Embryonic and Placental Development
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medical studies
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published 26/11/2007
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SummaryIn a description of the earliest stages of the human blastocyst, the wall of the primitive blastodermic vesicle was characterized as consisting of a single layer of ectoderm. As early as 72 hours after ovum fertilization, the 58-cell blastula had differentiated into 5 embryo-producing cells and 53 cells destined to form trophoblasts (Hertig, 1962). Although trophoblasts have not been distinguished before blastocyst implantation, both cytotrophoblasts and syncy-tiotrophoblast are present in the earliest implanted blastocyst of the monkey. Indeed, evidence has been presented that chorionic gonadotropin (hCG) is secreted by cells of the human blastocyst at the time of implantation.
Table of Contents
- EARLY BLASTOCYSTS
- EMBRYONIC DEVELOPMENT AFTER IMPLANTATION
- CYTOTROPHOBLAST INVASION OF DECIDUAL VESSELS
- GERM LAYERS
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