246 INTERNAL SECRETION 



GENERAL FEATURES OF THE ORGANS OF INTERNAL 



SECRETION 



It is of interest to note that the three organs which we 

 have discussed at length — the thyroid and parathyroids, 

 the suprarenals, and the pituitary — have the following 

 features in common : — 



1. Each is composed of two parts, which are distinct in 

 their development and structure, and appear to be distinct 

 in their functions. Whether such duahty is of biological 

 significance, or is mere fortuitous, we cannot say. 



2. The organs in the course of development undergo a 

 curious transformation in disposition, and sometimes in 

 their very nature. The medulla of the suprarenal originates 

 as a mass of migrating nerve cells ; the anterior lobe of the 

 pituitary is formed from a gland opening to the mouth. 



3. Their blood supply is remarkably profuse, indicating 

 a high degree of activity. 



4. In all cases complete extirpation causes death. 



5. Extract of one component is more active physio- 

 logically than extract of the other. 



Interaction of the Internal Secretions 



A feature of the internal secretions is that they all in- 

 fluence, in one direction or the other, certain fundamental 

 biological processes, such as carbohydrate metabohsm, 

 growth, and sexual development. As regards carbohydrate 

 metabohsm, sugar tolerance is diminished by injury to the 

 pancreas, by injection of adrenahn and by over-activity of 

 the thyroid or pituitary. It is increased by deficiency of 

 the thyroid or pituitary. Growth is influenced by the 

 thyroid, pituitary and the suprarenal cortex. Abnormal 

 sexuaUty is associated with hypertrophy of the cortex of 

 the suprarenal; arrested sexuaUty is found in cretinism 

 and subpituitarism. 



Furthermore, the glands are not without influence upon 



