Tissue Formation during Embryogenesis

The formation of functional organs and tissues during embryonic development is a complex process involving multiple cell types derived from ectoderm, mesoderm, endoderm, and the neural crest. These cell types interact via diverse mechanisms. Examples of such mechanisms are direct cell–cell contacts and paracrine signaling by morphogenic gradients. Cell behavior during organogenesis is dynamic and is dependent on cell movements of a subset of cells. Other cells revert their phenotype by a process called epithelial-to-mesenchyme transition and may become migratory. To obtain functional organs, cells respond to environmental signals like pulsatile blood flow by activation of adaptive signaling mechanisms, which direct tissue architecture. The timely, proper dosing and sequential integration of all these elements during organogenesis specifies cell types and shapes the organ's form and function in the embryo. Tissue engineering relies on reiteration of these developmental processes and aims to combine this knowledge with typical engineering disciplines to generate functional substitutes to replace lost or worn out tissue. This process is known as developmental (re)engineering.