Thyroid gland 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. Parathyroid glands The parathyroid glands are located on the posterior surfaces of the thyroid gland. They are tiny
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