Download FETAL MEMBRANES

FETAL MEMBRANES
AMNION, CHORION, UMBLICAL CORD, YOLK SAC
LEARNING OBJECTIVES
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By the end of the lecture, the student will be able to:
– Specify the development and functions of fetal membranes,
chorion, amnion
– Know the details of amnion, chorion.
– Describe the formation and function of amniotic fluid and its
disorders
– Discuss the disorder of related to amniotic fluid volume.
– Discuss the development of chorion and its complications.
FETAL MEMBRANES
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Fetal membranes, or chorioamniotic membranes, are
the amnion and chorion which surround and protect a
developing fetus.
The Chorion is the outer membrane it surrounds the
extraembryonic coelom.
AMNION
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Amnion is a membrane building the amniotic sac that surrounds
and protects an embryo.
It is developed in reptiles, birds, and mammals,
which are hence called “Amniota;” but not in
amphibia and fishes, which are termed
“Anamnia.”
AMNIOTIC CAVITY
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In the human embryo the youngest embryo has been studied to
have amnion which is already present as a
closed sac called the amniotic cavity.
Boundaries
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Roof is made up of a single stratum of
flattened, ectodermal cells,
the amniotic ectoderm
Floor consists of the prismatic
ectoderm of the embryonic disk.
Outside the amniotic ectoderm is a thin layer of mesoderm,
continuous with that of the somatopleure and is connected
by the body-stalk with the mesodermal lining of the chorion
AMNIOTIC FLUID
At first amnion is in contact with the embryo
By about 4th week fluid is secreted by the
aminoblast begin to accumulate.
Fluid increases in quantity and causes the
amnion to expand and ultimately to adhere
to the inner surface of the chorion, so that
the extra-embryonic part of the celom is
obliterated.
AMNIOTIC FLUID
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Amniotic fluid or liquor amnii is the nourishing and protecting
liquid contained by the amniotic sac.
Amniotic sac grows and begins to fill, mainly with water, approx.
two weeks after fertilization.
Fluid increases in quantity up to the 6th or 7th month of
pregnancy, after which it diminishes somewhat.
At the end of pregnancy it is about 1 liter.
FUNCTIONS OF AMNIOTIC FLUID
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Amniotic fluid is "inhaled" and "exhaled" by the fetus.
It is essential that fluid be breathed into the lungs in order for
them to develop normally.
Swallowed amniotic fluid also creates urine and contributes to the
formation of meconium.
FUNCTIONS OF AMNIOTIC FLUID CONT..
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Amniotic fluid protects the developing baby by
cushioning against blows to the mother's
abdomen
Allows for easier fetal movement
Promotes muscular/skeletal development
Helps protect the fetus from heat loss.
AMNIOCENTESIS
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Analysis of amniotic fluid, drawn out of the mother's abdomen
It can reveal many aspects of the baby's genetic health.
This is because the fluid also contains
fetal cells, which can be examined for
genetic defects.
DISORDER OF AMNIOTIC FLUID VOLUME
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Low volumes of amniotic fluid for any particular
gestational age-oligohydramnios-result in many
cases from placental insufficiency with diminished
placental blood flow.
Preterm rupture of the amniochorionic membrane
occurs in approximately 10% of pregnancies and is
the most common cause of oligohydramnios.
DISORDER OF AMNIOTIC FLUID VOLUME COT.
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When there is renal agenesis (failure of kidney
formation), the absence of fetal urine contribution
to the amniotic fluid is the main cause of
oligohydramnios.
OLIGOHYDRAMNIOS
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A similar decrease in fluid occurs when there is obstructive
uropathy (urinary tract obstruction).
Complications of oligohydramnios include
fetal abnormalities (pulmonary hypoplasia,
facial defects, and limb defects) that are
caused by fetal compression by the uterine
wall.
Compression of the umbilical cord is also a
potential complication of severe
oligohydramnios.
DISORDER OF AMNIOTIC FLUID VOLUME
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High volumes of amniotic fluidpolyhydramnios-result when the fetus does
not swallow the usual amount of amniotic
fluid.
Most cases of polyhydramnios (60%) are
idiopathic (unknown cause), 20% are caused
by maternal factors, and 20% are fetal in
origin.
POLYHYDRAMNIOS
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Polyhydramnios may be associated with severe anomalies of the
central nervous system, such as meroencephaly
(anencephaly).
