The document discusses the fetal membranes, which include the umbilical cord, amnion, amniotic fluid, yolk sac, and allantois. It describes the development, structure, function and abnormalities of each membrane. The umbilical cord connects the fetus to the placenta and transports nutrients. The amnion surrounds the fetus and amniotic fluid, protecting the fetus and allowing movement. The yolk sac provides early nutrition but later degenerates. The allantois contributes to blood and urinary system development. Abnormalities can impact fetal health.

2.  By the end of the lecture the student should be able
to:
 List the components of the fetal membranes.
 Describe the stages of development of the
components.
 Describe the structure and function of the
components.
 Describe their fate and the possible congenital
anomalies.

3.  Umbilical cord
(Connecting
Stalk)
 Amnion
 Amniotic Fluid
 Yolk Sac
 Allantois
1. Protection
2. Nutrition
3. Respiration
4. Excretion
5. Synthesis of Hormones
Functions

4.  It is a pathway which
connects the ventral aspect
of the embryo with the
placenta (chorion)
 It is a soft tortuous cord
measuring (30- 90) cm in
length (average 55) ,(1-2)
cm in diameter.
 It has a smooth surface
because it is covered by the
amnion

5.  1-Connecting stalk:
 Alantois + two Umbilical arteries +
two Umbilical veins
 The extra embryonic mesoderm
forms Wharton’s jelly
 2-Yolk stalk (Vitello-intestinal duct):
 A narrow, elongated duct which
connects gut to yolk sac
 It contains Vitelline Vessels
 Later on , it is obliterated and the
vitelline vessels disappear.

6.  Normally, it is attached to
a point near the centre of
the fetal surface of the
placenta

7.  (1) Abnormal Attachment:
 a-Battledore placenta :
 The UC is attached to the
margin of the placenta (it is
not dangerous).
 b-Velamentous insertion of
the cord :
 UC is attached to the
amnion away from
placenta, (It is dangerous
to the fetus due to rupture
of blood vessels during
labor)

8.  (2) Abnormalities in Length:
 a-Very Long Cord:
 It is dangerous , it may
surround the neck of the
fetus and causes its death.
 b-Very Short Cord:
 It is dangerous because it
may cause premature
separation of placenta, or the
cord itself may rupture

9.  (3) False and True knots
of umbilical cord:
a-False knots:
 UC looks tortuous due to
twisting of umbilical
vessels (umbilical vessels
are longer than the cord),
these knots are normal and
do not cause any harm to
the fetus
 b-True knots:
 Are rare (1%) of
pregnancy, but very
dangerous because they
may cause obstruction to
blood flow in umbilical
vessels, leading to fetal
anoxia & fetal death
True Knots in 20-weeks fetus

10. 3rd week: Appears as a
diverticulum from caudal wall of
Y.S. that extends into connecting
stalk.
2nd month: Its extra-
embryonic part degenerates.
3rd month: Its intra-embryonic
part extends from UB to UC as
thick tube , ‘(urachus) ’
After birth: the urachus is
obliterated and fibrosed to form
median umbilical ligament, that
extends from apex of UB to
umbilicus.

11. Blood formation in its wall
during 3rd to 5th week.
Its blood vessels persist as
the umbilical vein & arteries.

12.  It is essential in the transfer
of nutrients to the embryo
during 2nd & 3rd weeks,
when the uteroplacental
circulation is not established.
 It does not contain any yolk.
 Its development passes
through three stages:
 Primary yolk sac.
 Secondary yolk sac.
 Definitive yolk sac.

13. Appears in the Blastocyst
stage at 10-days, it lies
ventral to the embryonic
plate.
 Its roof is formed by
hypoblast (primary
endoderm),
 Its wall is formed by
exocoelomic membrane,
it lines the inner surface of
the cytotrophoblast, and
separated from it by the
extraembryonic
mesoderm

14.  Appears in the chorionic
vesicle stage
 Its roof is formed by
hypoblast (embryonic
endoderm), its wall is
formed by exocoelomic
membrane + inner layer
(splanchnic layer) of the
extraembryonic mesoderm.
 At day 16: a diverticulum
appears from its dorsocaudal
end (Allantois) into the
substance of the connecting
stalk

