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Blastocyst
 
 
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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
Inner cell mass

In early embryogenesis of most eutherian mammals, the inner cell mass is the mass of cells inside the primordial embryo that will eventually give rise to the definitive structures of the fetus....
 which subsequently forms the embryo proper, and an outer layer of cells, or trophoblast
Trophoblast

Trophoblasts are cells forming the outer layer of a blastocyst, which provide nutrients to the embryo and develop into a large part of the placenta....
 which later forms the placenta
Placenta

The placenta or afterbirth is a highly vascularized ephemeral organ present in Placentalia vertebrates that connects the developing fetal tissues to the uterine wall....
. The human blastocyst arises after compaction and comprises 70-100 cells
Cell (biology)

The cell is the structural and functional unit of all known Life organisms. It is the smallest unit of an organism that is classified as living, and is often called the building bricks of life....
. It is preceded by a zygote
Zygote

A zygote is a cell that is the result of fertilization. That is, two ploidy cells—usually an ovum from a female and a sperm cell from a male—merge into a single ploidy cell called the zygote ....
, the fertilized egg cell.

Blastocyst formation begins at day 5 in humans.






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Encyclopedia


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
Inner cell mass

In early embryogenesis of most eutherian mammals, the inner cell mass is the mass of cells inside the primordial embryo that will eventually give rise to the definitive structures of the fetus....
 which subsequently forms the embryo proper, and an outer layer of cells, or trophoblast
Trophoblast

Trophoblasts are cells forming the outer layer of a blastocyst, which provide nutrients to the embryo and develop into a large part of the placenta....
 which later forms the placenta
Placenta

The placenta or afterbirth is a highly vascularized ephemeral organ present in Placentalia vertebrates that connects the developing fetal tissues to the uterine wall....
. The human blastocyst arises after compaction and comprises 70-100 cells
Cell (biology)

The cell is the structural and functional unit of all known Life organisms. It is the smallest unit of an organism that is classified as living, and is often called the building bricks of life....
. It is preceded by a zygote
Zygote

A zygote is a cell that is the result of fertilization. That is, two ploidy cells—usually an ovum from a female and a sperm cell from a male—merge into a single ploidy cell called the zygote ....
, the fertilized egg cell.

Blastocyst formation begins at day 5 in humans. Differential gene expression 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 expessed at a higher level in the trophoblast than the ICM. 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
    Inner cell mass

    In early embryogenesis of most eutherian mammals, the inner cell mass is the mass of cells inside the primordial embryo that will eventually give rise to the definitive structures of the fetus....
    , also known as the "embryoblast"
  • the trophoblast
    Trophoblast

    Trophoblasts are cells forming the outer layer of a blastocyst, which provide nutrients to the embryo and develop into a large part of the placenta....


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
Endometrium

The endometrium is the inner membrane of the mammalian uterus....
 to form the placenta
Placenta

The placenta or afterbirth is a highly vascularized ephemeral organ present in Placentalia vertebrates that connects the developing fetal tissues to the uterine wall....
 in eutherian mammals.

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Category:Embryology