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.

In humans

The yolk sac is the first element seen in the gestational sac during pregnancy, usually at 3 days gestation. Identification of the gestational sac is a critical landmark in monitoring an early pregnancy, and can be reliably seen in human pregnancy using ultrasound.

The yolk sac is situated on the ventral aspect of the embryo; it is lined by extra-embryonic endoderm, outside of which is a layer of extra-embryonic mesenchyme, derived from the mesoderm.

Blood is conveyed to the wall of the yolk sac by the primitive aorta, and after circulating through a wide-meshed capillary plexus, is returned by the vitelline veins to the tubular heart of the embryo. This constitutes the vitelline circulation, and by means of it nutritive material is absorbed from the yolk sac and conveyed to the embryo.

Sacé

Sacé is a commune in the Mayenne department in north-western France.

See also

SAC

SAC or Sac may refer to:

Organizations

Computers

Education

Government and military

Sauk people

The Sac or Sauk are a group of Native Americans of the Eastern Woodlands culture group. Their autonym is oθaakiiwaki, and their exonym is Ozaagii(-wag) in Ojibwe. The latter name was transliterated into French and English by colonists of those cultures.

Today they have three federally recognized tribes, together with the Meskwaki (Fox), located in Iowa, Oklahoma and Kansas.

History

The Sauk, an Algonquian languages people, are believed to have developed as a people along the St. Lawrence River. They were driven by pressure from other tribes, especially the powerful Iroquois League or Haudenosaunee, to migrate to Michigan, where they settled around Saginaw Bay. Due to the yellow-clay soils found around Saginaw Bay, they called themselves the autonym of Oθaakiiwaki (often interpreted to mean "yellow-earth".)

The neighboring Ojibwe and Ottawa peoples referred to them by the exonym Ozaagii, meaning "those at the outlet". French colonists transliterated that as Sac and the English as "Sauk". Anishinaabe expansion and the Huron attempt to gain regional stability drove the Sac out of their territory. The Huron were armed with guns supplied by their French trading partners. The Sac moved south to territory in parts of what are now northern Illinois and Wisconsin.