alleryStart learning →What share of filtered potassium does the thick ascending limb reabsorb, and by what mechanism?
AAbout 20 percent, by simple diffusion
BAbout 20 percent, by symport with sodium
CAbout 65 percent, by active transport
DAbout 5 percent, by symport with chloride
Answer & Solution
Correct answer: B. About 20 percent, by symport with sodium
1. Potassium is reabsorbed early and secreted late along the nephron.
2. The proximal tubule takes about 65 percent of it by diffusion.
3. The thick ascending limb takes a further 20 percent, and it does so by symport.
4. That symport is the carrier bringing sodium, potassium and chloride into the cell together.
5. Beyond the loop the direction reverses: the distal tubule secretes potassium actively.
6. In the collecting duct that secretion is controlled by aldosterone.
7. Assigning simple diffusion to the ascending limb would ignore the symport carrier that defines the segment.
_Source: OpenStax Anatomy and Physiology (CC BY 4.0), Ch 25 "The Urinary System", section 25.6 Tubular Reabsorption_
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