Fetus and Placenta III
Umbilical Cord and AmnionThe cephalocaudal and lateral folding of the embryonic disk during the 2nd month of development lead to the formation of a ring at the junction of the amnion and the ectoderm. This ring is called the primitive umbilical ring that contains the following:
The umbilical cord and amnion:
1.the connecting stalk containing the allantois and two umbilical arteries and one umbilical vein.
2.the vitelline duct of the yolk sac or called the yolk sac stalk containing the vitelline vessels.
3.a canal connecting the intraembryonic cavity with the extraembryonic cavity.
The umbilical cord and amnion:
The amniotic cavity is enlarged to fill the extraembryonic chorionic cavity at the end of the 3rd month of pregnancy.
This will lead to compression and obliteration of the yolk sac in the chorionic cavity, also the enlarged amnion compresses the contents of the primitive umbilical ring and enclosing them to form the primitive umbilical cord which contains:
The umbilical cord and amnion:
1.distally; the vitelline duct and umbilical vessels.
2.proximally; the allantois , umbilical vessels and a loop of the intestine that herniated in the umbilical cord because of the small abdominal cavity. This hernia is called the physiological umbilical hernia that withdrawn into the abdomen at the end of the third moth.The allantois and the vitelline duct and vessels obliterate in the full term umbilical cord, therefore; the mature cord contains only the umbilical vessels surrounded by the proteoglycan material called Wharton jelly that protects the vessels.
The walls of the umbilical arteries are rich with muscular and elastic tissue to be contractible after birth.
The umbilical cord and amnion:
Features of the normal full term umbilical cord:
1.2cm in diameter. 50cm in length.Longer cord may encircle the fetal neck, and shorter cord pulls the placenta during delivery.
2.tortuous causing false knots.
3.contains two arteries and one vein. Vascular abnormality of the cord may be associated with cardiovascular anomalies.
The umbilical cord and amnion:
Features of the normal amniotic fluid:
This fluid produced by the amniotic cells but is derived from the maternal blood. It is :1.clear and watery.
2. 30ml at 10 weeks,
450 at 20 weeks,
800-1000ml at birth.
3. fetus swallow about half of the fluid in each day,
4.fetus urinate water in the amniotic fluid since the 5th month,
5.the fluid is replaced every 3hours.
The umbilical cord and amnion:
Features of the normal amniotic fluid:
Function of the amniotic fluid:
• protects the suspended fetus,
• absorb jolts
• allow fetal movement by preventing adhesion of the fetus with the amnion.
• act as a hydrostatic wedge (or bag) to dilate the birth canal.
The umbilical cord and amnion:
A: dizygotic twins (fraternal):
2/3 of twins …………. 7-11/1000they result from the fertilization of two ova, having the following criteria:
1.they differ in genes and so are dissimilar to each other in shape and may be in sex. .
2.each has its own implanted site and its own placenta, amnion, and chorion.
Sometimes the two placentas or the chorionic sac may be near together and fused, fusion of the placentae may cause exchange of the blood groups of the fetuses and this is called erythrocyte mosaicism.
The twins:
The twins:
dizygotic twins (fraternal):
B: monozygotic twins (identical):
result from splitting of the fertilized ova or zygote at any stage during the development. The splitting may occur:
1.at two cells stage; resulting in two separate embryos that implanted separately, each has its own placenta, amnion and chorion. Both embryos develop the same blood group, finger print, sex, and external appearance.
The twins:
B: monozygotic twins (identical):
2.at inner cell mass of the blastocyst stage; both embryos have the same placenta and chorion, but each of them has its own amnion.The twins:
B: monozygotic twins (identical):
3.at the bilaminar germ disc; both embryos have the same placenta, amnion, and chorion.The twins:
Twins
monozygotic twins
(identical):
3-4/1000
Twin pregnancies have a high incidence of perinatal mortality and morbidity and a tendency toward preterm delivery.
only 29% of women pregnant with twins actually give birth to two infants
vanishing twin refers to the death of one fetus.
twin transfusion syndrome, which occurs in 5 to 15% of monochorionic monozygotic pregnancies
Twin defects
At later stages of development, partial splitting of the primitive node and streak may result in formation of conjoined (Siamese) twins.
- thoracopagus ; pygopagus ; and craniopagus
Twin defects
• effacement (thinning and shortening) and dilatation of the cervix; this stage ends when the cervix is fully dilated
Parturition (Birth)
• 2. delivery of the fetus• 3. delivery of the placenta and fetal
• membranes.
contractions usually begin about 10 minutes apart; then, during the second stage of labor, they may occur less than 1 minute apart and last from 30 to 90 seconds.
Parturition (Birth)
NVD
CS
