PREGNANCY 



261 



FSH 

 LH 



>GESTERONEr 

 ANTERIOR LOBE tS^ESTRONE 



PITUITARY 



Fig. 169. A composite diagram of the relation between the pituitary, the 

 ovaries, the uterus, and the placenta. (1) action of FSH hormone; (2) action of 

 estrone on uterine wall; (3) effect of LH on formation of corpus luteum; 

 (4) progesterone and estrone from corpus luteum act on uterine wall; (5) fer- 

 tilization of ovum; (6) corpus luteum is necessary for implantation; (7) embryo 

 maintains corpus luteum; (8) corpus luteum is necessary for attachment of 

 placenta to wall of uterus; (9) relaxin relaxes pelvic ligaments. 



stances which cause the growth and maintenance of the corpus luteum and a 

 supply of progesterone and estrone for the uterine wall is insured. 



A number of changes follow the persistence of the corpus luteum. The 

 corpus luteum inhibits further ovulation. The inhibition of ovulation can be 

 shown to be due to the presence of the corpus luteum, because in some ani- 

 mals, such as the cow, the corpus luteum may be removed and ovulation will 

 follow in about 48 hours. Presumably this inhibition must involve the inhibi- 

 tion of the secretion of hormone by the pituitary. The corpus luteum hor- 

 mones exercise an inhibition over the pituitary, preventing its secretion of 

 FSH. The substance responsible is probably estrone. Estrone is produced by 



