The signaling described in the scenario is known as endocrine signaling.
What is endocrine signaling?
Endocrine signaling involves the release of hormones into the bloodstream by endocrine glands. In this case, cells in the pituitary gland release thyroid stimulating hormone into the bloodstream, and hyroid stimulating hormone travels to the thyroid gland.
The thyroid gland, in response to hyroid stimulating hormone, then produces hormones that travel throughout the body to regulate metabolism.
This is a classic example of endocrine signaling, where signaling hormones are released into the bloodstream to exert their effects on distant target cells.