Germ Layer Derivatives


Ectoderm Derivatives

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The ectoderm is the outermost germ layer, and it gives rise to the outermost tissues-- like the skin, hair, nails, and lens of the eye. During embryogenesis, the ectoderm invaginates to create the lining of the mouth (including the teeth) -- as well as the anus. Another key derivative of the ectoderm is the nervous system, and all of the sensory organs the relay to it. The nervous cells further differentiate to give rise to neuroendocrine tissues, such as the adrenal medulla, C-cells of the thyroid, and part of the pituitary gland.

Key Points

  • Ectoderm = outermost germ layer in embryologic development (“ecto” = outer)
    • Gives rise to tissues on the "outside" (e.g. skin)
  • Ectoderm Derivatives
    • Epidermis of skin, hair, nails, melanocytes
    • Epithelial linings of mouth (including teeth) and outer anus
    • Nervous system (central and peripheral)
      • Derived from neuroectoderm
    • Neuroendocrine organs including adrenal medulla
      • Neuroendocrine = secrete hormones (endocrine) in response to nervous signals (neural)
    • Pituitary gland
      • Anterior pituitary is derived from roof of oral cavity = surface ectoderm
      • Posterior pituitary is derived from neural tube = neuroectoderm
    • Mammary glands of breast
    • Sensory epithelia of eyes (including lens), ears, nose