Thyroid Doctor in Dombivli Functions of the Thyroid & parathyroid glands The main function of both these glands, as shared earlier, is to release hormones that help regulate the metabolism in the body. The thyroid uses dietary iodine to make T3 & T4. The hypothalamus and the pituitary glands, located in the brain, in-turn control the function of the thyroid and parathyroid glands. The Hypothalamus releases TRH (thyrotropin-releasing hormone) which stimulates the pituitary to release TSH (thyroid-stimulating hormone), thereby regulating the thyroid.