Pituitary Negative Feedback Control

The pituitary gland works via a negative feedback loop.

In general, this means that when one of the target glands that it controls is not producing enough of a certain hormone then the pituitary gland will be instructed by the hypothalamus to raise the level of the stimulating hormone. When the target endocrine gland responds and produces more of the required hormone, then once the hypothalamus notices the increase, it will stop requesting the pituitary gland to stimulate the target endocrine gland.

It's an extremely clever system and works really well, until it doesn't!