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A delicate Feedback Mechanism
By Wilma Ariza, Thyroid Cancer Advocate |
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Your thyroid gland is a small gland, normally weighing less than one ounce, located in the front of the neck. It is made up of two halves, called lobes, that lie along the windpipe (trachea) and are joined together by a narrow band of thyroid tissue, known as the isthmus.
The thyroid is situated just below your "Adams apple" or larynx. During development (inside the womb) the thyroid gland originates in the back of the tongue, but it normally migrates to the front of the neck before birth. Sometimes it fails to migrate properly and is located high in the neck or even in the back of the tongue (lingual thyroid) This is very rare. At other timesit may migrate too far and ends up in the chest (this is also rare).
The function of the thyroid gland is to take iodine, found in many foods, and convert it into thyroid hormones: thyroxine (T4) and triiodothyronine (T3). Thyroid cells are the only cells in the body which can absorb iodine. These cells combine iodine and the amino acid tyrosine to make T3 and T4. T3 and T4 are then released into the blood stream and are transported throughout the body where they control metabolism (conversion of oxygen and calories to energy).
Every cell in the body depends upon thyroid hormones for regulation of their metabolism. The normal thyroid gland produces about 80% T4 and about 20% T3, however, T3 possesses about four times the hormone "strength" as T4.
The thyroid gland is under the control of the pituitary gland, a small gland the size of a peanut at the base of the brain (shown here in orange). When the level of thyroid hormones (T3 & T4) drops too low, the pituitary gland produces Thyroid Stimulating Hormone (TSH) which stimulates the thyroid gland to produce more hormones. Under the influence of TSH, the thyroid will manufacture and secrete T3 and T4 thereby raising their blood levels. The pituitary senses this and responds by decreasing its TSH production. One can imagine the thyroid gland as a furnace and the pituitary gland as the thermostat.
Thyroid hormones are like heat. When the heat gets back to the thermostat, it turns the thermostat off. As the room cools (the thyroid hormone levels drop), the thermostat turns back on (TSH increases) and the furnace produces more heat (thyroid hormones).
The pituitary gland itself is regulated by another gland, known as the hypothalamus (shown in our picture in light blue). The hypothalamus is part of the brain and produces TSH Releasing Hormone (TRH) which tells the pituitary gland to stimulate the thyroid gland (release TSH). One might imagine the hypothalamus as the person who regulates the thermostat since it tells the pituitary gland at what level the thyroid should be set.
Common Thyroid Problems
The thyroid gland is prone to several very distinct problems, some of which are extremely common. These problems can be broken down into [1] those concerning the production of hormone (too much, or too little), [2] those due to increased growth of the thyroid causing compression of important neck structures or simply appearing as a mass in the neck, [3] the formation of nodules or lumps within the thyroid which are worrisome for the presence of thyroid cancer, and [4] those which are cancerous.
Goiters
~ A thyroid goiter is a dramatic enlargement of the thyroid gland. Goiters are often removed because of cosmetic reasons or, more commonly, because they compress other vital structures of the neck including the trachea and the esophagus making breathing and swallowing difficult. Sometimes goiters will actually grow into the chest where they can cause trouble as well. Several nice x-rays will help explain all types of thyroid goiter problems.
Thyroid Cancer
~ Thyroid cancer is a fairly common malignancy the vast majority of which have excellent long term survival. We now include a separate page on the characteristics of each type of thyroid cancer and its typical treatment, follow-up, and prognosis.
Solitary Thyroid Nodules
~ There are several characteristics of solitary nodules of the thyroid which make them suspicious for malignancy. Although as many as 50% of the population will have a nodule somewhere in their thyroid, the overwhelming majority of these are benign. Occasionally, thyroid nodules can take on characteristics of malignancy and require either a needle biopsy or surgical excision.
Hyperthyroidism ~
Hyperthyroidism means too much thyroid hormone. Current methods used for treating a hyperthyroid patient are radioactive iodine, anti-thyroid drugs, or surgery. Each method has advantages and disadvantages and is selected for individual patients. Many times the situation will suggest that all three methods are appropriate, while other circumstances will dictate a single best therapeutic option. Surgery is the least common treatment selected for hyperthyroidism.
