What triggers the release of ADH?

The release of antidiuretic hormone (ADH), also known as vasopressin, is primarily triggered by high plasma osmolarity. When the osmolarity of the blood increases, it typically indicates a higher concentration of solutes, such as sodium. This increase is detected by osmoreceptors located in the hypothalamus. In response, the hypothalamus signals the posterior pituitary gland to release ADH into the bloodstream.

ADH functions to conserve water by promoting water reabsorption in the kidneys, specifically in the collecting ducts. This helps to dilute the blood plasma and restore normal osmolarity levels. Higher osmolarity indicates a need for the body to retain water to prevent dehydration, making this mechanism crucial for maintaining fluid balance.

While other factors like low blood volume do stimulate ADH release, they are more related to the body's overall fluid status rather than direct osmotic changes. Thus, though several stimuli can lead to ADH release, high plasma osmolarity is a primary and direct trigger that prompts the hormone's secretion to help the body cope with increased solute concentration.