What change occurs in the kidneys when a person becomes dehydrated?

When a person becomes dehydrated, the balance of fluid in the body is disrupted, prompting the kidneys to adjust their function to conserve as much water as possible. In this state, the kidneys respond by increasing the reabsorption of water in the renal tubules, which minimizes water loss through urine. This process is largely regulated by the release of antidiuretic hormone (ADH), which enhances the permeability of the collecting ducts in the kidneys, allowing more water to be reabsorbed back into the bloodstream.

Increased reabsorption occurs while the filtration rate of water remains largely constant. The kidneys continue filtering blood at a steady rate, but the amount of water that is reabsorbed is heightened, effectively concentrating the urine and reducing total urine output. This physiological response is crucial for maintaining homeostasis and ensuring that vital functions continue despite a decreased availability of fluids.

Understanding this mechanism is vital for recognizing how the body adapts to dehydration and the critical role the kidneys play in fluid balance.