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The Collaborative International Dictionary

Mesoderm \Mes"o*derm\, n. [Meso- + Gr. de`rma skin.] (Biol.)

  1. The layer of the blastoderm, between the ectoderm and endoderm; mesoblast. See Illust. of Blastoderm and Ectoderm.

  2. The middle body layer in some invertebrates.

  3. The middle layer of tissue in some vegetable structures.

Douglas Harper's Etymology Dictionary

1858, from French mésoderme or German Mesoderm, literally "middle skin," coined by German physician Robert Remak (1815-1865) from meso- + Greek derma (see -derm).


n. (label en embryology) One of the three tissue layers in the embryo of a metazoan animal. Through embryonic development, it will produce many internal organ of the adult, e.g. muscles, spine and circulatory system.


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


In all bilaterian animals, the mesoderm is one of the three primary germ layers in the very early embryo. The other two layers are the ectoderm (outside layer) and endoderm (inside layer), with the mesoderm as the middle layer between them.

The mesoderm forms mesenchyme, mesothelium, non-epithelial blood cells and coelomocytes. Mesothelium lines coeloms. Mesoderm forms the muscles in a process known as myogenesis, septa (cross-wise partitions) and mesenteries (length-wise partitions); and forms part of the gonads (the rest being the gametes). Myogenesis is specifically a function of Mesenchyme.

The mesoderm differentiates from the rest of the embryo through intercellular signaling, after which the mesoderm is polarized by an organizing center. The position of the organizing center is in turn determined by the regions in which beta-catenin is protected from degradation by GSK-3. Beta-catenin acts as a co-factor that alters the activity of the transcription factor tcf-3 from repressing to activating, which initiates the synthesis of gene products critical for mesoderm differentiation and gastrulation. Furthermore, mesoderm has the capability to induce the growth of other structures, such as the neural plate, the precursor to the nervous system.

Usage examples of "mesoderm".

Not the original egg creature itself — the egg’s been altered too much for that — but mesoderm tissue in the form of fibrous protein.