Thyroid-stimulating? hormone? is mainly? responsible? for? regulating? the?? proliferation? of? thyroid? cells, thyroid? blood supply,? and? the? synthesis? and secretion? of? thyroid? hormone,? and? plays? the? most important? regulatory? role?? in? maintaining? normal thyroid? function.Diseases? of? the?? pituitary?? gland?? itself? can? directly?? affect? TSH? synthesis?? and?? release.When? the? thyroid? gland?? itself? causes?? abnormal? thyroid hormone? synthesis? and? secretion,? it? can? also? affect? the? secretion? of? pituitary? TSH? and? serum? TSH levels.? Similarly,? when? hypothalamic? disease? affects? TRH? secretion,? it? also? affects? pituitary? TSH secretion?? and?? serum TSH levels.