Extraembryonic Membranes

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The following article is from The Great Soviet Encyclopedia (1979). It might be outdated or ideologically biased.

Extraembryonic Membranes

 

the membranous structures that in some invertebrate animals, sharks, all higher vertebrates, and man provide for the life activities of the embryo and ensure its protection from injury.

As distinguished from the egg membranes, extraembryonic membranes are formed not during the maturation of the ovum but during embryonic development from the cells of the embryo. Among the extraembryonic membranes are the amnion, the chorion, and the allantois. The amnion is formed from the lateral folds of the extraembryonic ectoderm and the external layer of the lateral plates, which rise and close up over the embryo, or by means of the formation of a cavity among the embryo cells that is gradually transformed into the membrane that surrounds the embryo. The amnion is filled with fluid and protects the embryo from desiccation; it shields the embryo from contact with other membranes (sometimes very hard, such as the eggshell) and from mechanical injury.

The outer wall of the amniotic folds forms the chorion. In mammals and man the chorion is in direct contact with the wall of the uterus. In reptiles and birds this extraembryonic membrane is usually called the serosa. In mammals and man the chorion provides for the exchange of substances between the body of the mother and the fetus; it forms during the early stage of development, when the embryo is still a small vesicle (the so-called blastocyst) consisting of an aggregation of small cells, the so-called embryoblast, surrounded by a layer of larger cells, the trophoblast. The chorion arises from the cells of the trophoblast, which are then lined with the cells of the extraembryonic mesoderm. It has characteristic villi that take root in the tissue of the uterus and form the fetal part of the placenta. The villi are supplied with vessels that form in connection with the development of the yolk sac and the allantois. The allantois begins as an outgrowth of the posterior section of the intestinal tube of the embryo. In reptiles and birds it resembles a pouch in shape. It grows intensively and covers the amnion and yolk sac. Supplied with a large number of blood vessels, the allantois serves as the embryonic organ of respiration. The metabolic products of the embryo, principally urine, collect in the allantoic cavity. In mammals and man the allantois is small; the vessels of the umbilical cord, which connect the embryo with the placenta, are formed in its mesenchyme. In the later stages of development the urinary bladder (in mammals and man) and the cloaca (in birds and reptiles) form from the intraembryonic portion of the allantois.

REFERENCE

Ivanov, P. P. Obshchaia i sravnitel’naia embriologiia. Moscow, 1937.

A. P. DYBAN and V. S. BARANOV

The Great Soviet Encyclopedia, 3rd Edition (1970-1979). © 2010 The Gale Group, Inc. All rights reserved.
References in periodicals archive ?
The red material is probably not a sunscreen, because such a role would be better performed by material that remained distributed throughout the embryo rather than becoming sequestered into an extraembryonic mass and two restricted internal sites.
Once considered nullipotent, as they have lost the ability to differentiate spontaneously [37], studies would later reveal that F9 cells are capable of differentiating into extraembryonic endoderm-like cells [39, 40], and evidence would indicate that they share many characteristics of ESCs [41].
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The strongest increase in expression is observed for markers of extraembryonic endoderm (Gata4) and neuroectoderm (Pax6) in differentiating ES R1 and EC F9 cells.
Toyoda et al., "Cells of extraembryonic mesodermal origin confer human dystrophin in the mdx model of Duchenne muscular dystrophy," Journal of Cellular Physiology, vol.
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The use of extraembryonic tissues as stem cell reservoirs for tissue engineering offers many advantages over both embryonic and adult stem cell sources.
Yossi Buganim of the Hebrew University of Jerusalem (HU) and his team discovered a set of genes capable of transforming murine skin cells into all three of the cell types that comprise the early embryo: the embryo itself, the placenta and the extraembryonic tissues, such as the umbilical cord.
Cell Potency and Differentiation Cell Potency Differentiation Example Capacity Totipotent Can form all cell types in Embryonic cells within the Cells a body, also the first couple of cell extraembryonic or divisions after placental cells.
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