Which section of the nephron is mostly involved in sodium and chloride reabsorption?

The section of the nephron that is primarily involved in the reabsorption of sodium and chloride is the ascending Loop of Henle. This part of the nephron has a specialized impermeability to water, allowing for the active reabsorption of sodium and chloride without water following, which helps create a concentration gradient in the renal medulla. This gradient is crucial for the kidney's ability to concentrate urine and maintain fluid balance.

In the ascending Loop of Henle, sodium is reabsorbed actively through the Na+/K+/2Cl- co-transporter located in the epithelial cells of the thick ascending limb. This process is essential for establishing the countercurrent multiplication system, which aids in the kidney's ability to concentrate urine. As sodium and chloride ions are reabsorbed, the osmolarity of the tubular fluid decreases while the osmolarity of the surrounding interstitial fluid increases, facilitating water reabsorption in other parts of the nephron.

Other sections of the nephron, such as the proximal convoluted tubule, also reabsorb sodium and chloride, but they do so to a lesser extent and along with a variety of other substances. The descending Loop of Henle is primarily involved in the passive reabsorption of water and does