How do the kidneys help keep blood pH within a normal range?

The kidneys maintain blood pH within a normal range by regulating the balance of hydrogen ions and bicarbonate through filtration and secretion processes in the nephrons.1

The regulation of acid-base balance occurs through three primary mechanisms:

• Bicarbonate Reabsorption: The proximal tubules reabsorb filtered bicarbonate to maintain a constant plasma concentration. This process involves the enzyme carbonic anhydrase, which facilitates the conversion of carbon dioxide and water into bicarbonate and hydrogen ions, allowing the body to reclaim essential buffer bases.1
• Excretion of Titratable Acids: Hydrogen ions are secreted into the distal tubules, where they are buffered by substances such as dibasic phosphate. This forms monobasic phosphate, which is then excreted in the urine.1
• Ammonium Production: The kidneys generate ammonia from the amino acid glutamine. This ammonia combines with secreted hydrogen ions to form ammonium ions, which are trapped in the tubular lumen and excreted, effectively removing acid from the body while sparing other essential cations like sodium.1

Together, these processes allow the kidneys to adjust the acidity of urine, ensuring the blood remains at a stable, slightly alkaline pH of approximately 7.4.12