Yolk Sac
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The first of four extra-embryonic membranes to form during EMBRYOGENESIS. In REPTILES and BIRDS, it arises from endoderm and mesoderm to incorporate the EGG YOLK into the DIGESTIVE TRACT for nourishing the embryo. In placental MAMMALS, its nutritional function is vestigial; however, it is the source of INTESTINAL MUCOSA; BLOOD CELLS; and GERM CELLS. It is sometimes called the vitelline sac, which should not be confused with the VITELLINE MEMBRANE of the egg.
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Subject headings from Medical Subject Headings (MeSH) 2026, courtesy of the U.S. National Library of Medicine. ScieBeta is not affiliated with, nor endorsed by, the NLM or the NIH. Resources are linked from their original providers and open directly from them. Licence and credit are shown alongside every item.