What effect does ADH have on osmolality in the case of dehydration?

In the case of dehydration, the effect of Antidiuretic Hormone (ADH), also known as vasopressin, is to enable the body to retain water. When the body is dehydrated, the osmolality of the blood increases due to a higher concentration of solutes. ADH is released from the posterior pituitary gland in response to this increased osmolality, activating specific receptors in the kidneys.

ADH primarily acts on the collecting ducts in the kidneys, promoting the reabsorption of water back into the bloodstream. This process results in the production of concentrated urine, effectively reducing the volume of urine output. By retaining more water, the body can dilute the excess solutes in the bloodstream, thereby helping to normalize the osmolality levels. This mechanism is critical for maintaining fluid balance and overall homeostasis during states of dehydration.