When there are other anomalies, esophageal
atresia (blockage), for example, amniotic fluid
accumulates because it is unable to pass to the
fetal stomach and intestines for absorption.
Ultrasonography has become the technique of
choice for diagnosing oligo- and
polyhydramnios.
CHORION
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Chorion consists of two layers:
– Outer formed by the primitive ectoderm
or trophoblast.
– Inner formed by the somatic mesoderm; which is in contact
with amnion.
CHORION
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Trophoblast is made up of:
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Internal layer of cubical or prismatic cells,
the cytotrophoblast or layer of Langhans
External layer of richly nucleated protoplasm
devoid of cell boundaries,
the syncytiotrophoblas
CHORIONIC VILLI
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Chorion undergoes rapid proliferation and forms numerous
processes, the chorionic villi
which invade and destroy the uterine
decidua and at the same time absorb from
it nutritive materials for the growth of the
embryo.
Chorionic villi are at first small and nonvascular, and consist of trophoblast only,
called as Primary Villi
They increase in size and ramify,
CHORIONIC VILLI
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The mesoderm, carry branches of the umbilical vessels, grows
into them, and in this way they are vascularized.
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Villi cover the entire chorion by the end of the second month
pregnancy.
HYDATIDIFORM MOLE
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Hydatidiform mole is an overgrowth of placental tissue or an
abnormal growth
develops from a non-viable, fertilized egg
at the beginning of a pregnancy.
It often is referred to as a molar pregnancy.
Instead of the normal embryonic cell
division that results in the development of
a fetus, the placental material grows
uncontrolled and develops into a
shapeless mass of watery, small, blisterlike sacs (vesicles).
The cause of hydatidiform mole is unknown, but is thought to be
caused in part by chromosomal abnormalities.
CHORIOCARCINOMA
Choriocarcinoma is a malignant, trophoblastic and aggressive
cancer, usually of the placenta.
t is characterized by early hematogenous
spread to the lungs.
It belongs to the malignant end of the
spectrum in gestational trophoblastic
disease (GTD).
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It is also classified as a germ cell tumor and may arise in the
testis or ovary
CHORIOCARCINOMA
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Characteristic feature is the identification of
intimately related syncytiotrophoblasts and
cytotrophoblasts without formation of
definite placental type villi.
UMBILICAL CORD
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The umbilical cord attaches the fetus to the
placenta.
Length
At full time, as a rule, is about equal to
the length of the fetus i.e., about 50 cm. (20
inch)
It contains:
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Two arteries (carries deoxygenated
blood)
One vein (carries oxygenated blood)
Embedded in wharton’s jelly
DEVELOPMENT OF UMBILICAL CORD
Developed from yolk sac and allantois.
Replaces yolk sac for the supply of
nutrients to the fetus by the end of 5th week.
Not directly connected to mother but
connected to placenta.
Blood flow through umbilical cord increases
as the size of fetus increases
Yolk sac
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The yolk-sac is situated on the ventral
aspect of the embryo
It is lined by endoderm, outside of which is
a layer of mesoderm.
It is filled with vitelline fluid, which may be
utilized for the nourishment of the embryo
during the earlier stages of its existence.
VITELLINE CIRCULATION
Blood is conveyed to the wall of the yolk
sac by the primitive aortae, and after
circulating through a wide-meshed capillary
plexus, is returned by the vitelline veins to the
tubular heart of the embryo.
Function
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Nutritive material is absorbed from the
yolk-sac and conveyed to the embryo.
VITELLINE DUCT
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At the end of the fourth week the yolk-sac
presents the appearance of a small pear-shaped
vesicle (umbilical vesicle) opening into the
digestive tube by a long narrow tube, called
vitelline duct.
Persistence of vitelline vein is called as Meckel’s
Diverticulum
MECKEL’S DIVERTICULUM
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As a rule the vitelline duct undergoes complete obliteration
during the 7th week.
in about 2 to 3% of cases its proximal
part persists as a diverticulum from the
small intestine, Meckel’s diverticulum.
which is situated about 2 or 3 feet from
the ileocolic junction.
Diverticulum is 2 inch long
MECKEL’S DIVERTICULUM CONT..
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May be attached by a fibrous cord to the abdominal wall at the
umbilicus.
Sometimes a narrowing of the lumen of the ileum is seen
opposite the site of attachment of the duct.
REFERENCES
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Gray’s human anatomy.
Langman book of embryology
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