Download Types of extra embryonic membranes

Extra Embryonic Membranes:
Definition of Extra Embryonic Membrane:
The blastoderm in birds ,
reptiles and mammals not
only gives rise to embryo, but
also to certain structures
that lie outside the embryo.
These extra embryonic
structures are called Extra
Embryonic Membrane.
Types of extra embryonic membranes
•Yolk sac
•Amnion
•Chorion
•Allantois
Yolk Sac
Origin:
From the extra embryonic
splanchnopleur (endoderm on the inner
and Splanchnic mesoderm on the outer
side).
Yolk sac has a wide opening into the
midgut .
As development proceeds the passages
of midgut is reduced to a narrow
umblical stock..
The opening of umblical stock into the
midgut is called umblicus.
Yolk sac spreads more and more around
the yolk.
Passage left on ventral side to absorb
albumen.
On the first day mesoderm joins it and
on the ninth day it is fully formed.
Functions of the Yolk Sac :
Digest the yolk .
Transfer the products of digestion to the embryo.
Digestive surface increased by force off the walls of the yolk sacs called yolk sac septa .
In Mammals yolk sac is less nutritive organ then Reptiles and Aves .
In Mammals it functions as embryonic haemopoietic organ (site for blood cells formation).
After Hatching :
Yolk is digested.
Yolk sac become
small.
It is withdrawn into
the intestine and the
umbilicus closes.
Amnion
Origin:
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From somatopleur (ectoderm + somatic
mesoderm).
It develops as folds of somatopleur.
Fold over the head of the embryo is
called head of the embryo.
Fold over the tail is called tail of the
embryo.
The folds converge above the embryo,
meet and fuse.
The points of fusion is called
seroamniotic connection.
Fusion results two membrane over the
embryo: inner membrane = amnion and
outer membrane is called Chorion.
Functions of Amnion :
Amnion protects the
embryo from shock and
injury.
Amniotic fluid prevents its
desiccation.
Chorion
Origin:
•From somatopleur(ectoderm +
somatic mesoderm).
Fusion of head fold of amnion and
tail fold of amnion produces two
membranes over the embryo. Inner layer
is called amnion and outer is called
chorion.
Chorion is also called false amnion.
.
Functions of chorion :
It protects the foetus.
Provides place for the growth of allantois.
Helps in the formation of the placenta.
Allantois
Origin:
From Splanchnopleur(endoderm on inner side
and Splanchnic mesoderm on the outer side).
It develops from the floor of hindgut of the
foetus.
It goes into choriotic cavity.
Splanchnic mesoderm off Allantois fuses with
somatic mesoderm of the chorion forming
Allantochorion.
Allantochorion develops allantoic artries and
veins .
Allantois stock (connection between allantios
and hind gut).
Umbilical chord (somatopleur surround the
allantois stock and umbilical stock).
At hatching time umblical chord breaks .
Allantois left behind.
Place of attachment of the umblical chord to
the body heals up.
Permanent scarp, the umblicus is formed.
Functions of Allantois :
Store insoluble nitrogenous waste matter, uric acid.
Functions as extra embryonic lung .
Gaseous exchange taking place between blood and
external air through it.
Carries on excretion ,respiration and nutrition .
Allantois function as a soft, elastic cushion for protecting
the embryo from shock .
Allantois helps in a formation of umbilical chord.
Amniotic cavity
Definition:
The cavity enclosed between the
embryo and amnion is called amniotic
cavity.
The fluid filled in this cavity is
called amniotic cavity.
The embryo floats in this fluid .
functions of amniotic cavity :
Serves as water cushion to protect
the embryo.
Prevents the desiccation of the
embryo.
Check the stagnation of blood in
the embryonic blood vessels .
Choriotic cavity
Definition:
o The
space between the amnion and the
chorion is called choriotic cavity.
Functions of choriotic cavity
•Fluid of chorionic cavity provides the
protection to the embryo.
•Provides the space for the growth of the
allantios .
•Plays an important role in gaseous
exchange through the porous shell.
How extra Embryonic Membranes helps in the Placental
Formation ?
 Allantochorion comes in
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contact with uterine wall.
Develops large number of
projections called secondary
or chorionic villi.
They are formed on tenth
day of development.
Villi penetrates in
depressions called crypts.
Crypts become vascular.
•Intimate connection
established between
foetal membranes and
uterine wall is called
placenta.
The part of placenta
contributed by foetus
(Allantochorion) is called
foetal placenta.
•Part shared by mother
(uterine wall) called
maternal placenta.
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