What role does the thyroid gland play in the human body?

The thyroid gland lies against the pharynx at the base of the neck. It consists of two lateral lobes connected by an isthmus. The gland produces thyroxine, a hormone that regulates the rate of metabolism in the body. It also produces a second hormone, calcitonin, which regulates the level of calcium in the blood.

Thyroxine production depends on the availability of iodine. A deficiency of iodine causes thyroid gland enlargement, a condition called goiter. An undersecretion of thyroxine results in a condition known as cretinism (dwarfism with abnormal body proportions and possible mental retardation). In adults, an undersecretion results in myxedema (physical and mental sluggishness). Thyroxine oversecretion results in a high metabolic rate and Graves' disease.