A thin membrane surrounding the fetus during pregnancy. The amnion is the inner of the two fetal membranes (the chorion is the outer one). It contains the amniotic fluid.
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Innermost of the extraembryonic membranes enveloping the embryo in utero and containing the amniotic fluid; it consists of an internal embryonic layer with its ectodermal component, and an external somatic mesodermal component; in the later stages of pregnancy the a. expands to come in contact with and partially fuse to the inner wall of the chorionic vesicle; derived from the trophoblast cells. SYN: amnionic sac. [G. the membrane around the fetus, fr. amnios, lamb]
- a. nodosum nodules in the a. that consist of typical stratified squamous epithelium. SYN: squamous metaplasia of a..

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am·ni·on 'am-nē-.än, -ən n, pl amnions or am·nia -nē-ə a thin membrane forming a closed sac about the embryos and fetuses of reptiles, birds, and mammals and containing the amniotic fluid called also amniotic sac

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the membrane that forms initially over the dorsal part of the embryo but soon expands to enclose it completely within the amniotic cavity; it is connected to the embryo at the umbilical cord. It expands outwards and fuses with the chorion, obliterating virtually all the intervening cavity. The double membrane (amniochorion) normally ruptures at birth.
amniotic adj.

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am·ni·on (amґne-on) [Gr. “bowl”; “membrane enveloping the fetus”] the thin but tough extraembryonic membrane of reptiles, birds, and mammals that lines the chorion and contains the embryo and later the fetus, with the amniotic fluid around it; in mammals it is derived from trophoblast by folding or splitting. See also amniotic sac, under sac.

Amnion and other extraembryonic membranes surrounding a human embryo at 10 weeks; the amnion has enveloped the umbilical cord.

Medical dictionary. 2011.

Look at other dictionaries:

  • Amnĭon — Amnĭon, 1) (gr. Ant.), Opferschale zum Auffangen des Blutes; 2) (Amnium), Schafhäutchen, die innerste Haut der Eihüllen (s.d.), welche den Fötus der Säugethiere u. Menschen umschließen; sie scheidet eine Flüssigkeit (Amniumwasser, Amnii liquor,… …   Pierer's Universal-Lexikon

  • amnion — (n.) 1660s, Modern Latin, from Gk. amnion membrane around a fetus, said to be originally bowl in which the blood of victims was caught [Liddell & Scott], which is variously said to be of unknown origin, from ame bucket, or a dim. of amnos lamb …   Etymology dictionary

  • amnion — amnìōn m <G amnióna> DEFINICIJA fiziol. unutrašnjost embrijske ovojnice; poput mjehura obavija embrij i sadrži amnionsku tekućinu (plodovu vodu); amnij ETIMOLOGIJA nlat. ← grč. amníon: posteljica ≃ amnós: janje …   Hrvatski jezični portal

  • Amnion — Am ni*on, n. [Gr. ? the membrane round the fetus, dim. of ? lamb.] (Anat.) A thin membrane surrounding the embryos of mammals, birds, and reptiles. [1913 Webster] …   The Collaborative International Dictionary of English

  • amnion — amnion. См. амнион. (Источник: «Англо русский толковый словарь генетических терминов». Арефьев В.А., Лисовенко Л.А., Москва: Изд во ВНИРО, 1995 г.) …   Молекулярная биология и генетика. Толковый словарь.

  • Amnĭon — Amnĭon, s. Embryonalhüllen …   Meyers Großes Konversations-Lexikon

  • Amnion — Amnĭon (grch.), Schafhaut, die innerste Eihaut, die den Embryo der höhern Wirbeltiere (Reptilien. Vögel und Säugetiere, der Amniōten) umgibt, enthält eine eiweißhaltige Flüssigkeit (Amnionwasser, Fruchtwasser), in welcher der Fötus, vor Druck und …   Kleines Konversations-Lexikon

  • Amnion — (Schafhäutchen) heißt die innerste von den häutigen Hüllen, welche im menschlichen und thierischen Eie den Embryo umgeben. Sie ist dünn, dabei aber fest und schließt eine eigene Flüssigkeit, das Fruchtwasser in sich, in dem der Embryo gleichsam… …   Herders Conversations-Lexikon

  • Amnion — ⇒ Embryonalhüllen …   Deutsch wörterbuch der biologie

  • amnion — [am′nē ən, am′nēän΄] n. pl. amnions or amnia [am′nēə] [Gr, dim. of amnos, lamb < IE * agwhnos > YEAN, L agnus] 1. the innermost membrane of the sac enclosing the embryo of a mammal, reptile, or bird: it is filled with a watery fluid… …   English World dictionary

  • Amnion — Infobox Anatomy Name = Amnion Latin = GraySubject = 12 GrayPage = 56 Caption = Surface view of embryo of Hylobates concolor. Caption2 = Human fetus, enclosed in the amnion. System = MeshName = Amnion MeshNumber = A10.615.284.277 : For the alien… …   Wikipedia

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