Lecture Notes: Ectoderm Development and Derivatives

Introduction

• Discussion on ectoderm and its derivatives.
• Brief review of ectoderm development.

Development of the Ectoderm

• Bilaminar Disc Formation

  • Two layers: Epiblast (top layer) and Hypoblast (bottom layer).
  • Precordal plate towards the cranial end of the embryo.

• Primitive Streak Formation

  • Epiblast cells degrade and form the primitive streak.
  • Epiblast cells migrate through the primitive streak into the space between epiblast and hypoblast layers.

• Trilaminar Disc Formation

  • Epiblast cells invade hypoblast, forming the endoderm.
  • Cells between epiblast and endoderm form the mesoderm.
  • Remaining epiblast cells differentiate into ectoderm.
  • Gastrulation: Process transforming bilaminar to trilaminar disc.

Formation of the Notochord

• Epiblast (ectodermal) cells move through primitive node towards pre-cordial plate.
• Formation of a tubular structure called the notochord.
• Notochord secretes growth factors stimulating ectoderm proliferation into the neural plate.

Neural Plate to Neural Tube Development

• Neural Plate: Thickened ectoderm due to notochord signals.

• Neural Groove and Neural Folds

  • Formation of a groove in the neural plate.
  • Neural folds develop into neural crest cells.

• Neural Tube Formation

  • Neural folds fuse to form the neural tube.
  • Neural crest cells form alongside the neural tube.
  • Neural tube becomes the central nervous system.

Derivatives of the Neural Tube

• Central Nervous System (CNS)
  • Brain and spinal cord development.
  • Contains neurons, glial cells (astrocytes and oligodendrocytes).
  • Develops posterior pituitary, pineal gland, retina.

Neural Crest Cells

• Neurocrest cells derived from neural folds.
• Mnemonic: CREST CELLS
  • C: Chromaffin cells (adrenal medulla).
  • R: Rostral tissues (head/neck connective tissue, bone, muscles).
  • E: Enteric nervous system.
  • S: Satellite and Schwann cells (PNS glial cells).
  • T: Peripheral nervous tissue (spinal nerves and ganglia).
  • Cardiac Structures: Carotid bodies, endocardial cushions.
  • Melanocytes: Pigment cells.
  • Leptomeninges: Pia and arachnoid mater.

Other Ectoderm Derivatives

• Placodes: Develop at the neural plate stage.

  • Olfactory Placode: Becomes olfactory epithelium for smell.
  • Lens Placode: Develops into lens for vision accommodation.
  • Otic Placode: Forms inner ear structures (cochlea, vestibule, semicircular canals).

• Surface Ectoderm: Forms epithelial tissue.

  • Includes epidermis, nails, hair, sweat glands.
  • Lines initial cavities: nasal, oral, ear canal, and anus.
  • Rathke’s Pouch: Develops into anterior pituitary.

Mnemonic for Ectoderm Derivatives

• E: Epithelial tissue lining orifices.
• C: Central nervous system.
• T: Lens placode.
• O: Otic and olfactory placodes.
• D: Dang crest cells (with separate mnemonic).
• E: Eyes (retina).
• R: Rathke's pouch (anterior pituitary).
• M: Melatonin (pineal gland).

Conclusion

• Overview of ectoderm development and derivatives.
• Importance of understanding ectoderm and its derivatives in embryonic development.