Embryogenesis is a complex process, which is characterized by the gradual formation of organs and tissues. In most multicellular organisms, the embryo embryo consists of three layers: ectoderm, endoderm, mesoderm. What is mesoderm? And the chitinous skeleton of arthropods, and the epidermis of the skin, and the nervous system are of ectodermal origin. The digestive, endocrine and respiratory systems are formed from the endoderm. What organs and tissues gives rise to mesoderm? How is it formed?
What is mesoderm. Definition
Any tissue or organ system is formed from a specific layer of embryonic cells. What is mesoderm? In biology, the definition is as follows: this is one of the germ layers from which a number of organs and tissues are formed during embryogenesis. The second name of the mesoderm is the mesoblast. The formation of this layer is characteristic of most multicellular animals (exception: Sponge type and Intestinal type).
The mesoderm is located between the ectoderm and endoderm. Each of the nearby germ layers can take part in the formation of the mesoblast. Accordingly, two types of the middle germinal leaf are distinguished by origin: entomesoderm, exomesoderm. There are also situations when both structures are involved in the formation of the mesoblast.
Mesoderm as an independent germinal layer is formed at the stage of gastrulation.
The formation of mesoderm. Formation Features
What is mesoderm? In biology, it is generally accepted that each organ of a multicellular animal in embryogenesis is formed by one of the germ layers. The formation of the mesoderm is a characteristic aramorphosis of the type Flatworms, since the true median germ layer is formed for the first time in them. The type of Sponge and the type of Intestinal are representatives of two-layer animals: only ectoderm and endoderm are formed in embryogenesis.
How is the formation of the mesoderm?
There are three ways to form a mesoblast.
- Teloblastic. It is characteristic for primary animals. Each mesoderm cell is formed from teloblasts, which lie between the ecto- and endoderm. As a result, two strips of mesoderm are formed along the embryo embryo.
- Enterocele. This method of mesoderm formation is characteristic of most of the secondary ones (cyclostomes, fish, amphibians). Mesoderm cells are formed from separate sections of the primary intestine.
- From the ectoderm. This method has been found in reptiles, birds, and mammals. Its peculiarity is that the mesoderm is formed by the ectoderm swelling.
Mesoderm structure
What is mesoderm? This is not just an accumulation of identical cells, but an embryonic layer differentiated into several functional departments. Mesoblast separation occurs gradually, resulting in the following areas:
- Somites are paired ribbon-like formations between which a whole is formed - the secondary cavity of the body. Preserved in annelids and arthropods.
- The embryo of the chord is the site of the mesoderm, which in the future develops into a chord. A distinctive feature of vertebrates.
- In vertebrates, from each somite they are formed by sclerotis, dermatitis and myotomas.
- Splanchnotomas are lateral plates that are divided into two separate layers: inner and outer. Between them in vertebrates a whole is formed.
- Nephrotomes are paired structures connecting splanchnostomes.
After examining each part of the germinal leaf, scientists were able to determine what the mesoderm is and to understand what functions it performs.
Histogenesis
Mesoderm gives rise to several types of tissue.
- Parenchyma of flatworms that fills the space between organs. Formed from the mesoderm.
- Some epithelial tissues covering the organs outside. These include secretory cells, endocrine and exocrine glands.
- Loose fibrous and dense fibrous connective tissues are formed from the mesoderm. Including collagen and elastic fibers are formed.
- Blood cells also form from the mesoderm.
- Bone and cartilage tissues, their constituent elements are of mesodermal origin.
- By analogy with the formed elements of the blood, the mesoderm also takes part in the formation of cells of the immune system.
- All types of muscle tissue. Smooth muscles are laid in the walls of most organs. Cross-striped fibers are the structural elements of skeletal muscle. Do not forget about the striated cardiac muscle tissue, which forms the muscles of the heart.
Organogenesis
Tissues form organs, so it’s not difficult to guess which ones are of mesodermal origin. Classification is given for mesoderm sites:
- Dermatomas - form the dermis of the skin (sweat and sebaceous glands are part of the skin);
- from the sclerotomes, the passive part of the musculoskeletal apparatus (skeleton) is formed;
- from the myotome, respectively, - the active part of the musculoskeletal system (muscles);
- splanchnostomy give rise to mesothelium - a single-layer epithelium that lines the secondary cavity of the body;
- nephrostomy cells form the excretory and reproductive systems.
Provisional organs of mesodermal origin
It is worth mentioning those organs that are lost at different stages of ontogenesis after performing their functions. They are called provisional. These include:
- Amnion is one of the shells of the embryo, which performs several vital functions at once. The first is to create an aquatic environment for the development of the fetus. This is explained by the fact that the formation of an organism must take place in water. For vertebrates living on land, water in this case is a limiting factor, therefore this shell was formed in the process of evolution. Amnion also protects the fetus from mechanical damage, maintains a constant environment by maintaining the salt concentration at a constant level, and also protects the fetus from exposure to toxic substances.
- Allantois is another organ of the embryo that performs both nutrition and respiration functions. By origin, it is an outgrowth of the yolk sac, which means that it is also formed by cells of the endoderm and mesoderm. In man, allantois is less developed than in other representatives of vertebrates, however, blood vessels pass through it, which then enter the umbilical cord tissue.
- Yolk Sack. This temporary organ contains the nutrients necessary for the development of the fetus. Cells of both the mesoderm and the endoderm are involved in the formation of the yolk sac. An interesting feature of the organ is the formation in it of the very first blood cells of the body.
- Umbilical cord (umbilical cord) - connects the fetus and the placenta.
- Chorion is the membrane of the embryo, with the help of which it attaches to the uterus and the formation of the placenta.
- The placenta is the only organ in humans, formed by the tissues of two organisms: the mother and the fetus. From the mother’s blood, the fetus receives nutrients and oxygen through the placenta.
Mesoderm Functions
We examined what is mesoderm. What are the functions of this germinal leaf?
The development of mesoderm allowed flatworms to fill the gaps between the organs with parenchymal tissue. More advanced organisms do not have a parenchyma, but the principle is similar: tissues of mesodermal origin form boundary layers between organs. The most important function of the mesoblast is the formation of temporary organs in the embryo (allantois, umbilical cord, placenta, etc.) Also, mesoderm cells form the tissues of the internal environment: blood and lymph.
Conclusion
Now you can fully explain what a mesoderm is. Her education allowed animals to move to a new stage of development, as evidenced by the origin of many organs and tissues. In addition, the formation of the amniotic membrane led to a qualitative leap in the development of vertebrate animals. Therefore, the mesoderm is an important evolutionary element.