11. Germ Cell Viability and Movement and Abnormal Implantation Sites

  1. Sperm transport
    1. 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
      1. 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
      2. Transport time to the fertilization site is short and takes about an hour
      3. About 300 to 500 sperm reach the fertilization site
  2. Oocyte transport
    1. 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
      1. 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
  3. Fertilization site is in the tubal ampulla, its widest and longest portion
    1. UNFERTILIZED OOCYTES undergo dissociation in the uterus
  4. Abnormal fertilization
    1. PARTHENOGENESIS: oocyte is activated without sperm penetration and development may begin. No record of viable birth via this method
      1. Cleaving oocytes in ovary may develop into an ovarian teratoma
    2. 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.
    3. SUPERFETATION: ovulation and fertilization occur during an established pregnancy
  5. Viability of the germ cell
    1. SPERM remain alive in vivo for about a day or so
      1. Semen can be preserved in vitro for about 4 days and thus may actually survive that long in the female reproductive tract
      2. After freezing (-79? C to -196? C), semen may be kept for about 10 years
    2. OOCYTES are usually fertilized within 12 hours after ovulation
      1. Unfertilized oocytes, in vitro, die within 12-24 hours
  6. Abnormal implantation sites:
    1. 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
    2. 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
      1. Tubal pregnancy is the most frequent ectopic sit The tube usually ruptures during the second month of pregnancy, resulting in severe internal hemorrhaging
      2. Abdominal pregnancy: the peritoneal lining of the rectouterine cavity is the most frequent implantation sit Also on peritoneum of the intestinal tract or omentum
    3. 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
    4. FERTILIZED OVUM MAY ABNORMALLY MOVE to contralateral tube

germ cell viability and movement and abnormal implantation sites: image #1