Icon module 7

Learning aims

By the end of this module you should know about:

  • The differentiation of the embryonic germ layers, emanating from the trilaminar embryo
  • The mechanism of gastrulation and especially the morphogenetic role of the primitive streak
  • The arrangement of the intraembryonic mesoblast, its segmentation and the formation of the intraembryonic coelomic cavity
  • The formation of the notochord and its role in the differentiations of nerve tissue
  • The stages of neurulation and the first steps in the genesis of the central and peripheral nervous system

What you should already know

  • Placenta
  • Implantation

Delving deeper

  • Which mechanisms are needed in a developing embryo in order that migrating cells go to the right places?
  • Which genes are involved and through which processes do they determine the orientation and organization of the embryo that in the beginning is unpolarized? (Symmetry plan, axes, lateralization, segmentation).
  • How is a structured development of the embryo possible by means of the morphogenetic function of tissues that influence the differentiation and development of the neighboring germ layers?
  • Beginning with the anomalies that arise during the trilaminar stage of the germ disk, investigate the resulting structural and functional disorders of the organism after birth.


From the end of the 2nd to the 4th week the mass of cells out of which the embryo arises experiences numerous modifications. These lead to the genesis of the trilaminar embryo, the structure of which already exhibits the organizational plan of the tissues and the most important organs. These processes of proliferation and migration are called gastrulation.
At the end of this period differentiation of the various organ systems are already taking place. Especially large parts of the central nervous system (neural tube) and the peripheral nervous system (neural crest) are already formed. In addition, the primordia of the axial skeletal muscle system and the skin appear in the form of somites. The somites consist of metameric collections of mesoblastic cells. In the course of these processes transitory (temporary) structures can remain preserved and cause various malformations.