Situated in the neck, below the voicebox - or Adam's apple - is the thyroid. It is the largest of the endocrine glands and responsible for the body's rate of metabolism, due to the hormones it produces and secretes. These hormones are T3 (triiodothyronine) and T4 (thyroxine). Hormone production is simulated by TSH (thyroid stimulating hormone), released from the pituitary gland. The release of this hormone acts on the thyroid to stimulate production of T3 and T4. T3, T4 and TSH are measured in thyroid function tests to establish whether thyroid function is normal.
In the case of an overactive thyroid an individual can be diagnosed with hyperthyroidsim. An underactive thyroid is termed hypothyroidism. The majority of hyperthryoidism and hypothyroidism are caused by an incorrectly functioning thyroid gland, for a variety of reasons. Abnormal TSH production by the pituitary gland can also occur, although this is less common.
The thyroid has two lobes; a right and a left. Shaped like a butterfly, is has interconnecting tissue between the lobes known as the isthmus. The isthmus can have a pyramdial lobe attached to it, although this is not the case for the majority of people.
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Image of thyroid as it is in the neck This image is produced by Madhero88 who has released this image into the public domain |
Banner image showing thyroid follicle cells, courtsey of RachelHermosillo's photostream on Flickr. This image is available under the Creative Commons License, for non-commercial use and requiring attribution.
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