Oogenesis and the Ovarian Cycle Flashcards Preview

ESA 4 - Reproductive System > Oogenesis and the Ovarian Cycle > Flashcards

Flashcards in Oogenesis and the Ovarian Cycle Deck (78):
1

When does maturation of oocytes begin? 

Before birth 

2

Where do germ cells arise from? 

The yolk sac

3

What happens after germ cells have arisen from the yolk sac of the female? 

They colonise the gondal cortex and differentiate into oogonia

4

What happens once germ cells have differentiated into oogonia? 

They proliferate rapidly by mitosis, and some enter meisois

5

What is oogonias entry into meisois 1 stimulated by? 

Mesonephric cells 

6

What are mesonephric cells? 

Flattened epithelial cells, also called Follicular Cells 

7

What happens to the oogonia in meisosis 1? 

They arrest in the diplotene stage (a resting stage) of prophase 1 

8

What causes oogonia to arrest in the diplotene stage of prophase 1? 

Due to Oocyte Maturation Inhibitor

9

What secretes Oocyte Maturation Inhibitor? 

Follicular cells 

10

What are the oogonias that are arrested in the diplotene stage now known as? 

Primary oocytes 

11

When is the maximum number of germ cells reached? 

Mid-gestation 

12

What happens to the number of germ cells at mid-gestation? 

Cell death begins, and many oogonia and primary oocytes degenerate 

13

What is the process of degeneration of oogenia and primary oocytes known as? 

Atresia 

14

What has happened to the oogonia by the 7th month of gestation? 

The majority of oogonia have degenerated 

15

How many primary oogonia survive by the 7th month of gestation? 

˜2 million 

16

What has happened all surviving primary oocytes by the 7th month of gestation? 

They have entered meisosis I, and are surrounded by a flat layer of epithelial cells- follicular cells 

17

What are the primary oocytes surrounded by follicular cells now called? 

Primordial follicles 

18

How long to the primordial follicles remain in meiosis I? 

At least until puberty 

19

What happens to most oocytes during childhood? 

Most undergo atresia

20

How many oocytes remain by puberty? 

˜40,000 

21

What is the clinical relevance of a woman having all the oocytes she will ever have at birth? 

Some may remain arrested for 50 years before further development, increasing the chance of cell damage and thus accounting for the increased risk of foetal chromosomal abnormalities in pregnancies of older women 

22

What happens to oocytes from puberty onwards? 

˜15-20 oocytes start to mature each month 

23

What stages do oocytes go through when maturing? 

  1. Pre-antral 
  2. Antral
  3. Pre-ovulatory 

 

24

What happens in the pre-antral stage of maturation? 

  • Primary oocyte grows dramatically, but does not re-start meiosis
  • Flat follicular cells become cuboidal Granulosa cells, and proliferate, producing stratified epithelium 

 

25

What do Granulosa cells do in the pre-antral stage? 

Secrete glycoprotein 

26

What is the purpose of the glycoprotein secreted by the Granulosa cells in the pre-antral stage? 

It surrounds the oocyte with a Zona Pellicuida 

27

What do surrounding connective tissue (stroma) cells form in the pre-antral stage? 

A Theca Folliculi 

28

What does the Theca Follucli consist of? 

  • An inner Theca Interna
  • An outer Theca Externa 

 

29

What are the characteristics of the Theca Interna? 

  • Vascular 
  • Endocrine

 

30

What is the Theca Externa? 

A fibrous capsule 

31

What do Theca and Granulosa cells collaborate to do? 

Secrete oestrogens 

32

33

What is the primary oocyte known as after the pre-antral stage? 

Primary follicle

34

What happens in the Antral stage of maturation? 

Granulosa cells continue to proliferate, and a fluid appears between them 

35

What does the appearance of fluid between the granulosa cells in the antral stage form? 

The antrum 

36

What happens as more fluid forms in the Antral stage? 

The secondary, or Graffian, follicle expands 

37

How big does the secondary follicle expand to in the Antral stage? 

2mm in diameter, without stimulation from reproductive hormones 

38

What does continued development of the secondary follicle, past 2mm, depend on in the Antral stage? 

Reproductive hormones 

39

What reproductive hormones are required to continue the development of the antrum in the Antral stage? 

  • FSH
  • LH

 

40

What does FSH bind to in the Antral stage? 

The Granulosa cells only 

41

What does LH bind to in the Antral stage? 

Thecal cells only

42

What do Thecal cells do under the influence of LH? 

