What and Where Is Your Thyroid?

The thyroid is an endocrine gland located in the front of your neck underneath your Adam's apple. It is very light and small — a normal thyroid usually weighs less than 1 ounce. It is usually compared to the shape of a butterfly. The wings are called lobes, and each lobe sits on the side of your windpipe or trachea. The middle of the butterfly (called the isthmus) connects the two lobes.

Endocrine glands make hormones that are secreted into the bloodstream. Hormones are chemicals made in one part of the body that send messages to other parts of the body, regulating growth, metabolism, and mood. This is different from an exocrine gland, which secretes needed substances through a duct system — not through the bloodstream.

What Does Your Thyroid Do?

Your thyroid is responsible for making the hormones monoiodotyrosine (T1), diiodotyrosine (T2), triiodothyronine (T3), and thyroxine (T4). These hormones are made from tyrosine, which is a protein and the mineral iodine.

T1 has one atom of iodine attached to the molecule, T2 has two atoms of iodine attached, T3 has three atoms of iodine attached, and T4 has four atoms of iodine attached. Your thyroid needs iodine to make these hormones. Iodine must be supplied by your diet, since there is no other way to acquire it.

T1 and T2 functions are less known and are rarely mentioned in thyroid health guides — T3 and T4 are typically classified as your thyroid hormones. In fact, most literature geared toward patients does not even mention these hormones. The scientific community needs to perform more research to learn the specific significance of T1 and T2 on your thyroid.

According to the National Institute of Diabetes and Digestive Diseases and Kidney Disease, thyroid hormones affect:

  • Metabolism

  • Breathing

  • Heart and nervous-system functions

  • Body temperature

  • Muscle strength

  • Skin dryness

  • Menstrual cycles

  • Weight

  • Cholesterol levels

Thyroid hormones are particularly important in infants and children for proper growth and brain development.

If you do not have enough thyroid hormone, your metabolism will most likely be low, and there is a good chance you will have a problem controlling weight. Sometimes, people with too much thyroid hormone will lose weight unintentionally. Specialists do not endorse the use of thyroid hormones to lose weight, due to other undesired effects.

If an individual has had her thyroid removed, calcitonin replacement is not given. Despite the amount of research on the thyroid, there has not been a thyroid calcitonin deficiency syndrome identified. It is thought by many endocrinologists and other physicians that when the thyroid is removed, the only thyroid hormone that needs to be replaced is T4, because the body can make T3 out of T4.

Calcitonin is another hormone made by your thyroid. It is made by para-follicluar cells (sometimes called C cells), which are different than the cells that make the other thyroid hormones. Calcitonin is thought to be involved in calcium metabolism. When blood calcium is high, receptors on the C cells stimulate the release of this hormone. Calcitonin that is made in the thyroid is called TCT, or thyroid calcitonin. It is thought that calcitonin is also made in other tissues of the body.

Testing calcitonin levels in the blood is not part of a routine screening for thyroid function, but your physician may test levels if medullary thyroid cancer or another disease of the C cells is suspected or needs to be ruled out. Five to 8 percent of thyroid cancers are of this type, and it is the third most common type of thyroid cancer. If this cancer is diagnosed, the treatment may involve removing the thyroid gland.

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