Thyroid Disease

Thyroid Disease Summary
There are many types of thyroid disease. Some occur due to the function of the thyroid itself such as hypothyroidism, hyperthyroidism, Hashimoto's thyroiditis, etc. Some causes of thyroid disease occur due to problems with the structure of the thyroid gland such as goiters, thyroid nodules, and thyroid cancer. Treatment of thyroid disease depends on the cause of the disease.
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Thyroid disease facts

  • The thyroid is a gland responsible for production of thyroid hormones.
  • Thyroid hormones are essential to regulate metabolism and other key body functions.
  • Signs and symptoms of thyroid disease may occur if thyroid hormone levels are not in the normal range.
  • In addition to altered function, thyroid structural abnormalities may occur, ranging from benign (non cancerous) to malignant (cancer).
  • Depending on the underlying problem, blood tests, imaging, and biopsy may be used to make a diagnosis.
  • Treatment depends on the particular thyroid disease that is present.

Introduction to thyroid disease

As any endocrinologist (hormone specialist) knows, there are many subtopics within the broad topic of thyroid disease, and an article like this could go on for a hundred pages! This article is designed to present a "rough guide" to the thyroid, and provide an outline or introduction to many conditions that involve the thyroid gland. As you read through this, you will find a number of links that will take you to more in-depth articles dealing with the specific topic in question.

Thyroid 101: What is the thyroid and what does it do?

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The thyroid is a gland shaped like a butterfly and located in the front of the neck, just below the Adam's apple. The gland wraps around the windpipe (trachea), and its shape resembles a butterfly formed by two wings (lobes) attached by a middle part (isthmus). The thyroid gland works like a factory that uses iodine (mostly from the diet in foods such as seafood and salt) to produce thyroid hormones. These hormones help to regulate the body's metabolism and affect important processes, such as growth and other metabolism of the body.

The two most important thyroid hormones are thyroxine (T4) and triiodothyronine (T3), representing 99.9% and 0.1% of thyroid hormones, respectively. The hormone with the most biological power is T3. Once released from the thyroid gland into the blood, a large amount of T4 is converted to T3 - the active hormone that affects the metabolism of all cells.

Picture of the thyroid gland
Picture of the thyroid gland

Thyroid hormone regulation - the chain of command

The thyroid itself is regulated by another gland located in the brain, called the pituitary. In turn, the pituitary is regulated in part by the circulating thyroid hormones (via the "feedback" effect of thyroid hormone on the pituitary gland) and by another gland called the hypothalamus.

Picture of the pituitary gland
Picture of the pituitary gland

The hypothalamus releases a hormone called thyrotropin releasing hormone (TRH), which sends a signal to the pituitary gland to release thyroid stimulating hormone (TSH). In turn, TSH sends a signal to the thyroid to release thyroid hormones. If overactivity of any of these three glands occurs, an excessive amount of thyroid hormones can be produced, thereby resulting in hyperthyroidism. Similarly, if underactivity of any of these glands occurs, a deficiency of thyroid hormones can result, causing hypothyroidism.

Hypothalamus (releases - TRH)

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Pituitary gland (releases - TSH)

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Thyroid gland (releases - T4 and T3)

The rate of thyroid hormone production is controlled by the pituitary gland. When the pituitary senses an insufficient amount of thyroid hormone circulating in the blood, the pituitary gland releases TSH in an attempt to stimulate more thyroid hormone production by the thyroid. In contrast, when excessive amounts of thyroid hormones circulate, in the blood, the TSH level falls in order to decrease the production of thyroid hormones.

Specific cells in the thyroid produce another hormone called calcitonin. Unlike T3 and T4, calcitonin is not involved in the regulation of metabolism. Calcitonin regulates calcium by lowering calcium levels in the blood. Excess calcium in the blood is referred to as hypercalcemia.

Medically Reviewed by a Doctor on 8/7/2013

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