What is your thyroid and what are it's functions ?

Gland controlled by: the brain which manufactures & secrets thyroid hormone, endocrine molecules which alter metabolic response of cells body wide, complex; only partially understood. These days, suggest do your own research: https://www.google.com/search?q=thyroid; wikipedia often an OK place to start (I am 1 of many editors). Of course be mindful of the phone system (aka internet) being largely paid for by ads.