Gastrulation

Gastrulationis a phase early in the development of most animalembryos.In it, the embryo is dramatically restructured bycellmigration.

Gastrulation varies in differentphyla.It is followed byorganogenesis,when individual organs develop within the newly formedgerm layers.

Thegastrulais the double-walled stage of the embryo. During gastrulation, some of the cells of the blastula migrate inwards to make an inner layer, theendoderm.In some animals another cell layer forms, themesoderm,between the endoderm and theectoderm.

Germ layers[change|change source]

Amonganimals,spongesshow the simplest organization, having a single germ layer.Cnidariaandctenophoresshow an increase in complexity, having two germ layers, theendodermandectoderm.All higher animals (from flatworms to humans) possess amesodermas well as ectoderm and endoderm.

Development of germ layers[change|change source]

The purpose of gastrulation is to position the 3 embryonic germ layers, theendoderm,ectodermandmesoderm.These layers later develop into certain bodily systems.

The ectoderm develops into the skin, nails, theepitheliumof the nose, mouth and anal canal; the lens of the eye, theretinaand the nervous system.
The endoderm develops into the inner linings of thedigestivetract, as well as the linings of therespiratorypassages. It also forms many glands, such as theliverandpancreas.
The mesoderm forms the somites, thenotochord,and the mesenchyme, which give rise to the muscles, circulatory and excretory systems of the body. This key innovation evolved hundreds of millions of years ago and led to the evolution of nearly all large, complex animals. The formation of a mesoderm led to the development of acoelom.Organs formed inside a coelom can freely move, grow, and develop independently of the body wall while fluid cushions and protects them from shocks.^[1]