- yolk sac
- noun1. membranous structure that functions as the circulatory system in mammalian embryos until the heart becomes functional• Syn: ↑vitelline sac, ↑umbilical vesicle, ↑vesicula umbilicus• Hypernyms: ↑sac2. 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* * *
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]* * *
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* * *
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.* * *
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.