The thyroid gland, or simply the thyroid, is an endocrine gland in the neck, consisting of two lobes connected by an isthmus. It is found at the front of the neck, below the Adam's apple. The thyroid gland secretes three hormones, namely the thyroid hormones (thyroxine/T4 and triiodothyronine/T3) and calcitonin. The thyroid hormones primarily influence the metabolic rate and protein synthesis, but they also have many other effects including on development. The thyroid hormones are created from iodine and tyrosine. Calcitonin plays a role in calcium homeostasis.