Yolk Sac (also known as Sacs, Yolk, Sac, Yolk): 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 vestigia

NIH MeSH · D015017Anatomy

Yolk Sac

Also known asSacs, Yolk · Sac, Yolk · Yolk Sacs · Vitelline Sac of Embryo · Embryo Vitelline Sac · Embryo Vitelline Sacs

Definition

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.

MeSH classification

  • A10.615.284.981
  • A16.254.750.981
  • A16.331.800

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Related concepts

Allantois

An extra-embryonic membranous sac derived from the YOLK SAC of REPTILES; BIRDS; and MAMMALS. It lies between two other extra-embryonic membr…

Amnion

The innermost membranous sac that surrounds and protects the developing embryo which is bathed in the AMNIOTIC FLUID. Amnion cells are secre…

Common questions about Yolk Sac

What does Yolk Sac mean in medicine?
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. This definition is taken from the National Library of Medicine's MeSH (Medical Subject Headings) 2026 release, which is the standard vocabulary used to index PubMed and most medical literature.
Is Yolk Sac known by any other names?
Yes. Yolk Sac is also referred to as Sacs, Yolk, Sac, Yolk, Yolk Sacs, Vitelline Sac of Embryo in different clinical, research and patient-facing contexts. The MeSH descriptor groups all of these synonyms under a single canonical concept so research and records stay consistent.
Where does Yolk Sac sit in the medical classification?
Yolk Sac falls under the broader medical category "Anatomy" in the MeSH hierarchy (tree numbers: A10.615.284.981, A16.254.750.981, A16.331.800). Browsing the related concepts on this page takes you to neighbouring topics in the same branch of medicine.
Where can I get a plain-language explanation of Yolk Sac?
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Source: NIH MeSH 2026 (D015017) — National Library of Medicine, public domain. View official MeSH record ↗