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The thyroid is a small gland in the front of the neck just below the voicebox (larynx). It is made up of two parts, or lobes, and is part of the endocrine system. This system makes the body’s hormones that help to control and influence various functions.
The thyroid is sometimes known as the ‘activity’ gland because it produces the two main hormones thyroxine (T4) and triiodothyronine (T3). These keep the body functioning at its normal rate. The thyroid gland needs a regular supply of iodine, which is found in fish, seafood and dairy products, to produce thyroid hormones. We take in iodine from our diet.
The thyroid gland
View a large version of the image of the thyroid gland |
If the levels of T3 and T4 in the blood fall, a part of the brain called the hypothalamus senses this. It responds by sending out thyroid-releasing hormones (TRH) into the blood. As the level of TRH in the blood rises, it activates another gland in the brain called the pituitary gland to release thyroid-stimulating hormones (TSH). TSH stimulates the thyroid to produce more T3 and T4 thyroid hormones.
If the thyroid gland doesn’t produce enough hormones, you’ll feel tired and lethargic and put on weight easily.
This is called hypothyroidism or myxoedema. If the thyroid gland produces too many hormones, it’s called hyperthyroidism or thyrotoxicosis. You’ll lose weight, feel hungrier than normal, and shaky and anxious.
Your heartbeat may also be faster than normal or irregular.
Content last reviewed: 1 December 2012
Next planned review: 2014
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