294 



HORMONES 



by the pituitary gland about the twelfth to fourteenth day of the cycle 

 (see Fig. 11-1), and is maintained in that condition partly by LH and 

 partly by the luteotropic hormone. The corpus luteum, in turn, pro- 

 duces progesterone, which has a further profound effect on the lining of 

 the uterus, causing the lining and especially the tiny glands present in 

 it to develop enormously (Fig. 11-2) and to secrete a nutritive fluid. In 



Courtesy oi W. G. Black and the D(_pditment ot Genetics, University of Wisconsin. 

 Fig. 11-2. Effect of progesterone on the uterus. Spayed rabbits were 

 given 10 daily injections of 1 mg. each of progesterone in oil, and killed 

 24 hours after the last injection. Left, untreated control ; right, treated with 

 progesterone. 



this state the uterus is prepared to receive the ovum, in case fertilization 

 has occurred during its passage through the Fallopian tube. If fertiliza- 

 tion does not occur, the ovum dies a few hours after ovulation, and in a 

 few days the corpus luteum stops functioning and degenerates. Secre- 

 tion of progesterone consequently diminishes, and as a result much of 

 the lining of the uterus sloughs off, and in primates it is discharged as 

 the menstrual flow. 



In case the ovum has been fertilized, it becomes embedded in the spe- 

 cially prepared uterine lining and begins to grow. The corpus luteum 

 continues to secrete progesterone and thus to maintain the uterus in a 

 condition favorable for the developing fetus. Any deficiency or interrup- 

 tion in the supply of progesterone results in death of the embryo and 

 consequent miscarriage. This is one of the reasons why certain women 

 suffer repeated miscarriages and are unable to bear a living child. Thi§ 



