What has happened to the osmolarity of the fluid by the time it leaves the ascending loop?

1. Fluid entering the loop is isosmotic with blood, at roughly 278 to 300 mOsmol/kg. 2. In the descending limb water leaves and the fluid concentrates toward about 1200 mOsmol/kg at the hairpin. 3. In the ascending limb salt is pumped out while water is trapped, so the fluid is progressively diluted. 4. By the end of the ascending loop it has fallen to roughly 50 to 100 mOsmol/L. 5. The 1200 figure describes the deepest point of the loop and the medulla around it, not the fluid leaving the ascending limb. 6. The 300 figure describes the fluid entering the loop, before either limb has acted on it. _Source: OpenStax Anatomy and Physiology (CC BY 4.0), Ch 25 "The Urinary System", section 25.6 Tubular Reabsorption_