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

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.