yolk sac
The definitions used in this glossary of terminology either have been provided by the authors of the articles, or have been extracted wholly or in part, or paraphrased from the following sources: The American Medical Association Encyclopedia of Medicine, Charles B. Clayman, MD, Medical Editor, Random House, New York, 1989; Biotechnology from A to Z, 2d Edition, William Bains, Oxford University Press, New York, New York, 2002; A Dictionary of Genetics, 6th Edition, Robert C. King and William D. Stansfield, Oxford University Press, New York, New York, 2002; Dorland's Illustrated Medical Dictionary, 29th and 30th Editions, W. B. Saunders Company, Philadelphia, 2000, 2003; Genes VII, Benjamin Lewin, Oxford University Press, New York, New York, 2000; The Gale Encyclopedia of Genetic Disorders, Volumes I and II, Stacey L. Blachford, Ed., Thomson Learning, New York, New York, 2002; The Merriam-Webster Dictionary, Merriam-Webster, Inc., Springfield, Massachusetts, 1997; Molecular Biology of the Cell, 3rd Edition, Bruce Alberts, et al., Garland Publishing, 1994; The Random House Dictionary of the English Language, Unabridged Edition, 1966; Webster's Ninth New Collegiate Dictionary, 1991.
DEFINITION:
- yolk sac
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The extraembryonic membrane that connects with the midgut; at the end of the fourth week of development it expands into the pear-shaped umbilical vesicle connected to the body of the embryo by the long narrow yolk stalk. In marsupial and placental mammals, it produces a complete vitelline circulation in the early embryo and then undergoes regression; in oviparous vertebrates, it encloses the yolk mass, breaks down yolk, and makes it available to the developing organism. In human embryos it does not serve a primary nutritive function, but it is the first hematopoietic organ of the embryo. Called also vitelline sac .
Used in 8 Term definitions
Used in 8 Term definitions