In vertebrate anatomy, the thyroid gland or simply, the thyroid (pronounced /ˈθaɪrɔɪd .../), is one of the largest endocrine glands in the body. The thyroid gland is found in the neck, inferior to (below) the thyroid cartilage (also known as the Adam's Apple) and at approximately the same level as the cricoid cartilage. The thyroid controls how quickly the body uses energy, makes proteins, and controls how sensitive the body should be to other hormones.
The thyroid gland participates in these processes by producing thyroid hormones, the principal ones being triiodothyronine (T3) and thyroxine (T4). These hormones regulate the rate of metabolism and affect the growth and rate of function of many other systems in the body. T3 and T4 are synthesized utilizing both iodine and tyrosine. The thyroid gland also produces calcitonin, which plays a role in calcium homeostasis.
The thyroid gland is controlled by thyroid-stimulating hormone (TSH) produced by the pituitary (to be specific, the anterior pituitary) and thyrotropin-releasing hormone (TRH) produced by the hypothalamus. The thyroid gland gets its name from the Greek word for "shield", after the shape of the related thyroid cartilage. The most common problems of the thyroid gland consist of an overactive thyroid gland, referred to as hyperthyroidism, and an underactive thyroid gland, referred to as hypothyroidism.source: http://en.wikipedia.org/wiki/Thyroid
OTHER GREAT LINKS:
Your Thyroid Gland
Thyroid Gland and the Thyroid Hormones