The Transport of Carbon Dioxide

  • Respired carbon dioxide has to be removed:
    • 5% Dissolves as a gas in the plasma
    • 10% Combines with Haemoglobin (Carbaminohaemoglobin)
    • 85% Dissolved in the form of hydrogen carbonate ions HCO3
  • Carbonic acid is produced using the enzyme carbonic anhydrase:
    • CO2 + H2O  →  H2CO3
  • Carbonic acid in solution produces hydrogen ions and hydrogen carbonate ions:
    • H2CO3 → HCO3 + H+
  • Chloride shift:
    • The negatively charged hydrogen carbonate ions diffuse out of the red blood cells. To balance the charge, Cl ions move in.
  • Hydrogen ions cause the red blood cell to become acidic. To control this, haemoglobin takes up the hydrogen ions to form haemoglobinic acid. The haemoglobin acts as a buffer.
  • The Bohr Effect:
    • The hydrogen ions compete for the space on the haemoglobin originally taken up by oxygen.
    • The hydrogen ions displace the oxygen making the oxyhaemoglobin dissociate faster.
    • More CO2 → more H+ ions → more freely O2 dissociates from oxyhaemoglobin.


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