150 KINETIC HORMONES — II 



Follicle cells in the ovary stimulated by ICSH 



The release of oestrone, or other oestrogenic hormones, from 

 the vertebrate ovary appears also to be stimulated primarily 

 by the interstitial-cell-stimulating hormone, ICSH. Its 

 action may depend in some cases on the synergic effect of the 

 follicle-stimulating hormone, FSH; but the most important 

 action of the latter is to cause the growth of the follicle cells, along 

 with that of the ovum that they enclose. There are differences in 

 the relative importance and effects of these hormones between 

 different species and even more between different classes of 

 vertebrates. 



The release of oestrogens by ICSH results in the development 

 of the female genital ducts, but not as a rule in that of any secondary 

 sexual characters ; the external appearance of the female is usually 

 distinguishable from the male by the absence of male characters, 

 rather than by any positive features due to oestrogenic hormones. 



In the female mammal, whether the breeding season is short or 

 continuous, there is always an alternation, or cycle, of phases 

 within the breeding period and of these it is the oestrus phase 

 which results from the secretion of oestrogens (§ 4.323). The 

 feed-back reaction, whereby the accumulation of oestrogens 

 decreases ICSH secretion, is relatively rapid in the female and 

 makes way for the alternate phase of the cycle, whether this is 

 dioestrus, pregnancy or pseudopregnancy. In most species oestrus 

 only lasts for a few days each time. 



Corpora lutea in the ovary stimulated by LSH 



Mammalia. The endocrinokinetic hormone luteotrophin, 

 LSH, from the adenohypophysis, stimulates the secretion of 

 progesterone from the corpora lutea that form in the ovarian 

 follicles after the shedding of the ova. LSH is probably the same as 

 PROLACTIN, which causes the secretion of milk from crop and 

 mammary glands (§ 4.13) ; if it is the same it is the only one of the 

 endocrinokinetic hormones which has the power to stimulate any 

 exocrine glands as well as an endocrine gland (§ 4.323). It can only 

 affect the corpora lutea after their growth has been stimulated by 

 the morphogenetic luteinizing hormone, LH, also from the 



