Which parts of the nephron are impermeable to water?

The ascending loop of Henle and the distal convoluted tubule are indeed the parts of the nephron that are impermeable to water.

In the ascending loop of Henle, the walls are lined with thick and thin segments that have a low permeability to water. This segment is primarily involved in the active transport of ions, such as sodium and chloride, out of the tubular fluid, which helps in the creation of a hypertonic environment in the medulla. This unique property allows for the concentration of urine by enabling the countercurrent multiplication mechanism while preventing water from following the solutes back into the bloodstream.

Similarly, the distal convoluted tubule also exhibits low permeability to water under normal physiological conditions. Here, the regulation of water reabsorption is influenced primarily by hormones, such as aldosterone, but the tubule itself does not allow for passive water diffusion.

In contrast, the proximal convoluted tubule and the descending loop of Henle are permeable to water. The proximal convoluted tubule reabsorbs a significant amount of water along with solutes, and the descending loop of Henle allows water to be reabsorbed passively due to the surrounding hyperosmotic medullary interstitium.

Thus, identifying