The thyroid gland is part of the endocrine system. It produces a hormone in response to stimulation by a hormone from the pituitary gland. The thyroid gland affects every organ and cell in the body as it regulates how the body stores and uses the energy from dietary intake. It is located on either side of the trachea and consists of two lobes in the shape of a butterfly connected by a narrow piece of thyroid tissue known as isthmus of thyroid gland.

The parathyroid, a small pea size gland, is located on the four corners of the butterfly shape of the thyroid gland. It is unrelated to the thyroid and produces its own hormone that maintains the calcium level in the blood.

Hypothyroidism (hypo=under) means that the thyroid is not producing enough thyroid hormone for the body, leading to decreased metabolism, fatigue, slower heart rate, weight gain, depression, and a whole host of other symptoms. Hyperthyroidism (hyper=over), on the other hand, means that the body is producing an excess of the thyroid hormone, leading to increased metabolism, racing thoughts, anxiety, weight loss, and other such symptoms.