[Campbell Biology P.1037] The proximal tubule plays a crucial role in maintaining pH balance ... | Practice Question

The proximal tubule plays a crucial role in maintaining pH balance in body fluids. Which of the following mechanisms contributes to this function?

  • A: Secreting bicarbonate (HCO3-) into the filtrate.
  • B: Actively reabsorbing all urea from the filtrate.
  • C: Secreting H+ and synthesizing/secreting ammonia (NH3).
  • D: Passive reabsorption of NaCl and water only.

Explanation

The text states: 'Processing of filtrate in the proximal tubule helps maintain a relatively constant pH in body fluids. Cells of the transport epithelium secrete H+ into the lumen of the tubule but also synthesize and secrete ammonia, which acts as a buffer to trap H+ in the form of ammonium ions NH4+ .' Additionally, it mentions the reabsorption of bicarbonate HCO3- , which also contributes to pH balance.