Your amazing thyroid gland

If you've never been diagnosed with a thyroid problem, chances are you're not entirely certain where your thyroid gland is, let alone what it does. This small, butterfly-shaped gland weighs less than an ounce. When functioning normally, it perches unobtrusively with its "wings" wrapped around the front of your windpipe (trachea), below your voice box (larynx). 
Its slight size could easily fool you into underestimating the thyroid's importance to your health. Yet this gland influences the rate at which every cell, tissue, and organ in your body functions, from your muscles, bones, and skin to your digestive tract, brain, and heart. It does this primarily by secreting hormones that control how fast and efficiently cells convert nutrients into energy-a process known as metabolism.

How the thyroid gland works

Just as your car engine can't run without gasoline, your thyroid needs fuel to produce hormones. In the case of the thyroid, this fuel is iodine, which is found in such foods as seafood, bread, milk, and iodized table salt. When you eat these foods, the iodine passes into your bloodstream. Your thyroid then extracts the iodine from your blood and uses it to make thyroid hormone.

As the thyroid produces thyroid hormone, it stores it in a vast number of microscopic, spherical structures called follicles. When your body needs thyroid hormone, the thyroid secretes it into your bloodstream in quantities suitable to meet the metabolic needs of your cells. The hormone easily slips into cells in need and attaches to special receptors located in the cells' nuclei.

To return to the car analogy, your car engine burns fuel, but it is you who tells the engine how hard to work, by stepping on the gas pedal. The thyroid also needs to be told what to do. It takes its orders from your pituitary gland, located at the base of your brain. No larger than a pea, the pituitary is sometimes known as the "master" gland, because it controls the functions of other glands, including the thyroid. 

When things go wrong

Normally, this network of communication with the thyroid is highly efficient. The thyroid doles out just the right amount of hormone to keep your body running smoothly. TSH levels remain fairly constant, yet they respond to the slightest changes in thyroid hormone levels, and vice versa. But even the best network is subject to interference. Outside influences-such as disease or certain medicines-can disrupt communications. When this happens, the thyroid might not produce enough of its hormone. Too little thyroid hormone production slows down all of your body's functions, a condition known as hypothyroidism or underactive thyroid. Your thyroid also can produce too much hormone, sending your system into overdrive. This condition is known as hyperthyroidism or overactive thyroid.

Sometimes your thyroid is slightly overactive or underactive, but not enough to meet the definition of true (overt) hyperthyroidism or hypothyroidism. Doctors label this in-between state subclinical hyperthyroidism or hypothyroidism. 

When considering whether you have thyroid disease, your doctor will begin by addressing two questions: First, is the thyroid gland producing an abnormal amount of thyroid hormone? And second, is there a structural change in the thyroid, such as an enlargement (goiter) or a lump (nodule)? Although one of these characteristics does not necessarily imply that the other is present, many thyroid disorders have both.

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