yolk sac

yolk sac
noun
1. membranous structure that functions as the circulatory system in mammalian embryos until the heart becomes functional
• Hypernyms: ↑sac
2. membranous structure enclosing the yolk of eggs in birds, reptiles, marsupials, and some fishes; circulates nutrients to the developing embryo
• Hypernyms: ↑sac

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noun
: a membranous sac that is attached to an embryo and encloses food yolk (as in most vertebrates and cephalopods), that is continuous through the vitelline duct with the intestinal cavity of the embryo, that being abundantly supplied with blood vessels is throughout embryonic life and in some forms later the chief organ of nutrition, and that in placental mammals is nearly vestigial and functions chiefly prior to the elaboration of the placenta

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Embryol.
1. an extraembryonic membrane that encloses the yolk of eggs in birds, reptiles, and marsupials and that circulates nourishment from the yolk to the developing embryo.
2. a similar membrane in placental mammals that encloses a mostly hollow space and loses its nutritive function entirely as the placenta develops.
[1860-65]

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yolk sac noun (zoology)
The yolk-containing sac which is attached to the embryo by the yolk stalk, a short stalk by means of which yolk substance may pass into the alimentary canal of the embryo
• • •
Main Entry: ↑yolk

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yolk sac,
a membranous sac filled with yolk, attached to and providing food for the embryo. In cephalopods and lower vertebrates, it is the only source of food for the embryo, for these animals do not develop a placenta.

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n. Zoology a membranous sac containing yolk attached to the embryos of reptiles and birds and the larvae of some fishes
■ a sac lacking yolk in the early embryo of a mammal

Useful english dictionary. 2012.

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Look at other dictionaries:

  • yolk sac — n. Zool. 1. a saclike vascular membrane containing yolk, an outgrowth from the ventral surface of very yolky vertebrate embryos, as those of fishes, birds, or reptiles, that supplies nourishment to the embryo 2. a homologous organ in most… …   English World dictionary

  • yolk sac — yolk′ sac n. dvl an extraembryonic membrane that encloses the yolk of eggs • Etymology: 1860–65 …   From formal English to slang

  • yolk sac — yolk sac. См. желточный мешок. (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.

  • Yolk sac — Not all yolk has to do with birds’ eggs. Human embryos have a yolk sac, a membrane outside the embryo but connected by a tube (the yolk stalk) though the umbilical opening to the embryo’s midgut. The yolk sac serves as an early site for …   Medical dictionary

  • Yolk sac — Infobox Embryology Name = Yolk sac Latin = GraySubject = 11 GrayPage = 54 Caption = Human embryo of 2.6 mm. Caption2 = Human embryo from thirty one to thirty four days System = CarnegieStage = 5b Days = 9 Precursor = endoderm GivesRiseTo =… …   Wikipedia

  • yolk sac — thin membrane which surrounds the yolk of an egg and supplies nutrients to the embryo (in mammals, the yolk sac ceases to function when the placenta forms) …   English contemporary dictionary

  • yolk sac tumor — a malignant germ cell tumor of children that represents a proliferation of both yolk sac endoderm and extraembryonic mesenchyme. It is characterized by a labyrinthine glandular pattern with a papillary projection into a sinuslike space;… …   Medical dictionary

  • yolk-sac larva — a fish larva which has already hatched from the egg but has not started feeding yet and still absorbs the yolk in the ventrally attached yolk sac. At the end of this stage in development, the yolk and oil globule(s) have been used up, the major… …   Dictionary of ichthyology

  • yolk-sac placenta — the yolk sac helps in formation of a placenta which allows a connection of the embryo to the mother for nourishment …   Dictionary of ichthyology

  • yolk sac endoderm — the epithelial lining of the yolk sac …   Medical dictionary

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