Chapter 1
What is Hypothyroidism?
They do certainly give very strange, and newfangled,
names to diseases.--PlatoThe thyroid is not a particularly well-known or well-understood organ in the body. Some people have a vague idea of the thyroid as something in the neck that, when malfunctioning, makes you gain weight or develop a goiter. That's about all the information marry people can muster.
The thyroid gland, however, is an essential organ, governing basic aspects of nearly every facet of your health. In the long term, you can't live without the hormones produced by your thyroid. Those hormones regulate the body's use of energy, an essential function to life and health.
What Is The Thyroid?
The thyroid gland is shaped a little like a butterfly, and is located in the lower part of your neck, in front of your windpipe. You'll know generally where the thyroid is located if you think of it as sitting behind the Adam's apple, which usually sticks out farther from a man's neck than from a woman's.
The name "thyroid" comes from the Greek word, thyreoeides, meaning "shield-shaped." The two "wings" of the butterfly are known as the lobes of the thyroid, and the area connecting the two lobes is known as the isthmus. It's a small gland, and normally weighs only about an ounce.
Roughly speaking, a gland is a discrete and separate soft body made up of a large number of vessels that produce, store, and release-or secrete-some substance. Your thyroid is one of these glands.
Some glands secrete their products outside the body, some inside. Those that secrete their products on the inside of the body and, more specifically, secrete hormonal and metabolic substances, are known as endocrine glands. The thyroid is an endocrine gland, as are the parathyroids, the adrenal gland, the pancreas, and the pituitary gland. Diabetes, like thyroid disease, is considered an endocrine disorder. A doctor who specializes in treating patients with endocrine problems is called an endocrinologist.
Hormones are internal secretions carried in the blood to various organs. The thyroid's main purpose is to produce, store, and release two key thyroid hormones, triiodothyronine (T3) and thyroxine (T4). Thyroid cells are the only body cells that are able to absorb iodine. The thyroid takes in iodine, obtained through food, iodized salt, or supplements, and combines that iodine with the amino acid tyrosine, converting the iodine/tyrosine combination into T3 and T4. The "3" and the "4" refer to the number of iodine molecules in each thyroid hormone molecule. A healthy, functioning thyroid produces about 80 percent T4 and 20 percent T3. T3 is considered the biologically active hormone and is several times stronger than T4.
The T3 and T4 thyroid hormones travel through the bloodstream throughout the body helping cells to convert oxygen and calories into energy. Thyroid hormones control metabolism-the process by which oxygen and calories are converted to energy for use by cells and organs. There's not a single cell in your body that doesn't depend on thyroid hormone for regulation and for energy in some form.
The thyroid produces some T3, but the rest of the T3 needed by the body is actually formed from the mostly inactive T4 by the removal of one iodine molecule, a process sometimes referred to as T4 to T3 conversion, or by the more scientific term mono-deiodination. This conversion of T4 to T3 can take place in some organs other than the thyroid, including the hypothalamus, a part of your brain.
Now that you have some idea of what the thyroid is and its location and function, let's look in more detail at how it fits into the overall functioning of the body.
The Thyroid Gland: Setting the Pace
When the thyroid works normally, it produces and secretes the amount of T4 and T3 necessary to keep many bodily functions at their proper pace. However, the thyroid does not do this alone. It works instead as part of a system that also includes the pituitary gland and the hypothalamus. The pituitary gland is another endocrine gland, located at the base of your brain.
Here's how the system works. The hypothalamus constantly monitors the pace of many of the body's functions. It also monitors and reacts to a number of other factors, including outside environmental factors such as heat, cold, and stress. If the hypothalamus senses that certain adjustments are needed to react to any of these factors, then it produces thyrotropin-releasing hormone, (TRH).
TRH is sent from the hypothalamus to the pituitary gland. The pituitary gland then produces a substance called
thyrotropin, which is also known as
thyroid-stimulating hormone (TSH). The pituitary gland also monitors the body and can release TSH based on the thyroid hormones in the blood. TSH is sent to the thyroid gland, where it causes production, storage, and release of more T3 and T4.
Released thyroid hormones move into the bloodstream, carried by a plasma protein known as thyroxine-binding globulin (TBG).
Now in the bloodstream, the thyroid hormone travels throughout the body, carrying orders to the various bodily organs. Upon arriving at a particular tissue in the body, thyroid hormones interact with receptors located inside the nucleus of the cells. Interaction of the -hormone and the receptor will trigger a certain function, giving directions to that tissue regarding the rate at which it should operate.
When the hypothalamus senses that the need for increased thyroid hormone production has ended, it reduces production of TRH, the pituitary decreases production of TSH, and production of the thyroid hormone, in turn, decreases.By this system, many of the body's organs are kept working at the proper pace.
Continues...
Excerpted from Living Well with Hypothyroidism Rev Ed by Shomon, Mary J. Excerpted by permission.
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