What is the thyroid gland?
- The thyroid is an organ that is considered part of the endocrine, or hormone, system. It is located in the neck below the Adam's apple. The thyroid's main purpose is to produce thyroid hormones.
- These hormones then travel through the bloodstream to all the other tissues and organs to help control metabolism in adults and growth, development, and metabolism in children.
- The thyroid is shaped like a butterfly. The two "wings" of the butterfly are the right and left lobes of the thyroid, with lie on both sides of the trachea or main breathing tube. The connection between the wings is called the isthmus.
- The two hormones that the thyroid produces are L-thyroxine (T4) and tri-iodothyronine (T3).
- Location and picture of the thyroid gland. Note two lobes of the thyroid, similar to butterfly wings.
What hormones does the thyroid produce?
- The thyroxine (T4) and tri-iodothyronine (T3) hormones regulate your body's metabolic functions such as heat generation, and the utilization of carbohydrates, proteins, and fats. In children, thyroid hormones are responsible for growth and development.
- Regulatory hormones from different parts of the brain control the thyroid's production of T4 and T3. In the pituitary gland, thyrotropin-stimulating hormone (TSH) is released when more thyroid hormone is needed and travels via the bloodstream to the thyroid gland. TSH then stimulates the thyroid to produce T4 and T3.
- The pituitary gland acts like a thermostat. When there is too much thyroid hormone in the bloodstream, the pituitary releases less TSH to signal the thyroid to produce less thyroid hormone. When there is too little thyroid hormone in the bloodstream, the pituitary releases more TSH to signal the thyroid to increase thyroid hormone production. Through this "feedback" system, the production of thyroid hormone is tightly controlled.
Location and picture of the thyroid gland. Note two lobes of the thyroid, similar to butterfly wings.
What are some thyroid disorders and thyroid problems?
Over 20 million people are under treatment for thyroid disorders in the United States. Approximately two million people have an undiagnosed thyroid disease. Thyroid disorders are overall more common in women than in men and increase with age, especially if they also have a history ofdiabetes mellitus type 1, pernicious anemia, rheumatoid arthritis or another autoimmune disease.
- When the thyroid is underactive, and does not produce enough thyroid hormones, the result is hypothyroidism. The most common cause at birth is congential hypothyroidism. The most common cause in an adult is autoimmune Hashimoto's thyroiditis or after removal of the thyroid by surgery or a radioactive iodine treatment.
- When the thyroid is overactive, and produces too much thyroid hormone, the result is hyperthyroidism. The most common causes may be autoimmune Graves' thyroiditis, toxic multinodular goiter, toxic adenoma ("hot nodule") and subacute thyroiditis.
- Pain in the thyroid gland can occur as a result of inflammation, known as subacute thyroiditis. This condition is associated with a short period of hyperthyroidism and then a longer period of hypothyroidism. Ninety percent of patients will go back to normal thyroid function after about 6 months. This condition may occur after a viral infection and be very painful. This condition called postpartum subacute thyroiditis may also occur within a year of having a baby.
- A small area of the thyroid can enlarge to form a thyroid nodule. Solitary thyroid nodules are very common, and as people grow older, half of the population may have these nodules. They are usually benign. However, they must be evaluated for cancer with an ultrasound and biopsy if they grow in size.
- The entire thyroid can enlarge in size, known as a goiter. Usually goiters are made up of many small thyroid nodules. Goiters may be removed with surgery if they grow to cause problems breathing or swallowing, or for cosmetic reasons.
- Thyroid cancer accounts for less than 2% of cancers. Although thyroid cancer has greatly increased in incidence in recent years, it is usually treatable. Thyroid cancer is increasing in the US.
- Many thyroid medications exist to treat some of the above-mentioned conditions.
- Thyroid hormone can be used to treat an underactive thyroid or to prevent growth of thyroid tissue after surgery for thyroid cancer.
- Antithyroid medications can be used to decrease the production of thyroid hormones in the case of an overactive thyroid.
- Radioactive iodine can be used to remove, or ablate, over-functioning or cancerous thyroid tissue.
- The thyroid can be removed surgically to treat some of the above-mentioned conditions. Thyroid surgery is used in the case of an overactive or enlarged thyroid and thyroid cancer.
- Thyroid disorders can significantly impact pregnancy and fertility. Both over- and underactive thyroid disease can occur during pregnancy, or may be the cause of infertility.
A helpful resource for endocrine care is the "Find-an-endocrinologist" at www.hormone.org.
Medically reviewed by John A. Seibel, MD; Board Certified Internal Medicine with a subspecialty in Endocrinology & Metabolism
eMedicine.com. Thyroid Disease.
Previous contributing coauthor: Sonia Ananthakrishnan, MD, Fellow in Endocrinology, Boston Medical Center