yolk sac


: a membranous sac of most vertebrates that encloses the yolk, is attached in most forms (as in humans) through the yolk stalk with the intestinal cavity of the embryo, and is supplied with blood vessels that transport nutritive yolk products to the developing embryo

Examples of yolk sac in a Sentence

Recent Examples on the Web The models included cells that could develop into a yolk sac, placenta or embryo. Theara Coleman, The Week, 15 June 2023 There’s the amniotic and yolk sac. refinery29.com, 30 Nov. 2020 In mice, microglia originate in the yolk sac of an embryo and then infiltrate the brain early in development. Kristine Zengeler, Discover Magazine, 10 Dec. 2022 By day 8, a beating heart began to circulate blood through vessels forming around the embryo’s yolk sac. Megan Molteni, STAT, 2 Aug. 2022 McKenna Shea Xydias, of Senoia, Georgia, had an ovarian yolk sac tumor, according to Good Morning America, and went through four rounds of chemotherapy. Caitlin Keating, PEOPLE.com, 20 June 2019 But in the human embryo knockouts, placental cells and yolk sac cells also failed to form. Gretchen Vogel, Science | AAAS, 20 Sep. 2017

These examples are programmatically compiled from various online sources to illustrate current usage of the word 'yolk sac.' Any opinions expressed in the examples do not represent those of Merriam-Webster or its editors. Send us feedback about these examples.

Word History

First Known Use

1831, in the meaning defined above

Time Traveler
The first known use of yolk sac was in 1831

Dictionary Entries Near yolk sac

Cite this Entry

“Yolk sac.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/yolk%20sac. Accessed 26 May. 2024.

Medical Definition

yolk sac

: a membranous sac of most vertebrates that is attached to an embryo and encloses the yolk, that is continuous in most forms including humans through the omphalomesenteric duct with the intestinal cavity of the embryo, that is abundantly supplied with blood vessels which transport nutritive yolk products to the developing embryo, and that in placental mammals is nearly vestigial and functions chiefly prior to the formation of the placenta

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