Thyroid-releasing hormone signals the pituitary to release TSH, which acts on the thyroid to release T4 and T3.

“so in keeping with the theme of thyroid hormone you have thyroid releasing hor hormone in the brain tells the pituitary to release thyroid stimulating hormone and then the thyroid which we'll talk about in a moment releases thyroid hormones”

“the pituitary at the base of the brain is kind of like you can seen as a sensor or signal and when it senses that your body is low in this important biologically active thyroid hormones t3 it will send a signal like a wake-up call to the thyroid gland which is at the base of the neck”

“You have a hypothalamus. You have a pituitary. You have a thyroid. The hypothalamus secretes TR, thyroid releasing hormone. >> Right. >> To the pituitary. The pituitary secretes TSH, thyroid stimulating hormone to the thyroid gland to secrete T4.”