Slide 3

Stages of embryogenesis

The development of an organism from the moment of fertilization until birth or exit from the embryonic membranes.

1. Crushing the zygote.
2. Blastula formation.
3. Gastrulation.
4. Neirula.

Slide 4

The first stage of embryonic development

• The first stage of embryonic development is called cleavage. As a result of division from the zygote, first 2 cells are formed, then 4, 8, 16, etc. The cells that arise during cleavage are called blastomeres. In the process of cleavage, the number of cells grows rapidly, they become smaller and smaller and form a sphere, inside which a cavity appears - a blastocoel.
• From this point on, the embryo is called blastula.
• How do blastomeres divide and what set of chromosomes are contained in their nuclei?

Slide 5

Splitting up

Cleavage differs from ordinary mitotic division in the following features:

1. blastomeres do not reach the original size of the zygote;
2. blastomeres do not diverge, although they are independent cells.

Cleavage is the process of mitotic division of the zygote into daughter cells (blastomeres).
Blastula consists of:

1. blastoderm - blastomere sheaths;
2. blastocoels are cavities filled with fluid.

Human blastula is a blastocyst.

Slide 6

Gastrulation

• When the number of blastula cells reaches several hundred or thousands, the next stage of embryogenesis begins - gastrulation. Gastrulation is the process of formation of germ layers.
• Human gastrulation occurs in 2 stages.
• In which animals at this stage embryonic development ends?

Slide 7

Chorion formation

During the first stage, 2 germ layers (ecto- and endoderm), 2 provisional organs (amnion and yolk sac) are formed. In addition, immediately before the beginning of the first stage, the formation of such a provisional organ as the chorion occurs. Chorion formation is the second stage in the formation of the placenta.

Slide 8

The second stage of gastrulation

• The second stage of gastrulation is the formation of the third (middle) germ layer. It is called the mesoderm, because it is formed between the outer and inner sheets.
• In this case, retractions - pockets (coelomic sacs) are formed on both sides of the primary intestine. Inside the pockets there is a cavity, which is a continuation of the primary intestine - gastrocele. The coelomic sacs are completely detached from the primary intestine and grow between the ectoderm and endoderm. The cellular material of these areas gives rise to the middle germ layer - the mesoderm. The dorsal mesoderm, lying on the sides of the neural tube and notochord, is divided into segments - somites. Its ventral section forms a solid lateral plate located on the sides of the intestinal tube.

Slide 9

Slide 10

Histo- and organogenesis

Histo- and organogenesis (or differentiation of germ layers) is the process of transformation of tissue rudiments into tissues and organs, and then the formation of functional systems of the body.

Slide 11

Gastrulation

During gastrulation and after the formation of the germ layers, cells located in different layers or in different parts of the same germ layer influence each other. This influence is called induction. Induction is carried out by the release of chemicals (proteins), but there are physical methods of induction. Induction affects primarily the cell genome. As a result of induction, some genes are blocked, others free - working. The sum of free genes of a given cell is called its epigenome. The very process of epigenome formation, that is, the interaction of induction and genome, is called determination. After the formation of the epigenome, the cell becomes deterministic, i.e., programmed to develop in a certain direction.

Slide 12

Differentiation

After cell determination, i.e. after the final formation of the epigenome, differentiation begins - the process of morphological, biochemical and functional specialization of cells.

Slide 13

End of the second stage of gastrulation

At the end of the second stage of gastrulation, the embryo is called gastrula and consists of three germ layers - ectoderm, mesoderm and endoderm and four extraembryonic organs - chorion, amnion, yolk sac and allantois.
Simultaneously with the development of the second phase of gastrulation, an embryonic mesenchyme is formed through the migration of cells from all three germ layers.
At the 2nd - 3rd week, i.e., during the second phase of gastrulation and immediately after it, the primordium of the axial organs is laid:

1. chords;
2. neural tube;
3. intestinal tube.

Slide 14

Chorion and yolk sac functions

Chorion functions:

1. protective;
2. trophic, gas exchange, excretory and others, in which chorin takes part, being an integral part of the placenta and which the placenta performs.
3. The functions of the amnion are the formation of amniotic fluid and a protective function.

Functions of the yolk sac:

1. hematopoiesis (the formation of blood stem cells);
2. the formation of germ stem cells (gonoblasts);
3. trophic (in birds and fish).

Slide 15

Organ formation

The essence of the theory of germ layers is reduced to two main provisions:

1. organisms of multicellular animals develop from three germ layers: external, or ectoderm, middle, or mesoderm, internal, or endoderm;
2. each organ system in different groups of multicellular animals develops, as a rule, from the same leaf.

The embryonic leaves were first described in the work of the Russian academician H. Pander in 1817, who studied the embryonic development of the chicken embryo.

Slide 16

Baer's laws

Correctly describes the ovum in mammals and humans, spreads H. Pander's doctrine of germ layers to all vertebrates, formulates the law of "embryonic similarity", later named after him.

Baer's Laws:

• the most common signs of any large group of animals appear in the embryo earlier than less common signs;
• after the formation of the most general signs, less common ones appear and so on until the appearance of special signs characteristic of this group;
• the embryo of any animal species, as it develops, becomes less and less similar to the embryos of other species and does not go through the later stages of their development;
• the embryo of a highly organized species may resemble the embryo of a more primitive species, but it never resembles the adult form of this species.

Slide 17

Biogenetic law of Haeckel-Müller

• Each living creature in its individual development (ontogeny) repeats to a certain extent the forms passed by its ancestors or its species
• A striking example of the fulfillment of the biogenetic law is the development of a frog
• In the tadpole, as in lower fish and fish fry, the chord serves as the basis of the skeleton. The skull of the tadpole is cartilaginous, and well-developed cartilaginous arches adjoin it; breath is gill. The circulatory system is also built according to the fish type: the atrium has not yet divided into right and left halves.

Slide 18

Comparison of vertebrate embryos at different stages of development

Mesoderm

From the mesoderm are formed: skeleton, skeletal muscles, connective tissue basis of the skin (dermis), organs of the excretory and reproductive systems, cardiovascular system, lymphatic system, notochord, skin dermis, sclera.

Slide 23

Embryo development

• Fertilization of the egg.
• 1 day (Zygote) and 3 days (Morula).
• 5 days (Blastula) and 10 days (Gastrula).
• 3 put on. The beginning of organogenesis.
• 5 weeks. The embryo length is 10-15 mm.
• 6 week. The movement of the fetus and the contraction of the heart are recorded.
• 8-10 weeks. Fruit length 10 cm, all organs are formed.
• For 11 weeks and 12 weeks, the development of all body systems continues.
• 16 weeks and 18 weeks. The fetus grows rapidly and the mother senses its movement.
• 7 months. The final period of development.
• 9 months. The birth of a man.

Slide 24

Critical periods in human development

1. gametogenesis (spermato- and ovogenesis);
2. fertilization;
3. implantation (7-8 days);
4. placentation and laying of axial complexes (3 - 8th week);
5. the stage of increased brain growth (15 - 20 weeks);
6. the formation of the reproductive apparatus and other functional systems (20th - 24th week);
7. birth of a child;
8. neonatal period (up to 1 year);
9. puberty (11 - 16 years).

Slide 25

Questions for thought

What is the significance of knowledge about the development of the embryo?

View all slides

The embryonic similarity of fish (1), salamander (2), turtle (3), rat (4) and humans (5). Stage 1

The embryonic similarity of fish (1), salamander (2), turtle (3), rat (4) and humans (5). Stage 2

The embryonic similarity of fish (1), salamander (2), turtle (3), rat (4) and humans (5). Stage 3

General laws of development of the embryos of organisms. The generality of the structure of various organisms is manifested in the early stages of the development of their embryos. Distinctive features of the organism are created gradually and in strict sequence during the development of the embryo. Species differences are manifested in the later stages of embryo development.

4th week of pregnancy The baby in the 4th week of pregnancy is still very small - its length is from 0.36 to 1 mm. From this week, the embryonic period of development begins, which will last until the end of the tenth week. This is the time for the formation and development of all organs of the child, some of which will already begin to function.

7 week of pregnancy At 7 weeks of pregnancy, the baby grew to about 8 mm, he is like a pea (Moreover, at the beginning of the week his growth from the crown to the coccyx was 4-5 mm, and by the end up to mm). Weight - about 0.8 g. A big event this week - hands and feet appeared on the developing arms and legs!

10 week of pregnancy A man inside his mother is only the size of a plum, and his main organs, systems and body parts have already been formed and will now rapidly grow and “ripen”. The most critical embryonic stage has passed and the fetal period of development begins.

12th week of pregnancy After the 12th week of pregnancy, new organs are no longer formed, but the existing ones continue to grow and develop. Reflexes appeared this week! Local stimulation of the fetus can cause it to squint, open its mouth, or wiggle fingers or toes. The fingers will soon begin to bend and unbend, and the mouth will make sucking movements.

13 week of pregnancy At 13 weeks of pregnancy, fingerprints appeared on tiny fingers, veins and organs are clearly visible through the still very thin skin, and the body begins to catch up with the size of the head (which is now only a third of the total size). If there is a girl, more than 2 million eggs have already appeared in her ovaries.

14 week of pregnancy From 14 weeks of pregnancy, a baby can squint, frown, grimace, write and possibly suck his thumb. The kidneys produce urine, which he urinates into the amniotic fluid. The kid has grown - the length from the crown to the coccyx is 8-8.9 cm.

15 weeks pregnant The baby has reached approximately 9.3-10.4 cm in length from the crown to the coccyx. It trains in breathing by drawing in amniotic fluid (amniotic fluid) into the lungs and pushing it back out of the lungs. Amniotic fluid is "renewed" 8 - 10 times a day! This allows them to maintain their sterility while maintaining the desired chemical composition (the ratio of water, minerals and organic substances).

17 week of pregnancy At 17 weeks of pregnancy, the baby weighs about 100 grams, and its height from the crown to the coccyx is equal to cm. He has already developed all the joints, and the skeleton, which before that looks more like cartilage, is stiffening. Hearing improves. The umbilical cord that connects it to the placenta becomes thicker and stronger.

19 week of pregnancy The arms and legs are in proportion to each other and to the rest of the body. The kidneys continue to produce urine, and hair begins to cover the head. At 19 weeks of gestation, a critical moment has come for the development of five basic senses: the baby's brain defines special areas that will be responsible for smell, taste, hearing, sight and touch.

21 weeks of pregnancy The weight of the child is now somewhere in the gram. The eyebrows and eyelids are fully formed. And at the 21st week of pregnancy, the mother surely can feel his movements.

26 week of pregnancy The child has grown up to 32.5 cm and put on weight up to gr. The kid is getting better at distinguishing sounds. Children most of all love "The Four Seasons" by Vivaldi and Mozart. The lungs develop and he continues to take small breaths of amniotic fluid in preparation for his first breath of air.

28 weeks pregnant At 28 weeks pregnant, he blinks his eyes, on which cilia are visible! With the development of vision, the baby can already see the light shining through the stomach. Billions of neurons develop in the brain (until this time, the fetal brain was smooth, by the 28th week, characteristic grooves and convolutions begin to appear on it), the brain mass also increases, and the body acquires subcutaneous fat, preparing for life outside.

32 weeks pregnant 1.8 kg. and 42 cm.! Most of the wrinkles have disappeared from the baby's face. He has full toenails, fingernails and real hair, or at least noticeable down. By 32 weeks of gestation, the skin becomes soft and smooth, and the limbs are plump.

37 week of pregnancy Babies born within weeks are considered full-term. Those born earlier than 37 weeks - premature, and later 42 - premature.

