Gastrulation

Gastrulation is the early embryonic process that reorganizes a blastula into a gastrula and establishes the primary germ layers: ectoderm, mesoderm, and endoderm.

Invagination: The inward bending of a sheet of cells to form a pocket or tube. In many embryos, inward bending initiates the formation of the primitive gut.
Blastula: An early embryonic stage consisting of a sphere or mass of cells surrounding a cavity. It is the starting form that gastrulation reorganizes.
Xenopus laevis: An African clawed frog widely used as a model organism in developmental biology. Its large embryos make the cell movements of gastrulation especially accessible to study.
Body plan: The organized arrangement of an animal’s body structures and principal axes. Gastrulation lays down the basic spatial organization from which the body plan develops.
Cleavage: Rapid early embryonic cell divisions that partition the zygote without substantial growth. Cleavage increases cell number before gastrulation reorganizes those cells.
Involution: The inward rolling of an expanding cell sheet over an edge or opening. This movement carries cells inside the embryo during gastrulation in some species.
Gastrula: An embryonic stage formed by gastrulation, with cells arranged into primary germ layers. It is the developmental form produced by the process.
Chicken embryo: The developing embryo of a domestic chicken, a major model for vertebrate development. Its primitive streak provides a clear example of gastrulation in an amniote.
Embryonic germ layer: A primary embryonic tissue layer that gives rise to particular tissues and organs. The process establishes the germ layers that guide later tissue development.
Blastulation: The developmental process that forms a blastula from cleavage-stage cells. It creates gastrulation’s starting stage but does not establish the primary germ layers.

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