The main questions of the topic. Features of ontogenesis characteristic of humans. Reproductive health What type of ontogeny is characteristic for humans

Remember!

What type of development is typical for a person?

Direct development - this type of development is characteristic of organisms whose cubs are born already similar to adults. Direct intrauterine development.

What is the placenta?

The placenta ("baby's place") is the most important and absolutely unique organ that exists only during pregnancy. It connects two organisms - mother and fetus, providing it with the necessary nutrients.

How does the mother's lifestyle during pregnancy affect the health of the unborn child?

Throughout the entire time of intrauterine development, the fetus, directly connected with the mother's body through a unique organ - the placenta, is in constant dependence on the state of the mother's health. There has been a lot of controversy lately over whether smoking affects the unborn child. It is known that nicotine entering the mother's blood easily penetrates through the placenta into the fetal circulatory system and causes vasoconstriction. If blood supply to the fetus is limited, then its supply of oxygen and nutrients decreases, which can cause developmental delay. In women who smoke, a child at birth weighs an average of 300-350 g less than normal. There are other problems associated with smoking during pregnancy. These women are more likely to have premature births and miscarriages in late pregnancy. Children whose mothers were unable to quit cigarettes during pregnancy are 30% more likely to have early infant mortality and 50% more likely to develop heart defects.

Alcohol passes through the placenta just as easily. Drinking alcohol during pregnancy can cause the baby to develop a condition known as fetal alcohol syndrome. With this syndrome, mental retardation, microcephaly (underdevelopment of the brain), behavioral disorders (increased excitability, inability to concentrate), decreased growth rate, and muscle weakness are observed. Viral diseases of the mother during pregnancy pose a serious danger to the development of the fetus. The most dangerous are rubella, hepatitis B and HIV infection. In the case of rubella infection in the first month of pregnancy, 50% of children develop congenital defects: blindness, deafness, nervous system disorders and heart defects.

Review questions and assignments

1. Name the features of ontogenesis characteristic of humans. What are the benefits of these features?

1) Embryonic The process of human embryonic development lasts about 280 days and is divided into three periods: initial (1st week), embryonic (2-8 weeks) and fetal (from the 9th week to birth).

2) Postembryonic: divided into three periods: pre-reproductive, maturity (reproductive) and aging (post-reproductive).

Such features provide maximum survival and adaptation to the environmental conditions of the offspring.

2. How do nicotine, alcohol and drugs affect the development of the human embryo?

There has been a lot of controversy lately over whether smoking affects the unborn child. It is known that nicotine entering the mother's blood easily penetrates through the placenta into the fetal circulatory system and causes vasoconstriction. If blood supply to the fetus is limited, then its supply of oxygen and nutrients decreases, which can cause developmental delay. In women who smoke, a child at birth weighs an average of 300-350 g less than normal. There are other problems associated with smoking during pregnancy. These women are more likely to have premature births and miscarriages in late pregnancy. Children whose mothers were unable to quit cigarettes during pregnancy are 30% more likely to have early infant mortality and 50% more likely to develop heart defects. Alcohol passes through the placenta just as easily. Drinking alcohol during pregnancy can cause the baby to develop a condition known as fetal alcohol syndrome. With this syndrome, mental retardation, microcephaly (underdevelopment of the brain), behavioral disorders (increased excitability, inability to concentrate), decreased growth rate, muscle weakness are observed

3. What environmental factors influence the development of the human embryo?

All types of environmental factors are mutagens for the development of the embryo:

Chemical - solvent, alcohols, dietary supplements, drugs, etc.

Physical - temperature, radiation (radiation)

Biological - bacteria, viruses (rubella, HIV, hepatitis, etc.)

4. Name the periods of postembryonic human development.

The most important feature of man, acquired by him in the process of evolution, is the lengthening of the pre-reproductive period. Compared to other mammals, including great apes, human maturity occurs most late. Prolonged childhood and stunted growth and development increase opportunities for learning and the acquisition of social skills. The reproductive period is the longest stage of the post-embryonic development of a person, the completion of which indicates the onset of the post-productive period, or the aging period. The aging process affects all levels of the organization of living things. Aging inevitably leads to death - the final of the individual development of organisms common to all living things. Death is a prerequisite for the change of generations, that is, for the continuation of the existence and evolution of mankind as a whole.

5. What are the developmental consequences of vitamin D deficiency and malnutrition?

Vitamins of group D are formed under the action of ultraviolet radiation in tissues of animals and plants from sterols. Vitamins of group D include:

- vitamin D2 - ergocalciferol; isolated from yeast, ergosterol is its provitamin;

- vitamin D3 - cholecalciferol; isolated from animal tissues, its provitamin - 7-dehydrocholesterol;

- vitamin D4 - 22, 23-dihydro-ergocalciferol;

- vitamin D5 - 24-ethylcholecalciferol (sitocalciferol); isolated from wheat oils;

- vitamin D6 - 22-dihydroethylcalciferol (stigma-calciferol).

