GENERAL ZOOLOGY 



Cortical hormone promotes the reabsorption of sodium ions and inhibits re- 

 absorption of potassium ions. 



The general effect of the sugar-active hormones of the adrenal cortex, tested 

 in experimental animals, is to raise the blood-sugar level. This is accom- 

 plished by promoting the transformation of amino acids to glucose; this 

 glucose can be stored as glycogen, especially in the liver. The details of this 

 phenomenon have not been elucidated. 



Some of the steroid compounds recovered from adrenal cortical extracts 

 produce effects similar to those produced by the sex hormones. Under ab- 

 normal conditions, these substances, especially the one resembling the male 

 sex hormone, are released to the blood. This sometimes results in precocious 

 sexual maturity in young boys and in unusual hairiness in women. 



Cortical steroids have at least one other regulatory effect highly important 

 in the arsenal of protective devices which have accumulated during the evolu- 

 tion of vertebrates. The release of lymphocytes from the lymphatic organs 

 and their disruption with the liberation of gamma globulin (p. 64) appears 

 to be regulated by cortical hormone. 



Few of the endocrine glands are necessary for the continuation of life; they 

 regulate processes that continue in their absence. Vertebrates survive re- 

 moval of the hypophysis, thyroid, islands of Langerhans, and adrenal medulla, 

 although they are far from normal when deprived of these organs. The ad- 

 renal cortex is, however, essential for life; its removal from experimental 

 animals or its destruction by disease (Addison's disease) is always fatal unless 

 cortical salt-active products are administered. It is also a bulwark in the 

 struggle to maintain a relatively constant internal environment in the face of 

 the numerous stresses or tensions to which man is subject in the modern 

 world. Medical use of cortical hormones or of ACTH, which triggers their 

 release from the cortex, is widespread. When it is recalled that release of 

 ACTH is apparently stimulated by epinephrine, which is so responsive to 

 changes in emotional state, the importance of the adrenal cortex is obvious. 



The functions of the gonads in both sexes are regulated by endocrines and, 

 in turn, the gonads produce steroid hormones which regulate the responses 

 of other organs related to reproduction. The gonadotropic hormones of the 

 adenohypophysis are three in number: the follicle-stimulating hormone (FSH), 

 the luteinizing hormone (LH), and the luteotropic hormone. 



The testis requires FSH in order for the male germ cells to differentiate. 

 Elaboration of the male sex hormone, testosterone, occurs in the testis under 

 the influence of LH. Testosterone conditions the differentiation of the ac- 

 cessory glands of the male reproductive system (p. 130) as well as the sec- 

 ondary sex characters, such as the comb and wattles of roosters, and the 

 nerve reaction patterns of sex drive and pugnaciousness. 



The growth of the follicle which surrounds the egg cell in the ovary is 

 stimulated by FSH (Fig. 4.26). In mammals, the follicle becomes many- 

 layered and its cells remain functional after the egg is shed. As the follicle 

 reaches its full size, the ovary begins to respond to LH. A secretion known 



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