During respiratory acidosis, the kidney compensates by increasing acid excretion and generating new bicarbonate. In which nephron segment does this compensatory response primarily occur?

• A Proximal tubule via NHE3 and carbonic anhydrase
• B Collecting duct intercalated cells via H+-ATPase and H+/K+-ATPase ✓
• C Thick ascending limb via NKCC2
• D Distal convoluted tubule via NCC

Explanation

Chronic respiratory acidosis is compensated by increased H+ secretion and new HCO3- generation in the collecting duct, primarily by alpha-intercalated cells via apical H+-ATPase and H+/K+-ATPase, with basolateral Cl-/HCO3- exchange. The proximal tubule also increases HCO3- reabsorption, but the collecting duct is the site of new bicarbonate generation that raises serum HCO3-.

Reference: Ganong's Review of Medical Physiology, 26th ed.

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