What is the primary role of the kidneys in maintaining acid-base balance?

The primary role of the kidneys in maintaining acid-base balance involves the reabsorption of bicarbonate from urine. Bicarbonate (HCO3-) is a key buffer in the bloodstream that helps neutralize acids, thereby maintaining a stable pH level in the body.

When blood pH becomes too acidic, the kidneys work to reabsorb bicarbonate back into the bloodstream, preventing it from being lost in the urine. This process helps to increase the bicarbonate concentration in the blood, which can then bind to excess hydrogen ions (H+) and reduce acidity. In contrast, if the blood becomes too alkaline, the kidneys can adjust by allowing more bicarbonate to be excreted in the urine.

The other choices do not accurately reflect the main function of the kidneys in acid-base regulation. For instance, excreting bicarbonate into the urine would lower bicarbonate levels in the blood, which is contrary to the kidneys' role in maintaining balance. Producing hydrogen ions for the blood would increase acidity, which is not desirable for maintaining homeostasis. Absorbing acids from the bloodstream is less relevant because the kidneys typically excrete excess acids rather than absorbing them. Thus, the reabsorption of bicarbonate is crucial for the kidneys’ role