Excuse me doctor, but what can you tell me about a Thyroid?
Sunday, April 20, 2014 10:00 PM
I've received a request to write about thyroid gland problems. Thyroid problems are fairly common in a family medicine setting. For those who don't know what a thyroid is or does, keep reading.
Dr. John Roberts is a physician and one of the owners of The Paper. In addition to his weekly column, he writes a daily health tip that can be found on page A1.
The thyroid is an endocrine gland found in the neck. Endocrine glands secrete hormones into the bloodstream. The hormones then travel around the body and facilitate various biologic functions by interacting with cells in different tissues. You can think of hormones as microscopic fingers that flip switches on cells to make something happen in them.
The primary function of the thyroid gland is to control metabolism (energy use) in our cells. It does this by producing two hormones, T4 and T3. Both of these hormones contain iodine which is why it's important to get some iodine in our diets.
Our bodies contain sensors that constantly monitor body functions and tweak them to maintain "homeostasis," a balanced internal environment. Systems that maintain homeostasis are extremely elegant. Some can be compared to the thermostat connected to a furnace that turns it on or off based on the temperature in the room. Instead of using wires to communicate, the body uses hormones as chemical messengers.
The hypothalamus, found at the base of the brain, is the main thermostat in our body that interacts with the thyroid. When it detects that the body is cold or requires more energy production, it will release the hormone TRH (Thyrotropin Releasing Hormone). This hormone travels to an endocrine gland just below the hypothalamus, the pituitary, which in turn secretes TSH (Thyroid Stimulating Hormone) into the bloodstream. The TSH then stimulates the thyroid gland to release T4 and T3.
Once the hypothalamus has turned on the thyroid "furnace" via TRH and TSH, how does it get shut off? It's also done by the hypothalamus and pituitary gland that also monitor the levels of T4 and T3 in the bloodstream. When the hormones reach a certain level, they turn off the production of TRH and TSH.
Now that you know the physiology of the thyroid, hopefully it will make it easier to understand how things can get out of whack. There are two main problems that can develop with the thyroid. The first is hypothyroidism, a "low" thyroid state, where too little thyroid hormone is released. The other is hyperthyroidism or a "high" state where too much is released. Either one of these conditions can be very serious since homeostasis is knocked out of balance.
Hypothyroidism can result when any step of the complex hormonal pathway gets interrupted. The hypothalamus may not detect the body is cold or in need of energy. It may not produce or release TRH to stimulate the pituitary to secrete TSH. The pituitary may not make or release TSH or the thyroid gland itself may not respond to the TSH or make thyroid hormone properly.
Common symptoms of hypothyroidsm include: fatigue, weight gain, water retention, intolerance to cold, brittle hair and nails, dry skin, muscle cramps, joint aches, thyroid enlargement (goiter), low heart rate and constipation.
Hypothyroidism is confirmed by doing lab tests for various hormones. The level of TSH is the most sensitive test. Levels will be high in the blood because the pituitary is sensing the low levels of thyroid hormone and is trying to stimulate the thyroid to make more hormone. Depending on the situation, blood tests for T4 and T3 may also be checked.
Treatment of hypothyroidism usually involves taking synthetic thyroid hormone pills. Monitoring is performed by checking levels of thyroid hormones on a periodic basis and adjusting the dose accordingly.
Hyperthyroidism is most often caused by one of many possible problems with the thyroid gland itself, causing it to produce or release too much hormone. One condition, Hashimoto's thyroiditis, is caused by the immune system making antibodies that mimic TSH which keeps the thyroid constantly turned on. Other problems like thyroid growths can produce too much hormone.
Symptoms of hyperthyroidism include: weight loss, anxiety, tremor, intolerance to heat, rapid heartbeat or palpitations, thyroid enlargement, apathy or depression, and sometimes bulging eyeballs.
Like hypothyroidism, it is confirmed with lab testing. Usually the level of TSH is low since the pituitary sees plenty of thyroid hormone in the blood. Thyroid hormone levels are usually elevated. Additional testing may include ultrasound or nuclear imaging of the thyroid to look for growths or other abnormalities.
The treatment of hyperthyroidism varies based on the cause. It may require taking medication to suppress hormone production or taking radioactive iodine to destroy hyperactive thyroid tissue. Surgery is sometimes performed. Over-treating hyperthyroidism sometimes results in hypothyroidism and the need to take thyroid hormone pills.