The human thyroid gland weighs 20-30 grams and is the largest endocrine gland in the body. It is located on both sides of the upper trachea, below the thyroid cartilage, and is divided into two lobes, connected by a narrow isthmus in the middle, which is “H” shaped. The main function of the thyroid gland is to synthesize and secrete thyroid hormones. It has been described as the engine of the body. The main physiological functions of thyroid hormones are: 1. Promote metabolism, increase oxygen consumption in most tissues, and increase heat production, making you feel warm. 2.Promote growth and development, it is vital to the development and growth of long bones, brain and reproductive organs, especially in infancy, when lack of thyroid hormone, children will suffer from cretinism (not growing up and also stupid). 3.Increase the excitability of the central nervous system. So that you do not feel weak, easily tired and depressed. Thyroid disorders occur when various causes lead to changes in the structure and function of the thyroid gland.