Final answer:
True, the posterior pituitary releases antidiuretic hormone (ADH) in response to increased plasma osmolality, signaling the kidneys to reabsorb more water and reduce urine volume.
Step-by-step explanation:
The statement that antidiuretic hormone (ADH) is released by the posterior pituitary in response to increased plasma osmolality is true. ADH is produced by the hypothalamus and transported to the posterior pituitary gland for storage and release. When the osmoreceptors of the hypothalamus detect an increase in plasma osmolality, they signal the secretion of ADH. The effect of ADH is to increase water reabsorption in the kidneys, thereby decreasing the volume of urine and preserving body water. This hormone, which is also known as vasopressin, also has vasoconstrictive effects in high concentrations, which can increase blood pressure.