Respiratory regulation of acid base balance
The respiratory system acts as the second line of defense against acid base disturbances. An increase in PCO2 of ECF, decreases the pH, while a decrease in PCO2, increases the pH. Therefore, by adjusting the PCO2, the lungs effectively regulate the H+ ion concentration of the ECF.
An increase in ventilation removes CO2 from ECF thereby reducing the H+ ion concentration. Similarly, a decrease in ventilation, increases CO2 thus increasing H+ ion concentration in ECF.
Arterial PCO2 is inversely proportional to alveolar ventilation, i.e., if alveolar ventilation falls, PCO2 rises. Therefore, relatively small changes in ventilation has a profound effect on H+ ion concentration and pH.
Respiratory system acts as a typical negative feedback controller of H+ ion concentration.
An increase in the H+ concentration above the normal, stimulates the respiratory system and alveolar ventilation increases. This decreases the PCO2 in ECF and reduces H+ ions concentration back to normal.
