Question:hard
The components responsible for the counter-current mechanism in the kidney include all of the following EXCEPT:
The components responsible for the counter-current mechanism in the kidney include all of the following EXCEPT:
Show Hint
Which limb does the active sodium pumping - thick or thin? Pick the EXCEPT.
Updated On: Jul 6, 2026
- Sodium outflow in thick ascending limb
- Water outflow in thin descending limb
- Sodium outflow in thin ascending limb
- Flow of tubular fluid from PCT to DCT
Show Solution
The Correct Option is C
Solution and Explanation
Step 1: Recall how the loop of Henle generates a hyperosmotic medulla. The key engine is the single effect: active NaCl pumping out of the water-impermeable thick ascending limb, which is then multiplied along the length of the loop by counter-current flow.
Step 2: Confirm the legitimate parts. The thick ascending limb actively extrudes sodium (with K and Cl), the thin descending limb is water permeable and loses water to the interstitium, and tubular fluid must keep flowing through the loop from PCT toward DCT for the multiplier to work. All three are true components.
Step 3: Find the exception. In the thin ascending limb, sodium chloride leaves passively and the segment lacks the active sodium pump that powers the multiplier; calling 'sodium outflow in the thin ascending limb' an active driving component is incorrect. So it is the odd one out.
\[\boxed{\text{Sodium outflow in the thin ascending limb}}\]
Step 2: Confirm the legitimate parts. The thick ascending limb actively extrudes sodium (with K and Cl), the thin descending limb is water permeable and loses water to the interstitium, and tubular fluid must keep flowing through the loop from PCT toward DCT for the multiplier to work. All three are true components.
Step 3: Find the exception. In the thin ascending limb, sodium chloride leaves passively and the segment lacks the active sodium pump that powers the multiplier; calling 'sodium outflow in the thin ascending limb' an active driving component is incorrect. So it is the odd one out.
\[\boxed{\text{Sodium outflow in the thin ascending limb}}\]
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