The thyroid gland is the largest endocrine gland located inferior to the thyroid cartilage of the larynx in the neck. The thyroid gland can store enough hormone in the colloid to supply the body for about two months. It performs many important functions for the body. Sometimes, it malfunctions and it can become either overactive or under-active. Each of these conditions can cause a wide variety of puzzling and often debilitating symptoms. In this article will focus on the causes, symptoms and treatment of under-active thyroid.
Causes: The under-active thyroid, also called hypothyroidism, affects as many as 5 million Americans. Although the likelihood of developing thyroid disease may increase with age, it can occur at any time. Hypothyroidism can be caused when the thyroid is damaged by inflammation, destroying some portion of the gland. Portions of the thyroid gland may also be surgically removed if necessary for the treatment of goiter, cancer or benign nodules. The remaining, smaller portion of the thyroid can often continue to work effectively; but it may, at some point, become unable to bear the burden of the body's needs, and hypothyroidism could result. Your risk of developing hypothyroidism increases if one or more family members have thyroid disease.

Many disorders occur due to hypothyroidism like Cretinism, Myxedema, and Iodine deficiency Goitre. Cretinism is caused by deficiency of thyroid hormones in infants. A cretin has slow body growth and mental development of reduced metabolic rate. Other symptoms of this disorder are slow heart beat. Lower blood pressure, decrease in temperature, stunted growth, pot-belly, pigeon chest and protruding tongue and retarded sexual development. This disease can be treated by an early administration of thyroid hormones.
Myxedema is caused by deficiency of thyroid hormones in adults. This disease is characterized by puffy appearance due to accumulation of fat in the subcutaneous tissue because of low metabolic rate. The patient lack alertness, intelligence and initiative. He also suffers from slow heart beat, low body temperature and retarded sexual development. This disease can be treated by administration of thyroid hormones.
 Iodine Deficiency Goitre is caused by deficiency of iodine in diet because iodine is needed for the synthesis of thyroid hormones. It produces thyroid enlargement. It may lead to cretinism or myxedema. This disease is common in hilly areas. Addition of Iodides tot eh table salt prevents this disease.