The protein thyroglobulin is the chief component of the jellylike substance, called colloid, that is secreted by the follicles. Before it is released into the bloodstream, the thyroid hormone is converted into thyroxine and small quantities of the other closely related thyroid hormones. Metabolic disorders result when the thyroid secretes too little or too much thyroxine. A disease known as goiter results from the deficiency, although it has been virtually eliminated by the use of iodized salt. Hypothyroidism that results from glandular malfunction is known as myxedema in the adult and cretinism in infancy and childhood.
Treatment is by administration of thyroxine.
Excessive secretion of thyroxine, or hyperthyroidism, causes an increased metabolic rate, loss of weight despite good appetite, protrusion of the eyeballs, rapid pulse, and irritability. The condition, also known as Graves' disease, may be accompanied by enlargement of the thyroid. The thyroid gland also produces the hormone calcitonin, which is involved in the regulation of serum calcium in the body. See also endocrine system . The Columbia Encyclopedia, Sixth Edition.