Embryonic Germ Layer Derivatives
| Layer | Primary Derivatives |
|---|---|
| Ectoderm | Surface: Epidermis, lens, olfactory epithelium.
Neuroectoderm: Brain, spinal cord, retina, posterior pituitary. Neural Crest: PNS, melanocytes, facial bones, adrenal medulla. |
| Mesoderm | Muscle, bone, connective tissue, dermis, cardiovascular system, kidneys, spleen, ovaries, and testes. (Think “means of movement/support”). |
| Endoderm | Epithelial lining of GI, respiratory, and urogenital tracts; liver, pancreas, thyroid, thymus, parathyroids. (Think “internal organs/linings”). |
High-Yield Exceptions:
- Neural Crest (Ectoderm): Often tested as a “4th layer”—responsible for PNS, adrenal medulla, and pharyngeal arch skeletal components.
- Spleen: Although it is a lymphoid organ, it is derived from mesoderm (not endoderm).
- Notochord (Mesoderm): Induces the overlying ectoderm to form the neural plate.