Endocrine Control of Menstrual Cycle Flashcards
what are the hormones involved in female reproductive cycle produced by
- neurons in brain, pituitary gland, ovaries
list relevant (ovarian) steroid hormones involved in female reproductive cycle
- oestrogen
- progesterone
(produced in ovaries)
list relevant protein hormones involved in female reproductive cycle & what produced by
- gonadotrophin releasing hormone (GnRH) - hypothalamus
- follicle stimulating hormone (FSH) - pituitary gland
- luteinising hormone (LH) - pituitary gland
- inhibin - produced in ovaries
sources of environmental, metabolic and endocrine inputs that the brain receives as neuroendocrine input
- circadian cycle
- nutrition
- stress
- steroids (other hormones)
- many other cues
can impact neurons
which neurons are impacted by input into neuroendocrine system
- periventricular nucleus
- arcuate nucleus
what can the periventricular and arcuate neurons do once received input
- interact w hypothalamus
- modulate production GnRH
where does hypothalamus sit
where does pituitary gland sit
- hypothalamus: in brain
- pituitary gland: just below brain in skull
what is GnRH produced by & where is it transported to
- produced by hypothalamus
- transported to pituitary gland
at what point in cycle does pituitary gland respond to GnRH from hypothalamus & what is this response
- early in each new cycle
- responds by producing FSH & secreting into circulation
what happens to secreted FSH early in cycle by pituitary gland
- secreted into circulation
- carried into ovaries
- ovarian follicles express FSH receptor and FSH binds
- promotes further growth and proliferation of follicular cells in follicles -> causes oocyte to simultaneously grow and mature
does complete development of ovarian follicle occur in one 28 day cycle? what does occur?
- no
- last stages of folliculogenesis integrated in controlling menstrual cycle
what do granulosa cells in follicle produce
- oestradiol (type of oestrogen)
what is happening with regard to oestrogen from FSH release to follicles
- since follicles are growing with support of FSH -> incr granulosa cells
- increased oestrogen (oestradiol) secretion into blood
- secreted oestrgoen circulated back to brain & pituitary gland
what does the secreted oestrogen from growing follicles in cycle allow for measurement of
=> oestrogen levels = measure of stage of follicle development
describe how FSH suppression is reached after oestrogen release is stimulated from FSH early in cycle
- as cycle progressives, low but rising oestrogen levels (caused by granulosa cells of growing follicle) have negative feedback effect on both the cells of arcuate nucleus (for hypothalamus to release GnRH) and on pituitary gland -> suppressed FSH release
does negative feedback from oestrogen that suppresses FSH slow down the growth of the dominant follicle & why / why not
- does not
- because its development causes it to gain FSH independence
does negative feedback from oestrogen that suppresses FSH slow down the growth of the smaller follicles & why / why not
- yes
- smaller follicles are affected so that one or two dominant follicles emerge in each cycle -> continue to grow to pre-ovulatory stage of maturation
what do larger dominant follicles produce as they continue to grow
- increasing levels of oestrogen
as the dominant follicles grow and increasingly release oestrogen, what happens to oestrogen levels and what’s the result
- oestrogen levels rise in circulation
- higher oestrogen concentrations sensed by periventricular nucleus -> positive feedback on GnRH secretion
what does the positive feedback by oestrogen on periventricular neurons for GnRH secretion lead to
- promoted secretion of LH from pituitary gland
during what stage do follicles grow? what marks this stage?
- follicular phase
- start marked by gradual increase in FSH levels, followed by rise oestrogen levels later
- (progesterone levels stay low)
list 4 phases of menstrual cycle in order
- menstrual phase
- follicular phase (early and late)
- ovulation
- luteal phase
what does positive feedback effects of oestrogen on hypothalamus cause
- cause pulsatile release of GnRH from hypothalamus to increase in frequency and amplitude
- cause LH surge
does oestrogen rise in follicular phase cause negative or positive feedback loop
both
- negative to hypothalamus (arcuate nucleus in brain in particular) & to pituitary gland
- positive to hypothalamus (periventricular nucleus in brain in particular)
what is the link between GnRH pulses and patterns of LH release
- direct relationship
in days, when does LH surge occur in cycle
- at midpoint of cycle ~day 14 of 28 day cycle (day 14 from time of last menstruation)
what is considered start of cycle
- from time of last menstruation
- includes bleeding days
circulating LH from LH surge (~day 14 of cycle) is sensed by what cells to stimulate what
- sensed by granulosa cells (in ovary)
- stimulate gene expression change that results in ovulation (release of oocyte; subsequent differentiation of remaining follicle to form corpus luteum)
what does the corpus luteum secrete
- oestrogen (low levels)
- progesterone at very high levels
what does LH surge represent
- mid cycle
- switching from follicular phase to luteal phase
- ovulation occurs (day 14)
what is follicular phase & what is it controlled by
- period when follicles growing
- follicles controlling events thru hormones they secrete
what is luteal phase & what is it controlled by
- preparing uterus for pregnancy by thickening uterine lining / endometrium
(ie/ progesterone production) - controlled by corpus luteum thru hormones it secretes
what phase occurs concurrently with follicular phase
menstrual phase
provide approx days for each cycle
- menstrual cycle (day 1-5)
- follicular phase (day 1-13) [early 1-7; late 8-13]
- ovulation (day 14)
- luteal phase (day 15-28)
what does oestrogen produced by dominant ovarian follicle in later stages of follicular phase stimulate
- stimulates regeneration of endometrium - redeveloping its glandular and vascularised structure
- to prime it to support implantation (that would occur in ensuing luteal phase)
how is developed endometrium (from oestrogen produced from dominant follicle in late follicular phase) sustained in luteal phase
- rising oestrogen and progesterone levels from corpus luteum sustain developed endometrium
what does high progesterone from corpus luteum induce in endometrium (in addition to sustaining its development)
- induces decidualisation - final stage of endometrium preparation for embryo implantation
how is corpus luteum function sustained when implantation does occur
- developing placenta (trophoblast cells > cytotrophoblast cells) & uterus communicate -> produce hormones that help sustain function of corpus luteum (hCG by syncytiotrophoblast cells primarily maintain corpus luteum) -> this helps sustain uterine endometrium (CL keeps producing progesterone) and support embryo
in non-pregnant cycle, corpus luteum regresses (no indication of implantation from hCG ie/ indicating a developing placenta), leading to what
- loss of trophic support for endometrium (no CL -> lack progesterone production)
=> menstruation occurs & cycle resets
what event induces ovulation
LH surge
