Endoderm is one of the three primary germ cell layers in the very early embryo. The other two layers are the ectoderm (outside layer) and mesoderm (middle layer), with the endoderm as the innermost 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 following chart shows the products produced by the endoderm. The embryonic endoderm develops into the interior linings of two tubes in the body, the digestive and respiratory tube.
Liver and pancreas cells are believed to derive from a common precursor.
In humans,the endoderm can differentiate into distinguishable organs after 5 weeks of embryonic development.
Section through the embryo.
Section through ovum imbedded in the uterine decidua
This article incorporates text from a public domain edition of Gray's Anatomy.