The largest endocrine gland in the human body is the thyroid gland, the thyroid gland is located in the front of the neck, close to the trachea 3, 4 cricoid cartilage, butterfly distribution on both sides of the trachea, weighing about 25-30 grams, usually in the neck can not be seen or touched the thyroid, if you can see or feel the thyroid gland, it belongs to the thyroid gland is enlarged. The main hormone secreted by the thyroid gland is thyroid hormone, which is regulated by the hypothalamus-pituitary-thyroid axis. Thyroid hormone regulates human metabolism, promotes growth and development, especially the development of the skeletal motor system and the nervous system, and affects the production of heat, and the metabolism of sugar, protein, and fat, and excessive or inadequate thyroid hormone affects the body’s metabolic state, leading to symptoms of hyperthyroidism or hypothyroidism. symptoms of hyperthyroidism or hypothyroidism.