The outermost of the two fetal membranes—the amnion is the innermost —. which together surround the embryo. The chorion develops villi (vascular fingers) and gives rise to the placenta. In Greek, the word "chorion" means "skin or leather."
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The multilayered, outermost fetal membrane consisting of extraembryonic somatic mesoderm, trophoblast, and, on the maternal surface, villi bathed by maternal blood; as pregnancy progresses, part of the c. becomes the definitive fetal placenta. SYN: chorionic sac, membrana serosa (1). [G. c., membrane enclosing the fetus]
- c. frondosum the part of the c. where the villi persist, forming the fetal part of the placenta. SYN: shaggy c..
- c. laeve the portion of the c. from which the villi disappear in the later stages of pregnancy. SYN: smooth c..
- previllous c. SYN: primitive c..
- primitive c. the c. before its villi are well formed. SYN: previllous c..
- shaggy c. SYN: c. frondosum.
- smooth c. SYN: c. laeve.

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cho·ri·on 'kōr-ē-.än, 'kȯr- n the highly vascular outer embryonic membrane that is associated with the allantois in the formation of the placenta

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the embryonic membrane that totally surrounds the embryo from the time of implantation. It is formed from trophoblast lined with mesoderm and becomes closely associated with the allantois. The blood vessels (supplied by the allantois) are concentrated in the region of the chorion that is attached to the wall of the uterus and forms the placenta. See also villus.
chorionic adj.

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cho·ri·on (korґe-on) [Gr. “membrane”] 1. in human embryology, the cellular, outermost extraembryonic membrane, composed of trophoblast lined with mesoderm; it develops chorionic villi about 2 weeks after fertilization, is vascularized by allantoic vessels a week later, and gives rise to the fetal part of the placenta. 2. in mammalian embryology, the cellular, outer extraembryonic membrane, not necessarily developing villi. 3. in biology, the noncellular membrane covering eggs of various animals, including fish and insects. chorial, chorionic adj

Medical dictionary. 2011.

Look at other dictionaries:

  • chorion — [ kɔrjɔ̃ ] n. m. • 1541; gr. khorion 1 ♦ Biol. Membrane extérieure de l embryon des mammifères qui assure un contact intime avec la muqueuse utérine et joue un rôle dans la nutrition de l embryon. 2 ♦ Histol. Couche superficielle, hérissée de… …   Encyclopédie Universelle

  • Chorĭon [2] — Chorĭon (gr.), 1) Feld, Grundstück; daher Chorin dike, Klage, wegen Wegnahme od. widerrechtlicher Benutzung eines Feldes; 2) Bergfeste, Castell; so Chorion Kainon, Bergfeste im Innern von Pontos, wohin Mithridates seine Schätze flüchtete;… …   Pierer's Universal-Lexikon

  • chorion — [kôr′ē än΄] n. [ModL < Gr chorion, fetal membrane: for IE base see YARN] 1. the outermost of the two membranes that completely envelop a fetus 2. the outer membrane or shell of the eggs of insects and other invertebrates chorionic [kôr′ēän′ik] …   English World dictionary

  • Chorion — Cho ri*on, n. [NL., fr. Gr. ?.] 1. (Anat.) (a) The outer membrane which invests the fetus in the womb; also, the similar membrane investing many ova at certain stages of development. (b) The true skin, or cutis. [1913 Webster] 2. (Bot.) The outer …   The Collaborative International Dictionary of English

  • chorion — chorion. См. хорион. (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.

  • Chorĭon [1] — Chorĭon (gr., lat. Corium, Anat.), 1) eigentlich Haut, Leder, Lederhaut, s. Haut; 2) Ei od. Schalenhaut, äußerste Begrenzung des Eies, Anfangs rund, durchsichtig glatt (Ch. laeve, Ch. pellucĭdum); mit Vergrößerung des Eichens wird das Ch. zottig… …   Pierer's Universal-Lexikon

  • Chorĭon — (griech., lat. corium), Haut, Leder, die äußere Eischale, bei den höhern Wirbeltieren die äußerste Hülle des Embryos. S. Allantois und Ei …   Meyers Großes Konversations-Lexikon

  • Chorion — Chorĭon (grch.; lat. Corĭum), Lederhaut, mittlere Eihaut des Embryos …   Kleines Konversations-Lexikon

  • Chorion — Chorion, Haut, die Hülle der Leibesfrucht mit Ausschluß der innersten der Schafhaut (vergl. Amnion, Embryo, Fötus) …   Herders Conversations-Lexikon

  • Chorion — Chorion, 1) von Follikelzellen gebildete sekundäre Eihülle des Insekteneies; 2) vom Trophoblasten gebildetes embryonales Ernährungsorgan der Placentatiere, das der Gebärmutterschleimhaut anliegt, Ausstülpungen (Zotten) bildet, mit diesen in die… …   Deutsch wörterbuch der biologie

  • chorion — CHORION. s. m. Terme d Anatomie. Nom d une des membranes du foetus …   Dictionnaire de l'Académie Française 1798

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