by RayN

Created on: July 01, 2007

The thyroid is a large gland (organ that releases hormones in the bloodstream) of the endocrine system, located in the neck in the general vicinity of the "Adam's Apple". The etymology of the word "thyroid" is Greek, meaning "shield," named so due to its shape. The principal hormones produced and released by the thyroid are thyroxin (T4) and triiodothyronine (T3), both which rely heavily on iodine for their synthesis.

The thyroid gland is notable due to its essential and important influence in the process of regulating metabolism; mainly due its secretion of T3 and T4 into the bloodstream. The thyroid also plays an important role in protein synthesis and regulating the bodies overall sensitivity to other hormones of the endocrine system. The hypothalamus and the pituitary are also glands of the endocrine system and are very actively involved in regulating and maintaining the proper function of the thyroid; the pituitary releases thyroid-stimulating hormone (TSH), while the production of TSH itself is modulated by thyrotropin-releasing hormone (TRH), which is produced by the hypothalamus.

In a healthy person, the thyroid produces normal levels of mainly T3 and T4 (regulated by TSH), which stimulate metabolism, brain growth and development and other glandular functions. A diseased thyroid is usually indicated by marked underactivity (hypothyroidism) or overactivity (hyperthyroidism). Symptoms of hypothyroidism can include abnormal fatigue, weight gain, depression, constipation, daytime sleepiness, memory loss and decreased sex drive. Hyperthyroidism on the other hand is marked by nervousness, irritability, weight loss, and insomnia, among other symptoms. Tumors, cancerous growths are also common afflictions of the thyroid. And a goiter is simply an enlarged thyroid; an iodine deficiency that interferes with the production of TSH and TSR is usually the cause; the thyroid is overworked and grows larger to compensate. Most of these thyroid afflictions can be treated with doctor prescribed drug therapy, surgery, radiation and diet modification.

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