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Basic Human Reproduction > Oogenesis > Flashcards

Oogenesis Flashcards

1
Q

How long is the process of oogenesis?

A

85 days

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2
Q

What are the phases of oogenesis?

A
  1. Proliferative mitosis
  2. Meiosis
  3. Cytodifferentiation
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3
Q

How many follicles are present at birth?

A

2 million

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4
Q

How many follicles are present at puberty?

A

300 000

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5
Q

How many times will a woman ovulate during her lifetime?

A

400-450

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6
Q

What are the phases of follicle growth?

A
  1. Primordial —- 2. Primary/pre-antral —- 3. Secondary/antral —- 4. Preovulatory
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7
Q

What type of follicle is the Graafian/dominant follicle?

A

Antral

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8
Q

Which are the type of follicles visible on USS? And why?

A

Antral - due to the presence of the follicular fluid

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9
Q

What is the size of a primordial follicle?

A

20 micrometers

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10
Q

What type of oocyte do the primordial follicles contain?

A

Primary oocytes

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11
Q

From what are the primary oocytes derived?

A

Primordial germ cells (oogonia), these proliferate during mitosis while the female is a foetus, begin meiosis, again while the female is still a foetus, but cease meiosis at prophase I. It is upon this meiotic block that the oogonia become primary oocytes

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12
Q

When does mitosis occur in females?

A

While in-utero, i.e. while the female is a foetus

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13
Q

What cells is it that undergo mitosis in females?

A

Oogonia, i.e. PGCs

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14
Q

When does meiosis begin in females?

A

While in-utero, i.e. while the female is a foetus

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15
Q

At what point is the first meiotic block/meiotic arrest?

A

Prophase I

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16
Q

What is the point of the meiotic arrest?

A

We don’t currently know

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17
Q

At what follicular stage does mitosis and meiosis occur?

A

Primordial

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18
Q

At what follicular stage are oogonia transformed into primary oocytes?

A

Primordial

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19
Q

In the primordial follicle, in what is the primary oocyte contained?

A

Germinal vesicle

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20
Q

What cells surround the germinal vesicle/what cells are contained within the primordial follicle?

A

Condensed, squamous, granulosa cells

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21
Q

What is the content of the follicle contained within, i.e. what is the BM of the follicle?

A

Membrana propria

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22
Q

What surrounds the primordial follicles?

A

Interstitial cells set within the stroma

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23
Q

Which type of cell is homologous to sertoli cells in males?

A

Granulosa cells

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24
Q

Which type of cell is homologous to leydig cells in males?

A

Theca cells

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25
Q

At what follicular stage do theca cells not appear until?

A

Pre-antral/primary

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26
Q

What brings about growth in primordial follicles?

A

GH mediated by IGF-1, intraovarian cytokines, upon selection t grow into pre-astral/primary follicles

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27
Q

What cells in the follicle produce IGF-1?

A

Granulosa cells

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28
Q

How many primordial follicles are chosen to grow into pre-astral/primary follicles each day? + what brings about this selection?

A

A few. It is not clear how these primordial follicles are selected

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29
Q

What is the size of a pre-astral/primary follicle?

A

200-400 micrometers. The lecture given says the size ‘quadruples’ (clearly at least) compared to a primordial follicle

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30
Q

From what are the theca cells derived?

A

Formed from stromal cells on the outside of the follicles that condense on the membrane propria

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31
Q

In what order do the theca and granulosa cells proliferate?

A

Granulosa cell proliferation occurs before theca cell proliferation

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32
Q

At what follicular stage do the granulosa and theca cells proliferate?

A

Pre-antral/primary

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33
Q

What happens to the granulosa in the pre-antral follicles?

A

Proliferation, become several layers thick, + become cuboidal (from the squamous shape they were in the primordial follicle)

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34
Q

What shape do the granulosa cells become int he pre-antral follicle?

A

Cuboidal

35
Q

At what follicular stage does the primary oocyte reach its ‘final’ diameter?

A

Pre-antral follicle/primary

36
Q

What is the ‘final’ diameter of the primary oocyte

A

60-120 micrometers

37
Q

In what stage does the cytodifferentiation phase of oogenesis begin?

A

Pre-antral - remember in oogenesis meiosis and cytodifferentiation take place in tandem

38
Q

From what is the zona pellucida formed?

A

Glycoproteins

39
Q

From where do the glycoproteins that form the zona pellucida come from?

A

Secreted by the oocyte

40
Q

From what glycoproteins is the zona pellucida formed?

A

ZP1; ZP2; ZP3; ZP4

41
Q

At what follicular stage is the zona pellucida formed?

A

Pre-antral/primary

42
Q

What is the thickness of the zona pellucida?

A

5-10 micrometers

43
Q

From what does the zona pellucida separate the oocyte from?

A

Granulosa cells

44
Q

How is communication/transport maintained between granulosa cells and oocytes, despite the zona pellucida? + why is this maintenance of communication important?

A

Gap junctions. Important because the oocyte is avascular

45
Q

At what follicular stage do FSH receptors (only) form? On what cell do the FSH receptors form?

A

Pre-antral/primary. They form on the granulosa cells?

46
Q

In summary, what are the differences between primordial and pre-antral follicles?

A
  1. Size - growth of both the follicle and primary oocyte
  2. Theca cell apperance
  3. Granulosa and theca cell proliferation
  4. Zona pellucida formation
  5. FSH receptor formation
47
Q

What are the type of antral/secondary follicle?

A

Early and late

48
Q

At what stage do the theca cells form 2 layers?

A

Early antral

49
Q

What are the 2 layers of theca cells?