18 days after conception, the heartbeats of the embryo begin to be felt and a special, its own circulatory system comes into play. At 7 weeks, an unborn child has brain impulses, he has formed external and internal organs, eyes, nose, lips, tongue. At 12 weeks, when abortion is permitted under our legislation, all the organs of the child have formed and only development remains. The child is already turning his head, clenching his fist, grimacing, finding his mouth and sucking his thumb. Do you know that

HAVING AN ABORTION, in addition to mortal danger, you run the risk of remaining infertile or giving birth to sick and weakened children. By performing an operation to terminate a pregnancy, the doctor twice violates the Hippocratic oath: firstly, the Hippocratic oath directly prohibits such actions, and secondly, the first commandment of medicine is violated - “do no harm”. The sin of infanticide deprives parents of the grace of God. In ancient times, for such an act, the mother was excommunicated from the Church for 20 years on a par with murderers.

Critical periods of human development in embryogenesis. Implantation of the embryo into the wall of the uterus (6-7 days) 4-8 weeks - the period of laying the main organs and systems a week - the growth of the brain accelerates. Splitting up. Fragmentation is the process of increasing the number of cells, without increasing their size (there is no growth stage). Types of crushing: - complete: uniform and uneven - incomplete: superficial (in insects) and discoidal Types of blastula: - celloblastula is a hollow ball, one layer of blastoderm. - amphiblastula - the blastoderm is multilayer, the blastocoel is displaced to the apical pole. -discoblastula is an embryonic disc lying on a mass of unbroken yolk, a blastocoel between them. - morula is a ball of blastomeres, there is no blastocoel. - pereblastula - blastomeres are located on the surface, and in the center there is an unbroken yolk (in insects).

Gastrulation. Gastrulation is a complex process of chemical and morphogenetic changes that are accompanied by cell division, growth, movement and differentiation. Methods of gastrulation: - invagination (invagination) - immigration (eviction) - delamination (stratification) - epibolia (fouling) The genome is one. There is depression and gene repression. And in each cell type, this pattern will be different. Therefore, cell differentiation takes place.

Neurulation. Neurulation is part of organogenesis. An embryo is formed - neurula. At this point, the neurula contains an axial complex of organ rudiments (neural tube, chord, cavity of the primary intestine, ectoderm, endoderm, mesoderm differentiated into segmented mesoderm - somites and non-segmented - by splanchnotome).

“Our coming and going ... are mysterious - their goals

All the sages of the Earth were unable to comprehend.

Where is the beginning of this circle, where is the end?

Where did we come from, where do we go from here? "

Omar Khayyam

Lesson topic: "Embryonic development of the body"

to characterize the main stages of embryogenesis

Embryogenesis

Embryogenesis - the period of development of an individual from the moment of formation

zygotes before birth (for example, in mammals)

or the exit from the egg membranes (in birds).

crushing (blastulation)

neurulation and organogenesis

gastrulation

Embryogenesis

The embryonic period consists of a number of stages:

crushing (blastulation)

neurulation and organogenesis

gastrulation

1. Crushing (blastulation)

Splitting up - a series of successive mitotic divisions of the zygote, as a result of which a huge volume of the cytoplasm of the egg is divided into numerous smaller cells containing nuclei. As a result of cleavage, cells are formed, which are called blastomeres .

Rice. 312. Crushing of an amphibian ovum (frog):

1 - two-cell stage; 2 - four-cell stage; 3 - eight-celled stage; 4 - transition from the eight- to sixteen-cell stage (the cells of the animal pole have already divided, and the cells of the vegetative pole are just beginning to split; 5 - a later stage of cleavage; 6 - blastula; 7 - blastula in section.

However, fragmentation cannot proceed indefinitely. Since each division of cleavage is accompanied by a decrease in cell size, there is a gradual increase in the value of the nuclear-cytoplasmic ratio, reduced during the growth of the oocyte. A moment comes when this ratio reaches a value typical for somatic cells of a given species.

The biological significance of the crushing process is reduced to the following:

due to repetitive reproduction cycles, the zygote genotype multiplies;

there is an accumulation of cell mass for further transformations, i.e. the embryo is transformed from unicellular into multicellular.

The division of blastomeres is synchronous and asynchronous... In most species, it is asynchronous from the very beginning of development, in others it becomes so after the first divisions.

The nature of cleavage is determined, first of all, by the structure of the egg, mainly by the amount of yolk and the peculiarities of its distribution in the cytoplasm. In this regard, according to the method of crushing, two main types of eggs are distinguished (Fig. 313):

completely crushing;

crushing partially.

Complete crushing

Complete crushing is called when the cytoplasm of the egg is completely divided into blastomeres. It can be:

uniform in which all formed blastomeres have the same size and shape; it is characteristic of alecitic and isocyte oocytes;

uneven at which blastomeres unequal in size are formed; characteristic of telolecital eggs with a moderate yolk content; small blastomeres arise at the animal pole, large ones - in the area of ​​the vegetative pole of the embryo.

Rice. 313. Various types of crushing:

A - complete; B - partial; B - discoidal.

Partial crushing

Partial crushing- a type of cleavage in which the cytoplasm of the egg is not completely divided into blastomeres. One of the types of partial crushing is discoidal, in which only the yolk-free area of ​​the cytoplasm at the animal pole, where the nucleus is located, is subjected to cleavage. The section of the cytoplasm that has undergone cleavage is called the germinal disc. This type of cleavage is characteristic of sharply telolecitic eggs with a large amount of yolk (reptiles, birds, fish);

Blastula formation

Fragmentation in representatives of different groups of animals has its own characteristics, however, it ends with the formation of a structure similar in structure - blastula.

Blastula is a single-layer embryo. It consists of a layer of cells - blastoderm limiting the cavity - blastocoel, or primary body cavity... Blastula is formed from the early stages of cleavage, due to the divergence of blastomeres. The resulting cavity is filled with liquid.

Blastula types

The structure of the blastula largely depends on the type of cleavage (Fig. 314).

Celloblastula(typical blastula). Formed by uniform crushing. It looks like a single-layer vesicle with a large blastocele (in the lancelet).

Amphiblastula. When telolecital eggs are cleaved, the blastoderm is built of blastomeres of different sizes: micromeres on the animal and macromeres on the vegetative poles. In this case, the blastocoel is shifted towards the animal pole (in amphibians).

Rice. 314. Types of blastula:

1 - celloblastula; 2 - amphiblastula; 3 - discoblastula; 4 - blastocyst; 5 - embryoblast; 6 - trophoblast.

Discoblastula... Formed by discoidal cleavage. The blastula cavity looks like a narrow slit located under the embryonic disc (in birds).

Blastocyst... It is a single-layer bubble filled with liquid, in which one can distinguish embryoblast(the embryo develops from it) and trophoblast providing nutrition to the embryo (in mammals).

Gastrulation

After the blastula has formed, a new stage of embryogenesis begins - gastrulation(formation of germ layers). Gastrulation is characterized by intense movements of individual cells and cell masses. Cell division during gastrulation is absent or very weakly expressed. As a result of gastrulation, a two-layer and then a three-layer embryo is formed (in most animals) - gastrula(fig. 315). Initially, external ( ectoderm) and internal ( endoderm). Later, between the ecto- and endoderm, a third germ layer is laid - mesoderm .

Embryonic leaves - these are separate layers of cells that occupy a certain position in the embryo and give rise to the corresponding organs and organ systems. The germ layers arise not only as a result of the movement of cell masses, but also as a result of the differentiation of relatively homogeneous blastula cells that are similar to each other. In the process of gastrulation, the germ layers occupy a position corresponding to the plan of the structure of an adult organism. Differentiation- This is the process of the appearance and growth of morphological and functional differences between individual cells and parts of the embryo.

Gastrulation methods

Rice. 315. Gastrula.

4 - gastrocoel.

Intussusception

intestines, or gastrocoel blastopore, or primary mouth primary animals deuterostomes

Rice. 316. Types of gastruli:

Immigration -

Delamination

Epibolia

Mesoderm formation

Primary organogenesis

organogenesis

neurulation

Neurulation

neurula neuroectoderm

Rice. 317. Neirula:

neural plate nerve rollers nerve groove neurocele .

ganglion plate, or neural crest

Organ systems formation

From material ectoderm

chord coelomic bags. the whole).

Embryonic induction

embryonic induction

body growth;

Direct

nonlarge

Rice. 319. Frog Development

intrauterine

With the transformation

1. Crushing (blastulation)

Crushing ends with formation blastula- the stage at which a primary body cavity appears in the embryo - blastocoel (4).

Gastrulation methods

Rice. 315. Gastrula.

1 - ectoderm; 2 - endoderm; 3 - blastopore;

4 - gastrocoel.

Depending on the type of blastula and on the characteristics of cell movement, the following main methods of formation of a two-layer embryo are distinguished, or methods of gastrulation (Fig. 316):

Intussusception... With this method, one of the parts of the blastoderm begins to protrude into the blastocoel (near the lancelet). In this case, the blastocoel is almost completely displaced. A two-layer sac is formed, the outer wall of which is the primary ectoderm, and the inner wall is the primary endoderm lining the cavity with the primary

intestines, or gastrocoel... The hole through which the cavity communicates with the environment is called blastopore, or primary mouth... In representatives of different groups of animals, the fate of the blastopore is different. Have primary animals it turns into a mouth opening. Have deuterostomes the blastopore overgrows, and in its place the anus often arises, and the oral opening breaks out at the opposite pole (anterior end of the body).

Rice. 316. Types of gastruli:

1 - invagination; 2 - epibolic; 3 - immigration; 4 - delamination; a - ectoderm; b - endoderm; c - gastrocoel

Immigration - the expulsion of a part of the blastoderm cells into the blastocoel cavity (in higher vertebrates). Endoderm is formed from them.

Delamination occurs in animals with blastula without blastocoel (birds). With this method of gastrulation, cellular movements are minimal or completely absent, since stratification occurs - the outer cells of the blastula are transformed into ectoderm, and the inner ones form the endoderm.

Epibolia occurs when the smaller blastomeres of the animal pole split faster and overgrow the larger blastomeres of the vegetative pole, forming an ectoderm (in amphibians). The cells of the vegetative pole give rise to the internal germ layer, the endoderm.

The described methods of gastrulation are rarely found in their pure form, and their combinations are usually observed (intussusception with epiboly in amphibians or delamination with immigration in echinoderms).

Mesoderm formation

Most often, the cellular material of the mesoderm is part of the endoderm. It invades the blastocoel in the form of pocket-like outgrowths, which are then detached.

With the formation of the mesoderm, a secondary body cavity, or coelom, is formed.

Primary organogenesis

The process of organ formation in embryonic development is called organogenesis... Several tissues are involved in the construction of any organ. Therefore, the stage of organogenesis is also the stage of histogenesis.

Organogenesis can be divided into two phases:

neurulation- the formation of a complex of axial organs (neural tube, notochord, intestinal tube and mesoderm of somites), in which almost the entire embryo is involved;

the construction of other organs, the acquisition by various parts of the body of their typical shape and features of the internal organization, the establishment of certain proportions (spatially limited processes).

According to Karl Baer's theory of germ layers, the emergence of organs is due to the transformation of one or another germ layer - ecto-, meso- or endoderm. Some organs can be of mixed origin, that is, they are formed with the participation of several germ layers at once. For example, the musculature of the digestive tract is a derivative of the mesoderm, and its inner lining is a derivative of the endoderm. However, simplifying somewhat, the origin of the main organs and their systems can still be associated with certain germ layers.

