the menstrual cycle Flashcards
the first day of menstrual bleeding is designated as
day 1 of the menstrual cycle
average menstrual cycle
lasts for 28 days (but can be between 21-35 days)
average duration of menses (bleeding)
is between 3-8 days and blood loss is around 30ml
functions of the ovary
- generation of mature oocytes (folliculogenesis)
- production of steroid and peptide hormones
cell types within the ovary
- primary oogonia (derived from yolk sac) form follicles
- granulose cells create oestrogen from androgens supplied by the theca cells
- ovarian storm which consists of; interstitial cell which become theca cells, theca cells are responsible for converting pregenlone to androstenedione, connective tissue cells and contractile cells
on day 1 of menses
all sex hormones are present at low levels (FSH,LH,PROGESTERONE, OESTROGEN) this results in a low level of negative feedback on the hypothalamus which then secretes gonadotrophin releasing hormone which acts on the anterior pituitary to secrete FSH and LH
The LH
acts on the granulose cells to produce pregnelone which then diffuses into adjacent theca cells where it is converted to androstenedione
the androstenedione produced
then travels back to the granulose cell and is converted oestrogen via aromatase and then to estradiol via 17-beta-HSD
As the FSH and LH levels rise
it triggers the development of the follicle into a graafian follicle which can be ovulated
as oestrogen levels increase
there is a negative feedback affect on the hypothalamus cause GnRH levels to fall, however at around day 10 the oestrogen levels surpass a certain point and then cause a positive feedback affect on the hypothalamus causing the LH surge triggering ovulation
oestrogen aslo cuases
the proliferation of the endometrial lining causing it t become thicker it anticipation of implantation
after ovulation the follicular remnant
becomes vascularised and forms the corpus lute
the primary function of the croups luteum is to
secrete progesterone which is needed to maintain the endometrial lining
if there is no progesterone
then the endometrial lining cannot be maintained and implantation will not occur
the corpus lute remains
for around 10 days before it involutes causes menses but if implication occurs then the embryo make HCG which sustains the croups luteum (corpus luteum of pregnancy) which remains for around 10 weeks and producers progesterone until the placenta takes over