Clinical Correlates of pH Levels
Problem 6: Compensation for chronic metabolic alkalosis
For chronic metabolic alkalosis, effective compensation by the body involves:
expelling H+ in the kidney.
This would actually make matters worse.
retaining CO2 in the lung.
By mass action, an increase in CO2 in the lungs triggers an increase
in the H2CO3 intermediate, which, in turn, dissociates to bicarb and H+,
thus lowering pH.
expelling HCO3- in the kidney.
This might help a little, but is anyway overwhelmed by the real
retention of NH4+Cl- in the kidney.
This would help a little if it actually happened, but would be rather slow
and incomplete. Also, our bodies normally
convert waste ammonia to another product (urea) for excretion. NH4+Cl-
is, however, sometimes given as an infusion to patients with severe
metabolic alkalosis, since it, analogous to carbonic acid, is unstable,
breaking down to H+, Cl-, and NH3. Expiration of NH3 in the lung then
leaves behind H+ and Cl-, thus bringing down the pH.
expelling OH- in the kidney.
This might happen, but kidney adjustments are not the major means of
compensation for a metabolic defect.
The Biology Project
Department of Biochemistry and Molecular Biophysics
The University of Arizona
January 19, 1999
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