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Understanding Mesoderm and Its Derivatives

Feb 3, 2025

Mesoderm Lecture Notes

Introduction

  • Discussion on mesoderm formation and differentiation
  • Overview of gastrulation process: bilaminar disc to trilaminar disc
  • Importance of epiblast layer transformation

Gastrulation Process

  • Bilaminar Disc:
    • Amniotic cavity above
    • Epiblast layer (blue)
    • Hypoblast layer (green) beneath
  • Primitive Streak Formation:
    • Slit in epiblast with a node (primitive node)
    • Fibroblast Growth Factor (FGF8) causes epiblast cell movement

Formation of Three Germ Layers

  1. Endoderm:
    • Epiblast cells replace the hypoblast
  2. Mesoderm:
    • New layer between endoderm and epiblast
  3. Ectoderm:
    • Differentiation of epiblast cells

Role of Notochord

  • Secretes growth factors like Sonic Hedgehog protein
  • Triggers:
    • Neuralation Pathway: Formation of neural tube
    • Mesoderm Differentiation: Specialization into different mesoderm types

Mesoderm Differentiation

  • Medial to Lateral Sections:
    1. Paraxial Mesoderm
    2. Intermediate Mesoderm
    3. Lateral Plate Mesoderm
      • Subdivided into Somatic and Splanchnic layers

Paraxial Mesoderm

  • Forms somites, segmenting into:
    • Dermatomyotome:
      • Differentiates into dermis, subcutaneous tissue, and spinal meninges
    • Myotome:
      • Develops into skeletal muscles of trunk, back, and limbs
    • Sclerotome:
      • Develops vertebrae and ribs

Intermediate Mesoderm

  • Develops into:
    • Renal system (kidneys and ureters)
    • Gonads (testes or ovaries) and their ductal systems

Lateral Plate Mesoderm

  • Somatic Layer:
    • Forms body cavity linings (parietal layer)
    • Contributes to sternum and limb bones
  • Splanchnic Layer:
    • Forms visceral layer of body cavities
    • Develops adrenal cortex, lymph nodes, spleen, and smooth muscle of the GI tract
    • Involved in cardiovascular system development and myeloid/lymphoid stem cell production

Mnemonic for Mesoderm Derivatives

  • M - Myeloid stem cells
  • E - Erythroid stem cells
  • S - Spleen
  • O - Gonads
  • D - Dermis
  • E - Entire trunk
  • R - Renal system
  • M - Meninges
  • A - Adrenal cortex
  • L - Lymphoid stem cells
  • C - Cardiovascular system (including endothelium)
  • L - Linings of body cavities
  • L - Limbs
  • S - Smooth muscle of the GI tract

Conclusion

  • Recap on mesoderm derivations
  • Importance of understanding differentiation process

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