Today, vitamin D is called two vitamins - D2 and D3 - ergocalciferol and cholecalciferol - these are colorless and odorless crystals that are resistant to high temperatures. These vitamins are fat-soluble, i.e. soluble in fats and organic compounds and insoluble in water. Vitamin D is formed in the skin under the influence of sunlight from provitamins. Provitamins, in turn, partly enter the body in a ready-made form from plants (ergosterol, stigmasterol and sitosterol), and partly are formed in the tissues of their cholesterol (7-dehydrocholesterol (provitamin of vitamin D3). Provided that the body receives a sufficient amount of ultraviolet radiation , the need for vitamin D is fully compensated.However, the amount of vitamin D synthesized by sunlight depends on factors such as:

- the wavelength of light (the most effective is the average wavelength spectrum, which we receive in the morning and at sunset);

- the initial pigmentation of the skin and (the darker the skin, the less vitamin D is produced by sunlight);

- age (aging skin loses its ability to synthesize vitamin D);

- the level of air pollution (industrial emissions and dust do not transmit the spectrum of ultraviolet rays, potentiating the synthesis of vitamin D, this explains, in particular, the high prevalence of rickets among children living in Africa and Asia in industrial cities).

Additional food sources of vitamin D are dairy products, fish oil, and egg yolk. However, in practice, milk and dairy products do not always contain vitamin D or contain only trace (insignificant) amounts (for example, 100 g of cow's milk contains only 0.05 mg of vitamin D), so their consumption, unfortunately, cannot guarantee coverage of our needs for this vitamin. In addition, milk contains a large amount of phosphorus, which interferes with the absorption of vitamin D. The main function of vitamin D is to ensure normal growth and development of bones, prevent rickets and osteoporosis. It regulates mineral metabolism and promotes the deposition of calcium in bone tissue and dentin, thus preventing osteomalacia (softening) of bones. Entering the body, vitamin D is absorbed in the proximal part of the small intestine, and always in the presence of bile. Part of it is absorbed in the middle parts of the small intestine, a small part in the ileum. After absorption, calciferol is found in the composition of chylomicrons in free form and only partially in the form of ether. Bioavailability is 60-90%. Vitamin D affects the general metabolism in the metabolism of Ca2 + and phosphate (HPO2-4). First of all, it stimulates the absorption of calcium, phosphates and magnesium from the intestine. An important effect of the vitamin in this process is to increase the permeability of the intestinal epithelium for Ca2 + and P. Vitamin D is unique - it is the only vitamin that acts both as a vitamin and as a hormone. As a vitamin, it maintains the level of inorganic P and Ca in the blood plasma above the threshold value and increases the absorption of Ca in the small intestine.

Symptoms of hypovitaminosis

- The main symptom of vitamin D deficiency is rickets and softening of the bones (osteomalacia).

- milder forms of vitamin D deficiency are manifested by symptoms such as:

- loss of appetite, weight loss,

- a burning sensation in the mouth and throat,

- insomnia,

- deterioration of vision.

Think! Remember!

1. Discuss in class the importance of lengthening the pre-reproductive period in human evolution.

2. For which organisms do the concepts of "cell cycle" and "ontogeny" coincide?

For unicellular organisms, in which the life cycle is the life of a cell from the moment of its appearance until division or death.

4. Using additional literature and Internet resources, find out what acceleration is, what hypotheses currently exist about the causes of acceleration. Discuss in class the information you have found on this topic.

Acceleration or acceleration (from Latin acceleratio-acceleration) is the accelerated development of a living organism.

In support of acceleration, a variety of hypotheses have been proposed, which can be conditionally divided into several groups:

- First of all, nutraceutical, associated with a change (improvement) in the nature of nutrition, especially in the last three decades after the Second World War.

- Hypotheses associated with biological selection (the first reports on the accelerated development of children - Ghent, 1869; Roberts (Ch. Roberts), 1876), with an increase in the number of heterolocal (mixed) marriages - heterosis, an attraction to urban life, as a result of which the most developed inhabitants from rural areas - the hypothesis of Mauer (G. Mauer), 1887, as well as other hypotheses about constitutional selection - for example, the desire to occupy the upper strata of society or the resettlement of people with a more developed intellect to cities.

- A group of hypotheses related to the influence of environmental factors (hypotheses of the 30s) linked changes in the rate of growth and development with natural and artificial changes in environmental conditions. Koch (E. W. Koch), 1935, who proposed the term acceleration, attached importance to heliogenic influences, an increase in daylight hours due to electric lighting. Treiber (T. Treiber), 1941 associated acceleration with the influence of radio waves - although the acceleration of the growth of children began before the widespread use of radio on Earth, and Mills (C. A. Mills), 1950 - with an increase in the temperature of the Earth's atmosphere. There are other hypotheses, for example, related to radiation or cosmic radiation. But then the phenomenon had to manifest itself on all children in one locality. However, all authors note differences in the growth rate of children of different population groups.

