Final answer:
Thirst stimulates osmoreceptors, leading to the release of antidiuretic hormone (ADH) from the posterior pituitary gland, which increases water reabsorption in the kidneys to conserve water and regulate hydration.
Step-by-step explanation:
When one is thirsty and osmoreceptors are stimulated, antidiuretic hormone (ADH) is released from the posterior pituitary gland. ADH, also known as vasopressin, plays a crucial role in regulating the body's water balance. It prompts the kidneys to increase water reabsorption from the collecting ducts and tubules, resulting in concentrated urine and diluted blood plasma, effectively conserving water when dehydration occurs. The hypothalamus controls the mechanism of ADH release by monitoring blood osmolarity and volume, ensuring adequate hydration of the body.