Changes in acid-base balance are continuously occurring. The body must adjust to

The first line of defense against a change in pH involves buffering the hydrogen ions. This buffering primarily involves bicarbonate concentration of the plasma and the concentrations of phosphate and proteins within intracellular fluid. The binding of hydrogen ions to these molecules alters the relationship between pH and hydrogen ion concentration. Their binding removes the acid from solution, thereby preventing it from affecting pH. This buffering of hydrogen ions is the most rapid responder. However, this rapid response is limited in its ability to affect pH because it can only buffer changes and cannot reverse changes in pH. The second line of defense is respiratory compensation. Within minutes, any change in pH will be detected by the peripheral chemoreceptors. As pH decreases, ventilation increases to decrease arterial PCO2, which leads to the removal of hydrogen ions from solution, thereby increasing pH. The situation would be reversed if pH were to increase. If respiratory compensation is unable to return pH to control, then the final mechanism, renal compensation will be activated. Renal compensation requires hours or even days to be initiated. If hydrogen ion concentrations in the blood decrease, then secretion of hydrogen would be reduced while bicarbonate reabsorption would also be reduced. At the same time, the synthesis of new bicarbonate would also be reduced. The reverse would occur if pH were to remain below normal.