Ovulation is the release of an egg cell from a mature ovarian follicle (see figure 1-5 for ovulation).

Ovulation is stimulated by hormones from the anterior pituitary gland, which apparently causes the mature follicle to swell rapidly and eventually rupture. When this happens, the follicular fluid, accompanied by the egg cell, oozes outward from the surface of the ovary and enters the peritoneal cavity.

After it is expelled from the ovary, the egg cell and one or two layers of follicular cells surrounding it are usually propelled to the opening of a nearby uterine tube. If the cell is not fertilized by union of a sperm cell within a relatively short time, it will degenerate.