2.2 the menstrual cycle: control of the menstrual cycle Flashcards
(26 cards)
what are the oestrogen, progesterone and inhibin levels like at the beginning of the menstrual cycle?
low
where is GnRH secretion released from?
inhibition
how are the FSH and LH levels like at the beginning of the menstrual cycle?
LH + FSH tend to rise
FSH rises more
as low inhibin levels release FSH from selective inhibin at pituitary
what causes follicles to grow in the menstrual cycle?
FSH, followed by LH
what happens to oestrogen and inhibin secretion as the follicle begins to grow under the influence of FSH and LH?
oestrogen and inhibin secretion rises
how is FSH secretion inhibited?
selectively inhibited by inhibin
what does rising oestrogen lead to?
stimulation of GnRH and hence LH secretion
at about 12-14 days into the cycle, what stimulates the LH surge?
positive feedback of rising oestrogen stimulates LH surge
what influences the positive feedback of rising oestrogen stimulating LH surge?
environmental factors influence precise timing
what does LH surge produce?
ovulation
what happens to oestrogen during LH surge and ovulation?
oestrogen levels fall dramatically
what forms spontaneously from LH surge and ovulation?
corpus luteum
what does LH promote after ovulation?
oestrogen and progesterone secretion from corpus luteum
what happens as corpus luteum grows after ovulation?
more steroids are secreted
what happens to oestrogen after ovulation? why?
rising oestrogen levels do NOT exert positive feedback on LH
because progesterone levels are also rising
what happens to corpus luteum 14 days after ovulation? why?
in the absence of pregnancy, the corpus luteum regresses spontaneously
what happens to progesterone and oestrogen levels 14 days after ovulation?
fall
what happens as progesterone and oestrogen levels fall 14 days post ovulation?
triggers menstrual bleed
what happens when menstrual bleed is trigger 14 days after ovulation?
relieving inhibition on FSH and LH, so triggering the development of new follicles and the beginning of a new cycle
what happens if conception has occurred? (in terms of implanted embryo)
the implanted embryo develops a placenta which secretes human chorionic gonadotrophin (hCG)
what is the function of hCG?
prevents regression of the corpus luteum
what happens if corpus luteum is maintained by hCG?
continues to secrete oestrogen and progesterone
what is the function of the oestrogen and progesterone secreted by corpus luteum?
support early weeks of pregnancy
maintaining suppression of ovarian cycle
what are the durations of the follicular and luteal phases influenced by?
the ovary (the time it takes for follicle to mature, and lifespan of corpus luteum)
