Endoderm

Endoderm is the innermost of the three primary germ layers formed during early embryonic development. It arises during gastrulation as cells migrate inward to line the primitive gut tube, establishing the mucosal epithelium and associated glands of the internal tracts. The endoderm largely gives rise to the internal linings and secretory organs of the body’s internal cavities.

The major derivatives of the endoderm include the epithelial lining of the digestive tract from the foregut to the hindgut and the lining of the lower respiratory tract. It also forms the glandular organs that develop from these linings, such as the liver, pancreas, and biliary system (gallbladder and bile ducts). Endodermal tissue contributes to the thyroid gland, as well as the parathyroid glands and thymus through the pharyngeal pouches. In the urinary system, the epithelium of the lower urinary tract, including the urinary bladder and parts of the urethra, is endodermal in origin. The tympanic cavity and auditory tube also derive from endodermal lining of the foregut derivatives.

During development, endoderm interacts with mesoderm and ectoderm to form the organs’ architecture and vasculature. Abnormal endoderm formation or organogenesis can lead to congenital anomalies affecting the gut, liver, pancreas, thyroid, or urinary tract.

In summary, the endoderm provides the internal linings and essential glands and organs of the digestive, respiratory, endocrine, and some urogenital systems, playing a central role in forming the body’s internal environments.