yolk sac
Americannoun
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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.
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a similar membrane in placental mammals that encloses a mostly hollow space and loses its nutritive function entirely as the placenta develops.
noun
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the membranous sac that is attached to the ventral surface of the embryos of birds, reptiles, and some fishes and contains yolk
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the corresponding part in the embryo of mammals, which contains no yolk
Etymology
Origin of yolk sac
First recorded in 1860–65
Example Sentences
Examples are provided to illustrate real-world usage of words in context. Any opinions expressed do not reflect the views of Dictionary.com.
In these cases, the sheer size of the cell and the presence of a large yolk sac prevent the actin ring from fully closing.
From Science Daily
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
Definitions and idiom definitions from Dictionary.com Unabridged, based on the Random House Unabridged Dictionary, © Random House, Inc. 2023
Idioms from The American Heritage® Idioms Dictionary copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.