Hypothyroidism ~
Hypothyroidism means too little thyroid hormone and is a common problem. In fact, hypothyroidism is often present for a number of years before it is recognized and treated. There are several causes, but the number one reason for thyroid cancer patients and survivors is alteration or loss of thyroid function as a result of cancer or cancer treatment. Hypothyroidism can even be associated with pregnancy. Treatment for all types of hypothyroidism is usually straightforward.
Thyroiditis ~
Thyroiditis is an inflammatory process ongoing within the thyroid gland. Thyroiditis can present with a number of symptoms such as fever and pain, but it can also present as subtle findings of hypo or hyper-thyroidism.
The Thyroid TSH Reference Range
By Mary Shomon
Why The So-Called Experts Are Totally Confused!
Thursday August 14, 2008
Honestly, it's just mind-boggling. Almost six years ago, laboratory experts, and a committee of the nation's top endocrinologists both came out with recommendations to narrow the TSH reference range so that the high is 2.5 to 3.0, versus 5.0 to 5.5.
Since then, we have had study after study linking subclinical/mild/borderline hypothyroidism to a host of health risks, including infertility, high cholesterol, and heart disease.
In the meantime, the TSH test range is still up for debate. Should we lower the TSH reference range as recommended, or shouldn't we? Everyone has their opinions, but what's the latest? Sadly, what we get is more evidence of confusion among endocrinologists, in the form of the article and accompanying editorial in the August 2008 issue of Clinical Thyroidology.
The article on "Lowering the thyrotropin reference limit to 2.5..." makes it clear that the mean and median TSH levels of the population without any thyroid dysfunction are under 2.0., and the percentage of the supposedly normal population who have a TSH level less than 2.5 is "only" 80%.
Therefore, they reason, if the upper reference limit was lowered to 2.5, some 10-20% of the population in general (and 35% of those age 70 and above) who have a "normal" thyroid "might" be exposed many to unnecessary levothyroxine therapy.
Then, in an editorial, you have Martin Surks, MD weighing in on this, and explaining that the risk of progressing to hypothyroidism is increased in those who have antithyroid antibodies, adding that "since nearly 80% of subjects with TSH levels between 3.0 and 5.0 mIU/L do not have antithyroid antibodies, it is likely that the large majority of people with TSH in that range have little risk for the development of hypothyroidism."
Surks has been on this bandwagon before, and was apparently just as misguided back then. I theoretically understand the reluctance to change the official reference range. If you change it, then it nearly mandates treatment for anyone who falls outside that range.
Why give treatment to those who don't need it? And, in some people, especially the elderly, unnecessary thyroid treatment may even cause additional health problems. Endocrinologists will tell you that it's not all that rigid anyway, and that they use some common sense when evaluating people who are subclinical, and have the freedom to make judgments. But the truth is, most American's will never see an endocrinologist for their thyroid condition.
There is such a shortage of endocrinologists that there is only one endo for every 40,000 Americans! Most of us see GPs, or family doctors, or internists. And what the endocrinologists just aren't understanding is that by leaving the reference range where it is, it becomes a rigid barrier of ignorance that most doctors use as their hard-and-fast rule for diagnosis and treatment.
Inability to make subtle diagnosis prevents patients who need it from getting thyroid treatment. For example, a woman with thyroid symptoms, a family history of thyroid problems, and a TSH of 4.5 may be adamantly refused thyroid treatment, and told by her family doc, ob-gyn or internist that her thyroid is "normal" because it's in the so-called normal range. Yet, if that woman is also trying to conceive, failing to treat her elevated TSH level may be the difference between infertility and/or miscarriage, and a healthy pregnancy.
What about the risk that these elevated subclinical TSH levels present for other conditions besides hypothyroidism? Conditions like heart disease, metabolic syndrome, high cholesterol, and more.
You can read the August 2008 issue of Clinical Thyroidology online, in PDF form or click on > Thyroglobulin Measuring Tests
If you do not have Adobe Acrobat
Reader, you may download it at the Adobe website.
Other Common Disorders Associated with your endocrine system:
