View source for Mesoderm

{{Infobox Embryology |
  Name          = {{PAGENAME}} |
  Latin         = |
  GraySubject   = 6 |
  GrayPage      = 49|
  Image         = mesoderm.png |
  Caption       = Organs derived from mesoderm. |
  Image2        = Gray21.png |
  Caption2      = Section through the embryo |
  System        = |
  CarnegieStage = |
  Days          = 16 |
  Precursor     = |
  GivesRiseTo   = |
  MeshName      = Mesoderm |
  MeshNumber    = A16.254.425.660 |
  DorlandsPre   = |
  DorlandsSuf   = |
}}

[[Image:Image19.png|thumb|350px|Transverse section of a chick embryo of forty-five hours' incubation.<br/>
* ''Chordamesoderm:'' yellow, at the [[notochord]].<br/>
* ''Paraxial mesoderm:'' red, comprising the [[somite]]s.<br/>
* ''Intermediate mesoderm:'' purple, which includes the [[Wolffian duct]].<br/>
* ''Lateral plate mesoderm:'' purple, comprising somatic and splanchic mesoderm.]]

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==Overview==

The [[germ layer]] '''mesoderm''' forms in the [[embryo]]s of [[animal]]s more complex than [[cnidaria]]ns, 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 [[body cavity|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: [[flatworm]]s. 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.
*[[skeletal system|bones]] 
*most of the [[circulatory system]], including the [[heart]] and major blood vessels
*[[connective tissue]]s of the gut and [[integumentary system|integuments]]
*[[mesenchyme]]
*[[mesothelium]]
*[[muscular system|muscles]]
*[[peritoneum]] (lining of the coelom)
*[[reproductive system]]
*[[urinary system]], including the [[kidney]]s

===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==
*[[Ectoderm]]
*[[Endoderm]]
*[[Germ layer]]
*[[Histogenesis]]
*[[Organogenesis]]

==Additional images==
<gallery>
 Image:Gray35.jpg|Transverse section of a chorionic villus.
</gallery>

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

==External links==
* {{EmbryologyUNSW|Notes/skmus6}}
* {{EmbryologyTemple|EMBIII97/sld039}}

{{Embryology}}
{{Germ layer}}

[[Category:Developmental biology]]
[[Category:Embryology]]
[[Category:Gastrulation]]

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