Yolk sac

Contents in the cavity of the uterus seen at approximately 5 weeks of gestational age by obstetric ultrasonography.

Artificially colored, showing gestational sac, yolk sac and embryo (measuring 3 mm as the distance between the + signs).

The yolk sac is a membranous sac attached to an embryo, formed by cells of the hypoblast adjacent to the embryonic disk. This is alternatively called the umbilical vesicle by the Terminologia Embryologica (TE), though yolk sac is far more widely used. The yolk sac is important in early embryonic blood supply, and is incorporated into the primordial gut during the fourth week of development.

单词	Umbilical vesicles
释义	Umbilical vesicles 英语百科 Yolk sac The yolk sac is a membranous sac attached to an embryo, formed by cells of the hypoblast adjacent to the embryonic disk. This is alternatively called the umbilical vesicle by the Terminologia Embryologica (TE), though yolk sac is far more widely used. The yolk sac is important in early embryonic blood supply, and is incorporated into the primordial gut during the fourth week of development.
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Umbilical vesicles

Yolk sac