Thread: Physiology Of The Thyroid System
01-25-2004, 01:03 PM #1
Physiology Of The Thyroid System
I've noticed recently a lot of posts concerning T3/Clen. So why not post up a basic understanding of what it's effecting - RTB
Physiology of the thyroid system
The thyroid gland produces two main hormones -- T4, which is largely inactive, and T3 which possesses full physiologic activity. This process is being closely controlled by the thyroid's two chief "supervisors" residing in the brain, pituitary and hypothalamus, through the feedback loops whereby hypothalamus, upon sensing a certain level of T3 in the blood, secretes an appropriate amount of TRH -- thyrotropin releasing hormone to either stimulate or slow down the pituitary gland in its own production of TSH -- thyroid stimulating hormone. The TSH in its turn does the same to the thyroid gland depending upon the amount of TSH produced. It must be emphasized that the pituitary runs its own double checking system in case its superior, hypothalamus, fails.
The pituitary samples content of T3 in its own circulation from a conversion of inactive T4 into active T3 which it carries out within its own cells. The thyroid gland when stimulated by the TSH uses iodine, protein and amino acid tyrosine to produce enzymatically about 90% of the T4 and only 10% of T3. As one can tell from this ratio, prevailing T4 hormone by and in itself is insufficient to meet the metabolic needs of the body as its cells call primarily for active T3 hormone. So, another physiologic network system takes over and assures that with the aid of cortisone secreted by the adrenal glands, a proper conversion of T4 into T3 takes place in the liver and kidneys through their special enzymes. In the process of this conversion a small amount, we may call it a waste product, is being produced -- reverse T3 which does not possess any physiological activity.
The mere, even if normal, production of T3, however, does not complete the task, for the sole presence of hormones circulating in blood, and for that matter nutrients, is not sufficient by and of themselves to exert their physiologic function unless they connect properly with their main target -- cells. There the T3 has to get through cellular membranes and connect with the receptors of energy producing organelles -- mitochrondria and of cell nucleus. In order to complete the list of all the participants of the thyroid system, one has to include another major player -- a network of about 15 cytokines. The cytokines are one of the hottest items in contemporary medical research and represent hormone-like substances known, to modulate a broad range of physiologic functions. Some of then play a key role in the immune system (Interferons, Interleukines, Tumor Necrosis Factor etc.) and are known to have a direct impact on hypothalamic -- pituitary -- thyroid axis. They also are capable, of blocking T4[right arrow] T3 conversion. As a consequences, blood levels of some cytokines have been found to be inversely related to concentration of active T3 hormone.
To summarize this, the main components of the thyroid system are:
Thyroid gland and its enzymes
Iodine and protein supplies
Liver and its enzyme
Kidneys and their enzyme
Adrenal glands and glucocorticoids
Cell nuclear receptors.
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