As from inhibin, which results in only one

 

            As a child,
a female’s ovaries prevent the Gonadotropin-releasing hormone (GnHR) from being
released by constantly creating a little bit of estrogen. When GnHR is finally
released around the time of puberty, the follicle stimulating hormone (FSH) and
luteinizing hormone (LH) are produced as a response. Estrogen is directly released
by the granulosa cells while the LH cells release androgens that get turned
into estrogens. When these levels get too high, the hypothalamus and anterior
pituitary experience negative feedback and FSH and LH are no longer made. FSH
also experiences negative feedback from inhibin, which results in only one
living follicle that creates raised estrogen levels. Positive feedback happens
when the estrogen reaches a certain blood level, resulting in the release of
gonadotropin. When there is a lot of estrogen, LH is released which causes the
oocytle of the follicle to experience meiotic division resulting in another
oocyte. Ovulation takes place after about 14 days which is associated with an
ovary wall that becomes weaker. A portion of this wall breaks and the oocyte
goes through the broken hole. The follicle that burst turns into a corpus
luteum, which makes progesterone and estrogen. Negative feedback on the
hypothalamus and pituitary takes place when these progesterone and estrogen
levels get too high. If the egg is not fertilized, the blood levels go back
down, the estrogen and progesterone levels go back down and the corpus luteum
gets destroyed (Marieb 1058). The uterine cycle involves the changes that the endometrium
experiences in response to ovarian hormones. The changes experienced relate to
what is going on in the ovarian cycle. The first step of the uterine cycle is
called the menstrual phase and it occurs over a span of 1-5 days. In this phase
there is bleeding due to the shedding of the endometrium. On the last day, the
follicles make more estrogen. The next phase is the proliferative phase and its
span is 6-14 days. It involves the reformation of the endometrium that happens
under increased estrogen levels. At the end of this phase, ovulation occurs. The
secretory phase happens over a span of 15-24 days. This phase involves getting
ready for the embryo to implant. Progesterone levels increase to form the
cervical plug that keeps all unwanted things out, such as pathogens. This
increase also stops LH from being released. If fertilization does not occur, progesterone
levels decrease back to the normal range, LH blood levels go back down and the corpus
luteum deteriorates. Menstrual blood flow indicates the starting of this cycle
again (1059).

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