yolk sac
noun Embryology.
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.
a similar membrane in placental mammals that encloses a mostly hollow space and loses its nutritive function entirely as the placenta develops.
Origin of yolk sac
First recorded in 1860–65
Words nearby yolk sac
yokuts,
yolande,
yoldring,
yolk,
yolk membrane,
yolk sac,
yolk stalk,
yolk-sac tumor,
yolo,
yom kippur,
yom kippur war
Example sentences from the Web for yolk sac
British Dictionary definitions for yolk sac
yolk sac
noun zoology
the membranous sac that is attached to the ventral surface of the embryos of birds, reptiles, and some fishes and contains yolk
the corresponding part in the embryo of mammals, which contains no yolk
Medical definitions for yolk sac
yolk sac
n.
A membranous sac attached to an embryo, enclosing food yolk.
umbilical vesicle
Scientific definitions for yolk sac
yolk sac
A sac that is attached to the gut of an embryo and encloses the yolk in bony fish, sharks, reptiles, mammals, and birds. In most mammals, the yolk sac functions as part of the embryo's circulatory system before the placenta develops.