Each of the hypotheses separately could not explain all the phenomena of the secular trend, and data on the acceleration of ontogenetic development and an increase in body size, not only in humans, but also in various animals, would have been convincing evidence.

Question 1. What are the features of ontogenesis characteristic of humans?
An intrauterine type of development is characteristic of a person. After fertilization, during cleavage, a ball appears, consisting of two types of cells: darker, located inside and slowly dividing, and lighter, located outside. In the future, the body of the embryo will be formed from dark cells, from light cells - special organs that provide communication with the mother's body (embryonic membranes, umbilical cord, etc.).
The first 5-6 days, the embryo moves through the oviduct to the uterus. Further, it penetrates into its wall and begins to receive oxygen and nutrients from the mother. By this time, the stages of blastula and gastrula have already passed. After the appearance of the third germ layer, organogenesis begins: the notochord is laid, then the neural tube, then all the other organs. Organogenesis ends by week 9; from this moment, a rapid increase in the mass of the embryo begins and it is called "fetus".
In the next four weeks of embryonic development, all major organs are laid. Violation of the developmental process during this period leads to the most severe and multiple congenital malformations.
Long-term (38-40 weeks) pregnancy, typical for a person, allows the child to be born well-formed, capable of many movements, with a developed taste, hearing, etc. Another feature of human ontogenesis is an increase in the pre-reproductive period, which expands the possibilities of learning and acquiring social skills.

Question 2. How do nicotine, alcohol and drugs affect the development of the human embryo?
When the mother enters the body, nicotine easily penetrates the fetal bloodstream through the placenta, causing the fetal vasoconstriction. This leads to a deterioration in the supply of oxygen and nutrients to the baby, which can cause developmental delay. Women who smoke are more likely to have premature births or miscarriages in late pregnancy. Nicotine increases the likelihood of infant mortality by 30% and the likelihood of developing heart defects by 50%.
Alcohol also easily crosses the placenta, causing fetal mental retardation, microcephaly, behavioral disorders, decreased growth rate, and muscle weakness. Alcohol significantly increases the likelihood of developing abnormalities in the child.
Narcotic substances have a very strong effect on the fetus. They not only cause severe disturbances in its development, but can also lead to the formation of addiction, when, after birth, the child develops a withdrawal syndrome.

Question 3. What environmental factors influence the development of the human embryo?
The development of the embryo can be influenced by:
the level of supply of the mother's body with nutrients;
ecology of the environment;
the mother's use of nicotine, alcohol, narcotic and medicinal substances;
viral diseases of the mother during pregnancy: hepatitis, HIV, rubella, etc.;
stress tolerated by the mother (strong negative emotions, excessive physical activity).

Question 4. List the periods of postembryonic human development.
Postembryonic postnatal the period of human development, otherwise called postnatal, is divided into three periods:
Juvenile (before puberty). According to the accepted periodization, the juvenile period begins after birth and lasts up to 21 years for women, and up to 22 years for men.
Mature (adults, sexually mature). The mature period of ontogenesis, according to the accepted periodization, begins in men at 22 years old, and in women at 21 years old. The first period of adulthood is up to 35 years, the second period is from 36 to 60 years for men and up to 55 years for women.
A period of old age ending in death. The aging period in men begins after 60 years, and in women after 55. According to the modern classification, people who have reached 60 - 76 years old are called elderly, 75 - 89 old, and over 90 years - long-livers. Aging affects all levels of organization of the human body: there is a violation of DNA replication and protein synthesis, the intensity of metabolism in cells decreases, their division and tissue recovery after injuries slow down, and the work of all organ systems deteriorates. However, with a reasonable diet, an active lifestyle and proper medical care, this period can be extended by several decades.
In other words, it can be said that for humans it is also possible to distinguish pre-reproductive, reproductive and post-reproductive periods of postembryonic development. It should be borne in mind that any scheme is conditional, since the actual state of two people of the same age can differ significantly. Therefore, the concept of chronological (calendar) and biological age was introduced. Biological age is determined by the totality of metabolic, structural, functional characteristics of the organism, including its adaptive capabilities. It may not correspond to the calendar one.

