The thyroid is an endocrine gland which produces iodine-containing hormones. These hormones take part in the regulation of metabolism and production of energy. Essentially, this secretory organ is made up of follicular cells, which are its parenchymal cells that form follicles (small cavities or sacs). These are special epithelial cells which secrete two hormones: thyroxine (T4) and triidothyronine (T3). Thyroxine increases the metabolic rate (oxygen consumption) and regulates growth and development, while triidothyronine has also a varied effect on the body growth, body temperature and heart rate.
Anatomical Description
The thyroid gland consists of two lateral lobes, which are connected by a narrow isthmus of glandular tissue. Therefore, it sits over the trachea like a saddle, with one lobe on each lateral side and the isthmus in front, lying below the cricoid cartilage. Each lobe is pear-shaped, measuring between 2.5 and 4 cm in length, 1.5 and 2 cm in width, 1 and 1.5 cm in thickness. The gland weighs about 20 grams in a male adult and about 14 grams in a female.
The thyroid gland is supplied by the superior thyroid and the inferior thyroid artery, with the former arising from the external carotid artery and the latter from the thyrocervical trunk of the subclavian artery. It is drained by the superior, lateral, and inferior thyroid veins. Blood flow is ablut 5 mL per minute; however, in hyperthyroidism, it increases about a hundred-fold.
Below, schematic picture of thyroid gland
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