Mesoderm is the precursor of many organs and tissues

The ontogeny of any organism is characterized by the formation of embryonic sheets. In such primitive animal types as coelenterates and sponges, the embryo consists of only two layers: endoderm and ectoderm. With the passage of time, the third leaf, the mesoderm, appears in more progressive forms of organisms.

What is the mesoderm?

Ontogeny is a sequential development of the embryo, which is accompanied by a number of changes in the morphology and anatomy of the future of the young organism. Mesoderm is a germinal leaf that plays an important role in the formation of many organs and tissues. Such primitive multicellular animals as hydras, jellyfish, corals or sponges are not in vain called two-layered animals, since in the process of ontogenesis they had only two embryonic leaflets.

Formation of mesoderm

The process of laying the middle embryonic leaf in different taxonomic groups is different. There are three most well-known ways in which the mesoderm is formed: it is teloblastic, enterocemental and ectodermal.

1. The teloblastic path of mesoderm development is characteristic of many primitive animals, and is based on the formation of blastomeres. Some of them specialize in laying the middle germinal leaf, which eventually takes the form of two longitudinal parallel bands. These tapes give rise to the mesoderm.
2. The enterocele method is fundamentally different in that the mesodermal progenitor cells form an invagination (invagination) together with the endoderm. This invagination in the future forms the primary gut. The boundary between two leaves for a long time remains indistinguishable, and only after a long period of time the mesoderm as an independent layer disconnects from the endoderm. This way of development is characteristic of animals such as a lancelet or starfish.

3. Ectodermal way of development of mesoderm are such types of animals as reptiles, birds and mammals (including humans). The bottom line is that after the invagination, only the endoderm is formed. If we imagine a picture of the embryo in a section, then after gastrulation (formation of invagination) there will be free space between the ento- and ectoderm. There, and "budding" cells of ectodermal origin, which give rise to a new embryonic layer.

Morphology of the mesoderm

An important role in the formation of the embryo is mesoderm. This in biology is a good evolutionary sign, because the difference in the morphology of the middle germinal leaf in different groups of animals is used in taxonomy.

If we consider two longitudinal bands, which are formed with a teloblastic method of development, then the mesoderm will be represented by metamerically repeating regions. The back side of each such tape is divided into somites, lateral - to nephrotomes, and abdominal - to splanchnotomes.

What is the role of the mesoderm? Human organs formed from the mesoderm

Each embryonic layer is a kind of predecessor of the systems of organs and tissues of the future organism. The topology of the generative sheets largely determines their future destiny. Since the mesoderm is the middle germinal layer, it participates in the formation of tissues and organs that lie between the human veins and the innermost layers of the body. Which structures are of mesoderm origin?

1. The formation of connective tissue occurs just from mesoderm cells. This tissue is borderline between the outer and inner layers of almost any organ of the animal.
2. The musculoskeletal system, which consists of a skeleton and a muscle system, also has a mesodermal origin. Here we mean not only skeletal muscles, but also the muscular wall of blood vessels, heart and other internal organs and structures. The skeleton is represented in humans mainly by bone tissue, and in smaller - cartilaginous tissue. When it comes to chordates, at the embryonic stage of which the formation of the chord occurs, do not confuse the origin of this axial structure with the spine. If the latter has a truly mesodermal origin, then the chord is the cleavage of the intestine, and hence its origin is associated with the endoderm.
3. Sexual and excretory systems are also formed from the mesoderm. They are related to the majority of chordates, which means they are formed from the same embryonic leaf.
4. The blood system also has a mesodermal origin. Both the heart and the vessels are formed by the cells of the middle germinal leaf.

Conclusion

Mesoderm is a complex structure of the embryo, which eventually gives rise to a number of vital organs and tissues. In different taxonomic groups of animals, the formation and development of the middle leaf differs, and this is one of the evolutionary features. The presence of the mesoderm indicates a three-layered animal, which is a significant sign of the group's advancement.