Goiter(redirected from fibrous goiter)
Also found in: Dictionary, Thesaurus, Medical.
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.
in man, enlargement of the thyroid gland caused by the proliferation of its functional lymphoid tissue (parenchyma) or of its connective-tissue stroma. The proliferation of thyroid epithelium may embrace the entire thyroid parenchyma (diffuse goiter), or it may originate in a particular portion of the parenchyma (nodular goiter). Slight enlargement of the gland may occur in puberty or during menstruation, pregnancy, and lactation. Goiter may be associated with a number of conditions—diffuse toxic goiter, thyroiditis, thyroid tumor, and sporadic and endemic goiter.
A goiter may be unilateral or bilateral. Most often it is found in the neck; sometimes it is located behind the sternum (substernal goiter). A goiter usually alters the contours of the neck; although with substernal and deep-lying goiters the contours of the neck may remain normal. A goiter results in malfunction of the thyroid gland, but in the euthyroid form there need not be any functional impairment. Sporadic goiter is found in a number of localities and is caused by an endogenous (depending on internal factors) iodine deficiency in the body. Endemic goiter is found in certain biogeochemical areas where there is an insufficiency of iodine in the air, water, soil, and food products (instead of 200–220 μg, 20–80 μg of iodine or less enters the human body). Insufficiency of iodine in the environment may be aggravated by unfavorable exogenous (social, everyday, and sanitary-hygienic conditions) or endogenous (pregnancy, lactation, hypovitaminoses, helminthiases) factors. Iodine deficiency may result from infectious diseases or intoxications. A relative deficiency may occur when the ratio of iodine to certain chemical compounds (calcium, fluorine, and so forth) in the body is upset. Endemic goiter is found in almost every country, especially in mountainous regions, valleys, foothills, and watersheds and in swampy, sandy, and peaty regions. It is almost never found in chernozem zones.
Goiter prevention includes correcting unhealthy conditions in the throat and mouth, vermifuge treatment, and improvement of the conditions of sanitation and hygiene of daily life (keeping dwellings clean, maintaining the water supply properly, sound nutrition); individual and group iodine prophylaxis (iodized table salt); and early detection and dispensary observation of goiter patients. Treatment, depending on the form and symptoms of goiter, includes iodine preparations, thyroidin, triiodothyronine, and diiodothyrosine. Surgery is indicated for nodular and mixed goiter; it is also recommended for diffuse goiter if more conservative treatment proves ineffective.
L. M. GOL’BER