What Is Thyroid Disease?

The thyroid is a small gland located below the skin and muscles at the front of the neck, just at the spot where a bow tie would rest. It's brownish red, with left and right halves (called lobes) that look like a butterfly's wings. It's light like a butterfly, too, and usually weighs less than an ounce.

As small as it is, though, the thyroid has an enormously important job to do, especially for teens. It manufactures the hormones that help control metabolism and growth. To do its job, the thyroid needs a chemical element called iodine that the body absorbs from the foods you eat and the water you drink. The entire body contains about 50 milligrams of iodine. About 1/5 to 1/3 of that supply (10 to 15 milligrams) is stored in your thyroid. The thyroid combines the iodine with tyrosine (an essential amino acid) to make important hormones.

Thyroid hormones are released from the gland and travel through the bloodstream to your body's cells. They help control the growth and the structure of bones, sexual development (puberty), and many other body functions. By helping your cells convert oxygen and calories into the energy they need to work properly, these hormones are important in determining if your body will mature as it should. Thyroid hormones also directly affect how most of your organs function. So if your thyroid isn't operating properly, you can have problems in lots of other parts of your body.