thumb|Visualization of the three germ layers of a gastrula.

Endoderm is the innermost of the three primary germ layers in the very early embryo. The other two layers are the ectoderm (outside layer) and mesoderm (middle layer). Cells migrating inward along the archenteron form the inner layer of the gastrula, which develops into the endoderm.

The endoderm consists at first of flattened cells, which subsequently become columnar. It forms the epithelial lining of multiple systems. The endoderm epithelium forms the respiratory and gastrointestinal tracts through nodal signaling.

In plant biology, endoderm corresponds to the innermost part of the cortex (bark) in young shoots and young roots often consisting of a single cell layer. As the plant becomes older, more endoderm will lignify.

Formation of the Endoderm Layer

The endoderm is formed through the nodal signaling pathway. Pattern formation allows the initial endoderm cells to form the organs involved in each of these systems. || Gastrointestinal tract || the entire alimentary canal except part of the mouth, pharynx and the terminal part of the rectum (which are lined by involutions of the ectoderm), the lining cells of all the glands which open into the digestive tube, including those of the liver and pancreas

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| General || Respiratory tract || the trachea, bronchi, and alveoli of the lungs

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| General || Endocrine glands and organs || the lining of the follicles of the thyroid gland and the epithelial component of the thymus (i.e. thymic epithelial cells).

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| || Auditory system || the epithelium of the auditory tube and tympanic cavity

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| || Urinary system || the urinary bladder and part of the urethra

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Liver and pancreas cells are believed to derive from a common precursor.

Additional images

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File:Gray21.png|Section through the embryo.

File:Gray32.png|Section through ovum imbedded in the uterine decidua

Transcription factor network in endoderm induction..jpg|Signaling pathway to inducing endoderm

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See also

  • Hypoblast of primitive endoderm
  • Ectoderm
  • Germ layer
  • Histogenesis
  • Mesoderm
  • Organogenesis
  • Endodermal sinus tumor
  • Gastrulation
  • Cell differentiation
  • Triploblasty
  • List of human cell types derived from the germ layers

References