Most of us know that, in a perfect world, TSH is a pituitary hormone and its purpose is to stimulate the
thyroid to produce
thyroid hormones.
In that perfect world, the thyroid responds by producing the necessary hormones, which then decreases the TSH. When the thyroid malfunctions, for any number of reasons, it no longer pays attention to the pituitary gland, which continues to crank out TSH, as thyroid hormone levels go lower and lower and we become more and more hypo.