Question 5. What are the consequences of a lack of vitamin D and malnutrition in human development?
Vitamin deficiency D leads to a violation of phosphorus-calcium metabolism, resulting in rickets. Rickets- vitamin deficiency in childhood, a chronic disease of the whole organism, caused by a disorder of salt metabolism, mainly of phosphorus and calcium, as a result of which insufficient lime deposition in growing bones and their improper development are obtained. Vitamin deficiency in children is caused in large part by a deficiency of ultraviolet rays.
In case of an overdose of vitamin D severe toxic poisoning (hypervitaminosis) is observed: loss of appetite, nausea, vomiting, general weakness, irritability, sleep disturbance, fever, the appearance of protein, leukocytes in the urine. There are known cases of death of children from an overdose of vitamin D as a result of an increase in the level of calcium in the blood, calcification of the kidneys and heart. A blood and urine test is required.
Inadequate nutrition, and primarily a lack of animal proteins, leads to a slowdown in the growth of children and the appearance of mental disorders (mental retardation). This condition is called protein starvation. It is due to a deficiency in plant proteins of most of the essential amino acids necessary for our body. Proteins of animal origin (dairy, egg, meat, fish) can be partially replaced only by proteins of leguminous plants.

Ontogenesis is the process of individual development of various organisms from the beginning of existence to the very end of life. This term was proposed by a German scientist in 1886. In this article, we will briefly consider ontogeny, its types and their specificity in various species.

Ontogenesis of unicellular and multicellular organisms

In protozoa and bacteria, it almost coincides with. In these organisms, ontogeny begins with the emergence of a unicellular organism through division of the mother cell. This process ends with death, which occurs as a result of adverse influences, or the next division.

The ontogenesis of multicellular species that reproduce asexually begins with the separation of a group of cells from the mother's body (remember, for example, the process of hydra budding). By sharing mitosis, these cells form a new individual with all organs and systems. In sexually reproducing species, the process of ontogenesis begins with the fertilization of an egg, after which a zygote is formed, which is the first cell of a new individual.

Ontogeny is the transformation of an organism into an adult?

We hope you answered this question correctly, since at the beginning of the article the concept of interest to us is revealed. And the types of ontogenesis, and this process itself, as you remember, refer to the entire life of the organism. They cannot be reduced to the growth of an individual until it turns into an adult. Ontogenesis is a chain of complex processes that take place at all levels of the body. Their result is the formation of vital functions, structural features inherent in individuals of this species, and the ability to reproduce. Ontogenesis ends with processes that lead to aging and then to death.

The next 2 main periods are distinguished in ontogenesis - embryonic and postembryonic. On the first of them, an embryo is formed in animals. The main organ systems are being formed in him. Next comes the postembryonic period. During it, the formative processes end, then puberty occurs, then reproduction, aging and, finally, death.

Realization of hereditary information

The new individual receives a kind of instructions with the genes of the parents, which indicate what changes will occur in the body for the successful passage of its life path. Consequently, the process of interest to us is the implementation of hereditary information. Next, we will consider in more detail ontogenesis (types and their features).

Direct and indirect ontogenesis

With the direct type, the organism that was born is basically similar to the adult, there is no stage of metamorphosis. With the indirect type, a larva appears, which differs in its internal and external structure from the adult organism. It also differs in the way of movement, the nature of food, and also has a number of other features. The larva turns into an adult as a result of metamorphosis. It gives organisms great benefits. This type of development is sometimes called larval development. The direct type is found in intrauterine and non-larval forms.

Let's take a closer look at each of them.

Indirect ontogenesis: types, periods

The larvae that are born live independently. They actively feed, develop and grow. They have a number of special temporary ones that are absent in adults. The larval (indirect) type of development is complete or incomplete transformation. This division is carried out on the basis of the characteristics of metamorphosis, which characterizes this or that ontogenesis. Its types require more detailed consideration, so let's talk about them in more detail.

If we are talking about the larva born into the world, over time, it loses its larval organs and instead receives permanent ones, which are characteristic of adult organisms (remember, for example, grasshoppers). If development is carried out with complete transformation, then the larva first becomes a motionless doll. Then an adult emerges from it, which is very different from the larva (remember butterflies).

Why are larvae needed

The meaning of their existence, perhaps, lies in the fact that they do not use the same food as adults, due to which the food base of this species expands. You can compare, for example, the nutrition of caterpillars and butterflies (leaves and nectar, respectively) or tadpoles and frogs (zooplankton and insects). In addition, many species, being in the larval stage, are actively exploring new territories. Larvae, for example, are capable of swimming, which cannot be said about adults, which are practically immobile.

Development with metamorphosis in amphibians and fish

The types of development (ontogenesis) occurring with metamorphosis are characteristic of vertebrates such as amphibians and fish. For example, a tadpole (larva) is formed from the egg of a frog, which in its structure, habitat and lifestyle is very different from adults. The tadpole has gills, a tail, a lateral line organ, and a two-chambered heart. Like fish, it has one circle of blood circulation. When the larva reaches a certain level of development, its metamorphosis occurs, during which signs characteristic of an adult organism appear. This is how a tadpole turns into a frog over time.

