Knowra Hypothalamic–pituitary–thyroid axis Hypothalamic–pituitary–thyroid axis The hormonal feedback system in which the hypothalamus and pituitary regulate thyroid hormone production, while thyroid hormones feed back to regulate both upstream glands.
Thyrotropin-releasing hormone : A hypothalamic peptide hormone that stimulates pituitary thyrotrophs to release thyroid-stimulating hormone. It is the first hormonal signal in the axis, linking hypothalamic activity to pituitary output.
Hypothalamus : A brain region that coordinates autonomic, endocrine, and homeostatic functions. Its paraventricular neurons provide the axis’s releasing signal.
Thyroid function tests : Laboratory measurements, commonly TSH and free thyroxine, used to assess thyroid function. Their patterns reveal whether axis output is excessive, deficient, or discordant.
Circadian rhythm : A roughly 24-hour pattern in biological processes generated by internal timing systems. TSH secretion varies by time of day, complicating interpretation of single measurements.
Thyroid-stimulating hormone : A pituitary glycoprotein hormone that stimulates thyroid growth and the synthesis and release of thyroid hormones. It carries the pituitary signal that directly drives thyroid hormone production.
Pituitary gland : An endocrine gland beneath the hypothalamus that releases hormones regulating other glands and body functions. Its anterior lobe relays hypothalamic input to the thyroid.
Primary hypothyroidism : Insufficient thyroid hormone production caused by dysfunction of the thyroid gland. The axis typically responds with increased TSH when thyroid output falls.
Pulsatile secretion : Hormone release in discrete bursts rather than at a constant rate. Pulses in hypothalamic and pituitary signaling shape hormone patterns that averages can obscure.
Thyroid hormone : The iodine-containing hormones thyroxine and triiodothyronine that regulate metabolism, development, and other body functions. These are the axis’s outputs and the signals that feed back on the hypothalamus and pituitary.
Thyroid gland : An endocrine gland in the neck that produces thyroid hormones and calcitonin. It is the target gland whose hormone output the axis regulates.
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