ADH (antidiuretic hormone) helps the kidneys retain water by making the collecting duct
walls permeable to water.
When you're dehydrated, ADH levels rise. Water is reabsorbed from the duct into the
bloodstream.
When ADH is absent, ducts are impermeable. Water stays in the duct and becomes urine.
This process is part of osmoregulation, balancing water and salts to maintain homeostasis.
