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amnion |
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amnion the innermost of two membranes (see also chorion) enclosing an embryonic reptile, bird, or mammal amnion [′am·nē‚än] (embryology) A thin extraembryonic membrane forming a closed sac around the embryo in birds, reptiles, and mammals. Amnion A thin, cellular, extraembryonic membrane forming a closed sac surrounding the embryo in all reptiles, birds, and mammals. It is present only in these forms; the collective term amniotes is applied to these animals. The amnion contains a serous fluid in which the embryo is immersed. See Amniota Typically, the amnion wall is a tough, transparent, nerve-free, and nonvascular membrane consisting of two layers of cells: an inner, single-cell-thick layer of ectodermal epithelium and an outer covering of mesodermal, connective, and specialized smooth muscular tissue. Early after the formation of the amnion, waves of contraction of the muscles pass over the amniotic sac and produce a characteristic rocking of the embryo. See Germ layers The major function of the amnion and its fluid is to protect the delicate embryo. Thus, developmental stages of terrestrial animals are provided with the same type of cushioning against mechanical shock as is provided by the water environment of aquatic forms. See Fetal membrane How to thank TFD for its existence? Tell a friend about us, add a link to this page, add the site to iGoogle, or visit webmaster's page for free fun content. |
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| ? Mentioned in | ? References in periodicals archive | ||
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| Anthony Atala, director of the Institute for Regenerative Medicine
at Wake Forest University School of Medicine, reported that stem cells
in the amniotic fluid that fills the sac surrounding the fetus may be
just as versatile as embryonic stem cells. These stem cells are found in the amniotic fluid
of a woman, a substance that is usually discarded upon the birth of a
child. , and his colleagues
wondered whether some of the fetal cells in amniotic fluid are stem
cells. |
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