444 



ORGAN SYSTEMS OF MAN 



Fig. 16-33. A case of hyperthyroidism. 



per cent of all the iodine taken into the 

 body, it can be determined beforehand the 

 exact amount that will be delivered to 

 the gland shortly after swallowing isotopic 

 iodine. Furthermore, radiations are known 

 to destroy thyroid tissue; therefore, by feed- 

 ing radioactive iodine "cocktails" to the pa- 

 tient, a certain amount of success has been 

 had in destroying a part of the gland. Its 

 more satisfactory use, however, is in the 

 treatment of cancer of the tliyroid. 



The parathyroids 



In the early studies of the thyroid much 

 confusion resulted because in removing the 

 gland the four tiny parathyroids embedded 

 in the thyroid were inadvertently removed 

 also (Fig. 16-29). The symptoms that fol- 

 lowed this were not only the result of thy- 

 roid deficiency but also of parathyroid de- 

 ficiency. The small parathyroid glands were 

 discovered in 1891 and many years later 

 their true function was determined. 



If the parathyroids are removed from an 

 animal, injected extracts of a hormone 

 (parathormone) produced by the glands 

 will keep that animal in good health. If no 

 extract is given, the animal suffers from 

 severe muscular tremors, cramps, and fi- 

 nally convulsions. The composite symptoms 

 are called tetanus, and without treatment 

 the animal passes into a coma and death 

 soon follows. The parathyroids or their ex- 

 tracts are essential for life in mammals, in- 

 cluding man. The value of the parathyroids 

 seems to be in maintaining proper levels of 

 calcium and phosphorus in the blood. 

 When the glands are removed the blood 

 calcium level falls rapidly, which correlates 

 with the symptoms of the disease. Adminis- 

 tration of calcium will prevent symptoms 

 of parathyroid deficiency. If the glands pro- 

 duce an overabundance of the hormone, the 

 calcium level in the blood then rises too 

 high and even the calcium of the bones is 

 sacrificed, so that a weak, twisted skeleton 

 is the result, rendering the unfortunate in- 

 dividual a cripple. 



The adrenals 



The adrenals are located on the upper 

 inner edge of each kidney, as one might 

 guess from their name (Fig. 16-29). Their 

 combined weight is no more than an ounce, 

 and each is composed of two parts, an outer 

 covering called the cortex and an inner 

 dark-colored mass called the medulla. The 

 gland is therefore a composite one and each 

 part has a separate origin, the cortex com- 

 ing from the mesodermal lining of the coe- 

 lom whereas the medulla is derived from 

 a part of the neural tube. One might expect 

 structures of such different origins to pos- 

 sess different functions and they do. 



The medulla. The medullary portion of 

 the adrenal produces a single hormone 

 called adrenalin, or sometimes adrenin or 

 epinephrine. Adrenalin has been analyzed 

 chemically and its formula determined. It 

 has also been synthesized from sources 

 other than adrenal glands. Related syn- 



