Gastrulation marks the beginning of the embryonic stage of development and establishes three distinct cell layers (eg, ectoderm, mesoderm, endoderm) from which all tissues and organs are derived.

The gastrointestinal system is derived from components of each of the following cell layers:

• Ectoderm:  The ectoderm is composed of surface ectoderm, neural tube, and neural crest cells.  The surface ectoderm gives rise to the oral epithelial linings and salivary glands (Choice D).  The neural crest gives rise to neural ganglia, including enteric ganglion cells.  These cells are responsible for intestinal relaxation, and failure of neural crest cell migration to the distal colon during embryonic development leads to Hirschsprung disease (Choice A).

• Mesoderm:  The peritoneum and spleen are derivatives of the mesoderm (Choices C and E), which also gives rise to the smooth muscle component of the intestinal tract.

• Endoderm:  Gastrointestinal derivatives of the endoderm include the liver, pancreas, and epithelial lining.

Therefore, in this fetus with disrupted endoderm differentiation, pancreatic enzyme production is likely to be affected.  Other structures that could be affected in a patient with disrupted endoderm differentiation include the respiratory tract, thymus, parathyroid glands, and bladder/urethra.

Educational objective:
All tissues and organs are derived from the following distinct cell layers: ectoderm, mesoderm, and endoderm.  Derivatives of the endoderm include the gastrointestinal tract, liver, and pancreas.