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Science of Reproduction > Menstrual Cycle I > Flashcards

Menstrual Cycle I Flashcards

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1
Q

What is needed for correct menarche to occur?

A

Pulsatile release of both GnRH and gonadotrophins is key in maintaining HPG axis

Continuous release causes cessation

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2
Q

How is length of menstrual cycle measured?

A

The number of days between first day of menstrual bleeding of one cycle to onset of menses of the next cycle

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3
Q

What are the stages of the menstrual cycle?

A
  • menses
  • follicular phase
  • ovulation
  • luteal phase
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4
Q

What is the median duration of menstrual cycle?

A

Median duration of MC is 28 days with most cycles between 25=30 days

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5
Q

How long does menstruation last?

A

Menstruation lasts 3-8 days, written as 7/28 or 5-6/27-32

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6
Q

What is polymenorrhea?

A

MC < 21 days = polymenorrhea

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7
Q

What is oligomenorrhea?

A

MC>35 days=oligomenorrhea

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8
Q

When does the menstrual cycle become expectedly irregular

A

Menstrual cycle typically most irregular around extremes of reproductive life i.e menarche and menopause

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9
Q

Describe the levels of FSH throughout the cycle

A

FSH rise (MF) coinciding with antral follicle recruitment

Peaks with LH surge

Suppressed completely during luteal phase

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10
Q

How do LH levels change during the menstrual cycle?

A

LH rises with an exponential peak (LH surge), suppressed during luteal phase

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11
Q

Why do E2 levels rise?

A

E2 levels rise due to increase in antral follicle no. secreting more oestrogen
Large exponential rise due to dominant follicle selection → LH surge

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12
Q

Which hormone dominates the luteal phase?

A

Progesterone dominates luteal phase as secreted from CL.

Rise due to ovulation and demise due to lack of fertilisation

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13
Q

Which steroids are produced by the ovary?

A

Theca - androgen production

Granulosa - oestrogen production

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14
Q

Why do only granulosa cells produce oestrogen?

A

Aromatase only available in GC

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15
Q

What causes antral follicles to grow?

A

Selective FSH rise causes selection of antral follicles to grow

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16
Q

How does the dominant follicle survive?

A

Growing follicles pump out E2 (-ve) decline in FSH causes DF to survive only

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17
Q

How does DF survive and grow?

A

DF grows exponentially (MF) pumps out lots >300pmol of E2 (+ve) - LH surge

Ovulation of mature oocyte

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18
Q

What happens to remaining follicles (not DF)?

A

Remainder of oocyte converted into CL secreting P > E2 (-ve)

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19
Q

Describe the cyclical nature of mammals

A

All mammals have cyclical ovarian function & the same reproductive system (in terms of HPG axis) to produce a mature egg and the necessary sex steroids

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20
Q

Which mammals undergo menses?

A

Menstrual cycles occur only in humans, primates (apes and monkeys)

Named for regular appearance of menses i.e. shedding of the endometrial lining

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21
Q

What is meant by oestrous cycles?

A

The cyclic appearance of behavioural sexual activity (heat or oestrus)

No menstruation – the endometrium is reabsorbed if fertilization does not occur

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22
Q

Describe the feedback mechanisms of the HPO axis

A

-ve / +ve feedback from E2 & P

But also +ve/-ve feedback from activins and inhibins

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23
Q

Where is inhibin produced?

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A

Produced by testis (Sertoli cells) and ovary (Granulosa cells)

