abnormal primitive endoderm morphology 2011-06-20T02:15:10Z In rodents, the hypoblast cells form the parietal endoderm, parietal and visceral yolk sac as well as extraembryonic membranes, such as the extraembryonic endoderm, the yolk sac and the stalk that links it to the endodermal digestive tube. In human embryos, hypoblast cells migrate and line the blastocoelic cavity of the blastocyst, forming the primary yolk sac and Heuser's membrane. Although both the murine parietal yolk sac and the human primary yolk sac are transient structures, they are not developmental equivalents. A second wave of hypoblast cells migrates to form the definitive yolk sac which displaces the primary yolk sac and is equivalent to the murine visceral yolk sac. The primary yolk sac breaks up into small vesicles that can persist at the mural (abembryonic) pole. MP:0011183 MPheno.ontology abnormal PE morphology abnormal PrE morphology abnormal hypoblast morphology abnormal primary endoderm morphology any structural anomaly of the transient thin monolayer of cuboidal cells that comprise the lower layer of the bilaminar embryonic disk; the hypoblast cells contribute to several extraembryonic structures, but do not contribute to the embryo csmith abnormal bilaminar embryonic disc