Neurulation

The embryo at the stage of neurulation is called neurula(fig. 317). The material used to build the nervous system in vertebrates - neuroectoderm, is part of the dorsal (dorsal) part of the ectoderm. It is located above the

Rice. 317. Neirula:

1 - ectoderm; 2 - chord; 3 - secondary body cavity; 4 - mesoderm; 5 - endoderm; 6 - intestinal cavity; 7 - neural tube.

chord chat. The interaction of these primordia

is one of the most important in all development. First, in the area of ​​the neuroectoderm, a flattening of the cell layer occurs, which leads to the formation neural plate... Then the edges of the neural plate thicken and rise, forming nerve rollers... In the center of the plate, due to the movement of cells along the midline, nerve groove dividing the embryo into the future right and left halves. The neural plate begins to fold along the midline. Its edges touch and then close. As a result of these processes, a neural tube with a cavity appears - neurocele .

The closure of the ridges occurs first in the middle, and then in the back of the nerve groove. This happens last at the head, which is wider than the others. The anterior, expanded section further forms the brain, the rest of the neural tube - the dorsal. As a result, the neural plate turns into a neural tube that lies under the ectoderm.

During neurulation, some of the cells of the neural plate are not part of the neural tube. They form ganglion plate, or neural crest, - an accumulation of cells along the neural tube. Later, these cells migrate throughout the embryo, forming cells of nerve nodes, adrenal medulla, pigment cells, etc.

Organ systems formation

From material ectoderm In addition to the neural tube, the epidermis and its derivatives (feather, hair, nails, claws, skin glands, etc.), components of the organs of vision, hearing, smell, oral epithelium, and tooth enamel develop.

The mesodermal and endodermal organs are not formed after the formation of the neural tube, but simultaneously with it. Almost simultaneously with neurulation, the processes of laying the mesoderm and notochord take place. Initially, pockets or folds are formed along the lateral walls of the primary intestine by protruding the endoderm. The portion of the endoderm located between these folds thickens, sags, folds and detaches from the bulk of the endoderm. This is how it appears chord... The resulting pocket-like protrusions of the endoderm are detached from the primary intestine and turn into a series of segmented closed sacs, also called coelomic bags. Their walls are formed by mesoderm, and the cavity inside is a secondary body cavity (or the whole).

All types of connective tissue, dermis, skeleton, striated and smooth muscles, circulatory and lymphatic systems, and the reproductive system develop from the mesoderm.

The epithelium of the intestine and stomach, liver cells, secreting cells of the pancreas, intestinal and gastric glands develop from the material of the endoderm. The anterior section of the embryonic intestine forms the epithelium of the lungs and airways, secreting sections of the anterior and middle lobe of the pituitary gland, thyroid and parathyroid glands.

Embryonic induction

Observations of a fertilized frog egg made it possible to trace the path of development of cells that make up a particular part of the embryo. It turned out that certain cells, which occupy a corresponding place in the blastula, give rise to strictly defined organ rudiments. It was possible to find out which groups of cells give rise to the neural tube, chord, mesoderm, skin epithelium, etc. Indeed, in a developing organism, various groups of cells give rise to certain organs and tissues, and the cultivation of cells outside the embryo (in a test tube) does not lead to the formation of typical tissue structures that should have been formed from cells. What causes the transformation of certain cells of the embryo into specific tissues and organs?

In 1924, the results of the experiments of G. Spemann and G. Mangold, devoted to clarifying this issue, were published (Fig. 318). At the stage of early gastrula, the rudiment of the ectoderm, which under normal conditions should have developed into the structures of the nervous system, was transplanted from the embryo of the comb-like (unpigmented) newt under the ectoderm of the ventral side, giving rise to the epidermis of the skin, the embryo of the common (pigmented) newt. As a result, the neural tube and other components of the complex of axial organs first appeared on the abdominal side of the recipient embryo, and then an additional embryo was formed. Moreover, observations have shown that the tissues of the additional embryo are formed almost exclusively from the cellular material of the recipient.

These data prove that during embryogenesis, some parts of the embryo influence the developmental pathways of neighboring areas. This influence of one rudiment on another is called embryonic induction... How important is the role of embryonic induction in development is shown by the following experience. If at the stage of early gastrula is completely removed

Fig. 318. Embryonic induction:

1 - primordium of chordomesoderm; 2 - blastula cavity; 3 - induced neural tube; 4 - induced chord; 5 - primary neural tube; 6 - primary chord; 7 - the formation of a secondary embryo connected to the host embryo.

the primordium of the notochord, the neural tube does not develop at all. The ectoderm on the dorsal side of the embryo, from which the neural tube normally forms, forms the cutaneous epithelium.

Upon further study of the development of the embryos, it turned out that the anlage of the chordomesoderm is not only an inductor of the neural tube, but itself, for differentiation, needs an inducing influence from the primordium of the nervous system. During embryonic development, it is not unilateral induction that takes place, but the interaction of parts of the developing embryo. Thus, embryonic induction can be defined as a phenomenon in which, in the process of embryogenesis, one primordium affects another, determining the path of its development, and, in addition, itself is subjected to an inducing effect from the first primordium.

38.6. Postembryonic development

The postembryonic period of development begins at the moment of birth or release of the organism from the egg membranes and continues until its death. Postembryonic development includes:

body growth;

establishing the final proportions of the body;

transition of organ systems to the regime of an adult organism (in particular, puberty).

Types of postembryonic development

There are two main types of postembryonic development:

Direct, in which an individual emerges from the mother's body or egg membranes, which differs from the adult only in its smaller size (birds, mammals). Distinguish:

nonlarge(ovipositor) type in which the embryo develops inside the egg (fish, bird);

Rice. 319. Frog Development

intrauterine the type in which the embryo develops inside the mother's body and is connected to it through the placenta (placental mammals).

With the transformation(metamorphosis), in which a larva emerges from the egg, arranged simpler than an adult animal (sometimes very different from it); as a rule, it has special larval organs that are absent in an adult animal, and is not capable of reproduction; often the larva leads a different way of life than the adult animal (insects, some arachnids, amphibians).

An example of animals with postembryonic development with metamorphosis are tailless amphibians (Fig. 319). A larva emerges from the egg shells of amphibians - a tadpole, more reminiscent of a fish than an amphibian. It has a streamlined body, caudal fin, gill slits and gills, lateral line organs, two-chambered heart, one circle of blood circulation. Over time, under the influence of the thyroid hormone, the tadpole undergoes metamorphosis. His tail dissolves, limbs appear,

the lateral line disappears, the lungs and the second circle of blood circulation develop, that is, gradually it acquires signs characteristic of amphibians.

In mammals, it is formed blastocyst - a single-layer bubble filled with liquid, in which one can distinguish embryoblast (5), an embryo develops from it and trophoblast (6) providing nutrition to the embryo.

Blastocyst

2. Gastrulation

Gastrulation- the stage of formation of germ layers

Blastula in section 1-blastomere 2-blastocoel

The beginning of the formation of gastrula 3-endoderm

Gastrula 4-ectoderm 5-primary mouth 6-primary intestine

Gastrulation methods

Rice. 315. Gastrula.

1 - ectoderm; 2 - endoderm; 3 - blastopore;

4 - gastrocoel.

Depending on the type of blastula and on the characteristics of cell movement, the following main methods of formation of a two-layer embryo are distinguished, or methods of gastrulation (Fig. 316):

Intussusception... With this method, one of the parts of the blastoderm begins to protrude into the blastocoel (near the lancelet). In this case, the blastocoel is almost completely displaced. A two-layer sac is formed, the outer wall of which is the primary ectoderm, and the inner wall is the primary endoderm lining the cavity with the primary

intestines, or gastrocoel... The hole through which the cavity communicates with the environment is called blastopore, or primary mouth... In representatives of different groups of animals, the fate of the blastopore is different. Have primary animals it turns into a mouth opening. Have deuterostomes the blastopore overgrows, and in its place the anus often arises, and the oral opening breaks out at the opposite pole (anterior end of the body).

Rice. 316. Types of gastruli:

1 - invagination; 2 - epibolic; 3 - immigration; 4 - delamination; a - ectoderm; b - endoderm; c - gastrocoel

Immigration - the expulsion of a part of the blastoderm cells into the blastocoel cavity (in higher vertebrates). Endoderm is formed from them.

Delamination occurs in animals with blastula without blastocoel (birds). With this method of gastrulation, cellular movements are minimal or completely absent, since stratification occurs - the outer cells of the blastula are transformed into ectoderm, and the inner ones form the endoderm.

Epibolia occurs when the smaller blastomeres of the animal pole split faster and overgrow the larger blastomeres of the vegetative pole, forming an ectoderm (in amphibians). The cells of the vegetative pole give rise to the internal germ layer, the endoderm.

The described methods of gastrulation are rarely found in their pure form, and their combinations are usually observed (intussusception with epiboly in amphibians or delamination with immigration in echinoderms).

Mesoderm formation

Most often, the cellular material of the mesoderm is part of the endoderm. It invades the blastocoel in the form of pocket-like outgrowths, which are then detached.

With the formation of the mesoderm, a secondary body cavity, or coelom, is formed.

Primary organogenesis

The process of organ formation in embryonic development is called organogenesis... Several tissues are involved in the construction of any organ. Therefore, the stage of organogenesis is also the stage of histogenesis.

Organogenesis can be divided into two phases:

neurulation- the formation of a complex of axial organs (neural tube, notochord, intestinal tube and mesoderm of somites), in which almost the entire embryo is involved;

the construction of other organs, the acquisition by various parts of the body of their typical shape and features of the internal organization, the establishment of certain proportions (spatially limited processes).

According to Karl Baer's theory of germ layers, the emergence of organs is due to the transformation of one or another germ layer - ecto-, meso- or endoderm. Some organs can be of mixed origin, that is, they are formed with the participation of several germ layers at once. For example, the musculature of the digestive tract is a derivative of the mesoderm, and its inner lining is a derivative of the endoderm. However, simplifying somewhat, the origin of the main organs and their systems can still be associated with certain germ layers.

Neurulation

The embryo at the stage of neurulation is called neurula(fig. 317). The material used to build the nervous system in vertebrates - neuroectoderm, is part of the dorsal (dorsal) part of the ectoderm. It is located above the

Rice. 317. Neirula:

1 - ectoderm; 2 - chord; 3 - secondary body cavity; 4 - mesoderm; 5 - endoderm; 6 - intestinal cavity; 7 - neural tube.

chord chat. The interaction of these primordia

is one of the most important in all development. First, in the area of ​​the neuroectoderm, a flattening of the cell layer occurs, which leads to the formation neural plate... Then the edges of the neural plate thicken and rise, forming nerve rollers... In the center of the plate, due to the movement of cells along the midline, nerve groove dividing the embryo into the future right and left halves. The neural plate begins to fold along the midline. Its edges touch and then close. As a result of these processes, a neural tube with a cavity appears - neurocele .

The closure of the ridges occurs first in the middle, and then in the back of the nerve groove. This happens last at the head, which is wider than the others. The anterior, expanded section further forms the brain, the rest of the neural tube - the dorsal. As a result, the neural plate turns into a neural tube that lies under the ectoderm.

During neurulation, some of the cells of the neural plate are not part of the neural tube. They form ganglion plate, or neural crest, - an accumulation of cells along the neural tube. Later, these cells migrate throughout the embryo, forming cells of nerve nodes, adrenal medulla, pigment cells, etc.

Organ systems formation

From material ectoderm In addition to the neural tube, the epidermis and its derivatives (feather, hair, nails, claws, skin glands, etc.), components of the organs of vision, hearing, smell, oral epithelium, and tooth enamel develop.

