GASTRULATION
Blastula
Early gastrula
Gastrula
Ectoderm
Endoderm
Mesoderm
Archenteron
Blastopore
Page 3: GASTRULATION
Definition:
A highly coordinated process of cell and tissue movements that dramatically reorganizes the cells of a blastula.
Page 4: GASTRULATION
Gastrulation Results:
Rearranges blastula cells into a three-layered embryo known as gastrula, which features a primitive gut.
The three embryonic germ layers formed during gastrulation:
Ectoderm: Forms the outer layer.
Endoderm: Lines the digestive tract.
Mesoderm: Partially fills the space between ectoderm and endoderm.
Page 5: Diploblastic vs. Triploblastic
Diploblasts:
Animals with two embryonic germ layers: endoderm (inner layer or mesendoderm) and ectoderm (outer layer).
Non-living middle layer (mesoglea) exists between the ectoderm and endoderm.
Triploblasts:
Animals with three germ layers, forming the majority of higher animals.
Develop true organs (e.g., heart, kidneys, lungs).
Page 6: Diploblastic vs. Triploblastic
Mesoglea:
The non-living middle layer in cnidarians (e.g., coral, jellyfish) and ctenophores, functioning as a hydrostatic skeleton.
Page 7: GASTRULATION Components
Key Structures:
Gastrula, Mesoderm, Blastula, Ectoderm, Endoderm, Blastocoel, Blastopore, Archenteron.
Page 8: GASTRULATION Functions
Establishment of the three basic germ layers (Ectoderm, Mesoderm, Endoderm).
Proper positioning of cell groups for organ systems and tissue development.
Positioning of cell groups to influence each other's differentiation.
Page 9: Changes during Gastrulation
Involves changes in cell shape and cell adhesion.
Page 10: Cytoskeletal Events
Microtubule elongation drives cell shape changes.
Apical actin filament bundles contract, narrowing cells at their apices.
Contraction of adhesion belts drives apical constriction.
Page 11: Questions to Consider
How are tissue layers established?
How do cells reach their proper positions for development?
Answer lies in Morphogenetic Movements.
Page 12: Morphogenetic Movements
Involve coordinated movements of the entire embryo.
Cell migrations in one area must be synchronized with other movements in different areas of the gastrulating embryo.
Page 13: INVAGINATION
Definition:
Infolding of a region of cells, analogous to the indenting of a soft rubber ball when poked.
Page 14: VAGINATION
Refers to movements similar to invagination but involves different dynamics in the gastrulation process.
Page 15: INVOLUTION
Definition:
Inward movement of an expanding outer layer that spreads over the internal surface of remaining external cells.
Page 16: Morphogenetic Movements Continuum
Types of Movements:
Invagination
Involution
Ingression
Delamination
Epiboly
Page 17: INGRESSION
Definition:
The migration of individual cells from the surface layer into the embryo's interior.
Page 18: INGRESSION Definition Confirmed
Cytological details and mechanisms of ingression continue to evolve through research.
Page 19: DELAMINATION
Definition:
The splitting of one cellular sheet into two parallel sheets, contributing to complex structure formation during gastrulation.
Page 20: DELAMINATION Details
Further clarification on delamination processes and implications in embryonic structural development.
Page 21: EPIBOLY
Definition:
Movement of epithelial sheets, typically ectodermal cells, that spread as a unit instead of as individual cells to enclose deeper embryo layers.
Page 22: EPIBOLY Example
Observed in zebrafish embryos, demonstrating the practical application of epiboly in development.
Page 23: Morphogenetic Movements Overview
Various types of movements including Invagination, Ingression, Involution discussed in context of cellular layout.
Page 24: Morphogenetic Movements Breakdown
Detailed diagrams showing the roles of ectoderm, mesoderm, endoderm, and friendly terms like primitive streak and extraembryonic tissue roles.
Page 25: Types of Movement in Gastrulation
Description of local inward buckling, individual cell movements, spreading of cell layers, etc.
Page 26: Changes in Cell Shape
Complex changes in cell shape can lead to elongation or shortening of flat sheets of cells.
Cell Intercalation: Movement between rows of cells to create a longer and thinner structure.
Convergent Extension: Highly directional intercalation involved in streak formation.
Page 27: Intercalation and Convergent Extension
Important processes driving structural designs in embryonic formations, especially prominent in avian and mammalian development.
Page 28: PRINCIPLES OF DEVELOPMENT
Reference to developmental biology principles; convergence and extension highlighted.
Page 29: Major Tissue Regions after Gastrulation
Detailed layout of various embryonic structures including ectoderm, mesoderm, endoderm, and their respective derivatives.
Page 30: Adult Derivatives of Germ Layers
Comprehensive list showing derivatives from ectoderm, mesoderm, and endoderm throughout vertebrate development.
Page 31: ECTODERM, MESODERM, ENDODERM
Detailed breakdown of organ and tissue types formed from each embryonic germ layer.
Page 32: Germ Layer Functions
Overview of how each germ layer contributes to organismal anatomy and physiology.
Page 33: Gastrulation in Sea Urchin
Cell migration and role of blastopore in embryonic development. Formation processes outlined.
Page 34: Gastrulation in Sea Urchin Example
Key structures visualized detailing the processes involved in sea urchin gastrulation.
