Extrusion of the first polar body occurs around the time of

In the tertiary follicle, the primary oocyte completes its meiosis I to divide to unequal large secondary oocyte and a tiny first polar body. Soon, the tertiary follicle transforms to Graafian follicle and is ready for ovulation. The primary oocyte emits the first polar body before ovulation. The second polar body is extruded from the oocyte as a consequence of oocyte activation triggered by the fertilizing spermatozoon.