The Henderson-Hasselbalch equation in medicine Carbon dioxide (CO2) and bicarbon

Question

The Henderson-Hasselbalch equation in medicine

Carbon dioxide (CO2) and bicarbonate (HCO3?) concentrations in the bloodstream are physiologically controlled to keep blood pH constant at a normal value of 7.40.

Physicians use the following modified form of the Henderson-Hasselbalch equation to track changes in blood pH:

pH=pKa+log[HCO3?](0.030)(PCO2)

where [HCO3?] is given in millimoles/liter and the arterial blood partial pressure of CO2 is given in mmHg. The pKa of carbonic acid is 6.1. Hyperventilation causes a physiological state in which the concentration of CO2 in the bloodstream drops. The drop in the partial pressure of CO2constricts arteries and reduces blood flow to the brain, causing dizziness or even fainting.

Part B

If the normal physiological concentration of HCO3? is 24 mM, what is the pH of blood if PCO2 drops to 25.0mmHg ?

Express your answer numerically using two decimal places.

Explanation / Answer

the equation is

pH = pKa + log [HC03] x 0.03 x PC02

given

[HC03-] = 24 mM

PC02 = 25

pKa = 6.1

so

pH = 6.1 + log 24 x 0.03 x 25

pH = 7.36

so the pH of blood will be 7.36

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