Where is salt actively reabsorbed in the nephron?

The correct answer is that salt is actively reabsorbed in the diluting segment of the nephron, which corresponds to the thick ascending limb of the loop of Henle. This segment is characterized by its ability to reabsorb sodium, potassium, and chloride ions via various transport mechanisms. The thick ascending limb is unique in that it is impermeable to water, which allows for the dilution of the filtrate while actively transporting sodium and chloride ions out of the tubular fluid into the interstitium, creating a concentration gradient that is important for the kidney's ability to concentrate urine.

In the distal convoluted tubule and proximal convoluted tubule, there is also active reabsorption of salt, but the context of the question specifies the segment most associated with significant salt reabsorption without water, which is characteristic of the diluting segment.

In the collecting duct, while there is some reabsorption of sodium, it is modulated by hormones such as aldosterone, and the primary function here is more about fine-tuning the final content of the urine rather than the active transport of salt as seen in the diluting segment.

Thus, the diluting segment plays a crucial role in managing the osmolarity of urine and overall body