From such a germinal leaf brunki are created. Germ layers: coverage, short description, functions. History of the development of the theory of germ layers

The ectoderm develops: nervous system, epidermis of the skin, epithelium of the skin and mammary glands, horny structures (hair, hair, feathers, nails), epithelium of the skin, crystalline eye, auditory bulb, peripheral sensitive apparatus, dental enamel.

Z endoderm: notochord, epithelial lining of the intestine and its like parts – liver, subslunt, scull and intestinal tracts; epithelial tissue that lines the organs of the respiratory system and part of the sechostatic system, as well as the secretory parts of the anterior and middle parts of the pituitary gland, the thyroid and parathyroid glands.

Z mesoderm: From the outer (lateral) part of the somites, the dermatome, the skin tissue - the dermis - is formed. In the middle (central) part of the somites, the myotome, transverse skeletal muscles are formed. The inner (medial) part of the somites, the sclerotome, gives rise to the supporting tissues, the cartilaginous cord, and then the cystic tissue (just before the body of the ridges) and the associated tissue that forms the axial skeleton around the notochord.

The legs of the somites (nephrogonatomy) give rise to the organs of vision (nirkovian tubules) and plant organs.

The cells that create the visceral and parietal layers of the splanchnotome, together with the epithelial lining of the secondary vasculature of the whole. These splanchnotomes also create the tissues of the internal organs, the circulatory system, the smooth muscles of the intestine, the respiratory and secretory pathways, and skeletal mesenchyme, which gives rise to the rudiments of the skeleton of the ends.

Chapter 3. Provisional authorities

Provisional organs are special post-embryonic organs that ensure the connection of the embryo with the midsection during embryonic development.

Small 6. Provisory organs of the spine.

a – anamnesis; b – non-placental amniotes; c – placental amniotic fluid; 1 – germ; 2 – bean bag; 3 – amnion; 4 - alantois; 5 - chorion; 6 – chorion villi; 7 – placenta; 8 – umbilical cord; 9 - reduced bean bag; 10 - reduction of alantois.

Since the embryonic development of organisms with different types of development (special, non-larval, intrauterine) occurs in different minds, the stage of development and functions of the test organs differ in them.

3.1. Zhovtkovy bag

The beetle sac is characteristic of all creatures with a non-larval type of development, the eggs of which are rich in beetles (fish, reptiles, birds). In fish, the ovary sac is formed from the cell material of three germ layers, which are the mesoderm. In reptiles and birds, the inner ball of the beetle sac is endodermal, and the outer ball is mesodermal.

In young animals, although they do not have a harvester in their egg supply, they have a harvester sac. This can be done with important secondary functions. It resolves due to splanchnopleura, which is due to the establishment of mesodermal and endodermal circulation. The splanchnopleura splits into internal and post-nucleated parts. A bean bag is formed from the embryonic part.

Blood vessels grow at the wall of the belly sac, creating a thick capillary barrier. The walls of the beetle sac contain enzymes that break down the living parts of the beetle, which reach the blood capillaries and pass into the body of the fetus. In this manner, the bean bag is consigned trophic function. The beetle sac is also a place where blood cells multiply, causing it to die hemorrhagic function.

In savages the endoderm of the ovum sac This is the place where the first state cells are created. In addition, the sac is filled with sap, which is enhanced by a high concentration of amino acids and glucose, which indicates the ability protein turnover at the honey bear. Different savants have a bag of excuses in different ways: the khizhaks have a large bag of excuses due to a greatly aggravated range of vessels. And in primates, they wrinkle very much and go all the way to the top.

The share of the honey sac varies among different animals. In birds, until the end of incubation, the excess beetle sac is located in the middle of the embryo, after which it can be easily seen and revealed. In sucklings, the ovary sac enters before the placenta.

In the process of differentiation Primary ectoderm(epiblast) includes the formation of the scutaneous ectoderm, neuroectoderm, auditory and crystalline placodes, prechordal plates, the material of the primordial mat and the primordial ectoderm, as well as the post-germinal ectoderm from which the epithelium is formed ial duct to the amnion.