The mesodermal and endodermal organs are not formed after the formation of the neural tube, but simultaneously with it. Almost simultaneously with neurulation, the processes of laying the mesoderm and notochord take place. Initially, pockets or folds are formed along the lateral walls of the primary intestine by protruding the endoderm. The portion of the endoderm located between these folds thickens, sags, folds and detaches from the bulk of the endoderm. This is how it appears chord... The resulting pocket-like protrusions of the endoderm are detached from the primary intestine and turn into a series of segmented closed sacs, also called coelomic bags. Their walls are formed by mesoderm, and the cavity inside is a secondary body cavity (or the whole).

All types of connective tissue, dermis, skeleton, striated and smooth muscles, circulatory and lymphatic systems, and the reproductive system develop from the mesoderm.

The epithelium of the intestine and stomach, liver cells, secreting cells of the pancreas, intestinal and gastric glands develop from the material of the endoderm. The anterior section of the embryonic intestine forms the epithelium of the lungs and airways, secreting sections of the anterior and middle lobe of the pituitary gland, thyroid and parathyroid glands.

Embryonic induction

Observations of a fertilized frog egg made it possible to trace the path of development of cells that make up a particular part of the embryo. It turned out that certain cells, which occupy a corresponding place in the blastula, give rise to strictly defined organ rudiments. It was possible to find out which groups of cells give rise to the neural tube, chord, mesoderm, skin epithelium, etc. Indeed, in a developing organism, various groups of cells give rise to certain organs and tissues, and the cultivation of cells outside the embryo (in a test tube) does not lead to the formation of typical tissue structures that should have been formed from cells. What causes the transformation of certain cells of the embryo into specific tissues and organs?

In 1924, the results of the experiments of G. Spemann and G. Mangold, devoted to clarifying this issue, were published (Fig. 318). At the stage of early gastrula, the rudiment of the ectoderm, which under normal conditions should have developed into the structures of the nervous system, was transplanted from the embryo of the comb-like (unpigmented) newt under the ectoderm of the ventral side, giving rise to the epidermis of the skin, the embryo of the common (pigmented) newt. As a result, the neural tube and other components of the complex of axial organs first appeared on the abdominal side of the recipient embryo, and then an additional embryo was formed. Moreover, observations have shown that the tissues of the additional embryo are formed almost exclusively from the cellular material of the recipient.

These data prove that during embryogenesis, some parts of the embryo influence the developmental pathways of neighboring areas. This influence of one rudiment on another is called embryonic induction... How important is the role of embryonic induction in development is shown by the following experience. If at the stage of early gastrula is completely removed

Fig. 318. Embryonic induction:

1 - primordium of chordomesoderm; 2 - blastula cavity; 3 - induced neural tube; 4 - induced chord; 5 - primary neural tube; 6 - primary chord; 7 - the formation of a secondary embryo connected to the host embryo.

the primordium of the notochord, the neural tube does not develop at all. The ectoderm on the dorsal side of the embryo, from which the neural tube normally forms, forms the cutaneous epithelium.

Upon further study of the development of the embryos, it turned out that the anlage of the chordomesoderm is not only an inductor of the neural tube, but itself, for differentiation, needs an inducing influence from the primordium of the nervous system. During embryonic development, it is not unilateral induction that takes place, but the interaction of parts of the developing embryo. Thus, embryonic induction can be defined as a phenomenon in which, in the process of embryogenesis, one primordium affects another, determining the path of its development, and, in addition, itself is subjected to an inducing effect from the first primordium.

38.6. Postembryonic development

The postembryonic period of development begins at the moment of birth or release of the organism from the egg membranes and continues until its death. Postembryonic development includes:

body growth;

establishing the final proportions of the body;

transition of organ systems to the regime of an adult organism (in particular, puberty).

Types of postembryonic development

There are two main types of postembryonic development:

Direct, in which an individual emerges from the mother's body or egg membranes, which differs from the adult only in its smaller size (birds, mammals). Distinguish:

nonlarge(ovipositor) type in which the embryo develops inside the egg (fish, bird);

Rice. 319. Frog Development

intrauterine the type in which the embryo develops inside the mother's body and is connected to it through the placenta (placental mammals).

With the transformation(metamorphosis), in which a larva emerges from the egg, arranged simpler than an adult animal (sometimes very different from it); as a rule, it has special larval organs that are absent in an adult animal, and is not capable of reproduction; often the larva leads a different way of life than the adult animal (insects, some arachnids, amphibians).

An example of animals with postembryonic development with metamorphosis are tailless amphibians (Fig. 319). A larva emerges from the egg shells of amphibians - a tadpole, more reminiscent of a fish than an amphibian. It has a streamlined body, caudal fin, gill slits and gills, lateral line organs, two-chambered heart, one circle of blood circulation. Over time, under the influence of the thyroid hormone, the tadpole undergoes metamorphosis. His tail dissolves, limbs appear,

the lateral line disappears, the lungs and the second circle of blood circulation develop, that is, gradually it acquires signs characteristic of amphibians.

Gastrulation is characterized by intense movements of individual cells and cell masses. Cell division absent or pronounced very weak. A two-layer and then a three-layer embryo is formed(in most animals) - gastrula. later, between the ecto- and endoderm, the third germ layer is laid - mesoderm.

3. Neurulation

Neurulation- the stage of formation of tissues and organs of the future

animal (formation of a complex of axial organs)

Gastrulation methods

Rice. 315. Gastrula.

1 - ectoderm; 2 - endoderm; 3 - blastopore;

4 - gastrocoel.

Depending on the type of blastula and on the characteristics of cell movement, the following main methods of formation of a two-layer embryo are distinguished, or methods of gastrulation (Fig. 316):

Intussusception... With this method, one of the parts of the blastoderm begins to protrude into the blastocoel (near the lancelet). In this case, the blastocoel is almost completely displaced. A two-layer sac is formed, the outer wall of which is the primary ectoderm, and the inner wall is the primary endoderm lining the cavity with the primary

intestines, or gastrocoel... The hole through which the cavity communicates with the environment is called blastopore, or primary mouth... In representatives of different groups of animals, the fate of the blastopore is different. Have primary animals it turns into a mouth opening. Have deuterostomes the blastopore overgrows, and in its place the anus often arises, and the oral opening breaks out at the opposite pole (anterior end of the body).

Rice. 316. Types of gastruli:

1 - invagination; 2 - epibolic; 3 - immigration; 4 - delamination; a - ectoderm; b - endoderm; c - gastrocoel

Immigration - the expulsion of a part of the blastoderm cells into the blastocoel cavity (in higher vertebrates). Endoderm is formed from them.

Delamination occurs in animals with blastula without blastocoel (birds). With this method of gastrulation, cellular movements are minimal or completely absent, since stratification occurs - the outer cells of the blastula are transformed into ectoderm, and the inner ones form the endoderm.

Epibolia occurs when the smaller blastomeres of the animal pole split faster and overgrow the larger blastomeres of the vegetative pole, forming an ectoderm (in amphibians). The cells of the vegetative pole give rise to the internal germ layer, the endoderm.

The described methods of gastrulation are rarely found in their pure form, and their combinations are usually observed (intussusception with epiboly in amphibians or delamination with immigration in echinoderms).

Mesoderm formation

Most often, the cellular material of the mesoderm is part of the endoderm. It invades the blastocoel in the form of pocket-like outgrowths, which are then detached.

With the formation of the mesoderm, a secondary body cavity, or coelom, is formed.

Primary organogenesis

The process of organ formation in embryonic development is called organogenesis... Several tissues are involved in the construction of any organ. Therefore, the stage of organogenesis is also the stage of histogenesis.

Organogenesis can be divided into two phases:

neurulation- the formation of a complex of axial organs (neural tube, notochord, intestinal tube and mesoderm of somites), in which almost the entire embryo is involved;

the construction of other organs, the acquisition by various parts of the body of their typical shape and features of the internal organization, the establishment of certain proportions (spatially limited processes).

According to Karl Baer's theory of germ layers, the emergence of organs is due to the transformation of one or another germ layer - ecto-, meso- or endoderm. Some organs can be of mixed origin, that is, they are formed with the participation of several germ layers at once. For example, the musculature of the digestive tract is a derivative of the mesoderm, and its inner lining is a derivative of the endoderm. However, simplifying somewhat, the origin of the main organs and their systems can still be associated with certain germ layers.

Neurulation

The embryo at the stage of neurulation is called neurula(fig. 317). The material used to build the nervous system in vertebrates - neuroectoderm, is part of the dorsal (dorsal) part of the ectoderm. It is located above the

Rice. 317. Neirula:

1 - ectoderm; 2 - chord; 3 - secondary body cavity; 4 - mesoderm; 5 - endoderm; 6 - intestinal cavity; 7 - neural tube.

chord chat. The interaction of these primordia

is one of the most important in all development. First, in the area of ​​the neuroectoderm, a flattening of the cell layer occurs, which leads to the formation neural plate... Then the edges of the neural plate thicken and rise, forming nerve rollers... In the center of the plate, due to the movement of cells along the midline, nerve groove dividing the embryo into the future right and left halves. The neural plate begins to fold along the midline. Its edges touch and then close. As a result of these processes, a neural tube with a cavity appears - neurocele .

The closure of the ridges occurs first in the middle, and then in the back of the nerve groove. This happens last at the head, which is wider than the others. The anterior, expanded section further forms the brain, the rest of the neural tube - the dorsal. As a result, the neural plate turns into a neural tube that lies under the ectoderm.

During neurulation, some of the cells of the neural plate are not part of the neural tube. They form ganglion plate, or neural crest, - an accumulation of cells along the neural tube. Later, these cells migrate throughout the embryo, forming cells of nerve nodes, adrenal medulla, pigment cells, etc.

Organ systems formation

From material ectoderm In addition to the neural tube, the epidermis and its derivatives (feather, hair, nails, claws, skin glands, etc.), components of the organs of vision, hearing, smell, oral epithelium, and tooth enamel develop.

The mesodermal and endodermal organs are not formed after the formation of the neural tube, but simultaneously with it. Almost simultaneously with neurulation, the processes of laying the mesoderm and notochord take place. Initially, pockets or folds are formed along the lateral walls of the primary intestine by protruding the endoderm. The portion of the endoderm located between these folds thickens, sags, folds and detaches from the bulk of the endoderm. This is how it appears chord... The resulting pocket-like protrusions of the endoderm are detached from the primary intestine and turn into a series of segmented closed sacs, also called coelomic bags. Their walls are formed by mesoderm, and the cavity inside is a secondary body cavity (or the whole).

All types of connective tissue, dermis, skeleton, striated and smooth muscles, circulatory and lymphatic systems, and the reproductive system develop from the mesoderm.

The epithelium of the intestine and stomach, liver cells, secreting cells of the pancreas, intestinal and gastric glands develop from the material of the endoderm. The anterior section of the embryonic intestine forms the epithelium of the lungs and airways, secreting sections of the anterior and middle lobe of the pituitary gland, thyroid and parathyroid glands.

Embryonic induction

Observations of a fertilized frog egg made it possible to trace the path of development of cells that make up a particular part of the embryo. It turned out that certain cells, which occupy a corresponding place in the blastula, give rise to strictly defined organ rudiments. It was possible to find out which groups of cells give rise to the neural tube, chord, mesoderm, skin epithelium, etc. Indeed, in a developing organism, various groups of cells give rise to certain organs and tissues, and the cultivation of cells outside the embryo (in a test tube) does not lead to the formation of typical tissue structures that should have been formed from cells. What causes the transformation of certain cells of the embryo into specific tissues and organs?

