Comparative Anatomy Early Embryology

Comparative AnatomyComparative AnatomyEarly EmbryologyEarly Embryology

KardongKardongChapter 5Chapter 5

Part 7Part 7

Vertebrate EggVertebrate Egg

Amniotic egg- amnion presentAmniotic egg- amnion present Reptilian egg- possesses shell(cleidoic)Reptilian egg- possesses shell(cleidoic)

Figure 7.1. Cledoic egg.

Egg TypeEgg Type

Microlecithal egg- small amount of yolkMicrolecithal egg- small amount of yolk MammalsMammals

Mesolecithal egg- moderate amount of yolkMesolecithal egg- moderate amount of yolk AmphibiansAmphibians

Macrolecithal egg- large amounts of yolkMacrolecithal egg- large amounts of yolk Reptiles, birds, sharksReptiles, birds, sharks

Types of CleavageTypes of Cleavage

Holoblastic- division into Holoblastic- division into two equal sized cells two equal sized cells (e.g., in mammals)(e.g., in mammals)

Meroblastic- restricted Meroblastic- restricted to periphery, usually in to periphery, usually in embryos with large embryos with large amounts of yolk. amounts of yolk. Meroblastic discoidal - Meroblastic discoidal -

Blastodiscs occur in Blastodiscs occur in some fishes, reptiles, birds, some fishes, reptiles, birds, and monotremes and monotremes Figure 7.2. Blastodisc.

Amphibian EmbryogenesisAmphibian Embryogenesis

Figure 7.3. Frog development; stages of embryogenesis (book fig. 5-12)

Cleavage StagesCleavage Stages

Initial: fertilized egg with fertilization

membrane (arrows)

2 cell stage; 1st cleavage

4 cell stage; 4 blastomeres

8 cell stage; micromeres and macromeres

16 cell stage (not shown)

64 cell stage; blastula with blastocoel cavity

32 cell stage; morula

Figure 7.4.

Cells push inward to form gastrula Cells push inward to form gastrula Eventually eliminates blastocoelEventually eliminates blastocoel

Cleavage Stages Cleavage Stages (cont’d.)(cont’d.)

Figure 7.5.

GastrulationGastrulation

Archenteron- primitive gutArchenteron- primitive gut BlastoporeBlastopore

Gives rise to anus in deuterostomesGives rise to anus in deuterostomes Gives rise to mouth in protostomesGives rise to mouth in protostomes

3 primary germ layers3 primary germ layers

Figure 7.6. Gastrulation.

Figure 7.7. Cross section of frog gastrula.

Dorsal lip - invagination of cellsDorsal lip - invagination of cells Move around yolk cellsMove around yolk cells Yolk plugYolk plug

Notochord forms from mesodermal cellsNotochord forms from mesodermal cells

Figure 7.8. Early frog gastrula.

NeurulationNeurulation

Neural plate thickens and Neural plate thickens and pushed inwardpushed inward

Neurectoderm- gives rise to Neurectoderm- gives rise to nerve tubenerve tube

Neural crest cells- between Neural crest cells- between nerve tube and ectodermnerve tube and ectoderm Dorsal root ganglion, branchial Dorsal root ganglion, branchial

cartilages cells, and pigment cellscartilages cells, and pigment cells Anterior cells- dermis of face, Anterior cells- dermis of face,

cephalic armor, sensory capsulescephalic armor, sensory capsules

Figure 7.9. Embryonic neurulation.

Figure 7.10. Neural crest cell differentiation. (Table 5.2; page 189).

Dorsal MesodermDorsal Mesoderm

Dermatome- associated with ectodermDermatome- associated with ectoderm Dermis in most of bodyDermis in most of body

MyotomeMyotome Skeletal muscleSkeletal muscle

Sclerotone- associated with nerve tubeSclerotone- associated with nerve tube Skeletal and vertebral columnSkeletal and vertebral column

Figure 7.11.

Dorsal mesoderm (somite) Dorsal mesoderm (somite) splits to form coelom cavitysplits to form coelom cavity Somatic mesoderm - Somatic mesoderm -

bound to ectodermbound to ectoderm Splanchnic mesoderm- Splanchnic mesoderm-

bound to endodermbound to endoderm Somatopleure - somatic Somatopleure - somatic

mesoderm meets ectodermmesoderm meets ectoderm Splanchnopleure - Splanchnopleure -

splanchnic mesoderm splanchnic mesoderm meets ectodermmeets ectoderm

Figure 7.12. Mesoderm specialization (book Fig. 5.6).

Dorsal Mesoderm DifferentiationDorsal Mesoderm Differentiation

Dorsal mesoderm (somite)- Epimeric mesodermDorsal mesoderm (somite)- Epimeric mesoderm Intermediate mesoderm- Mesomeric mesodermIntermediate mesoderm- Mesomeric mesoderm Lateral plate mesoderm- Hypomeric mesodermLateral plate mesoderm- Hypomeric mesoderm

Figure 7.13.

Primary Germ LayersPrimary Germ Layers

Figure 7.14. Formation of the three primary germ layers.

Germ Layers Germ Layers (cont’d.)(cont’d.)

Figure 7.15. Organs derived from the germ layers.

Structures formed from Structures formed from the three germ layers.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.