foetal membranes-chick

8/11/2019 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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foetal membranes-chick

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