The scutaneous ectoderm creates the epidermis of the body, the spherical squamous epithelium of the cornea and the conjunctiva of the eye, the organs of the oral cavity, the anal region of the rectum and the membranes. It is where the enamel and cuticle of the teeth are created. From the material of the neuroectoderm, which grows over the notochord, the nerve tube and ganglion plate are formed (they are responsible for the development of the organs of the nervous system, analyzers and chromaffin tissue of the medullary tract of the supraneural glands). The prechordal plate gives rise to the notochord, as well as to the spheroidal epithelium of the anterior femoral tract.

Please note that some of the tissues of the epiblast take part in the development of the hypoblast and the formation of the endoderm.

The primary endoderm (hypoblast) is the core of the creation of the intestinal (secondary, germinal) endoderm and post-germinal endoderm of the ovary sac and alantois. The intestinal endoderm forms the epithelial lining of the vulva, the intestines and their ducts, the parenchyma of the liver, the subgusal duct and the epithelium that lines their ducts and the biliary tract.

The mesoderm is part of the mesenchyme. Vaughn is divided into zaryodkova and pozazarodkova. The mesoderm is divided into segmented and non-segmented parts. Up to the segmented mesoderm there are somites, which include the body (dermatome, miotome and sclerotome) and legs (nephrogonadotom). The unsegmented part consists of the sheets of the splanchnotome (visceral and parietal) and the caudal vedullum – nephrogenic tissue. The dermatome contains the soft tissue part of the skin (dermis). Myotomi is the source of the development of somatic tissues. Sclerotomes treat skeletal tissues (cartilage, bone, dentin and cement). Nephrogonadotomy and nephrogenic tissue give rise to the sechostate system. The leaves of the splanchnotomes are formed by the mesothelium of the serous membranes and the cortical lining of the supraperebral glands. The visceral leaf of the splanchnotome follows the same fate as the tissue of the heart. Mesenchyme is responsible for the development of all types of tissue of organs and embryonic and post-embryo systems, smooth meat tissue, blood vessels, blood cells and hematopoietic organs, microglia.

Amnion

Amnion , Or the amniotic membrane, which ensures the formation of the aqueous medium (amniotic fluid), in which the development of the embryo occurs, creates an extraplacental humoral connection between the organisms of the mother and the fetus. The evolutionary amnion plays a role in the process of creatures reaching land. In embryogenesis, the vein appears in the first phase of gastrulation, perhaps simultaneously with the ovary sac, in the form of an amniotic plaque, which is localized above the embryonic disc, at the ligament with which there is an epiblast. In one of its sections, the amniotic bulb is attached to the mesoderm, which extends in the middle of the chorionic membrane. Here the so-called amniotic, or embryonic, leg is formed, which in the future turns into an umbilical cord.

The wall of the amniotic bulb is composed of two balls: the post-germ ectoderm and the adjacent post-germ mesoderm, which is an extension of the parietal layer of the splanchnotome.

The embryonic ectoderm involves the development of an amniotic unispherical epithelium, which performs both secretory (in the area of ​​placentomas) and resorptive (in other zones of the amnion) functions. The germinal mesoderm gives rise to mesenchyme, from which the germinal tissue of the wall of the amnion develops, which creates two balls. One of them, directly adjacent to the basal membrane of the amniotic epithelium, is composed of thick fibrous tissue, and the other, external, is composed of a fluffy mucous membrane of solid tissue (spongy ball), which consists of a small Lots of collagen fibers and acidic glycosaminoglyc.

As the embryo grows, the amniotic membranes quickly increase in size and the entire body gradually bleeds. As a result of the secretory activity of the amniotic epithelium, the empty fur is filled with raw material, as a result of which the embryo appears completely congested. Between the labial globule of the amnion and the spongiform base of the chorionic membrane there is an amnio-choral space, which, with the increased size of the amniotic urinary tract, changes to a minimum and the labial globulus of the amnion It basically connects with the wall of the chorion. In the area of ​​the amniotic limb, the vein grows with it, as a result of which the umbilical cord, which forms further from the amniotic limb, appears covered with amniotic epithelium.

The main function of the amnion is the fertilization of the amniotic fluid, which is the core of the development of the embryo, which protects its type from mechanical development. In addition, the amnion takes part in the waste products of fetal metabolism, as well as in maintaining the necessary storage and concentration of electrolytes, acid-hydraulic fluid, thereby ensuring homeostasis. The amnion plays a great role as a barrier for unkind speeches.

