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Repro > The Menstrual Cycle > Flashcards

The Menstrual Cycle Flashcards

1
Q

What are the aims of the menstrual cycle?

A
  • Selection of a single oocyte
  • Regular spontaneous ovulation
  • Correct number of chromosomes in eggs i.e. haploid
  • Cyclical changes in the vagina, cervix and fallopian tube
  • Preparation of the uterus
  • Support of the fertilised dividing egg
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2
Q

Why does GnRH need to be pulsatile?

A

To make LH/FSH.

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3
Q

What happens when GnRH is administered in a continuous way?

A

The LH levels fall and switch off production. Production restored on resumption of pulsatile administration.

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4
Q

How many phases of the menstrual cycle are there?

A

2

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5
Q

When does the menstrual cycle begin?

A

On day 1 - the first day of bleeding

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6
Q

What is the follicular phase?

A

14 days after the first day of bleeding i.e. growth of follicle

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7
Q

When does ovulation occur?

A

At the end of the follicular phase (i.e. the middle of the cycle).

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8
Q

What does the empty follicle become?

A

The corpus luteum

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9
Q

What is the next phase after ovulation?

A

The luteal phase i.e. dominated by corpus luteum

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10
Q

When does menstruation occur?

A

At the end of the menstrual cycle

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11
Q

What happens during the follicular phase?

A

Growth of follicles up to ovulation dominanted by oestradiol production from dominant follicle.

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12
Q

What happens during the luteal phase?

A

Formation of corpus luteum from the empty follicle dominated by progesterone productoin from corpus luteum.

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13
Q

How do we work out the cycle of a woman clinically?

A

Ask from the 1st day of bleeding to the 1st day of bleeding in the next cycle.

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14
Q

What type of feedback controls the luteal phase?

A

Negative feedback of progesterone

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15
Q

What type of feedback controls the follicular phase?

A

Variable

  1. Release of negative feedback
  2. Negative feedback then reinstated, then
  3. Switch from negative to positive feedback
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16
Q

Describe the HPG axis feedback

A

Pulsatile release controls the release of hormones from the hypothalamus, this control the pituitary in a positive feedback manner. Then positive feedback to the ovary causing the release of oestrogen, progesterone and testosterone. This can cause an increase/decrease in the release of hormones from the pituitary or hypothalamus.

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17
Q

Summarise the menstrual cycle

A
  • At the end of the cycle (end of the luteal phase), the corpus luteum, which is the left over follicle after ovulation, is dying and the progesterone that is makes starts to fall.
  • This high P was exerting negative feedback at level of hyp/pit, thereby keeping levels of LH/FSH low.
  • As the levels fall, the brake on negative feedback is lost but in such a way that it causes FSH levels to increase preferentially.
  • This stimulates follicles to grow and they make oestradiol.
  • The E2 feeds back to hyp-pit and inhibits FSH release, so levels fall again.
  • Meanwhile, LH levels have been rising a little across the follicular phase and this allows a single follicle to grow and grow and become the dominant follicle.
  • This DF will make massive amounts of E2, after 2 days of E2 which reach levels of >300pmol, the negative feedback becomes positive and there is a huge release of LH that causes the egg to be released.
  • The remaining follicle becomes the corpus luteum that makes progesterone and this causes negative feedback again.
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18
Q

Why is the inter-cycle rise and fall in FSH important?

A

It is important because it allows selection of a single follicle, that will go on to beomce the dominant follicle that will ovulate.

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19
Q

What is the peak of FSH below the LH peak a result of?

A

It is a result of an “artefact” of gonadotrophin stimulation of pituitary by oestrodiol.

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20
Q

What is the “window of opportunity” for the follicle?

A

This is the exact moment when FSH goes up and selects a follicle and then as FSH declines, other follicles die.

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21
Q

What happens to the selected follicle?

A

It doubles in size every 24hrs and makes lots of E2 that exerts negative feedback on H-P to decrease FSH.

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22
Q

What is the FSH threshold hypothesis?

A

One follicle from the group of antral follicles in ovary is just at the right stage at the right time. This becomes the dominant follicle that goes onto ovulate. This is called selection.

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23
Q

What prevents further follicle growth?

A

Oestradiol levels rising reinstating negative feedback at pituitary causing FSH levels to fall.

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24
Q

What happens during dominant follicle selection?

A

As FSH falls, LH increases. Dominant follicle acquires LH receptors on granulosa cells. Other follicles do not, so they loose their stimulant and die.

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25
Q

How does the dominant follicle survive a fall in FSH?