Page 35: Micromeres and Macromeres
Explanation of the migration patterns and cell types in sea urchin gastrulation process.
Page 36: Step 1: Primary Mesenchyme Ingression
Description of the ingressing mesenchyme cells and their role in embryonic development.
Page 37: Extracellular Matrix and Mesenchyme Ingression
Diagram clarifying the role of extracellular matrix in mesenchymal cell dynamics.
Page 38: Changes in Cell Adhesion
Describes the importance of cellular adhesion changes during the various stages of gastrulation.
Page 39: Primary Mesenchyme Migration
Visualizing the invaginating primary mesenchyme on the extracellular matrix.
Page 40: Filopodia Functionality in Mesenchyme Cells
Details on how primary mesenchyme cells utilize filopodia for migration during development.
Page 41: Spicule Formation
Primary mesenchyme cells fusing to form skeletal structures.
Page 42: Step 2: Invagination and Archenteron Formation
Detailed mechanism of archenteron creation throughout gastrulation stages.
Page 43: Apical Constriction
Describes how apical constriction affects invagination during gastrulation.
Page 44: Invagination Mechanism
Elucidates the changes in the extracellular matrix during the invagination of the vegetal plate.
Page 45: Step 3: Cell Intercalation and Tube Formation
Overview of how cell shapes and arrangements convert the archenteron into a gut tube.
Page 46: Secondary Mesenchyme Pulling Mechanism
Describes secondary mesenchyme cells' roles in the developing gut tube through the use of filopodia.
Page 47: Skeletal Rod Formation
Discussion of structure formation in relation to primary mesenchyme activity.
Page 48: Gastrulation in Frog
Overview of frog blastula characteristics and invagination results, concluding gastrulation processes.
Page 49: Reiteration of Frog Gastrulation Processes
Detailed summary of cell movements and invagination leading to endoderm and mesoderm formation.
Page 50: Cleavage Initiation in Xenopus
Explains the start of gastrulation in Xenopus species illustrating cleavage stages.
Page 51: Functions of the Blastocoel
Functions:
Prevent premature cell interactions.
Provides space for migrating cells during gastrulation.
Page 52: Fate Map in Xenopus Blastula
Overview of cell fates illustrating endoderm and mesoderm differentiation in early cleavage.
Page 53: Blastopore Formation
Details cellular movements and morphogenetic implications during blastopore formation.
Page 54: Mechanism #1 Apical Constriction
Exploring how apical constriction further induces blastopore invagination.
Page 55: Mechanism #2 Involution of Marginal Zone Cells
Description of how marginal zone cells undergo involution during gastrulation.
Page 56: Involution and Fibronectin's Role
Explaining the critical role of fibronectin in facilitating involution during the gastrulation process.
Page 57: Fibronectin and Mesodermal Cell Involution
Discussing the dependency of mesodermal cell movement on fibronectin presence.
Page 58: Archenteron Formation
Outlining convergent extension as a driving force for archenteron formation.
Page 59: Ectoderm Epiboly Mechanisms
Discussing the roles of ectodermal epiboly and related structural movements.
Page 60: Further Epiboly Dynamics
Visualization of epiboly processes during developmental stages via embryonic architecture.
Page 61: Mesenchyme Migration in Gastrulation Context
Comparative analysis of mesenchyme migration in different organisms including sea urchins and frogs during gastrulation.
Page 62: Gastrulation in Chick Embryo
Processes occurring during chick gastrulation involving epiblast movement and primitive streak dynamics.
Page 63: Chick Gastrulation Overview
Visual layout illustrating cell types in gastrulation and their migratory pathways.
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Page 65: Gastrulation Mechanisms in Birds
Detailed visual explanation of structures like the primitive streak and mesodermal/ectodermal precursors during chick development.
Page 66: Cleavage and Gastrulation Connection in Xenopus
Linking initial cleavage stages to subsequent gastrulation delineating developmental milestones.
Page 67: Mammalian Gastrulation Overview
Description of mammalian-specific features in gastrulation process.
Page 68: In mammals, gastrulation initiates
Discussion on the formation of the placental connection and subsequent early embryonic arrangement.
Page 69: Mammalian Gastrulation and Development
Visual representations of mammalian gastrulation across various species and focused on key developmental structures.
Page 70: Mammalian Development Characteristics
Features outlining differences in mammalian embryo development vis-a-vis other classes.
Page 71: Completion of Cleavage and Gastrulation Initiation
Discusses the transition from blastocyst to established germ layers and their relevance.
Page 72: Trophoblast and Embryonic Development
Overview of trophoblast's role in implantation and subsequent embryonic layer formation.
Page 73: Early Human Embryonic Development
Detailing trophoblast function alongside epiblast and hypoblast contributions in early human development.
Page 74: Human Gastrulation in Depth
Exploring further on trophoblast and role alterations leading to fully established embryonic structures after gastrulation.
Page 75: Continuing Early Embryonic Human Development
Description of the various structures developing from early embryonic layers focused on membranes and organ systems.
Page 76: Ectoderm, Mesoderm, Endoderm Roles
Summary of how each germ layer contributes to the formations and outcomes of organ systems across species.
Page 77: Four Stages of Early Human Development
Comprehensive overview including the trophoblast role, maternal interactions, and embryonic formation concluding gastrulation.