AskDefine | Define mesoderm

Dictionary Definition

mesoderm n : the middle germ layer that develops into muscle and bone and cartilage and blood and connective tissue [syn: mesoblast]

User Contributed Dictionary



  1. One of the three tissue layers in the embryo of a metazoan animal. Through development, it will produce the muscles of the adult.

See also

Extensive Definition

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.

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



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


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

Additional images


  • Evers, Christine A., Lisa Starr. Biology:Concepts and Applications. 6th ed. United States:Thomson, 2006. ISBN 0-534-46224-3.

External links

mesoderm in Arabic: أديم متوسط
mesoderm in Czech: Mezoderm
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mesoderm in Spanish: Mesodermo
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mesoderm in French: Mésoderme
mesoderm in Italian: Mesoderma
mesoderm in Lithuanian: Mezoderma
mesoderm in Dutch: Mesoderm
mesoderm in Polish: Mezoderma
mesoderm in Portuguese: Mesoderme
mesoderm in Finnish: Mesodermi
mesoderm in Swedish: Mesoderm
mesoderm in Turkish: Mezoderm
mesoderm in Ukrainian: Мезодерма
mesoderm in Chinese: 中胚层
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