Inner Cell Mass – Embryonic Development & Stem Cells …

Embryonic Development of the Inner Cell Mass:

The fourth cleavage event of the developing embryo results in a nonpolarizedinner cell mass(ICM, pluriblast,embryoblast), enveloped by the outer, polarizedtrophoblastlayer of cells. The trophoblast cells form an inner cavity (blastocoele), whose formation indicates the bastocyst stage. While the trophoblast will ultimately form the outerchorionicsac and the fetal component of theplacenta, the inner cell mass, will give rise to all embryonic tissues and to some of the extraembryonic membranes.

The ICM segregates into abilaminar embryonic disc(bilaminar blastoderm) which consists of two epithelial layers, each of a distinct lineage: the external (dorsal)epiblastand the internal (ventral)hypoblast. The next developmental stage is gastrulation, in which waves of migrating cells convert the ICM into a trilaminar embryonic disc, which is comprised of three germ layers (ectoderm, mesoderm and endoderm) that contribute to the formation of many organs, often with contributions of two or all three of the germ layers.

The ectoderm forms the central andperipheral nervous systemsandepidermis, and contributes to theadiposeandheartas well as to numerous other organs. The ectoderm forms many of thesensory organs(eye, ear, nose), and is also the source of Rathke's pouch, an invaginating diverticulum of the stomodeal roof which ultimately detaches from the stomodeum and becomes the adenohypophysis of the pituitary gland.

The mesoderm produces and contributes to theblood,endothelium,heart,kidney,reproductive system,bones,skeletal, smooth muscleand connective tissues. The mesoderm also contributes totendons,ligaments,dermisandcartilage.

The endoderm produces thegut tubeand its derived organs, including the cecum, intestine, stomach, thymus, liver,pancreas,lungs,thyroidandprostate.

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Inner Cell Mass - Embryonic Development & Stem Cells ...