How does feedback regulation maintain pH within a narrow range?

• A. Buffers alone maintain pH; respiration and renal handling have no role.
• B. Buffers, respiratory adjustments, and renal handling of H+ and HCO3- work together in feedback to stabilize pH.
• C. Only renal excretion of bicarbonate maintains pH.
• D. pH is not regulated; it fluctuates with diet.

Answer: (B)

Maintaining pH in a narrow range relies on a layered feedback system that uses buffers, ventilation, and kidney function together. Buffers provide instant, first-line resistance by binding free hydrogen ions, dampening abrupt pH changes, though their capacity is limited. When pH shifts, the respiratory system adjusts CO2 levels: increasing ventilation blows off CO2, shifting the balance to reduce hydrogen ion concentration and raise pH; decreasing ventilation raises CO2 and lowers pH. Sensory receptors in the body detect changes in CO2 and H+ and drive these respiratory adjustments as needed. For longer-term stabilization, the kidneys modulate excretion and reclamation of hydrogen ions and bicarbonate: they can excrete more H+ and generate new bicarbonate, or conserve and reabsorb bicarbonate, to slowly restore pH toward normal. Together, these feedback loops keep pH around 7.35–7.45 by coordinating immediate buffering with rapid respiratory changes and slower renal adjustments.