Foetal Membranes-Chick
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Transcript of Foetal Membranes-Chick
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Picture showing incubated egg of chick (embryo)-40hours
The heart can be seen c lear ly . The blood vessels at dif ferent regions of the foetal membranes are seen
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Graphical representation of the egg showing- the foetal membranes
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FOET L MEMEBR NES IN CHICK
These are special embryonic structure developed in close association with
the developing embryonic reptiles, birds and mammals. These are called
extra embryonic membranes because they do not contribute directly to the
developing embryo but, they perform certain specific functions required for
the development of the embryo. They are also called foetal membranessince they are closely associated with the developing foetus.
The foetal membranes in chick are:
The Yolk Sac
The Amnion
The Chorion
The Allentois
Based on the presence of the extra embryonic membranes, the vertebrates
are classified as Amniotes and An-amniotes. Fishes and amphibians are an-amniotes as the extra embryonic membranes are absent during the
development.
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yolk. Outgrowths are formed on the inner surface of the yolk sac to
accommodate the blood vessels from the network of Area Vasculosa.
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Picture showing the formation of the guts and then body folds
The outgrowths grow deep in the yolk and helps in absorption. However, the
entire stock of the yolk is not used up during the development.
Folds begin to appear all around the embryo. These are called body folds
The folds comprises all 3 germ layers-ectoderm, endoderm and the
mesoderm. The folds grow downwards and inwards-separating the embryofrom the yolk sac. The first fold to appear is the head fold. The head
fold lies below the region of the head (anterior part of the embryo).
Similarly, a tail foldalso appears posterior. Both the major folds along
with the other minor folds contract under the embryo and form a Stalk
which encloses the blood vessels that reach the yolk which lies below.The stalk (yolk stalk) is made up of an outer layer of endoderm that
surrounds the canal (canal of the stalk) and connects the abdominal cavity
with the cavity of the yolk sac( which has yolk in it)
The splanchnopleure folds itself to form the gut of the developing embryo.
Once the development of the head fold and the tail fold is complete, thefore gutand the hind gutbecome differentiated.
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Since the wall of the midgut is continuous and open into the yolk-which lie below
it (the midgut is connected to the yolk by a narrow opening through the yolk sac
called Umbilicus)
The foregut open into the midgut by anterior intestinal portal veinand the hindgut
open in the midgut by the posterior intestinal portalvein Gradually both the guts
(the fore and the midgut) come close together and form the floor of the midgut
SIGNIFIC NCE OF THE YOLK S C
The yolk sac encloses the yolk-which is a main source of nourishment to
the developing embryo.
Outgrowths of the inner surface of the yolk sac grow deep into the yolk
which helps in breaking down the yolk.
The yolk stalk encloses the blood vessels that bring the nourishment to
the embryo form the yolk through the yolk sac.
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Exchange of the general gases also takes place through the vascularised
wall of the yolk sac.
THE MNION
The amnion is formed by the amniotic folds that originate from the Area Pellucida
and grow upwards. The amniotic folds are seen outer to the body folds. The
amniotic folds grow and meet above the dorsal surface and provide extra
protection from mechanical shock and desiccation.
FORMATION
A transverse fold arises near the head region, which bend backwards
forming a hood like structure over the head.
The lateral ends of the head fold extend backwards along the sides of theembryo.
The lateral ends meet above the head region and gradually covers the
embryo.
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A fold appears at the tail region simultaneously at the tail region of the
embryo-Chorion.
The free ends of the folds meets above the embryo forming amniotic cavity.
FUNCTIONING
The amniotic cavity encloses the embryo completely. The cavity at first is
small and narrow, but gradually grows bigger as it gets filled with the
amniotic fluid. The embryo is now in an aquatic environment. This signifies-
the embryo recaptures the ancestral trait proving that its ancestors were
aquatic forms.
STRUCTURE
The amniotic fold that is formed near the head region is made up of a layer of
extra embryonic ectoderm. The lateral folds are made of extra embryonic
mesoderm. The inner surface of the folds that form the amnion is made of a
layer of extra embryonic ectoderm adjacent to the embryo above the layerwhich is a layer of extra embryonic mesoderm
SIGNIFICANCE
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The amniotic sac provides the embryo an aquatic environment for the
development.
It protects the embryo from mechanical injury. It acts like a shock absorber.
Keeps the embryo enclosed.
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Picture showing the formation of Amnion and Chorion
The Chorion
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The formation of the amnion takes place by the formation of the amniotic folds.
These folds have 2 surfaces- an outer surface(close to the embryo)and an
inner surface(comparatively far from the embryo).when the folds meet the innersurface and fuse to form the amnion enclosing the amniotic cavity, the outer
surface also fuses to form a continuous layer and forms theChorion
. Thus,the
amnion and the Chorion are formed simultaneously
STRUCTURE
The outer surface of the folds that form the Chorion is made up with the same
layers as the inner surface of the amnion, but are arranged in the reverse order.
The extra embryonic ectoderm is outside under which, is the somatic mesoderm.
The layers of the ectoderm and the mesoderm of the Chorion are continuous withthe ectoderm and the mesoderm of the yolk stalk.
The cavity between the two surfaces is the extra embryonic coelom which is
continuous with the coelom of the embryo.
SIGNIFICANCE
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The Chorion is protective in function. In mammals the Chorion takes an active
part in the formation of the placenta- chorionic placenta.
Picture showing Chorion membrane along with other membranes
THE LL NTOIS
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The Allantois is the urinary bladder of the embryo which serves to collect the
nitrogenous wastes. The Allantois originates as an outgrowth of the hind gut.
The Allantois initially is a small bag like structure. It gradually growsbigger and enters the extra embryonic cavity (between amnion and Chorion)
and weighs itself between the yolk sac and the amniotic sac. The free end
of the Allantois expands but, is still connected to the hindgut by a narrow
neck When the body folds contract below the embryo and form the yolk
sac, the neck of the Allantois is also enclosed with it. This forms theumbilical cord.
The Allantois keeps expanding and soon it occupies the extra embryonic
space between the amnion and the Chorion. The distal end becomes flattened
and one end lies between the amnion and the yolk sac while the other lies
between the amnion and the Chorion. Blood vessels develop in the Allantoiswhich form a network and are connected to the blood vessels in the
umbilical cord. A pair of umbilical arteries arising from the dorsal aorta,
posterior to the vitelline arteries supply blood to the Allantois. The blood
is returned to the heart through the umbilical veins that flow into the left
and right cuverian duct.
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After a period of time, the right umbilical artery and right umbilical vein
disappear. The left umbilical veins join up with the hepatic vein and the
connection with the cuverian duct is closed.
STRUCTUREIt is made of a layer of endoderm covered by the mesoderm (meaning-the
endoderm is inside and the mesoderm is outside)
SIGNIFICANCE
It acts as a reservoir of the embryonic excretory wastes such as uric acid.
The chorio-allantoic membrane of the Allantois and the Chorion act like a
respiratory surface of the embryo.The shell is porous and allows entry of oxygen and exit of carbon-di-oxide.
The four extra embryonic membranes are devices which
provide adequate nutrition, protection and all the metabolicrequirements to the developing embryo.
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The National Degree College (Autonomous)
Basavangudi, bangalore560 004
A brief report on-
Extra-embryonic membranes in chick
By,
Arun S
(09NCBS1002)
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