Thyroid Disease

When I was asked to write an article on "thyroid disease", I took a very deep breath. The task seemed daunting. As any Endocrinologist (hormone specialist) knows, there are many subtopics within this giant topic, and an article like this could go on for a hundred pages! So, once I caught my breath, I decided to simply design this article to present a "rough guide" to the thyroid. This article will be an outline or introduction to many conditions that involve the thyroid gland. As you read through this, you will find a number of links that will take you to more in-depth articles dealing with the specific topic in question.

The thyroid is a butterfly-shaped gland located in the front of the neck just below the Adams apple. The gland wraps around the windpipe (trachea) and has a shape that is similar to a butterfly formed by two wings (lobes) and attached by a middle part (isthmus). The thyroid gland works like a tiny factory that uses iodine (mostly from the diet in foods such as seafood and salt) to produce thyroid hormones. These hormones help to regulate the body's metabolism and effects processes, such as growth and other important functions of the body.

The two most important thyroid hormones are thyroxine (T4) and triiodothyronine (T3), representing 99.9% and 0.1% of thyroid hormones respectively. The hormone with the most biological power is actually T3. Once released from the thyroid gland into the blood, a large amount of T4 is converted to T3 - the active hormone that affects the metabolism of cells throughout our body.

Thyroid hormone regulation - the chain of command

The thyroid itself is regulated by another gland located in the brain, called the pituitary. In turn, the pituitary is regulated in part by the thyroid (via a "feedback" effect of thyroid hormone on the pituitary gland) and by another gland called the hypothalamus.

The hypothalamus releases a hormone called thyrotropin releasing hormone (TRH), which sends a signal to the pituitary to release thyroid stimulating hormone (TSH). In turn, TSH sends a signal to the thyroid to release thyroid hormones. If overactivity of any of these three glands occurs, an excessive amount of thyroid hormones can be produced, thereby resulting in hyperthyroidism. Similarly, if underactivity of any of these glands occurs, a deficiency of thyroid hormones can result, causing hypothyroidism.

Hypothalamus - TRH

Pituitary- TSH

Thyroid - T4 and T3

The rate of thyroid hormone production is controlled by the pituitary gland. If there is an insufficient amount of thyroid hormone circulating in the body to allow for normal functioning, the release of TSH is increased by the pituitary in an attempt to stimulate more thyroid hormone production. In contrast, when there is an excessive amount of circulating thyroid hormone, TSH levels fall as the pituitary attempts to decrease the production of thyroid hormone.

There is another hormone that is produced by the thyroid called calcitonin. Calcitonin is produced by specific cells in the thyroid gland, and unlike T3 and T4, it is not involved in this regulation of metabolism. Calcitonin is a hormone that contributes to the regulation of calcium and helps to lower calcium levels in the blood. Excess calcium in the blood is referred to as hypercalcemia.

Source: MedicineNet.com
http://www.medicinenet.com/thyroid_disease/article.htm