Thyroid

thyroid /thy·roid/ (thi´roid)

1. the thyroid gland; see under gland.

2. pertaining to the thyroid gland.

3. scutiform.

4. a preparation of thyroid gland from domesticated food animals, containing levothyroxine and liothyronine and used as replacement therapy in the diagnosis and treatment of hypothyroidism and the prophylaxis and treatment of goiter and thyroid carcinoma.

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thy·roid (throid)

n.

1. The thyroid gland.

2. The thyroid cartilage.

3. A powdered preparation of the thyroid gland of certain domestic animals, used in the treatment of cretinism and myxedema, in certain cases of obesity, and in skin disorders.

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thyroid adj.

thy·roidal adj.

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Thyroid

A gland in the neck overlying the windpipe that regulates the speed of metabolic processes by producing a hormone, thyroxin.

Mentioned in: Exophthalmos, Gynecomastia, Hypothermia

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thyroid

1. resembling a shield.

2. the thyroid gland (see below) secreting thyroid hormones (see below).

3. a pharmaceutical preparation of cleaned, dried, powdered thyroid gland, obtained from those domesticated animals used for food by humans.

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accessory thyroid

an additional thyroid located anywhere from the larynx to diaphragm, e.g. intrapericordial aorta; may be sufficient to supply the patient's need of thyroid hormone. Most common in dogs.

thyroid C cell

see c cell.

thyroid cartilage

the shield-shaped cartilage of the larynx.

thyroid diverticulum

primordium of the thyroid gland; appears as an outgrowth of the foregut between the first two pharyngeal pouches. This tube of epithelial cells grows ventrally into mesenchyme; the tube becomes the thyroglossal duct, the tip divides into two lobes, the thyroid glands.

thyroid dysfunction

see hypothyroidism, hyperthyroidism.

ectopic thyroid

migration of thyroid diverticulum tissue to aberrant sites occurs, e.g. thyroid tissue in the thymus. These cause no apparent abnormality.

thyroid extract

a pharmaceutical substance derived from thyroid glands, used in the treatment of hypothyroidism. See thyroid (3) (above).

thyroid function tests

used to assess the functional capacity of the thyroid glands; most commonly employed in dogs and cats. Include plasma T₄, plasma T₃, free T₄ radioiodine uptake, and TSH response tests.

thyroid gland

the largest of the endocrine glands, situated in the neck caudal to the larynx. It produces hormones (see below) that are vital in maintaining normal growth and metabolism. It also serves as a storehouse for iodine.

Microscopic appearance of the thyroid gland. By permission from Guyton R, Hall JE, Textbook of Medical Physiology, Saunders, 2000

thyroid hormones

iodothyronines secreted by the thyroid gland, principally thyroxine (tetraiodothyronine, T₄) and tri-iodothyronine (T₃); derived from iodination of tyrosyl residues in thyroglobulin. The pharmaceutical names for T₄ and T₃ are levothyroxine and liothyronine, respectively. Regulate basal metabolic rate.

thyroid parafollicular cell

see c cell.

thyroid radioiodine uptake

used as a thyroid function test but superseded these days by estimates of T₄ (thyroxine).

thyroid-stimulating hormone (TSH)

see thyrotropin.

thyroid tumor

mostly follicular adenomas in old-aged dogs, cats and horses; papillary adenomas are rare.