- Oogenesis : The process of formation of ovum from oogonia.
- Oogonia are germ cells in ovary.
- Ovary is female gonad seen in 10th week of intrauterine life.
- 5th month of intrauterine life : maximum number of oogonia/germ cells are present in ovary.They are ~7 millions.
- 7th month of intrauterine life : Oogonia undergoes atresia to leave behind primary oocyte surrounded by follicle cells.This primary oocyte surrounded by follicle cells is known as primordial follicle.
- At birth : primary oocyte enters into prophase meiosis 1 and is arrested in this stage.This arrest is due to inhibition by OMI(ovulatory maturation inhibitor).
- This arrest is continued till puberty.
- At puberty : Menses cycle begins and thus ovulation.Here primordial follicle begins growing further.15-20 follicles are selected every month from pool of follicles.They are passed through 3 stages here-primary follicle,secondary follicle or graffian follicle and preovulatory stage.
- 36 hrs before ovulation : meiosis 1 is completed to form secondary oocyte and first polar body.
- 3 hrs before ovulation : secondary oocyte enters into metaphase meiosis 2 and arrested in this stage.
- Further progression of secondary oocyte occurs if fertilization occurs.Without fertilization secondary oocyte is degenerated.
