The thyroid is a small butterfly-shaped gland inside the neck, located in front of the trachea (windpipe) and below the larynx (voicebox). It produces two thyroid hormones—triiodothyronine (T3) and thyroxine (T4)—that travel though the blood to all tissues of the body.
Thyroid hormones regulate how the body breaks down food and either uses that energy immediately or stores it for the future. In other words, our thyroid hormones regulate our body's metabolism.
Another gland, called the pituitary gland, actually controls how well the thyroid works. The pituitary gland is located at the base of the brain and produces thyroid-stimulating hormone (TSH). The bloodstream carries TSH to the thyroid gland, where it tells the thyroid to produce more thyroid hormones, as needed.
Thyroid hormones influence virtually every organ system in the body. They tell organs how fast or slow they should work. Thyroid hormones also regulate the consumption of oxygen and the production of heat.
Endocrinologists—physicians and scientists who study and care for patients with endocrine gland and hormone problems—study and treat several major disorders of the thyroid gland. We will briefly describe these disorders here. You can link to any of the thyroid conditions that you may wish to learn more about, and see the thyroid basics infographic for more.
Too much thyroid hormone from an overactive thyroid gland is called hyperthyroidism, because it speeds up the body's metabolism. This hormone imbalance occurs in about 1 percent of all women, who get hyperthyroidism more often than men. One of the most common forms of hyperthyroidism is known as Graves' disease. This autoimmune disorder (when your body’s defense system attacks your own cells) tends to run in families.
Because the thyroid gland is producing too much hormone in hyperthyroidism, the body develops an increased metabolic state, with many body systems developing abnormal function. (Read more about Hyperthyroidism.)
Too little thyroid hormone from an underactive thyroid gland is called hypothyroidism. In hypothyroidism, the body's metabolism is slowed. Several causes for this condition exist, most of which affect the thyroid gland directly, impairing its ability to make enough hormone. More rarely, there may be a pituitary gland tumor, which blocks the pituitary from producing TSH.
Whether the problem is caused by the thyroid or by the pituitary gland, the result is that the thyroid is producing too few hormones, causing many physical and mental processes to become sluggish. The body consumes less oxygen and produces less body heat. (Read more about Hypothyroidism.)
A thyroid nodule is a small lump in the thyroid gland. Thyroid nodules are common. These nodules can be either a growth of thyroid tissue or a fluid-filled cyst, which forms a lump in the thyroid gland. Almost half of the population will have tiny thyroid nodules at some point in their lives but, typically, these are not noticeable until they become large and affect normal thyroid size. About 5 percent of people develop large nodules, more than a half inch across (about 1 centimeter). (Read more about Thyroid Nodules.)
Although most nodules are not cancerous, people who have them should seek medical attention to rule out cancer. Also, some thyroid nodules may produce too much thyroid hormone and cause hyperthyroidism, or become too large, interfering with breathing or swallowing or causing neck discomfort.
Other thyroid problems include cancer, thyroiditis (swelling of the thyroid gland), or a goiter, which is an enlargement of the thyroid gland.
Leonard Wartofsky, MD, MACP
Washington Hospital Center
Georgetown University School of Medicine
Bryan Haugen, MD
University of Colorado Denver School of Medicine
Last Review: May 2013