What happens to water as filtrate passes through the nephron?

As filtrate passes through the nephron, its composition is continuously altered through the selective reabsorption of water and other constituents back into the blood.1

The process of water recovery is critical for maintaining bodily fluid balance and concentrating urine:

• Proximal Convoluted Tubule: Much of the water and essential solutes are reabsorbed here before the filtrate reaches the loop of Henle.2
• Loop of Henle: The thin descending limb is permeable to water, allowing it to leave the tubule as the filtrate moves into the concentrated environment of the medulla.2
• Collecting Ducts: The final concentration of water in the urine is regulated by antidiuretic hormone (ADH). In the presence of ADH, the ducts become permeable to water, allowing it to be reabsorbed into the blood, which concentrates the urine. In the absence of ADH, the ducts remain impermeable to water, resulting in the excretion of dilute urine.3

This complex system ensures the body conserves water efficiently, especially in arid environments or during periods of dehydration.23