Thyroid-stimulating hormone (TSH) is the main regulator of thyroid cell growth and thyroid hormone synthesis and secretion. This 30KD protein TSH is synthesized and secreted by tsh cells of pituitary gland, and it can have negative feedback to the synthesis and secretion process. The fluctuation of TSH is faster and more significant than thyroid hormones when thyroid function was changed, it is a hypothalamic-pituitary-thyroid function.