noun
definition
One of the three tissue layers in the embryo of a metazoan animal. Through embryonic development, it will produce many internal organs of the adult, e.g. muscles, spine and circulatory system.
Examples of mesoderm in a Sentence
The mesoderm arises for the most part from the endoderm.
The mesoderm seems to be formed entirely from the proliferation of the cells of the mesoblastic somites.
The pericycle, medullary rays, endocycle and mesoderm all form parts of one tissue system, the external conjunctive, and are only topographically separable.
This third mass of cells is the mesoderm.
It has usually been regarded as representing both endoderm and mesoderm, and the groove which usually leads to its formation has been compared to the abnormally elongated blastopore of a typical gastrula.
No doubt can be entertained that the greater part of the inner layer corresponds to the mesoderm of more ordinary embryos, for the coelomic pouches, the germ-cells, the musculature and the vascular system all arise from it.
In the cockroach embryo, before the segmentation of the germ-band has begun, the primitive germ-cells can be recognized at the hinder end of the mesoderm, from whose ordinary cells they can be distinguished by their larger size.
It must, of course, be understood that the germinal epithelium covering the ridge, and the mesenchyme inside it, are both derived from the mesoderm or middle layer of the embryo.
True nephridia do not primarily open into the coelom, as was formerly taught, but are intra-cellular ducts in the mesoderm.
When the segmentation is unequal one of the megameres gives rise by successive divisions to two primary mesoderm cells called mesomeres; these divide to form two masses of cells called mesoblastic bands.
This is the primitive method, but in other cases the organs mentioned may be formed separately in the mesoderm.
In the remaining Metazoa certain cells are budded off at an early stage of development from one or both of the two original layers, to form later a third layer, the mesoderm, which lies between the ectoderm and endoderm; such forms have therefore received the name Triploblastica.
At the same time it is necessary to observe that it is by no means certain that the mesoderm found in various groups of Metazoa is a similar or homologous formation in all cases.
The mesogloea is in itself an inert non-cellular secretion, but the immigration of muscular and other cells into its substance, from both ectoderm and endoderm, gives it in many cases a strong resemblance to the mesoderm of Triploblastica, - a resemblance which, while probably superficial, may yet serve to indicate the path of evolution of the mesoderm.
The mesoderm becomes segmented, and the parapodia subsequently develop from before backwards; but almost all internal traces of segmentation are lost in the adult.
The first cells of this sort to form in the embryo are called the ectoderm, the mesoderm and the endoderm.
Here we show that expression of active forms of MEK or of MAP kinase induces ventral mesoderm of the kind elicited by FGF.
The interpretation of this experiment, therefore, is that contact with endodermal cells cause the ectodermal cells to form mesoderm.
The kidneys begin to develop around the 3rd week of fetal life from the intermediate mesoderm.
On this view Wheeler, however, compares with the " dorsal organ " the peculiar the entire food-canal in most Hexapoda must be regarded as of extra embryonic membrane or indusium which he has observed ectodermal origin, the " endoblast " represents mesoderm only, between serosa and amnion in the embryo of the grasshopper and the median furrow whence it arises can be no longer compared Xiphidium.
The mesoderm develops into muscles, bones, heart tissue, lungs, reproductive organs, lymphatic tissue, and other tissues.
The mesoderm cells then make the circulatory, skeletal, and muscular systems.