Renal Response to Acid-Base Imbalance

Overview
  • The kidneys respond to acid-base disturbances by modulating both renal acid excretion and renal bicarbonate excretion. These processes are coordinated to return the extracellular fluid pH, and thus blood pH, to normal following a derangement. Below we discuss the coordinated renal response to such acid-base disturbances.
Renal Response to Acidosis
  • Acidosis refers to an excess extracellular fluid H+ concentration and thus abnormally low pH. The overall renal response to acidosis involves the net urinary excretion of hydrogen, resorption of nearly all filtered bicarbonate, and the generation of novel bicarbonate which is added to the extracellular fluid. Processes of renal acid excretion result in both direct secretion of free hydrogen ions, thus acidifying the urine, as well as secretion of hydrogen in the form of ammonium. These mechanisms are molecularly coupled to the generation of fresh bicarbonate, which is added to the extracellular fluid. Additionally, as discussed in renal bicarbonate excretion, nearly all filtered bicarbonate is resorbed and thus its urinary loss is minimized. Together, these processes slowly reduce ECF hydrogen ions and increase ECF bicarbonate concentrations, thus gradually raising blood pH to its normal value.
Renal Response to Alkalosis
  • Alkalosis refers to a insufficient extracellular fluid H+ concentration and thus abnormally high pH. The overall response to alkalosis involves reduced urinary secretion of hydrogen and the urinary excretion of filtered bicarbonate. Renal acid excretion is minimized in the context of alkalosis, thus preventing further increases in the ECF pH. Instead, renal bicarbonate excretion is increased, resulting in loss of bicarbonate from the extracellular fluid, and an alkalinization of the urine. Together these processes reduce ECF bicarbonate concentrations and in doing so can gradually reduce the blood pH to normal. Ultimate correction an alkalosis will require replacement of the deficient hydrogen ions by those generated through normal metabolic processes.