At birth, the ovaries contain approximately 4 million immature Premordial Follicles. Their sizes range from 0.25 to 1 mm. Each primordial follicle contains an egg in its core surrounded by layers of stromal cells. The stromal cells produce hormones- Estrogen and Progesterone.
From Menarche (beginning of menses) at puberty until Menopause (Cessation of menses) every month approximately 1000 primordial follicles begin to develop out of which 20 are recruited for further development. The best amongst them takes the lead and mature into Graffian follicle of about 1 cm size.
At middle of the cycle around 14th day, the mature follicle ruptures to release the egg free into the peritoneal cavity. This process is called as Ovulation. This free egg along with its surrounding stromal cells is picked up by the fallopian tubes through the negative suction pressure.
After ovulation the released egg undergoes the process of sexual/reduction division called Meiosis and forms Primary ovarian follicle and primary polar body which contains 23 chromosomes each instead of 46. Since they contain half the number of inherited chromosome, they are called haploid cells. The life of this egg is approximately 24 hours.
During the process of sexual intercourse, males ejaculate their semen inside the woman’s vagina. The released semen is initially thick and dense to ensure the higher concentration of sperms delivered. Under the effect of female’s body temperature and proteolytic enzymes present in vaginal secretions, it liquefies, so that sperms can easily swim upstream into the uterine cavity in liquid media.
During this period of survival, the millions of sperms meet a single egg in the ampullary part of the fallopian tube.
The proteolytic enzymes present in the acrosome of sperms, collectively erode and weaken the wall of the egg. And then, the single most efficient sperm amongst the folk enters and fertilize the egg to form the single diploid zygote at the ampullary part of fallopian tube that contain normal number of 46 chromosomes. This zygote then travels to the uterine cavity for implantation and further development into embryo.
During embryogenesis, with the process of mitotic division, the single celled zygote forms multi-celled blastocyst. The trophoblastic tissue subsequently forms the fetus, placenta and amniotic membranes with the help of differentiation.
To provide initial nourishment to the developing zygote, the inner endometrial lining of the uterus grows approximately 1.5 cm thick under the influence of ovarian hormones estrogen and progesterone till the fetus forms its placenta.
The remnant of ovarian Graffian follicle undergoes process of leutinization to form the corpus luteum that produces estrogen and progesterone to support pregnancy. The life of corpus luteum is 10 days.
The embryo helps own survival by producing Human Chorionic Gonadotropin, that prolongs the life of corpus luteum by 3 months so that it can produce required hormones to support pregnancy till the placenta is formed and takes over.
In the absence of pregnancy and HCG hormone, the corpus luteum degenerates into corpus albicans, that do not produce progesterone hormone and hence the inner endometrial lining sheds in the form of menstrual blood. This is nature’s way to form a new endometrial lining for newer egg.
The information is shared to create awareness towards Pregnancy and Childcare to reduce maternal and child deaths. Atmost care has been taken by the author to include the verified information from authentic sources. However, kindly discuss the same with your health care provider before implementation.