10. Composition of Amniotic Fluid
⢠99 % is water
⢠Desquamated fetal epithelial cells
⢠Organic & inorganic salts
⢠Protein, carbohydrates, fats, enzymes, hormones
⢠Meconium & urine in the late stage
Abnormalities of amniotic fluid
⢠Oligo-hydramnios: the volume of the amniotic fluid is less than ½ litre. This may lead to
adhesions between the embryo and the amnion.
⢠Poly-hydramnios: the volume of the amniotic fluid is more than 2 litres. This may lead to
premature rupture of the amnion.
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11. Significance of Amniotic Fluid
⢠Permits symmetrical external growth of the embryo and fetus
⢠Acts as a barrier to infection
⢠During labor it help dilatation of the cervix of the uterus and It wash birth canal and
protect the fetus against infections
⢠Prevents adherence of amnion to fetus
⢠Cushions & protects the embryo and fetus
⢠Helps maintain the body temperature
⢠Enables the fetus to move freely
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12. Yolk Sac
⢠It is large at 32 days
⢠Shrinks to 5mm pear shaped
remnant by 10th week &
connected to the midgut by a
narrow yolk stalk
⢠Becomes very small at 20
weeks
⢠Usually not visible thereafter
Primary yolk sac
secondary yolk sac
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13. Significance of Yolk Sac
⢠Has a role in transfer of nutrients during the 2nd and
3rd weeks
⢠Blood development first occurs here
⢠Incorporate into the endoderm of embryo as a
primordial gut
⢠Primordial germ cells appear in the endodermal lining
of the wall of the yolk sac in the 3rd week
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14. Fate of Yolk Sac
⢠At 10 weeks lies in the chorionic cavity between chorionic and amniotic sac
⢠Atrophies as pregnancy advances
⢠Sometimes it persists throughout the pregnancy but of no significance
⢠In about 2% of adults the proximal intra-abdominal part of yolk stalk persists
as an ileal diverticulum or Meckel diverticulum
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15. Allantois
⢠In the 3rd week it appears as a
sausagelike diverticulum from the
caudal wall of yolk sac that extends
into the connecting stalk
⢠During the 2nd month, the
extraembryonic part of the allantois
degenerates Mohamed el fiky
16. Functions of Allantois
⢠Blood formation occurs in the wall during the 3rd to 5th
week
⢠Its blood vessels persist as the umbilical vein and
arteries
⢠Becomes Urachus and after birth is transformed into
median umbilical ligament extends from the apex of
the bladder to the umbilicus
Anomalies of allantois:
⢠Urachal fistula: The urachus remains patent, urine
discharges from the umbilicus.
⢠Urachal sinus: The upper end of the urachus remains
patent.
⢠Urachal cyst :The middle part of the urachus remains
patent.
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18. Structure: It consists of mesodermal
connective tissue called Wharton's
jelly, covered by amnion.
It contains:
1. One umbilical vein carries
oxygenated blood from the placenta
to the foetus
2. Two umbilical arteries carry
deoxygenated blood from the foetus
to the placenta,
3. Remnants of the yolk sac and
allantois.
The Umbilical Cord
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19. Insertion:
â˘The cord is inserted in
the foetal surface of the
placenta near the center
"eccentric insertion"
(70%)
⢠Or at the center "central
insertion" (30%).
The Umbilical Cord
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21. (A) Abnormal cord insertion
1. Marginal insertion : in the placenta ( battledore insertion).
2. Velamentous insertion: in the membranes and vessels
connect the cord to the edge of the placenta.
⢠If these vessels pass at the region of the internal os , the
condition is called " Vasa praevia".
1. Short cord which may lead to :
i-Intrapartum haemorrhage due to premature separation of the
placenta,
ii-Delayed descent of the foetus druing labour,
iii-Inversion of the uterus.
2. Long cord which may lead to
i-Cord presentation and cord prolapse,
ii-Coiling of the cord around the neck,
iii-True knots of the cord. Mohamed el fiky
Velamentous insertion(B) Abnormal cord length
22. Chorion
Chorion
1- extraembryonic mesoderm
2- cytotrophoblast
3- Syncytiotrophoblast
Chorion
⢠Definition : Chorion is the name given
to the trophoblast after the formation
of the extraembryonic mesoderm
from its inner surface.
