yolk sac

American  

noun

Embryology.

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.

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yolk sac British  

noun

1. the membranous sac that is attached to the ventral surface of the embryos of birds, reptiles, and some fishes and contains yolk

2. the corresponding part in the embryo of mammals, which contains no yolk

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yolk sac Scientific  

1. 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.

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Etymology

Origin of yolk sac

First recorded in 1860–65

Example Sentences

The study led by at the University of Exeter Living Systems Institute has revealed how early embryo cells decide between contributing to the foetus or to the supporting yolk sac.

From Science Daily

What is important is that gastruloids recapitulate some features of early development even without the external cues from the placenta or yolk sac that typically direct the organization of an early embryo.

From Scientific American

There is a yolk sac, which has some of the roles of the liver and kidneys, and a bilaminar embryonic disc - one of the key hallmarks of this stage of embryo development.

From BBC

Like chickens, duck-billed platypuses, and other animals that hatch from eggs, you had a yolk sac when you were an embryo.

From Science Magazine

Each team’s models vary in the techniques used and how complete they are, he said, with some mirroring not just the embryo but the very beginnings of the placenta and yolk sac, too.

From Washington Times