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.
Mesoderm Derivatives
General
The body organs, tissues and systems derived from the mesoderm in most
triploblastic animals can be listed as follows:
Vertebrates
Transverse section of a chick embryo of forty-five hours' incubation.
- Paraxial mesoderm: red, comprising the somites.
- 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
See also
