In the proximal tubule, Na+ reabsorption is coupled to the reabsorption of glucose, amino acids, and phosphate via specific apical symporters. What provides the ultimate driving force for all these secondary active transport processes?

• A Apical membrane Na+/H+ exchanger (NHE3)
• B Apical ROMK channel
• C Paracellular electrochemical gradient
• D Basolateral Na+/K+-ATPase ✓

Explanation

The basolateral Na+/K+-ATPase pumps three Na+ out of the cell, keeping intracellular Na+ low. This creates the downhill Na+ gradient from lumen to cell that powers all apical Na+-coupled symporters. NHE3 is one of many transporters using that gradient; ROMK is in the TAL and CCD, not the proximal tubule.

Reference: BRS Physiology, 7th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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