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
  • 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