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when are you more likely to have variations in cycle length?
Just after menarche
and approaching the menopause
what does the hypothalamus release? what does this do?
stimulates the pituitary to release LH and FSH
what does the pituitary gland release? what do these do?
LH and FSH
stimulate the ovaries to produce steroids and gametes
what can cause natural supression of menstruation?
what are the key events in the ovarian cycle?
what are the components of a follicle?
oocyte, antrum, granulosa cells, theca cells, blood vessels, cumulus cells
what involvement does FSH have with follicle selection?
large follicles are less dependent of FSH as they are producing growth factors and oestradiol. When FSH is being inhibited by the inhibin, smaller follicles are not receiving enough FSH to continue
what Are the symptoms of PCOS?
irregular menstrual cycles
dysfunctional uterine bleeding
male-pattern hair loss
what differences in hormone production from the pituitary gland occur in PCOS?
how do anovualtion and disturbed cycles occur in PCOS?
The follicle growth is disturbed by the change in hormone production by the pituitary gland
what is the mechanism which causes LH surge?
high levels of oestradiol for long enough causes an increase in GnRH release and the pituitary becomes more sensitive to GnRH
what happens between LH surge and oocyte release?
1st meiotic division is completed
2nd meiotic division starts but doesn't complete
enzyme induction from loosening cumulus and follicle wall
how does the follicle turn into the corpus luteum?
theca cells and blood vessels invade the ruptured follicle
granulosa cells hypertrophy and terminally differentiate
what change is there in steroid secretion after the corpus luteum develops?
there is progesterone and oestradiol secretion
what maintains the corpus luteum? how strong is the signal?
LH at low levels but the corpus luteum is very sensitive
what keeps LH and FSH low once the corpus luteum has developed?
steroids giving negative feedback to both the hypothalamus and the pituitary gland
why does the corpus luteum degenerate?
the corpus luteum has a reduction in sensitivity to LH and the LH level is insufficient to carry on maintaining it
what happens after the corpus luteum degenerates?
the negative feedback from the steroids is reduced and FSH and LH rises again and new follicles are stimulated
what happens as the steroid production falls?
gradual shrinking of endometrial tissue
spiral arteries become highly coiled
how do ishcaemic tissues tear and rupture?
individual spiral arteries re-opening and different times
what is the cervical mucus like in the lead up to menstruation? why?
thick and rubbery with high viscosity
sperm cannot penetrate
what is the difference between fertile mucus and infertile mucus?
furrows in the fertile mucus so sperm can get through
infertile mucus is all meshed so sperm cannot get through
Four methods for trying to identify the fertile period?
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