The female reproductive system ensures the production of eggs, sex hormones and keeps fertilized eggs viable as they grow into a mature fetus and ready for birth. Oogenesis is the cycle by which female egg cells mature by meiotic division; it begins with creating oogonia, which is accomplished by converting primordial follicles into primary oocytes (Girsh, 2021). In the follicular phase of the ovarian cycle, high amounts of follicle-stimulating hormone (FSH) cause primary vesicles to convert to secondary sacs. Primordial follicles, which grow in the ovary as a fetus during conception, give rise to primary vesicles. Of the secondary sacs, a healthy one stays while the rest get disintegrated. The surviving vesicle, also known as the dominant sac, releases massive estrogen levels throughout this phase.
The high estrogen levels cause a subsequent rise in luteinizing hormone, enabling the secondary follicles to transform into a tertiary follicle that later exits the ovary in the ovulation phase (Kevin, 2018). During the luteal stage, a corpus luteum develops from the empty vesicle and produces progesterone to ensure conception. Moreover, meiosis II begins from the secondary oocyte but is, however, stopped in the metaphase II to ensure fertilization happens (Kevin, 2018). As meiosis II concludes, an ootid and a polar body form; the polar body degenerates, leaving the ootid to turn into a mature ovum.
The endometrial lining goes through a series of changes known as the uterine cycle. The endometrium starts by developing a thick tissue lining with blood-rich vessels during the first phase of the uterine cycle which creates a conducive setting for blastocyte attachment once they get to the uterus; additionally, estrogen levels rise, signaling the onset of the follicular phase (Smirnova, 2019). Due to the effect of progesterone, the endometrium converts into a secretory lining following ovulation, in readiness for the potential implantation of an embryo to begin conception in the proliferative phase (Smirnova, 2019). Finally, in the secretory phase, if a blastocyte implants, the lining stays and forms a component of the placenta, which supports and protects the embryo during pregnancy. Progesterone and estrogen levels decline after implantation fails, triggering menstruation.
Girsh, E. (2021). A textbook of clinical embryology. Cambridge University Press.
Kevin, P. (2018). Anatomy & physiology laboratory manual and e-labs (10th ed.). Mosby.
Smirnova, O. (2019). The physiology of the endocrine system. Cambridge Scholars Publishing.