| Blastocyst | |
|---|---|
| Latin | blastocystis |
| Carnegie stage | 3 |
| Days | 8
Precursor = Morula |
| Gives rise to | Gastrula, Inner cell mass |
| Code | TE E2.0.1.2.0.0.12 |
| MeSH | Blastocyst |
The blastocyst is a structure formed in the early embryogenesis of mammals, after the formation of the morula. It is a specifically mammalian example of a blastula. It possesses an inner cell mass (ICM), or embryoblast, which subsequently forms the embryo, and an outer layer of cells, or trophoblast, which later forms the placenta. The trophoblast surrounds the inner cell mass and a fluid-filled blastocyst cavity known as the blastocoele or the blastocystic cavity. The human blastocyst comprises 70-100 cells.
Blastocyst formation begins at day 5 after fertilization in humans, when the blastocoele opens up in the morula, a process known as hatching.
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The blastocyst consists of two primary cell types:
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.
The morula is a solid ball of about 16 undifferentiated, spherical cells. As cell division continues in the morula, the blastomeres change their shape and tightly align themselves against each other. This is called compaction and is likely mediated by cell surface adhesion glycoproteins.
This article was originally based on an entry from a public domain edition of Gray's Anatomy. As such, some of the information contained within it may be outdated.
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