Thyroid Gland Health Article

Calcitonin

The thyroid gland also secretes calcitonin. The thyroid's C-cells are stimulated to secrete calcitonin when there is a high concentration of calcium in the blood stream. The function of calcitonin is to inhibit the amount

of resorption of calcium from the bone and to regulate the amount of calcium in the blood stream.

Role in human health

The hormones T4 and T3 produced by the thyroid gland are involved in growth, development and metabolism, and it is likely that most cells are targets for these hormones. Some researchers feel that T4 is only an inactive prohormone while T3 is the biochemically active form of the thyroid hormone. Some T3 is produced in the thyroid but most of it is produced from the conversion of T4 outside of the liver. Receptors on cells bind some T4 but preferentially bind T3. The thyroid hormones stimulate the metabolic activities of most tissues and cause an increase in basal metabolic rate. Normal levels of T4 and T3 are necessary for normal development of the brain and normal growth in childhood. The thyroid hormones are also involved in regulating heart rate and increasing cardiac contractility and output. These hormones also have effects on the central nervous system, since decreased thyroid hormone levels are associated with decreased ability to concentrate and think, and increased levels are associated with anxiety. The reproductive system also requires normal thyroid hormone levels, and decreased levels of these hormones can result in infertility.

Iodine deficiency or excess

Dietary intake of iodine is necessary for the normal synthesis of T3 and T4. A deficiency or excess consumption of iodine can result in a deficiency in these hormones (hypothyroidism) or an excess of these hormones (hyperthyroidism). Iodine deficiency is less common in developed countries where table salt contains iodine. Disorders which lead to a deficiency of iodide in the thyroid can also cause hypothyroidism.