Biochemistry at The Biology Project

Clinical Correlates of pH Levels
Problem Set

Problem 3: Rapid response to mild acidosis

The bicarbonate buffering system of blood can respond quickly to mild metabolic acidosis (between pH 7.15 and 7.35) by:

A. expelling CO2 in the lung.
This removal of CO2 from the system then elicits a shift in the bicarbonate equilibrium, consuming H+ and HCO3- to replace the vanished CO2 (with water as the other product). Since H+ ions are consumed, pH is raised. (HCO3- is also consumed, but this is not a problem with mild acidosis, since the CO2 is constantly produced via the processes of normal metabolism and will gradually balance the bicarbonate reaction back the other way, restoring equilibrium.)
B. retaining HCO3- in the kidney.
Although this measure does, in fact, help the situation, it is neither rapid nor complete.
C. excreting H+ in the kidney.
This does happen, but is slow and incomplete compared to the real way the body deals with a little excess acid.
D. direct buffering action of the H2CO3 central intermediate.
H2CO3 can only serve as an effective buffer within a pH unit of its pKa, which is about 6.1.
E. retaining CO2 in the lung.
This would actually make the situation worse.

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January 19, 1999
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