Final answer:
Water reabsorption in the loop of Henle involves a concentration gradient that decreases osmolality as water leaves the filtrate. Aquaporins aid this process, and different permeability in the descending and ascending limbs facilitate ion and water movement optimizing urine concentration.
Step-by-step explanation:
Water is reabsorbed along concentration gradients established in the loop of Henle which decreases the osmolality inside the loop. The descending limb of the loop of Henle is water permeable, allowing water to flow from the filtrate to the interstitial fluid, hence the osmolality inside the limb increases as it descends into the renal medulla.
In contrast, the ascending limb is not permeable to water, and sodium (Na+) and chloride (Cl-) ions exit through ion channels present in the cell membrane, which is a process that further decreases osmolality. The aquaporin proteins help regulate water movement across membranes, influencing the osmolarity of the blood.