development of Chick embryo

1. Growth and Development in
animals

2. Embryology
The study of growth and differentiation undergone by an organism in the course of development from a
single fertilized egg into highly complex and an independent living being like his parents,

3. Development
•It is an ordered series of irreversible steps
•Each step setting up the necessary conditions for next step
•As all animals are related to each pother through evolution, so they have some similarities in their various
forms during development

4. Key events in animal
development

5. Development of Chick

6. Fertilization and incubation
1: chick egg ( called yolk ) is surrounded by
various accessory coverings , secreted by
female reproductive tract .
2: fertilization is internal . It takes place just the
ovum enters to the oviduct
3: when the egg passes through the uterus (
shell gland) , the shell is secreted around the
egg

7. Uterus or shell gland
when the egg passes through the uterus ( shell
gland) , the shell is secreted around the egg

8. Incubation
When the egg is laid , the development ceases
until it matches with the mother hen
temperature .
In incubating eggs artificially , the incubators
are usually regulated at temperature between
36-38 degree , and on 21st day , chick
completes its development and hatch.

9. 1: Cleavage
•After the fertilization, egg undergoes a series
of mitotic division called cleavage
•Discoid Cleavage
In bird’s egg , there is a small disc of
protoplasm lying on the surface of yolk at
animal pole. Cell division is confined to this
disc, that’s why it is also called Discoidal
Cleavage

10. Stages of cleavage
•The cleavage furrows start in the clear
cytoplasmic region .
•The first two cleavage planes are vertical but
the third runs horizontally parallel to the
surface and thus cuts underneath the
cytoplasm and separates it from the yolk.
•The successive cleavages become irregular
and number of cells increase

11. Morula
•Cleavage results in the rounded closely packed
mass of blastomeres
•It consists of disc shaped mass of cells (
blastoderm) two or more layers of thickness
lying close to yolk.
•In the center of blastoderm the cells are
smaller and completely defined , while those
present at the periphery are flattened and
larger.

12. Blastula
•The morula stage is short lived and soon
changes into blastula .
•It contains segmentation cavity called
blastocoel
•The Discoidal cavity above the blastocoel is
called blastoderm
•The margin of the blastoderm in which the
cells remain undetached from the yolk and
closely adherent to it is called the zone of
junction

13. Gastrulation
It is characterized by the movement and
rearrangement if the cells in embryo
During this stage, the blastoderm splits into
two layers
1: Epiblast -- the upper layer of the cells (
it is presumptive of ectoderm and mesoderm)
2: Hypoblast - the lower layer of the cells ( it
is presumptive of endoderm
The hypoblast cells grow outward over the
surface of yolk , then downward around it
forming endodermal lining of yolk sac.

16. Area Pellucida and Area Opaca
Area Pellucida - it is the central area , in
which the central cells of blastoderm get
separated by yolk , and giving a translucent
appearance called area of Pellucida
Area Opaca - the peripheral part of
blastoderm , where the cells remain
unseparated from the yolk is called area
Opaca. It is white area that transmits light

17. Notochord and mesoderm
formation
Primitive streak  in chick the mesoderm cells
don't invaginate like in amphibians , but they
migrate medially and caudally from both sides
and create a mid line thickening called
primitive streak.
Which grows rapidly in length as more and
more presumptive mesoderm cells continue to
aggregate inward
The shape of blastoderm at this stage changes
from circular to pear shape.

19. Primitive node The anterior end of primitive
streak is occupied by an aggregation – the
primitive node or notochordal cells while rest
of the cells are mesodermal cells
The primitive streak represents both the lateral
and dorsal lip of blastopore

22. Primitive Ridges and primitive groove -
The continuous migration of the cells take
place between epiblast and hypoblast result in
the formation of groove along the whole
length of primitive streak . This is called
primitive groove marked by thick margins
called primitive ridges
Henson's node- At the anterior end of the
primitive streak , closely packed cells form a
thickening called Henson's node.

23. Notochord formation
After the primitive streak has been formed,
and the endodermal well established , the cells
begin to push in from the region of Henson’s
Node to from the rod like structure called
notochord in the midline beneath the
ectoderm.
It is the most prominent feature in 18 hour
chick embryo .

25. Gastrocoel and primitive gut
After the formation of primitive streak , the
endoderm is well established .
Cells begin to push in from the region of
Henson node to form the rod like notochord in
the midline beneath the ectoderm
In the embryo of 18 hours the notochord is one
of the prominent structure.
In 18 to 20 hours of incubated embryo the
ectoderm has spread and become organized
into coherent layer of cells merging
peripherally with the yolk and the marginal
area where the expanding germ layers merge
underlying yolk is germ wall and the cavity
between the yolk and the endoderm which has
been called as gastrocoel is now called
primitive gut

26. Somites
From henson node . Dorsal mesoderm is
formed and organized into somites . ( paired
masses of mesoderm)
It has two types
a) Somatic mesoderm - that is found at
the periphery of the embryo. It is also
called as lateral plat mesoderm
b) Splanchnic mesoderm -- which is
adjacent to the endoderm and yolk sac,
forms the heart as well as the visceral
layer of the serous pericardium and blood
vessels. It also contributes to the smooth
muscle and connective tissues of the
respiratory and digestive organs. It is also
called as visceral mesoderm
Coelom  the cavity formed between
splanchnic and somatic mesoderm is
called as coelom.

27. Somatic and splanchnic mesoderm

28. Neurulation
On the dorsal surface of gastrula , over the
notochord , presumptive neural ectoderm is
present in the form of band,
As gastrula elongates , the band thickens to
form a neural plate
In chick of 18 hours , neural plate is seen as flat
, thickened area of ectoderm
In embryo of 21-22 hours , a longitudinal
folding has occurred , creating neural groove in
mid dorsal line, on either side of neural folds.
In 24 hours of embryo . The folding of neural
plate is clearly visible
At this point the embryo is called neurula

29. Neural tube, nervous system and
neurocoel
The anterior end of the neural groove forms
future brain and rest of it forms spinal cord
In the mean time the neural plate sinks and the
neural folds grow towards one another and
meet at mid dorsal line and forms a neural
tube
At each end of neural tube , a small opening
called anterior and posterior neural pores are
also seen, which close at later
With the formation of neural tube , there is
also formation of central nervous system and
the cavity enclosed is called neurocoel .
This whole process is called Neurulation

31. Video links
• https://www.youtube.com/watch?v=LKvez9duEHQ
• https://www.youtube.com/watch?v=-Ah-gT0hTto
• https://www.youtube.com/watch?v=wnnhMZtCvnQ