Yolk Sac

The yolk sac is a 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.

Read more about Yolk SacIn Humans, In Fish, Histogenesis, Modifications, Additional Images

Other articles related to "yolk sac, yolk, sac":

Formation of The Amniotic Cavity
... membrane along with hypoblast forms the primary yolk sac ... The embryonic disc now lies between the amniotic cavity and the primary yolk sac ... Cells from the yolk sac endoderm form a layer of connective tissue, the extraembryonic mesoderm, which surrounds the amnion and yolk sac ...
Yolk Sac - Additional Images
... of allantoic development with commencing constriction of the yolk-sac Diagram illustrating a later stage in the development of the umbilical cord Fetus of about eight weeks, enclosed in the amnion ... Digestive tube and yolk sac in median section ...
Milk Shark - Biology and Ecology - Life History
... embryonic length of 63–65 mm (2.5–2.6 in), the embryo relies on yolk for sustenance and gas exchange occurs across its surface integument and possibly also the yolk sac ... embryonic length of 81–104 mm (3.2–4.1 in), the external gill filaments develop and the yolk sac begins to be resorbed, the embyo ingesting histotroph (a nutritious ... the third phase, lasting six to eight months, the depleted yolk sac is converted into a placental connection through which the fetus receives nourishment until birth ...
Bilaminar Blastocyst - Formation of The Yolk Sac and Chorionic Cavity - Yolk Sac During Development
... Like the amnion, the yolk sac is simply an extraembryonic membrane that surrounds a cavity ... Formation of the definitive yolk sac happens after the extraembryonic mesoderm splits, and it becomes a double layered structure with hypoblast-derived ... The definitive yolk sac contributes greatly to the embryo during the 4th week of development and it executes critical functions for the embryo ...
Vitelline Circulation
... to the system of blood flowing from the embryo to the yolk sac and back again ... The yolk-sac is situated on the ventral aspect of the embryo it is lined by endoderm, outside of which is a layer of mesoderm ... Blood is conveyed to the wall of the sac by the primitive aortæ, and after circulating through a wide-meshed capillary plexus, is returned by the vitelline veins to the tubular heart of the embryo ...