As a child,a female’s ovaries prevent the Gonadotropin-releasing hormone (GnHR) from beingreleased by constantly creating a little bit of estrogen. When GnHR is finallyreleased around the time of puberty, the follicle stimulating hormone (FSH) andluteinizing hormone (LH) are produced as a response. Estrogen is directly releasedby the granulosa cells while the LH cells release androgens that get turnedinto estrogens.
When these levels get too high, the hypothalamus and anteriorpituitary experience negative feedback and FSH and LH are not able to beproduced. FSH also experiences negative feedback from inhibin, which results inonly one living follicle that creates raised estrogen levels. Positive feedbackhappens when the estrogen reaches a certain blood level, resulting in therelease of gonadotropin. When there is a lot of estrogen, LH is released which causesthe oocytle of the follicle to experience meiotic division resulting in anotheroocyte. Ovulation takes place after about 14 days which is associated with anovary wall that becomes weaker. A portion of this wall breaks and the oocytegoes through the broken hole. The follicle that burst turns into a corpusluteum, which makes progesterone and estrogen.
Negative feedback on thehypothalamus and pituitary takes place when the progesterone and estrogenlevels get too high. If the egg is not fertilized, the blood levels go backdown, the estrogen and progesterone levels go back down and the corpus luteumgets destroyed (Marieb 1058). The uterine cycle involves the changes that the endometriumexperiences in response to ovarian hormones. The changes experienced relate towhat is going on in the ovarian cycle. The first step of the uterine cycle iscalled the menstrual phase and it occurs over a span of 1-5 days. In this phasethere is bleeding due to the shedding of the endometrium. On the last day, thefollicles make more estrogen.
The next phase is the proliferative phase and itsspan is 6-14 days. It involves the reformation of the endometrium that happensunder increased estrogen levels. At the end of this phase, ovulation occurs. Thesecretory phase happens over a span of 15-24 days. This phase involves gettingready for the embryo to implant. Progesterone levels increase to form thecervical plug that keeps all unwanted things out, such as pathogens. Thisincrease also stops LH from being released.
If fertilization does not occur, progesteronelevels decrease back to the normal range, LH blood levels go back down and the corpusluteum deteriorates. Menstrual blood flow indicates the starting of this cycleagain (1059).