Menstrual Cycle I Flashcards
What is the key requirement to maintain the HPG axis?
Pulsatility of release of GnRH and gonadotrophins
The length of a menstrual cycle is..
period of time between start of menstrual bleeding (day 1) in one cycle
—>
the onset of menses of the next cycle.
Median duration of Menstrual cycle is how many days?
28 days with most cycles between 25-30 days
(Luteal phase is fixed)
Menstruation lasts… (how many days?)
3-8 days
Polymenorrheic
MC<21 days
Oligomenorrheic
MC>35 days
Which steroids are made where?
The Menstrual Cycle (the follicular stages)
HPO axis
Negative & positive feedback
Follicular phase
Negative feedback
luteal phase
Inhibin is produced by..
Testis (Sertoli cells)
&
Ovary (Granulosa cells)
Both forms of Inhibin specifically suppress..
FSH secretion by pituitary without affecting LH secretion
Activins from where _______ stimulate what?
Activins from follicular fluid stimulate FSH secretion
Follistatin - where what does it generally known for?
What does it specifically do?
Another FSH-suppressing protein from follicular fluid.
Binds activin with high affinity » neutralizes FSH-stimulating ability of activins
Effect of Inhibin/Activin sub-types (table)
Activins correlation with FSH rise in Early follicular phase of MC
Inhibin with FSH fall in Late Follicular Phase of MC
levels of activin high at start of MC (EFP) but fall by luteal phase of MC,
whereas inhibin start to rise in LFP of MC and peak in luteal phase.
AMH is a _______ and also a member of the ___________
AMH is a glycoprotein and also a member of the TGFβ superfamily
When is AMH expressed in Males?
What does it cause?
How?
In males expressed from week 8 of development
causes regression of the Müllerian ducts by a wave of apoptosis.
AMH is expressed by which cells?
When do levels peak?
Ovarian granulosa cells.
Levels peak in selectable follicles (large preantral and small antral follicles) » then decrease.
AMH has 2 windows of action on folliculogenesis:
Inhibits transition from primordial –> primary follicles
Inhibits FSH-dependent cyclical recruitment of follicles by inhibiting FSH-stimulated aromatase and FSH receptor expression.
In the normal cycle would act to prevent over-recruitment of growing follicles
FSH threshold hypothesis
Raised FSH present a “window” of opportunity
One follicle from the group of antral follicles in either ovary is just at the right stage at the right time….
This becomes the dominant follicle which survives fall in FSH and goes onto ovulate
Known as “selection”
What causes FSH levels to fall to prevent further follicle growth?
Oestradiol levels rise reinstating negative feedback at pituitary
Once primordial follicles start growing and progressing, they become ______ independent
Once primordial follicles start growing and progressing, they become FSH independent
How does the dominant follicle survive the fall in FSH?
As FSH falls, LH increases.
Dominant follicle acquires LH receptors on granulosa cells.
Other follicles do not, so they loose their stimulant and die.
Which type of receptors are present on Granulosa cells?
Have FSHRr, then LHr acquired from mid-follicular phase onwards.
What steroids are produced as a consequence in the granulose cells?
FSH drives Oestrogen production in follicular phase and
LH drives progesterone production in luteal phase.
Which type of receptors are present on Theca cells?
Always LHr, NEVER FSHr
What steroids are produced as a consequence in the theca cells?
LH drives androgen and progesterone production from theca
Inhibin B levels in follicular phases
Highest in early-mid Follicular Phase (ratio of activin: inhibin)
and declines in Late Follicular Phase (small peak at LH surge)
ZERO in luteal phase.
Inhibin A levels in follicular phases
Increases in late Follicular Phase with highest levels in luteal phase (being made by Corpus Luteum which contributes to inhibition of FSH in this phase.
The dramatic decline in Inhibin A at the end of the luteal phase allows for increase in FSH.
(picture to review)
Characteristic changes occur in reproductive tract tissues due to varying concentrations of E2 & P in different parts of MC:
Endometrium
Oviduct/Fallopian tubes
Cervix
Vagina - changes in vaginal epithelial cells
