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The hypothalamic–pituitary–thyroid axis (HPT axis for short, a.k.a. thyroid homeostasis or thyrotropic feedback control) is part of the neuroendocrine system responsible for the regulation of metabolism and also responds to stress. As its name suggests, it depends upon the hypothalamus, the pituitary gland, and the thyroid gland.
Negative correlation of Jostel's TSH index to the urinary excretion of certain phthalates suggests that endocrine disruptors may affect the central set point of thyroid homeostasis. [28] Drugs that reduce the TSH index, probably via effects on the central set point of the feedback loop, include mirtazapine [29] and oxcarbazepine. [30]
SimThyr is a free continuous dynamic simulation program for the pituitary-thyroid feedback control system. [1] The open-source program is based on a nonlinear model of thyroid homeostasis. [2] [3] [4] In addition to simulations in the time domain the software supports various methods of sensitivity analysis.
The concentration of thyroid hormones (T 3 and T 4) in the blood regulates the pituitary release of TSH; when T 3 and T 4 concentrations are low, the production of TSH is increased, and, conversely, when T 3 and T 4 concentrations are high, TSH production is decreased. This is an example of a negative feedback loop. [5]
Such anticipatory reactions are open loop systems which are based, essentially, on "guess work", and are not self-correcting. [82] Anticipatory responses always require a closed loop negative feedback system to correct the 'over-shoots' and 'under-shoots' to which the anticipatory systems are prone.
This is an example of a homeostatic negative feedback loop. Breakdown of the hormone. Exocytosis and other methods of membrane transport are used to secrete hormones when the endocrine glands are signaled. The hierarchical model is an oversimplification of the hormonal signaling process.
For example, thyrotropin-releasing hormone (TRH) is released from the hypothalamus in response to low levels of secretion of thyroid-stimulating hormone (TSH) from the pituitary gland. The TSH in turn is under feedback control by the thyroid hormones T4 and T3. When the level of TSH is too high, they feed back on the brain to shut down the ...
Thyroid gland. follicular cells of the thyroid gland produce and secrete T 3 and T 4 in response to elevated levels of TRH, produced by the hypothalamus, and subsequent elevated levels of TSH, produced by the anterior pituitary gland, which further regulates the metabolic activity and rate of all cells, including cell growth and tissue ...