Many people do not know where the thyroid gland is located, but most people are not unfamiliar with “thick neck disease”, which is actually an enlarged thyroid gland, which tells us that the thyroid gland is located in the neck. It is divided into two lobes and isthmus, below the thyroid cartilage, on both sides of the trachea, shaped like a butterfly, like a shield nail, so called the thyroid gland. Although the iodine content in the thyroid gland is 25 to 50 times higher than that in the blood, 1/3 of the daily dietary iodine intake still enters the thyroid gland, and 90% of the total body iodine content is concentrated in the thyroid gland. Thyroxine is a hormone secreted by the thyroid gland. The physiological functions of thyroxine are: 1. Promote metabolism, increase tissue oxygen consumption, and increase heat production. 2. 2. Promote growth and development, which is essential for the development and growth of long bones, brain and reproductive organs, especially in infancy. Lack of thyroid hormone at this time will suffer from cretinism. 3.Increase the excitability of the central nervous system. In addition, it also strengthens and regulates the effects of other hormones and accelerates heart rate, strengthens heart contraction force and increases cardiac output, etc.