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Your amazing bodyThyroid
Though it weighs barely 28.5 grams (an ounce ), the thyroid gland, which is located just below the Adam's Apple in the neck has an amazing and far-reaching influence on our health. The thyroid secretes iodine-containing hormones that balance your metabolic rate - the speed at which you use the energy from your food. Iodine also helps the body to burn off excess fat, and efficiently regulate your energy level whilst stimulating cell growth. The thyroid supports a wide range of functions from controlling our weight, heart rate, cholesterol level in the blood, muscle strength and skin condition to our eyesight and emotions. A healthy thyroid is essential for all-round health.
How the thyroid is constructedAppropriately, given its location, the thyroid is shaped like a bow tie. Its two wings, or lobes, straddle the windpipe at the front part of the throat and are joined by a strip of tissue called the isthmus. Although it lies near the surface, the thyroid is normally small and soft, and can scarcely be felt through the skin. It is composed of two sets of cells, which secrete hormones. The production of these hormones depends on the body being able to derive sufficient iodine from the food we eat. Millions of hollow, spherical follicular cells, which make up most of the thyroid, secrete iodine-containing hormones into the bloodstream. The most important of these hormones is thyroxine (T4), which accounts for 99.9 percent of the thyroid hormones in the blood. Another hormone, tri-odothyronine (T3), accounts for the other 0.1 percent. The remaining cells, known as parafollicular cells, occur singly or in small groups in the spaces between the follicles and secrete a hormone called calcitonin.  What the thyroid doesThe thyroid works closely with two other hormone-producing glands, the pituitary and the hypothalamus. These three act in concert to balance the thyroid's hormone output, enabling the body to produce just the right amount of energy just when it needs it - low during sleep, higher when we are awake, higher still when we are active. The pituitary, a pea-sized gland at the base of the brain, controls the thyroid's function with its own thyroid-releasing hormone. The pituitary itself is activated by thyrotropin-releasing hormone from the hypothalamus, a cherry-sized region of the brain just above the pituitary. It is the T3 and T4 hormones secreted by the thyroid that play a major role in controlling the way our body functions are maintained and our energy is created and used up (our metabolism). They are essential for children's normal physical growth and mental development. Calcium is also key to growth and healthy bones. Calcium levels are regulated by calcitonin from the thyroid and by parathyroid hormone, which is produced by four pea-sized parathyroid glands located just behind the thyroid. What can go wrong with the thyroidThe most common thyroid disorder is an under-active thyroid, or hypothyroidism - the thyroid fails to produce enough hormone due to insufficient intake of iodine, and shrivels away. On the other hand, in Hashimoto's disease, the thyroid may enlarge, sometimes severely, resulting in a swelling known as a goitre. This occurs when the immune system produces antibodies that damage the thyroid, encouraging the pituitary to secrete more hormone which makes the thyroid work harder, causing it to enlarge. In many countries, goitre has been largely eliminated by the widespread use of iodised salt, but at one time it was common in areas where the soil and rocks lack iodine, as in Derbyshire, where the disease was called 'Derbyshire Neck'. Hypothyroidism can also result from a glandular malfunction known as myxoedema in adults and cretinism in infancy and childhood. Hypothyroidism may go undetected for years because the symptoms, such as forgetfulness and fatigue, can easily be confused with other conditions, with natural ageing or with the menopause or stress. Other symptoms include hoarseness, lassitude and apathy, difficulty in swallowing, intolerance to cold and dry or coarse hair and skin. However, even mild hypothyroidism can be detected by a blood test to check hormone levels, and is easily treated by supplementing the body's naturally produced hormone with a synthetic hormone tablet, generally taken daily for life. Hyperthyroidism, a less common thyroid disorder, occurs when the thyroid gland becomes overactive and produces too much hormone (Graves' disease). It is more prevalent among women, particularly those in their 30s and 40s. Besides goitre, symptoms include sleep disturbance, muscle weakness or tremors, irregular menstrual periods, palpitations, heat intolerance, weight loss despite good appetite, protrusion of the eyeball or vision problems. Treatment to reduce hormone production with drug therapy may be complex and prolonged. Surgery may also be used to treat the condition. Other disorders of the thyroid are rare. They include genetic defects, infection, cysts and benign or malignant tumours. For more information about thyroid disease see our factsheet How to maintain a healthy thyroidEvery adult needs iodine, but only one ten thousandth part of a gram per day. Food usually supplies this because iodine occurs in most soils and is taken up by plants. A balanced diet without too much processed food and which includes fresh fruit and vegetables should ensure an adequate intake. There is also iodine in meat (especially liver), enriched cereals, seafood (including seaweed, or kelp) and drinking water. Most people needn't worry about having too much iodine in their diet as any excess is lost in urine. Some multi-vitamins may contain iodine, but isolated iodine supplements are both difficult to obtain and rarely necessary. However, there is some research to suggest that in areas of iodine deficiency taking extra iodine during pregnancy may reduce the frequency of hypothyroidism problems in young children (see link below). If you are concerned about this talk to your GP. Links: - - - - - - - - - January 2002 Back to the'Your amazing body' index. |
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