Zhovtkovy bag

In evolutionary terms, the honey sac is older than the amnion. In animals with polylecithal types of eggs, there is a sufficient number of living ovules (chews) to ensure the development of the embryo. In placental humans, the trophic role of the honey sac is not great. Its empty container only holds a small amount of protein.

The end of the sac is the hypoblast of the embryonic disc, the wall is composed of the post-germinal (zubular) endoderm and the post-germ mesoderm (visceral layer of the splanchnotome). Posterior mesoderm leads to the development of mesenchyme. Immediately at the mesenchyme of the wall of the stomach sac, blood islands emerge and the first blood vessels are formed to ensure the transfer of sourness and living fluids. The blood islanders have primary hematopoiesis. After the hematopoietic function of the fetus is taken over by the liver, the ovary sac undergoes involution, and its surplus is stored in the umbilical cord warehouse. It is important to note that the gonoregions are primarily localized in the ovary sac, which migrate through the system of blood vessels to the gonads.

Alantois

The allantois is created from the endoderm of the caudal vulva of the ovary sac, which is like a finger-like invagination, embedded in the embryonic visceral mesoderm, which forms the lower part of the embryo. Thus, its wall is composed of two balls: endodermal epithelium and mesenchyme, which transforms into embryonic tissue. In several species of savages (VRH, horses), the alantois, growing between the amnion and chorion, reaches significant sizes and assumes the role of one of the embryonic membranes. In other animals and humans, the allantois is weakly differentiated, however, its role in the early stages of embryogenesis is essential, since the semitissue base of the allantois is the conductor of the blood vessels of the future umbilical cord. In addition, alantois takes part in gas exchange and visible products of embryonic metabolism. In the world, the development of the vascular and visual systems of the fetus, the alantois, is subject to reduction, and its proximal part appears at the umbilical cord storage area right up to birth.

A characteristic feature of the alantois of birds is that on one side its semi-tissue ball grows from a semi-tissue base Serosi , and from the other – from the similar post-primordial mesoderm of the amnion and the ovary sac. At the site of their growth, a dense network of blood vessels is formed, which ensures that the body that is developing is acidic.

Umbilical cord

The umbilical cord of the greatest savants. Vaughn is born from the amniotic (embryo) leg. The basis of the umbilical cord is made of a thick consistency of mucus-rich tissue, in which collagen fibers are laid in the main cord, rich in acid GAG (chondroitin sulfate, hyaluronic acid) and glycoproteins. The top is covered with amniotic epithelium. At the umbilical cord of the mature placenta there are two arteries and a vein, as well as redundancies of the allantois and the ovary sac. Through the blood vessels of the umbilical cord, which are rich in chorionic acid, live substances, plastic material, jelly and metabolic products are delivered to the fetus from the maternal body.

Chorion

The chorion, or the villous membrane, evolves in placental individuals. Its development consists of the trophoblast and the embryonic parietal mesoderm. Initially, the trophoblast creates one ball of cells (blastomeres), which at very early stages is another non-cell ball and, thus, the trophoblast becomes a two-ball: the inner ball of the cell is the cytotrophoblast (CT), and the external one is non-clinical - symplastotroph syncytiotrophoblast (ST). In this case, the CT resembles the cytotrophoblast as a successor to the incomplete mitotic subsection of the cells (endomitosis). On the surface of the CT, small deposits are formed - primary villi, which vibrate enzymes that have high proteolytic activity. This is due to the destruction of maternal tissues and implantation of the embryo in the mucous membrane of the uterus (endometrium), which is important for people and animals with hemochorial type of placentas.

During the process of migration from the embryonic disc, the embryonic mesoderm transforms into mesenchyme, which acquires a bispherical trophoblast in the middle and simultaneously forms Chorion (Mal. 4) .

Small 4. Budova’s walls to chorion. 1 – blood vesselYin the chorial plateau; 2 – villus; 3 – trophoblast. G.-e. (Drug by N.P. Barsukov).

Next, a rapid and rapid transformation takes place: the primary trophoblastic villi are transformed into the second successor to the growth of mesenchymes in them, which even quickly differentiates the embryonic tissue. The number of secondary villi rapidly increases, and in their rich tissue stroma vasculogenesis begins, at which point the villi are called tertiary (Fig. 4). At the end of the uterine villi, the synthesis of proteolytic enzymes begins, which actively flow into the structural components of the uterine mucosa - placentogenesis begins.

