Feedback Mechanisms and Feedback Loops

Of course the thyroid does not simply produce T-4 continuously. This is due to the "checks and balances" nature included called "feedback-mechanisms". In the care of thyroid function the feedback-mechanism or loop involves the hypothalamus (secretes TRH), pituitary gland (secretes TSH), thyroid gland (secretes T-4), and the liver (converts T-4 into T-3). A feedback-mechanism or loop can trigger the release of another hormone (positive feed-back), or inhibit its release (negative feed-back) thus maintaining that balance. This means high levels of T-4 or T-3 initiate a negative feed-back loop that tells the hypothalamus to produce less TRH, and low levels of T-4 or T-3 initiate a positive feed-back loop that tells the hypothalamus to produce more TRH.

individuals reported the utilization of doctor prescribed blood tests for their personal average thyroid hormone levels before, during, and after thyroid drug administration as a means of base line dosage requirements and assessment.

*Thyroid gland function also regulates calcitonin which combats elevated levels of calcium.

*The normal thyroid gland (human) contains about 200 MCG of T-4, and 15 MCG of T-3 per gram)

* About 80% of circulatory T-3 comes from Monodeiodination (T-4 to T-3 liver conversion) of T-4.

*It should be noted that only "free" or unbound thyroid hormones are active and the bound form is not. When reviewing blood test results and reference ranges this is an important factor to assess. The human body normally produces about 76 MCG/daily of T-4 and 26 MCG/daily of T-3. A mid range test result/reference would express these approximate averages. Over 99% circulating hormones are bound. Thyroid Binding Globulin (TBg) Thyroid binding pre albumin (TBPA) and albumin (TBA) .

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