9. It is the wall of chorionic vesicle.
Time: Chorionic vesicle is formed at the 12th
day
by the formation of extra-embryonic mesoderm.
Structure of chorion:
1- Syncytiotrophoblast.
2- Cytotrophoblast.
3- Somatic extra-embryonic mesoderm.
Chorionic velli:
1- Primary.
2- Secondary.
3- Tertiary.
Dr. Sherif Fahmy
15. 1- Primary chorionic velli (start of 3rd
week):
cyncytiotropholblasts and cytotrophoblast.
2- Secondary chorionic velli (middle of 3rd
week):
Cyncytiotrophoblast, cytotrophoblast and
mesoderm (in the central core).
3- Tertiary chorionic velli (end of 3rd
week):
formation of fetal blood vessels in the mesoderm.
-Tertiary velli, opposite decidua basalis form side
branches and called chorion frondosum while under
decidua capsularis it will degenerates to form chorion
leave.
Dr. Sherif Fahmy
Dr. Sherif Fahmy
17. Morphology of Placenta
• It is the organ of exchange of materials between fetal
and maternal blood.
• Shape: Disc like.
• Surfaces:
• -Fetal surface: It is covered with amnion and fetal blood
vessels. Umbilical cord is attached near the center of this
surface.
• -Maternal surface: Shows 15 – 20 rounded elevations
(cotyledons) with septa inbetween).
• Diameter: 15 -25 cm.
• Thickness: About 3 cm.
• Weight: About 500 – 600 gm
• Site: At original implantation site which is upper part of
posterior wall of uterus.
Dr. Sherif Fahmy
Dr. Sherif Fahmy
26. Structure of Placenta
• The placenta is developed from 2 parts:
Chorion frondosum (tertiary velli) and
Decidua basalis. The internal structure of
placenta is described as follow:
• 1- Chorionic velli: They are stem and
absorbing (floating). They are composed
of syncytiotrophoblast, cytotrophoblast,
mesoderm and fetal blood vessels.
• 2- Intervillous spaces: They are spaces
between stem villi that are filled with
maternal blood.
Dr. Sherif Fahmy
Dr. Sherif Fahmy
27. 3- Cytotrophoblastic shell; complete
sheet of cytotrophoblastic cells that is
present between decidua basalis and
intervillous spaces.
4- Decidual septa: They descend from roof
of intervillous spaces. Each septum is
composed of decidua basalis,
cytotrophoblast and cyncytiotrophoblasts.
There is a groove opposite each septum
which are separated from each other by
cotyledones.
5- Chorionic plate: composed of amnion,
extraembryonic mesoderm,cytotrophoblast
and syncytiotrophoblast.
Dr. Sherif Fahmy
Dr. Sherif Fahmy
28. 6- Decidual plate: composed of:
- Syncytiotrophoblast.
- Cytotrophoblast.
- Decidua basalis.
Dr. Sherif Fahmy
Dr. Sherif Fahmy
29. Placental barrier:
It is the separation between fetal and maternal
blood.
Structure:
1- Syncytiotrophoblast.
2- Cytotrophoblast.
3- Extraembryonic mesoderm.
4- Endothelium of fetal blood vessels.
Functions of the barrier:
1- Separates between fetal and maternal blood.
2- Permites gaseous and nutritive exchange.
3- Prevents passage of bacteria, most viruses
and damaging factors.
Disappear in 2nd
½ of pregnancy
Dr. Sherif Fahmy
Dr. Sherif Fahmy
30. Placental circulation:
1- Maternal part: Maternal blood flow from
endometrial arterioles to the intervillous
spaces where floating velli are bathed in
maternal blood. Exchange of gases and
nutritive materials occurs. Then blood flows
back from chorionic plate to endometrial
veins.
2- Fetal part: umbilical arteries carry
venous blood of the fetus to placenta while
umbilical veins carry blood loaded with
nutritive material and oxygen. Dr. Sherif Fahmy
Dr. Sherif Fahmy
31. Functions of placenta
1- Exchange of gases and metabolites.
2- Transmission of maternal antibodies
starting from 14th
week.
3- Production of hormones as progesterone,
estrogen, HCG and somatomammotropin
3- Barrier against bacteria and most of viruses.
4- Excretory function as it excretes urea and
creatinine.
Dr. Sherif Fahmy
Dr. Sherif Fahmy
32. Anomalies of Placenta
1- Abnormalities in position:
A- Placenta previa parietalis.
B- Placenta brevia marginalis.
C- Placenta brevia centralis.
2- Abnormality in shape:
A- biloped placenta.
B- Triloped placenta.
3- Abnormality in number:
A- Twin placenta.
B- Accessory placenta.
