How does excretion help maintain acid-base balance in the blood?

The kidneys play a vital role in maintaining the acid-base balance of the blood by regulating the concentration of hydrogen ions and bicarbonate in the body.12

This process occurs through three primary mechanisms:

• Bicarbonate Reabsorption: The proximal tubules reabsorb filtered bicarbonate, which acts as a crucial buffer in the blood. By keeping plasma bicarbonate levels constant, the kidneys prevent excessive acidity.1
• Excretion of Titratable Acids: Hydrogen ions are secreted into the tubular fluid, where they are buffered by substances such as dibasic phosphate. This process, known as titratable acidity, allows for the safe removal of excess acid in the urine.1
• Ammonium Production: The kidneys manufacture ammonia from the amino acid glutamine. This ammonia combines with secreted hydrogen ions to form ammonium ions, which are trapped in the urine and excreted. This mechanism is particularly important for eliminating large amounts of acid while conserving essential cations like sodium.12

Through these coordinated actions, the renal system ensures that the blood's pH remains within a narrow, healthy range.3