In amphibians, the existence of the larval stage provides the opportunity to live in a different environment, as well as to use different food. A tadpole, for example, lives in water and eats plant foods. The frog, on the other hand, eats animal food and leads a mostly terrestrial life. A similar phenomenon is observed in many insects. Changing the habitat, and hence the lifestyle during the transition from the larval stage to the adult stage, reduces the intensity of the struggle for survival within a given species.

Direct type of development

We continue to describe the main types of ontogenesis and move on to the next - direct. It is also called non-large. It is intrauterine and ovipositor. Let us briefly characterize these types, the stages of ontogenesis of which differ significantly from each other.

Ovipositor type

It is observed in a number of vertebrates, as well as in birds, reptiles, fish and some mammals, in which eggs are rich in yolk. In this case, the embryo develops inside the egg for a long time. The main vital functions are carried out by the embryonic membranes - special provisional organs.

Mammals laying eggs

There are 3 types of mammals that lay eggs, which is generally not characteristic of this class. However, the young are fed with milk. This is typical of mammals in general. (pictured above), long-nosed and short-nosed echidna. They live in Australia, Tasmania and New Guinea and belong to the order Monotremes.

These animals resemble reptiles not only by laying eggs, but also by the structure of the excretory, reproductive and digestive systems, as well as many anatomical features (the structure of the spine, ribs and shoulder girdle, the structure of the eye). Monotremes, however, are classified as mammals, since their heart has 4 chambers, they are warm-blooded, covered with fur, and feed their young with milk. In addition, mammals are characterized by a number of structural features of their skeleton.

Intrauterine type

The topic "Types of ontogenesis and their characteristics" is practically disclosed by us. However, we have not yet talked about the last, intrauterine type. It is characteristic of humans and higher mammals, in whose eggs there is practically no protein. In this case, all vital functions of the formed embryo are realized through the maternal organism. For this purpose, the placenta, a special provisional organ, develops from the tissues of the embryo and the mother.

Placenta

This organ only exists during pregnancy. The placenta in humans is located in the body of the uterus more often along its back wall, less often along the front. It is fully formed at about 15-16 weeks of gestation. At the 20th week, an active exchange begins to occur through the placental vessels.

The human placenta is a round, flat disc. By the time of delivery, its mass is about 500-600 g, its thickness is 2-3 cm, and its diameter is 15-18 cm. The placenta has 2 surfaces: fruit and maternal.

At the end of pregnancy, a physiological one occurs. It is accompanied by the appearance of areas of salt deposition, a reduction in the area of the exchange surface. Ontogenesis continues with the process of childbearing.

The types that we have considered have only been briefly described. We hope you have found all the information you need in this article. The definition and types of ontogeny should be well known if you are preparing for the exam in biology.

1. The concept of ontogeny, its types, periods and characteristic features in animals and humans.

2. The concept of embryogenesis. Embryonic similarity law, biogenetic law, phylembryogenesis theory.

3. Stages of embryogenesis.

4. Classification of eggs and types of crushing, give examples.

5. Crushing, its characteristics in different animals. Blastula types.

6. Gastrula, its structure and methods of education.

7. Methods for the formation of mesoderm.

8. Laying of axial organs. Neirula, its structure in animals.

9. Histo- and organogenesis. Embryonic induction concept.

10. Provisional organs of the embryo.

11. Critical periods of development.

Motivational characteristics. The study of the patterns of embryonic development using the example of the development of vertebrate embryos helps to understand the complex mechanisms of embryogenesis in humans. It is important to know that in the development of the embryo there are critical periods of development when the risk of intrauterine death or development along a pathological path increases sharply.

BRIEF CONTENT OF THE TOPIC

Individual development of an organism, or ontogenesis, - it is a set of successive morphological, physiological and biochemical transformations that the body undergoes from the moment of its inception to death. In ontogenesis, the hereditary information received by the body from the parents is realized.

There are the following main types of ontogenesis: indirect and direct. Indirect development occurs in the larval form, and direct development in non-larval and intrauterine forms.

Nonlarge the type of development takes place in fish, reptiles, birds, whose eggs are rich in yolk. Nutrition, respiration and excretion in these embryos are carried out by the provisional organs developing in them.

Intrauterine the type of development is characteristic of higher mammals and humans. Mammalian eggs contain a small amount of yolk, all vital functions of the embryo are carried out through the maternal organism. In this regard, complex provisional organs, primarily the placenta, are formed from the tissues of the mother and the embryo. This is the latest type of ontogeny in phylogenetic terms.

Periodization of ontogenesis. In ontogenesis, there are two main periods - embryonic and postembryonic. For higher animals and humans, the division into prenatal (before birth), intranatal (during birth) and postnatal (after birth) is accepted. Ontogenesis is due to the long-term process of phylogenetic development of each species. The relationship between individual and historical development is reflected in the following laws.

