The thyroid gland is located directly below the laryngeal nodes in the neck and is covered by the skin, with the two lobes of the gland connected by the isthmus and shaped like a butterfly node. Under normal circumstances, it is not visible to the naked eye and is less likely to be palpable. When the thyroid gland is enlarged, it is easily palpable and is visible as a bulge in the lower part of the laryngeal node or on both sides. The thyroid gland takes in an element called iodine, which is found in water and food, and processes it into thyroid hormones. Thyroid hormones are present in two ways: one is thyroxine (T4), which is produced in the thyroid gland, is present for a short time and has a small effect on the body’s metabolic rate; T4 is converted to metabolically active triiodothyronine (T3) in the liver and other organs. About 80% of T3 is produced during the conversion of T4, with the remaining 20% produced by the thyroid gland itself. The thyroid gland secretes thyroid hormones into the blood circulation. Thyroid hormones accelerate the rate of organ metabolism by stimulating protein synthesis in almost all tissues and increasing cellular oxygen consumption. The mechanism by which the body regulates thyroid hormone levels is such that there is feedback regulation between the hypothalamus, pituitary gland and the thyroid gland. The hypothalamus first secretes thyrotropin-releasing hormone (TRH), which stimulates the pituitary gland to produce thyroid stimulating hormone (TSH), which in turn stimulates the thyroid gland to synthesize thyroid hormone. When the blood thyroid hormone concentration increases, it in turn acts on the hypothalamus to inhibit TRH secretion and on the pituitary gland to inhibit TSH secretion, thereby reducing thyroid hormone secretion by the thyroid gland. Many factors, including the hypothalamus, pituitary gland, thyroid gland, thyroid hormone binding protein, and the conversion process of T4 to T3 in other tissues, coordinate with each other to maintain normal thyroid function.