What happens to the loop of Henle when ADH is released?

When antidiuretic hormone (ADH) is released, it primarily acts on the kidneys to increase water reabsorption in the collecting ducts. However, it also has effects on the loop of Henle, specifically increasing the osmotic gradient in the medullary interstitium. Though the most significant action of ADH occurs at the collecting duct, the presence of ADH enhances the overall concentration of urine by promoting the reabsorption of water, which can indirectly affect how solutes like sodium are handled throughout the nephron, including the loop of Henle.

To clarify concerning the context of the question, saying that ADH "stops fluid offloading" suggests a misunderstanding of the term "offloading," which typically refers to the excretion of water. Instead, when ADH is present, it facilitates water retention rather than stopping the reabsorption processes altogether. This results in a net increase in the concentration of urine as more water is reabsorbed.

In essence, the correct understanding is that ADH increases water reabsorption, enhancing the kidney's ability to concentrate urine and manage the body's fluid balance rather than halting or completely stopping any renal function.