Embryonic Similarity Law (K. Baer)- in the process of embryonic development, first of all, common typical signs are found, and then particular signs of a class, order, family appear, and last of all, signs of a genus and species.

Biogenetic law (E. Haeckel) - ontogeny is a brief repetition of phylogeny. This means that in individual development one can observe ancestral traits - palingenesis. For example: the formation of a notochord, gill slits, etc. in mammalian embryos. However, in the course of evolution, new signs appear - cenogenesis (the formation of provisional organs or extraembryonic organs in fish, birds, mammals).

Theory of phylembryogenesis (A.N.Severtsov) - repetition in the course of embryonic development of certain signs of lower-organized animals. An example of recapitulation in human embryogenesis is the change of three forms of the skeleton (notochord, cartilaginous skeleton and bone skeleton), the formation and preservation of the tail up to three months of age of the fetus, etc.

The embryonic period begins with the formation of a zygote and ends with the birth or exit from the egg or embryonic membranes of a young individual. Embryogenesis- This is a complex and long-term morphogenetic process, during which a new multicellular organism is formed from the paternal and maternal germ cells, capable of independent life in the external environment. The embryonic period can be represented as a series of biological processes successively replacing each other.

Splitting up- a series of repeated mitotic divisions of the zygote and its daughter cells - blastomeres without their subsequent growth to the size of the mother cell. New cells do not diverge, but closely adjoin each other. The crushing rhythm depends on the type of animal and ranges from tens of minutes to ten or more hours. The crushing rate is not kept constant, but is regulated by many factors. With the radial method of crushing, the first and second strips (furrows) of crushing run in the meridial plane, but the crushing stripes are at right angles to each other. The plane of the third crushing strip lies at right angles to the planes of the first two crushing strips and the main axis of the egg (latitudinal or equatorial). The alternation of meridian and latitudinal cleavage bands causes an increase in the number of blastomeres. In some vertebrates, a tangential cleavage band appears that runs parallel to the surface of the cell cluster. The nature of cleavage is determined by the amount of yolk and its different distribution in the cytoplasm of the egg.

Oocyte classification by yolk count

§ Alecital, oligolecital, with a small amount of yolk (lancelet)

§ Mesolecital with an average amount of yolk (sturgeon fish, amphibians)

§ Polylecital, with a large amount of yolk (reptiles, birds, oviparous mammals)

Oocyte classification by yolk distribution by egg volume

Telolecital- the amount of yolk increases from the animal pole to the vegetative one; it is found in mollusks, amphibians, reptiles and birds.

Isolecital (homolecital)- yolk granules are evenly distributed in the thickness of the egg, typical of lower chordates and mammals.

Centrolecytal eggs are found in insects. In them, the cytoplasm, free from yolk granules, is located immediately under the egg shell, around the nucleus, which occupies a central position, and in the form of thin strands connecting the named areas, the intermediate space is filled with yolk.

Classification of crushing types

1. Holoblastic type - complete separation of the egg and blastomeres by cleavage furrows (a-, oligo-, mesolecitic, isocyte oocytes).

2. Meroblastic type - partial separation of the egg. Cleavage furrows penetrate deep into the egg, but do not completely separate it. The yolk remains undivided.

- Surface crushing(polyilecital, centrolecytic oocytes) - separation of the surface layer of the cytoplasm with single (previously repeatedly divided) nuclei by means of partitions directed towards the surface of the egg. The central part of the egg remains intact.

- Discoidal crushing(polyilecital, telolecital eggs) - grooves are formed following the division of nuclei, but they do not divide the whole egg, but only one of its poles.

Based on the volumes resulting from crushing.

- Uniform- the volumes of blastomeres are the same.

- Uneven- the volumes of blastomeres are not the same.

On the basis of the duration of karyo - and cytotomy in different blastomeres of the cleaving egg.

- Synchronous- cleavage begins and ends in all blastomeres simultaneously.

- Asynchronous- the onset and time of division in different blastomeres is not the same.

Based on the relative position of blastomeres in the cleaving egg.

- Radial- the relative position of the blastomeres is such that the initial polar axis of the egg serves as the axis of radial symmetry of the cleaving embryo.

- Spiral- progressive violation of the symmetry of the cleaving egg as a result of spiral displacement, completing its division of blastomeres relative to each other.

- Bilateral- blastomeres are located so that only one plane of symmetry can be drawn through the embryo.

- Anarchic- lack of regularity in the arrangement of blastomeres in organisms of the same species.

