Amniotic cavity

Model of human embryo

Amniotic Cavity

The amniotic cavity refers to the enclosed sac positioned between the embryo and the amnion, primarily containing the amniotic fluid. This sac originates from the fusion of sections of the amniotic fold. Initially manifesting at the cephalic extremity, it gradually extends to the caudal end and lateral sections of the embryo. As the amniotic fold elevates and fuses across the embryo's dorsal side, it results in the formation of the amniotic cavity.

Formation

The formation of the amniotic cavity can be traced back to the embryonic stage. In the early phase of the second week post-fertilization, a distinct cavity starts to emerge within the inner cell mass. As this cavity expands, it evolves into the amniotic cavity. Notably, the base of this cavity is structured by the epiblast, a layer of cells from which the embryo develops. As the epiblast migrates between its disc and the trophoblast, these cells travel between the embryoblast and trophoblast. The primary structure is thus the epiblast, which eventually differentiates into the ectoderm. The remaining cells nestled between the embryoblast and trophoblast are identified as amnioblasts, which are flattened cells. These particular cells also originate from the epiblast, which subsequently becomes the ectoderm.

Furthermore, the amniotic cavity is encased by a specialized membrane known as the amnion. As the blastocyst implants further, a diminutive space emerges in the embryoblast, which serves as the foundational structure of the amniotic cavity. Shortly after, amniogenic cells, responsible for forming the amnion, detach from the epiblast, eventually lining the amnion. This process leads to the encapsulation of the amniotic cavity by the amnion.

Another noteworthy feature is that while the epiblast shapes the base of the amniotic cavity, it also seamlessly extends around the edges with the amnion. Conversely, the hypoblast, another embryonic layer, constructs the ceiling of the exocoelomic cavity and connects with the delicate exocoelomic membrane. This specific membrane, in combination with the hypoblast, gives rise to the primary yolk sac. Presently, the embryonic disc is situated between the primary yolk sac and the amniotic cavity. Crucially, cells extracted from the yolk sac endoderm converge to form a connective tissue layer, the extraembryonic mesoderm. This layer envelopes both the amnion and the yolk sac.

See Also

• Amnion
• Blastocyst
• Epiblast
• Hypoblast

External Links

• Amniotic Egg Development
• Implantation Details

Amniotic cavity Resources
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