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Repro > menstrual cycle > Flashcards

menstrual cycle Flashcards

1
Q

what is day one of the menstrual cycle

A

the first day of bleeding (period)

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2
Q

what are the two phases of the menstrual cycle

A

1 - follicular phase

2 - luteal phase

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3
Q

what is the follicular phase

A

growth of the recruited early antral follicles.
one to become the dominant follicle.
follicular phase is dominaed by oestradiol production from the dominant follicle.
follicular phase lasts until ovulation

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4
Q

what is the luteal phase

A

corpus luteum is the dominant structure of the luteal phase, the phase is dominated by progesterone secretion from the corpus luteum

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5
Q

Role of HPGA in luteal phase in females

A

high progesterone production by corpus luteum.

-ve feedback to hypothalamus and pituitary. turns down secretion of GnRH and gonadotrophins

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6
Q

role of HPGA in males

A

-ve feedback of testosterone

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7
Q

role of HPGA in late luteal/ early follicular phase

A
  1. Corpus luteum dies at the end of luteal phase .’. progesterone falls. -ve feedback ceases so rise in FSH.
  2. As antral follicles grow, oestrogen starts to be produced .’. -ve feedback is reinstated .’. LH/FSH falls.
  3. As dominant follicule matures& we get closer to middle of cycle, oestrogen levels shoot up and there is a switch to +ve feedback.
  4. Oestrogen = +ve feedback .’. increased levels of gonadotrophins
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8
Q

role of HPGA in midfollicular phase

A

recruited antral follicles start to produce oestradiol.
.’. -ve feedback on hypothalamus/pituitary and causes big decline in FSH. this decline in FSH results in death of all but one follicle (dominant follicle)

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9
Q

what ultimately selects the dominant follicle

A

rise and fall in FSH

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10
Q

Role of HPGA midcycle

A
  • dominant follicle undergoes rapid growth.
  • proliferation of granulosa cells .;. E2 rise further
  • sustained E2 = switch to +ve feedback
  • so increase in LH (LH surge)
  • LH surge causes final maturation of oocyte within dominant follicle -
    completion of meiosis 1 and ovulation
  • high LH causes empty follicle to become corpus luteum which starts to produce progesterone
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11
Q

role of HPGA in mid-luteal phase

A
  • high progesterone (due to c.Luteum) = -ve feedback .’. decrease in LH/LSH
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12
Q

why do we need LH/FSH to fall in mid luteal phase

A

by this thime ovulated oocyte should have been fertilised + implantation should occur
if fertilisation has occured we need to sustain the fertilised embryo and not growing new follicles

so turning LH/FSH would enable a SINGLE embryo to grow

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13
Q

what is the importance of the intercycle rise and fall in FSH

A

allows secretion of the dominant follicle

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14
Q

why there an intercycle rise and fall in FSH

A

at beginning of menstrual cycle.
progesterone is decreasing so -ve feedback ceases
so selective increase in FSH
Increase in FSH = antral follicles grow.
as they grow they produce oestrogen
.’. -ve feedback .’. FSH falls

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15
Q

what is the window of opportunity

A

The point in the cycle where the dominant follicle is selected

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16
Q

how does follicle selection occur

A
  • a cohort of preantral follicles start growing 90 days prior
  • when at right size, need FSH to progress.
  • follicles that reach size before there is a rise in FSH die off
  • recruited antral follicles grow more and release E2 .’. FSH falls
  • too small follicles reaching antrum die off.
    window is presented
  • one of recruited follicles is selected to be dominant follicle
    .’. expansion of granulosa cells - E2 rises further .’. -ve feedback enhanced further. suppression of other folicles so only dominant ones can grow
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17
Q

How come the dominant follicle survives the fall in FSH?

