Where does water reabsorption primarily occur in the nephron?

Water reabsorption primarily occurs in the proximal tubule and the Loop of Henle. In the proximal tubule, about 65-70% of the filtered water is reabsorbed along with solutes such as sodium, glucose, and amino acids. This segment has a high permeability to water due to the presence of aquaporin channels, allowing water to follow the solutes through osmosis.

The Loop of Henle further plays a crucial role in the reabsorption of water, particularly in the descending limb, which is highly permeable to water but not to solutes. This allows for the concentration of urine by creating a hyperosmotic medullary interstitium, facilitating the reabsorption of water in the collecting duct later.

In contrast, the renal corpuscle is primarily involved in filtration, where blood plasma is filtered to produce the initial filtrate containing water, ions, and small molecules. The distal convoluted tubule and the collecting duct do participate in water reabsorption, but the majority of it occurs earlier in the nephron, specifically in the proximal tubule and Loop of Henle. This understanding of where water reabsorption primarily occurs is fundamental in comprehending how the kidneys regulate fluid balance and osmolar