amino acids: Amino acids are the buildings blocks used to make proteins. There are about 80 amino acids in nature, but the human body needs only 20 of these for metabolism and growth. Essential amino acids are supplied by the foods we eat. Nonessential amino acids are in foods, but they also can be produced by the body.

autoimmune disease: This is a malfunction of the body's immune system. Normally, the immune system works to defend the body and eliminate infections by destroying bacteria, viruses, and other invading microbes. When the immune system is not working properly, it may mistakenly attack the normal cells, tissues, and organs of a person's own body. Examples of autoimmune diseases include lupus, Hashimoto's thyroiditis, Graves disease, and Guillain-Barré syndrome.

biopsy: A biopsy is a test in which a sample of tissue or fluid is removed from the body and examined with a microscope. A biopsy is usually done to help doctors diagnose cancer and other diseases.

cyst: Located in body tissue, a cyst is a walled-off sack of gaseous, liquid, semisolid, or solid material.

gland: A gland is a group of cells or an organ that produces and releases a substance for use elsewhere in the body. Many glands produce hormones, whereas others release such substances as saliva, sweat, mucous, and tears.

goiter: This is a thyroid gland that is enlarged to the point that the enlargement is visible.

hormone: Hormones are substances that regulate processes such as growth, metabolism, and reproduction and influence behavior and the functioning of the immune system. They are made by an organ, gland, or group of cells and travel (often through the bloodstream) to other parts of the body.

inflammation: This is the body's reaction to irritation, infection, or injury. Signs of inflammation can include redness, heat, pain, or swelling.

metabolism: Metabolism refers to the group of physical and chemical processes by which a living cell or organism converts oxygen and food into energy.

nodule: This is a small mass of rounded or irregularly shaped tissue.

thyroid hormones: The two major hormones produced and released by the thyroid gland are thyroxine (T4) and triiodothyronine (T3). These hormones travel to other body tissues through the bloodstream and play a key role in regulating metabolism, growth, and many other body functions.

Reviewed by: Steven Dowshen, MD
Date reviewed: February 2012