INTRODUCTION 21 



Duality of the Endocrin Organs 



A striking anatomical peculiarity of several of the organs of internal 

 secretion is their so-called duality. The pituitary body consists of two 

 major distinct structures, the anterior or parenchyma!, and the posterior 

 or nervous lobe. Associated with the posterior lobe are the pars inter- 

 media and the pars tuberalis. From the posterior lobe may be derived a 

 potent extract which has a marked effect upon the circulatory apparatus 

 and other parts of the body. Extracts of the anterior lobe, on the other 

 hand, are quite without significant pharmacodynamic effects. The thyro- 

 parathyroid apparatus is also composed of two different sorts of tissue, 

 the thyroid gland proper and the parathyroid bodies. In most animals 

 the parathyroids are in close apposition to the thyroid lobes; in some 

 they are imbedded in the thyroid tissue. The suprarenal body in mammals 

 consists of the medulla and, surrounding it, the cortex. From the medulla 

 alone is the active substance epinephrin obtained. Extracts of the cortex, 

 when injected into the blood stream, are without notable effect. In the 

 ovary, at certain periods, is found the corpus luteum, a structure that 

 has an important influence on body functions quite independent of that 

 of the organ in which it is imbedded. The same may be said of the inter- 

 stitial cells of both the ovary and the testis. 



These close anatomical associations are not found, however, in all 

 cases. The parathyroids are sometimes separated from the thyroids, and 

 in such forms .as the elasmobranch fishes, the two parts of the suprarenal 

 are represented by distinct organs, the interrenal and the adrenal bodies. 

 In some cases the associated structures have a similar embryonic origin, 

 but in the case of the pituitary and suprarenals the two parts arise 

 independently. 



Whether or not any functional significance is to be ascribed to the 

 association of these different structures has not been determined. In 

 case of the suprarenal glands a theory has been offered that the cortex, 

 although it does not afford a potent extract, does elaborate a precursor of 

 epinephrin, which is then transferred to the medulla to be transformed 

 into the finished product, A similar theory has been held in regard to 

 the pituitary. In neither case has conclusive evidence been offered as to 

 the validity of the theory. Moreover, in the case of both the pituitary 

 and the suprarenal bodies, the evidence of distinct functions of the com- 

 ponent parts is fairly conclusive. So far as the writer is aware phyloge- 

 netic studies fail to throw any light on the problem, aside from showing 

 that secondary displacements of tissues not infrequently occur as a result 

 merely of major adaptive morphologic changes, The occurrence of 

 hematopoietic tissues in the cavity of long bones shows that propinquity 

 does not necessarily imply functional relationship. 