15.  After folding, part of Yolk Sac is
enclosed within the embryo to form the
Gut (Foregut, Midgut & Hindgut).
 The remainder of Yolk Sac that remains
outside the embryo becomes the
Definitive Yolk Sac
 The midgut is temporarily connected to
Definitive Yolk Sac by a narrow duct
Vitello-intestinal duct (Yolk stalk),
which is incorporated inside the
umbilical cord.
 This is fibrosed and degenerated by
the end of (6th week)

16. 3rd week:
 (a) Blood formationt
First formed in the extra-embryonic
mesoderm covering the wall of the yolk sac,
until hemopoietic activity begins in the liver
during 6th week
4th week: endoderm of yolk sac is
incorporated into the embryo to form
primordial gut
Epithelium of Respiratory system &G.I.T.
(b)Primordial germ cells in the endodermal lining of the wall of caudal end of
the yolk sac migrate into the developing sex glands to differentiate into germ
cells (spermatogonia or oogonia)

17. Yolk stalk detached from midgut by the
end of 6th week. In (2%) of adults, its
proximal intra-abdominal part persists as
ileal diverticulum (Meckel diverticulum).
At 10 week, small definitive yolk sac lies
in the chorionic cavity between amniotic
& chorionic sacs
At 20 weeks, as pregnancy advances,
definitive yolk sac atrophies and becomes
a very small cyst.
In unusual cases, it persists under the
amnion near the attachment of Umbilical
cord, on the fetal surface of the placenta.
Its persistence is of no significance

18.  It is a thin, transparent & tough fluid-
filled, membranous sac surrounding the
embryo.
 At First : It is seen as a small cavity lying
dorsal to the embryonic plate.
 At Stage of Chorionic Vesicle: The
amnion becomes separated from the
chorion by chorionic cavity or extra
embryonic coelom.
 After Folding: the amnion expands
greatly and is becomes on the ventral
surface of the embryo.
 As a result of expansion of the amnion,
the extra embryonic coelom is gradually
obliterated and amnion forms the
epithelial covering of umbilical cord.

19.  It is a watery fluid inside the
amniotic cavity (sac).
 It has a major role in fetal growth &
development
 It increases slowly, to become (700-
1000) ml by full term (37) weeks.
 Composition:
 99% of amniotic fluid is water
 It contains un-dissolved material of
desquamated fetal epithelial cells +
organic + inorganic salts
 As pregnancy advances,
composition of amniotic fluid
changes as fetal excreta (meconium
= fetal feces & urine) are added

20.  Fetal & Maternal Sources:
 Initially, some amniotic fluid
is secreted by amniotic cells.
 Most of fluid is derived from
Maternal tissue by:
 1-Diffusion across amnio-
chorionic membrane from
placenta.
 2-Diffusion across chorionic
plate (chorionic wall related to
placenta) from the maternal
blood in the intervillous
spaces.
 Later, it is derived from
Fetus through:
 Skin, Fetal Respiratory
Tract & mostly by Excreting
Urine (at beginning of 11th
week)

21.  Provides symmetrical external growth of the
embryo
 Acts as a barrier to infection (it is an aseptic
medium)
 Permits normal fetal lung development
 Prevents adherence of embryo to amnion
 It protects embryo against external injuries
 Keeps the fetal body temperature constant
 Allows the embryo to move freely, aiding
muscular development in the limbs
 It is involved in maintaining homeostasis of
fluids & electrolytes
 It permits studies on fetal enzymes, hormones and
diagnosis of fetal sex and chromosomal
abnormalities

22.  Amniotic fluid remains constant & in balance
 --Most of fluid is swallowed and few passes into lungs by fetus,
and absorbed into fetal blood, where it is metabolised
 -- Part of fluid passes through placental membrane into
maternal blood in intervillus space,
 Other part of fluid is excreted by fetal kidneys into amniotic
sac

23.  (1) Oligohydramnios:
 The volume is less than ½ liters
 Causes :
 Placental insufficiency with low
placental blood flow
 Preterm rupture of amnio-chorionic
membrane occurs in 10% of
pregnancies
 Renal Agenesis (failure of kidney
development)
 Obstructive Uropathy (urinary tract
obstruction) lead to absence of fetal
urine (the main source)
 Complications :
 Fetal abnormalities (pulmonary,
facial & limb defects)

