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Understanding Gastrulation: The Formation of a Three-Layered Embryo

Gastrulation is a crucial developmental process that rearranges the blastula into a three-layered embryo known as the gastrula, composed of three primary germ layers: ectoderm, mesoderm, and endoderm. Each layer has specific contributions to the developing organism. The ectoderm forms structures such as the brain and skin. The mesoderm gives rise to the heart, muscles, and bones. The endoderm develops into the gut lining and organs like the liver. Additionally, extraembryonic membranes like the amnion, yolk sac, allantois, and chorion provide essential support and protection during embryonic development.

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Understanding Gastrulation: The Formation of a Three-Layered Embryo

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  1. Human Development Ch 28

  2. Gastrulation rearranges the blastula to form a three-layered embryo with a primitive gut • Gastrulation rearranges the embryo into a triploblastic gastrula. Primary Germ Layers Ectoderm Endoderm Mesoderm

  3. Fates of the Primary Germ Layers • Ectoderm • hair, nails, epidermis, brain, nerves • Mesoderm • notochord (in chordates), dermis, blood vessels, heart, bones, cartilage, muscle • Endoderm • internal lining of the gut and respiratory pathways, liver, pancreas

  4. Body Cavities coelom Mesoderm Eucoelomate- body cavity completely lined with mesoderm gut Ectoderm Endoderm

  5. The Formation of Primary Germ Layers

  6. Gastrulation

  7. Extraembryonic Membranes • Amnion: epiblast cells form a transparent sac filled with amniotic fluid • Provides a buoyant environment that protects the embryo • Helps maintain a constant homeostatic temperature • Allows freedom of movement and prevents parts from fusing together • Amniotic fluid comes from maternal blood, and later, fetal urine amnion

  8. Extraembryonic Membranes • Yolk sac: a sac that hangs from the ventral surface of the embryo • Forms part of the digestive tube • Source of the earliest blood cells and blood vessels Yolk sac

  9. Extraembryonic Membranes • Allantois: a small outpocketing at the caudal end of the yolk sac • Structural base for the umbilical cord • Becomes part of the urinary bladder • Chorion: helps form the placenta • Encloses the embryonic body and all other membranes Allantosis Chorion

  10. Neurulation A: Embryonic disc accomplished gastrulation - ectoderm thickens B: Neural plate forms neural folds and neural groove

  11. Neurulation C: Neural folds close D: Neural tube detached from surface ectoderm

  12. Embryonic Folding

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