Thyroid TSH is thyroid stimulating hormone, which is a hormone secreted by pituitary cells, and its main function is to promote the secretion of synthetic thyroid hormones, including free thyroid hormone and free triiodothyronine, by thyroid cells. These two hormones also have a feedback inhibitory effect on the thyrotropic hormone secreted by the pituitary gland, that is, when the level of thyroid hormone secreted by thyroid follicular cells increases, the level of thyrotropic hormone decreases, and when the level of thyroid hormone decreases, the level of thyrotropic hormone increases, so thyrotropic hormone and thyrotropic hormone secreted by thyroid cells have a mutual inhibitory and regulatory effect on each other. Therefore, thyroid stimulating hormone and thyroid hormone secreted by thyroid cells have a mutually suppressing and regulating effect to ensure that human thyroid function is within normal levels.