A sac-like expansion of the ventral wall of the intestine, narrowed into a yolk stalk near the body[Hyman's]. Membranous sac attached to an embryo, providing early nourishment in the form of yolk in bony fishes, sharks, reptiles, birds, and primitive mammals. It functions as the developmental circulatory system of the human embryo, before internal circulation begins. In the mouse, the yolk sac is the first site of blood formation, generating primitive macrophages and erythrocytes[WP]. [ http://en.wikipedia.org/wiki/Yolk_sac ]

This is just here as a test because I lose it

Term information

database cross reference

uberon_slim, efo_slim, pheno_slim

depicted by


editor note

consider splitting class

external definition

the extraembryonic tissue membrane, formed from the visceral endoderm and the extraembryonic mesoderm, which is located ventral to the embryonic disc and is connected to the presumptive midgut of the embryo; the yolk that it contains is the site of embryonic hematopoiesis and vitelline circulation is involved in early embryonic circulation; it is the origin of the primordial germ cells
One of the extraembryonic fetal membranes that balloons out from the fetal midgut. [TFD][VHOG]

has related synonym

vesicula umbilicalis
saccus vitellinus

homology notes

Structures homologous to the four extraembryonic membranes of reptiles and birds appear in mammals: amnion, chorion, yolk sac, and allantois.[well established][VHOG]



taxon notes

In therians, a structure homologous to the yolk sac is is present, but contains no yolk platelets. Instead it is filled with fluid [ISBN:0073040584 (Vertebrates, Kardong)]