The thyroid is one of the larger endocrine glands in the body. It is a double-lobed structure located in the neck and produces hormones, principally thyroxine (T₄) and triiodothyronine (T₃), that regulate the rate of metabolism and affect the growth and rate of function of many other systems in the body. Iodine is necessary for the production of both hormones. Hyperthyroidism (overactive thyroid) and hypothyroidism (underactive thyroid) are the most common problems of the thyroid gland.

Anatomy

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The thyroid is situated on the front side of the neck, at the level of C5 to T1 vertebral bodies, just below the laryngeal prominence (Adam's apple), near the thyroid cartilage over the trachea but covered by layers of skin and muscle. The thyroid is one of the larger endocrine glands - 10-20 grams in adults- and butterfly-shaped: the wings correspond to the lobes and the body to the isthmus of the thyroid. It may enlarge substantially during pregnancy and when affected by a variety of diseases.

Blood supply

The thyroid gland is supplied by two pairs of arteries: the superior and inferior thyroid arteries of each side. The superior thyroid artery is the first branch of the external carotid, and supplies mostly the upper half of the thyroid gland, while the inferior thyroid artery is the major branch of the thyrocervical trunk, which comes off of the subclavian artery. In 10% of people, there is an additional thyroid artery, the thyreoidea ima, that arises from the brachiocephalic trunk or the arch of the aorta. Lymph drainage follows the arterial supply.

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