The thyroid gland is an endocrine gland in your neck. It makes two hormones that are secreted into the blood: thyroxine (T4) and triiodothyronine (T3). These hormones are necessary for all the cells in your body to work normally. Thyroid disorders are very common and tend mainly to occur in women, although anybody - men, teenagers, children and babies, too - can be affected. About one in 20 people has some kind of thyroid disorder, which may be temporary or permanent.
The thyroid gland lies in the front of your neck in a position just below your Adam’s apple. It is made up of two lobes - the right lobe and the left lobe, each about the size of a plum cut in half - and these two lobes are joined by a small bridge of thyroid tissue called the isthmus. The two lobes lie on either side of your wind-pipe.
The thyroid makes two hormones that it secretes into the blood stream. One is called thyroxine; this hormone contains four atoms of iodine and is often called T4. The other is called triiodothyronine, which contains three atoms of iodine and is often called T3. In the cells and tissues of the body the T4 is converted to T3. It is the T3, derived from T4 or secreted as T3 from the thyroid gland, which is biologically active and influences the activity of all the cells and tissues of your body.
The T4, or rather the T3 derived from it, and the T3 secreted directly by the thyroid gland influence the metabolism of your body cells. In other words, it regulates the speed with which your body cells work. If too much of the thyroid hormones are secreted, the body cells work faster than normal, and you have hyperthyroidism. If you become hyperthyroid because of too much secretion of the hormones from the thyroid gland, the increased activity of your body cells or body organs may lead, for example, to a quickening of your heart rate or increased activity of your intestine so that you have frequent bowel motions or even diarrhoea.
On the other hand if too little of the thyroid hormones are produced (known as hypothyroidism), the cells and organs of your body slow down. If you become hypothyroid, your heart rate, for example, may be slower than normal and your intestines work sluggishly, so you become constipated.
Hypothyroidism is the most common disorder.
Sometimes there are very few symptoms. A blood test from your doctor will confirm whether or not you have a thyroid disorder.
There has to be some sort of mechanism that regulates very carefully the amount of T4 and T3 secreted by your thyroid gland so that the right - the normal - amounts are manufactured and delivered into the blood stream. The mechanism is very similar to that which regulates the central heating in a house where there is a thermostat in, say, the living room, which is set to a particular temperature and which activates the gas- or oil-fired furnace, or boiler that heats the hot water. In the case of the thyroid the ‘thermostat’ consists of a little gland, called the pituitary gland that lies underneath your brain in your skull. The pituitary senses the level of thyroid hormones in your blood stream, just as the thermostat in your living room senses the temperature. Under normal circumstances, if the level drops just a little below normal, the pituitary reacts by secreting a hormone called the thyroid stimulating hormone, also known as TSH, and this hormone activates the thyroid gland to put out more T4 and T3.
Conversely, when the thyroid hormone levels rise above normal the ‘thermostat’ senses this and the pituitary stops secreting TSH so that the thyroid gland stops working so hard and the secretion of T4 and T3 is reduced.
There are many different causes of the different thyroid disorders. Most commonly the cause is due to autoimmune thyroid disease - a self-destructive process in which the body’s immune system attacks the thyroid cells as though they were foreign cells. In response the thyroid gland becomes underactive (hypothyroidism) or overactive (hyperthyroidism). You may find that other members of your family have thyroid problems or another autoimmune disorder.
Your doctor will be able to get a good idea about the activity of your thyroid gland by listening to your symptoms, asking you some questions and by examining your neck. However, by taking a small sample of your blood he or she can assess exactly your thyroid secretory state. On this single sample of blood, for example, the levels of the hormones involved can be measured in the laboratory. By this means it is possible to find out if too much or too little T4 and/or T3 is being secreted, and how active the pituitary is by measuring the TSH. A single blood test will normally confirm the diagnosis, but sometimes other tests are required.
Yes – your thyroid disorder and many of the symptoms, too, can be treated. Most thyroid disorders are treated with daily medication. There are other treatments for those thyroid disorders that cannot be controlled with medication. You can read more details under the specific thyroid disorders.
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British Association of Endocrine and Thyroid Surgeons - the representative body of British Surgeons who have a specialist interest in surgery of the endocrine glands (thyroid, parathyroid and adrenal)