he thyroid gland is located in the anterior part of the neck. It consists of two lobes lying on each side of the thyroid cartilage (Adam's apple) and connected by a band of tissue called the isthmus.The thyroid gland is a collection of small, generally globular sacs, called follicles, filled with the prohormone known as thyroglobulin. The function of the cells lining these globules is to synthesize thyroid hormones and to secrete them directly into the circulation.
HyperthyroidismAn abnormal condition characterized by excessive secretion of thyroid hormones due to the over-activity of the thyroid gland.Hyperthyroidism is usually accompanied by enlargement of the gland, known as a goitre. A normal thyroid gland weighs 25 gm, a goitrous gland as much as 1 kg. A very large or extensive goitre may produce choking and difficulty in breathing and swallowing. Hyperthyroidism is the result of an increased metabolic rate and hyperactivity of the autonomic nervous system. This results in increased heart rate, heart palpitations, and shortness of breath, excessive sweating, nervousness, excitability, hyperactive behaviour, tremors, increased appetite, and protruding eyes.
The most common type of hyperthyroidism is Graves' disease. This is an autoimmune disorder caused by the body's production of antibodies to the thyroid. Another type of hyperthyroidism is toxic multinodular goitre (Plummer's disease), which results from a benign tumour of the thyroid gland. Hyperthyroidism is treated by drugs that block or suppress the production of hormones, or by surgical removal of part of the gland (thyroidectomy).
Hypothyroidism is characterized by the deficiency of thyroid hormones.
It may be caused by inadequate iodine intake (iodine being a key constituent of thyroid hormone), a defect in the synthesis of thyroid hormone, excessive intake of iodine metabolism blocking agent, inborn error, inadequate secretion of thyroid stimulating hormone and autoimmunity. If the thyroid gland grows abnormally large, in an attempt to compensate for the lack of iodine, the condition is known as endemic, or colloid, goitre. If the gland underfunctions from birth and there is no compensatory treatment, it results in cretinism; if occurring later in life, the condition is known as myxedema. Hypothyroidism is treated by replacement therapy using synthetic or natural thyroid hormones.
Hypothyroidism in the young is characterized by thick, dry, wrinkled skin; enlarged tongue; open, drooling mouth with thick lips; broad, flat face and nose. Intelligence level is below average. In an untreated case, the child becomes a physical and mental dwarf. With thyroid and iodine treatment administered sufficiently early, the juvenile myxedema patient may show marked recovery.
Iodine deficiency is most simply prevented by eating seafood regularly and by the use of iodized table salt. Foods such as cabbage and turnips contain a potentially dangerous pro-goitrin substance believed to inhibit normal intake of iodine by body tissues. During of cooking, however, the offending enzyme usually is destroyed.