In placental mammals and humans, the ovum is low-yolk - secondary isocytic. The cleavage is complete, however, according to the nature of the structure of blastomeres and the regularities of the appearance of new blastomeres, it is classified as uneven asynchronous. Thus, the main result of the cleavage process is an increase in the number of embryonic cells to such a critical value, at which mechanical stresses begin to appear in the cell layers, initiating the movement of cells to certain areas of the embryo. Crushing ends in formation blastula- a multicellular structure with a more or less pronounced cavity inside (blastocoel).

Blastul classification

Celloblastula consists of a single-layer blastoderm with more or less identical blastomeres and a large blastocele inside, formed as a result of complete uniform cleavage.

Amphiblastula consists of unequal micromeres and macromeres. The blastocoel is small and shifted towards the animal pole.

Periblastula does not have a blastocoel and is formed as a result of surface crushing.

Discoblastula is a disc of blastomeres lying on an unbroken yolk. Formed due to incomplete discoidal cleavage. A blastula in the form of a two-layer plate with a slit cavity is called crying. There are no differences between the blastomeres of the blastula associated with differential gene activity. Blastomeres differ in size, amount of yolk, quality of cytoplasmic inclusions, and their location in the embryo.

In mammals, as a result of complete asynchronous cleavage, an embryonic vesicle or blastocyst. In blastula, a wall is distinguished - a blastoderm, and a cavity - a blastocoel, filled with fluid. In turn, the roof (animal pole of cleavage), the bottom (vegetative pole of cleavage), the marginal zone located between the two above-mentioned parts of the blastula are distinguished in the blastoderm.

Gastrulation. The result of active cell division, growth and directional movements (migrations) of cell flows with the formation of a multilayer embryo, or gastrula (the emergence of layer-by-layer, separated from each other by a distinct gap of germ layers: external - ectoderm, middle - mesoderm, internal - endoderm).

The movement of cells occurs in a strictly defined area of the embryo - in the area of the sickle. The latter was described by W. Roux in 1888; in a fertilized amphibian egg, a gray sickle appears as a colored area on the side opposite to the penetration of sperm. This site is believed to be the location of the factors necessary for gastrulation.

In different vertebrates, gastrulation occurs in several ways.

Immigration- groups of blastoderm cells move out either unipolarly or multipolarly and form endoderm (sponges, coelenterates).

Intussusception- protrusion of the vegetative pole towards the animal, by compression and displacement of the blastocoel and the formation of a gastrocoel (lancelet). The resulting cavity of the primary intestine (gastrocoel) communicates with the external environment blastopore (primary mouth).

Epibolia- overgrowth of the vegetative pole of the blastula with animal (due to the multiplication of small animal cells and their sliding over the surface of large vegetative cells). This method is typical for arthropods.

Delamination- splitting of the blastodisc with the formation of the outer (epiblast) and inner (hypoblast) sheets. Delamination is noted in many invertebrates and higher vertebrates. With any method of gastrulation, the leading forces are uneven cell proliferation in different parts of the embryo, the level of metabolic processes in cells located in different parts of the embryo, the activity of amoeboid cell movements, as well as inductive factors (proteins, nucleoproteins, steroids, etc.).

In mammals, during the cleavage period, early isolation of cells that form extraembryonic structures occurs. This is interpreted as an evolutionary acquisition associated with the intrauterine mode of development of mammals. For example, in primates, during the first three days after fertilization, the embryo moves along the fallopian tube and by the end of 4 days there is a well-developed trophoblast. After 5 days, the embryo enters the uterus and is implanted on the 6-7th day. Embryo implantation proceeds in parallel with gastrulation. However, it is advisable to describe these processes separately.

Implantation. From the earliest stages of development to the end of pregnancy, the human embryo needs a close connection with the mother's body. Such a connection is established due to the immersion (implantation) of the blastocyst into the mucous membrane of the uterus and the subsequent formation of special extraembryonic organs - the fetal part of the placenta and umbilical cord. In humans, implantation is submerged or interstitial. This means that the blastocyst completely goes deep into the mucous membrane of the uterus and continues its development there. Implantation is carried out quite quickly - in one day the blastocyst is immersed in the endometrium by almost half, and after 40 hours - completely.

Implantation conventionally consists of two phases:

1. The phase of adhesion (adhesion) of the blastocyst to the uterine mucosa.

2. The phase of immersion (invasion) of the blastocyst into the depth of the mucosa.

On the 6th day of embryogenesis, the blastocyst adheres to the endometrial epithelium (usually by the embryonic pole in the posterior or ventral wall at the uterine angle). This topography of attachment is extremely important, because later in this area the placenta will form, which only with this arrangement will be born during childbirth after the baby, without disrupting its supply of oxygen and nutrients. If adhesion and invasion occur in the lower segment of the uterus, then this will lead to low attachment (presentation) of the placenta and its premature detachment during labor, followed by the occurrence of hypoxia (or even asphyxia) of the fetus.

