Mesoderm

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

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Overview

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

Derivatives

General

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

• bones
• most of the circulatory system, including the heart and major blood vessels
• connective tissues of the gut and integuments
• mesenchyme
• mesothelium
• muscles
• peritoneum (lining of the coelom)
• reproductive system
• urinary system, including the kidneys

Vertebrates

Transverse section of a chick embryo of forty-five hours' incubation.
* Chordamesoderm: yellow, at the notochord.
* Paraxial mesoderm: red, comprising the somites.
* Intermediate mesoderm: purple, which includes the Wolffian duct.
* Lateral plate mesoderm: purple, comprising somatic and splanchic mesoderm.

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

Gray32.jpg Section through ovum imbedded in the uterine decidua

Transverse section of a chorionic villus.

Gray36.png Primary chorionic villi. Diagrammatic.

Gray37.png Secondary chorionic villi. Diagrammatic.

References

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

External links

• Embryology at UNSW Notes/skmus6
• Embryology at Temple EMBIII97/sld039

cs:Mezoderm da:Mesoderm de:Mesodermeo:Mezodermo fr:Mésoderme it:Mesoderma lt:Mezoderma nl:Mesodermfi:Mesodermi sv:Mesoderm uk:Мезодерма

Acknowledgement and Attribution Regarding Sources of Content

Some of the initial content on this page may be incorporated in part from copyleft sources in the public domain including wikis such as Wikipedia and AskDrWiki. Drug information for patients came from the The National Library of Medicine. Infectious disease information may have come from the Centers for Disease Control (CDC). Differential Diagnoses are drawn from clinicians as well as an amalgamation of 3 sources: 1.The Disease Database; 2. Kahan, Scott, Smith, Ellen G. In A Page: Signs and Symptoms. Malden, Massachusetts: Blackwell Publishing, 2004:3; 3. Sailer, Christian, Wasner, Susanne. Differential Diagnosis Pocket. Hermosa Beach, CA: Borm Bruckmeir Publishing LLC, 2002:7 .