Approximately what fraction of filtered potassium is reabsorbed in the proximal tubule, and by what route?
- A About 25 percent, via the paracellular pathway driven by solvent drag
- B About 50 percent, via transcellular active uptake linked to sodium-glucose cotransport
- C About 65 percent, predominantly paracellular, following water and sodium reabsorption ✓
- D About 90 percent, via apical H-K ATPase identical to the intercalated cell pump
Correct answer: C. About 65 percent, predominantly paracellular, following water and sodium reabsorption
Explanation
Roughly 65 percent of filtered potassium is reabsorbed in the proximal tubule, mostly passively through paracellular routes coupled to the bulk reabsorption of sodium and water. The thin descending limb adds another 25 to 30 percent, so nearly all filtered K reaches the distal nephron regardless of intake. Regulated secretion by principal cells in the collecting duct then determines final urinary K.
Reference: Vander's Renal Physiology, 8th ed.
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Written and medically reviewed by the StethoPrep medical team.