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 = | GraySubject = | GrayPage = | Image = Blastocyst English.svg| Caption = | Image2 = | Caption2 = | System = | CarnegieStage = 3 | Days = 5 | Precursor = | GivesRiseTo = | 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] {{developmental-biology-stub}} {{Gray's}} {{Embryology}}[[Category:Embryology]] [[de:Blastozyste]] [[fr:Blastocyste]] [[nl:Blastocyste]] [[no:Blastocyst]] [[pl:Blastocysta]] [[pt:Blástula]] [[ru:Бластоциста]] [[sk:Blastocysta]] [[sr:Бластоцист]] [[fi:Alkiorakkula]] [[tr:Blastokist]]