Question
Which segment of the nephron has the lowest osmolality under the influence of antidiuretic hormone (ADH)?
| A. |
Early distal tubule
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| B. |
Descending limb of the loop of Henle
|
| C. |
Collecting duct
|
| D. |
Late distal tubule
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Show Answer
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Correct Answer � D
Explanation
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Nephron Segment with Lowest Osmolality under ADH Influence – Late Distal Tubule
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Antidiuretic Hormone (ADH) acts primarily on the collecting ducts to increase water reabsorption by inserting aquaporin-2 channels.
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However, ADH also has indirect effects that influence osmolality in various parts of the nephron.
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The late distal tubule is the site with the lowest tubular fluid osmolality under the influence of ADH.
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This is because by the time the filtrate reaches the late distal tubule:
– Significant Na⁺ reabsorption has occurred
– Water permeability is low in the distal tubule (except under ADH action)
– Resulting in a diluted (hypoosmotic) tubular fluid
Osmolality in Various Nephron Segments:
A. Early Distal Tubule
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Also called the diluting segment
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Low osmolality due to NaCl reabsorption without water, but not as low as in the late distal tubule under ADH.
B. Descending Limb of Loop of Henle
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Highly permeable to water, but not to solutes
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Water exits into the hypertonic medulla, making this segment highly hyperosmotic, not low.
C. Collecting Duct
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Under ADH, becomes water permeable
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Water reabsorption occurs here, concentrating the urine → higher osmolality, not lower.
