Gastrulation is a phase early in the embryonic development of most animals, during which the single-layered blastula is reorganized into a trilaminar ("three-layered") structure known as the gastrula. These three germ layers are known as the ectoderm, mesoderm, and endoderm.

Gastrulation takes place after cleavage and the formation of the blastula and primitive streak. Gastrulation is followed by organogenesis, when individual organs develop within the newly formed germ layers. Each layer gives rise to specific tissues and organs in the developing embryo. The ectoderm gives rise to epidermis, and to the neural crest and other tissues that will later form the nervous system. The mesoderm is found between the ectoderm and the endoderm and gives rise to somites, which form muscle; the cartilage of the ribs and vertebrae; the dermis, the notochord, blood and blood vessels, bone, and connective tissue. The endoderm gives rise to the epithelium of the digestive system and respiratory system, and organs associated with the digestive system, such as the liver and pancreas. Following gastrulation, cells in the body are either organized into sheets of connected cells (as in epithelia), or as a mesh of isolated cells, such as mesenchyme.

The molecular mechanism and timing of gastrulation is different in different organisms. However, some common features of gastrulation across triploblastic organisms include: (1) A change in the topological structure of the embryo, from a simply connected surface (sphere-like), to a non-simply connected surface (torus-like); (2) the differentiation of cells into one of three types (endodermal, mesodermal, and ectodermal); and (3) the digestive function of a large number of endodermal cells.

Lewis Wolpert, pioneering developmental biologist in the field, has been credited for noting that "It is not birth, marriage, or death, but gastrulation, which is truly the most important time in your life."

The terms "gastrula" and "gastrulation" were coined by Ernst Haeckel, in his 1872 work "Biology of Calcareous Sponges".

Other articles related to "gastrulation":

Neural Development In Humans - Embryonic Stage - Neurulation
... It follows gastrulation in all vertebrates ... During gastrulation cells migrate to the interior of embryo, forming three germ layers— the endoderm (the deepest layer), mesoderm and ectoderm (the ... After gastrulation the notochord—a flexible, rod-shaped body that runs along the back of the embryo—has been formed from the mesoderm ...
Formation of The Archenteron in Sea Urchins
... See Gastrulation ... At this point gastrulation is complete, and the gastrula has a functional digestive tube ... During Gastrulation, the Archenteron develops into the digestive tube, with the blastopore developing into either the mouth (Protostome) or the anus (Deuterostome) ...
Primitive Streak
... streak will establish bilateral symmetry, determine the site of gastrulation and initiate germ layer formation ... as the place where cells will ingress and migrate during the process of gastrulation and germ layer formation ... event in the embryo, and marks the beginning of gastrulation ...
Bilaminar Blastocyst - Epiblast Cells During Gastrulation
... and the formation of the primitive streak sparks the beginning of gastrulation ... Gastrulation is when the three germ cell layers develop as well as an organism’s body plan ... During gastrulation, cells of the epiblast, a layer of the bilaminar blastocyst, migrate towards the primitive streak, enter it, and then move apart from it through a process called ingression ...