Your metabolism – the rate at which you produce and use energy – is regulated by the pituitary and thyroid glands, and the hypothalamus (in the brain), but the actual energy release occurs inside the body’s individual cells. It is here that the thyroid’s role is literally felt.
Each cell has an “energy-generating station” called the mitochondrion, which uses enzymes to combine carbon, hydrogen, and oxygen atoms, forming carbon dioxide and water, and releasing chemical energy.
What Does the Thyroid Do In the Energy Process?
The thyroid produces hormones which do two important things:
- They help the necessary enzymes and electrolytes pass into the cell
- They help the actual processes of energy production in the mitochondria.
Four types of hormone are involved: T4 (tetraiodothyronine or thyroxine); T3 (tri-iodothyronine or liothyronine); T2 (di-iodothyronine) and T1 (mono-iodothyronine).
What Does Thyroxine (T4) Do In the Body?
The thyroid gland makes more of this hormone than any other (15 times more T4 than T3), but it is essentially inactive until converted into T3. The thyroxine travels around the body in the bloodstream until it is needed – when the body is cold, for instance, and needs to warm up. The hypothalamus, which operates as a kind of interface between the brain and the endocrine system, responds to this “I’m cold!” message by making TRH (thyrotrophin release hormone). This travels in the bloodstream to the pituitary gland, which picks up the “message”, and produces TSH (thyroid stimulating hormone). The thyroid then produces T4 (thyroxine), and off it goes into the bloodstream.
The thyroid actually produces some T3 at this point too, for instant energy. This is soon used up, but it provides a very short-term “instant solution” for the body while waiting for the T4 to be converted.
What Happens to the Thyroxine (T4) Once It Is In the Blood?
Each T4 compound has four iodine molecules; T3 has three iodine molecules, T2 has two, and T1 has one. When T4 needs to be converted, a deiodinasing enzymes removes one of its four iodine molecules, taking the total down to three – converting the T4 to T3. This is the active form of the hormone.
In a much smaller proportion of conversions, the enzyme removes a different iodine molecule, resulting in a “reverse T3” (rT3) molecule. This is a contentious area in endocrinology, as some doctors believe the body can produce far too much rT3, over long periods of time, while others think this is unlikely or even impossible.
What Does Tri-iodothyronine (T3) Do Once It Is In the Blood?
T3 has five times the metabolic power of T4, and around 80% of it is produced from T4 by conversion in liver and kidney (only that small initial “hit” of T3 energy is released by the thyroid in response to TSH).
The T3 raises the basal metabolic rate of almost all the cells in the body. It also increases the breakdown of fat, stimulates protein synthesis and degradation, stimulates the heart, and potentates (“arms” ) the fight-or-flight hormones (the catecholamines). These adrenal hormones help explain why adrenal insufficiency can play such an important role in the functioning of the thyroid gland and the T4-T3 conversion process.
T3 gives you energy; it is like fuel for the engine room of the body.
What About T2 and T1 – What Do They Do?
Both of these hormones are supplied as part of natural thyroid hormone therapy (taken from animal glands), but do not form part of standardised medical treatment, because many doctors feel they play no role in the metabolic processes.
Until recently T1 and T2 were thought to play a role only as part of the conversion process, with no actual effect of their own. However, T2 has been found to have a stimulatory effect on the activity of the enzyme that converts T4 to T3; in other words, it helps in the vital conversion process. It is also effective in increasing liver metabolism, and the metabolism of the heart, muscle tissue and “brown fat” (the fat that is burned away, rather than stored in the body). (1) T2 can also help in the breakdown of fat, while not breaking down muscle, which has made this hormone a popular tool for weight loss and body-building, despite a lack of government accreditation.
Read More:
Hypothyrodism and the Adrenals
Notes
- “Calorigenic effect of diiodothyronine in the rat”, Lanni, Moreno, Guglia; Journal of Physiology 1996; 494; 831–837.
