Hypothyroidism has reached almost epidemic proportions, especially amongst in women. It’s becoming more common that people realize, and yet many are suffering from low thyroid symptoms have yet to be diagnosed. As incidence is skyrocketing, more and more people are presenting to doctors for appropriate treatment and diagnosis, yet the reality is most will be ignored, mis-diagnosed, or dismissed.
Thyroid health is without a doubt one of the most poorly managed medical conditions. Lack of proper evaluation and inadequate treatment by most doctors can have a serious negative impact on quality of life. Having an in-depth understanding of the entire thyroid hormone chain is crucial to properly identifying and treating the cause of your thyroid dysfunction.
The thyroid gland is a butterfly shaped gland located at the base of your neck, just above your collarbones. It is the first gland and hormone that comes to mind when we think of “metabolism”. Your thyroid gland is responsible for setting the metabolic rate of every cell of our your body. For example, the thyroid hormone sets the rate at which our skin and hair cells turn over and regenerate, which impacts healing from cuts and our rate of hair loss. It affects how quickly we recover and repair our muscles and joints from a tough workout. It also sets the rate of neuron transmission in our brain and how quickly our neurons fire, impacting mood and cognitive function. Thyroid hormones interact with every other system in our body including our digestive, neurological, cardiovascular, musculoskeletal, and hormonal systems.
“Every cell in the body has receptor sites for thyroid hormones. Thyroid hormones are responsible for the most basic and fundamental aspect of physiology, the basal metabolic rate. Lack of ideal thyroid hormone leads to global decline in cellular function of all bodily systems. The thyroid is the central gear in the complex web of metabolism and extremely sensitive to minor imbalances in other areas of physiology.” Datis Kharrazian, D.C
The hypothalamus is the master regulator in our brain. It releases TRH, which acts on the pituitary gland and stimulates it to make TSH. TSH then travels to the thyroid gland to make thyroid hormone. There are two types of thyroid hormone made by the thyroid gland, T4 (93%) and T3 (7%).
Thyroid hormone (T4 and T3) is released from the thyroid gland in a free, active form but must travel to the liver to become bound to a protein so that it does not cause over stimulation of our metabolic rate. In the liver, thyroid binding globulin protein is produced and binds to T4 and T3, which can now circulate throughout our body. This form is now inactive and unusable by our cells, which is good because it helps normalize our metabolic rate. At this point, approximately 99% of thyroid hormone is bound, and only 1% is free in circulation.
T3 is the metabolically active form of thyroid hormone, and T4 must be converted to T3 to be useable by our cells. To do this, T4 goes to our liver to get transformed into T3 by an enzyme called 5’-deiodinase. T4 can also be converted into reverse T3, which is irreversibly metabolically inactive. T4 can also be made into T3 sulfate or T3 acetic acid, which are also inactive, but they can travel to the gut where they are converted to active T3 by our gut bacteria.
To cause an action at the cellular level, active T3 must travel through the cell membrane and act at the receptor inside the cell on the nucleus to create a metabolic response, which will depend on which tissue the hormone lands.
As you can see, thyroid hormone physiology involves so much more than just the thyroid gland itself. In the entire process, from initial hormonal production to causing an action at the cell, we have the hypothalamus and pituitary glands in our brain involved, our thyroid gland, our liver, our gut, and our cells receptors all acting as part of this complex thyroid hormone chain. It gets even more complex once we add other hormones, like cortisol, estrogen, and testosterone to the picture, but I’ll save that for a future post. For now, just understand that there is more to thyroid disorders than just the thyroid gland itself and we need to look at the whole picture to properly treat your thyroid hormone disorder.