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10.1 Early development and implantation
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Fig. 1 - From the oocyte to the morula |
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Legend |
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Fig 1.:
0h: Secondary oocyte (1 polar body) at the time of fertilization
18h: Zygote, female and male pronuclei are visible (at 5 o'clock) as well as two polar bodies under the zona pellucida (at 1 o'clock)
24h: Embryo in the two-cell-stage
48h: Cleavage: the blastomeres that form the morula are surrounded by the zona pellucida
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These morula cells serve as the origin for the embryo and its membranes, and also for the placenta and its associated structures. The development and differentiation continues with the cleavages. After the eight-cell stage the outer, originally round blastomeres, which stick to each other only a little, begin to flatten out. The contact among them is strengthened by special connections (tight junctions). This compaction (consolidation) leads to a partitioning of the cells, whereby one part goes to the center and the other forms the periphery.
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