Fundamentals Of Thyroid Physiology
Today we will learn the basics of thyroid function. This will allow us to better understand why we are ill and where does this low or high TSH come from? I invite you to read the article!
At the beginning – what is thyroid?
Thyroid is a kind of hormone store – it contains thyroglobulin, which is a store of thyroxine and triiodothyronine (thyroglobulin is actually a precursor to hormones, so when it comes to attacking this tissue, you can suddenly release hormones from it). Thyroid gland has a fundamental function in the work of our body – it is responsible for the production of hormones. In addition, there is another type of cell within the thyroid gland. They are so-called C cells that produce the calcitonin polypeptide associated with the regulation of the calcium-phosphate balance.
Who among you knew that TSH (thyrotropin) is not a thyroid hormone?
TSH is the pituitary hormone, specifically the pituitary gland.
Hormones exert a wide-ranging effect on the processes of the human body – with severe hypothyroidism, cretinism, or impairment of fetal development function, can occur.
What is affected by thyroid?
Would it be a big mistake saying proper thyroid function affects every cell of our body? As you can see – rather not. Someone may say okay, but for example, testosterone is mainly responsible for the man’s libido, and vitamin D for bone mineralization – surely, that’s right. Remember, however, that the production of these or other compounds by our body depends on whether it will be necessary to translate the appropriate information from DNA to protein, so we need to stimulate the cell nucleus, and that’s where the thyroid hormone receptors are located. What’s more, each cell of our body contains such a receptor for thyroid hormones.
It is now easier for us to understand why people with thyroid disease feel so bad and have different symptoms.
The proper function of the thyroid also takes care of the proper temperature of our body, so when we suspect hypothyroidism, it’s worth to examine your own temperature, especially in your mouth. And body temperature drops, because we have a lower so-called thermogenesis. It turns out that in the case of hypothyroidism it is often lowered, while in hyperthyroidism it is raised.
So that we can produce thyroid hormones efficiently, we also need tyrosine. Tyrosine is an amino acid, we find it in protein, e.g. eggs, meat or fish. Tyrosine is also a substrate for the formation of thyroid hormones.
+ iodine → thyroglobulin → thyroid hormones
So the conclusion is that without the sufficient amount of protein and amino acids in the diet, thyroid hormones may have a problem – they simply will not be there because you will not have thyroglobulin. The latter is fortunately an endogenous amino acid, i.e. the human body and most of the animals are able to synthesize it provided that there is sufficient supply of phenylalanine – this amino acid must already be supplied from the diet (because its exogenous amino acid) . Tyrosine is very important for the proper functioning of the thyroid gland and the pituitary gland. The lack of this amino acid induces hypothyroidism, which can show itself in the form of fatigue and exhaustion.
T3 and T4 are iodinated tyrosine derivatives. In other words, it is iodized tyrosine, and even simpler – tyrosine and iodine.
Tyrosine takes place with the participation of thyreoperoxidase, which catalyses / overwatch the attachment of iodine to tyrosine. Iodine oxidation occurs earlier.
Curiosity about thyroids
Because thyroglobulin is produced in case of almost every type of differentiated thyroid cancer, it is commonly used as a marker for this cancer.
It is very important, however, that only tyrosine, which was previously incorporated in the thyroglobulin molecule, is used for the formation of thyroid hormones, not the tyrosine-free form. Free tyrosine will not be used in this process.
So does supplementation with high doses of tyrosine make sense? Or is it more about allowing body to effectively use it? Or maybe the most is the use of amino acids from the diet?
When two DIT (Diiodotyrosine) molecules are combined, T4 will form, i.e. a thyroxin (four iodine molecules and a tyrosine molecule).
However, when DIT and MIT (monoiodotyrosine) molecules are combined, the formation of T3, i.e. triiodothyronine (three iodine molecules and tyrosine molecule).
Oxidation of iodide by thyroglobulin is an indispensable process for the formation of MIT and DIT molecules.
As you can see, iodine is essential for proper thyroid function, but of course as with everything, excessive amounts of it can be unhealthy. With everything you need to be careful, however, the guidelines for the use of iodine are strongly underestimated, which often lead to undesired effects. But iodine can do a lot of damage with Hashimoto. It is not recommended to supplement it in case of this disease.
In the process of stimulation of the thyroid by TSH, 7 times more molecules T4 than T3 are formed. Therefore, as we shall see later, T4 is more PROHORMONE and T3 is HORMONE.
If you know thyroid-inhibiting drugs, so-called thyreostathies, used for hyperthyroidism, e.g. Thyrozol, act to inhibit the oxidation of iodides.
We already know the basics of thyroid hormone construction and the iodination process. What else do we need to know?
The content of hormones in the colloid is enough to maintain their normal concentration in the blood for about 3 months, even when they are not re-synthesized. Put simply – even in the absence of iodine for three more months you will have thyroid hormones in the body, because your thyroid is being stored for a “rainy day”.
Everything starts from the head. When our hypothalamus gets a signal Hey! We need you, thyroid, give us hormones! the hypothalamus will secrete TRH – thyroidoliberine, whose task is to stimulate the pituitary to secrete.
What to secrete?
To secrete TSH, or thyrotropin. Without TRH there is no stimulation for secretion of TSH. Without TSH, there is no stimulation to secrete thyroid hormones.
Tyreolberine is simply a hormone that stimulates the pituitary gland to secrete TSH.
When TSH stimulates the thyroid to work, it will start producing thyroid hormones, T4 and T3. At least that’s what should happen to a healthy person.
Our thyroid produces about 60% of hormones under the influence of TSH. T4, and T3 in the amount of about 20%. About 20 times more T4 than T3 is released from the thyroid gland. T4 is transported in 99.9% in plasma in temporary bond with proteins, and only 0.1% of T4 circulates in free form as FT4, which is the most commonly studied.
Why are we testing free hormones?
Because they are metabolically active – they will bind to the receptor and trigger the effect that we want. Do you know testosterone testing in men? The free and total fractions can also be examined there, but the free one shows how much de facto testosterone can be currently used by organism. So we stay with the free factions. We can have a lot of T4 in total, but very little of free T4, so our body will have a problem. It will not be able to use T4 in the body’s metabolism. Therefore, total T4 level is rarely used in diagnostics.
Interestingly, T4 is considered more a prohormone because it is 2-4 times less active than T3. It is recognized that T3 is a biologically active hormone that acts on target cells in our body. In other words, it causes us to have energy and a willingness to act or that our hair does not fall out. And its concentration should especially interest every lady, as well as every gentleman!
Now, let’s look how those hormones are actually metabolised
A sufficient amount of zinc, selenium, iron and copper is needed for the conversion process. So once again properly balanced diet, healthy lifestyle and eventual supplementation are the keys for success.