Regulation of Potassium Balance
Potassium excretion is controlled mainly by controlling the rate of
a. potassium reabsorption in the proximal tubule.
b. potassium reabsorption in the distal nephron.
c. potassium secretion in the proximal tubule.
d. potassium secretion in the distal nephron.
(d) The distal nephron both reabsorbs and secretes potassium. Quantitatively, the main control is exerted over the rate of secretion.
In the thick ascending limb
a. the net amounts of potassium and sodium that are reabsorbed are about the same.
b. the major pathway for moving potassium from lumen to cell is via the Na-K-ATPase.
c. most of the potassium that is reabsorbed into the cells leaks back into the lumen via potassium channels.
d. the major pathway for moving potassium from cell to interstitium is via the Na-K-2Cl multiporter.
(c) The lumen contains far less potassium than sodium. In order to allow continuous operation of the Na–K–2Cl multiporter, most of the potassium leaks back.
For which substance is it possible to excrete more than is filtered?
d. It is not possible to excrete any of these ions in amounts greater than the filtered loads.
(b) Even under conditions of major natriuresis, most of the filtered sodium and chloride is reabsorbed, but with a high potassium load, high secretion in the distal nephron can lead to more potassium excretion than filtration.
After a potassium-rich meal, the key action of insulin that prevents a large increase in plasma potassium is to
a. decrease absorption of potassium from the GI tract.
b. increase uptake of potassium by tissue cells.
c. increase the filtered load of potassium.
d. increase tubular secretion of potassium.
(b) A large dietary load of potassium is absorbed from the GI tract and taken up by tissue cells (mostly muscle), stimulated by insulin, before being released slowly and excreted.
A key role of “BK” potassium channels in the kidney is to