1. Cavitation 2. Compaction 3. Implantation 4. Cleavage
3 – 1 – 2 – 4
4 – 2 – 1 – 3
2 – 4 – 1 – 3
4 – 2 – 3 – 1
The correct order of the listed events of the pre-embryonic period is: Cleavage-Compaction-Cavitation-Implantation.
Events of the pre-embryonic phase of development
- Cleavage: Formation of blastomeres; the cells are loosely arranged until the 8-cell stage.
- Compaction: After 3 cleavages, the blastomeres are held together by tight junctions.
- Differentiation: The compacted 8-cell stage divides to form a 16-cell morula.
- Cavitation: Formation of the blastocyst with inner cell and outer cell mass.
- Hatching of the blastocyst: Release of the blastocyst from the zona pellucida.
- Implantation: Attachment of developing embryo to the uterine endometrium.
- Cell mass differentiation: Differentiation of the embryoblast (inner cell mass) into columnar epiblast cells and cuboidal hypoblast cells.
- Bilaminar disc formation: Formation of the bilaminar disc suspended by the connecting stalk. It has two layers (epiblast and hypoblast) and two cavities (amniotic and yolk sac).