24
Q

Describe the structure of inhibin

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A

Disulphide-linked protein dimers

Common α-subunit with different β-subunits giving two forms of Inhibin

25
How do inhibins affect FSH secretion?
Both forms specifically suppress FSH secretion by pituitary without affecting LH secretion
26
Where are activins found?
Isolated Activins from follicular fluid
27
What is the role of activin?
stimulate FSH secretion
28
What is follistatin?
Another FSH-suppressing protein from follicular fluid
29
How does Follistatin produce its FSH-suppressing efefcts?
Binds activin with high affinity » neutralizes FSH-stimulating ability of activin
30
How are inhibis and activins produced?
Biosynthesis of inhibins and activins occurs from 3 genes, makes precursor protein: > from TGFb superfamily - a-protein specific for inhibin - Ba-protein can form either activin / inhibin - Bb-protein can form either activin / inhibin
31
What are the different forms of inhibin?
Inhibins take 2 forms depending on β-chain composition | - Inhibin A and Inhibin B
32
What are the various forms of activins?
Activins take 3 forms depending on β-chain composition ``` Activin A (βA-homodimer), Activin B (βB-homodimer) Activin AB (βAβB-heterodimer) ```
33
Which cells secrete activin / inhibin?
Activin and inhibin released by granulosa cells
34
How does activin:inhibin ratio change throughout the menstrual cycle?
Ratio of Activin:Inhibin decreases as the cycle progresses - Activins = ↑FSH in EFP - Inhibins = ↓FSH in LFP
35
What other factor can affect activin activity?
Activin activity can be further regulated by how much follistatin is in the follicular fluid - can bind and reduce activity
36
Describe the follicle size in the late follicular phase
Late follicular phase corresponds with larger antral follicles
37
What is AMH?
Anti-Mullerian Hormone is a glycoprotein and member of the TGFβ superfamily
38
When is AMH expressed in males?
In males expressed from week 8 of development; causes regression of Müllerian ducts by a wave of apoptosis
39
Where is AMH secreted in the ovaries?
Expressed by ovarian granulosa cells with levels peaking in selectable follicles (large preantral and small antral follicles) » then decreasing AMH produced primarily in early antral follicles and then dies off as follicles grow
40
What are the 2 actions of AMH on folliculogenesis?
1. Inhibits transition from primordial → primary follicles | 2. Inhibits FSH-dependent cyclical recruitment of follicles
41
What is the evidence that AMH limits primordial-primary follicle transition?
Born with resting primordial follicles - slowly activate and grow k/o AMH = follicle growth
42
How does AMH inhibit FSH-dependent recruitment of follicles?
Inhibits FSH-stimulated aromatase and FSH receptor expression → in normal cycle would act to prevent over-recruitment of growing follicles
43
Describe the process of follicular growth of preantral follicles
Preantral follicular growth occurs continuously once follicles activated Grow slow + regulated - reach point where FSH required ↑FSH = desired size follicles continue to grow and enter next stage - smaller cohort chosen
44
Outline the growth of antral follicles and the DF
Antral follicles grow Granulosa cells multiply Activins activated to enhance stimulation + follicle growth Follicles grow = E2 production and inhibins resulting in -ve feedback = ↓FSH ⇒ dominant follicle selected as other follicles in cohort die away due to lack of FSH
45
What stimulates dominant follicle selection?
Raised FSH present a “window” of opportunity E2 levels rise reinstating negative feedback at pituitary causing FSH levels to fall prevents further follicle growth
46
How does the DF survive the lack of FSH?
As FSH falls, LH increases. Dominant follicle acquires LH receptors on granulosa cells. Other follicles do not, so they lose their stimulant and die.
47
Which androgens are stimulated by gonadotropins during the menstrual cycle phases?
Follicular phase - FSH drives oestrogen production Luteal phase - LH drives progesterone
48
Which receptors are expressed by Granulosa cells?
Granulosa have FSHr | Later acquire LHr in mid-follicular phase onwards
49
Which receptors do theca cells express?
Theca always has LHr, never FSHr
50
Describe how the levels of inhibin B vary in the menstrual cycle
highest in early-mid FP - (activin: inhibin) Declines in LFP - small peak at LH surge Zero in luteal phase
51
Outline the levels of inhibin A in the menstrual cycle
Increases in late FP Highest levels in luteal phase (made by CL) – contributes to inhibition of FSH. Decline in Inhibin A at end of luteal phase allows for FSH increase
52
What other factors provide energy for mothers during pregnancy?
Pregnancy is an energy demanding process for mother - requires input from adipose tissues, insulin etc.
53
How may pathophysiological processes get disrupted during pregnancy?
If the mother becomes: - Anorexic: exercise induced /eating disorders - Overweight: insulin resistance
54
Why do changes occur in the reproductive tract during menstrual cycle?
Characteristic changes occur in reproductive tract tissues due to varying concentrations of E2 & P in different parts of MC
55
Which areas of the reproductive tract are affected by menstrual cycle hormonal changes?
Endometrium Oviduct/Fallopian tubes Cervix Vagina: changes in vaginal epithelial cells

Science of Reproduction (32 decks)

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