⢠The chorion is composed of :
⢠Syncito-trophoblast (outer layer).
⢠Cytotrophoblast (middle layer).
⢠Extra-embryonic mesoderm (inner
layer).
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24. Chorion
⢠Chorionic villi cover the entire chorionic sac until the beginning of 8th week
⢠As this sac grows, the villi associated with decidua capsularis are compressed, reducing the
blood supply to them
⢠These villi soon degenerates producing an avascular bare area smooth chorion (chorion
laeve)
⢠As the villi disappear, those associated with the decidua basalis rapidly increase in number
⢠Branch profusely and enlarge
⢠This bushy part of the chorionic sac is villous chorion
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25. CHORIONIC VELLI
⢠By the beginning of the third week, the trophoblast is characterized by
primary villi that consist of a cytotrophoblastic core covered by a syncytial
layer. During further development, mesodermal cells penetrate the core of
primary villi and grow toward the decidua. The newly formed structure is
known as a secondary villus .
⢠By the end of the third week, mesodermal cells in the core of the villus begin
to differentiate into blood cells and small blood vessels, forming the villous
capillary system . The villus is now known as a tertiary villus or definitive
placental villus. Mohamed el fiky
28. Tertiary villus
During 3rd week, arterioles,
venules & capillaries
develop in the mesenchyme
of villi & join umbilical
vessels
By the end of 3rd week,
embryonic blood begins to
flow slowly through
capillaries in chorionic villi
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30. Parts of decidua
⢠Decidua basalis: It is the part of decidua
between blastocyst and myometrium. It
forms the fetal part of placenta.
⢠Decidua capsularis: It covers the
blastocyst except embryonic pole and
separates it from uterine cavity.
⢠Decidua parietalis: It is the rest of
endometrium that lines the rest of
uterine cavity. Mohamed el fiky
32. 32
PLACENTA
⢠This is a fetomaternal organ.
⢠It has two components:
⢠Fetal part â develops from the chorion
frondosum )
⢠Maternal part â derived from the decidua
basalis )
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34. ⢠During the 4th and 5th month, the decidua forms a number of
decidual septa, which project into the intervillous space.
⢠As a result of this septum formation, the placenta is divided
into a number of compartments (cotyledons).
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36. 36
It separates fetal from maternal
blood.
It prevents mixing of them.
It is an incomplete barrier as it
only prevents large molecules to
pass ( heparin & bacteria)
But cannot prevents passage of
viruses(e.g. rubella), micro-
organisms(toxoplama, treponema
pallidum) drugs and hormones.
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37. is discoid in shape.
n Diameter = 15-25 cm,
n 2-3 cm thick,
n Weight = 0.5 kg.
n Umbilical cord is attached to its center.
nPosition : in the upper uterine
segment (99.5%), either in the posterior
surface (2/3) or the anterior surface (1/3).
The full term placenta
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43. 3- Abnormal attachment of umbilical cord:
a- Velamentous attachment:
The cord does not reach the placenta itself but is attached to amniotic membrane over the
fetal surface of placenta. The umbilical vessels pass in the membrane to reach the placenta.
It is easly torn.
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46. Twins
⢠Di-zygotic twins
⢠Incidece : more common (70%).
⢠Mechanism of development : results from fertilization of 2 ova (from 2
ovaries ) during an overian cycle by 2 separate sperms.
⢠Placenta : 2 separate placentae.
⢠Chorion : 2 separate chorionic sacs.
⢠Sex : may be of the same or different sex.
⢠Features : different fetures. Mohamed el fiky
47. Twins
â˘zygotic -Mono
⢠Incidece : less common. results from fertilization of one ova by one sperms.
⢠Mechanism of development : results from division of a single fertilized ovum
during one of the following stages of development:
⢠Two cell stage.
⢠Stage of blastocyst, where the inner cell mass divides into 2 masses.
⢠Placenta : single common placenta.
⢠Chorion : single common chorionic sac.
⢠Sex : always of the same sex.
⢠Features : exactly identical.
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