A
  • Increased sensitivity to FSH
  • Increased FSH receptors
  • Increased by numbers of granulosa cells
  • Acquisition of LH receptors
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26
Q

Describe the formation of the androgens

A

Acetate -> cholesterol -> pregnenolone (via a side chain cleavage enzyme) -> progesterone -> androgens: testosterone/androstenedione (via 17 alpha hydroxylase, 12,20 lyase)

27
Q

Describe the formation of oestrogens

A

Androgens converted to oestrogen via aromatase

28
Q

What do both theca and granulosa cells contain?

A

Cholesterol, pregneneolone, Progesterone

29
Q

What do theca cells have only?

A

The androgens

30
Q

What do granulosa cells have only?

A

Oestrogens

31
Q

Where do steroids originate from?

A

Cholesterol from the sequential removal of C atoms by a series of enzymes

32
Q

Describe the LH surge

A
  • During the follicular phase, E2 feedback is negative.
  • At the end of the follicular phase, when the E2 levels are raised for long and high enough the feedback switches from negative to positive.
  • Causes a release of LH from the pituitary and there is an exponential rise in LH in serum.
  • This triggers an ovulation cascade and the egg is released. The corpus luteum is formed. Corpus luteum has both luteinised granulosa and theca cells.
  • E2 production falls, but still produced and P is stimulated and dominates.
33
Q

Describe the events of ovulation

A
  • 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.
34
Q

What is released at the beginning of ovulation?

A

12-18 hrs after peak of LH, the follicle wall is digested and ovulation occurs with release of cumulus-oocyte-complex (COC).

35
Q

How does the egg progress down the fallopian tube?

A

By peristalsis and action of cilia

36
Q

How long does the process of the LH surge and ovulation take?

A

15 minutes

37
Q

What happens to the oocyte after the LH surge?

A

The nucleus of the oocyte in the dominant follicle completes the first meiotic division.

38
Q

What is the 1st polar body?

A

1/2 the chromosomes are put into the small package

39
Q

When does the egg become a secondary oocyte?

A

When the 1st polar body is released from the process.

40
Q

What is the largest cell in the body?

A

The oocyte

41
Q

What is the smallest cell in the body?

A

The sperm - but the fastest

42
Q

What does the oocyte support?

A

It supports all of the early cell divisions of the dividing embryo until it establishes attachment to the placenta.

43
Q

How long is the oocyte in the uterine tube?

A

2-3 days

44
Q

What happens to the follicle after ovulation?

A

The corpus luteum is formed, “yellow body”. Progesterone production increases greatly, also E2.

45
Q

What supports the CL?

A

CL contains large No. LH receptors. CL supported by LH and hCG (from implanting embryo, if a pregnancy occurs) which also bind to LHR.

46
Q

Describe the hormone changes during pregnancy

A

At the end of ovulation, there is an large surge in hCG and a gradual increase in oestrogen. The corpus luteum is maintained and releases progesterone.

47
Q

Why does the CL secrete progesterone?

A
  • Supports oocyte in its journey
  • Maintains the CL
  • Prepares the endometrium
  • Controls cells in the fallopian tubes
  • Alters secretions of cervix
48
Q

Why does the CL secrete oestradiol?

A
  • For the endometrium
49
Q

How does the CL demise occur?

A
  • If fertilisation does not occur, CL has a 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
50
Q

How can the disruption of negative feedback affect the cycle?

A

It can cause infertility and need to be treated by clomid.

51
Q

What can be used if there is constant negative feedback?

A

OCP that prevents LH and FSH release

52
Q

What can be used to replace hormones?

A

HRT - hormone replacement therapy

53
Q

What can be used to reduce gonadotrophin release?

A

Analogues of GnRH

54
Q

What can be used to stimulate gonadotrophin release?

A

Analogues of GnRH

55
Q

What can be used to treat infertility?

A

Injections of LH/FSH

56
Q

What controls the HP ovarian axis?

A

It requires input from a lot of other systems in the body detecting fitness to reproduce as it is an important and calorific process.

57
Q

What are the signs of ovulation?

A
  • A slight rise in basal body temperature (BBT), typically 0.5 to 1 degree, measured by a thermometre.
  • Tender breasts
  • Abdominal bloating
  • Light spotting
  • Changes in cervical mucus
  • Slight pain or ache on one side of the abdomen
58
Q

How much does your BBT increase by after ovulation?

A

by about 0.4 to 1.0 degree Fahrenheit

59
Q

Which hormone is being detected in ovulation?

A

Progesterone

60
Q

How do ovulation prediction kits work?

A
  • E3G is a urinary metabolite of oestradiol, allowing women to identify days of high fertility leading up to ovulation.
61
Q

What is the lifespan of the egg?

A

Up to 24h after ovulation

62
Q

What is the lifespan of sperm?

A

1.5 days but sperm can survive up to 5 days in the sperm supportive mucus of fertile days.

63
Q

What is sperm survival dependent on?

A

The type and quantity of mucus within the cervix and the quality of the sperm.

Repro (11 decks)

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