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Regulation of Potassium Balance

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Potassium excretion is controlled mainly by controlling the rate of

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a. potassium reabsorption in the proximal tubule.

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b. potassium reabsorption in the distal nephron.

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c. potassium secretion in the proximal tubule.

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d. potassium secretion in the distal nephron.

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(d) The distal nephron both reabsorbs and secretes potassium. Quantitatively, the main control is exerted over the rate of secretion.

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In the thick ascending limb

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a. the net amounts of potassium and sodium that are reabsorbed are about the same.

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b. the major pathway for moving potassium from lumen to cell is via the Na-K-ATPase.

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c. most of the potassium that is reabsorbed into the cells leaks back into the lumen via potassium channels.

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d. the major pathway for moving potassium from cell to interstitium is via the Na-K-2Cl multiporter.

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(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.

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For which substance is it possible to excrete more than is filtered?

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a. Sodium

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b. Potassium

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c. Chloride

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d. It is not possible to excrete any of these ions in amounts greater than the filtered loads.

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(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.

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After a potassium-rich meal, the key action of insulin that prevents a large increase in plasma potassium is to

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a. decrease absorption of potassium from the GI tract.

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b. increase uptake of potassium by tissue cells.

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c. increase the filtered load of potassium.

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d. increase tubular secretion of potassium.

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(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.

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A key role of “BK” potassium channels in the kidney is to

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