Fertilization of a secondary oocyte by a spermato wan usually occurs in the

After the secondary oocyte is released from the ovary, it is captured by the fimbriae of the uterine tube. In the uterine tube, the oocyte enters the funnel-shaped infundibulum, reaches the abdominal ostium, and pas­ses through the ampulla. Here, a spermatozoan typi­cally fertilizes the oocyte. The fertilized ovum or the unfertilized secondary oocyte then moves through the narrow isthmus of the uterine tube to reach the intra­mural or uterine portion of the tube (that pan of the tube that is within the wall of the uterus). After the fertilized ovum enters the uterus, it implants in the uterine wall. By this time, the embryo has developed into the blastocyst stage. If passage of the fertilized ovum through the uterine tube is restricted, implanta­tion into the tubal wall may occur.