Deficiency of iodine in humans leads to enlargement of thyroid gland resulting in goiter. The thyroid gland of the adult which normally weighs about 25 g. may weigh as much as 200 to 500 g. or even more in goiter due to overgrowth of glandular tissue.
In children severe iodine deficiency results in cretinism.
Hypothyroidism means a decreased activity of the thyroid gland which may affect all body functions. The rate of metabolism slows down causing mental and physical sluggishness. The most severe form of hypothyroidism is myxedema. Hypothyroidism can be caused by a problem with the thyroid itself (primary), or by the malfunction of the pituitary gland or the hypothalamus (secondary).
Primary and secondary hypothyroidism: may result due to
Inability of gland to produce the required quantity of thyroid hormones.
Lack of stimulation of thyroid gland by pituitary.