An endocrine gland in the neck, the thyroid regulates the body's metabolic rate. Disorders result when the thyroid secretes too little or too much thyroxine.
A deficiency of thyroxine secretion (hypothyroidism) occurs when insufficient Iodine is taken in with the diet, a condition prevalent in certain areas of the world, particularly ones remote from salt water. In this condition, all body processes slow down and metabolic rate lowers dramatically. The result of such a deficiency is usually goitre, or enlargement of the thyroid.
Excessive secretion of thyroxine (hyperthyroidism) causes an increased metabolic rate, loss of weight despite healthy appetite, protrusion of the eyeballs, rapid pulse, and irritability. The condition (also known as Grave's disease) may be accompanied by enlargement of the thyroid. Treatment is by surgical removal of part of the gland, by administering antithyroid drugs (chemicals that inhibits thyroxine formation), or by administering radioactive Iodine, which destroys over-functioning thyroid tissue.