The thyroid is a butterfly-like gland located in the lower half of the neck, below the larynx, and in front of the trachea. It consists of two lobes, each measuring between 2 and 4 centimeters, and interconnected by a central narrowed part. Thyroxine and triiodothyronine secrete their hormones into the blood. The work of the thyroid gland in physiological circumstances is controlled by the hypothalamus and pituitary gland. In the control of thyroid function, the most important is the pituitary gland, which uses thyrotropin to stimulate the thyroid gland to produce hormones, but also to grow, which can lead to an increase in the thyroid gland or goiter.