Placenta & Amnion (General Embryology)

Placenta & Amnion

1. 13
th
day
Endodermal
cells
Secondary yolk
sac
Exocoelomic cyst
Somatic
mesoderm
Connecting stalk
Somatic
mesoderem
Splanchnic
mesoderm
1ry chorionic villi
Extra-
embryonic
coelom
Chorionic
cavity)
Dr. Sherif Fahmy

2. 13
th
day
Somatic
mesoderm
Connecting stalk
1ry chorionic villi
Cyto-
trophoblast
Intervillous
space
Syncytio-
trophoblast
Dr. Sherif Fahmy

3. Tertiary Chorionic Velli
Dr. Sherif Fahmy
Syncytio-
trophoblast
Cyto-
trophoblast
Somatic
extraembryoni
c mesoderm
Fetal blood
vessels
Dr. Sherif Fahmy

4. Types of Tertiary
Chorionic Velli

5. Decidua
basalis
(Decidual
plate)
Chorion frondosum
Chorionic
plate
Chorion leave
Dr. Sherif Fahmy

6. Fetal Membranes
Dr. Sherif Fahmy

7. Fetal membranes:
1- Chorion and placenta.
2- Amnion.
3- Umbilical cord.
4- Yolk sac.
Dr. Sherif Fahmy

8. Chorion
Dr. Sherif Fahmy

9. It is the wall of chorionic vesicle.
Time: Chorionic vesicle is formed at the 12
th
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

10. Somatic
mesoderm
Connecting stalk
Secondary yolk sac
Somatic mesoderm
Extra-embryonic
coelom
Amniotic cavity
Splanchnic
mesoderm
Syncytio-
trophoblast
Cyto-
trophoblast
Chorion
Exocoelomic cyst
Embryonic
disc
Chorionic Vesicle
Dr. Sherif Fahmy
Endodermal cells
Dr. Sherif Fahmy
Dr. Sherif Fahmy

11. Dr. Sherif Fahmy
Primary
chorionic
villus
Cyto-
trophoblast
Syncytio-
trophoblast
Dr. Sherif Fahmy

12. Dr. Sherif Fahmy
Syncytio-
trophoblast
Cyto-
trophoblast
Somatic
mesoderm
Secondary
chorionic villus
Dr. Sherif Fahmy

13. Dr. Sherif Fahmy
Syncytio-
trophoblast
Cyto-
trophoblast
Mesoderm
Fetal blood
vessels
Tertiary
chorioniv villus

14. Dr. Sherif Fahmy
Dr. Sherif Fahmy

15. 1- Primary chorionic velli (start of 3
rd
week):
cyncytiotropholblasts and cytotrophoblast.
2- Secondary chorionic velli (middle of 3
rd

week):
Cyncytiotrophoblast, cytotrophoblast and
mesoderm (in the central core).
3- Tertiary chorionic velli (end of 3
rd
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

16. PLACENT
A
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

18. Cotyledon
Groove between
cotyledons
Umbilical cord
Maternal surface
Dr. Sherif Fahmy
Dr. Sherif Fahmy

19. Fetal surface covered
with amnion
Umbilical cord
Dr. Sherif Fahmy
Dr. Sherif Fahmy

20. Formation of Placenta

21. Dr. Sherif Fahmy

22. Dr. Sherif Fahmy

23. Structure of Placenta

24. Dr. Sherif Fahmy
Dr. Sherif Fahmy

25. Decidua basalis
Arteriol
Venule
Decidual septum
Cytotrophoblastic shell
Decidual plate
Stem
villous
Floating
velli
Intervillous
space
Chorionic
plate
Umbilical veinUmbilical artery
Amnion
Mesoderm
Syncytiotrophoblast
Cytotrophoblast
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 2
nd

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 14
th
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

