Hypothyroidism

Medical Revising Author: Ruchi Mathur, MD, FRCP(C)
Medical Editor: William C. Shiel, Jr., MD, FACP, FACR

• What is hypothyroidism?
• What are the thyroid hormones?
• Thyroid hormone regulation - the chain of command
• What causes hypothyroidism?
• What are the symptoms of hypothyroidism?
• How is hypothyroidism diagnosed?
• How is hypothyroidism treated?
• What is subclinical hypothyroidism?
• What's best for you?
• Hypothyroidism At A Glance
• Related Hypothyroidism articles:
  Hypothyroidism - on WebMD
  Hypothyroidism - on eMedicineHealth

What is hypothyroidism?

Hypothyroidism refers to any state in which thyroid hormone production is below normal. There are many disorders that result in hypothyroidism. These disorders may directly or indirectly involve the thyroid gland. Because thyroid hormone affects growth, development, and many cellular processes, inadequate thyroid hormone has widespread consequences for the body.

This article will focus specifically on hypothyroidism in adults.

What are thyroid hormones?

Thyroid hormones are produced by the thyroid gland. This gland is located in the lower part of the neck, below the Adam's apple. The gland wraps around the windpipe (trachea) and has a shape that is similar to a butterfly - formed by two wings (lobes) and attached by a middle part (isthmus).

The thyroid gland uses iodine (mostly available from the diet in foods such as seafood, bread, and salt) to produce thyroid hormones. The two most important thyroid hormones are thyroxine (T4) and triiodothyronine (T3), which account for 99.9% and 0.1% of thyroid hormones present in the blood respectively. However, the hormone with the most biological activity is T3. Once released from the thyroid gland into the blood, a large amount of T4 is converted into T3 - the active hormone that affects the metabolism of cells.

Next: Thyroid hormone regulation - the chain of command »

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From the Doctors at MedicineNet.com

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Last Editorial Review: 7/27/2005