Blood Vessels

• The heart acts as the pump for the circulatory system
• Blood vessels


  1. Arteries carry blood away from the heart

  2. Capillaries exchange nutrients and oxygen with tissues

  3. Veins carry blood back to the heart
• Arteries


  • Carry blood directly from the heart
  • Blood inside is at high pressures
  • Have thick layers of muscle and elastic tissue to be strong and elastic
• Capillaries


  • Very small vessels that come into close contact with cells
  • Walls are only one cell thick and permeable
  • Total cross-sectional area is much higher than arteries, so blood flows more slowly
• Veins


  • Relatively large vessels with big lumens
  • Walls are thin with small layers of elastic and muscle tissue
  • Have valves to prevent backwards blood flow
• Calculating rate of blood flow

  Divide volume of blood by time taken
• 2500 ml of blood passes through the aorta in 8 minutes
• Arteries


  Carry very high pressure blood from the heart to the organs in the body
• Arteries


  • Have very thick muscular walls to withstand the very high pressure of the blood
  • Contain elastic fibers that stretch when the surge of blood passes through and then recoil in between the surges to keep the blood moving
• Capillaries


  Where substances such as glucose and oxygen diffuse from the blood to the cells, and carbon dioxide diffuses from the cells back to the blood
• Capillaries


  • Have very thin walls so the diffusion pathway is very short, allowing substances to diffuse rapidly between the blood and the body cells
• Veins


  Carry blood back to the heart
• Veins


  • Have thin walls because the blood pressure is low
  • Contain valves that stop blood flow backwards when the blood is flowing in the correct direction
• Blood travels through the arteries and surges every time the heart beats, and this surge can be felt in the wrist as your pulse
• Once the blood has passed through the organs, it now makes its way back to the heart through the veins