Question:hard
Hyperosmolarity of the renal medulla is most importantly due to:
Hyperosmolarity of the renal medulla is most importantly due to:
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The countercurrent mechanism deposits mainly NaCl; sodium is the dominant solute.
Updated On: Jun 24, 2026
- Potassium
- Sodium
- Glucose
- Chloride
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The Correct Option is B
Solution and Explanation
Step 1: Picture the loop of Henle as a countercurrent multiplier. Its thick ascending limb actively extrudes salt without letting water follow, loading the surrounding medulla with solute.
Step 2: The transporter responsible is the Na-K-2Cl symporter, but the driving and dominant ion is sodium. The explanation explicitly notes that NaCl is the most important solute for maintaining a high medullary interstitial osmolarity.
Step 3: Glucose has no part in medullary hypertonicity, and although potassium and chloride accompany sodium across the membrane, sodium is the principal osmotic agent. Therefore, of the listed single ions, sodium is the best answer.
\[\boxed{Sodium\ (as\ NaCl)}\]
Step 2: The transporter responsible is the Na-K-2Cl symporter, but the driving and dominant ion is sodium. The explanation explicitly notes that NaCl is the most important solute for maintaining a high medullary interstitial osmolarity.
Step 3: Glucose has no part in medullary hypertonicity, and although potassium and chloride accompany sodium across the membrane, sodium is the principal osmotic agent. Therefore, of the listed single ions, sodium is the best answer.
\[\boxed{Sodium\ (as\ NaCl)}\]
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