In 1924, the results of the experiments of G. Spemann and G. Mangold, devoted to clarifying this issue, were published (Fig. 318). At the stage of early gastrula, the rudiment of the ectoderm, which under normal conditions should have developed into the structures of the nervous system, was transplanted from the embryo of the comb-like (unpigmented) newt under the ectoderm of the ventral side, giving rise to the epidermis of the skin, the embryo of the common (pigmented) newt. As a result, the neural tube and other components of the complex of axial organs first appeared on the abdominal side of the recipient embryo, and then an additional embryo was formed. Moreover, observations have shown that the tissues of the additional embryo are formed almost exclusively from the cellular material of the recipient.

These data prove that during embryogenesis, some parts of the embryo influence the developmental pathways of neighboring areas. This influence of one rudiment on another is called embryonic induction... How important is the role of embryonic induction in development is shown by the following experience. If at the stage of early gastrula is completely removed

Fig. 318. Embryonic induction:

1 - primordium of chordomesoderm; 2 - blastula cavity; 3 - induced neural tube; 4 - induced chord; 5 - primary neural tube; 6 - primary chord; 7 - the formation of a secondary embryo connected to the host embryo.

the primordium of the notochord, the neural tube does not develop at all. The ectoderm on the dorsal side of the embryo, from which the neural tube normally forms, forms the cutaneous epithelium.

Upon further study of the development of the embryos, it turned out that the anlage of the chordomesoderm is not only an inductor of the neural tube, but itself, for differentiation, needs an inducing influence from the primordium of the nervous system. During embryonic development, it is not unilateral induction that takes place, but the interaction of parts of the developing embryo. Thus, embryonic induction can be defined as a phenomenon in which, in the process of embryogenesis, one primordium affects another, determining the path of its development, and, in addition, itself is subjected to an inducing effect from the first primordium.

38.6. Postembryonic development

The postembryonic period of development begins at the moment of birth or release of the organism from the egg membranes and continues until its death. Postembryonic development includes:

body growth;

establishing the final proportions of the body;

transition of organ systems to the regime of an adult organism (in particular, puberty).

Types of postembryonic development

There are two main types of postembryonic development:

Direct, in which an individual emerges from the mother's body or egg membranes, which differs from the adult only in its smaller size (birds, mammals). Distinguish:

nonlarge(ovipositor) type in which the embryo develops inside the egg (fish, bird);

Rice. 319. Frog Development

intrauterine the type in which the embryo develops inside the mother's body and is connected to it through the placenta (placental mammals).

With the transformation(metamorphosis), in which a larva emerges from the egg, arranged simpler than an adult animal (sometimes very different from it); as a rule, it has special larval organs that are absent in an adult animal, and is not capable of reproduction; often the larva leads a different way of life than the adult animal (insects, some arachnids, amphibians).

An example of animals with postembryonic development with metamorphosis are tailless amphibians (Fig. 319). A larva emerges from the egg shells of amphibians - a tadpole, more reminiscent of a fish than an amphibian. It has a streamlined body, caudal fin, gill slits and gills, lateral line organs, two-chambered heart, one circle of blood circulation. Over time, under the influence of the thyroid hormone, the tadpole undergoes metamorphosis. His tail dissolves, limbs appear,

the lateral line disappears, the lungs and the second circle of blood circulation develop, that is, gradually it acquires signs characteristic of amphibians.

Early neurula Neirula

7- neural plate 9- mesoderm 8- chord 10- secondary body cavity

Organogenesis.

Organogenesis

in embryonic development.

Ectoderm

epidermis and its derivatives

(feather, hair, nails, claws,

skin glands, etc.)

neural tube

Gastrulation methods

Rice. 315. Gastrula.

1 - ectoderm; 2 - endoderm; 3 - blastopore;

4 - gastrocoel.

Depending on the type of blastula and on the characteristics of cell movement, the following main methods of formation of a two-layer embryo are distinguished, or methods of gastrulation (Fig. 316):

Intussusception... With this method, one of the parts of the blastoderm begins to protrude into the blastocoel (near the lancelet). In this case, the blastocoel is almost completely displaced. A two-layer sac is formed, the outer wall of which is the primary ectoderm, and the inner wall is the primary endoderm lining the cavity with the primary

intestines, or gastrocoel... The hole through which the cavity communicates with the environment is called blastopore, or primary mouth... In representatives of different groups of animals, the fate of the blastopore is different. Have primary animals it turns into a mouth opening. Have deuterostomes the blastopore overgrows, and in its place the anus often arises, and the oral opening breaks out at the opposite pole (anterior end of the body).

Rice. 316. Types of gastruli:

1 - invagination; 2 - epibolic; 3 - immigration; 4 - delamination; a - ectoderm; b - endoderm; c - gastrocoel

Immigration - the expulsion of a part of the blastoderm cells into the blastocoel cavity (in higher vertebrates). Endoderm is formed from them.

Delamination occurs in animals with blastula without blastocoel (birds). With this method of gastrulation, cellular movements are minimal or completely absent, since stratification occurs - the outer cells of the blastula are transformed into ectoderm, and the inner ones form the endoderm.

Epibolia occurs when the smaller blastomeres of the animal pole split faster and overgrow the larger blastomeres of the vegetative pole, forming an ectoderm (in amphibians). The cells of the vegetative pole give rise to the internal germ layer, the endoderm.

The described methods of gastrulation are rarely found in their pure form, and their combinations are usually observed (intussusception with epiboly in amphibians or delamination with immigration in echinoderms).

Mesoderm formation

Most often, the cellular material of the mesoderm is part of the endoderm. It invades the blastocoel in the form of pocket-like outgrowths, which are then detached.

With the formation of the mesoderm, a secondary body cavity, or coelom, is formed.

Primary organogenesis

The process of organ formation in embryonic development is called organogenesis... Several tissues are involved in the construction of any organ. Therefore, the stage of organogenesis is also the stage of histogenesis.

Organogenesis can be divided into two phases:

neurulation- the formation of a complex of axial organs (neural tube, notochord, intestinal tube and mesoderm of somites), in which almost the entire embryo is involved;

the construction of other organs, the acquisition by various parts of the body of their typical shape and features of the internal organization, the establishment of certain proportions (spatially limited processes).

According to Karl Baer's theory of germ layers, the emergence of organs is due to the transformation of one or another germ layer - ecto-, meso- or endoderm. Some organs can be of mixed origin, that is, they are formed with the participation of several germ layers at once. For example, the musculature of the digestive tract is a derivative of the mesoderm, and its inner lining is a derivative of the endoderm. However, simplifying somewhat, the origin of the main organs and their systems can still be associated with certain germ layers.

Neurulation

The embryo at the stage of neurulation is called neurula(fig. 317). The material used to build the nervous system in vertebrates - neuroectoderm, is part of the dorsal (dorsal) part of the ectoderm. It is located above the

Rice. 317. Neirula:

1 - ectoderm; 2 - chord; 3 - secondary body cavity; 4 - mesoderm; 5 - endoderm; 6 - intestinal cavity; 7 - neural tube.

chord chat. The interaction of these primordia

is one of the most important in all development. First, in the area of ​​the neuroectoderm, a flattening of the cell layer occurs, which leads to the formation neural plate... Then the edges of the neural plate thicken and rise, forming nerve rollers... In the center of the plate, due to the movement of cells along the midline, nerve groove dividing the embryo into the future right and left halves. The neural plate begins to fold along the midline. Its edges touch and then close. As a result of these processes, a neural tube with a cavity appears - neurocele .

The closure of the ridges occurs first in the middle, and then in the back of the nerve groove. This happens last at the head, which is wider than the others. The anterior, expanded section further forms the brain, the rest of the neural tube - the dorsal. As a result, the neural plate turns into a neural tube that lies under the ectoderm.

During neurulation, some of the cells of the neural plate are not part of the neural tube. They form ganglion plate, or neural crest, - an accumulation of cells along the neural tube. Later, these cells migrate throughout the embryo, forming cells of nerve nodes, adrenal medulla, pigment cells, etc.

Organ systems formation

From material ectoderm In addition to the neural tube, the epidermis and its derivatives (feather, hair, nails, claws, skin glands, etc.), components of the organs of vision, hearing, smell, oral epithelium, and tooth enamel develop.

The mesodermal and endodermal organs are not formed after the formation of the neural tube, but simultaneously with it. Almost simultaneously with neurulation, the processes of laying the mesoderm and notochord take place. Initially, pockets or folds are formed along the lateral walls of the primary intestine by protruding the endoderm. The portion of the endoderm located between these folds thickens, sags, folds and detaches from the bulk of the endoderm. This is how it appears chord... The resulting pocket-like protrusions of the endoderm are detached from the primary intestine and turn into a series of segmented closed sacs, also called coelomic bags. Their walls are formed by mesoderm, and the cavity inside is a secondary body cavity (or the whole).

All types of connective tissue, dermis, skeleton, striated and smooth muscles, circulatory and lymphatic systems, and the reproductive system develop from the mesoderm.

The epithelium of the intestine and stomach, liver cells, secreting cells of the pancreas, intestinal and gastric glands develop from the material of the endoderm. The anterior section of the embryonic intestine forms the epithelium of the lungs and airways, secreting sections of the anterior and middle lobe of the pituitary gland, thyroid and parathyroid glands.

Embryonic induction

Observations of a fertilized frog egg made it possible to trace the path of development of cells that make up a particular part of the embryo. It turned out that certain cells, which occupy a corresponding place in the blastula, give rise to strictly defined organ rudiments. It was possible to find out which groups of cells give rise to the neural tube, chord, mesoderm, skin epithelium, etc. Indeed, in a developing organism, various groups of cells give rise to certain organs and tissues, and the cultivation of cells outside the embryo (in a test tube) does not lead to the formation of typical tissue structures that should have been formed from cells. What causes the transformation of certain cells of the embryo into specific tissues and organs?

In 1924, the results of the experiments of G. Spemann and G. Mangold, devoted to clarifying this issue, were published (Fig. 318). At the stage of early gastrula, the rudiment of the ectoderm, which under normal conditions should have developed into the structures of the nervous system, was transplanted from the embryo of the comb-like (unpigmented) newt under the ectoderm of the ventral side, giving rise to the epidermis of the skin, the embryo of the common (pigmented) newt. As a result, the neural tube and other components of the complex of axial organs first appeared on the abdominal side of the recipient embryo, and then an additional embryo was formed. Moreover, observations have shown that the tissues of the additional embryo are formed almost exclusively from the cellular material of the recipient.

These data prove that during embryogenesis, some parts of the embryo influence the developmental pathways of neighboring areas. This influence of one rudiment on another is called embryonic induction... How important is the role of embryonic induction in development is shown by the following experience. If at the stage of early gastrula is completely removed

Fig. 318. Embryonic induction:

1 - primordium of chordomesoderm; 2 - blastula cavity; 3 - induced neural tube; 4 - induced chord; 5 - primary neural tube; 6 - primary chord; 7 - the formation of a secondary embryo connected to the host embryo.

the primordium of the notochord, the neural tube does not develop at all. The ectoderm on the dorsal side of the embryo, from which the neural tube normally forms, forms the cutaneous epithelium.

Upon further study of the development of the embryos, it turned out that the anlage of the chordomesoderm is not only an inductor of the neural tube, but itself, for differentiation, needs an inducing influence from the primordium of the nervous system. During embryonic development, it is not unilateral induction that takes place, but the interaction of parts of the developing embryo. Thus, embryonic induction can be defined as a phenomenon in which, in the process of embryogenesis, one primordium affects another, determining the path of its development, and, in addition, itself is subjected to an inducing effect from the first primordium.

