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Physiology & Science: Reproduction > The Menstrual Cycle > Flashcards

The Menstrual Cycle Flashcards

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1
Q

What are the 4 stages of the menstrual cycle?

A
  1. menstrual phase
  2. follicular phase
  3. ovulation phase
  4. luteal phase
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2
Q

What are the aims of the menstrual cycle?

A
  • selection of a single oocyte
  • regular spontaneous ovulation
  • correct number of chromosomes in eggs
  • cyclical changes in vagina, cervix + fallopian tube
  • preparation of the uterus
  • support of the fertilised dividing egg
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3
Q

How often do humans ovulate each year?

A

12x / year

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4
Q

How long is a typical cycle?

A
  • typically 28 days (most are 30 days)
  • day 1 = menses (bleeding starts)
  • day 1-14 follicular phase
  • day 14 = ovulation
  • day 14-28 = luteal phase
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5
Q

What is the follicular phase and when is it?

A
  • growth of follicles up to ovulation
  • dominated by oestradiol production from dominant follicle
  • day 1 - 14
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6
Q

What is the luteal phase and when is it?

A
  • formation of corpus luteum from empty follicle
  • dominated by progesterone production from corpus luteum
  • day 14-28
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7
Q

How does the luteal phase impact on the HPG axis?

A
  • progesterone released
  • -> negative feedback
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8
Q

How does the follicular phase impact on the HPG axis?

A
  • variable + more complex
  • release/removal of negative feedback (like foot off the break)
  • negative feedback then reinstated (oestrogen builds up, so reinstated)
  • then switch from negative to positive feedback
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9
Q

Describe the changes in the menstrual cycle

A
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10
Q

What is the inter-cycle rise referring to?

A
  • the rise in FSH
  • occurs in late luteal / early follicular phase
  • progresterone declines as the corpus luteum dies out
  • therefore less negative feedback
  • allowing for an increase in FSH
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11
Q

Why is the inter-cycle rise (and fall) important?

A
  • allows for selection of a single follicle
  • as FSH increased, will recruit + accelerate growth of antral follicles
  • as FSH declines, other follicles die
  • selected follicle doubles in size every 24hrs + makes lots of E2
  • this exerts -ve feedback on H-P to decrease FSH
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12
Q

Raised FSH present a “window” of opportunity - what is the FSH threshold hypothesis?

A
  • one follicle from the group fo antral follicles in ovary is just at the right stage at the right time…
  • this becomes the dominant follicle -> goes onto ovulate
  • known as selection
  • can be in either ovary
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13
Q

After the inter-cycle rise, why does the FSH drop?

A
  • the dominant follicle releases oestradiol
  • oestradiol levels rise
  • reinstate negative feedback at pituitary
  • causing FSH levels to fall
  • prevents further follicle growth
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14
Q

How does the dominant follicle survive the fall in FSH?

A
  • as FSH falls
  • LH increases
  • dominant follicle acquires LH receptors on granulosa cells
  • other follicles do not, so they lose their stimulant + die
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15
Q

What receptors do Theca cells have?

A
  • always have LHr
  • never FSHr
  • remember LH drives androgen + progesterone production from theca
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16
Q

What receptors do granulosa cells have?

A
  • have FSHr
  • LHr acquired from mid-follicular phase onwards
  • FSH + then LH drive oestrogen prod
17
Q

What causes ovulation?

A
  • LH
  • allows completion of meiosis I
  • allows oocyte to enter meiosis II
18
Q

What is the process of steroidogenesis?

A
  • all steroids originate from cholesterol
  • made by sequential removal of C atoms
  • by series of enzymes, which are distributed through cellular components of the follicle
19
Q

What other hormones are released aside from oestrogen + progesterone (and androgens) from the ovary that impact on the HPG axis?

A
  • activin
  • inhibin
  • peptide hormones
20
Q

How long does menstruation (bleeding) last?

A
  • starts day 1
  • last 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
21
Q

What is the lifespan of the corpus luteum?

