Thyroid Hormones

The thyroid gland is essential to the endocrine system. It is located in front of the neck and is responsible for the production of thyroid hormones. The thyroid gland releases triiodothyronine (T3) and thyroxine (T4). These hormones play an important role in regulation of your weight, energy levels, internal temperature, skin, hair, nail growth, and more.

What is T4?

Thyroxine (T4) is produced by the thyroid gland under regulation from the hypothalamus and pituitary gland. The feedback loop signals to the hypothalamus in to release thyrotropin-releasing hormone, which then stimulates the pituitary gland to release the thyroid stimulating hormone.

What is T3?

T3 is a second thyroid hormone that is produced by the thyroid gland, but also in other tissues through deiodination (enzymatic conversion) of T4. T3 helps maintain muscle control, brain function and development, heart and digestive functions. It also plays a role in the body’s metabolic rate and the maintenance of bone health.

Problems Associated with T3 and T4? 

Having too much T3 in the bloodstream is referred to as thyrotoxicosis. This condition often results from overactivity in the thyroid gland, or hyperthyroidism. Hyperthyroidism occurs in conditions such as Graves’ disease, inflammation of the thyroid or a benign tumor. Signs of thyrotoxicosis include weight loss, increased appetite, palpitations, irregular menstrual cycle, tiredness, irritability, and hair thinning. Hyperthyroidism can also occur when supplements with T3 are ingested.

Hypothyroidism is a condition that occurs if the thyroid gland does not produce enough of the thyroid hormone. This may be due to autoimmune conditions, such as Hashimoto’s thyroiditis or certain medications. Hypothyroidism can also occur in pituitary dysfunction, such as pituitary tumors or inflammation.

Hypothyroidism tends to run in families and more common in adults, as well as women. Symptoms may include tiredness, mental depression, feeling cold, weight gain, dry skin, constipation, and menstrual irregularities.

Questions to Ask Your Healthcare Team

  • Are my thyroid hormone levels normal?
  • What test should I have to check my thyroid function?
  • Could my symptoms be due to thyroid hormone abnormalities?
  • If my thyroid hormone levels are too high or too low. What are the treatment options?
  • Should I see a thyroid specialist or endocrinologist?

Edited: January, 2019
Editor: Irina Bancos, MD