What is the Thyroid Gland and What Does it Do?
The thyroid gland is normally located in the neck just a bit below the thyroid cartilage, the “adams apple.” If you are intensely curious to actually locate your thyroid gland or someone else’s, you need to first put your thumbs on the thyroid cartilage (gently). Next, slide them down the front of the neck about half an inch until you reach a lump, this is the cricoid cartilage. Next. slide your thumbs down a bit and you should be feeling the isthmus of the thyroid, the part of the thyroid that bridges the right and left lobes. The lobes have upper and lower poles but the upper ones are more prominent. The thyroid gland looks a lot like a butterfly. You may not be able to feel the thyroid gland as it is normally quite small. Watch someone swallow and see if a small butterfly-like shape slides up and then down in the neck where you would expect the thyroid gland to be.
In many medical schools, students are taught to feel the thyroid gland standing behind the patient. The idea is that one can use the fingers the feel the gland rather than the opposed thumbs; the fingers are supposed to be more sensitive than the thumbs for feeling nodules and who know what. In my opinion, any advantage in sensitivity is off-set by one’s being unable to see what is going on.
What does the thyroid gland do?
The thyroid gland is basically a factory for thyroid hormones, called T4 and T3 (mostly T4). Think of thyroid hormones as the gas pedal on a car, which controls the speed of the vehicle. Thyroid hormones control the body metabolic rate. If the thyroid hormone levels are low, the metabolic rate decreases and this is called hypothyroidism. Typical signs and symptoms include fatigue, weight gain, swelling of the feet, constipation, and dry skin. Severe hypothyroidism is very serious and can lead to heart failure. The other side of the coin, hyperthyroidism, is associated with rapid heart rate, nervousness, weight loss, heat intolerance, and excessive sweating. In some forms of hyperthyroidism there is prominence of the eyes, called exophthalmos. In adults, hyperthyroidism can be associated with an arrhythmia of the heart called atrial fibrillation.
It is relatively easy to diagnose thyroid conditions. thyroid hormones circulate in the blood and can be measured very accurately by most laboratories. Generally the best test to assess blood levels of thyroid hormone is called “free T4.” This is the portion of the circulating thyroid hormone, tetraiodothyronine (a thyronine molecule with 4 iodine molecules attached) that is not tightly bound to serum proteins and best reflects the metabolic state. One other hormone, thyrotropin, or TSH (thyroid-stimulating hormone) is also useful to measure. TSH is produced by the pituitary gland in the brain and regulates thyroid hormone production. If there is too much circulating free T4, the pituitary gland decreases the secretion of TSH thereby slowing down the production of T4 in the thyroid gland. Conversely, if the circulating level of free T4 is too low, TSH levels go up in an effort to drive the thyroid gland to produce more T4. If the gland is damaged or affected by certain drugs, it can’t respond to the pituitary message and the free T4 level stays low. Sometimes, the TSH message succeeds in stimulating the thyroid gland to make enough T4 to get the free T4 level back to normal but only if the TSH stays elevated. That condition is called compensated hypothyroidism.
So what’s the bottom line?
In summary, except in very rare circumstances, if the blood levels of free T4 and TSH are in the normal range, hypothyroidism is highly unlikely (as is hyperthyroidism). If a person has compensated hypothyroidism (normal free T4 and elevated TSH) it would be very unusal for them to have any symptoms due to hypothyroidism- they might have signs or symptoms that suggest hypothyroidism, such as fatigue and weight gain, yet not have them the result of hypothyroidism.
Mysticism and the thyroid gland
Some physicians believe that many patients have hypothyroidism even though the test results are normal. Their reasons vary but in my experience, they don’t make any sense and are inconsistent with our very firm understanding of thyroid gland physiology and pathophysiology. Quite a number of people who do not have hypothyroidism are treated long-term with thyroid hormone. The other side of the coin are the many people who do have hypothyroidism and are not being treated. For example, hypothyroidism is very common in people over the age of 40 years, mostly women. It’s easy to diagnose, right? Just have your physician order a serum free T4 and a serum TSH.
- Obesity: What To Do About It
- Hypothyroidism in Children: What Causes it?