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How do the hypothalamus and pituitary gland regulate the thyroid gland?

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Diagram showing the locations of major human endocrine glands in male and female bodies, including pineal gland, hypothalamus, pituitary gland, parathyroid glands, thyroid gland, thymus, adrenal glands, pancreas, kidneys, testes, and ovaries. — Endocrine system The glands of the human endocrine system.

The hypothalamus and pituitary gland regulate the thyroid gland through the hypothalamic-pituitary-thyroid axis, a system governed by negative feedback.1

The process functions as follows:

Hypothalamic Stimulation: The hypothalamus secretes thyrotropin-releasing hormone (TRH), which travels to the anterior pituitary gland.12
Pituitary Response: In response to TRH, the anterior pituitary secretes thyrotropin—also known as thyroid-stimulating hormone (TSH)—into the bloodstream.13
Thyroid Activation: TSH stimulates the thyroid gland to produce and secrete the hormones thyroxine and triiodothyronine.1
Negative Feedback Loop: To maintain hormone levels within a narrow range, thyroid hormones exert an inhibitory effect on the hypothalamus and pituitary gland. When thyroid hormone concentrations are high, they inhibit the production of both TRH and TSH. Conversely, when thyroid hormone levels are low, the inhibition is lifted, leading to increased TSH secretion to stimulate the thyroid and restore balance.12