[Campbell Biology P.1039] Based on Figure 44.14 and its accompanying text, if the drug furose... | Practice Question

Based on Figure 44.14 and its accompanying text, if the drug furosemide blocks Na+ and Cl- cotransporters in the ascending limb of the loop of Henle, what would be the expected effect on urine volume?

  • A: Urine volume would decrease significantly.
  • B: Urine volume would increase significantly.
  • C: Urine volume would remain unchanged.
  • D: Urine volume would initially decrease then increase.

Explanation

The ascending limb of the loop of Henle is responsible for actively transporting NaCl out of the filtrate, which is crucial for maintaining the high osmolarity of the interstitial fluid in the renal medulla. This high osmolarity drives water reabsorption from the descending limb and the collecting duct by osmosis. If furosemide blocks the Na+ and Cl- cotransporters, NaCl reabsorption will be impaired. This will reduce the medullary osmotic gradient. As a result, less water will be reabsorbed from the filtrate in the descending limb and the collecting duct, leading to a significantly increased volume of more dilute urine.