What is the thyroid gland?
Your endocrine system is a group of glands in your body (such as the pituitary, thyroid, pancreas, ovaries and testes) that secrete hormones (like growth hormone, thyroid hormone, insulin, estrogen and testosterone) that regulate functions such as metabolism, growth, development and reproduction.
The thyroid gland is the largest gland in the endocrine system. It is a butterfly-shaped organ that sits roughly in the middle of the neck, just below where the Adam’s apple is in men. In your physical exam, when your doctor places a hand on the front of your neck and asks you to swallow, they are doing so to feel your thyroid gland.
What does the thyroid gland do?
The thyroid gland produces three hormones: Thyroxine (T4), Triiodothyronine (T3) and Calcitonin. T4 and T3 are what most people think of as “thyroid hormones.” These hormones play a significant role in your metabolism and in energy regulation in the body. T4 and T3 are made in the thyroid gland from using the building blocks iodine (a trace mineral) and tyrosine (an amino acid). T3 has three molecules of iodine, and T4 has four. You make about four times the amount of T4 as you do T3.
After T4 and T3 are made, they are released by the thyroid gland into circulation. This release happens in response to stimulus from a part of your brain called the pituitary that makes a substance called Thyroid Releasing Hormone (TRH). TRH tells the thyroid gland to release thyroid hormones into your blood stream.
Thyroid hormones act on almost every kind of cell in your body to increase cellular activity or metabolism. If there is too much or too little thyroid hormone, the metabolism of your entire body is impacted.