Thyroid hormones are involved in many metabolic functions, including maintain temperature homeostasis.
When body temperature drops, the hypothalamus secretes thyroid-releasing hormone (TRH).
TRH stimulates the anterior pituitary to secrete thyroid-stimulating hormone (TSH).
TSH then stimulates the thyroid gland to synthesize the thyroid hormones T3 and T4.
T3 and T4 in turn exert negative feedback on the hypothalamus and anterior pituitary and inhibit release of TRH and TSH.