Oogenesis Flashcards
What cells are gametes derived from?
Primordial Germ Cells (PGCs)
Were are PGCs formed? Then they move to…
Epiblast, then move to wall of Yolk Sac (WEEK 2)
What happens after PGCs move to YS?
They migrate to gonads (WEEK 4)
When do PGCs arrive at gonads?
Week 5 - increase in number by mitosis
When PGCs arrive at Female Gonads…
They differentiate into Oogonia (many mitotic devisions forming clusters by month 3)
What are found around oogonia clusters?
Flat epithelial Follicular cells
Primary oocytes phase?
Arrested in prophase of Meiosis I
What happens by Month 7 of oogenesis?
Most primary oocytes + oogonia degenerate, any surviving enter Prophase of Mei-1 and surrounded by follicular epithelial cells = PRIMORDIAL FOLLICLE
What happens to Primary oocytes near birth?
Enter Meiosis 1 but Do not enter metaphase, they enter diplotene stage
What is Diplotene stage? + What causes it?
Primary oocytes remain arrested and do not enter metaphase until puberty, Oocyte maturation inhibitor OMI (formed by follicular cells)
How many oocytes become ovulated?
Only around 500 of the original 7 million
How many follicles are selected each month to mature?
15 - 20, some die and some accumulate in antrum entering Antral/vesicular stage
What happens to follicles before ovulation?
Fluid accumulates in the follicle calling them Mature vesicular follicles (Graafian follicles)
What happens to follicular cells as primordial follicles grow?
They change from flat to cuboidal, form a stratified epithelium of Granulosa cells = Primary Follicle
What forms the Zona Pellucida?
Granulosa cells and Oocyte
Outer Theca
Formed by ovarian conn. tissue, Theca folliculi separates Theca interna from externa
Antrum
Is a fluid accumulation forming a Vesicular/Antral follicle
What is Mature follicle called?
Mature vesicular (Graafian) follicle, Cumulus oophorus around oocyte
Hormones in follicle maturity + Outcome
Surge in Luteinizing hormone (LH)
What happens after surge of LH
Meiosis 1 completed, forms 2 daughter cells, only one has cytoplasm = Secondary Oocyte, other is first polar body
Step after secondary oocyte + polar body form
The Secondary oocyte enters Meiosis II but does NOT complete it until Fertilization
