423During each menstrual cycle, an egg is released by one of the ovaries. This is called ovulation. The egg travels into the fallopian tube. If fertilization is to occur, sperm ejaculated into the vagina must swim up through the uterus and into the fallopian tube, where the sperm penetrates the egg, as shown here. The fertilized egg travels into the uterus, where it imbeds itself in the wall of the uterus, or endometrium.
