Living Well with Graves' Disease and Hyperthyroidism What Your Doctor Doesn't Tell You...That You Need to Know Chapter One Your Thyroid, Graves' Disease, and Hyperthyroidism What Is the Thyroid? The word thyroid comes from the Greek word thyreoeides , meaning "shield-shaped." The two lobes of the thyroid are known as the "wings of the butterfly" and the area connecting the two lobes is known as the "isthmus." Generally 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. The thyroid is a small gland normally weighing only about an ounce. It is located in the lower part of the neck in front of the windpipe. You'll know where the thyroid is if you think of it as sitting behind your Adam's apple. Glands that secrete their products inside the body, and more specifically those that secrete hormonal and metabolic substances, are known as endocrine glands. This makes your thyroid an endocrine gland, along with 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. Your thyroid's main purpose is to produce, store, and release two key thyroid hormones: triiodothyronine (T3) and thyroxine (T4). The numbers refer to the amount of iodine molecules attached to each hormone. Thyroid cells absorb iodine. The thyroid obtains iodine through food, iodized salt, and supplements, then combines it with the amino acid tyrosine, converting the iodine/tyrosine combination into T4 and T3. A healthy, functioning gland produces about 80 percent T4 and 20 percent T3. T3 is, however, the biologically active hormone that is used by the cells and is several times stronger than T4. The body converts the inactive T4 it produces to active T3 by removing one iodine molecule. This process is sometimes referred to as T4 to T3 conversion, or by the more scientific term monodeiodination. This conversion can take place in organs other than the thyroid, including the hypothalamus, a part of your brain. T4 and T3 exist in two forms: free/unbound and bound. Free or unbound T4 or T3 is biologically active, and the bound part is bound to the thyroxine-binding globulin (TBG) protein. When measured in the blood, the free or unbound T4 and T3 levels tend to be most representative of the actual hormone available for use by the body. The role of thyroid hormones is to control your metabolism -- the process by which oxygen and calories are converted to energy for use by your cells and organs. There's not a single cell in your body that doesn't depend on thyroid hormones for regulation and for energy in some form. Thyroid hormones have a number of functions as they travel through the bloodstream: Thyroid hormones help cells convert oxygen and calories into energy. Thyroid hormones help you properly process carbohydrates. Thyroid hormones aid in the proper functioning of your muscles. Thyroid hormones help your heart pump properly and effectively. Thyroid hormones help you breathe normally. Thyroid hormones help your intestinal system properly digest and eliminate food. Thyroid hormones help strengthen your hair, nails, and skin. Thyroid hormones help your brain function properly. Thyroid hormones help with proper sexual development and functioning. Thyroid hormones help with normal bone growth. 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 your thyroid works normally, it produces and secretes the amount of T4 and T3 necessary to keep various bodily functions moving at their proper pace. However, the thyroid does not do this alone. It works as part of a bigger system that includes the pituitary gland -- an endocrine gland located at the base of your brain -- and the hypothalamus. Here's how the system works. The hypothalamus constantly monitors the pace of many of the body's functions. It also observes and reacts to a number of other factors, including environmental conditions such as heat, cold, and stress. If the hypothalamus senses that certain adjustments are needed to react to any of these factors, 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, better known as thyroid-stimulating hormone (TSH). The pituitary gland also monitors the body and can release TSH based on the thyroid hormones circulating in your blood. TSH is sent to the thyroid gland, where it causes your gland to produce, store, and release more T3 and T4. Released thyroid hormones are carried through the bloodstream by a plasma protein known as thyroxine-binding globulin (TBG). Now in the bloodstream, the thyroid hormone travels throughout the body, carrying orders to various organs. Upon arriving at a particular tissue in the body, thyroid hormones interact with receptors located inside the nucleus of your 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, which causes the pituitary to decrease production of TSH, which then slows production of thyroid hormone. This system keeps many of the body's organs working at the proper pace. Think of the entire feedback loop as resembling the thermostat in your house. It's set to maintain a particular temperature, and when it detects that your house has become too hot, it signals the heating system to stop blowing heat. Similarly, when the house becomes too cold, the heat will kick on (or the air conditioning will turn off). Like a thermostat set to a particular temperature, your body is wired to maintain a certain level of circulating thyroid hormone function. When thyroid disease or conditions interfere with the system and the feedback process doesn't work, thyroid problems can develop. Living Well with Graves' Disease and Hyperthyroidism What Your Doctor Doesn't Tell You...That You Need to Know . Copyright © by Mary Shomon. Reprinted by permission of HarperCollins Publishers, Inc. All rights reserved. Available now wherever books are sold. Excerpted from Graves' Disease and Hyperthyroidism: What Your Doctor Doesn't Tell You... That You Need to Know by Mary J. Shomon All rights reserved by the original copyright owners. Excerpts are provided for display purposes only and may not be reproduced, reprinted or distributed without the written permission of the publisher.
