The thyroid gland is a butterfly-shaped organ that weighs about one ounce and is located in the front of the neck below the Adam’s apple. The thyroid, an endocrine gland that secretes hormones in the blood, circulates its products to all tissues of the body, where they control vital functions in every cell. There are two kinds of thyroid hormones: T4 and T3, the number indicates how many iodide atoms are attached to the molecule (T4 has four and T3 has three iodide atoms). Normal levels of thyroid hormone help the brain, heart, intestines, muscles and reproductive system function normally. Thyroid hormones control the metabolism of the body. In the thyroid disease of hyperthyroidism (hyper: above or over), there is increased production of thyroid hormones which will make all the above organ systems run faster and in hypothyroidism (hypo: below or under), there is less production of hormones and everything runs slower.
The thyroid gland is also prone to autoimmune insults that can cause a variety of diseases. Like every other organ in the body, the thyroid can form benign or cancerous nodules.
It is important to mention an important hormone called TSH (thyroid stimulating hormone) which is produced by the pituitary gland (a pea size gland that sits at the base of the brain) and stimulates the thyroid gland to produce its hormones. The pituitary gland is so sensitive to the circulating levels of thyroid hormones that even minimal changes in those hormones will lead to significant changes in the thyroid stimulating hormone levels that usually happen in the opposite direction. For example, a drop in the thyroid hormones will lead to a rise in the thyroid stimulation hormone. Together with the thyroid hormones, the thyroid gland will release in the blood a protein called Thyroglobulin which is also secreted by certain types of cancer. This thyroid-produced protein can be used as a cancer marker to determine how much tumor remains in the body. Monitoring this thyroid protein is one way to remain vigilant against certain types of disease.