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Mesoderm



Mesoderm
Organs derived from mesoderm.
Section through the embryo
Gray's subject #6 49
Days 16
MeSH Mesoderm

The germ layer mesoderm forms in the embryos of animals more complex than cnidarians, making them triploblastic. Mesoderm forms during gastrulation when some of the cells migrating inward to form the endoderm form an additional layer between the endoderm and the ectoderm.

This key innovation evolved hundreds of millions of years ago and led to the evolution of nearly all large, complex animals. The formation of a mesoderm led to the formation of a coelom. Organs formed inside a coelom (body cavity) can freely move, grow, and develop independently of the body wall while fluid cushions and protects them from shocks.

Additional recommended knowledge

Contents

Categorizing animals

Not all triploblastic animals have a coelom, like the simplest animals with organs that form from three tissue layers: flatworms. Three different configurations of mesoderm in relation to ectoderm form a method of categorizing animals.

  • Acoelomates
    • no coelom
    • tissues and organs packed between gut and body wall
  • Pseudocoelomates
    • false coelom
    • unlined or partially lined body cavity between gut and body wall
  • Coelomates
    • proper coelom
    • lined cavity between gut and body wall

Derivatives

General

Note: Not all triploblasts produce all of the items listed.

Vertebrates

 

In addition to the general list, the mesoderm of a developing vertebrate differentiates into the following:

  • Chordamesoderm
  • Paraxial mesoderm
  • Intermediate mesoderm
  • Lateral plate mesoderm

See also

Additional images

References

  • Evers, Christine A., Lisa Starr. Biology:Concepts and Applications. 6th ed. United States:Thomson, 2006. ISBN 0-534-46224-3.
 
This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Mesoderm". A list of authors is available in Wikipedia.
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