The thyroid, or thyroid , is an endocrine within the neck consisting of two connected lobes. The lower two thirds of the lobes are connected by a skinny band of tissue called the thyroid isthmus. The thyroid is found at the front of the neck, below the Adam's apple. Microscopically, the functional unit of the thyroid is that the spherical thyroid follicle, lined with follicular cells (thyrocytes), and occasional parafollicular cells that surround a lumen containing colloid. The thyroid gland secretes three hormones: the two thyroid hormones – triiodothyronine and thyroxine – and a peptide hormone, calcitonin. The thyroid hormones influence the rate and protein synthesis, and in children, growth and development. Calcitonin plays a role in calcium homeostasis.Secretion of the two thyroid hormones is regulated by thyroid-stimulating hormone (TSH), which is secreted from the anterior pituitary gland. TSH is regulated by thyrotropin-releasing hormone (TRH), which is produced by the hypothalamus.