Transcript GROWTH AND DEVELOPMENT IN ANIMALS GROWTH AND DEVELOPMENT IN ANIMALS • • • In the early stages of development, the organism is called embryo.

GROWTH AND DEVELOPMENT IN
ANIMALS
GROWTH AND DEVELOPMENT IN
ANIMALS
•
•
•
In the early stages of development, the
organism is called embryo. The basic
processes in development of embryo
include;
Cleavage (Segmentasyon)
Growth (Büyüme)
Differentiation (Farklılaşma)
CLEAVAGE
 After fertilization, the zygote begins a
series of cell divisions known as cleavage.
 During cleavage, the fertilized egg
divides by mitosis and each division
decreases cell size.
*** During cleavage, the cells do not grow.
The cells formed during cleavage are called
blastomere.
CLEAVAGE
mitosis
zygote
mitosis
mitosis
1st division
2nd division
(2 blastomeres)
(4 blastomeres)
3rd division
(8 blastomeres)
Sea urchin egg
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MORULA
 The early divisions of cleavage result in a
solid ball of cells, which is called morula.
 Blastomeres that form the morula are
same size.
*** The cells that make up the morula has
been formed by mitosis so they carry the
same genetic information.
Morula latince dut
anlamına gelmektedir.
***
BLASTULA
As the cells of the morula continue to
divide, they are rearranged to form a
hollow sphere.
Usually, the layer of cells in the sphere is
only one cell thick. The inside of the
sphere is filled with fluid. At this stage
the embryo is called blastula and the
fluid filled inside of the sphere is called
blastocoel. (birinci karın boşluğu ).
animal pole
*** There is still no differentiation of cells at
that stage.
vegetal pole
www.luc.edu/depts/ biology/dev/urchega.jpg
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1.Blastocoel
2.Enterocoelic pouch
3.Mouth
4.Archenteron
5.Blastopore (anus)
•blue=Ectoderm
•red=Mesoderm
•yellow=Endoderm
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GASTRULATION
As the blastula develops, it
reaches a point at which the
cells begin to grow before
dividing. At this time mitotic
division continues along with
the growth.
The cells at the lower part of
the blastula or vegetal pole,
move inward and form a twolayered embryo called the
gastrula.
The opening created is
called the blastopore. It later
becomes
one
of
the
openings to the digestive
system.
GASTRULATION
The outer layer of cells in the
gastrula is called ectoderm.
The inner layer is endoderm.
The cavity within the gastrula is
called the primitive gut
(archenteron). It later becomes
the digestive system.
Archenteron grows inside the
blastocoel towards the ectoderm
and a new opening is created at
the opposite side of the
blastopore, which will be the
second opening of the digestive
system.
After the endoderm and ectoderm are established, a
third cell layer, mesoderm forms between them.
**In Sponges and Coelenterata (Hydra), embryonic
development stops at the gastrulation phase. Therefore,
their bodies are made up of two layer of cells.
**Including earthworms, all of the other animals have
mesoderm.
GROWTH AND DIFFERENTIATION
Histogenesis and Organogenesis
 The embryonic layers (germ layers)
formed during gastrula, may give rise to
tissues
(histogenesis)
or
organs
(organogenesis)
of
the
multicellular
animals.
 The changing of unspecialized embryonic
cells into the specialized cells, tissues, and
organs is called differentiation.
Development of Organs and Organ Systems from the Germ Layers
ECTODERM
MESODERM
ENDODERM
•nervous system
•brain
•spinal cord,
nerves
•sense organs
•epidermis of skin
•hair, nails, sweat
gland, lens of the
eye
•bones
•muscles
•blood and blood
vessels
•reproductive and
excretory systems
•inner layer of skin
( dermis)
•connective tissue
•lining of
digestive tract
urinary
bladder
•lining of
trachea,
bronchi, lungs
•liver,pancreas
thyroid,
parathyroid,
thymus
NEURALATION
On the upper surface of ectoderm, the cells divide,
forming a neural plate that has two raised edges,
called neural folds.
The neural folds come together over the center of
the neural plate and form neural tube. Later the
neural tube forms the brain and spinal cord. This is
called neuralation.
