Final answer:
When over-hydrated, the hypothalamus reduces the release of antidiuretic hormone, leading to less water reabsorption by the kidneys and the production of a higher volume of dilute urine to restore normal plasma osmolality.
Step-by-step explanation:
When we are over-hydrated, the plasma volume in our blood increases, and this causes a reduction in plasma osmolality. The hypothalamus detects this change and responds by reducing the production and release of antidiuretic hormone (ADH, also known as vasopressin) from the posterior pituitary gland. As a result, the kidneys reabsorb less water, leading to the production of a larger volume of dilute urine, often of a lighter color. This process helps to return plasma osmolality to normal levels by excreting excess water in the body.