HORMONES 



293 



j^rimary follicles, in the cortex of the ovary to start growing. After about 

 13 to 15 days the mature, or Graafian, follicle bursts, releasing an egg 

 cell or ovum (ovulation). The bursting of the Graafian follicle is caused 

 by LH. The egg finds its way into one of the Fallopian tubes and thence 

 to the uterus. The developing follicle, and to a lesser extent the entire 

 ovary, secrete estradiol in increasing amounts after about the fourth day. 

 Estradiol causes the endometrial cells in the mucosa of the uterus to 

 start dividing so that by the time of ovulation the mucosa is actively 

 growing. A similar effect is produced on the cells lining the vagina. 

 Any substance which produces these effects is called an estrogenic hor- 

 mone, or an estrogen. In female animals, estrogens also produce sexual 

 heat or estrus; hence, the name. 



After discharging its ovum the remainder of the follicle changes into 

 another structure called the corpus luteum. The corpus luteum develops 

 into a mature state under the influence of LH, which starts to be secreted 



Pituitary 



Pituitary 

 Hormone 

 Factors 



Ovary 



Anterior 

 Lobe 



Follicle 



Stimulating 



Ilnrnioni' 



>' 



4b 



Po^^tcrior 

 Lobe 



LutoinizinR Lutcotrophic 



Jlonnone Hormone 



|l'riiiiordial Developing Maturing 

 Follicle Follicle Follicle 



Ovulation 



Do\elo|)ing 

 T'orpus I^utrnni 



.Mature 

 r|ius Liiliuni 



Degenerating 

 ( 'ni|]iis Luteum 



Ovarian 



Hormone 



Factors 



Uterine » 



Endometrium 



Phases Repair IMohlVratmn Srcrrlmy Menstrual idii 



Days I 1 I .J I 6 17 I .S I !l Hul 1 1112 11311 111. JllGl I7llsl I'jl2ul.'ll22l23l 24l2ol2(il27l2Sl i\2\S\ 



Courtesy of J. C Stucki and the Department of Zoology, University of Wisconsin. 

 Fig. 11-1. Hormonal control of the menstrual cycle. This is a simplified 

 diagram which does not take into account interactions between the three 

 pituitaiy hormones nor the action of the ovarian hormones on the pituitary 

 gland. The curves indicate approximate variations in the urinary excre- 

 tion of ovarian hormones during the cycle. For further explanation see 

 text. 



