Biology Homeostasis PMDC Conceptual Practice
PMDC Verified Question 72 of 99
The active outward transport of \(\text{Na}^+\) ions into the medullary interstitium without accompanying water movement occurs at the:
A
Ascending loop of Henle
B
Descending loop of Henle
C
Proximal tubule
D
Collecting duct
Tap any option to test your recall and reveal the step-by-step Propolis autopsy.

Propolis Cognitive Error Autopsy

Official Correct Choice:
Option A: Ascending loop of Henle
Concept: Function of the thick ascending limb.

Solution: The thick ascending loop of Henle actively pumps sodium and chloride out of the lumen while remaining impermeable to water, creating a hypertonic medullary interstitium.

Why other options are incorrect:
  • Option B (Descending loop): Highly permeable to water, but lacks active ion transport mechanisms.

  • Option C (Proximal tubule): Reabsorbs solutes and water together isothermally.

  • Option D (Collecting duct): Reabsorbs water in the presence of ADH, but does not create the initial medullary salt gradient.

Quality & Fidelity Assurance: Every question on BeambePrep is rigorously curated against the official PMDC syllabus with zero filler, zero out-of-syllabus content, and zero typos. When an authentic past paper originally contained a historical mistake or ambiguity from the examining board (such as UHS or NUMS), BeambePrep faithfully reflects the original paper while detailing the nuance and scientific consensus in the autopsy above.

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