Transcript Comparative Anatomy Early Embryo

Comparative Anatomy
Early Embryology
Kardong
Chapter 5
Part 7
Vertebrate Egg
Figure 7.1. Cledoic egg.
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Amniotic egg- amnion present
Reptilian egg- possesses shell(cleidoic)
Egg Type
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Microlecithal egg- small amount of yolk
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Mesolecithal egg- moderate amount of yolk
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Mammals
Amphibians
Macrolecithal egg- large amounts of yolk
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Reptiles, birds, sharks
Types of Cleavage
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Holoblastic- division
into two equal sized
cells (e.g., in mammals)
Meroblastic- restricted
to periphery, usually in
embryos with large
amounts of yolk.
Meroblastic discoidal Blastodiscs occur in
some fishes, reptiles, birds,
and monotremes
Figure 7.2. Blastodisc.
Amphibian Embryogenesis
Figure 7.3. Frog development; stages of embryogenesis (book fig. 5-12)
Figure 7.4.
Cleavage Stages
Initial: fertilized egg
with fertilization
membrane (arrows)
8 cell stage;
micromeres and
macromeres
16 cell stage (not shown)
2 cell stage;
1st cleavage
32 cell stage;
morula
4 cell stage;
4 blastomeres
64 cell stage;
blastula with
blastocoel cavity
Cleavage Stages (cont’d.)
Figure 7.5.
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Cells push inward to form gastrula
Eventually eliminates blastocoel
Gastrulation
Figure 7.6. Gastrulation.
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Archenteron- primitive gut
Blastopore
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Gives rise to anus in
deuterostomes
Gives rise to mouth in
protostomes
3 primary germ layers
Figure 7.7. Cross section of frog gastrula.
Figure 7.8. Early frog gastrula.
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Dorsal lip - invagination of cells
 Move around yolk cells
 Yolk plug
Notochord forms from mesodermal cells
Neurulation
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Neural plate thickens and
pushed inward
Neurectoderm- gives rise to
nerve tube
Neural crest cells- between
nerve tube and ectoderm
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Dorsal root ganglion, branchial
cartilages cells, and pigment cells
Anterior cells- dermis of face,
cephalic armor, sensory capsules
Figure 7.9. Embryonic neurulation.
Figure 7.10. Neural crest cell differentiation. (Table 5.2; page 189).
Dorsal Mesoderm
Figure 7.11.
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Dermatome- associated with ectoderm
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Myotome
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Dermis in most of body
Skeletal muscle
Sclerotone- associated with nerve tube
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Skeletal and vertebral column
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Dorsal mesoderm (somite)
splits to form coelom cavity
 Somatic mesoderm bound to ectoderm
 Splanchnic mesodermbound to endoderm
Somatopleure - somatic
mesoderm meets ectoderm
Splanchnopleure splanchnic mesoderm
meets ectoderm
Figure 7.12. Mesoderm specialization (book Fig. 5.6).
Dorsal Mesoderm Differentiation
Figure 7.13.
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Dorsal mesoderm (somite)- Epimeric mesoderm
Intermediate mesoderm- Mesomeric mesoderm
Lateral plate mesoderm- Hypomeric mesoderm
Primary Germ Layers
Figure 7.14. Formation of the three primary germ layers.
Germ Layers (cont’d.)
Figure 7.15. Organs derived from the germ layers.
Structures formed from
the three germ layers.
Figure 7.16.
Ectodermal placodes
in a representative
vertebrate.
Figure 7.17.
Extraembryonic Membranes
Figure 7.18. Extraembryonic membranes of cledoic egg.
Extraembryonic Membrane Formation in a Bird
Figure 7.19. Extraembryonic membranes.
Principles of Embryology
Figure 7.20. Embryological development.