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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.
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]
According to newer theories, [2] elevated concentrations of TSH and thyroid hormones in type 2 allostasis result from an up-regulated set point of the feedback loop, which ensues from increased TRH expression in the basolateral amygdala and the paraventricular nucleus of the hypothalamus in response to stress.
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 ...
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.
The endocrine glands belong to the body's control system. The hormones which they produce help to regulate the functions of cells and tissues throughout the body. Endocrine organs are activated to release their hormones by humoral, neural, or hormonal stimuli. Negative feedback is important in regulating hormone levels in the blood.
They control the body's response to stress [8] and infection. [9] They regulate the body's metabolism, influencing eating and drinking behaviour, and influence how energy intake is utilised, that is, how fat is metabolised. [10] They influence and regulate mood, [11] body fluid and electrolyte homeostasis, [12] and blood pressure. [13]
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]