Endocrine Mechanisms 



749 



adult female than in the male. Both female and male pituitaries normally 

 produee FSH and LH in relatixely large amounts. The primary difference 

 hetvveen male and female pituitaries is one of cycle differences. Oyarian 

 implants, but not testis implants, suppress FSH production by the adult 

 pituitary in castrated females; in castrated males only testis implants will 

 suppress FSH production. Thus, the adult pituitary is differentiated into 

 differently responding male and female types, in contrast vyith its sexually in- 

 different condition in nevy-born mammals. 



During the growth of a young mammal there is a gradual increase in the 

 production of gonadotropins up to the time of sexual maturity, when the 

 gonads are consequently brought to their completely functional state and 



^^,ry\ OVARY 



ENVIRONMENT! PITUITARY 



inhibition 



Fig. 283. Diagrain representing the major endocrine influences operating during the 

 normal reproductive cycle of the adult female mammal. 



Fig. 284. Diagram representing the major endocrine influences operating during the 

 normal reproductive cycle of the adult male mammal. 



their estrogens and androgens contribute to the full differentiation of the 

 secondary and accessory sexual characteristics. The animal is now capable of 

 normal reproductive activity. This is, in the vertebrates, typically a cyclical 

 phenomenon with the periodicity often correlated with the annual solar 

 cycle in such an adapti'/e fashion as to assure the young of a favorable time 

 of year for birth and early postnatal development. In some species the re- 

 productive periodicity bears much less or no relationship to external en- 

 vironmental stimuh and appears to result from a wholly inherent rhythmical 

 mechanism, as in the case of the rat, mouse, man, etc. 



