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Repro Phys > The Menstrual Cycle > Flashcards

The Menstrual Cycle Flashcards

1
Q

Follicular phase

A

the phase of the menstrual cycle associated with growth of the follicles and selection of the dominant follicle. It is characterised by oestrogen production.

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2
Q

Ovulation

A

the release of a mature haploid oocyte from the dominant follicle in response to a surge in LH

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3
Q

Luteal phase

A

the phase of the menstrual cycle associated with formation the corpus luteum after ovulation. It is characterised by progesterone production

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4
Q

Dominant follicle

A

the follicle that is selected from the growing cohort of antral follicles to become the pre-ovulatory follicle and release a mature egg at ovulation

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5
Q

Corpus luteum

A

the structure formed from the granulosa and theca cells of the follicle after ovulation, which is triggered by the surge in LH and causes luteinisation of the granulosa and theca cells.

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6
Q

Menses

A

the shedding of the endometrial tissue lining along with blood

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7
Q

Polar body

A

the small structure contains half the chromosomes after the completion of meiosis I.

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8
Q

What are the aims of the menstrual cycle?

A
  • selection of a single oocyte
  • correct number of chromosomes in eggs i.e. haploid
  • regular spontaneous ovulation
  • cyclical changes in the vagina, cervix and Fallopian tube
  • preparation of the uterus
  • support of the fertilised dividing egg
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9
Q

Control of Menstrual Cycle

A

diagram

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10
Q

GnRH has to be pulsatile

A

diagrams

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11
Q

the menstrual cycle summary

A

diagram
•In a 28-day cycle day 1 is typically the 1st day of menses
•Follicular phase = growth of follicles up to ovulation → dominated by
oestradiol production from follicles
•Luteal phase = formation of corpus luteum from the empty follicle →
dominated by progesterone production from corpus luteum

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12
Q

Menstrual Cycle

A

• 2 phases separated by ovulation
• Cycle begins on day 1=first day of bleeding
• Next 14 days are follicular phase i.e. growth of antral
follicles
• Ovulation occurs at end of the follicular phase (i.e. in
the middle of the cycle)
• Remnant of the follicle becomes the corpus luteum
• Next 14 days are luteal phase i.e dominated by corpus
luteum
• Menstruation occurs at the end if there is no pregnancy

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13
Q

hypothalamic/ pituitary/ ovarian axis

A

diagram
Luteal phase=Negative feedback → Progesterone
Follicular phase=variable
1. Release of negative feedback
2. Negative feedback then reinstated, then
3. Switch from negative to positive feedback

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14
Q

phases and cycle

A

diagram

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15
Q

The Inter-Cycle Rise in FSH

A

diagram
The inter-cycle rise and fall in FSH is very important because it allows selection of a single follicle, which will go onto become the dominant follicle that will ovulate

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16
Q

The window of opportunity

A

diagram

17
Q

Follicle Selection

A

• Raised FSH present a “window” of opportunity to recruit antral follicles that are at the right stage to continue growth
• FSH threshold hypothesis
– One follicle from the group of antral follicles in ovary is just at the right stage at the right time to survive declining FSH
– This becomes the dominant follicle which goes onto ovulate
– Known as “selection”
– Can be in either ovary
• Oestradiol levels rise reinstating negative feedback at pituitary causing FSH levels to fall prevents further follicle growth
How does the dominant follicle survive the fall in FSH?

18
Q

Dominant Follicle Selection - LH

A

diagram
• As FSH falls, LH increases. Dominant follicle acquires LH receptors on granulosa
cells
• Other follicles do not, so they lose their stimulant and die
*(look at the steroidogenesis slide in the folliculogenesis lecture)

19
Q

The Dominant Follicle characteristics

A

Dominant follicle survives fall in FSH by
• increases sensitivity to FSH = increased FSH receptors
• increased numbers of granulosa cells
» 2-5 million GC in EFP and 50-100 million at ovulation
» increases E2 production because of increased aromatase levels
» 200x more E2 in DF than in others
• acquisition of LH receptors
» the LHR (LH receptor) gene is switched on by FSH

20
Q

steroidogenesis

A

diagram

21
Q

LH surge

A

• Throughout follicular phase E2 feedback was negative
• At end of follicular phase if E2 levels raised for long enough
(48h) and high enough (>300pM) enough → feedback switches from negative to positive
• Causes massive release of LH from pituitary
• Exponential rise in LH in serum
• Triggers ovulation cascade
- Egg is released
- Above result in changes in follicle cells = luteinisation i.e. formation of
the corpus luteum
- Corpus luteum has both luteinised granulosa and theca cells
- E2 production falls, but still produced and P is stimulated & dominates

