Medicine and Health related Information

a) The cells of the trophoblast gives origin to a mass of cells called the extra embryonic mesoderm or primary mesoderm. These cells come to lie between the trophoblast and the flattened endodermal cells lining the yolk sac. Thus separating them from each other. These cells also separate the wall of amniotic cavity from the trophoblast, this mesoderm is called “EXTRA-EMBRYONIC” because it lies otside the embryonic disc.

b) Small cavities appear in extraembryonic mesoderm, gradually these join together to form larger spaces and ultimately one larger space is formed. This cavity is called “EXTRA-EMBRYONIC COELOM”. With its formation the extramembryonic mesoderm splits into two layers, the part lining the inside of the trophoblast and the outside of the amniotic cavity is called ” PARIETAL or SOMATOPLEUORIC EXTRAEMBRYONIC MESODERM “. It will be seen that the extraembryonic coelom does not extend into that part of the extraembryonic mesoderm which attaches the wall of the amniotic cavity to the trophoblast. The developing embryo along with the amniotic cavity and the yolk sac is now suspended in the extraembryonic coelom and is attached to the wall of the blastocyst only by this unsplit part of the extramembryonic mesoderm. This mesoderm forms a structure called ” CONNECTING STALK”.