Paraaxial, intermediate, lateral plate mesoderm

The intraembryonic mesoderm differentiates into:

  1. Paraaxial mesoderm
  2. Intermediate mesoderm
  3. Lateral plate mesoderm


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Paraaxial mesoderm

Transverse grooves appear dividing it into somites, from cranial to caudal end.

42 to 44 somites form;

  • 4 occipital
  • 8 cervical
  • 12 thoracic
  • 5 lumbar
  • 5 sacral
  • 8 – 10 coccygeal

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The somites then differentiate in a cranio-caudal direction into:

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  1. Sclerotome – forms connective tissue, cartilage cells and bone cells of axial skeleton 
  2. Myotomes – differentiate into myoblasts, which then forms skeletal muscles of the body
  3. Dermatome – forms dermis of skin


Intermediate mesoderm

  • Cervical – segmented
  • Thoracic – partially segmented
  • Lumbar – unsegmented. forms nephrogenic cord (source of urinary system)

Origin to:

  • Cortex of suprarenal gland
  • Nephrons
  • Gonads


Lateral plate mesoderm

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Due to formation of intraembryonic coelom, it is divided into:

1. Somatic layer:

  • Adherent to ectoderm
  • Forms muscles and connective tissue of body wall

2. Splanchnic layer:

  • Adherent to endoderm
  • Forms serous membranes: Pleura, Pericardium, Peritoneum
  • Smooth muscles
  • Connective tissue of GIT, respiratory tracts
  • Cardiovascular system

The intraembryonic coelom forms:

  • Pericardial cavity
  • Peritoneal cavity
  • Pleural cavity


Other derivatives of the mesoderm:

  • All skeletal, smooth and cardiac muscles
  • Bone marrow and blood cells
  • Spleen
  • Lymph nodes
  • Dura matter

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