The Ascending Loop of Henle is highly permeable to which substance?

The ascending loop of Henle is characterized by its high permeability to sodium chloride (NaCl) while being impermeable to water. This segment of the nephron plays a critical role in the concentration of urine and the regulation of electrolytes.

As the filtrate passes through the ascending loop, sodium and chloride ions are actively transported out of the tubular fluid and into the interstitial fluid, contributing to a concentration gradient that is essential for the kidney’s ability to concentrate urine. This process does not involve water movement; rather, it helps create a hypertonic environment in the medulla, which is crucial for the reabsorption of water that occurs in the collecting ducts later.

This specific function of the ascending loop enables it to play a significant role in the counter-current multiplication system, allowing for the variation in urine concentration depending on the body's hydration status.