Body Talk

The small but powerful thyroid

The thyroid gland is another important organ in the amazing human body. 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 supports a wide range of functions from controlling our weight, heart rate, cholesterol level in the blood, muscle strength and skin condition . A healthy thyroid is essential for all-round 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 regulates your energy level whilst stimulating cell growth..

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 per cent of the thyroid hormones in the blood. Another hormone, tri-odothyronine (T3), accounts for the other 0.1 per cent.

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.

The 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 a 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 a key to growth and healthy bones. Calcium levels are regulated by calcitonin from the thyroid and by the parathyroid hormone, which is produced by four pea-sized parathyroid glands located just behind the thyroid.

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For a healthy thyroid

Every 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.

Interesting facts ...

* How fast does the heart beat?

The beat of your heart depends on the size. In general, the larger the person, the slower the heartbeat. A man's heart beats about 70 times a minute, a woman's a little faster and a baby's about 130 times a minute.

Did you know that an elephant's very large heart beats only about 25 times a minute?

* What is the difference between a vein and an artery?

An artery carries blood away from the heart, while a vein carries blood toward the heart. T he blood in the artery contains dissolved, fresh oxygen, which has entered the heart chambers, by way of major blood vessels, from tiny air sacs located in the lungs.

The blood in the veins contain waste material which it carries up to the heart. These waste gases from the veins are filtered through to the air sacs in the lungs. When you exhale, you get rid of these waste gases as carbon dioxide.

* How long do you think all the blood vessels would be if they are straightened out?

About 100,000 miles (161,000 kilometres) long! This is long enough to circle the world four times at the equator.

* How can the human body hold so many miles of blood vessels?

The body can hold so much blood vessels because most of the blood vessels are thinner than a hair's breadth.

The largest blood vessels are the arteries and the veins. You can think of them as the super highways of the body. But, there are also millions of tiny capillaries which are invisible, except through a microscope.