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The fetal membranes separate maternal tissue from fetal tissue at a basic mechanical level. The fetal membrane is composed of a thick cellular chorion covering a thin amnion composed of dense collagen fibrils. The amnion is in contact with the amniotic fluid and ensures structural integrity of the sac due to its mechanical strength.
The gestational sac is spherical in shape, and is usually located in the upper part (fundus) of the uterus.By approximately nine weeks of gestational age, due to folding of the trilaminar germ disc, the amniotic sac expands and occupy the majority of the volume of the gestational sac, eventually reducing the extraembryonic coelom (the gestational sac or the chorionic cavity) to a thin layer ...
Amniotic embryo. a=embryo, b=yolk, c=allantois, d=amnion, e=chorion. In reptiles, birds, and monotremes, the chorion is one of the four extraembryonic membranes that make up the amniotic egg that provide for the nutrients and protection needed for the embryo's survival. It is located inside the albumen, which is the white of the egg.
Amniotic cavity in human embryo 1.3 mm. long. The amniotic cavity is the closed sac between the embryo and the amnion, containing the amniotic fluid. The amniotic cavity is formed by the fusion of the parts of the amniotic fold, which first makes its appearance at the cephalic extremity and subsequently at the caudal end and sides of the embryo ...
This, the amniotic fold, first makes its appearance at the cephalic extremity, and subsequently at the caudal end and sides of the embryo, and gradually rising, its different parts meet and fuse over the dorsal aspect of the embryo, and enclose a cavity, the amniotic cavity. This kind of amnion is known as pleuroamnion (formed by folding), as ...
In humans, blastocyst formation begins about five days after fertilization when a fluid-filled cavity opens up in the morula, the early embryonic stage of a ball of 16 cells. The blastocyst has a diameter of about 0.1–0.2 mm and comprises 100-200 cells following 7-8 rounds of cleavage (cell division without cell growth).
Beginning on day eight, the amniotic sac is the first new cavity to form during the second week of development. [4] Fluid collects between the epiblast and the hypoblast, which splits the epiblast into two portions. The layer at the embryonic pole grows around the amniotic sac, creating a barrier from the cytotrophoblast.
The extraembryonic membranes in insects include a serous membrane (serosa) originating from blastoderm cells, an amnion or amniotic cavity whose expression is controlled by the Zerknüllt gene, and a yolk sac. [3]