Infobox Embryology
Name = Blastocyte
Latin =
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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 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 cells. It is preceded by a zygote, the fertilized egg cell, and succeeded by an embryo.

Blastocyte formation begins at day 5cite web |url= |title=UNSW Embryology- Week 1 |accessdate=2007-12-30 |format= |work=] . 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.


External links

* [ Blastocyst photos at different stages of development]
* [ Diagram at]

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Look at other dictionaries:

  • Blastocyst — Blas to*cyst, n. [Gr. blasto s sprout + E. cyst.] (Biol.) The germinal vesicle. [1913 Webster] …   The Collaborative International Dictionary of English

  • blastocyst — (n.) 1876, from BLASTO (Cf. blasto ) + CYST (Cf. cyst) …   Etymology dictionary

  • blastocyst — [blas′tōsist΄, blas′təsist΄] n. [ BLASTO + CYST] BLASTULA …   English World dictionary

  • Blastocyst — A stage in the early embryonic development of mammals in which there is a hollow sphere with an outer layer of cells and inside the hollow sphere, there is a cluster of cells called the inner cell mass. If development continues, the outer layer… …   Medical dictionary

  • blastocyst — n. an early stage of embryonic development that consists of a hollow ball of cells with a localized thickening (the inner cell mass) that will develop into the actual embryo; the remainder of the blastocyst is composed of trophoblast . At first… …   The new mediacal dictionary

  • blastocyst — In mammalian development, cleavage produces a thin walled hollow sphere, whose wall is the trophoblast, with the embryo proper being represented by a mass of cells at one side. The blastocyst is formed before implantation and is equivalent to the …   Dictionary of molecular biology

  • blastocyst — /blas teuh sist/, n. Embryol. the blastula of the mammalian embryo, consisting of an inner cell mass, a cavity, and an outer layer, the trophoblast. [1885 90; BLASTO + CYST] * * * ▪ embryo phase       a distinctive stage of a mammalian embryo. It …   Universalium

  • blastocyst — noun Date: circa 1881 the modified blastula of a placental mammal having an outer layer composed of the trophoblast …   New Collegiate Dictionary

  • blastocyst — n. [Gr. blastos, bud; kystis, bladder] (PLATYHELMINTHES: Cestoda) In Trypanorhynca, a posterior bladder of the metacestode into which the body is withdrawn …   Dictionary of invertebrate zoology

  • blastocyst — noun The mammalian blastula …   Wiktionary

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