A

As FSH falls, LH increases
dominant follicle aquires LH receptors on its granulosa cells.
- other follicles don’t & so lose their stimulant and die off
- dominant follicle has more FSH receptors which are more FSH sensitive
so despite FSH being lower, it is enough to maintain growth

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18
Q

receptor on theca cells

A

LHr

NEVER FSHr

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19
Q

receptor on granulosa cells

A

FSHr

later acquire LHr (at midfollicular phase onwards)

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20
Q

where are androgens formed

A

in theca cell

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21
Q

does luteal phase have -ve or +ve feedback mechanism

A

only -ve feedback

22
Q

in follicular phase is there -ve or +ve feedback

A 
both
a switch (no negative feedback -> negative feedback -> positive feedback).
23
Q

what are the other factors produced from the ovary that control feedback

A
  • activins
  • inhibins
  • Nutritional systems
  • Adipocytes via leptin
  • Pancreas feeds into the cycle via insulin
  • Liver feeds in via IGF-1
  • Adrenals feed in e.g. corisol
  • VEGF, TGF-beta also feed in
24
Q

what is the lifespan of the corpus luteum

A

14 days

25
Q

how is the dominant follicle adapted for its rapid growth (doubling in 7 days)

A

rapid neoangiogenesis

allows transfer of growth factors, nutrients and steroids

26
Q

what causes the LH surge at the end of the follicular phase

A

throughout follicular phase, E2 feedback is -ve.
near end of follicular phase E2 levels are raised enough that feedback switches to +ve
so get massive release in LH

27
Q

what does the LH surge trigger

A

the ovulation cascase

28
Q

what is the ovulation cascade

A
  • cumulous oocyte complex gets released
  • empty follicle is lutenised (formes corpus luteum)
  • lutenisation of granulosa and theca cells
  • E2 production falls and progesterone secretion is stimulated
29
Q

what is meant by lutenisation

A

the transformation of the mature ovarian follicle into a corpus luteum

30
Q

what is the mechanism of ovulation

A
  • bf to preovulatory follicle increases. increase in vascular permeability .’. increased intrafollicular pressure
  • follicle moved back to cortex of ovary .’. apex appearance on ovary wall
  • local release proteases which break down protein of ovary wall
  • 18hr after LH peak, hole appears in follicle wall and ovulation occurs
31
Q

what is the ovulated structure called

A

cumulus oocyte

which is oocyte surrounded by cumulus cells

32
Q

how is egg ovulated

A

cumulus oocyte is extruded from ovary under pressure
egg is collected by fimbria of uterine tube
egg pregresses down the uterine tube by peristalsis and action of cilia

33
Q

how does dominant follicle appear on ultrasound

A

appear black as are fluid filled

34
Q

How does a patient work out when they are going to ovulate?

regular cycle

A

simply 14 days from the first day of bleeding you will ovulate.

35
Q

How does a patient work out when they are going to ovulate?

irregular cycle

A

1 - monitor temperature (it inc when you’re about to ovulate; not v reliable)
2 - coitus 3 times a week. sperm survive about 5 days so by chance you will have sex around ovulation. (not always feasible)
3 - ultrasound monitoring - dominant follicle can be seen (not practical)

36
Q

How does a patient work out when they are going to ovulate?

irregular cycle

A

1 - monitor temperature (it inc when you’re about to ovulate; not v reliable)
2 - coitus 3 times a week. sperm survive about 5 days so by chance you will have sex around ovulation. (not always feasible)
3 - ultrasound monitoring - dominant follicle can be seen (not practical)
4 - ovulation sticks - detect LH (which surges 18hrs after ovulation) but expensive

37
Q

how is oocyte prepared for ovulation

A

oocyte packaged in follicle.
is haploid and arrested in meiosis 1 @ anaphase
allows oocyte to retain all its DNA
in response to 1st LH surge, nucleus of oocyte completes first meiotic division.
secondary oocyte begins meiosis 2. arrests again. remains in meiosis 2 until fertilised (or not fertilised and lost)

38
Q

how is is the dominant follicle (diploid) made to be haploid

A

until ovulated, the follicle remains arrested in meiosis 1 @ anaphase
LH Surge -> first meiotic division completes. Here half chromosomes put into the 1st polar body in the egg(at this point called secondary oocyte).
unequal division. secindary oocyte contains almost all cytoplasm, organelles, proteins etc/

