Single and Double Circulatory Systems

• Single circulatory system


  • Blood only passes through the heart once as it moves around the circulatory system
• Double circulatory system


  • Blood passes through the heart twice
  • Ensures blood moves to body tissues rapidly and under high pressure
  • Can deliver oxygen more efficiently than a single circulatory system
• Closed circulatory system


  • Blood is always contained in blood vessels as it travels to and from the heart
  • Blood can move relatively rapidly
  • Amount of blood passing to different organs can be controlled by constricting or dilating blood vessels
• Open circulatory system


  • Insects do not contain blood, instead they contain a fluid called hemolymph
  • Hemolymph is pumped out of the insect's heart and passes directly into the body cavity
  • Molecules are transferred between the hemolymph and the body cells
  • Hemolymph then makes its way back into the heart
  • Hemolymph is not carried in vessels
• In an open circulatory system, the hemolymph cannot move rapidly around the insect and the insect cannot easily change the amount of hemolymph moving to different parts of its body
• Open circulatory systems


  Blood does not move around the body in blood vessels. Instead, cells are bathed by blood or a fluid called haemolymph in a fluid filled space around the organs called a haemocoel, which returns slowly to the dorsal, tube shaped-heart, e.g. insects. There is no need for a respiratory pigment as oxygen is supplied directly to tissues via the tracheal system.
• Open circulatory systems


  • Relatively inefficient
  • Not responsible for the distribution of respiratory gases in insects
• Closed circulatory systems


  Blood can be transported more quickly under a higher pressure, to all parts of the animal's body.
• Single circulatory system


  1. Blood passing through the heart once during its passage around the body

  2. Found in fish where blood is pumped to the gills and onto the body organs before returning to the heart

  3. Also found in the earthworm where five pairs of 'pseudohearts' (which are thickened muscular blood vessels) pump blood from the dorsal vessel to the ventral vessel
• Double circulatory system


  1. Blood passing through the heart twice

  2. In mammals involves one circuit which supplies the lungs where blood is oxygenated (pulmonary circulation)

  3. A second circuit which supplies the body with oxygenated blood (systemic circulation)
• Advantages of double circulation over single circulation

  • Allows a higher blood pressure and faster circulation to be sustained in systemic circulation
  • Oxygenated and deoxygenated blood are kept separate, which improves oxygen distribution