The Thyroid: Beyond the Immune System, part II - Dr. Steven Geanopulos

Dr. Steven Geanopulos

The Thyroid: Beyond the Immune System, part II

Posted on September 28, 2015 by Dr. G

This week’s post will continue exploring the mystery of the thyroid. Part I of this series on thyroid health introduced the importance and function of the thyroid, as well as an explanation of how Thyroid Stimulating Hormone affects thyroid health. This week we will focus on the science of the thyroid and take an in-depth look into hypothyroidism.

Click Here to read Part I of this series.

Click Here to read Part III.

Click Here to read part IV


The thyroid hormone story: It all starts in the brain.

The messages originate in a part of the brain called the hypothalamus, the area that responds to changing environments related to light, time of day, stress, love, hunger, exercise, sleep, and much more.

The hypothalamus starts the whole thyroid hormone process by releasing a hormone called TRH. TRH then travels to the pituitary gland (the main gland in charge of all the other glands in the body that make hormones) to initiate the release of TSH (thyroid stimulating hormone). This first step requires proper responses related to brain chemicals called dopamine and serotonin.

TSH from the pituitary will then go to the thyroid and activate enzymes that begin the production of thyroid hormone by the thyroid gland, which is a butterfly-shaped gland in your neck.

When stimulated properly by the pituitary gland via the hormone TSH, the thyroid will then produce two hormones, T3 and T4.

T3 makes up only 7 percent of what the thyroid produces, and T4 makes up 93 percent of what the thyroid produces. The problem is that T3 is the active form of the hormone, and T4 is the “travel” form of the hormone.

In other words, if the thyroid gland is doing its job and working fine, it will produce sufficient amounts of T4 hormone. If T4 is over-produced, the TSH will drop below normal, and you will be diagnosed hyperthyroid. If T4 is under-produced, the TSH will elevate above normal, and you will be diagnosed hypothyroid.

This post explains what can go wrong after the thyroid produces enough T4, which is called being euthyroid or having normal thyroid functions.

Once produced or taken as medication, T4 must be converted to T3.

The T4 (travel form) of the hormone has to go through a multistep process to be converted to T3, then free T3, and then enter our cell nucleus to directly impact the DNA and activate specific genes that start the machinery of the cell in motion (metabolism).

If T4 leaves the normal thyroid and fails in this conversion process to free T3, then a person can have a normal thyroid and still suffer all of the effects and symptoms of hypothyroidism.

How does T4 to T3 conversion occur?

T4 to T3 conversion occurs in different tissues and organs and can be impacted by various states of health. Forty percent of the conversion occurs in the liver, 20 percent in the digestive tract, and 20 percent occurs in our muscles and other organ systems (the last 20 percent is rendered permanently inactive as a safety valve). Conversion requires a healthy environment in each of these systems as well as the presence of sufficient enzymes and enzyme co-factors (enzymes need co-factors to work properly), which can include vitamins, minerals, and other hormones.

Transport protein: Can something go wrong while the hormone is traveling to its intended destination?

There is also the issue of transport of the T3 hormone into the cell itself. For example, once T4 is converted to T3 in the liver or GI tract, it will then have to be transported to tissues all over the body that need it. What tissues and cells need thyroid hormone? All of them.

The thyroid hormone, as we have already stated, affects every cell in the body from your hair to your toes. This transportation occurs on a transport protein, which is kind of like a taxi cab that transports the hormone to its workplace. Once the hormone arrives at the office building, it has to jump out of the cab (transport protein), and enter the building to get to work.

Transport proteins are made from an abundant protein called albumin which is dependent on proper liver health to be available. We mentioned above that the thyroid hormone can exist in a free state (able to go to work), or it can be bound to a protein (in a cab on its way to work). It turns out that 99.7 percent of the available hormone is protein-bound (in the cab) and .3 percent of the hormone is free to go to work. So why is it important to measure both?

The total number of T3 and T4 is important because it tells us the ability of the thyroid gland to produce a sufficient quantity of hormones. The free (unbound to protein) number for T3 and T4 are necessary because it accurately tells us how much of the hormone can actually bind to cell receptors and turn on the mitochondria.

If your doctor is not ordering total T3 and T4 as well as free T3 and T4, then you are not getting a big chunk of the story. But wait, there’s more.

Stay tuned for the next part of this series. Next week, we will take a look at how the thyroid can affect many parts of the body.

Thanks for reading!

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Click Here for part III

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