Blastocyst

The blastocyst is an embryo formed between 4° to 5°days after the fertilization. We can observe the formation of blastula consisting of a set of cells and the formation of a central cavity, the blastocele. 
The cells of the inner man cell, now called the embryoblast, are located in poles, while those of the outer mass the trophoblast flatten and from the epithelial wall of the blastocyst. The internal cell mass will give rise to the tissues of the embryo itself, while the external cell mass would from the trophoblast that later contributed to the formation of the placenta. 


Reference:SADDLER, T. W. Embriologia Médica,7.ed. Editora Longman, 1995

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