Hypothyroidism is a condition in which the thyroid gland does not produce enough thyroid hormones. Insufficient amounts of hormones slow down all the chemical reactions in the body, causing mental and physical changes.

Makes iodine-containing hormones

The thyroid is a small gland that is wrapped around the windpipe (trachea) below the Adam’s apple. It has the shape of a butterfly, with two "wings" attached by a middle part.

The thyroid takes iodine from the food you eat to make iodine-containing hormones, of which thyroxine (T4, which has four iodine molecules attached to its structure) and triiodothyroxine (T3, with three iodine molecules) are the most important. Iodine is found in seafood, bread, salt and seaweed.

These hormones are one of the things that regulate the rate at which a person burns kilojoules for energy. They regulate growth and the rate of chemical reactions (metabolism) in the body.

Normally the rate of thyroid hormone production is controlled by the pituitary gland located at the base of the brain. When the supply of thyroid hormones is insufficient, the pituitary gland releases thyroid-stimulating hormone (TSH) to trigger the production of thyroid hormones in the thyroid gland.

If the thyroid gland is unable to produce the thyroid hormones, the pituitary releases more and more TSH. By measuring the amount of TSH, it is possible to test if your thyroid is underactive. 

Read more: 

Causes of hypothyroidism 

Symptoms of hypothyroidism 

Treating hypothyroidism

Reviewed by Dr Wayne May, Endocrinologist Kingsbury Hospital, Cape Town February 2015.

Previously reviewed by Dr P.H.S. van Zijl, MB.Ch B. MMed (Int).

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