BLASTOCYST DEVELOPMENT; DIFFERENCE MECHAN？SMS OF CELL LAYERS

Zygotes formed after fertilization undergo successive mitotic divisions, the first three mitosis divisions are symmetric and morphologically identical 8 blastomeres are formed. Important morphological changes occur in the embryo in 8-cell stage. These are compaction, polarization, and asymmetric cell division. Following these changes, the primary lineage differentiation in the cells of the embryo in the 8-32 cell morulae, consist of namely inner cell mass (ICM) and outer cell mass (Trofoektoderm; TE). Shortly after the ICM, epiblast (EPI) and primitive endoderm (PE) cell lines differentiate in the process called secondary progeny differentiation. In this review, the stages of blastocyst development in the preimplantation period will be elaborated sequentially and via molecular pathways