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Menstruation (Foetal/neonatal life (Mitosis (proliferation) of primordial…
Menstruation
Foetal/neonatal life
Mitosis (proliferation) of primordial germ cells occurs in utero
(during 3rd month of embryonic development)
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Primordial follicle (functional unit of ovary) contains
mesenchymal (granulosa) cells, oocytes and basement membrane
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2m primary oocytes in infant, 300-400k
at puberty; 400 mature over reproductive yrs
Menstrual
cycle
Ovulation
Oestrogen from the dominant follicle stimulates altered GnRH pulsatility, causing LH release from the anterior pituitary
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Luteal
(secretory)
phase
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Progesterone causes secretory
changes in the endometrium (thickening, vascularity)
Corpus luteum has fixed lifespan of 14d (hence why
luteal phase is ALWAYS 14d, even if follicular phase is longer)
Corpus leuteum undergoes programmed cell death
and involution to become corpus albicans (white body);
reduced oestrogen and progesterone initiates menstruation
If implantation occurs, production of hCG rescues the
corpus luteum, allowing continual progesterone release
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Cycles, pain
and bleeding
Pain
Normal due to vasospasm and ischemia
Highly variable, may interfere with function
Bleeding
Normally 1-7d (Average 3-5d)
Abnormal if IMB, PCB, erratic/constant
Cycles
Length
Normally 21-32 days
Variation due to follicular phase (luteal always 14d)
Shorter/longer usually due to oligo/anovulation
Peri-menopausal commonly has increased cycle length
Regularity
Normally regular
After menarche, can be irregular for
mths-yrs as HPO axis matures
Peri-menopausal can be irregular
due to fewer oocytes, thus anovulatory cycles
and ovarian resistance to gonadotropins
Definitions
Menstruation
Co-ordinated hormonal control of the
endometrium allowing regular shedding
(menses) or pregnancy
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