The thyroid gland is part of the body's endocrine system, a complex group of glands that secrete hormones into the bloodstream. Hormones are chemicals that regulate the development and function of cells, tissue, and organs in the body. The thyroid gland is responsible for regulating the body's metabolism (the process of creating and using energy).
How It Works
In his book, The Harvard Medical School Guide to Overcoming Thyroid Problems, Dr. Jeffrey Garber likens the function of the thyroid to that of a car engine. In the same way the engine produces the energy required for a car to move at a given speed, the thyroid gland produces the optimal amount of thyroid hormone that allows the body's cells to function at a certain rate.
The fuel for the thyroid gland is iodine, which can be obtained by eating certain foods, including iodized salt, fish, and dairy products. The thyroid uses iodine to manufacture two kinds of hormones—thyroxine (T4) and triiodothyronine (T3)—and stores the chemicals until they are released into the bloodstream, as needed.
The thyroid functions as part of a network that also includes the pituitary gland and the hypothalamus. The thyroid needs guidance in determining how much hormone to produce and takes direction from the pituitary gland, which communicates with the thyroid using thyroid-stimulating hormone (TSH). As it monitors the level of hormone in the blood, the pituitary gets pertinent information from the hypothalamus. This efficient network is aptly referred to as the hypothalamic-pituitary-thyroid axis (HPT axis).
Problems occur when the thyroid slows or stops the production of hormone, usually because of disease, damage, or side effects from certain medications. This condition is known as hypothyroidism (underactive thyroid) and causes a shortage of thyroid hormone in the body, which in turn slows metabolism and can cause an array of symptoms, including fatigue, constipation, weight gain, depression, and joint or muscle pain.
On the other hand, sometimes the thyroid continues producing hormone even when there is an adequate amount in the bloodstream. This condition is called hyperthyroidism (overactive thyroid) and leads to high levels of thyroid hormone in the body. The symptoms include nervousness, difficulty concentrating, weight loss, and increased bowel movements.
These two conditions—hypothyroidism and hyperthyroidism—are often the features of an underlying thyroid disorder.
To learn about common thyroid disorders, click here.