- After severe diarrhoea, the plasma K+ concentration became low (i.e, hypokalemia developed) in a human subject. The following statements are proposed to explain the mechanism of plasma K+ regulation by kidney in this condition:
A. The principal cells present in distal tubule and collecting duct of nephron regulate Kexcretion.
B. Hypokalemia stimulates Na+, K+ -ATPase activity in the basolateral mem-brane of principal cells.
C. The intracellular K+ concentration of the principal cells is increased.
D. The electrochemical gradient for efflux of K across the apical membrane of principal cells is increased.
E. The permeability of apical membrane to K+ is decreased.
F. The plasma aldosterone level is decreased which inhibits K+ secretion by principal cells.
Which one of the following options represents the combination of all INCORRECT statements?
(1) A, B, C (2) B, C, D
(3) C, D, E (4) D, E, F
Severe diarrhea leads to significant potassium loss from the body, often resulting in hypokalemia—a condition characterized by low plasma potassium (K+) concentration. The kidneys play a crucial role in regulating potassium balance, adapting their function to maintain homeostasis under such stress. Understanding these regulatory mechanisms is essential for comprehending the kidney’s role in electrolyte balance after conditions like diarrhea.
The Role of Principal Cells in Potassium Regulation
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Principal cells in the distal tubule and collecting duct are primary regulators of potassium secretion into the tubular fluid, facilitating potassium excretion.emedicine.medscape
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They achieve this by modulating various ion channels and transporters, especially in response to changes in plasma potassium levels and hormonal signals.
Evaluation of the Proposed Statements
A. Principal cells in distal tubule and collecting duct regulate potassium excretion.
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Correct. Principal cells adjust potassium secretion based on the body’s potassium status.derangedphysiology+1
B. Hypokalemia stimulates Na+, K+-ATPase activity in the basolateral membrane of principal cells.
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Incorrect. Hypokalemia typically decreases Na+, K+-ATPase activity because lower extracellular potassium reduces the pump’s substrate, leading to reduced cellular uptake of potassium.emedicine.medscape+1
C. Intracellular potassium concentration of principal cells is increased.
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Incorrect. In hypokalemia, decreased plasma potassium usually results in decreased intracellular K+ in principal cells, reflecting the reduced extracellular availability.derangedphysiology
D. Electrochemical gradient for K+ efflux across the apical membrane of principal cells is increased.
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Incorrect. Hypokalemia reduces the gradient for potassium secretion (efflux) from cells into the tubular lumen, as extracellular potassium is low.derangedphysiology
E. Permeability of apical membrane to K+ is decreased.
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Correct. Hypokalemia decreases the activity of apical potassium channels (e.g., ROMK), reducing potassium secretion to conserve plasma potassium.derangedphysiology
F. Plasma aldosterone level is decreased, which inhibits K+ secretion by principal cells.
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Correct. Hypokalemia typically triggers a decrease in aldosterone secretion, reducing potassium secretion by principal cells to conserve potassium.emedicine.medscape+1
Summary Table
Statement Correctness Explanation A Correct Principal cells regulate potassium secretion B Incorrect Hypokalemia decreases Na+, K+-ATPase activity C Incorrect Intracellular K+ decreases in hypokalemia D Incorrect Gradient for K+ efflux is reduced in hypokalemia E Correct Apical K+ permeability decreases to reduce K+ secretion F Correct Decreased aldosterone reduces K+ secretion The Combination of Incorrect Statements
The incorrect statements are B, C, and D.
Therefore, the correct answer is: (2) B, C, D
Detailed Explanation
After severe diarrhea, potassium is lost from the body, lowering plasma potassium levels. The kidneys compensate by reducing potassium secretion. This involves:
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Lower Na+, K+-ATPase activity: Reduced substrate (K+) limits pump activity.
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Reduced intracellular K+: Cells lose potassium due to decreased availability.
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Decreased electrochemical gradient for potassium secretion: Limits potassium loss in urine.
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Reduced apical K+ channel activity: Limits K+ movement into tubule lumen.
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Lower aldosterone secretion: Hormonal signaling reduces potassium excretion.
These adjustments help conserve potassium, mitigating hypokalemia.
Conclusion
In the setting of hypokalemia following severe diarrhea, the kidney reduces potassium excretion primarily by decreasing apical membrane permeability to potassium, lowering aldosterone secretion, and reducing the gradient needed for potassium secretion. The statements that are incorrect regarding this mechanism are:
B, C, and D
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