What does the loop of Henle do in urine formation?

The primary function of the loop of Henle is the recovery of water and sodium chloride from the filtrate within the nephron, a process essential for producing concentrated urine and conserving body water.1

The loop achieves this through a mechanism known as countercurrent multiplication:2

• Descending Limb: This segment is permeable to water, allowing it to leave the tubule as the surrounding fluid becomes increasingly concentrated with salt and urea.1
• Ascending Limb: In this section, sodium chloride is removed from the tubule—initially by diffusion and subsequently through active transport in the thick ascending limb—to create a high-salt environment in the surrounding medullary fluid.12

By maintaining this high osmotic pressure in the medulla, the loop of Henle enables the collecting ducts to reabsorb water efficiently, regulated by antidiuretic hormone. This system ensures the body can balance salt and water levels based on intake and hydration status.12