Pre-Medicine

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MCAT

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Germ Layer Derivatives

Endoderm Derivatives

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Summary

The endoderm is the innermost germ layer that is formed during embryogenesis. It is responsible for forming many internal structures. Specifically, it gives rise to the lining of the digestive and respiratory tracts, the bladder, urethra, liver, pancreas, and most of the thyroid gland.

Key Points

  • Endoderm = innermost germ layer in embryonic development (“endo” = inner)
    • Gives rise to innards and internal organs
  • Endoderm Derivatives
    • GI tract from throat to inner anus (including stomach and intestines)
      • Except mouth and outer anus (derived from invaginations of surface ectoderm)
    • Other GI organs like liver and pancreas
    • Respiratory tracts including airways and lung
    • Most parts of Thyroid
      • except C-cells (derived from ectoderm)
    • Bladder and Urethra (lower urinary tract)
      • Note: not kidneys (derived from mesoderm)
    • Thymus
      • Lymph node-like tissue where T-cells develop