Notes

Gastrulation Gastrulation is defined as an early developmental process in which an embryo transforms form a one-dimensional layer of epithelial cells (blastula) and re-organizes into a multi-layered and multi-dimensional structure called the gastrula. In reptiles, avians and mammals, which are triploblastic organisms, gastrulation derives a three tissue-layered organism composed of endoderm, mesoderm and ectoderm. Each derm layer corresponds to the development of specific primitive systems during organogenesis. In addition to setting the embryo up for organ formation, gastrulation provides a mechanism to develop a multi-leveled body plan that demarcates anatomical axis formation with dorsal/ventral and cranial/caudal axis (also termed anterior or rostral/posterior, respectively), retention of global left/right symmetry, and the loss of bilateral symmetry in specific systems (e.g., heart).