Co2 transport

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“Carbon Dioxide Transport in Blood

  • Forms of co2 in blood
    • CO2 is carried in the blood in three forms:
      • as dissolved CO2
      • as carbaminohemoglobin (CO2 bound to hemoglobin
      • as bicarbonate (HCO3-), which is a chemically modified form of CO2.
        • HCO3- is quantitatively the most important of these forms.
      • Dissolved CO2
        • Henry’s law,
          • concentration of CO2 in blood is the partial pressure multiplied by the solubility of CO2.
        • The solubility of CO2 is 0.07 mL CO2/100 mL blood/mm Hg;
        • concentration of dissolved CO2 in arterial blood, = 8 mL CO2/100 mL blood (40 mm Hg x  0.07 mL CO2/100 mL blood/mm Hg),
        • it is approximately 5% of the total CO2 content of blood. (MCQ)
        • because of the lower solubility of O2, compared with CO2, dissolved O2 is only 2% of the total O2 content of blood(MCQ)
      • Carbaminohemoglobin
        • CO2 binds to terminal amino groups on proteins (e.g., hemoglobin and plasma proteins such as albumin).
        • When CO2 is bound to hemoglobin, it is called carbaminohemoglobin, which accounts for about 3% of the total CO2. (MCQ)
        • CO2 binds to hemoglobin at a different site than O2 binds to hemoglobin.
        • Bohr effect(MCQ)
          • CO2 binding to hemoglobin reduces its affinity for O2 and causes a right-shift of the O2-hemoglobin dissociation curve (Bohr effect).
        • Haldane effect(MCQ)
          • In turn, O2 bound to hemoglobin changes its affinity for CO2
          • when less O2 is bound, the affinity of hemoglobin for CO2 increases (the Haldane effect).
        • HCO3–
          • Almost all of the CO2 carried in blood is in a chemically modified form, HCO3– accounts for more than 90% of the total CO2.
          • The reactions that produce HCO3- from CO2
            • involves the combination of CO2 and H2O to form the weak acid H2CO3.
            • This reaction is catalyzed by the enzyme carbonic anhydrase(MCQ)
            • In turn, H2CO3 dissociates into H+ and HCO3-.
            • In the tissues,
              • CO2 generated from aerobic metabolism is added to systemic capillary blood, converted to HCO3-
              • transported to the lungs
            • In the lungs, HCO3- is reconverted to CO2 and expired.

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