The carriage of carbon dioxide

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  • Created by: Lois
  • Created on: 14-12-12 09:56
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  • Carriage of carbon dioxide
    • How carbon dioxide is transported
      • Carbon dioxide ia released from respiring tissues.
        • It must be removed from these tissues and transported to the lungs.
      • Carbon dioxide in the blood is transported in 3 ways:
        • 5% is dissolves directly in the plasma
          • 10% is combined directly with haemoglobin to form the compound carbamino-haemoglobin
            • 85% is transported in the form hydrogen-carbonate ions (HCO3-)
    • How hydrogen-carbonate ions are formed
      • 1) As CO2 diffuses into the blood, some of it enters the red blood cells.
        • It combines with water to form the weak acid carbonic acid.
          • This is catalysed by the enzyme carbonic anhydrase: CO2+H2O=H2CO3
    • Releasing oxygen
      • As the blood enters respiring tissues, the haemoglobin is carrying oxygen in the form of oxyhaemoglobin.
        • The oxygen tension of the respiring tissues is lower than that in the lungs
          • this is because oxygen has been used in respiration.
            • As a result the oxyhaemoglobin begins to dissociate and releases oxygen to te tissues.
    • Releasing more oxygen - the bohr effect
      • The hydrogen ions released from the dissociation of carbonic acid compete for the space taken up by the oxygen on the haemoglobin molecule.
        • So when the co2 is present, the H+ ions displace the oxygen on the haemoglobin.
          • AS a result the oxyhaemoglobin releases more oxygen to the tissues.
            • Where tissues (such as contracting muscles) are respiring more, there will be more co2.
              • As a result there will be more hydrogen ions produced in the red blood cells.
                • This make the oxyhaemoglobin release more oxygen. This is the bohr effect.
                  • At any particular oxygen tension, the oxyhaemoglobin releases more oxygen when more co2 is present.
                    • So when more co2 is present, haemoglobin is less saturated in oxygen.
                      • This makes the oxyhaemoglobin dissociation curve shift downwards and to the right (the bohr shift).
                        • The bohr effect result in oxygen being more readily released where more co2 is produced from respiration.
                          • This is just what the muscles need for aerobic respiration to continue.
  • 3) The hydrogen ions could cause the contents of the red blood cell to become very acidic.
    • How hydrogen-carbonate ions are formed
      • 1) As CO2 diffuses into the blood, some of it enters the red blood cells.
        • It combines with water to form the weak acid carbonic acid.
          • This is catalysed by the enzyme carbonic anhydrase: CO2+H2O=H2CO3
    • To prevent this, the hydrogen ions are taken up by the haemoglobin to produce haemoglobinic acid.
      • The haemoglobin is acting as a buffer (a compound that can maintain a constant pH).

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