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T3 & T4

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The thyroid gland is responsible for regulating body metabolism through its production of thyroxine (T4) and triiodothyronine (T3) tyrosine-based hormones.

You may have heard about the T3 and T4 hormones before, but may not realize their importance in your body. The T3 and T4 hormones are produced by the thyroid gland and are secreted into the bloodstream to regulate the body's metabolism.

Functions of T3 and T4

These hormones are essential to the growth of the body. The T3 and T4 hormones act on almost every cell, increasing the metabolic rate, affecting protein synthesis, and regulating bone growth. Too much or too little of these hormones can greatly affect various functions in the body which can cause ill effects or symptoms.

The Production of T3 and T4

We need to go back to where the T3 and T4 hormones are produced. The thyroid gland is a butterfly-shaped gland located on the front part of the neck, underneath a person's Adam’s apple. There are two lobes connected by a “bridge” in the middle, and this is the site where the T3 and T4 hormones, known as the thyroid hormones are produced.

However, the thyroid gland does not work alone in producing these hormones, the pituitary gland plays a role as well. The pituitary gland is a peanut-shaped gland located in the back part of the brain.

The pituitary gland produces TSH (thyroid-stimulating hormone), which prompts the thyroid gland to produce and secrete T3 and T4 hormones. The pituitary gland's production of TSH is prompted by another part of the body, the hypothalamus.

Looking at things from a bigger perspective, you can see the interplay of the hypothalamus, the pituitary gland, and the thyroid and how these three different body parts greatly affect the production of the T3 and T4 hormones.

T3 Hormone

The T3 hormone is also known as triiodothyronine, is an active hormone. T3 is four times as potent as the T4 Hormone. There are two types of T3 Hormone:

  • Regular T3, which is attached to the proteins in the blood
  • Free T3, which is not united to proteins or substance in the body

The T3 is a converted form of T4. At first, the thyroid gland produces the T4 hormone which is then converted by a deiodinase enzyme to form the T3 hormone in the liver. The other organs in the body may also break down the T4, but only in smaller amounts.

T4 Hormone

The T4 hormone is the  “partner” of the T3 Hormone. Also known as thyroxine, the T4 hormone consists of four iodine atoms. Most thyroid hormones are bound to protein atoms, but a small fraction of these hormones are free or unbound.

What Happens If There Are Not Enough T3 and T4 Hormones?

The saying, “Less is more” isn’t applicable in this situation. The low levels of T3 and T4 hormones can lead to Hypothyroidism or underactive thyroid, which have the following symptoms:

Symptoms of Hypothyroidism
Dull, brittle hair
Difficulty in concentration
Difficulty in losing weight
Dry skin

People who are experiencing hypothyroidism may also face dangerous consequences such as infertility and high blood pressure in men, and miscarriages in women.

What Happens If There Is Too Much T3 and T4 Hormones?

High levels of T3 and T4 hormones can cause hyperthyroidism, which may cause these symptoms:

Symptoms of Hyperthyroidism
Difficulty concentrating
High possibility of developing goiter

If you have reasons to believe that your body does not produce enough T3 and T4 hormones, or that your body produces way too much T3 and T4 hormones, contact your doctor so you will have appropriate means of regulating the hormones and live a healthy life.

Next Article: Thyroid Health | How to Boost T3 and T4 Levels