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

They designed stem cell models to study formation of yolk sac founders, called hypoblast.

From Science Daily • May 31, 2024

Understanding this decision is important because the yolk sac is essential for later development in the womb.

From Science Daily • May 31, 2024

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 • Nov. 9, 2023

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 • Sep. 6, 2023

They took no food, living on the large yolk sac.

From "Silent Spring" by Rachel Carson