Final answer:
Active transport of NaCl in the ascending limb of the loop of Henle leads to the dilution of filtrate, not the interstitial fluid, making it hyposmotic.
Step-by-step explanation:
The active transport of NaCl in the ascending limb of the loop of Henle does not lead to hyposmotic fluid in the interstitial region but rather to the dilution of the filtrate inside the limb. As the filtrate rises in the ascending limb, Na+ and Cl- are removed from the filtrate, decreasing its osmolarity. Initially, these ions exit through ion channels, and further up the limb, Na+ is actively transported out of the filtrate, with Cl- following.
The result is the production of a hyposmotic or diluted urine, as the filtrate osmolarity decreases. This process contributes to the ability of the kidneys to concentrate urine and maintain water balance in the body.