The Controller and Acid-Base Physiology: An Introduction to a Complex Process
Compensatory Mechanisms
Use Animated Figure 7-6 to select a primary acid-base disturbance and play the primary disorder animation to observe the effect on the pH caused by the change in PCO2 or bicarbonate. Then play the secondary (compensatory) process and note how it serves to move the pH back toward normal.
🎬 Animated Figure 7-6 Acid-Base Compensatory Mechanisms
Select a primary disorder and then use the buttons to view the disorder followed by its compensation (secondary disorder). Observe the effects on the pH due to the changes in PCO2 and bicarbonate. The development of the primary disorder and its compensation are shown sequentially here for simplicity, but they may overlap temporally in real life. Note that PCO2 is used as a marker for carbonic acid on the balance (seesaw) shown here because PCO2 is easier to measure and is in equilibrium with carbonic acid. Alkalemia and acidemia are terms that are used when the pH of the blood is above or below normal, respectively.
The goal of these compensatory mechanisms is to restore the pH of the blood to normal or near-normal levels. However, the compensation never results in a pH that is all the way back to 7.40, with the exception of the metabolic compensation for a chronic respiratory alkalosis. If the pH is fully restored to 7.40 or beyond, you should look for the presence of two, simultaneous, primary acid-base disturbances (more on how to recognize this in the next section).
Respiratory compensation for metabolic acid-base disorders can occur within seconds to minutes. The sensitivity of the chemoreceptors and the timely response of the controller to changes in their output ensure this. Metabolic compensation for respiratory disorders, however, generally requires 2 to 5 days to be fully evident. The kidneys’ ability to adjust levels of hydrogen ion and bicarbonate is not as rapid as the respiratory response.