What is the primary role of the descending loop of Henle?

The primary role of the descending loop of Henle is to reabsorb water via osmosis. This segment of the nephron is permeable to water but not to solutes, which allows water to exit the tubular fluid into the surrounding hyperosmotic interstitial fluid in the medulla. As the filtrate moves down the descending limb, water is reabsorbed, leading to an increase in the concentration of solutes (such as sodium and urea) within the tubular fluid. This process is critical for the concentration of urine and overall homeostasis in the body, allowing for the conservation of water.

Other processes like reabsorbing sodium occur primarily in other segments of the nephron, such as the ascending loop of Henle and the distal convoluted tubule. The secretion of hydrogen ions is also primarily associated with the distal tubule and collecting ducts, rather than the descending loop. Filtering blood is a function performed by the glomerulus and not specifically attributed to the descending loop of Henle, which primarily deals with the processing of the filtrate after it has been formed.