39
Q

why is it important for oocyte to be so big

A

the oocyte has to support all of the early cell divisions of the dividing embryo until it establishes attachement to the placenta

40
Q

why is sperm so small and egg so big

A

egg contains all nutrients to support early pregnancy and chromosomes
sperm only contains chromosomes

41
Q

what happens to the oocyte in the uterine tube

A

spends 2-3 days here.
may meet sperm and be fertilised.
-> finish meiosis 2-> produced 2nd polar body with identical sister chromatids.
2 nuclei meet so we get a diploid cell (from mother and father)

42
Q

what happens to the empty follicle after ovulation

A

get lutenised into corpus luteum

43
Q

what is the role of the corpus luteum

A

secretes progesterone (increases progesterone greatly)
also some E2 secretion
supports the embryo until the placenta is formed

44
Q

how is the corpus luteum itself maintained

A

it has LH receptors

if pregnancy occurs: maintained by LH and hCG (latter secreted by trophoblast of embryo)

45
Q

what happens to corpus luteum if pregnancy doesnt occur

A

dies after 14 days
death essential to start next cycle
cell death occurs. vasculature breaks down. CL shrinks.
process not well known

46
Q

what are the secretions of the corpus luteum

A
  • progesterone

- E2

47
Q

role of progesterone secreted by the corpus luteum

A
  • supports oocyte
  • prepares the endometrium
  • controls cells in uterine tubes
  • alters secretion of cervix (more thick + gloopy)
48
Q

role of E2 secretions of the corpus luteum

A
  • required for endometrial functioning and implantation
49
Q

describe the menstrual cycle as a whole

A

1 - end of luteal phase, CL dies. decrease in Progesterone. -ve feedback ceased so rise in FSH
2 - rise in FSH = window of opportunity. cohort of antral follicles recruited to continue growth
3- as cohort grows they secrete oestrogen so -ve feedback reinstated. so FSH falls
4 - FSH drop = selection of a single dominant follicle. secretes more oestrogen so further FSH fall
5 - other follicles die (low FSH)
6 - dominant follicle continues to grow + granulosa cells start t express LH receptors
7 - dominant follicle doesnt die due to LHr present.
8 - sustained hogh oestrogen .’. switch to +ve feedback at end of Follicular phase. LH surge here.
9 - 18hr post-LH surge = meiosis 1 complete. cumulous oocyte complex ovulated. empty follicle left behind, is lutenised (c.luteum) NOW luteal phase
10 - C.luteum secretes progesterone .’. -ve feedback .’. LH/FSH falls. rise in oestroe

50
Q

describe the menstrual cycle as a whole

A

1 - end of luteal phase, CL dies. decrease in Progesterone. -ve feedback ceased so rise in FSH
2 - rise in FSH = window of opportunity. cohort of antral follicles recruited to continue growth
3- as cohort grows they secrete oestrogen so -ve feedback reinstated. so FSH falls
4 - FSH drop = selection of a single dominant follicle. secretes more oestrogen so further FSH fall
5 - other follicles die (low FSH)
6 - dominant follicle continues to grow + granulosa cells start t express LH receptors
7 - dominant follicle doesnt die due to LHr present.
8 - sustained hogh oestrogen .’. switch to +ve feedback at end of Follicular phase. LH surge here.
9 - 18hr post-LH surge = meiosis 1 complete. cumulous oocyte complex ovulated. empty follicle left behind, is lutenised (c.luteum) NOW luteal phase
10 - C.luteum secretes progesterone .’. -ve feedback .’. LH/FSH falls. rise in oestrogen. massive rise in Progesterone

51
Q

what and where are the two peaks of E2

A

one caused by secretion by granulosa cells of dominant follicle (+other antral)
- second by corpus luteum in the luteal phase but progesterone dominates this phase

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