A
  • 14 days
  • after 14 days CL will degenerate
  • if a long cycle - then it’s to do with change in follicular phase
22
Q

What changes occur following dominant follicle selection?

A
  • grows rapidly, doubling in diameter in 7 days from 7mm -> 14mm
  • needs masses of growth factors, nutrients + steroids
  • rapid neoangiogenesis
  • oestrogen released from follicle into circulation
23
Q

What causes the massive release of LH from the pituitary?

A
  • throughout follicular phase, E2 feedback was negative
  • at end of follicular phase E2 levels raised for long enough -> feedback switches from negative to POSITIVE
  • causes mass release of LH from pituitary
  • exponential rise in LH in serum
24
Q

What does this mass release of LH trigger?

A
  • triggers ovulation cascade
  • egg is released
  • results in changes in follicle cells -> luteinisation (formation of corpus luteum)
  • E2 production falls + progesterone is stimulated
25
Q

What are the cascade of events that result in ovulation?

A
  • blood flow to follicle increases dramatically (inc in vasc perm increases intra-follicular pressure)
  • appearance of apex or stigma or ovary wall
  • local release of proteases
  • enzymatic breakdown of protein of the ovary wall
26
Q

How long after the peak in LH does ovulation occur?

A

12-18 hrs after peak of LH, hole appears in follicle wall + ovulation occurs

27
Q

What happens next when the oocyte is released from the follicle during ovulation?

A
  • oocyte w/ cumulus cells is extruded from ovary under pressure
  • follicular fluid may pour into Pouch of Douglas
  • egg collected by fimbria of fallopian tube (due to signal from fluid)
  • egg progresses down tube by peristalsis + action of cilia
28
Q

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

A
  • if cycles are regular then it’s easy
  • but if cycles are irregular it’s harder
  • intercourse 2-3x/week is enough
  • scanning by ultrasound best to detect ovulation
29
Q

What hormone is primarily being detected by ovulation sticks?

A
  • LH
  • LH surge detected in urine
  • that LH surge preceeds ovulation BUT need to have a lot of sticks
30
Q

From its formation as a primary oocyte in the fetal ovary up until ovulation, the oocyte has been arrested in the first meiotic divison (meiosis I). What is beneficial about this?

A

This permitss the oocyte to retain all of the DNA + remain as large as possible during its long wait

31
Q

What happens in terms of divison following the LH surge?

A
  • LH surge
  • -> nucleus of oocyte in dominant follicle completes meiosis I but it does not divide!
32
Q

Describe meiosis and extrusion of the polar body

A
  • half of the chromosomes are put into a small package in the egg called the 1st polar body
  • the egg is now called a secondary oocyte
  • the 1st polar body plays no further part in the process + does not divide again
  • oocyte begins the 2nd meiotic divison, but arrests again
33
Q

Describe the life of a 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)
  • oocyte has to support all of the early cell divisons of dividing embryo until it establishes attachment to placenta
  • spends 2-3 days in uterine tube
34
Q

How is the corpus luteum formed and maintained?

A
  • after ovulation the follicle collapses
  • corpus luteum is formed, ‘yellow body’
  • progesterone production increases greatly, also E2
  • CL contains large # of LH receptors
  • CL supported by LH and hCG … if a pregnancy occurs
35
Q

What are the secretions of the corpus luteum?

A
  • progesterone
  • oestradiol
36
Q

What is the progesterone from the CL for?

A
  • supports oocyte in its journey
  • prepares endometrium
  • controls cells in fallopian tubes
  • alters secretions of cervix

(oestradiol also for endometrium)

37
Q

What happens to the corpus luteum if fertilisation does not occur?

A
  • 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 not well understood
38
Q

What info do you need to enter into a period tracker app?

A
  • typical period + cycle length
  • enter in symptoms of premenstrual syndrome
  • app uses this info to predict future periods + ovulations days
  • need to enter in a few months of data, to get accurate personalised data
39
Q

Summary graph of hormone level changes throughout menstrual cycle

A

Physiology & Science: Reproduction (18 decks)

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