Organogenesis is the process by which the three germ layers (ectoderm, mesoderm, and endoderm) develop into internal organs through cell proliferation, migration, aggregation, and differentiation. During organogenesis, the germ layers form organs through processes like folding, splitting, and condensation. Organs continue developing and differentiating after gastrulation through the end of the 8th week of human development. Key events include the formation of the neural tube from ectoderm and the development of connective tissues, ribs, lungs, and other structures from mesoderm. The endoderm forms organs like the stomach, liver, and intestines.

1. Organogenesis
Name: Mubeen Tahira Mirza
Roll No: 881
Semester: 6th
Subject: Analysis of Development
Teacher: Dr. Sagheer Ahmad

2. Organogenesis
Organogenesis is the process by which ectoderm
mesoderm and endoderm develop into the internal organ
of the organism . Cells of each germ layer proliferate
migrate aggregate and differentiate into various tissues
that forms the organs
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3. Stages in early animal development
There are four general stages in early animal development:
Fertilization: the process of a single sperm cell combining with single egg cell to
form a zygote.
Cleavage: rapid, multiple rounds of mitotic cell division where the overall size of
the embryo does not increase. The developing embryos is called a blastula
following completion of cleavage.
Gastrulation: the dramatic rearrangement (movement) of cells in the blastula to
create the embryonic tissue layers. These tissue layers will go on to produce the
tissues and organs of the adult animal.
Organogenesis : the process of organ and tissue formation via cell division and
differentiation.
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4. How does organogenesis occur?
⊳ The germ layers in organogenesis differ by three
processes:
⊳ • Folds,
• Splits, and
• Condensation
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5. Organogenesis
Folds: form in the germinal sheet of cells and usually form an
enclosed tube which we can see in the development of
vertebrates neural tube.
Splits :or pockets may form in the germinal sheet of cells
forming vesicles or elongations. The lungs and glands of the
organism may develop this way.
Organogenesis occur after gastrulation or between forth to
eighth week, we can say that Organogenesis followed by
gastrulation

6. Gastrulation:
The term gastrulation states that: “The dramatic rearrangement (movement)
of cells in the blastula to create the embryonic tissue layers. These tissue
layers will go on to produce the tissues and organs of the adult animal.” The
purpose of gastrulation is to position the three embryonic germ layers, the
endoderm, ectoderm and mesoderm. These layers later develop into certain
bodily systems..
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7. Morphogenesis
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Morphogenesis: Morphogenesis stated that: The origin
and development of morphological characteristics.
Gastrulation and organogenesis together contribute to
morphogenesis: the biological processes that results in
an organism’s shape and body organization

8. .
organogenesis
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9. . Organs form from the germ layers through the differentiation: the process by which a less-specialized cell becomes a
more-specialized cell type. This must occur many times as a zygote becomes a fully-developed organism.
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10. Ectoderm
In vertebrates, one of the primary steps during organogenesis is the
formation of the neural system. The ectoderm forms epithelial cells
and tissues, as well as neuronal tissues. During the formation of the
neural system, special signaling molecules called growth factors signal
some cells at the edge of the ectoderm to become epidermis cells.
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12. The remaining cells in the center form the
neural plate. If the signaling by growth factors
were disrupted, then the entire ectoderm
would differentiate into neural tissue. The
neural plate undergoes a series of cell
movements where it rolls up and forms a tube
called the neural tube. In further development,
the neural tube will give rise to the brain and
the spinal cord.
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13. ⊳ Mesoderm
⊳ The mesoderm that lies on either side of the vertebrate
neural tube will develop into the various connective tissues of
the animal body. A spatial pattern of gene expression
reorganizes the mesoderm into groups of cells called smites,
with spaces between them. The smites will further develop
into the ribs, lungs, and segmental (spine) muscle. The
mesoderm also forms a structure called the notochord,
which is rod-shaped and forms the central axis of the animal
body.
⊳
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15. Endoderm
The endoderm consists, at first, of flattened cells, which
subsequently become columnar. It forms the epithelial lining of
the whole of the digestive tube (except part of the mouth and
pharynx) and the terminal part of the rectum (which is lined by
involutions of the ectoderm). It also forms the lining cells of all
the glands which open into the digestive tube, including those of
the liver and pancreas; the epithelium of the auditory tube and
tympanic cavity; ; the trachea, bronchi, and air cells of the lungs;
the urinary bladder and part of the urethra; and the follicle lining
of the thyroid gland and thymus.
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16. Endoderm (Cont.)
Additionally, the endoderm forms internal organs
including the stomach, the colon, the liver, the
pancreas, the urinary bladder, the epithelial parts of
trachea, the lungs, the pharynx, the thyroid, the
parathyroid, and the intestines.
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17. Organogenesis of Frog
The primary organ rudiments from ectoderm, mesoderm and
endoderm get well established during the processes of gastrulation
and neurulation. In the next stage the primary organ rudiments
subdivide into secondary organ rudiments. These rudiments get
differentiated into various organs and organ systems.
The development of ectodermal organs
The neurula of frog has three kinds of ectodermal tissues namely,
epidermal ectoderm, neural ectoderm and neural crest cells.
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Epidermal ectoderm
⊳ The epidermal derivatives are the skin, olfactory sense organs, ear, lateral
line sense organs, median fins, external gills and lining of mouth and anus
⊳ Neural ectoderm
⊳ This layer of cells form the central nervous system and peripheral nervous
systems.
⊳ The development of mesodermal organs
⊳ The mesodermal derivatives are the limbs, endoskeleton, heart, blood
vessels, kidney, coelom and reproductive organs.
⊳ .

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⊳ The development of endodermal organs
⊳ The predominant endodermal organs are the organs of the alimentary
canal, lungs, pancreas and urinary bladder
⊳ Development of heart in Frog
⊳ The heart is a mesodermal derivative. It develops on the ventral side of
pharynx. It is formed from the lateral plate mesoderm. Initially the heart is
formed as a straight tube. Later it gets folded to form the chambered
heart.

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In humans this process takes place between
about week 3 to the end of week 8. At the end
of this period the embryo is referred to as a
fetus.
The development of the limbs is a good
example of the types of processes that are
involved in organogenesis.

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25. Diagrams and infographics
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