blood to the heart
• 1. Heart pumps blood out at high pressure so the artery walls are strong and elastic
  2. Artery walls are thick compared to the size of the lumen
  3. Contain thick layers of muscle to make them strong, and elastic fibres to allow them to stretch and spring back
• Arteries branch into capillaries
• 1. Capillaries are really tiny
  2. They carry blood really close to every cell in the body to exchange substances with them
  3. have Permeable walls, so the substances can diffuse in and out
  4. Supply food and oxygen, take away waste like CO2
  5. Walls are usually 1 cell thick, increases the rate of diffusion by decreasing the distance
• capillaries eventually join up to form veins
• 1. The blood is low pressure in the veins so the walls don’t need to be as thick as artery walls
  2. Have a bigger linen than arteries to help the blood flow, despite the low pressure
  3. Have valves to help keep the blood flowing in the right direction
• Rate of blood flow = volume of blood / number of minutes