Origine and further development of mesenchyme

Mesenchyme is a loosely organized embryonic connective tissue composed of undifferentiated, motile cells embedded in an extracellular matrix (ECM).

It plays a central role in organ formation, contributing to several tissue including connective tissue, cartilage, bone, muscle, and parts of the vascular system.

Some mesenchymal cells can arise through epithelial–mesenchymal transition (EMT), where epithelial cells acquire migratory properties, but the majority of mesenchyme originates directly from mesoderm or neural crest cells.

Embryological Origin

Mesodermal Mesenchyme

• Paraxial mesoderm → somites → skeletal muscle, dermis, vertebrae
• Lateral plate mesoderm → limb skeleton, connective tissue, heart and blood vessels
• 

  mesoderm
  Intermediate mesoderm → urogenital system

Mesoderm is the major source of mesenchyme throughout the embryo

Neural Crest-Derived Mesenchyme

• 

  neural crest cells migration
  Neural crest cells, arising from the dorsal neural tube, migrate extensively and differentiate into:
  • Craniofacial cartilage and bones
  • Peripheral neurons and glial cells
  • Melanocytes and some connective tissue

Endodermal Contribution

• Certain organs, such as the liver and pancreas, have mesenchyme derived from the endodermal epithelium.

Role of EMT

• During gastrulation and neural crest migration, some epithelial cells become mesenchymal by;

〇loosing cell-to-cell adhition

〇loosing polarity

〇gaining invading property

• 

  EMT
  This process, called epithelial–mesenchymal transition (EMT), is a minor pahway in overall formation of mesenchyme but still important in specific developmental event.

Histological Features of Mesenchyme

a cell in mesenchyme

• Cell shape: spindle-shaped or stellate, loosely arranged tissue
• Cytoplasm: rich in vimentinfilament
• Nucleus: large, euchromatic, prominent nucleoli
• Extracellular matrix (ECM): abundant glycosaminoglycans and proteoglycans, few fibers initially
• Vascularization: sparse at first, increasing as differentiation progresses
• Mesenchymal cells are highly motile compared to epithelial cells, facilitating migration during organogenesis.

Differentiation of Mesenchyme

Mesenchyme gives rise to multiple tissues and organs:

Connective Tissue

• Fibroblasts → produce collagen and ECM
• Adipocytes → lipid storage cells

Cartilage and Bone

• Chondrogenesis → cartilage
• Osteogenesis → bone
• Differentiation occurs via intramembranous or endochondral ossification

Muscle

• Skeletal muscle → from somite-derived mesenchyme
• Smooth muscle → from mesoderm of organs and blood vessels

Vascular System

• Angioblasts → endothelial cells
• Hemangioblasts → blood cells
• Pericytes → support vascular stability

Other Derivatives

• Tendons and ligaments
• Part of the heart and urogenital stroma

conclusion

Mesenchyme is a multipotent, loosely organized enbryonic connective tissue essential for organogenesis.

Most mesenchyme is mostly mesoderm- or neural crest-derived.

It differentiates into connective tissue, cartilage, bone, muscle, and components of the vascular system, forming the structural framework of virtually all organs.

Sources

1. Sadler, T. W. Langman’s Medical Embryology, 14th edition
2. Junqueira, L. C., Carneiro, J. Basic Histology: Text and Atlas, 15th edition
3. slides from MUDr. Adriana Hermanová