Figure 1.

Structural changes in the dominant follicle during ovulation. Before the LH surge, the oocyte (pink) is surrounded by the zona pellucida (gray) and tight cumulus granulosa cells (light green); mural granulosa cells (dark green) surround the follicular fluid (yellow). Outside the granulosa cell basement membrane (gray), stromal components include theca cells (purple) and small vessels (red). The follicle apex is covered by the ovarian surface epithelium (blue). In response to the LH surge, the oocyte resumes meiosis and produces the first polar body. The cumulus expands and detaches from the mural granulosa cells. Luteinization includes hypertrophy of granulosa cells and invasion of theca cells and new vessels into the granulosa cell layer. A breach in the ovarian surface epithelium, underlying stroma, and mural granulosa cells results in rupture at the follicle apex. Mural granulosa cells protrude through the rupture site to form an ovulatory stigmata. The ovulatory canal permits release of the cumulus-oocyte complex (COC).