Our clinic sees a lot of thyroid conditions. Hypothyroidism, hyperthyroidism, Hashimoto’s, and Graves’ Disease. A lot of people get diagnosed with these conditions, but few actually understand what they mean. Here we will break down how the thyroid works and what that might mean to you. See our other posts on specific conditions and diagnosing those conditions.
What is the Thyroid?
The thyroid is a butterfly shaped gland that sits at the base of your neck. It is responsible for producing 2 main hormones: T4 and T3. These 2 hormones are responsible for regulating metabolism through adulthood and promoting growth in children.
Every day, the thyroid gland produces T3 and T4 in response to signals from our environment as well as our metabolic need. If we get signals from our body that we need to increase our metabolism, this gland gets stimulated. These things can include exercise, stress, mental activity, illness and inflammation.
What Does Thyroid Hormone Do?
Like we said above, the thyroid is responsible for producing it’s 2 main hormones: T3 and T4. These hormones stimulate almost every cell in our body to increase it’s metabolism. Here are some examples:
- Cardiac (heart): increases heart rate and blood flow
- Metabolic: improves heat production, oxygen usage, blood sugar usage
- Respiratory: Increases breathing rate and oxygen delivery to tissues
- Nerves: Increases energy, alertness, responsiveness and reflexes
- Gut: Improves stomach tone and motility
- Bones: Increases bone and connective tissue mobility
- Reproductive: regulates reproductive hormones in men and women (ovulation and sperm formation)
- Kidney: promotes renal flow and increases renal clearance.
If T3 or T4 are low or high, there are changes in all of these areas. It can either cause an overstimulation (as in hyperthyroidism) or an under-stimulation (as in hypothyroidism).
The Thyroid Hormones
T4 and T3 are important hormones in the body for reasons above, but it’s important to understand how they both work.
T4 (thyroxine) is the main hormone produced in the thyroid gland. In fact, 90% of the hormones produced in the thyroid gland are T4. But T4 is the inactive form of thyroid hormone. It does not have any stimulatory effects as listed above.
T4 is primarily used as storage for T3. When T4 gets to the tissues it needs to get to to be active, it converts to T3. This is extremely helpful, because T4 can stick around in the body much longer than T3. In fact, it can last in the body up to 5-7 days before it is broken down.
T3 (triiodothyronine) on the other hand is the active form of thyroid hormone. It is the hormone that causes all of those effects we listed above. Because T3 is so active, it is used up quickly wherever it is. In comparison to T4, it can only last in the body up to 1 day, which is why only 10% of it is produced in the thyroid gland itself. The rest of T3 is produced in the tissues when T4 converts to it.
Another hormone that can be produced in the connective tissue is reverse T3 (rT3). Reverse T3 is an inactive hormone that T4 breaks down into when it can’t break down into T3. This can happen when there is too much T3 and T4. It can also happen when there are problems converting T4 to T3 (nutrient depletion, genetic mutations…etc.)
What is TSH?
We’ve talked a lot about T3 and T4, but not a lot about TSH. TSH is the most common lab test that is measured to look at thyroid hormone function. But TSH is not produced in the thyroid, it is produced in the brain (pituitary gland). TSH stands for Thyroid Stimulating Hormone. And it does exactly that: it stimulates the thyroid gland.
When levels of T3 fall in the blood, it sends a signal to the brain that causes the thyroid gland to make more T4/T3. This causes an inverse relationship between TSH and T4/T3. So when T3 or T4 are low, TSH is high. And when T3 or T4 are high, TSH is low.
What is The Takeaway?
Thyroid hormone is an important metabolic hormone that is produced in our body. If too little is produced, then we have problems with our organs working well. If too much is produced, we have problems with our organs overworking. So regulation is important.
There are lots of things that can cause the thyroid to overproduce or underproduce thyroid hormone. We will explore those in other blog posts.
If you have question about your thyroid function, or want to get tested, call our office to schedule an appt with our knowledgeable physicians.
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