Hypothyroidism

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thyroid gland

thyroid gland, endocrine gland, situated in the neck, that secretes hormones necessary for growth and proper metabolism. It consists of two lobes connected by a narrow segment called the isthmus. The lobes lie on either side of the trachea, the isthmus in front of it. Thyroid tissue is composed of millions of tiny saclike follicles, which store thyroid hormone in the form of thyroglobulin, a glycoprotein. Blood capillaries attached to the gland yield a constant supply of plasma. The protein thyroglobulin is the chief component of the jellylike substance, called colloid, that is secreted by the follicles. It attaches to the thyroid hormone for storage purposes; when the hormone is ready to be released, the protein detaches itself. Before it is released into the bloodstream, the thyroid hormone is converted into thyroxine and small quantities of the other closely related thyroid hormones. The amount of thyroxine production (and therefore the metabolic rate) is dependent on a sufficient intake of iodine and on stimulation by thyroid-stimulating hormone (TSH) from the pituitary gland. The thyroid gland also produces the hormone calcitonin, which is involved in the regulation of serum calcium in the body.

Metabolic disorders result when the thyroid secretes too little or too much thyroxine. Deficiencies in thyroid secretion (hypothyroidism) occur when there is insufficient iodine in the diet. A disease known as goiter results from the deficiency, although it has been virtually eliminated by the use of iodized salt. Hypothyroidism that results from glandular malfunction is known as myxedema in the adult and cretinism in infancy and childhood. Treatment is by administration of the synthetic hormone levothyroxine. Excessive secretion of thyroxine, or hyperthyroidism, causes an increased metabolic rate, loss of weight despite good appetite, protrusion of the eyeballs, rapid pulse, and irritability. The condition, also known as Graves' disease, may be accompanied by enlargement of the thyroid. Hyperthyroidism may be treated through the use of medicines that block thryroxine production or the administration of radioactive iodine to kill thyroid cells.

See also endocrine system.

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The following article is from The Great Soviet Encyclopedia (1979). It might be outdated or ideologically biased.

Hypothyroidism

 

decreased functioning of the thyroid gland. Hypothyroidism is a mild form of myxedema. Its basic symptoms are fatigue, slowing down of physical and mental activity, somnolence, sluggishness, decreased memory, sensitivity to cold, puffiness of the face, edematous eyelids, dryness of skin, loss of hair, constipation, and lowered basal metabolism. The treatment for hypothyroidism is hormone therapy.

The Great Soviet Encyclopedia, 3rd Edition (1970-1979). © 2010 The Gale Group, Inc. All rights reserved.

hypothyroidism

[¦hī·pō′thī‚rȯi‚diz·əm]
(medicine)
Condition caused by deficient secretion of the thyroid hormone.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.
References in periodicals archive ?
It never crossed my mind that it could be a thyroid issue, with the symptoms seeming to scream 'menopause' at me, but the doctor sent me for a blood test to check my hormone levels, and it turned out that I had a very underactive thyroid - in fact the level of the hormone in your brain that regulates the thyroid is meant to be under five and mine was over 100!
Other symptoms of underactive thyroid include weight gain, sluggish bowel movements, decreased appetite, falling, incontinence, and increased sensitivity to cold.
People with an underactive thyroid gland produce insufficient amounts of the hormones required for optimal body functioning.
"Light exercise could help, but it's worth getting tests for anaemia or an underactive thyroid gland
"Underactive thyroid is a particularly nasty thing to have and it can lead to other long-term health problems.
The team from the Centre for Health Services Studies at the University of Kent found doctors in the region had recorded 30 per cent higher than expected rates of underactive thyroid.
The abnormally large size of the gland is rarely due to cancer and is usually an indication of hyperthyroidism (an overactive thyroid gland) or hypothyroidism (an underactive thyroid gland).
Common symptoms, similar to an underactive thyroid, are feeling tired, mood swings, weight gain, heart palpations, sweating and lighter periods.
Also available was the TSH (thyroid-stimulating hormone) test for women, which measures thyroid hormone levels and identifies overactive and underactive thyroid glands, which can be the root of various health problems.
It's usual to feel low and lethargic but sometimes WATCH OUT it could indicate an underactive thyroid gland