HORMONES 



rapid formation of antihormones and the inversion of effects caused by 

 the injection of gonadotropins isolated from the gland. 



The preparation of active protein hormones that will not 

 produce antihormones is one of the outstanding problems endocri- 

 nology must solve. Meanwhile, the formation of antihormones imposes 

 an important limitation on prolonged therapeutic application of 

 certain hormones, particularly those of the pituitary and parathyroid. 

 This is one of the causes of the discrepancy existing between, on the 

 one hand, the great functional importance of the hypophysis as demon- 

 strated by experiment and by the study of disease in man, and, on the 

 other, the limited possibilities realized thus far from therapeutic ap- 

 plications. 



The chemical mechanisms by which hormones act upon cells 

 are not yet known. It has not yet been proved that they participate 

 in enzyme systems, as is the case for vitamins such as thiamin, niacin, 

 and riboflavin. The hormones are chemical regulators that probably 

 modify some link in the chain of metabolic reactions, a field of study 

 which has remained almost unexplored to date, in spite of its great 

 importance. 



Role 



Some endocrine organs, phylogenetically, begin as external 

 secretion glands that cast their secretions into the digestive system but 

 afterward lose their excretory function and change into internal secre- 

 tion glands. The pituitary, thyroid, and pancreatic islets of Langer- 

 hans have evolved in some such way. The parathyroid, regulator of the 

 metabolism of calcium and phosphorus, derives from the branchial 

 arches. The ovarium, testicle, and adrenals, which produce the 

 steroid hormones with sexual and metabolic actions, derive from the 

 coelomic epithelium. The adrenal medulla that secretes adrenalin 

 derives from the nervous sympathetic system, and the neurohypophysis 

 from the diencephalon. 



The hormones of the vertebrates are better known than those of 

 the invertebrates. In the latter, certain processes have been shown to 

 be regulated by hormones, such as metamorphosis, color (in the case of 

 Crustacea), and sexual dimorphism in some instances. The hormones 

 regulate functions that exist before hormones appear and which often 

 persist without them. Thus, all animal and plant cells consume glu- 



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