The thy roid gland is a small organ located at the base of the neck, classified as an endocrine gland. It is responsible for the production and release of two hormones: triiodothyronine (T3) and thyroxine (T4), which regulate the function of most of the body's tissues, and affect our body's metabolism and thermogenesis (heat production). The most noticeable effect seems to be on the cardiovascular system.