The thyroid is an endocrine gland which produces and releases the thyroid hormones thyroxine (T4) and triiodothyronine (T3) into the blood circulation. These hormones play a role in basal metabolism. For example, they promote growth and stimulate the use of fats and sugars.
Production of thyroid hormones is stimulated by thyroid stimulating hormone (TSH) which is produced by the pituitary gland.
The thyroid is located at the base of the neck and is butterfly shaped, its wings surrounding the trachea. The four parathyroid glands are a few millimetres in diameter and are located on the posterior surface of the thyroid.
The thyroid measures approximately 6 centimetres high and 6 to 8 centimetres long, making it the largest endocrine gland in the human body. It has a highly vascularised structure, supplied by two arteries and three main veins.
Located in the neck, the thyroid is the largest gland in the human body. © Brooks/Cole