The transport of carbon dioxide in the blood

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  • The transport of carbon dioxide in blood
    • When the respiration rate increases (e.g. during exercise), more CO2 is produced
      • Some CO2 is transported in red blood cells, but the majority of CO2 is transported as hydrocarbonate ions in the plasma
    • 1. CO2 from respiring cells diffuses into RBC's
      • 2. The CO2 reacts with water to form carbonic acid (H2CO3). The reaction is catalysed by carbonic anhydrase
        • 3. The carbonic acid then dissociates into positively charged hydrogen ions and negatively charged hydrocarbonate ions
          • 4. The hydrocarbonate ions diffuse out of the RBC into the plasma. This is balanced by the diffusion of chloride ions in the opposite direction, maintaining electro chemical neutrality. This is called the chloride shift
            • 5. The dissociation of carbonic acid increases the acidity of the blood (decreases the pH), lowering the affinity that Hb has for O2. This means more O2 will be unloaded from the Hb and the O2 dissociation curve will shift to the right. This is called the Bohr effect
              • The advantage of this is;
                • The lower blood pH causes Hb to have a lower affinity for O2
                  • So more O2 in unloaded/dissociates at the same pO2
                    • Maintaining a higher respiration rate
                      • Hydrogen ions react with oxyhaemoglobin to for haemoglobonic acid. This reduces the acidity of the blood. This buffering action allows large quantities of carbon dioxide to be carried in the blood to the lungs without major changes in blood pH
                        • 6. This causes more oxygen to be unloaded at the same pO2, so it can diffuse out of the RBC into the respiring tissues
    • The chloride shift refers to the influx of chloride ions into red blood cells to preserve electrical neutrality

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