The Endocrine Glands - 405 



In fact the commonest form of hyperthyroid- 

 ism is found in exophthalmic goiter, or 

 Graves' disease. In this condition the swell- 

 ing is apt to be moderate, although the de- 

 gree of hyperactivity may be very great. 



The basal metabolism of a hyperthyroid 

 patient may be more than doubled, and such 

 an acceleration of the metabolism of the tis- 

 sues has drastic consequences. The nervous 

 and muscular systems become hyperirritable; 

 and there is profuse sweating, insomnia, and 

 muscular tremors. The subject eats more 

 food, yet loses weight. The blood pressure 

 rises and the heart may be overworked to a 

 serious degree. Moreover this type of goiter 

 is usually marked by a protrusion of the eye- 

 balls (exophthalmos), although the under- 

 lying cause of this peculiar symptom prob- 

 ably lies in the pituitary gland, rather than 

 in the thyroid. In fact, the factor that in- 

 duces the goiter and drives the gland to such 

 extremes of activity seems to be an overpro- 

 duction of the thyrotrophic hormone (p. 

 411) by the pituitary gland. To alleviate the 

 condition, however, the surgeon usually re- 

 moves a certain proportion of the thyroid, 

 guiding his judgment by preliminary meas- 

 urements of the metabolic rate. Also x-rays 

 and radium may be used to destroy some of 

 the thyroid tissue. More recently also, radio- 

 active iodine, 4 which accumulates sufficiently 

 in the thyroid gland to dampen the activity 

 of the secretory cells, and certain drugs that 

 inhibit thyroxin synthesis, have yielded 

 promising results. 



THE PARATHYROID GLANDS 



In 1957, Howard Rasmussen and co-work- 

 ers at The Rockefeller Institute in New 

 York, first succeeded in isolating and identify- 

 ing the parathyroid hormone. Like insulin 

 (p. 408), this hormone proved to be a rela- 

 tively simple protein-type compound — a 

 polypeptide chain, consisting of 83 amino 



4 Perhaps an even more important recent use of 

 radioactive iodine has been to arrest the growth of 

 malignant tumors of the thyroid gland. 



acid units. The isolation was an exceedingly 

 difficult task, however, and required more 

 than five years of very intensive work. It in- 

 volved extraction of the protein components 

 of the parathyroid glands from more than 

 300 head of cattle, separating these compo- 

 nents on the basis of their differential solu- 

 bility in various organic media. 



The parathyroids are essential to life, and 

 without replacement therapy the animal dies 

 in about three weeks after the parathyroids 

 are removed. This result is amply substanti- 

 ated in a variety of species, including man. 

 In surgical history there are records of sev- 

 eral cases in which the parathyroids were 

 sacrificed inadvertently, during operations 

 on the thyroid (see Fig. 22-1). 



Usually within two to three days after the 

 removal of all the parathyroid tissue, an ani- 

 mal displays severe muscular tremulations 

 and then violent cramps and convulsions. 

 Such a condition of tetany gradually pro- 

 gresses to the point of exhaustion, and the 

 victim dies in a comatose state. Rarely, the 

 tetanic phase of the disorder does not ap- 

 pear, in which case there are only muscular 

 weakness and a very slow wasting of the 

 tissues. 



The parathyroids appear to have a critical 

 effect upon the metabolism of calcium and 

 phosphorus in the tissues. Following the re- 

 moval of the glands, the blood calcium level 

 falls, and the severity of the symptoms runs 

 parallel, at least roughly, to the degree of 

 calcium depletion. Moreover, the symptoms 

 of parathyroid insufficiency are held in abey- 

 ance quite indefinitely by injections either 

 of parathyroid concentrates or of calcium 

 solutions — although best results are obtained 

 when both are used. With overdoses of para- 

 thyroid concentrates, the level of calcium in 

 the blood becomes too high, but the blood 

 content of phosphorus tends to fall away. 

 Also there is a marked depletion of both 

 calcium and phosphorus compound in the 

 tissues, especially in the bones. 



Recent studies, utilizing newly available 

 purified parathyroid hormone, have yielded 



