Oogenesis and the ovarian cycle Flashcards
4 stages of gametogenesis
1) germ cells migrate to gonads
2) increase in germ cell number
3) reduction of chromosome number
4) maturation
What are premordial germ cells
common ancestors of oocytes spermatozoa
What happens at the beginning of phase 1 of gametogenesis
Primordiol germ cells leave the primary ectoderm and move to yolk sac wall, collecting near exit of allantois
What happens at week 6 during phase 1 of gametogenesis?
Primordiol germ cells leave yolkd sac and migrates along the vitelline and dorsal mesentery into gonadal ridge.
What happens at week 7 during phase 1 of gametogenesis?
Testosterone produced if male infant encoded for by Y chromosome
What happens in phase 2 of gametogenesis
There is an increase in germ cell number
When do oogonia undergo intensive mitosis?
2 to 5 months in embryonic ovary of maternal pregnancy
How many diploid cells are produced by each germ clel in phase 2?
2 (2n)
What two cell divisions occur in phase 3 of gametogenesis?
Meiosis 1- reduction division. 2n–1n
Meiosis 2- equatorial division. Independent reassortment of maternal and paternal chromosome
What 4 events occur in phase 3 of gametogenesis?
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
When do oogonia enter first meiotic division?
Late fetal period
When does primary oocyte complete meiosis 1?
shortly before ovulation with each menstrual cycle
What is produced from meiosis 1?
Secondary oocyte and first polar body
Where is meiosis 2 arrested?
Metaphase
What triggers completion of metaphase 2
Fertilisation
What is produced by meiosis 2
Fertilised egg and second polar body
What happens in phase 4 of gametogenesis?
Structural and functional maturation
How many primary oocyte are present at birth?
2,000,000
How many primary oocytes survive to puberty?
40,000
What happens to the oogonia as meiosis begins?
Surrounded by other ovarian cells to form primordiol follicle
What are granulosa cells?
Cells surrounding the primary oocyte
What makes up the zona pellucida?
Contributes from oocyte and granulosa cells
What cells form a second layer around the follicle
Early theca cells
What do thecal cells secrete
Angiogenic factors
What stimulates further development of the primary follicle
FSH
What is the effect of FSH of the follicle?
Stimulates oestrogen production by granulosa cells.
Cavity called antrum formed now a secondary follicle
What is required for further follicle enlargement and maturation
Activin (stimulates granulosa cell proliferation)
What hormone is required to enlarge/ mature the cell after activin?
LH
What is the effect of increased LH production?
Stimulates testosterone production from theca cells
Effect of testosterone in follicle
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
What is the role of oestrogen from follicle
Prepares reproductive tract for fertilisation
What is contained in the antrum
Enzymes and proteoglycans
Role of enzymes and proteoglycans in antrum
Enzymes= digest follicular wall Proteoglycans= negative charge to attract water molecules
What happens when the follicle is ready for ovulation
Expulsion of oocyte
Oocyte swept into oviduct
Peristatic action carries oocyte to uterus
What is menarche
First menstruation
What happens in the months leading up to menarche?
Pulses of GNRH causes fluctuations of oestrogen levels
Oestrogen levels fluctuate because of follicular development to reach ovulation
How do fluctuating oestrogen levels affect endometrium?
Undergoes cycles of proliferation and regression
When does first ovulation occur?
6-9 months after mencarche
Name the three stages of ovulation
Follicular stage
Ovulatory stage
Luteal stage
If a women’s cycle is long, which stage is long
Follicular stage
What happens during follicular phase of ovarian cycle?
days 1-10
5-12 premordiol follicles stimulated to grow and develop
only one will form mature follicle
What happens during the ovulatory phase of ovarian cycle?
11-14. preparation for ovulation. Mature follicle bulges from wall of ovary.
What happens during the luteal phase of the ovarian cycle?
15-28
Menstruation
Granulosa cells divide and form corpus luteum
Secretes hormones that maintain the maternal endometrium
