Chapter 11. Germ Cell Viability and Movement and Abnormal Implantation Sites - Review of Medical Embryology Book

THREE TO FIVE-HUNDRED MILLION SPERM are placed in the posterior fornix of the vagina during intercourse, near the external os of the cervical canal

The sperm pass through the cervical canal by movement of their tails, whereas passage through the uterus and uterine tubes is facilitated by the muscular contractions of the walls of these organs
Transport time to the fertilization site is short and takes about an hour
About 300 to 500 sperm reach the fertilization site

THE OOCYTE, at ovulation, is carried in a peritoneal fluid stream, produced by the movements of the fimbriae of the uterine tube, into the infundibulum of the tube

The oocyte passes into the ampulla of the uterine tube due to action of the cilia of the epithelial cells and by muscular contraction of the tubal wall

PARTHENOGENESIS: oocyte is activated without sperm penetration and development may begin. No record of viable birth via this method

SUPERFECUNDATION may follow polyovulation. An oocyte is fertilized by spermatozoa from one male and another oocyte is fertilized by a second male. Seen in various mammals, not usual in man.
SUPERFETATION: ovulation and fertilization occur during an established pregnancy

Semen can be preserved in vitro for about 4 days and thus may actually survive that long in the female reproductive tract
After freezing (-79? C to -196? C), semen may be kept for about 10 years

THE HUMAN BLASTOCYST normally implants in the endometrium along the posterior wall of the body of the uterus, where it becomes attached between the openings of the endometrial glands or occasionally in the mouth of a glandular duct
NOT INFREQUENTLY, THE BLASTOCYST IMPLANTS IN ABNORMAL LOCATIONS outside the uterine body. This usually leads to the death of the embryo and severe hemorrhage of the mother during the second month of pregnancy. Such an implantation is called an extrauterine or ectopic pregnancy and may occur in the abdominal cavity, the ovary, the uterine tube or pelvis. Rarely does an extrauterine embryo come to full term

Tubal pregnancy is the most frequent ectopic sit The tube usually ruptures during the second month of pregnancy, resulting in severe internal hemorrhaging
Abdominal pregnancy: the peritoneal lining of the rectouterine cavity is the most frequent implantation sit Also on peritoneum of the intestinal tract or omentum

OCCASIONALLY, IMPLANTATION IN THE UTERUS ITSELF may lead to serious complications, particularly if implantation occurs near the internal os (low uterus). The placenta then bridges the os and we have what is called placenta previa which results in severe bleeding in the latter or second part of pregnancy and during delivery
FERTILIZED OVUM MAY ABNORMALLY MOVE to contralateral tube