The Blood Vessels

• Arteries - Carry blood away from the heart

  Capillaries - Involved in the exchange of materials at tissues

  Veins - Carry blood to the heart
• Properties of Arteries

  • Strong and elastic walls as heart pumps blood at hight pressure
  • Walls are thick compared to the size of the lumen
  • Thick layers of muscle to make them strong and elastic fibres allow them to stretch and spring back
  • They branch into arterioles
• Properties of veins

  • Blood is low pressure so is not as thick as artery walls
  • Bigger lumen than arteries to help low pressure blood flow
  • Have valves to keep blood flowing in correct direction
• As the total cross section of blood vessels increases, the velocity of blood flow decrease. This is why blood in the capillaries move so slowly, as there are so many that it has a large cross section
• The mean pressure of blood is highest in the arteries as they are the closest to the heart
• Capillaries having large cross sectional area is good as they are slow to give substances time to diffuse