Extracellular and intracellular buffering

1. Response of extracellular in almost instantaneous

2. Response of intracellular can take min-hr to complete

3. Metabolic disorders

   1. resulting from addition of non-volatile acids of alkali to body fluids

   2. buffered primarily in the EXTRAcellular fluid

   3. metabolic acidosis

      1. low pH

      2. low bicarb

   4. metabolic alkalosis

      1. high pH

      2. high bicarb

4. CO₂ / HCO₃^- buffer system most important EXC buffer

   1. CO₂ + H₂O  H₂CO₃  HCO₃^- + H⁺

5. Can use Henderson-Hasselbach equation in any buffer system

   1. pH = pK + log [base/acid]

   2. for bicarb system

      1. pH = pK + log [HCO₃-] / [CO₂]

   3. since amount of CO2 in solution depends on it’s partial pressure and solubility:

      1. pH = pK + log [HCO₃-] /  x P_CO2

         1. alpha = solubility = 0.03

   4. so equation used in clinical setting looks like this:

      1. [H+] = 24 x P_CO2

[HCO₃-]

11. Other extracellular buffers

    1. phosphate

    2. proteins

12. Intracellular buffering of metabolic disorders

    1. buffering of non-volatile acid

       1. movement of H+ into cell

    2. buffering of non-volatile alkali

       1. movement of H+ out of cells

    3. H+ is titrated inside cells by phosphate and proteins

13. Respiratory AB disorders

    1. Resulting from alterations in H₂CO₃ or P_CO2

       1. H₂CO₃ determined directly by P_CO2

       2. virtually all buffering occurs intracellularly

          1.  P_CO2  diffusion of CO2 into cell and buildup of CO2 inside cell forces the bicarbonate rxn towards formation of bicarbonate

          2. bicarb diffuses across its gradient out into the plasma

Category: Biochemistry Notes