EMBRYONIC DEVELOPMENT...............pptx

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1. EMBRYONIC DEVELOPMENT

2. RECAP OF 1 st WEEK

3. 2 nd WEEK OF DEVELOPMENT

4. Formation of bilaminar germ disc with two cavities The embryoblast rearranges Fast hypoblast or flat cell layer formed facing blastocele The Other cells of embryoblast become columnar to form epiblast towards the embryonic plate

5. The epiblast cells got a small cavity between them the cells split and Surround the cavity Amnioblasts line the roof of the cavity While the floor of the cavity is lined by epiblast This is amniotic cavity Now the hypoblast cells produce a new generation of cells and these cells migrate and line the blastocele These new cells layer is Heuser’s membrane

6. Formation of Extra-embryonic mesoderm The Yolk sac secrets a new generation of cells The cells occupied the area just inside the trophoblastic layers Now the bilaminar germ disc with amniotic cavity and primary yolk sac is surrounded by a new mass of cells and the cell is known as extra-embryonic mesoderm

7. Layers of mesoderm In the extra-embryonic mesoderm there is the formation of a cavity This cavity splits the mesoderm into two layers The layer adjacent to the trophoblast and amniotic cavity is known as somatopleuric mesoderm The layer around the primary yolk sac is known as splanchopleuric mesoderm The cytotrophoblast and the somatopleuric layer is known as chorion The cavity is known as the chorionic cavity

8. Formation of secondary yolk sac The hypoblast cell layer produces one new generation of cells the cells form a membrane inside the Heuser's membrane So a new smaller cavity formed and this known as secondary yolk sack So the primary yolk sac splits into two cavities smaller is secondary yolk sac The larger residual part of the cavity forms an exocoelomic cyst that lies in the chorionic cavity

9. Formation of prochordal plate The hypoblast cells near one end differentiate into long columnar cells These known as prochordal plate It is the site of the future mouth, so it decides the cranial end of the germ disc

10. GASTRULATION process of forming trilaminar germ disc

11. Formation of primitive streak It is a thick linear band Produced by epiblast cells Appears on 15th day Appearance of streak induces the process of gastrulation It decides the craniocaudal axis, ventral dorsal surface and right and left side

12. Formation of primitive node It is an elevated interior end of the primitive streak Also produced by epiblast cells Also known as Hensen's node