Your thyroid explained

For such a small gland, the thyroid has a huge influence on both our physical and psychological wellbeing. It affects everything from our heart rate, metabolism, circulation and bone health. It even influences how we think and feel!

Watch our short film explaining the thyroid gland and its vital role in our bodies. You will also learn about different thyroid disorders, their symptoms, and how they are treated.

What is a thyroid gland?

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 mainly 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 windpipe.

What does my thyroid gland do?

The thyroid makes two hormones that are released into the bloodstream. 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.

What do my thyroid hormones do for me?

The T4, or rather the T3 derived from it, and the T3 released 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 released, the body cells work faster than normal, and you have hyperthyroidism (overactive thyroid). If you become hyperthyroid because of too much thyroid hormone, 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, the cells and organs of your body slow down. This is known as hypothyroidism (underactive thyroid). If you become hypothyroid, your heart rate, for example, may be slower than normal and your intestines may work sluggishly, so you become constipated.

What can go wrong with my thyroid?

• Hypothyroidism (underactive thyroid) - not enough thyroxine is produced for the body’s needs. This is the most common thyroid disorder.
• Hyperthyroidism (overactive thyroid) - too much thyroxine is produced for the body’s needs.

What are the most common symptoms of the most common thyroid disorders that I might experience?

Hypothyroidism: tiredness, feeling cold, weight gain, poor concentration, depression.

Hyperthyroidism: weight loss, heat intolerance, anxiety, and, sometimes, sore and gritty eyes.

Sometimes there are very few symptoms. A blood test from your doctor will confirm whether or not you have a thyroid disorder.

What other disorders are there?

• Thyroid eye disease – this affects some people who have an overactive thyroid due to Graves’ disease. More rarely, it can occur in patients with hypothyroidism or even normal thyroid function.
• Nodules or swellings – these lumps can stop the thyroid gland from working properly, or are simply uncomfortable.
• Thyroid cancer – this is very rare, but it is important to ask your doctor to check any lump in your neck.
• Having a baby can sometimes trigger a thyroid disorder. This is known as postpartum thyroiditis. It is usually temporary but can return each time you have a baby.

How is my thyroid gland controlled?

There has to be some sort of mechanism that regulates very carefully the amount of T4 and T3 released by your thyroid gland so that the right amounts are manufactured and delivered into the bloodstream. 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 bloodstream, 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 releasing a hormone called the Thyroid-Stimulating Hormone, also known as TSH, and this hormone activates the thyroid gland to produce more T4 and T3.

On the other hand, when the thyroid hormone levels rise above normal, the ‘thermostat’ senses this and the pituitary stops releasing TSH so that the thyroid gland stops working so hard and releases less T4 and T3.

What causes a thyroid disorder?

There are many causes of the different thyroid disorders. Most commonly the cause is due to autoimmune thyroid disease. This is a 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). The autoimmune form of hypothyroidism is called Hashimoto’s thyroiditis. The autoimmune form of hyperthyroidism is called Graves’ disease. You may find that other members of your family have thyroid problems or another autoimmune disorder.

How are thyroid disorders diagnosed?

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 how well your thyroid is working. From a single sample of blood, the laboratory can measure the level of thyroid hormones in your blood. This makes it possible to find out if too much or too little T4 and/or T3 is being released. By measuring the TSH it will be possible to find out how active the pituitary is. A single blood test will normally confirm your diagnosis, but sometimes other tests are required.

Can thyroid disorders be treated?

Yes, your thyroid disorder and many of the symptoms 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 about thyroid conditions and their treatments here:

Patient leaflets

Treatments for thyroid conditions

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