22
Q

Ovulation

A

• ovulation occurs via cascade of events:
– blood flow to the follicle increases dramatically
– appearance of apex or stigma on ovary wall
– Local release of proteases and inflammatory mediators
– Enzymatic breakdown of protein of the ovary wall
• 12-18 hrs after peak of LH, the follicle wall is digested and ovulation occurs with release of cumulus-oocyte
complex (COC)

23
Q

Ovulation cont…

A

• Oocyte with cumulus cells is extruded from the ovary
• Follicular fluid may pour into Pouch of Douglas
• egg ‘collected’ by fimbria of Fallopian tube
• egg progresses down tube by peristalsis and action of cilia
diagrams

24
Q

Meiosis & Extrusion of the Polar Body

A
  • In response to the LH surge, the nucleus of the oocyte in the dominant follicle completes the first meiotic division.
  • ½ the chromosomes are put into a small “package” in the egg called the 1st polar body
  • The egg (with most of the cytoplasm) is now a secondary oocyte
  • The 1st polar body plays no further part in the process and does not divide again
  • Oocyte begins the 2nd meiotic division, but arrests again.
25
Q

Secondary Oocyte

A
  • Unlike sperm we only want a single oocyte
  • The oocyte is the largest cell in the body (sperm are smallest…..but fastest!)
  • The oocyte has to support all of the early cell divisions of the dividing embryo until it establishes attachment to the placenta
  • Spends 2-3 days in the uterine tube
  • So the oocyte is now on its way into the tube….will it meet a sperm? The story continues later…
26
Q

corpus luteum formation

A
  • after ovulation the follicle collapses
  • corpus luteum is formed, ‘yellow body’
  • progesterone production increases greatly, also E2
  • CL contains large numbers of LH receptors
  • CL supported by LH and hCG (from implanting embryo, if a pregnancy occurs) which also bind to LHR
27
Q

Hormone Changes during Pregnancy

A

diagrams

28
Q

CL secretion (8) and demise (4)

A 
secretions of CL
• progesterone: 
– supports oocyte in its journey
– Maintains the CL
– prepares the endometrium
– controls cells in Fallopian tubes
– alters secretions of cervix
• oestradiol:
– for endometrium

demise of CL
• If fertilisation does not occur, CL has finite lifespan of 14 days.
• removal of CL essential to initiate new cycle
• Cell death occurs, vasculature breakdown, CL shrinks
• Process is not well understood

29
Q

clinical applications – all centre around the

concept of feedback

A

diagram

30
Q

Hypothalamic/pituitary/ovarian axis

A

diagram

31
Q

the menstrual cycle days

A

• Day 1 is first day of bleeding
•Menstruation lasts 3-8 days, written in notes as 7/28 or 5-6/27-32
•Regular cycle should have no more than 4 days variation from
month to month

32
Q

How does a patient work out when they are

going to ovulate?

A

How does a patient work out when they are going to ovulate?
• If cycles are regular then it’s easy
• But if cycles are irregular?
• Question – if a woman has a 32-day cycle on what day will she ovulate?
• If having intercourse 3 times/week probably
OK….but many will not be
• Ultrasound monitoring if having induction of ovulation, How does a patient work out when they are going to ovulate?

33
Q

Signs of Ovulation

A

• A slight rise in basal body temperature, typically 0.5 to 1 degree,
measured by a thermometer
– Need to keep a chart of basal body temp from
day 1 of LMP
– Why? diagrams
• Tender breasts
• Abdominal bloating
• Light spotting
• Changes in cervical mucus
• Slight pain or ache on one side of the
abdomen

34
Q

Ovulation prediction

A

• Ovulation prediction kits
– Fertile period spans 6 days and is affected by:
• Lifespan of the egg → up to 24h after ovulation
• Lifespan of sperm → median=1.5days but sperm can survive up to 5 days in
the sperm supportive mucus of fertile days of cycle » sperm survival is
dependent on the type & quantity of mucus within cervix AND the quality of
the sperm

E3G is urinary metabolite of oestradiol, allowing women to identify days of high fertility leading up to ovulation

diagrams

35
Q

Main Points To Remember

A
  • Inter-cycle rise in FSH followed by slow decline
  • slow rise in LH in follicular phase to exponential mid-cycle rise
  • 2 peaks in oestradiol- different shapes ——–
  • single luteal phase rise in progesterone ——–

diagrams

Repro Phys (12 decks)

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