USMLE

CO2 Transport

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Cardiovascular
  1. Cardiovascular Overview
  2. CO2 Transport
  3. Heart
  4. Cardiac Impulse
  5. Blood Pressure
  6. Arteries and Arterioles
  7. Veins and Venules
  8. Capillaries
  9. Circulation
  10. Blood
  11. Hemoglobin
  12. Blood Clotting
  • Topic Anchor: CO2 Transport
    • Gaseous CO2 in RBCs is converted into carbonic acid and bicarbonate to allow water-soluble transport in blood
      • CO2 + H2O <--> H2CO3 <--> HCO3— + H+
      • CO2 mainly carried as bicarbonate ion in blood
      • Catalyzed by carbonic anhydrase
      • pCO2 drives CO2 transport
        • In tissues
          • High pCO2 generated by respiration of tissues
            • drives reaction forward
          • Conversion of CO2 → bicarbonate
            • Bicarbonate diffuses into plasma, allowing reaction to continue
        • In lungs
          • Low pCO2 due to exhalation
            • drives the reaction backward
          • Conversion of bicarbonate → CO2
            • Bicarbonate diffuses from plasma into RBC to supply this reaction
    • Used to buffer pH of blood
      • When blood is too acidic, reverse reaction is favored to increase pH
      • When blood is too basic, forward reaction is favored to decrease pH