What is a function of the loop of Henle?

The loop of Henle plays a crucial role in the kidney's ability to concentrate urine, and it achieves this by generating an osmotic gradient in the renal medulla. This part of the nephron consists of a descending limb and an ascending limb, which work together to create a countercurrent multiplier system.

As filtrate moves down the descending limb, water is reabsorbed into the surrounding interstitial fluid due to osmosis, while the filtrate becomes more concentrated. In contrast, the ascending limb is impermeable to water and actively transports sodium and chloride ions out of the filtrate, which dilutes the reported osmolarity. This process effectively establishes a high osmolarity in the medullary interstitium, allowing for water reabsorption in the collecting ducts, thus concentrating the urine.

The loop of Henle enables the kidneys to conserve water while excreting waste products effectively, which is vital for maintaining body fluid and electrolyte balance. This osmotic gradient is essential for the kidneys' ability to produce urine with varying concentrations, responding to the body's hydration status.