Thursday, August 13, 2009

Homeostatic Negative Feedback Control Mechanism

Negative Feedback Mechanism

- It’s the physiological inhibition loop controlling most of the endocrine hormones. In negative feedback, any change or variation from the normal range of function is divergent, or resisted. The change or variation in the controlled value signals the response that brings the function of organ back within the normal range. The mechanism primarily depends on factors which manipulate the metabolism and flow of the hormones. Therefore, the high concentration of the hormone alone will not trigger the negative feedback mechanism because it must be triggered by the effect and result of overproduction on the hormone.

A simple example of an endocrine feedback loop is the hypothalamic-pituitary-thyroidal axis. The hypothalamus produces the hypophysiotropic hormone, thyrotropin-releasing hormone (TRH), and releases it into the portal system where it directs the thyrotrophs in the anterior pituitary to secrete thyroid-stimulating hormone (TSH). TSH circulates to the thyroid and stimulates several steps in the thyroid that are critical in the production and release of thyroid hormone. Thyroxine is released in the blood and circulates to the hypothalamus and pituitary to suppress further TRH and TSH production.

References: Fundamentals of Clinical Chemistry by Bishop et al

Clinical Laboratory Diagnosis by John Bernard Henry et al (19th Edition)

Images: original is File:ACTH Negative Feedback.jpg


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