Amnion & Umbilical Cord (General Embryology)

Amnion & Umbilical Cord

1. AMNION

2. 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

3. -During 4
th
week, expansion of amniotic cavity
leads to folding of the embryonic disc and amnio-
ectodermal junction will be present at primitive
umbilical ring.
-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.
Dr. Sherif Fahmy

4. 8
th
day of pregnancy
Dr. Sherif Fahmy
Endometrium
Cytotrophoblast
Amnioblast
Amniotic cavity
Epiblast Hypoblast
Dr. Sherif Fahmy

5. 9
th
& 10
th
days
Dr. Sherif Fahmy
Cyto-
trophoblast
Amnioblast
Amniotic
cavity
Epiblast
Hypoblast
Dr. Sherif Fahmy

6. 13
th
daySecondary yolk
sac
Connecting stalk
Extra-
embryonic
coelom
(Chorionic
cavity)
Dr.Sherif Fahmy
Amniotic
cavity
Chorionic
Vesicle

7. Amnion & Folding

8. Dr. Sherif Fahmy
Dr. Sherif Fahmy

9. Dr. Sherif Fahmy
Dr. Sherif Fahmy

10. Definitive yolk sac
Vitelline duct
Midgut

11. Expansion of
Amniotic Cavity

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

13. Dr. Sherif Fahmy
Dr. Sherif Fahmy

14. Dr. Sherif Fahmy
Decidua
parietalis
Decidua
capsularis
Uterine
cavity
Amniotic cavity
Fused decidua
parietalis and
capsularis
Amniotic
cavity
Chorionic cavity
Dr. Sherif Fahmy

15. Amniotic fluid
-Normal volume is 1000 – 1500 cc clear
watery fluid at full term.
-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

16. 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

17. 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

18. 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

19. UMBILICAL
CORD

20. Morphology of Umbilical Cord
It is the connection between placenta and
fetus.
•Length: 50 – 60 cm
•Diameter: 2 cm.
•Shape: Tortous, showing false notes.
•Contents: 2 umbilical arteries, one umbilical vein
embedded in wharton’s jelly and surrounded by
amniotic membrane.
•Attachments: It is attached to fetal surface of placenta
near its center, the other attachment is to ventral
aspect of fetal abdominal wall.
•Functions:
–It contains umbilical vessels that connect the fetus to the
placenta.
–Allows free mobility of the fetus.

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

23. Development of the Cord
1- Primitive umbilical ring.
2- Primitive umbilical cord.
3- Definitive umbilical cord.

24. Primitive Umbilical Ring
Expansion of amniotic cavity, leads to folding with
ventral shifting of amnio-ectodermal junction and
formation of primitive umbilical ring.
Contents:
Connecting stalk containing allantois and
umbilical vessels.
Vitelline duct and vitelline vessels.
Connection between intra-embryonic and extra-
embryonic coelom.

25. Expansion of amniotic cavity, leads to
elongation of umbilical cord.
Contents:
1- Yolk sac and vitelline duct.
2- Connecting stalk with remnant of
allantois.
3- Umbilical and vitelline vessels.
4- Intestinal loop in its proximal part.
Primitive umbilical cord

26. Return of intestinal loop to abdominal
cavity at 3
rd
month.
Obliteration of extra-embryonic part of
vitelline vessels and one umbilical vein
with persistence of other vein and 2
umbilical arteries.
Degeneration of vitelline duct and
allantois
Transformation of mesoderm of
connecting stalk into wharton’s jelly.
Definitive Umbilical Cord

27. Development

28. 1- Primitive umbilical ring

29. Embryonic disc with removed
ectoderm
Intra-
embryonic
ceolom

32. Connecting
stalk
Allantois
Umbilical
vessels
Definitive yolk
sac
Vitelline vessels
Vitelline duct
Primitive umbilical ring

33. 2- Primitive umbilical cord

36. 3-Definitive umbilical cord

38. •Abnormalities of Umbilical Cord
•1- Short cord: leads to premature separation
of placenta.
•2- Long cord: It may encircle neck of fetus and
may form true knots.
•3- Congenital umbilical hernia
(omphalocele): the cord contains coils of
intestine.
•4- Presence of one umbilical artery.
•5- Abnormal attachment of the cord:
–Marginal attachment (battledore)
–Through membranes (velamentous).