38.6. Postembryonic development

The postembryonic period of development begins at the moment of birth or release of the organism from the egg membranes and continues until its death. Postembryonic development includes:

body growth;

establishing the final proportions of the body;

transition of organ systems to the regime of an adult organism (in particular, puberty).

Types of postembryonic development

There are two main types of postembryonic development:

Direct, in which an individual emerges from the mother's body or egg membranes, which differs from the adult only in its smaller size (birds, mammals). Distinguish:

nonlarge(ovipositor) type in which the embryo develops inside the egg (fish, bird);

Rice. 319. Frog Development

intrauterine the type in which the embryo develops inside the mother's body and is connected to it through the placenta (placental mammals).

With the transformation(metamorphosis), in which a larva emerges from the egg, arranged simpler than an adult animal (sometimes very different from it); as a rule, it has special larval organs that are absent in an adult animal, and is not capable of reproduction; often the larva leads a different way of life than the adult animal (insects, some arachnids, amphibians).

An example of animals with postembryonic development with metamorphosis are tailless amphibians (Fig. 319). A larva emerges from the egg shells of amphibians - a tadpole, more reminiscent of a fish than an amphibian. It has a streamlined body, caudal fin, gill slits and gills, lateral line organs, two-chambered heart, one circle of blood circulation. Over time, under the influence of the thyroid hormone, the tadpole undergoes metamorphosis. His tail dissolves, limbs appear,

the lateral line disappears, the lungs and the second circle of blood circulation develop, that is, gradually it acquires signs characteristic of amphibians.

oral epithelium

enamel of teeth;

components of the organs of vision,

hearing, smelling

Organogenesis.

Organogenesis- the process of organ formation

in embryonic development.

Endoderm

intestinal epithelium

and stomach

liver cells,

pancreas

Gastrulation methods

Rice. 315. Gastrula.

1 - ectoderm; 2 - endoderm; 3 - blastopore;

4 - gastrocoel.

Depending on the type of blastula and on the characteristics of cell movement, the following main methods of formation of a two-layer embryo are distinguished, or methods of gastrulation (Fig. 316):

Intussusception... With this method, one of the parts of the blastoderm begins to protrude into the blastocoel (near the lancelet). In this case, the blastocoel is almost completely displaced. A two-layer sac is formed, the outer wall of which is the primary ectoderm, and the inner wall is the primary endoderm lining the cavity with the primary

intestines, or gastrocoel... The hole through which the cavity communicates with the environment is called blastopore, or primary mouth... In representatives of different groups of animals, the fate of the blastopore is different. Have primary animals it turns into a mouth opening. Have deuterostomes the blastopore overgrows, and in its place the anus often arises, and the oral opening breaks out at the opposite pole (anterior end of the body).

Rice. 316. Types of gastruli:

1 - invagination; 2 - epibolic; 3 - immigration; 4 - delamination; a - ectoderm; b - endoderm; c - gastrocoel

Immigration - the expulsion of a part of the blastoderm cells into the blastocoel cavity (in higher vertebrates). Endoderm is formed from them.

Delamination occurs in animals with blastula without blastocoel (birds). With this method of gastrulation, cellular movements are minimal or completely absent, since stratification occurs - the outer cells of the blastula are transformed into ectoderm, and the inner ones form the endoderm.

Epibolia occurs when the smaller blastomeres of the animal pole split faster and overgrow the larger blastomeres of the vegetative pole, forming an ectoderm (in amphibians). The cells of the vegetative pole give rise to the internal germ layer, the endoderm.

The described methods of gastrulation are rarely found in their pure form, and their combinations are usually observed (intussusception with epiboly in amphibians or delamination with immigration in echinoderms).

Mesoderm formation

Most often, the cellular material of the mesoderm is part of the endoderm. It invades the blastocoel in the form of pocket-like outgrowths, which are then detached.

With the formation of the mesoderm, a secondary body cavity, or coelom, is formed.

Primary organogenesis

The process of organ formation in embryonic development is called organogenesis... Several tissues are involved in the construction of any organ. Therefore, the stage of organogenesis is also the stage of histogenesis.

Organogenesis can be divided into two phases:

neurulation- the formation of a complex of axial organs (neural tube, notochord, intestinal tube and mesoderm of somites), in which almost the entire embryo is involved;

the construction of other organs, the acquisition by various parts of the body of their typical shape and features of the internal organization, the establishment of certain proportions (spatially limited processes).

According to Karl Baer's theory of germ layers, the emergence of organs is due to the transformation of one or another germ layer - ecto-, meso- or endoderm. Some organs can be of mixed origin, that is, they are formed with the participation of several germ layers at once. For example, the musculature of the digestive tract is a derivative of the mesoderm, and its inner lining is a derivative of the endoderm. However, simplifying somewhat, the origin of the main organs and their systems can still be associated with certain germ layers.

Neurulation

The embryo at the stage of neurulation is called neurula(fig. 317). The material used to build the nervous system in vertebrates - neuroectoderm, is part of the dorsal (dorsal) part of the ectoderm. It is located above the

Rice. 317. Neirula:

1 - ectoderm; 2 - chord; 3 - secondary body cavity; 4 - mesoderm; 5 - endoderm; 6 - intestinal cavity; 7 - neural tube.

chord chat. The interaction of these primordia

is one of the most important in all development. First, in the area of ​​the neuroectoderm, a flattening of the cell layer occurs, which leads to the formation neural plate... Then the edges of the neural plate thicken and rise, forming nerve rollers... In the center of the plate, due to the movement of cells along the midline, nerve groove dividing the embryo into the future right and left halves. The neural plate begins to fold along the midline. Its edges touch and then close. As a result of these processes, a neural tube with a cavity appears - neurocele .

The closure of the ridges occurs first in the middle, and then in the back of the nerve groove. This happens last at the head, which is wider than the others. The anterior, expanded section further forms the brain, the rest of the neural tube - the dorsal. As a result, the neural plate turns into a neural tube that lies under the ectoderm.

During neurulation, some of the cells of the neural plate are not part of the neural tube. They form ganglion plate, or neural crest, - an accumulation of cells along the neural tube. Later, these cells migrate throughout the embryo, forming cells of nerve nodes, adrenal medulla, pigment cells, etc.

Organ systems formation

From material ectoderm In addition to the neural tube, the epidermis and its derivatives (feather, hair, nails, claws, skin glands, etc.), components of the organs of vision, hearing, smell, oral epithelium, and tooth enamel develop.

The mesodermal and endodermal organs are not formed after the formation of the neural tube, but simultaneously with it. Almost simultaneously with neurulation, the processes of laying the mesoderm and notochord take place. Initially, pockets or folds are formed along the lateral walls of the primary intestine by protruding the endoderm. The portion of the endoderm located between these folds thickens, sags, folds and detaches from the bulk of the endoderm. This is how it appears chord... The resulting pocket-like protrusions of the endoderm are detached from the primary intestine and turn into a series of segmented closed sacs, also called coelomic bags. Their walls are formed by mesoderm, and the cavity inside is a secondary body cavity (or the whole).

All types of connective tissue, dermis, skeleton, striated and smooth muscles, circulatory and lymphatic systems, and the reproductive system develop from the mesoderm.

The epithelium of the intestine and stomach, liver cells, secreting cells of the pancreas, intestinal and gastric glands develop from the material of the endoderm. The anterior section of the embryonic intestine forms the epithelium of the lungs and airways, secreting sections of the anterior and middle lobe of the pituitary gland, thyroid and parathyroid glands.

Embryonic induction

Observations of a fertilized frog egg made it possible to trace the path of development of cells that make up a particular part of the embryo. It turned out that certain cells, which occupy a corresponding place in the blastula, give rise to strictly defined organ rudiments. It was possible to find out which groups of cells give rise to the neural tube, chord, mesoderm, skin epithelium, etc. Indeed, in a developing organism, various groups of cells give rise to certain organs and tissues, and the cultivation of cells outside the embryo (in a test tube) does not lead to the formation of typical tissue structures that should have been formed from cells. What causes the transformation of certain cells of the embryo into specific tissues and organs?

In 1924, the results of the experiments of G. Spemann and G. Mangold, devoted to clarifying this issue, were published (Fig. 318). At the stage of early gastrula, the rudiment of the ectoderm, which under normal conditions should have developed into the structures of the nervous system, was transplanted from the embryo of the comb-like (unpigmented) newt under the ectoderm of the ventral side, giving rise to the epidermis of the skin, the embryo of the common (pigmented) newt. As a result, the neural tube and other components of the complex of axial organs first appeared on the abdominal side of the recipient embryo, and then an additional embryo was formed. Moreover, observations have shown that the tissues of the additional embryo are formed almost exclusively from the cellular material of the recipient.

These data prove that during embryogenesis, some parts of the embryo influence the developmental pathways of neighboring areas. This influence of one rudiment on another is called embryonic induction... How important is the role of embryonic induction in development is shown by the following experience. If at the stage of early gastrula is completely removed

Fig. 318. Embryonic induction:

1 - primordium of chordomesoderm; 2 - blastula cavity; 3 - induced neural tube; 4 - induced chord; 5 - primary neural tube; 6 - primary chord; 7 - the formation of a secondary embryo connected to the host embryo.

the primordium of the notochord, the neural tube does not develop at all. The ectoderm on the dorsal side of the embryo, from which the neural tube normally forms, forms the cutaneous epithelium.

Upon further study of the development of the embryos, it turned out that the anlage of the chordomesoderm is not only an inductor of the neural tube, but itself, for differentiation, needs an inducing influence from the primordium of the nervous system. During embryonic development, it is not unilateral induction that takes place, but the interaction of parts of the developing embryo. Thus, embryonic induction can be defined as a phenomenon in which, in the process of embryogenesis, one primordium affects another, determining the path of its development, and, in addition, itself is subjected to an inducing effect from the first primordium.

38.6. Postembryonic development

The postembryonic period of development begins at the moment of birth or release of the organism from the egg membranes and continues until its death. Postembryonic development includes:

body growth;

establishing the final proportions of the body;

transition of organ systems to the regime of an adult organism (in particular, puberty).

Types of postembryonic development

There are two main types of postembryonic development:

Direct, in which an individual emerges from the mother's body or egg membranes, which differs from the adult only in its smaller size (birds, mammals). Distinguish:

nonlarge(ovipositor) type in which the embryo develops inside the egg (fish, bird);

Rice. 319. Frog Development

intrauterine the type in which the embryo develops inside the mother's body and is connected to it through the placenta (placental mammals).

With the transformation(metamorphosis), in which a larva emerges from the egg, arranged simpler than an adult animal (sometimes very different from it); as a rule, it has special larval organs that are absent in an adult animal, and is not capable of reproduction; often the larva leads a different way of life than the adult animal (insects, some arachnids, amphibians).

An example of animals with postembryonic development with metamorphosis are tailless amphibians (Fig. 319). A larva emerges from the egg shells of amphibians - a tadpole, more reminiscent of a fish than an amphibian. It has a streamlined body, caudal fin, gill slits and gills, lateral line organs, two-chambered heart, one circle of blood circulation. Over time, under the influence of the thyroid hormone, the tadpole undergoes metamorphosis. His tail dissolves, limbs appear,

the lateral line disappears, the lungs and the second circle of blood circulation develop, that is, gradually it acquires signs characteristic of amphibians.

middle ear cavity.,

thyroid

Organogenesis.

Organogenesis- the process of organ formation

in embryonic development.

Mesoderm

and musculature

circulatory

and the lymphatic system

Gastrulation methods

Rice. 315. Gastrula.

1 - ectoderm; 2 - endoderm; 3 - blastopore;

4 - gastrocoel.

