Transport in animals - circulatory systems

• Circulatory system


  A system of blood vessels with a pump and valves to ensure the one-way flow of blood
• Circulatory system


  1. Heart contracts

  2. Blood flows through arteries at high pressures

  3. Arteries lead to smaller arterials

  4. Arterials split into capillaries

  5. Pressure falls, blood slows to facilitate exchange

  6. Capillaries merge into venules

  7. Venules lead into veins

  8. Blood returns to heart
• Valves


  • Present in veins and within the heart to ensure blood only flows in one direction
• Single circulation (fish)


  Blood moves through the heart once for each complete circulation of the body
• Single circulation (fish)


  • Simple heart with two chambers: atrium and ventricle
  • Blood pumped from ventricle to gills to become oxygenated
  • Blood then flows to all parts of the body
  • Blood directed back to atrium in veins with valves
• Single circulation systems are relatively inefficient as blood loses pressure and slows down in the capillaries of the gills but still needs to pass through all other organs before pressure is increased again
• Double circulation (mammals)


  Blood passes through the heart twice for each complete circulation of the body
• Double circulation (mammals)


  1. Right side of heart receives deoxygenated blood from body and sends it to lungs

  2. Oxygenated blood returns to left side of heart

  3. Left side of heart contracts, sending blood to body's tissues
• Double circulation (mammals)


  • Maintains high blood pressure to all organs
  • Blood loses pressure in narrow lung capillaries but second passage through heart increases pressure again
• Double circulation allows efficient delivery of oxygen to even the most distant tissues