The thyroid is the largest endocrine in our body. It is butterfly-shaped and situated in the neck region. It consists of two lobes on either side of trachea that are connected by isthmus. Each lobe consists of many follicles that secrete thyroid hormones that control the metabolism of the body. In between follicles are parafollicular cells that secrete calcitonin. On the posterior side of thyroid, two pairs of parathyroid glands are seen and these secrete PTH (parathormone). Calcitonin and parathormone maintain calcium metabolism. Calcitonin causes blood calcium level to decrease. This is done by deposition of calcium in bones, increasing absorption of calcium by kidneys etc.