Which part of the nephron is permeable to water but not salt?

The descending loop of Henle is the part of the nephron that is specifically permeable to water while being relatively impermeable to salts (sodium and chloride ions). This segment plays a crucial role in the concentration of urine. As the filtrate moves down the descending limb, water exits the tubule into the surrounding hyperosmotic medullary interstitium, leading to an increase in the concentration of solutes in the filtrate. This occurs through the process of osmosis, where water moves from an area of lower solute concentration (inside the tubule) to an area of higher solute concentration (surrounding interstitial fluid).

In contrast, the ascending limb of the loop of Henle is impermeable to water, allowing salts to be actively transported out of the filtrate, which helps to create a concentration gradient that is essential for the kidney's ability to concentrate urine. The distal convoluted tubule also primarily handles salt reabsorption but is not significantly involved in water permeability. The proximal convoluted tubule reabsorbs both water and solutes (such as salts and glucose) but is not characterized by selective water permeability without accompanying salt movement like the descending loop. Thus, the unique properties of the descending loop of