Oogenesis and the ovarian cycle

Question 1

4 stages of gametogenesis

Answer 1

1) germ cells migrate to gonads
2) increase in germ cell number
3) reduction of chromosome number
4) maturation

Question 2

What are premordial germ cells

Answer 2

common ancestors of oocytes spermatozoa

Question 3

What happens at the beginning of phase 1 of gametogenesis

Answer 3

Primordiol germ cells leave the primary ectoderm and move to yolk sac wall, collecting near exit of allantois

Question 4

What happens at week 6 during phase 1 of gametogenesis?

Answer 4

Primordiol germ cells leave yolkd sac and migrates along the vitelline and dorsal mesentery into gonadal ridge.

Question 5

What happens at week 7 during phase 1 of gametogenesis?

Answer 5

Testosterone produced if male infant encoded for by Y chromosome

Question 6

What happens in phase 2 of gametogenesis

Answer 6

There is an increase in germ cell number

Question 7

When do oogonia undergo intensive mitosis?

Answer 7

2 to 5 months in embryonic ovary of maternal pregnancy

Question 8

How many diploid cells are produced by each germ clel in phase 2?

Answer 8

2 (2n)

Question 9

What two cell divisions occur in phase 3 of gametogenesis?

Answer 9

Meiosis 1- reduction division. 2n–1n

Meiosis 2- equatorial division. Independent reassortment of maternal and paternal chromosome

Question 10

What 4 events occur in phase 3 of gametogenesis?

Answer 10

1- DNA replication but still 2n and 2c
2- Pairing of homologous chromosomes. Four chromatids= tetrads. Cells now 2n 4c
3- Separation of chromosomes due to first meiotic division. 2 daughter cells have 1n and 2c
4- seperation of chomatids occurs as result of second meiotic division. 1n and 1c

Question 11

When do oogonia enter first meiotic division?

Answer 11

Late fetal period

Question 12

When does primary oocyte complete meiosis 1?

Answer 12

shortly before ovulation with each menstrual cycle

Question 13

What is produced from meiosis 1?

Answer 13

Secondary oocyte and first polar body

Question 14

Where is meiosis 2 arrested?

Answer 14

Metaphase

Question 15

What triggers completion of metaphase 2

Answer 15

Fertilisation

Question 16

What is produced by meiosis 2

Answer 16

Fertilised egg and second polar body

Question 17

What happens in phase 4 of gametogenesis?

Answer 17

Structural and functional maturation

Question 18

How many primary oocyte are present at birth?

Answer 18

2,000,000

Question 19

How many primary oocytes survive to puberty?

Answer 19

40,000

Question 20

What happens to the oogonia as meiosis begins?

Answer 20

Surrounded by other ovarian cells to form primordiol follicle

Question 21

What are granulosa cells?

Answer 21

Cells surrounding the primary oocyte

Question 22

What makes up the zona pellucida?

Answer 22

Contributes from oocyte and granulosa cells

Question 23

What cells form a second layer around the follicle

Answer 23

Early theca cells

Question 24

What do thecal cells secrete

Answer 24

Angiogenic factors

Question 25

What stimulates further development of the primary follicle

Answer 25

FSH

Question 26

What is the effect of FSH of the follicle?

Answer 26

Stimulates oestrogen production by granulosa cells. | Cavity called antrum formed now a secondary follicle

Question 27

What is required for further follicle enlargement and maturation

Answer 27

Activin (stimulates granulosa cell proliferation)

Question 28

What hormone is required to enlarge/ mature the cell after activin?

Answer 28

LH

Question 29

What is the effect of increased LH production?

Answer 29

Stimulates testosterone production from theca cells

Question 30

Effect of testosterone in follicle

Answer 30

Enters granulosa cells and converted to oestrogen by aromatase Oestradiol stimulates formation of LH receptors on granulosa cells Enables follicles to respond to LH surge

Question 31

What is the role of oestrogen from follicle

Answer 31

Prepares reproductive tract for fertilisation

Question 32

What is contained in the antrum

Answer 32

Enzymes and proteoglycans

Question 33

Role of enzymes and proteoglycans in antrum

Answer 33

``` Enzymes= digest follicular wall Proteoglycans= negative charge to attract water molecules ```

Question 34

What happens when the follicle is ready for ovulation

Answer 34

Expulsion of oocyte Oocyte swept into oviduct Peristatic action carries oocyte to uterus

Question 35

What is menarche

Answer 35

First menstruation

Question 36

What happens in the months leading up to menarche?

Answer 36

Pulses of GNRH causes fluctuations of oestrogen levels | Oestrogen levels fluctuate because of follicular development to reach ovulation

Question 37

How do fluctuating oestrogen levels affect endometrium?

Answer 37

Undergoes cycles of proliferation and regression

Question 38

When does first ovulation occur?

Answer 38

6-9 months after mencarche

Question 39

Name the three stages of ovulation

Answer 39

Follicular stage Ovulatory stage Luteal stage

Question 40

If a women's cycle is long, which stage is long

Answer 40

Follicular stage

Question 41

What happens during follicular phase of ovarian cycle?

Answer 41

days 1-10 5-12 premordiol follicles stimulated to grow and develop only one will form mature follicle

Question 42

What happens during the ovulatory phase of ovarian cycle?

Answer 42

11-14. preparation for ovulation. Mature follicle bulges from wall of ovary.

Question 43

What happens during the luteal phase of the ovarian cycle?

Answer 43

15-28 Menstruation Granulosa cells divide and form corpus luteum Secretes hormones that maintain the maternal endometrium