The thyroid gland is an endocrine gland. This means that it is a gland that manufactures certain hormones, which are chemical substances secreted into the blood-stream and act as messengers to affect cells and tissues in distant parts of your body.
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 and the left lobes, 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 for short 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 direct 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 is 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 is produced (known as hypothyroidism), the cells and organs of your body slow down. Thus if you become hypothyroid, your heart rate, for example, may be slower than normal and your intestines work sluggishly so you become constipated.
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 just 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 makes less T4 and T3.
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 you. By taking a small sample of blood the levels of the hormones involved can be measured in the laboratory. By this means it is possible to find out whether too much or too little T4 and/or T3 is being secreted by measuring the T4, T3 and TSH.These blood tests are essential in obtaining a diagnosis of a thyroid disturbance. Thyroid antibodies can also be measured to alert your doctor to the fact that you may be developing an autoimmune disorder, which may eventually lead to a thyroid disorder.
Hypothyroidism: thyroxine is available as a synthetic hormone and is taken daily.
Hyperthyroidism: the available treatment consists of drugs to reduce the formation of thyroid hormones (anti-thyroid drugs), surgical removal of part of the gland (partial thyroidectomy) or reducing the gland’s activity by giving radioiodine. You should ask your doctor to fully discuss management and treatment of your thyroid disorder with you. Further information is available in pamphlets available to members of the British Thyroid Foundation.
- Thyroid Cancer Patient Information Book
1 THE THYROID GLAND AND THYROID CANCER: Introduction, Tests and Treatment
- Thyroid Cancer Patient Information Book
2 THYROID SURGERY: THINGS YOU NEED TO KNOW ABOUT HAVING A THYROIDECTOMY
- Thyroid Cancer Patient Information Book
3 THINGS YOU NEED TO KNOW ABOUT RADIO-IODINE ABLATION TREATMENT
- thyroid eye disease
- some heart conditions
- altered cholesterol levels
- osteoporosis
- psychological symptoms
- infertility
- nodules and goitres
- rheumatism
Autoimmune disorders tend to run in families. The following
conditions may be associated with autoimmune thyroid disease:
- Addison’s disease
- diabetes mellitus
- vitiligo
- pernicious anaemia
- polymyalgia rheumatica and giant-cell arteritis
- alopecia
- myasthenia gravis
- premature ovarian failure
- rheumatoid arthritis
It is therefore very important for you and your doctor to be aware of your thyroid condition and understand all the related signs and symptoms in order to obtain the best possible means of treatment to manage the thyroid levels within a ‘normal’ functioning range.