Depending on the type of blastula and on the characteristics of cell movement, the following main methods of formation of a two-layer embryo are distinguished, or methods of gastrulation (Fig. 316):

Intussusception... With this method, one of the parts of the blastoderm begins to protrude into the blastocoel (near the lancelet). In this case, the blastocoel is almost completely displaced. A two-layer sac is formed, the outer wall of which is the primary ectoderm, and the inner wall is the primary endoderm lining the cavity with the primary

intestines, or gastrocoel... The hole through which the cavity communicates with the environment is called blastopore, or primary mouth... In representatives of different groups of animals, the fate of the blastopore is different. Have primary animals it turns into a mouth opening. Have deuterostomes the blastopore overgrows, and in its place the anus often arises, and the oral opening breaks out at the opposite pole (anterior end of the body).

Rice. 316. Types of gastruli:

1 - invagination; 2 - epibolic; 3 - immigration; 4 - delamination; a - ectoderm; b - endoderm; c - gastrocoel

Immigration - the expulsion of a part of the blastoderm cells into the blastocoel cavity (in higher vertebrates). Endoderm is formed from them.

Delamination occurs in animals with blastula without blastocoel (birds). With this method of gastrulation, cellular movements are minimal or completely absent, since stratification occurs - the outer cells of the blastula are transformed into ectoderm, and the inner ones form the endoderm.

Epibolia occurs when the smaller blastomeres of the animal pole split faster and overgrow the larger blastomeres of the vegetative pole, forming an ectoderm (in amphibians). The cells of the vegetative pole give rise to the internal germ layer, the endoderm.

The described methods of gastrulation are rarely found in their pure form, and their combinations are usually observed (intussusception with epiboly in amphibians or delamination with immigration in echinoderms).

Mesoderm formation

Most often, the cellular material of the mesoderm is part of the endoderm. It invades the blastocoel in the form of pocket-like outgrowths, which are then detached.

With the formation of the mesoderm, a secondary body cavity, or coelom, is formed.

Primary organogenesis

The process of organ formation in embryonic development is called organogenesis... Several tissues are involved in the construction of any organ. Therefore, the stage of organogenesis is also the stage of histogenesis.

Organogenesis can be divided into two phases:

neurulation- the formation of a complex of axial organs (neural tube, notochord, intestinal tube and mesoderm of somites), in which almost the entire embryo is involved;

the construction of other organs, the acquisition by various parts of the body of their typical shape and features of the internal organization, the establishment of certain proportions (spatially limited processes).

According to Karl Baer's theory of germ layers, the emergence of organs is due to the transformation of one or another germ layer - ecto-, meso- or endoderm. Some organs can be of mixed origin, that is, they are formed with the participation of several germ layers at once. For example, the musculature of the digestive tract is a derivative of the mesoderm, and its inner lining is a derivative of the endoderm. However, simplifying somewhat, the origin of the main organs and their systems can still be associated with certain germ layers.

Neurulation

The embryo at the stage of neurulation is called neurula(fig. 317). The material used to build the nervous system in vertebrates - neuroectoderm, is part of the dorsal (dorsal) part of the ectoderm. It is located above the

Rice. 317. Neirula:

1 - ectoderm; 2 - chord; 3 - secondary body cavity; 4 - mesoderm; 5 - endoderm; 6 - intestinal cavity; 7 - neural tube.

chord chat. The interaction of these primordia

is one of the most important in all development. First, in the area of ​​the neuroectoderm, a flattening of the cell layer occurs, which leads to the formation neural plate... Then the edges of the neural plate thicken and rise, forming nerve rollers... In the center of the plate, due to the movement of cells along the midline, nerve groove dividing the embryo into the future right and left halves. The neural plate begins to fold along the midline. Its edges touch and then close. As a result of these processes, a neural tube with a cavity appears - neurocele .

The closure of the ridges occurs first in the middle, and then in the back of the nerve groove. This happens last at the head, which is wider than the others. The anterior, expanded section further forms the brain, the rest of the neural tube - the dorsal. As a result, the neural plate turns into a neural tube that lies under the ectoderm.

During neurulation, some of the cells of the neural plate are not part of the neural tube. They form ganglion plate, or neural crest, - an accumulation of cells along the neural tube. Later, these cells migrate throughout the embryo, forming cells of nerve nodes, adrenal medulla, pigment cells, etc.

Organ systems formation

From material ectoderm In addition to the neural tube, the epidermis and its derivatives (feather, hair, nails, claws, skin glands, etc.), components of the organs of vision, hearing, smell, oral epithelium, and tooth enamel develop.

The mesodermal and endodermal organs are not formed after the formation of the neural tube, but simultaneously with it. Almost simultaneously with neurulation, the processes of laying the mesoderm and notochord take place. Initially, pockets or folds are formed along the lateral walls of the primary intestine by protruding the endoderm. The portion of the endoderm located between these folds thickens, sags, folds and detaches from the bulk of the endoderm. This is how it appears chord... The resulting pocket-like protrusions of the endoderm are detached from the primary intestine and turn into a series of segmented closed sacs, also called coelomic bags. Their walls are formed by mesoderm, and the cavity inside is a secondary body cavity (or the whole).

All types of connective tissue, dermis, skeleton, striated and smooth muscles, circulatory and lymphatic systems, and the reproductive system develop from the mesoderm.

The epithelium of the intestine and stomach, liver cells, secreting cells of the pancreas, intestinal and gastric glands develop from the material of the endoderm. The anterior section of the embryonic intestine forms the epithelium of the lungs and airways, secreting sections of the anterior and middle lobe of the pituitary gland, thyroid and parathyroid glands.

Embryonic induction

Observations of a fertilized frog egg made it possible to trace the path of development of cells that make up a particular part of the embryo. It turned out that certain cells, which occupy a corresponding place in the blastula, give rise to strictly defined organ rudiments. It was possible to find out which groups of cells give rise to the neural tube, chord, mesoderm, skin epithelium, etc. Indeed, in a developing organism, various groups of cells give rise to certain organs and tissues, and the cultivation of cells outside the embryo (in a test tube) does not lead to the formation of typical tissue structures that should have been formed from cells. What causes the transformation of certain cells of the embryo into specific tissues and organs?

In 1924, the results of the experiments of G. Spemann and G. Mangold, devoted to clarifying this issue, were published (Fig. 318). At the stage of early gastrula, the rudiment of the ectoderm, which under normal conditions should have developed into the structures of the nervous system, was transplanted from the embryo of the comb-like (unpigmented) newt under the ectoderm of the ventral side, giving rise to the epidermis of the skin, the embryo of the common (pigmented) newt. As a result, the neural tube and other components of the complex of axial organs first appeared on the abdominal side of the recipient embryo, and then an additional embryo was formed. Moreover, observations have shown that the tissues of the additional embryo are formed almost exclusively from the cellular material of the recipient.

These data prove that during embryogenesis, some parts of the embryo influence the developmental pathways of neighboring areas. This influence of one rudiment on another is called embryonic induction... How important is the role of embryonic induction in development is shown by the following experience. If at the stage of early gastrula is completely removed

Fig. 318. Embryonic induction:

1 - primordium of chordomesoderm; 2 - blastula cavity; 3 - induced neural tube; 4 - induced chord; 5 - primary neural tube; 6 - primary chord; 7 - the formation of a secondary embryo connected to the host embryo.

the primordium of the notochord, the neural tube does not develop at all. The ectoderm on the dorsal side of the embryo, from which the neural tube normally forms, forms the cutaneous epithelium.

Upon further study of the development of the embryos, it turned out that the anlage of the chordomesoderm is not only an inductor of the neural tube, but itself, for differentiation, needs an inducing influence from the primordium of the nervous system. During embryonic development, it is not unilateral induction that takes place, but the interaction of parts of the developing embryo. Thus, embryonic induction can be defined as a phenomenon in which, in the process of embryogenesis, one primordium affects another, determining the path of its development, and, in addition, itself is subjected to an inducing effect from the first primordium.

38.6. Postembryonic development

The postembryonic period of development begins at the moment of birth or release of the organism from the egg membranes and continues until its death. Postembryonic development includes:

body growth;

establishing the final proportions of the body;

transition of organ systems to the regime of an adult organism (in particular, puberty).

Types of postembryonic development

There are two main types of postembryonic development:

Direct, in which an individual emerges from the mother's body or egg membranes, which differs from the adult only in its smaller size (birds, mammals). Distinguish:

nonlarge(ovipositor) type in which the embryo develops inside the egg (fish, bird);

Rice. 319. Frog Development

intrauterine the type in which the embryo develops inside the mother's body and is connected to it through the placenta (placental mammals).

With the transformation(metamorphosis), in which a larva emerges from the egg, arranged simpler than an adult animal (sometimes very different from it); as a rule, it has special larval organs that are absent in an adult animal, and is not capable of reproduction; often the larva leads a different way of life than the adult animal (insects, some arachnids, amphibians).

An example of animals with postembryonic development with metamorphosis are tailless amphibians (Fig. 319). A larva emerges from the egg shells of amphibians - a tadpole, more reminiscent of a fish than an amphibian. It has a streamlined body, caudal fin, gill slits and gills, lateral line organs, two-chambered heart, one circle of blood circulation. Over time, under the influence of the thyroid hormone, the tadpole undergoes metamorphosis. His tail dissolves, limbs appear,

the lateral line disappears, the lungs and the second circle of blood circulation develop, that is, gradually it acquires signs characteristic of amphibians.

excretory system

reproductive system

Embryonic induction.

The experiments of G. Spemann

Embryonic induction- a phenomenon in which, in the process of embryogenesis, one rudiment affects another, determining the path of its development

1 - primordium of chordomesoderm

2 - blastula cavity

3 - induced neural tube

4 - induced chord

5 - primary neural tube

6 - primary chord

7 - the formation of a secondary embryo connected to the host embryo.

Embryonic induction

38.6. Postembryonic development

The postembryonic period of development begins at the moment of birth or release of the organism from the egg membranes and continues until its death. Postembryonic development includes:

body growth;

establishing the final proportions of the body;

transition of organ systems to the regime of an adult organism (in particular, puberty).

Types of postembryonic development

There are two main types of postembryonic development:

Direct, in which an individual emerges from the mother's body or egg membranes, which differs from the adult only in its smaller size (birds, mammals). Distinguish:

nonlarge(ovipositor) type in which the embryo develops inside the egg (fish, bird);

Rice. 319. Frog Development

intrauterine the type in which the embryo develops inside the mother's body and is connected to it through the placenta (placental mammals).

With the transformation(metamorphosis), in which a larva emerges from the egg, arranged simpler than an adult animal (sometimes very different from it); as a rule, it has special larval organs that are absent in an adult animal, and is not capable of reproduction; often the larva leads a different way of life than the adult animal (insects, some arachnids, amphibians).

An example of animals with postembryonic development with metamorphosis are tailless amphibians (Fig. 319). A larva emerges from the egg shells of amphibians - a tadpole, more reminiscent of a fish than an amphibian. It has a streamlined body, caudal fin, gill slits and gills, lateral line organs, two-chambered heart, one circle of blood circulation. Over time, under the influence of the thyroid hormone, the tadpole undergoes metamorphosis. His tail dissolves, limbs appear,

the lateral line disappears, the lungs and the second circle of blood circulation develop, that is, gradually it acquires signs characteristic of amphibians.

Five week embryo

has the rudiments of all organs. It rests snugly in a fluid-filled amniotic sac.

Through the umbilical cord, it is connected to the placenta, a lozenge-like organ on the wall of the uterus.

Through the placenta, the embryo receives oxygen and nutrients from the mother's body, and gives off carbon dioxide and decay products.

