THYROID, in anatomy, a term applied (I) to the largest of the cartilages of the larynx (see RESPIRATORY SYSTEM), (2) to one of two arteries which lie near the thyroid cartilage and gland (see ARTERIES), and (3) to a vascular ductless gland, which rests on the larynx and upper part of the trachea. In human beings two conditions may occur both the result of a lack of thyroid secre tion, but differing according as the condition is congenital or has started in early life, i.e., cretinism (q.v.), or occurs later in life, i.e., myxoedema (q.v.). (See also DUCTLESS GLANDS.) The thyroid gland is used in medicine in two forms. Thy roideum siccum is a light, dull brown powder, prepared by drying the thyroid gland of a sheep. Its chief constituent is a proteid known as thyreoglobulin, the active principle of which contains 9.3% of iodine and 0.5% of phosphorus, and is known as iodothyrin or thyroiodin. The dried gland easily becomes damp and deteriorates. Liquor thyroidei is a pink turbid liquid made by macerating the fresh gland of a sheep with glycerin and phenol. The active principle in pure form—thyroxin—was isolated in 1914 by E. C. Kendall at the Mayo Clinic, Rochester,
Minnesota.
Thyroid gland administered to man increases the pulse rate, causes increased and enfeebled cardiac beat and leads to increased metabolism, consequently excess of urea, uric acid and phosphates are excreted in the urine ; it therefore reduces the body weight. Glycosuria develops from the inability of the body to ingest glucose. Overdoses of thyroid cause rapid pulse, headache and vomiting, together with diarrhoea and pruritus, emaciation and weakness. These symptoms are known as thyroidism.
Thyroid gland was introduced for the treatment of goitre, myxoedema and cretinism (q.v.). It has also been used in dwarf ism, excessive obesity, psoriasis and scleroderma.
Rodagen is a white powder consisting of the dried milk of thy roidectomized goats, mixed with 5o% of milk sugar. In exoph thalmic goitre this preparation causes a reduction of the swelling and of the pulse rate, and an increase of body weight.