Secrete androgens 

43

What happens to the androgens secreted from the Thecal cells? 

They are converted to oestrogens by Granulosa cells 

44

What is the conversion of androgens to oestrogens by the Granulosa cells under the influence of? 

FSH

45

When does the Pre-ovulatory phase begin? 

37 hours before ovulation 

46

What happens in the Pre-ovulatory stage? 

Oestrogen causes receptors for LH to appear on outer Granulosa cells 

 

47

What stimulates the LH receptors on the outside of Granulosa cells in the Pre-ovulatory stage? 

LH surge

48

What is the result of the stimulation of the receptors on the outer Granulosa cells by the LH surge? 

Rapid changes in the follicle 

49

What happens within 3 hours of the LH surge? 

The follicle restarts meiosis, and the first meitoic division is complete 

50

What is true of the first meiotic division in the pre-ovulatory stage? 

It is asymmetric

51

What is meant by the first meiotic division in the pre-ovulatory stage being asymmetric? 

Cytoplasm remains with one daughter cell, and the other forms a condensed polar body 

52

What happens after the first meiotic division in the pre-ovulatory stage? 

The secondary follicle enters meiosis II, and arrests again 3 hours prior to ovulation 

53

What happens to the follicle in the pre-ovulatory stage? 

It increases dramatically, to 25mm diameter 

54

Why does the follicle size increase dramatically in the pre-ovulatory stage? 

Due to increase in antral fluid volume 

55

What happens once the follicle has increased in size in the pre-ovulatory stage? 

The structure begins to weaken 

56

What happens to the weakened structure in the pre-ovulatory stage? 

LH stimulates collagease activity, leading to follicle rupture 

57

What happens to the ruptured follicle? 

The ovum is carried out in the fluid, and gathered up into the fallopian tube by the fimbria 

58

When is meiosis completed in the pre-ovulatory phase? 

When the ovum is fertilised

Not completed unless the ovum is fertilised 

59

What happens to unfertilised cells? 

They degenerate 24 hours after ovulation 

60

What promotes the development of the corpeus luteum? 

LH 

61

What happens in the development of the corpeus luteum? 

  • Remaining granulosa and theca interna cells become vascularised
  • Develop yellowish pigment and change into lutein cells 

 

62

What does the corpeus luteum do? 

Secretes oestrogen and progesterone 

63

What is the purpose of the secretion of oestrogen and progesterone by the corpus luteum? 

Stimulates uterine mucosa to enter secretory stage 

64

What is the purpose of the stimulation of the uterine mucosa to enter the secretory stage? 

It prepares for embyro implantation 

65

What happens to the corpeus luteum if no fertilisation occurs? 

Degenerates after 14 days 

66

What happens in the degeneration of the corpus luteum? 

  • Forms corpus albicans 
  • Progesterone production decreases 

 

67

What is the corpus albicans? 

A mass of fibrotic scar tissue 

68

What does a decrease in progesterone production precipitate? 

Menstrual bleeding 

69

What happens to the corpus luteum if fertilisation occurs? 

  • Degeneration of CL prevented by human chorionic gonadotrophin 
  • Corpus luteum continues to grow
  • Cells continue to secrete progrestone until about 4th month 

 

70

What secretes human chorionic gonadotrophin? 

The developing embryo

71

What does the continuation of growth of the corpus luteum when fertilisation occurs form? 

The corpus luteum of pregnancy, the corpus luteum graviditatis 

 

 

72

Why does the corpus luteum stop secreting progesterone at about the 4th month? 

The secretion of progesterone by the placenta then becomes adequate

73

What is the role of LH and FSH in ovulation? 

They stimulate the rapid growth of follicles several days before ovulation 

74

What is the mature follicle called? 

Graafian follicle

75

What does the LH surge cause? 

  • Increase in collagenase activity
  • Prostaglandin increase 

 

76

What do prostaglandins cause in ovulation? 

Local muscular contractions in ovarian wall, leading to the oocyte being extruded and breaking free from ovary 

77

What happens in oocyte transport? 

  • Shortly before ovulation, fimbriae sweep over surface of ovary, and uterine tubes begin to contract rhymthically 
  • Oocyte is carried into tube by sweeping movements of fimbriae, and by motion of cilia on epithelial linings 
  • Oocyte then propelled by peristaltic muscular contractions of tube and cila in the mucosa

 

78

How long does it take for the oocyte to reach the uterine lumen if fertilised? 

3 to 4 days