Three follicular stages are recognised,
1) Primary/Preantral Follicles (with primary oocyte inside)
2) Secondary/Antral Follicles (with primary oocyte inside)
3) Pre Ovulatory Follicles (with secondary oocyte inside)
Pre ovulatory Follicles are formed ~36 hrs before ovulation at time of LH surge. This coincides with completion of Meiosis I and formation of the secondary oocyte. The secondary oocyte immediately enters Meosis II.
Appx. 3 hrs before ovulation, the Pre ovulatory Follicle (with the secondary oocyte inside) is arrested in the metaphase of Meiosis II and is extruded out of the ovary - a process called as Ovulation.
It comes to rest in the ampulla of the fallopian tube and here it is fertilised. As the sperm pronucleus is released into the cytoplasm, the Secondary Oocyte (now called the ovum) completes Meiosis II and releases the second polar body.
Hope this helps.
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