Question

Which of the following comparisons of osmolarity within the kidneys is INCORRECT?

1) The fluid in the proximal tubule is iso-osmotic with cortical interstitial fluid.
2) Osmolarity of the ascending limb of the loop of Henle is greater than that of the descending limb.
3) Osmolarity of the descending limb of the loop of Henle is iso-osmotic with the medullary interstitial fluid.
4) The osmolarity of plasma in the vasa recta varies with its location in the renal medulla.
5) Osmolarity of fluid in the proximal tubule is greater than the osmolarity of fluid in the end of the loop of Henle as it enters the distal tubule

Answer 1

The incorrect comparison regarding kidney osmolarity is asserting that the osmolarity of the ascending limb of the loop of Henle is greater than that of the descending limb. It's the opposite; the descending limb has higher osmolarity due to water permeability.Hence, the correct answer is option 2.

Step-by-step explanation:

The comparison of osmolarity within the kidneys that is INCORRECT is assertion 2) Osmolarity of the ascending limb of the loop of Henle is greater than that of the descending limb. In fact, the descending limb of the loop of Henle is water permeable, which means water flows out of the filtrate into the interstitial fluid as it moves deeper into the high salt concentration of the renal medulla. This results in an increase in osmolality inside this limb. In contrast, the ascending limb of the loop of Henle is impermeable to water but allows for the active and passive transport of Na+ and Cl- ions out of the filtrate, which decreases osmolality. Therefore, the osmolarity is higher in the descending limb when compared to the ascending limb.