ACTIVITIES OF THE OVARY 91 



of the egg follicle, but also, after ovulation or the discharge of the egg from 

 the egg follicle, the remaining granulosa cells, and also, some of the theca 

 interna cells of the follicle are induced by the LH factor to form the corpus 

 luteum (figs. 30, 49). Corpora lutea also may be induced by estrogens. This, 

 however, appears to be an indirect stimulus aroused through estrogenic stimu- 

 lation of the pituitary gland to secrete added amounts of the LH factor (Evans 

 and Simpson in Pincus and Thimann, '50, p. 359). 



A further pituitary principle, however, seems to be involved in the func- 

 tional behavior of the corpus luteum. This principle, referred to as luteotrophin 

 (LTH), is associated with the lactogenic-hormone complex produced by the 

 anterior lobe of the pituitary body; it induces the morphologically developed 

 corpus luteum to secrete progesterone. (Consult Evans and Simpson in Pincus 

 and Thimann, '50, pp. 359, 360; Turner, '48, p. 379, for references.) 



The structural formula of progesterone is as follows: 



^/X/X/ 



2) Effects of Progesterone. Progesterone reduces the irritability of the ac- 

 cessory structures and stimulates the mucosa of the uterus to undergo further 

 development. This increased developmental and functional condition of the 



Fig. 53. Relationship of the pituitary gonadotrophins and ovarian hormones to the de- 

 veloping Graafian follicle and reproductive-duct change in a polyestrous female mammal. 



The Graafian follicle responds to the pituitary gonadotrophins. FSH and LH, with the 

 subsequent growth and ultimate rupture of the follicle and ovulation. Ovulation termi- 

 nates the follicular phase of the cycle. Under the influence of the LH factor the corpus 

 luteum is established. The latter becomes functional as a result of stimulation by the 

 luteotrophic (lactogenic) hormone. The progestational hormone (progesterone) then is 

 elaborated by the luteal cells. The activity of the latter together with estrogen controls 

 the luteal phase of the cycle. 



The rising level of estrogen in the blood suppresses FSH secretion, and together pos- 

 sibly with small amounts of progesterone stimulates LH secretion. Estrogen and small 

 amounts of progesterone also probably stimulate the secretion of large quantities of LTH, 

 and the latter stimulates the secretion of progesterone from the recently formed corpus 

 luteum. When the estrogen level falls, FSH again is secreted. 



When the estrogen level rises, the endometrium of the uterus and vaginal mucosa are 

 stimulated. The presence of progesterone suppresses vaginal development, but the uterine 

 mucosa is stimulated to greater activity. Observe that the involution of the endometrial 

 lining in most mammals is gradual but in primates it is precipitous and violent, resulting 

 in menstruation (Cf. fig. 59). (The diestrous period on this chart is shown as a rela- 

 tively brief period compared to the other aspects of the reproductive cycle. However, 

 it may be very long in females which do not experience a polyestrous condition and in 

 some species it may last a good portion of a year.) (Compiled from various sources in 

 the literature. The portion of the chart showing pituitary and gonadal hormonal rela- 

 tionships is based on data obtained from The Schering Corporation, Bloomfield, N. J.) 



