endoderm

endoderm, in biology, inner layer of tissue formed in the gastrula stage of the developing embryo. At the end of the blastula stage, cells of the embryo are arranged in the form of a hollow ball. Cell movement results in an invagination of the bottom region, or vegetal hemisphere, of the embryo so that it resembles a double-walled cup. The inner layer of the cup is the endoderm; the outer layer is the ectoderm; a middle layer, the mesoderm, forms from a marginal zone. The endoderm is the germ layer from which are formed the digestive system, many glands, and part of the respiratory system. See embryo.

Endoderm, (sometimes called Entoderm) is one of the germ layers formed during animal embryogenesis. 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 the whole of the digestive tube 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, the epithelium of the auditory tube and tympanic cavity, of the trachea, bronchi, and alveoli of the lungs, of the urinary bladder and part of the urethra, and that which lines the follicles of the thyroid gland and thymus.

Production

The following graph represents the products produced by the endoderm.

Germ Layer	Category	Product
Endoderm	General	Gastrointestinal tract
Endoderm	General	Respiratory tract
Endoderm	General	Endocrine glands and organs (liver and pancreas)

Additional images

See also

• Ectoderm
• Germ layer
• Histogenesis
• Mesoderm
• Organogenesis
• Endodermal sinus tumor

Notes

References

• Evers, Christine A., Lisa Starr. Biology:Concepts and Applications. 6th ed. United States:Thomson, 2006. ISBN 0-534-46224-3.