HORMONES 



ablation very much increases the secretion of pituitary corticotropin; 

 (c) in clinical cases of endocrine hyperfunction supernormal effects 

 are observed, similar in many cases to those produced by excessive 

 administration of hormones. 



Hyperfunction of the endocrine glands is observed under 

 several circumstances: (a) pathologic hyperplasias and tumors (be- 

 nign, or adenomata, and malign) in which are produced exaggerated 

 secretion of either normal or abnormal hormones; (b) injection of 

 either glandular extracts or hormones; (c) excitation by a supernumary 

 gland (for example, parabiosis of a castrated animal with a normal 

 one); (d) rupture of the endocrine equilibrium. 



In some cases either hypo- or hyperfunction takes a certain 

 time to develop. Thus if 95% of the pancreatic tissue of a rat is 

 removed, the residual tissue is still able to keep a normal blood sugar 

 level for two or three months, but later on a progressive diabetes de- 

 velops. Following certain operations on the ovary (grafting, ligation, 

 partial fragmentation), a hypersecretion of pituitary gonadotropin 

 gradually develops, which, by promoting excessive secretion of ovaric 

 estrogens, produces a marked hypertrophy of the uterus, hyperplasia 

 of the endometrium, etc. In this case a new hyjDophyso-ovaric equi- 

 librium is established at an abnormal level. 



Types of Endocrine Functional Associations 



The functional associations belong to various types. (/) A 

 gland, such as the anterohypophysis, can develop and maintain the 

 structure and function of one or several other glands, as the thyroid, 

 adrenal cortex, ovary, or testicle. (2) One gland can moderate the 

 function of another, e. g., the sexual hormones moderate the gonado- 

 tropic pituitary function.* (3) Actions, sometimes antagonistic and 

 sometimes synergetic, can be observed between two glands (or their 

 hormones), as in the case of the ovary (or estrogens) and the corpus 

 luteum (or progesterone). (4) Certain hormones increase the sensi- 

 tivity to others, e. g., estrogens to the effect of progesterone upon the 

 endometrium or upon the mammary gland, and thyroxine to the effect 



* In fact, the position is more complex, because estrogens, if given in in^li 

 doses, may induce an increased secretion of luteinizing, adrenotropliic, and lacto- 

 genic hormones of the anterior pituitary, but, in larger doses, suppress them all. 



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