33. Placenta
previa
Marginalis &
parietalis
Dr. Sherif Fahmy
Dr. Sherif Fahmy

34. Placenta
previa
centralis
Dr. Sherif Fahmy
Dr. Sherif Fahmy

35. Velamentous
placenta
Dr. Sherif Fahmy
Dr. Sherif Fahmy

36. Battle door placenta
Dr. Sherif Fahmy
Dr. Sherif Fahmy

37. Accessory placenta
Dr. Sherif Fahmy
Dr. Sherif Fahmy

38. Placenta acreta
Placenta percreta
Dr. Sherif Fahmy
Dr. Sherif Fahmy

39. AMNION

40. Dr. Sherif Fahmy
Extraembryonic coelom
(Chorionic Cavity)
Dr. Sherif Fahmy

41. Dr. Sherif Fahmy
Dr. Sherif Fahmy

42. AMNION
-It is a membrane that enclose amniotic cavity.
-Formation:
-It is formed at the 8
th
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 12
th
day it becomes separated from
cytotrophoblasts by primary mesoderm
(Extraembryonic).
-Amnio-ectodermal junction is at the margin
of oval embryonic disc at the 3
rd
week.
Dr. Sherif Fahmy
Dr. Sherif Fahmy

43. 8
th
day of pregnancy
Dr. Sherif Fahmy
Endometrium
Syncytio-
trophoblast
Cytotrophoblast
BlastoceleAmnioblast
Amniotic cavity
Epiblast Hypoblast Trophoblast
Dr. Sherif Fahmy

44. 9
th
& 10
th
days
Dr. Sherif Fahmy
Cyto-
trophoblast
Amnioblast
Amniotic
cavity
Epiblast
Hypoblast
Heuser’s membrane
Primary yolk sac
Fibrin clot
Dr. Sherif Fahmy

45. Dr. Sherif Fahmy
Dr. Sherif Fahmy

46. -At 3
rd
month amnion comes in contact with
chorion to form amnio-chorionic membrane with
obliteration of chorionic cavity.
-By the end of 3
rd
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

47. Dr. Sherif Fahmy
Dr. Sherif Fahmy

48. Dr. Sherif Fahmy
Dr. Sherif Fahmy

49. Dr. Sherif Fahmy
Dr. Sherif Fahmy

50. Dr. Sherif Fahmy
Extraembryonic coelom
(Chorionic Cavity)
Dr. Sherif Fahmy

51. Dr. Sherif Fahmy
Dr. Sherif Fahmy

52. Dr. Sherif Fahmy
Decidua basalis
Decidua
parietalis
Decidua
capsularis
Chorion
frondosum
Uterine
cavity
Amniotic cavity
Chorion
frondosum
Fused decidua
parietalis and
capsularis
Amniotic
cavity
Decidua
basalis
Chorionic cavity
Dr. Sherif Fahmy

53. Amniotic fluid
-Normal volume is 1000 – 1500 cc clear
watery fluid.
-Source: 1
st
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

57. YOLK SAC

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 9
th
& 10
th
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 13
th
day.
•Defenitive yolk sac: During 3
rd
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

59. 7
th
day:
Dr. Sherif Fahmy
Dr. Sherif Fahmy

60. 8
TH
Day of Pregnancy
Endometrium
Cytotrophoblasts Hypoblasts
Amniotic cavity
Epiblast
Dr.Sherif Fahmy
Dr. Sherif Fahmy

61. 9
th
& 10
th
days
Primary yolk sac
Heuser’s
membrane
Syncytio-
trophoblast
Hypoblast
Amniotic
cavity
Epiblast
Cyto-
trophoblast
Dr. Sherif Fahmy

62. 13
th
day
Endodermal
cells
Secondary yolk
sac
Exocoelomic cyst
Connecting stalk
Splanchnic
mesoderm
Extra-
embryonic
coelom
Chorionic
cavity)
Dr.Sherif Fahmy
Chorionic
Vesicle
Dr. Sherif Fahmy

64. 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

67. Dr. Sherif Fahmy

68. Dr. Sherif Fahmy