Carbon dioxide (CO2) and bicarbonate (HCO3) concentrations in the bloodstream ar
ID: 881794 • Letter: C
Question
Carbon dioxide (CO2) and bicarbonate (HCO3) concentrations in the bloodstream are physiologically controlled to keep blood pH constant at a normal value of 7.4.
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 CO2 constricts arteries and reduces blood flow to the brain, causing dizziness or even fainting.
If the normal physiological concentration of HCO3 is 24 mM, what is the pH of blood if PCO2drops to 34.0 mmHg ?
Explanation / Answer
Given: P(CO2) = 34.0 mmHg, pka = 6.1 , [HCO3- ]= 24 mM
We use Henderson equation ,
pH=pKa+log[HCO3](0.030)(PCO2)
pH = 6.1 + log ([ 24 / ( 0.030*34.0 )
= 7.47
pH of blood = 7.47