Thyroid-stimulating hormone (TSH) is produced by and stored in the
pituitary gland, which is located beneath the brain. The release of TSH into
the bloodstream stimulates the thyroid gland to release its hormones, called
thyroxine (T4) and triiodothyronine (T3).
When the pituitary gland detects that thyroid hormone levels are
too low, it secretes more TSH. If the pituitary gland detects too much thyroid
hormone, it releases less TSH.