Yolk Sac

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.

Year introduced: 1978

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Tree Number(s): A10.615.284.981, A16.254.750.981, A16.331.800

MeSH Unique ID: D015017

Entry Terms:

• Sacs, Yolk
• Sac, Yolk
• Yolk Sacs
• Vitelline Sac of Embryo
• Embryo Vitelline Sac
• Embryo Vitelline Sacs

Previous Indexing:

• Chick Embryo (1966-1972)
• Fetal Membranes (1966-1972)
• Vitelline Membrane (1966-1974)

All MeSH Categories
Anatomy Category
Tissues
Membranes
Extraembryonic Membranes
Yolk Sac

All MeSH Categories
Anatomy Category
Embryonic Structures
Embryo, Mammalian
Extraembryonic Membranes
Yolk Sac

All MeSH Categories
Anatomy Category
Embryonic Structures
Embryo, Nonmammalian
Yolk Sac