4- Abnormality in attachement of umbilical cord:
A- Velamentous.
B- Battle door. Dr. Sherif Fahmy
Dr. Sherif Fahmy
42. AMNION
-It is a membrane that enclose amniotic cavity.
-Formation:
-It is formed at the 8th
day as a small cavity in
epiblast cells with formation of amnioblasts.
-So, floor of the cavity is epiblast while the
roof is formed from amnioblasts.
-By the 12th
day it becomes separated from
cytotrophoblasts by primary mesoderm
(Extraembryonic).
-Amnio-ectodermal junction is at the margin
of oval embryonic disc at the 3rd
week.Dr. Sherif Fahmy
Dr. Sherif Fahmy
43. 8th
day of pregnancy
Dr. Sherif Fahmy
Endometrium
Syncytio-
trophoblast
CytotrophoblastBlastocele Amnioblast
Amniotic cavity
Epiblast Hypoblast Trophoblast
Dr. Sherif Fahmy
44. 9th
& 10th
days
Dr. Sherif Fahmy
Cyto-
trophoblast
Amnioblast
Amniotic
cavity
Epiblast
Hypoblast
Heuser’s membrane
Primary yolk sac
Fibrin clot
Dr. Sherif Fahmy
46. -At 3rd
month amnion comes in contact with
chorion to form amnio-chorionic membrane with
obliteration of chorionic cavity.
-By the end of 3rd
month, uterine cavity is
obliterated due to expansion of amniotic cavity.
-Finally, the amniotic cavity surrounds the fetus
and forms a tubular sheath around the umbilical
cord.
-Expansion of amniotic cavity leads to folding of
the embryonic disc and amnio-ectodermal
junction will be present at primitive umbilical ring.
Dr. Sherif Fahmy
53. Amniotic fluid
- Normal volume is 1000 – 1500 cc clear
watery fluid.
- Source: 1st
from amnioblast then from
kidney.
- If the volume is less than 500 cc it is
called oligohydramnios.
-If the volume is more than 2000 cc is
called polyhydramnios. Dr. Sherif Fahmy
Dr. Sherif Fahmy
54. Functions of amniotic fluid:
1- At early pregnancy:
1- Acts as water cushion that absorbs external
shocks.
2- Acts as heat insulator.
3- Prevents adhesion of embryo to wall of uterus.
4- Prevents adhesion of fetal parts.
2- At late pregnancy:
1- A space for accumulated urine.
2- Allows fetal movements to help body muscles
to develop.
3- Help suckling training and development of gut
muscles. Dr. Sherif Fahmy
Dr. Sherif Fahmy
55. 3- During labor:
1- Protects against uterine contractions.
2- Formation of bag of water that gradually
dilate the cervix.
3- Sterile amniotic washes vagina before
passage of baby.
4- Rupture of amniotic sac is a sign of start
of delivery.
Dr. Sherif Fahmy
Dr. Sherif Fahmy
56. Abnormalities of amniotic fluid:
1- Polyhydramnios.
Causes:
1- No cause (35 %).
2- Maternal diabetes.
3- Congenital malformation e.g.
anencephaly and esophageal atresia.
2- Oligohydramnios.
Cause:
-Renal agenesis.
Dr. Sherif Fahmy
Dr. Sherif Fahmy
58. Fate & development of yolk sac
• Primary yolk sac: It replaces cavity of blastocyst
after the formation of Heuser’s membrane which is
formed of flat cells that originate from hypoblast
cells at 9th
& 10th
day.
• Secondary yolk sac: additional cells from
hypoblast cells will line the Heuser’s membrane,
reduction of size of yolk sac and formation of
allantois. This occurs in the 13th
day.
• Defenitive yolk sac: During 3rd
week, hypoblast
become replaced by endoderm. After folding, it
shares in formation of gut and the part remains
outside the embryo is called defenitive yolk sac. It is
connected to yolk sac by vitello-intestinal duct.
Dr. Sherif Fahmy
65. Functions of yolk sac:
• Gut: foregut, midgut and hindgut.
• Allantois: forms part of urinary bladder.
• Primordial germ cells: Which are
spermatogonia and oogonia which are
formed in its caudal part (hind gut).
• Vitelline vessels: develop from mesoderm
around vitelline duct. Intra-embryonic part
form portal vein and arteries of intestine.
• Blood cells: develop in the mesoderm
around the yolk sac.
Dr. Sherif Fahmy
66. Abnormalities of Yolk
Sac
• 1- Vitelline cyst and fistula
due to persistence of vitelline
duct.
• 2- Urachal cyst and fistula due
to persistence of urachus
from allantois.
Dr. Sherif Fahmy