<P> For ovulation to be successful, the ovum must be supported by the corona radiata and cumulus oophorous granulosa cells . The latter undergo a period of proliferation and mucification known as cumulus expansion . Mucification is the secretion of a hyaluronic acid - rich cocktail that disperses and gathers the cumulus cell network in a sticky matrix around the ovum . This network stays with the ovum after ovulation and has been shown to be necessary for fertilization . </P> <P> An increase in cumulus cell number causes a concomitant increase in antrum fluid volume that can swell the follicle to over 20 mm in diameter . It forms a pronounced bulge at the surface of the ovary called the blister . </P> <P> Estrogen levels peak towards the end of the follicular phase . This causes a surge in levels of luteinizing hormone (LH) and follicle - stimulating hormone (FSH). This lasts from 24 to 36 hours, and results in the rupture of the ovarian follicles, causing the oocyte to be released from the ovary . </P> <P> Through a signal transduction cascade initiated by LH, proteolytic enzymes are secreted by the follicle that degrade the follicular tissue at the site of the blister, forming a hole called the stigma . The secondary oocyte leaves the ruptured follicle and moves out into the peritoneal cavity through the stigma, where it is caught by the fimbriae at the end of the fallopian tube . After entering the fallopian tube, the oocyte is pushed along by cilia, beginning its journey toward the uterus . </P>

When does ovulation occur in the ovarian cycle
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