After neuralation, all of the organs of the body
start to form by a series interactions between the
cells.
EMBRYONIC INDUCTION
As an embryo develops, there must be a coordination
between its tissues. By the late blastula and early gastrula,
the way in which groups of cells will develop has been
determined. Cells in certain regions develop along certain
lines.
For ex, there is a particular place in the frog embryo that
normally develops into eye. If this tissue is removed from the
embryo and placed into culture medium, it develops into an
irregular mass of cells.
During the development of the embryo, the mechanism by
which one group of cells (tissues) influences the development
of an adjacent group of cells is called induction.
SPEMANN EXPERIMENTS
Hypothesis 1 Experiment Result
Conclusion
Ectoderm
that is
removed
from the
embryo can
give rise to
nerve
tissues.
Ectoderm
should be
attached to
the embryo
in order to
form nerve
tissue.
Ectoderm
is removed
and placed
in a special
medium.
Ectoderm
that is
isolated
does not
give rise to
nerve
tissue in
the
medium.
Hypothesis 2 Experiment
Mesoderm
that is
responsible
for the
formation of
nerve tissue,
cause
ectoderm to
form nerve
tissues.
Ectoderm
layer of
embryo is
folded
upwards and
mesoderm
layer is
removed.
Ectoderm is
straightened
and embryo is
put into a
culture
medium.
Result
Conclusion
Nerve
tissue of
the
embryo
doesn't
form.
Mesoderm
induces
ectoderm to
give rise to
nerve tissue.
upper
ectoderm
upper
mesoderm
Embryo that its upper
mesoderm is removed
Nerve tissue
doesn’t form in
this embryo
Hypothesis 3 Experiment
Any
ectoderm
layer that
touches to
the dorsal
mesoderm
(sırt
mezodermi)
can give rise
to nerve
tissue.
•Dorsal
mesoderm of 1st
embryo is
removed.
•Ventral
mesoderm
(karın
mesodermi) of
2nd embryo is
removed.
•Dorsal
mesoderm of 1st
is placed
instead of
ventral
mesoderm of
the 2nd embryo.
Result
Conclusion
In 2nd
embryo (that
has two
dorsal
mesoderms),
two distinct
nerve
tissues are
formed. Twin
embryos
that are
attached to
each other
are formed.
Dorsal
mesoderm
induces
ectoderm and
controls the
differentiation
of nerve
tissue.
ectoderm
blastocoel
donor embryo
blastopore
Neural plates
second notochord
develops and larvae with
two head forms
Embryonic Induction in the Formation
of the Eye of a Vertebrate
 During the differentiation of cells that form
the vertebrate eye, inductions of two
ectoderm take place.
 Optic cup (optic vesicle =göz çukuru) is
formed by the induction of brain ectoderm
and lens of the eye is formed by the
induction of lens ectoderm. In order for lens
to develop, brain ectoderm must induce lens
ectoderm.
@
1. The eye begins
to take shape
from an outgrowth
of the developing
brain (the optic
vesicle) and an
adjacent group of
cells on the body
surface
(lens
ectoderm).
2. As a result of earlier
inductions, some of
the cells of the optic
vesicle
and
lens
ectoderm
undergo
changes
and
fold
inwards. The optic
vesicle transforms into
the optic cup, which
will become retina and
the optic stalk, which
will become the optic
nerve.
3. Cells of the
optic cup
induce the lens
ectoderm to
start forming
the lens.
4. Finally, the
cells of the
developing
lens
induce
development
of the cornea.
Role of nucleus and Cytoplasm in
Differentiation
 Different sections of the DNA in a cell can be
turned off or on. This results in the formation of
different types of cells. If this was not the case,
differentiation would not take place, and all the
cells of an embryo would be same.
 The interaction between the DNA and certain
things in the cytoplasm controls development. As a
result, parts of the hereditary material are switched
on and off, and this in turn determines the direction
of cellular differentiation.
Factors that have role in differentiation;




Interaction between DNA and
cytoplasm (genes that are switched on
or off)
Embryonic induction (role of
neighbouring cells)
Cell migrations
Controlled cell deaths (apoptosis)