5-Revisions_Chronology of Systems, the 5 Phases of Embryology

Embryology is structured around five key phases: fertilization, gastrulation, neurulation, metamerization, and delimitation. Embryonic development begins with the establishment of an axis between the polar bodies, essential for the formation of the digestive system. The latter emerges rapidly, initiated by autocrine fluid movements, allowing the embryo to know itself before it can digest and exchange nutrients. The development of the connective circulatory endocrine system follows, with a hierarchy where the enteric system, considered the first brain, precedes cerebralization.

The formation of the vitelline cavity and the external cellulome occurs in the uterine lining, where the trophoblast plays a crucial role. This process leads to the appearance of a cavity, the blastocoel, which evolves into a structure integrating nutrients and promoting growth. The dynamics of growth, influenced by the speed of development of the different cell layers, create points of support and tears, such as Heuser's membrane, which maintains the cavity. The transformation of the embryo into an S-shape, as well as flexion and fluid dynamics, are essential for axial development, influencing the formation of vital organs such as the heart and liver, while establishing functional connections between different parts of the body.