Understanding Your Thyroid Gland

If you're like most people, you may not have given much thought to your thyroid gland. Over the years, you've probably heard about other people having thyroid problems; but the truth is that most of know very little about this gland. In fact, we usually don't feel we need to know much about it ... until it causes us a problem. Then, many of us want to gain a better understanding of how this small but powerful gland can have such a dramatic impact on our health.

One in ten Americans is affected by thyroid problems. And unfortunately, as many as half of those people have not been diagnosed. The reasons for the large number of undiagnosed cases include lack of public awareness about thyroid disorders as well as lack of knowledge about the thyroid gland itself. To lay a foundation for a better understanding of thyroid disorders, let's first examine the thyroid gland and its function.

The Thyroid Gland

The thyroid gland is located at the front of your throat, just below your voice box (larynx). It is a light purplish-red, about the size of a hen's egg, weighs less than three-quarters of an ounce, and is encased in a thin layer of tissue.

Shaped like a butterfly, the thyroid has "wings," or rubbery lobes , that are about two to three inches long. The middle section of the so-called butterfly shape is the isthmus.

How the Thyroid Gland Works

A complex organ, the thyroid gland produces hormones that are responsible for keeping virtually every cell and organ in your body functioning normally. You might think of these hormones as a "fuel additive" that makes the "human machine" run smoothly. They help cells convert oxygen and calories into energy.

The thyroid gland works in concert with the hypothalamus and the pituitary gland in the brain to produce thyroid hormones that influence the function of your heart, brain, eyes, skin, muscle, bone, liver, kidneys, and intestines. These hormones also affect growth and development; influence the protein that builds muscle; and are largely responsible for regulating your body temperature, heart rate, mood, alertness, and even the texture and growth of your hair and nails. The functioning of the thyroid gland can also affect weight gain or loss because the gland regulates metabolism, the process by which your body uses up nutrients. The rate at which metabolism occurs is called the basal metabolic rate, or BMR; thyroid hormones help regulate your BMR.

If the thyroid hormones and other chemicals with which they interact get out of balance, a variety of troublesome symptoms can occur. So, take a bit of time and read on to learn about these important chemicals, their functions, and their interdependence with other key organs.

How Thyroid Hormone Is Produced

Chemistry may or may not be one of your favorite subjects, but to gain an understanding of how thyroid hormones can affect your health, it will be helpful if you follow along for a short lesson in chemistry on how your body produces thyroid hormone. Understanding this hormone is the foundation for understanding thyroid disorders. And, t he two hormones that make up thyroid hormone will be referred to by medical professionals repeatedly as you are being tested or treated for a thyroid disorder. So for this reason, having a basic understanding of the chemistry will be helpful to you.

The thyroid gland produces thyroid hormone through a series of chemical interactions. Among these interactions is the absorption of iodine from the bloodstream. Iodine combines with other chemicals to create the hormone thyroxine, also referred to as T4. It's called T4 because it has four atoms of iodine in each molecule. T4 is stored in the thyroid gland attached to the main thyroid protein, thyroglobulin. By itself, T4 is relatively weak and inactive, so to do its work, most T4 is converted into the more active hormone triiodothyronine, known as T3. As you might guess, T3 has three iodine atoms per molecule. These two hormones, thyroxine and triiodothyronine, together make up thyroid hormone.

Now, there is another important aspect to understand about these two hormones, T3 and T4. It relates to whether the hormones are able to do their jobs in helping cells convert oxygen and calories into energy. As these hormones travel through the bloodstream, the vast majority cling to proteins (called thyroid binding globulin or TGB). When the hormones are attached to these proteins, they cannot do their work in helping the body's organs work smoothly. On the other hand, a small amount of thyroid hormone is not stuck to proteins and is floating freely through the bloodstream. Only when the hormone is free can it do its job in keeping the body's metabolism running well.

Accordingly, when doctors talk to you about your thyroid hormone levels, they may speak of the "total" hormone level or the "free" hormone level. The terms are defined as follows:

Total thyroxine (TT4): the body's total amount of thyroxine, most of which is inactive because it is "tied up" with protein.

Free thyroxine (FT4): the active form of the hormone thyroxine, which is not tied to proteins and floats freely in the bloodstream, helping the body's organs work efficiently.

Total triiodothyronine (TT3): the total amount of the body's triiodothyronine, most of which is "tied" to proteins, making it inactive.

Free triiodothyronine (FT3): the active form of the hormone triiodothyronine, which travels freely through the bloodstream, able to do its work.

"Lock and Key" Analogy

If you find the chemistry lesson here a bit confusing, consider an analogy that will add clarity. Think of a locked door and key. The body's organs are the "locks on the door," and the free hormone is the "key." The free hormone can unlock the door, enter the organ, and do its work in making the body function normally. However, because the total hormone is bound up in protein, it is like a key that doesn't fit into the lock. As a result, the hormone cannot do its work.

How the Body Regulates Thyroid Hormone

Like a juggler with fragile balls in the air, your thyroid regulates organs and systems throughout the body by shifting and compensating to maintain a hormonal balance. This balancing act is regulated by a feedback loop system. When too much thyroid hormone is being produced, the brain decreases the secretion of two hormones that slow the production andrelease of thyroid hormone. These hormones are called thyrotropin releasing hormone, or TRH, and thyrotropin or thyroid...