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75 terms

Control of ovarian function and the menstrual cycle

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what is menarche?
the first period
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?
GnRH
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 type of molecules are LH and FSH?
Gonadotrophins
what are the steroids which the ovaries release?
oestradiol and progesterone
what is the most potent natural oestrogen?
oestradiol-17ß (oestrodiol, E₂)
in what fashion is LH released? why?
pulses becuase GnRH is released in pulses
what can cause natural supression of menstruation?
before puberty
lactation
diet- anorexia/malnutrition
what are the key events in the ovarian cycle?
follicular growth
ovulation
luteal function
luteal regression
what are the two phases in the ovarian cycle?
follicular phase and luteal phase
in what fashion are the steroids produced?
cyclically
what hormones are involved in the follicular phase?
oestradiol
what hormones are involved in the luteal phase?
progesterone and oestradiol
what are the components of a follicle?
oocyte, antrum, granulosa cells, theca cells, blood vessels, cumulus cells
what is the zona pellucida?
the non cellular glycoprotein coat around the oocyte
what are the primary oocytes in primordial follicles like?
arrested in the 1st meiotic division
when does mitosis of primordial germ cells stop?
during foetal life
how many germ cells does a foetus have at 6 months gestation?
7 million
how many germ cells does a baby have at birth?
around 2 million
how many germ cells does a woman have at puberty?
about 300,000
how many germ cells are lost by atresia?
99.9%
how many follicles are growing at the start of a cycle?
30-50
when do follicles begin growing?
2-3 months before the cycle they are involved in
what do follicles produce as they grow?
increasing amounts of oestradiol
what does the oestradiol secreted by the follicles do to the hypothalamus?
inhibits it
what inhibits FSH and where is it from?
inhibin from the ovaries
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
which cells in the follicle produce androgens?
theca cells
what stimulates production of androgens?
LH
how are androgens converted to oestradiol? and by what?
they are aromatized by granulosa cells
where in the follicle is inhibin produced?
granulosa cells
what Are the symptoms of PCOS?
irregular menstrual cycles
anovulation
dysfunctional uterine bleeding
hirsutism
acne
male-pattern hair loss
overweight
what differences in hormone production from the pituitary gland occur in PCOS?
raised LH
lowered FSH
how do anovualtion and disturbed cycles occur in PCOS?
The follicle growth is disturbed by the change in hormone production by the pituitary gland
why does hirsutism occur in PCOS?
high LH leads to high androgen secretion from the theca
how is abnormal LH and FSH secretion reinforced in PCOS?
by the disturbed steroid feedback
what percentage of infertility is due to disorders in ovulation?
30%
what causes ovulation?
a surge in LH
what causes the LH surge?
high levels of oestradiol from a mature follicle
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
how long between the LH surge and the oocyte release?
36 hours
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
what is the corpus luteum?
"yellow body" formed from the ruptured follicle
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 is the name for the granulosa cells terminally differentiating?
luteinisation
what change is there in steroid secretion after the corpus luteum develops?
there is progesterone and oestradiol secretion
what steroid dominates in the follicular phase?
oestradiol
What steroid dominates the luteal phase?
progesterone
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 are the phases in the endometrial cycle?
proliferative phase
secretory phase
what causes an increase in endometrial thickness?
oestradiol
what appears in the thickened endometrium?
spiral arteries
where is the optimal time for implantation?
day 20
what is decidualisation?
the terminal differentiation of stromal cells in the endometrium
what occurs just before menstruation?
fall in the steroid levels
what happens as the steroid production falls?
gradual shrinking of endometrial tissue
spiral arteries become highly coiled
when does the intense constriction of the spiral arteries occur?
4-24 hours before menstruation
what is caused by reduction in blood flow to the superficial layers?
ischaemic hypoxia and damage
how do ishcaemic tissues tear and rupture?
individual spiral arteries re-opening and different times
how much tissue is lost as bleeding? what happens to the rest?
50%, the rest is reabsorbed
what is the cervical mucus like in the lead up to ovulation?
low viscosity
what happens to the mucus at the time of ovulation?
abundant mucus lick raw egg white
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
what is the characteristic pattern of mucus dried on a glass slide?
'fernlike'
what happens to basal body temperature just after ovulation?
typically rises by 0.5°C
Four methods for trying to identify the fertile period?
Calendar method
Temperature method
Cervical changes
Hormonal methods
what is the calendar method?
based on previous menstrual history
what is the temperature method?
using the rise in body temperature as a sign for ovulation
how are cervical changes used to identify fertile period?
feel the cervix and cervical mucus
how are hormonal methods used to identify fertile period?
over the counter kits measure urine hormone levels