A
  1. Theca externa - a fibrous capsule

2. Theca interna - an inner glandular and highly vascular layer

50
Q

At what follicular stage is follicular fluid first formed?

A

Early antral

51
Q

From what is follicular fluid formed?

A
  1. Granulosa cell secretion + 2. Serum transudate
52
Q

Where does the follicular fluid collect in the early antral follicle?

A

Between the granulosa cells

53
Q

What is the follicular antrum?

A

When droplets of follicular fluid coalesce

54
Q

What does the appearance of the follicular antrum mark?

A

The beginning of the antral stage

55
Q

How many antral follicles are rescued from atresia in each ovary in each menstrual cycle?

A

7-10 (therefore 14-20 total)

56
Q

What is atresia?

A

Oocyte and granulosa cell apoptotic death, leukocyte and macrophage invasion of the follicle and fibrous tissue formation

57
Q

At what point are the antral follicles rescued int he menstrual cycle?

A

At the start of each new menstrual cycle

58
Q

What is it that rescues antral follicles from atresia?

A

FSH (hence this is the basis of stimulation in IVF - exogenous FSH, Gonal F, is given to increase the number of antral follicles rescued/recruited). Therefore, the theory goes that the antral follicles with the most FSH receptor not heir granulosa cells are the follicles most likely to be recruited

59
Q

What is the cumulus oopherus?

A

Layer of granulosa cells that surround the oocyte suspended in the follicular antrum (of follicular fluid)

60
Q

At what stage does the cumulus oopherus become apparent?

A

Antral stage

61
Q

How is an antral follicle selected to become dominant?

A

Involvement of cytokines, e.g. IGF. And it is FSH that stimulates the availability of IGF for follicular growth, and so a dominant follicle may be more responsive to FSH, i.e. may have more FSH receptors

62
Q

What are the actions of the dominant follicles?

A
  1. Inhibin A production, under action of LH
  2. Androgen production, also under the action of LH. It is androgens that cause the atresia of the other antral follicles
  3. Increased aromatase activity in granolas cells - resulting in increased theca androgens being converted to oestrogen. The increase in oestrogen will ultimately bring about the positive feedback needed to bring about the LH surge required for ovulation
63
Q

Where are LH receptors found?

A

Theca cells

64
Q

What happens with regard to LH receptors of the dominant antral follicle?

A

FSH and the increase in oestrogen cause LH receptors to form on the granulosa cells (not usually found there). Both theca AND granulosa cells need to be able to bind LH in order for the transition from antral to pre-ovulatory follicle to take place

65
Q

At what point after the LH surge does ovulation occur?

A

24-36 hours after

66
Q

What are the 3 changes that LH cause to the pre-ovulatory follicle?

A
  1. Causes oocyte expulsion; 2. Causes LH-induced follicular fluid expansion; 3. Changes the whole endocrinology of the follicle
67
Q

How is the oocyte expelled from the dominant follicle?

A
  1. The nuclear membrane disintegrates; 2. The meiotic arrest at PI is reversed, resulting in a secondary oocyte; 3. Cytoplasm maturation occurs within the secondary oocyte
68
Q

At what meiotic stage is the oocyte upon explosion from the dominant follicle?

A

MII of meiosis

69
Q

What are the events involved in the reversal of meiotic arrest?

A

The oocyte undergoes its first meiotic division in which there is cell division with unequal cytokinesis. One cell receives almost all the cytoplasm - this is the secondary oocyte. The other ‘cell’ is discarded as the 1st polar body (PB). A seance meiotic arrest occurs at MII int he presence of cytostatic factor

70
Q

What are the events involved in secondary oocyte cytoplasmic maturation?

A
  1. The cytoplasmic processes between the oocyte and cumulus oopherus are broken; 2. lysosomal-like granules from he Golgi migrate to the periphery of the oocyte to form the cortical granules; 3. centrioles are lost; 4. new types of proteins are formed
71
Q

What is the cause of the second meiotic arrest at MII

A

The presence of a protein complex called cytostatic factor. Cytostatic factor contains c-Mos

72
Q

From what are the cortical granules derived?

A

Lysosomal granules from the Golgi

73
Q

How does LH change the endocrinology of the follicle?

A

Amortisation is stopped. Granulosa cell begin to produce progesterone instead, under the action of LH on their newly-acquired LH receptors. Granulosa cells stop being able to bind FSH and oestrogen, + instead bind progestins. There is an exponential rise in progesterone in the hours before ovulation as a result

74
Q

What are the roles of progesterone before the LH surge?

A
  1. Depresses the growth of less mature developing follicles; 2. Need for ovulation itself; 3. Used for the transition into the progesterone dominant phase of the ovarian cycle
75
Q

What is the purpose of the LH-induced follicular fluid expansion int he pre-ovulatory follicle?

A

Causes the follicle to bulge. The bulging wall = the stigma. The stigma becomes avascular, the tissue break down and the follicle ruptures

76
Q

What is the corpus luteum?

A

= the collapsed rupture dominant follicle. Looks like a molluscum on the surface of the ovary

77
Q

What do the granulosa cells become in the corpus luteum?

A

Large lutein cells

78
Q

What do the theca cells become int he corpus luteum?

A

Small lutein cells

79
Q

What hormones does the corpus luteum secrete?

A
  1. Progesterone; 2. Inhibin A; 3. Oxytocin
80
Q

What is the action of inhibin A in the corpus luteum?

A

Promotes progesterone synthesis

81
Q

When does luteolysis occur?

A

10-12 days post-ovulation should the woman not become pregnant

82
Q

What does the corpus luteum form following luteolysis?

A

Corpus albicans

83
Q

Why does luteolysis occur?

A

LH levels falling post-ovulation

Basic Human Reproduction (13 decks)

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