How do the kidneys assist in buffering the pH of the blood?

• A. They remove carbon dioxide.
• B. They produce bicarbonate.
• C. They remove red blood cells.
• D. They produce urea.

Answer: (B)

The kidneys buffer blood pH primarily by generating and reabsorbing bicarbonate, the main extracellular buffer. When there’s extra acid, the kidneys reclaim almost all filtered bicarbonate and also make new bicarbonate as they excrete hydrogen ions (often as ammonium), adding it back to the blood. This increases the buffering capacity and helps restore a normal pH. This function is distinct from the lungs, which buffer by removing CO2, and it’s separate from pathways like red blood cell removal or urea production. So, producing bicarbonate best explains the renal role in pH buffering.