24.  (2) Polyhydramnios
(Hydramnios):
 The volume is more than 2
liters, it is diagnosed by
Ultrasonography.
 Causes
 Fetal ( 1-20% ) :
Esophageal atresia.
 Maternal (2-20%) :
defects in maternal
circulation.
 Idiopathic (3-60%)

25. 25
PLACENTA
 This is a fetomaternal organ.
 It has two components:
 Fetal part – develops from the chorionic sac ( chorion
frondosum )
 Maternal part – derived from the endometrium ( functional
layer – decidua basalis )
 The placenta and the umbilical cord are a transport system for
substances between the mother and the fetus.( vessels in
umbilical cord )
 Function Of The Placenta:
1. Protection
2. Nutrition
3. Respiration
4. Excretion
5. Hormone production

26. 26
DECIDUA
 DECIDUA is the
endometrium of the
gravid (pregnant)
uterus.
 It has four parts:
 Decidua basalis: it
forms the maternal
part of the placenta
 Decidua
capsularis: it covers
the conceptus
 Decidua parietalis:
the rest of the
endometrium
 Decidua reflexa:
 Junction between
capsularis &
parietalis.

27. 27
DEVELOPMENT OF PLACENTA
 Until the beginning of the
8th week, the entire
chorionic sac is covered
with villi.
 After that, as the sac grows,
only the part that is
associated with Decidua
basalis retain its villi.
 Villi of Decidua capsularis
compressed by the
developing sac.
 Thus, two types of chorion
are formed:
 Chorion frondosum
(villous chorion)
 Chorion laeve – bare
(smooth) chorion
 About 18 weeks old, it
covers 15-30% of the
decidua and weights
about 1 6 of fetus

28. 28
DEVELOPMENT OF PLACENTA
 The villous chorion (
increase in number,
enlarge and branch )
will form the fetal
part of the placenta.
 The decidua basalis
will form the
maternal part of the
placenta.
 The placenta will grow
rapidly.
 By the end of the 4th
month, the decidua
basalis is almost
entirely replaced by
the fetal part of the
placenta.

29. 29
FULL-TERM PLACENTA  Cotyledons –about 15 to 20
slightly bulging villous areas.
Their surface is covered by shreds
of decidua basalis from the
uterine wall.
 After birth, the placenta is always
inspected for missing
cotyledons. Cotyledons
remaining attached to the uterine
wall after birth may cause severe
bleeding.
 Grooves – formerly occupied by
placental septa
Maternal side

30. 30
FULL-TERM PLACENTA
( Discoid shape -500- 600 gm- Diameter 15-20 cm –
Thickness of 2-3 cm)  Fetal surface:
 This side is smooth and
shiny. It is covered by
amnion.
 The umbilical cord is
attached close to the
center of the placenta.
 The umbilical vessels
radiate from the
umbilical cord.
 They branch on the fetal
surface to form
chorionic vessels.
 They enter the chorionic
villi to form
arteriocapillary-
venous system.
Fetal side

31. 31
PLACENTAL MEMBRANE
 This is a composite
structure that consists of
the extra-fetal tissues
separating the fetal blood
from the maternal blood.
 It has four layers:
 Syncytiotrophoblast
 Cytotrophoblast
 Connective tissue of villus
 Endothelium of fetal
capillaries
 After the 20th week, the
cytotrophoblastic cells
disappear and the
placental membrane
consists only of three
layers.

32. 32
TRANSFER ACROSS
THE PLACENTAL
MEMBRANE
Viruses:
measles;poliomyelitis
Microorganism:
treponema pallidum
of syphilis ; T.g which
produce destructive
change in the eye;
brain .
IgG( gamma globulin) ,
IgS;IgM (
immunoglobulin S;M )

33. Placental endocrine synthesis
 The syncytiotrophoblast synthesizes protein &
steroid hormones
 The protein hormones
1- human chorionic gonadotropin
2- human chorionic somatomammotropin
3- human chorionic thyrotropin
4- human chorionic corticotropin
The steroid hormones
Progesterone & Estrogens

34. 34
Third trimester bleeding is the
common sign of these anomalies
 Placental anomalies

35. 35

36. 36

37. Thank you
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