extra embryonic membranes in birds. easy notes on it. you can read and understand it easily. this is in simple English language

2. INTRODUCTION
• These are the membranes which do not form any part of the embryo but
performs various functions which assist in the development of embryo.
• The Extraembryonic Membrane are discarded at the time of hatching.
• These membranes are formed outside the embryo.
• They performs roles in nutrition, gas exchange & waste removal from the
embryo.
• All the Extraembryonic Membranes are discarded at hatching while the
yolk sac is incorporated into the Small Intestine.
• Chorion is outer most membrane enclosing all the outer membrane.
• Amnion is the inner most membrane.

3. On the basis of extraembryonic membrane
AMNIOTES
These are the vertebrates
group whose eggs contain
extraembryonic membranes
for protecting the embryo.
They lay eggs on the land.
E.g.:- Reptiles, Birds &
Mammals.
ANAMNIOTES
These are the vertebrates
group whose eggs don’t
contain extraembryonic
membranes during embryonic
development.
They lay eggs in water
E.g.:- Fish, Amphibia.

4. Types of Extraembryonic Membranes in Birds
• There are four types of extra embryonic membranes are
found in Birds.
i.e.:-
1) Yolk Sac :- Splanchnic Mesoderm(O) & Endoderm(I)
2) Amnion :- Somatic Mesoderm(O) & Ectoderm(I)
3) Chorion :- Ectoderm(O) & Somatic Mesoderm(I)
4) Allantois :- Splanchnic Mesoderm(O) & Endoderm(I)

5. DEVELOPMENT OF YOLK SAC
• It is the 1st extraembryonic membrane that appear in a embryo.
• It is formed of Splanchnopleure (Splanchnic mesoderm &
Endoderm).
• The yolk sac never surrounds the yolk fully.
• With the formation of the yolk sac, the intra embryonic
Splanchnopleure is subjected to folds resembling with the most
resembling body fold.
• The endoderm of yolk sac secrets enzyme which break the yolk
into diffusible substances.
• The yolk sac is formed completely on the 9th day of incubation.

6. Functions of Yolk Sac
• Yolk is absorbed in embryo by
vitelline veins of yolk sac &
nourishes it.
• The yolk sac gradually reduces
with the absorption of yolk.
• The function of yolk sac is to
digest the yolk & to transfer the
products of digestion to the
embryo.

7. Development of Amnion
• Formed of somatopleure (inner ectoderm and outer mesoderm).
• It surrounds the embryo.
• It appears after 30 hours of incubation.
• A amniotic cavity is present between the amnion membrane and
the embryo, which filled with the amniotic fluid.
• In this fluid filled cavity embryo floats.
• The fusion of amniotic folds produces 2 sac like membrane & 2
cavities.
• The region where the union of amniotic folds occurs is called
seroamniotic connection

8. Functions of Amnion
• Protection of the embryo from
the mechanical injury and
desiccation.
• Amniotic fluid acts as shock
absorber.
• Protect from sudden
temperature changes.

9. Development of Chorion
• Formed of somatopleure (outer ectoderm and inner mesoderm).
• The outer somatopleuric sheet become the chorion.
• It forms the outermost boundary.
• Space between amnion and chorion is called chorionic cavity which
further provides protection to the embryo.
• The mesoderm emerge from respective part of embryo start
growing & folding upon the dorsal side where both fused to form
outer chorion & inner amnion.

10. Functions of Chorion
• In reptiles, birds and
prototherians, chorion along
with allantois acts as extra
embryonic lung and helps in
exchange of gases.
• The function of chorion is to
protect & nurture the
embryo.
• The chorionic fluid protects
the embryo from shock &
the chorionic villi allow the
exchange of nutrients,
oxygen.

11. Development of Allantois
• Formed of Splanchnopleure (inner endoderm and outer splanchnic
mesoderm).
• About the 3rd day of incubation the region of the future floor of endodermal
hind gut begins to bulge as precocious urinary bladder called the allantois.
• The allantois arises as a ventral outgrowth of the Splanchnopleure from the
hind gut.
• The allantoic outgrowth consists of endoderm with splanchnic or visceral
mesoderm layer covering it from out side.
• The allantois grows very fast & soon penetrates into the extraembryonic
coelom, the space between the yolk sac, the amnion & the chorion.
• The distal part of the allantois expands & remain connected with the hind
gut of the embryo by means of a narrow allantoic stalk.

12. Functions of Allantois:
• The cavity of the allantois serves as a
urinary bladder.
• It stores the protein breakdown
products in the form of water
insoluble crystal of uric acid inside of
egg up to the time of hatching.
• The vascular chorioallantoic
membranes of allantois & chorion acts
as an extraembryonic lung which
supply oxygen to the developing
embryo.
• Gaseous exchange takes place
between the blood circulating in the
chorioallantoic membrane & the
external air through the porous shell.

13. Thank You