Blastocyst
444337
225936555
2008-07-16T02:41:10Z
71.178.66.135
undid vandalism replacing all instances of "blastocyst" with "blastocyte"
{{Infobox Embryology |
Name = {{Blastocyte}} |
Latin = |
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Image = Blastocyst English.svg|
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CarnegieStage = 3 |
Days = 5 |
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MeshName = Blastocyst |
MeshNumber = A16.254.085 |
DorlandsPre = b_14 |
DorlandsSuf = 12187695 |
}}
The '''blastocyst''' is the structure formed in early [[embryogenesis]], after the formation of the [[blastocoel]], but before [[implantation]].
It possesses an inner cell mass, or [[inner cell mass|embryoblast]] which subsequently forms the embryo, and an outer cell mass, or [[trophoblast]] which forms the [[placenta]]. The human blastocyst arises after compaction and comprises 70-100 [[Cell (biology)|cells]]. It is preceded by a [[zygote]], the fertilized egg cell, and succeeded by an [[embryo]].
Blastocyte formation begins at day 5<ref name="titleUNSW Embryology- Week 1">{{cite web |url=http://embryology.med.unsw.edu.au/Notes/week1.htm |title=UNSW Embryology- Week 1 |accessdate=2007-12-30 |format= |work=}}</ref>. Differential expression of cells in the morula is thought to be the cause of the lineage divergence of different cell types. For example, the [[Oct-3/4]] transcription factor is restricted to the ICM, whereas Cdx2 is restricted to the trophoblast. This differential transcription factor expression is likely to be the result of positional effect - cells in the middle of the preceding zygote are in a different environment to those on the outside, thus causing differential expression.
==Formation of the blastocyst==
The blastocyst consists of two primary cell lines:
* the [[inner cell mass]], also known as the "embryoblast"
* the [[trophoblast]]
The former is the source of [[embryonic stem cells]] and gives rise to all later structures of the adult organism. The latter combines with the maternal [[endometrium]] to form the [[placenta]] in [[eutherian]] mammals.
==References==
{{reflist}}
* [[Prenate]]
==External links==
* [http://www.advancedfertility.com/blastocystimages.htm Blastocyst photos at different stages of development]
* [http://departments.weber.edu/chfam/Prenatal/blastocyst.html Diagram at weber.edu]
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{{Embryology}}[[Category:Embryology]]
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