Second month (6 weeks): the embryo has all the internal organs. His heart is beating, brain cells are working. The weight of the embryo is 30 g.

Third month (10 weeks): the fetus is fully formed. He knows how to suck his thumb, feels pain.

Fifth month (19 weeks).

The child actively moves and responds to sounds.

Seventh month (28 weeks).

The child is preparing for an independent life. He falls asleep and wakes up with his mother, listening to her voice.

Historical reference

Founder of modern embryology - Academician of the Russian Academy Karl Maksimovich Baer (1792 -1876) .

man develops according to a single plan with all vertebrates.

At the beginning of the twentieth century. Fritz Müller (1821 - 1897) and Ernst Haeckel (1834 - 1919) have formulated biogenetic law:

individual development of each individual ( ontogenesis) there is a short and quick repetition of historical development ( phylogenesis ) of the form

Alexey Nikolaevich Severtsov (1866 - 1936) clarified the wording:

"The signs are repeated not adult ancestors, but their embryos. "

Repetition

Repetition

• What is indicated in the figure by numbers 1-9?
• What is typical for the period of blastulation?
• What is the name of mammalian blastula?
• What is formed from blastocoel in animals?

Repetition

• What are the processes shown in the figure?
• What is typical for the period of gastrulation?
• When can a fetus be called a neurula?
• How is neurula formed?

Repetition

• What is indicated in the figure by numbers 10-11?
• What experience did G. Spemann conduct?

1 of 32

Presentation on the topic: critical periods of pregnancy

Slide No. 1

Slide Description:

STATE MEDICAL UNIVERSITY OF SEMEY CITY DEPARTMENT OF MOLECULAR BIOLOGY AND MEDICAL GENETICS OF CDS Topic: "Critical periods of embryonic development. Teratogenic factors. Teratogenesis" Completed: student A.K. Bolatova. Omf, 123 group Checked: Semey-2013

Slide No. 2

Slide Description:

Plan 1. Introduction 2. Critical periods of embryonic development 3. Influence of teratogenic factors 4. Teratogenic factors in embryology a) Physical factors b) Chemical factors c) Viral effects on the fetus d) Endocrine diseases of the mother 5. Conclusion 6. List of used literature

Slide No. 3

Slide Description:

Introduction Human development is a complex biological process, which is a set of regular, interconnected, characterized by a certain temporal sequence of structural, physiological and metabolic changes from primordia with a simple structure to complex organs. This process of human development is commonly referred to as ontogenesis. The term "ontogeny" was introduced by E. Haeckel (1866) when he formulated the biogenetic law. Ontogenesis includes growth, that is, an increase in body weight, size, differentiation. Ontogenesis is based on a complex process of realization at different stages of the organism's development of hereditary information embedded in each of its cells.

Slide No. 4

Slide Description:

Embryonic development is the development of an organism from fertilization to birth. Embryonic development is possible only with an optimal combination of internal and external conditions. Each subsequent stage of development of an embryo or fetus follows from the previous one and from the current conditions of development. If some external or internal condition is not enough, or if an unusual external factor arises that can dramatically affect the course of fetal development, embryogenesis may deviate from the normal path.

Slide No. 5

Slide Description:

"Critical periods" - what does it mean? Critical periods of pregnancy, or critical periods in the development of the embryo and fetus, are those periods when their sensitivity increases, and adaptive capabilities decrease and the embryo becomes especially vulnerable. These periods are characterized by active cellular and tissue processes and a significant increase in metabolism.

Slide No. 6

Slide Description:

In human embiogenesis, critical periods include: 1) fertilization; 2) implantation (7 - 8th day of embryogenesis); 3) development of the axial complex of organ rudiments and placentation (3 - 8 weeks); 4) development of the brain (15 - 20 weeks); 5) the formation of the main body systems, including the reproductive system (20-24 weeks). During these periods, the occurrence of various anomalies and malformations in the fetus is most likely.

Slide No. 7

Slide Description:

Also, critical periods can be called certain periods of pregnancy, when the danger of its termination is especially high. As a rule, the threat of miscarriage at these periods is due to the usual physiological processes, which become pathological under the influence of unfavorable factors. For each critical period, the most characteristic causes of abortion can be identified.

Slide No. 8

Slide Description:

The effect of unfavorable environmental factors: A) lack of oxygen (hypoxia), B) hypothermia, C) overheating, D) medical preparations, E) toxins, E) products of chemical production, G) causative agents of viral and bacterial infections, etc., Depending on the stage of development of the embryo, it can be extremely dangerous and even destructive for it.

Slide No. 9

Slide Description:

Slide No. 10

Slide Description:

Slide No. 11

Slide Description:

At this time, implantation of the ovum occurs, i.e. its introduction into the lining of the uterus. The implantation process can be disrupted: - with anomalies in the structure of the uterus (infantilism, two-horned or saddle uterus, the presence of a septum in the uterine cavity); - with injuries of the endometrium, i.e. the inner layer of the uterus as a result of artificial abortion and inflammatory diseases (chronic endometritis); - in the presence of uterine fibroids; - with a scar on the uterus after cesarean section and other operations.

Slide No. 12

Slide Description:

Slide No. 13

Slide Description:

Slide No. 14

Slide Description:

Dysfunction of the ovaries can be congenital or a consequence of abortion, inflammation or dysfunction of other endocrine glands - the pituitary gland, adrenal glands, thyroid gland. Most often, there is a lack of progesterone - the ovarian hormone necessary to maintain pregnancy in its early stages.

Slide No. 15

Slide Description:

A decrease in progesterone levels leads to the threat of termination of pregnancy. In some cases, both the level of progesterone and other ovarian hormones, especially estrogens, may be initially lowered. The latter, in particular, affect the growth and development of the uterus. With a lack of estrogen, there is an underdevelopment of the uterus and its mucous membrane - the endometrium. After fertilization, the ovum is implanted into the endometrium. If it is not developed enough, then the process of embryo introduction into the wall of the uterus may be disrupted, which leads to miscarriage.

Slide No. 16

Slide Description:

Slide No. 17

Slide Description:

At this stage, the danger is the low location and placenta previa (complete, incomplete). If a woman still had the pathological phenomena described above in the first trimester, and any infectious diseases were found, then the placenta becomes vulnerable, and an incorrect location can provoke its detachment and bleeding.

Slide No. 18

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3. Isthmic - cervical insufficiency Isthmic-cervical insufficiency is a pathology of the cervix, in which it is unable to perform this function. Under the influence of gravity, the ovum gradually descends, the cervix opens and ... pregnancy is terminated To eliminate isthmic-cervical insufficiency, it is necessary to put a suture on the cervix before the critical period

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Slide No. 20

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The next stage of intensive growth of the fetus and uterus falls on a period of 28-32 weeks. Violation of the development of pregnancy during these periods can cause complications such as late gestosis, placental insufficiency and placental abruption. Termination of pregnancy at this time is called preterm labor. the child is born viable, but his condition requires serious rehabilitation

Slide No. 21

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Slide No. 22

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Influence of teratogenic factors. The study of the epidemiology of congenital malformations (CM) is an urgent problem of modern medicine. CDMs rank second or third in the structure of infant mortality. Moreover, the lower the infant mortality rate, the greater the role of congenital anomalies in it. The so-called teratogenic factors play an important role in the occurrence of congenital malformations. Teratology is a science that studies the causes, development and prevention of congenital malformations. The term "congenital defects" should be understood as persistent morphological changes in an organ or the whole organism that go beyond the variation of their structures. Development EPs arise in utero as a result of a violation of the developmental processes of the embryo or (much less often) after the birth of a child, as a result of a violation of the further formation of organs.

Slide No. 23

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Teratogenic factors in embryology 1) Physical factors. a) radiation exposure. Ionizing radiation does not give a specific complex of defects, however, most often in such cases, defects of the nervous system and skull are observed. b) mechanical impact. Possibly abnormal formation of fetal organs (there are congenital amputations of fingers or feet, fusion of individual organs, etc.). In some cases, fetal death may occur. 2) Chemical factors. All researchers agree that it is better not to prescribe chemicals, including medicines, to pregnant women until clinical testing for teratogenicity. But if the use of drugs is necessary, then one should take into account the chemical structure of the substance, its ability to overcome the placental barrier, the total and one-time dose of a substance introduced into the body of a pregnant woman, and the rate of spread of the substance. The dose of the substance is of great importance. It is also important how the medication is administered: in fractional doses and a "shock" dose of the drug is received repeatedly or in a short period of time

Slide No. 24

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Chemicals used in everyday life and industry The greatest interest of researchers was attracted by alcohol. The importance of the mother's chronic alcoholism in the origin of congenital malformations has long been pointed out. Back in 1959 L.A. Bogdanovich wrote that in women who chronically consume alcoholic beverages, children are born prematurely in 34.5% of cases, physically weakened in 19%, and developmental EPs are observed in 3% of cases. In such cases, children are born with a deficit in height, body weight, general retardation of physical and mental development. The central nervous system was frequently affected. Heart and kidney defects are not uncommon

Slide No. 25

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The causal relationship between smoking and congenital malformations has not been established, however, it is known that the body weight of newborns in mothers who smoke are lower than in non-smokers, ruptures of the membranes and premature placental abruption are more common. This is all explained by the direct effect of nicotine on the mother's blood vessels and a change in the composition of the mother's blood. Gasoline, benzene, phenols, nitric oxide, many pesticides, as well as lead and mercury vapor, widely used in industry and agriculture, have embryotoxic properties. Their exposure can cause the death of the fetus or the birth of a weakened child.

Slide No. 26

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Drugs. Substances of different chemical groups have a different effect on the mother's body, and as a result, on the fetus. Opiates have a mosaic effect (some centers activate, others inhibit). Cocaine, hemp drugs cause hallucinations. Common to all groups of drugs: they cause strong addiction, especially opiates, both mental (due to euphoria) and physical (so embedded in the metabolism, mediator processes of the brain, that when deprived of the drug cause "withdrawal" - an abstructive syndrome. All groups drugs are addictive - for euphoria it is required to increase the dose Paralyze the will, social functions, lead to crime (get a dose) When morphine and its analogues are injected, the respiratory center is strongly inhibited, deaths from respiratory arrest are not uncommon.

Slide No. 27

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3) Viral effects. Almost all genital infections can lead to premature termination of pregnancy, intrauterine infection of the fetus and infection of the newborn during childbirth. Syphilis is passed from mother to fetus. Microorganisms that cause syphilis affect the fetus, quickly penetrating almost all of its tissues and organs, destroying the kidneys, liver, blood vessels, and lungs. If the child survives, then the threat of acute pneumonia or loss of vision will constantly hang over him. Acquired Immune Deficiency Syndrome (AIDS). Identification of HIV infection during pregnancy poses a threat not only to the expectant mother, but also to her child. A large percentage (according to experts from 20 to 65%) of children born to mothers - carriers of the HIV virus, already within the first 6 months after birth, bear signs of developing infection. During pregnancy, a mother can pass the virus from her bloodstream through the placenta to the fetus.

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List of used literature: Beckman D.A., Brent R.L. The mechanism of teratogenesis. - M .: "Medicine", 1992 Shepard T. H. "Catalog of teratogenic factors", 1992 Physiology of child development / Ed. V.I.Kozlova and D.A. Farber. - M .: Education, 1983 Davydov I.O., Kalpunov G.S. Critical periods of development. - SPb .: "Phoenix", 2004 Great Medical Encyclopedia, vol. 2, ed. "Young Medic", 1998 Gorenov A.V. Major fetal malformations. - M .: "AstraMed", 2001 Langmur TS, Saprikonova S.Ya. Course of embryology, histology. - M .: "Medicine", 1995

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