Fig. 2. A Davenport diagram, a graphical representation of the Henderson Hasselbalch equation (pH=pK+log[HCO₃^-]/[CO₂]), demonstrating a typical time course for compensation of extracellular (blood) acidosis. Numbers between points represent time (h). Within 1 h of acidotic stress (A—B), extracellular pH generally drops according to the buffering capacity of the plasma. Over the next 12-24 h (B—C), bicarbonate (y-axis; mmol l^-1) is transported into the cell (or protons out) in order to shift the equilibrium towards higher pH values. Upon return to normal seawater CO₂ tensions, there is a rapid increase in pH (C—D), due again to passive reactions, followed by a slower decompensation phase (D—A) leading to restoration of the original acid—base status. Intracellular pH and bicarbonate concentrations generally follow those in the extracellular fluid. See Cameron (1989) for additional details on acid—base balance.

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