Overview
The TSH–thyroid Feedback Loop
Thyroid stimulating hormone (TSH) is produced by the pituitary gland.
NCLEX-RN
NCLEX-RN
Thyroid-stimulating hormone (TSH) is produced by the pituitary gland. It signals the thyroid gland to produce thyroxine (T4) and triiodothyronine (T3). Circulating thyroid hormone then feeds back to suppress further TSH release. This feedback loop makes TSH a sensitive first test when thyroid dysfunction is suspected. If the thyroid gland itself underproduces hormone, the pituitary senses the deficit and increases TSH. If the gland produces too much hormone, pituitary TSH secretion falls. TSH is most reliable when the pituitary and hypothalamus are functioning normally. A patient with pituitary or hypothalamic disease may have low free T4 without the expected rise in TSH. In that setting, a normal or low TSH is not reassuring; it is inappropriately low for the free T4 concentration.
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