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

In humans, the mesoderm is one of the three primary germ cell layers - the other two are the ectoderm and endoderm - in the very early embryo. The mesoderm is the middle layer. It differentiates to gives rise to a number of tissues and structures including bone, muscle, connective tissue, and the middle layer of the skin. Some cells in mesodermal tissues retain the capacity to differentiate in diverse directions. For example, some cells in the bone marrow (mesoderm) can become liver (endoderm).

More generally, the mesoderm is one of the three germ layers found in the embryos of animals more complex than cnidarians, making them triploblastic. Mesoderm forms in the embryo during gastrulation when some of the cells migrating inward to form the endoderm, produce an additional layer that lies between the endoderm and the ectoderm.

Mesoderm is found in all large, complex animals, and allows the formation of a coelom, which allows more room for independent growth of the body organs.

[edit] Mesoderm Derivatives

[edit] General

The body organs, tissues and systems derived from the mesoderm in most triploblastic animals can be listed as follows:

• bones
• cartilage
• 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 abdominal cavity)
• reproductive system
• spleen
• urinary system, including the kidneys

[edit] 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 splanchnic mesoderm.

Before formation of the items in the above list, the mesoderm of a developing vertebrate transitionally differentiates into the following sub-types:

• Chordamesoderm (also known as axial mesoderm) which later on gives rise to notochord in all chordates
• Paraxial mesoderm
• Intermediate mesoderm
• Lateral plate mesoderm

[edit] See also

• Embryo
• Embryogenesis
• Embryology
• Ectoderm
• Endoderm
• Germ layer
• Histogenesis
• Organogenesis

[edit] References

Look up mesoderm in Wiktionary, the free dictionary.

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

[edit] External links

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