8 



THE MAMMALIAN FEMALE REPRODUCTIVE 



CYCLE AND ITS CONTROLLING 



MECHANISMS 



John W. Everett, Ph.D. 



PROFESSOR OF ANATOMY, DUKE UNIVERSITY 

 DURHAM, NORTH CAROLINA 



I. Introduction 497 



II. Cycles Spontaneously Interrcpted. 498 



III. PiTUITARY-OVARIAN DORMANCY 499 



A. The Ovary in Anestrum 500 



B. The Hypophysis 500 



C. Relationship of the Anestrum to the 



Seasons 501 



IV. Attainment of Maturity. Emer- 

 gence OF Full Ovarian Function. . 502 

 V. Follicular Cycles. Growth and 



Atresia 504 



A. Correlation of Ovarian Secretion 



with the Follicular Cycle 507 



B. Cyclic Manifestations after Ovari- 



ectomy or Hypophysectomy 509 



C. Cyclic Manifestations in the Ab- 



sence of Ovarian Follicles 509 



D. Hypothalamus and Gonadotrophin 



Secretion. General Considera- 

 tions 510 



VI. Follicle Maturation and Ovula- 

 tion 513 



A. Time of Ovulation 513 



B. Ovarian Steroids and Ovulation. . . 514 



1. Estrogens 514 



2. Gestagens 517 



C. Role of the Nervous System in Ovu- 



lation " 520 



1. The hypophyseal portal veins and 



the chemotransmitter hypoth- 

 esis ' 523 



2. Central depressants and ovula- 



tion 526 



3. The central nervous system as a 



timing mechanism for ovula- 

 tion 520 



D. Persistent Follicle 529 



VII. The Luteal Phase 530 



1. Luteotrophic substances 530 



2. "Nonfunctional" corpora lutea. . 531 

 A. Pseudopregnancy 532 



1. Duration of pseudopregnancy. .. . 533 



2. Neural factors in pseudopreg- 



nancy 534 



B. Luteolytic Mechanisms 537 



C. Effect of the Uterus on Luteal Func- 



tion 538 



VIII. Concluding Comments 540 



IX. References 541 



I. Introduction 



The chain of events that constitutes the 

 female reproductive process is character- 

 istically repeated from time to time with 

 considerable regularity during the adult life 

 of an individual, and is therefore a cycle. 

 In the broad sense, this sequence begins 

 with ovogenesis and terminates when the 

 progeny require no further shelter and 

 nurture. In mammals this has become a 

 highly complex process, involving profound 

 maternal adjustments synchronized with 

 successive stages in development of the 

 ovum, fetus, and offspring. The complete 

 mammalian cycle comprises a sequence of 

 stages which may be identified as follows: 

 (II follicle growth, including growth of the 

 ovocyte; (2) ovulation, a progressive proc- 

 ess including preovulatory maturation of 

 follicles and ova, and the structural change 

 of ruptured follicles to corpora lutea; (3) 

 progravidity; (4) gravidity; (5) parturi- 

 tion; and (6) postpartum nurture, including 

 lactation, protection, and training. Although 

 it is obvious that this full sequence is often 

 realized, it may nevertheless be retarded or 

 frankly interrupted at almost any point. 



In advanced human societies economic 

 and social factors have diminished the num- 

 ber of complete cycles to such degree that 

 they are rarities in the lifetime of an in- 



497 