Germ layers are groups of spore cells that strengthen during the hour of gastrulation and give rise to song organs.

In all animals, during gastrulation, two balls of cells are strengthened - the ectoderm (outer ball) and the endoderm (inner ball). Yak shown in Fig. 152 in the toad, the third, intermediate ball is reinforced - the mesoderm. Most other creatures (except intestinal emptying ones) also have three balls - ectoderm, endoderm and mesoderm, skin buds from the vocal group of blastomeres, so all the cells between one ball are ancestors. These groups of tissues that may perform secret activities and produce song, organs and tissues of mature creatures are called germinal leaves.

In all creatures, however, new organs emerge from that same germinal leaf. The ectoderm provides the external structures of the nervous system. The endoderm is where most of the grass tract and grass buds are created (in spinal worms - the liver, the subcutaneous tract, and the lungs). The mesoderm forms other organs: flesh, the inner lining of the body, the circulatory organs, the visual and articular systems, and in spinal and cervical animals - the internal skeleton. (The mother needs to take into account that most of the organs of an adult animal include tissues, so take an ear from two or all three germinal leaves.) This is an important summary: all animals have basic organ systems There may be a secret walk, and they can be matched. For example, the central nervous system has a secret similarity to that sense, which in evolution resembles the subcutaneous plexus of nerves, similar to the nerve medulla of the hydra, and in ontogenesis – from the external germ layer.

Previously, it was important that there were clear boundaries between the germ layers: the branches of one leaf could not pass to another. Facts have gradually accumulated that are not invested in this scheme. For example, it has been shown that during regeneration in certain animals, the entire body is regenerated from the plots, and the tissue of one leaf is absent. The cells of the mesoderm vary widely: after gastrulation, some of them hang from the ectoderm, and some from the endoderm. In the endoderm of most animals, a special part of the nervous system may be formed immediately. The crests of spinal bones develop from the cells of the neural crest - similar to the ectoderm. The cells of the nervous and meatus systems may be close relatives: in nematodes, the nerve and meatus cells may be “close sisters”. All these facts do not simply confirm the findings about germinal leaves, but rather show that in this case there is little blame from the legal rule.

Germ leaves, and embryonic layers are the balls of the body of the embryo of rich-celled creatures that are formed in the process and give rise to various organs and tissues.

Odors are formed in the process of differentiation of similar homogeneous cells.

Gastrulation- the process of illumination two germ leaves(Ento-i ectoderm).

During the process of gastrulation, the structure of dry cells is formed and formed gastrula- A two-ball germinal sac, in the middle of which there is empty space - gastrocel tied with the first mouth ( blastopore) from the external middle.

Gastrulation is completed with the development of the third germ layer. mesoderm, spread between the ectoderm and the endoderm.

Most organisms (except intestinal emptying ones) develop three germ layers:

- External - ectoderm,
- Internal - endodermі
- Middle - mesoderm.

After completion of gastrulation, a complex of axial organs is established in the embryo: neural tube, notochord, intestinal tube. This stage neuruli.

Osvita embryonic leaves- The beginning of the transformation of rich cell tissue into the body, in which cells become differentiated and tissues and organs eventually develop.

Then, the zygote begins to divide, increasing the number of cells. Having gained sufficient mass, the body begins the offensive stage - the cells begin to collapse - the stench moves to the periphery, settling blastodermic bulb.

At one end of this, the bulbs of the walls are grouped and create an internal void - this and that inner germ layer - endoderm.

Outer cells of the germ (outermost ball) ectoderm.

The ball clinches between these two germinal leaves. mesoderm, These cells are formed partly in the ecto- and partly in the endoderm.

• This type of leaflet is typical for all great creatures;
• at simple creatures- i - only 2 germ leaves(External and internal).

Axle butt power supply EDI from biology just on the topic:

1. The ectoderm develops: the ear and the cerebrum;

2. from the endoderm – liver, legs, intestines, slut, subslit;

3. from the mesoderm - pulp, blood vessels, cysts.

Germ leaves were better than described by the Russian academician X. Pandera 1817 r., how the embryonic development of the chicken embryo has grown. The classical works of another Russian academician played a particularly important role in the investigation of the germinal leaves of spinal creatures. Carla Bera, Which showed that germinal leaves are present in the embryos of other spinal vertebrates (fish, amphibians, creepers).