Implantation should not be considered as a unidirectional effect of the embryo on the uterine mucosa - it is a process of complex physiological interaction between blastocytes and endometrium. So, in the adhesion of blastocytes, an important role is played by substances of the integrin group, produced by epithelial cells of the uterine mucosa. Normally, a woman has between 19-24 days of the menstrual cycle, i.e. at the most optimal time for interaction with the blastocyst, the expression of the integrin gene is observed in the epithelial cells of the uterine mucosa. As it invades the uterine mucosa, the embryonic trophoblast synthesizes different isoforms of integrins, which provide consistent (as immersion) reception and communication of the trophoblast with elements of the uterine mucosa (epithelium, basement membrane, intercellular substance of the endometrial stroma). At the same time, during different periods of immersion, the synthesis of different groups of proteolytic enzymes is activated in the cells of the trophoblast, destroying the elements of the mucous membrane and causing the so-called decidual reaction of the endometrium, accompanied by active angiogenesis at the site of implantation. If the blastocyst does not completely submerge into the uterine lining, this is the cause of hypoxia and the death of the embryo.

Thus, embryo implantation is the most important event in embryogenesis, which ensures the continuation of previously initiated morphogenetic processes, both in the embryo and in extraembryonic organs.

The next period of embryogenesis is histo- and organogenesis. Histogenesis Is a complex of processes of proliferation, cell growth, migration, intercellular interactions, differentiation, determination and programmed cell death coordinated in time and space. The formation of a complex of axial primordia is shown in Fig. 4.

I. Embryonic period development (from the Greek word embryon - embryo) -

First 8 weeks of development: splitting up - the formation of a single-layer embryo of blastula; gastrulation - the formation of first two, and then a three-layer embryo - gastrula, the resulting layers are called germ layers; histogenesis - tissue formation; organogenesis - the formation of organs.

Each of the germ layers gives rise to one or another organ. From ectoderm formed: the nervous system, the epidermis of the skin and its derivatives (horny scales, feathers and hair, teeth). From mesoderm musculature, skeleton, excretory, reproductive and circulatory systems are formed. From endoderm the digestive system and its glands (liver, pancreas) and the respiratory system are formed.

I - zygote;

II - 2 blastomeres;

II - 8 blastomeres;

II - 32 blastomeres (morula);

III - stage of blastula;

IV - gastrula;

V - laying of tissues and organs:

1 - neural tube;

2 - chord;

3 - ectoderm;

4 - endoderm;

5 - mesoderm.

Rice. Early stages of lancelet development

Fetal (fetal) period of development. (fetis - fetus). From the 9th week, when the embryo already has all the organ systems. Starting at 9 weeks, the human embryo is called fruit ... In humans, antenatal development lasts 38-42 weeks (from the Greek "ante" - before, "natus" - birth)

II. Postembryonic the period of development - from the moment of birth to the death of the organism.

Juvenile period(before puberty) proceeds depending on the type of ontogenesis: direct type or develop with metamorphosis

Straight type of development - a nascent organism has all the basic characteristics of an adult animal, it differs mainly in the size and proportions of the body. For higher mammals and humans, the intrauterine type of development is characteristic, for reptiles and birds - the ovipositor.

Exception: oviparous mammals - platypus and yachidna.

Indirect type of development - embryonic development leads to the development of a larva, which, in terms of external and internal characteristics, differs from the adult organism. It is characteristic of many invertebrates, often fish. Example: a caterpillar develops from eggs of butterflies, from eggs of a frog tadpoles.

Depending on the characteristics of the transformation of the larva into the adult form, there are 2 types of indirect ontogenesis:

WITH incomplete transformation - the larvae develop gradually, consistently losing temporary larval organs and acquiring permanent ones characteristic of an adult. Example: tadpoles - live in the aquatic environment, have temporary organs of the gill, tail, 2-chambered heart; adult frogs - lungs, 3-chambered heart, limbs. Also typical for: ticks, bugs, orthoptera (grasshoppers, lice, dragonflies, cockroaches). in the process of growth and development, the larvae molt several times (cockroaches molt 6 times) and after each molt they become more and more like an adult.

WITH complete transformation (metamorphosis ) is characteristic of several orders of insects, butterflies, beetles, dipterans (mosquitoes, flies), hymenoptera (bees, wasps, ants), fleas, etc. The larvae have a worm-like structure and are completely different from adults.

Rice. Insect development with incomplete (I) and complete (II) cessation. 1 - eggs, 2,3,4,5,6 - larvae; 7 - pupa; 8 - adult form (imago).

At the end of the feeding period, the larva turns into a stationary stage - chrysalis covered with a dense chitinous sheath. Inside the pupa, special enzymes lyse all organs except for a few cells called imaginal discs. From the cells of the disc, adult organs develop.

Mature, puberty... It is characterized by the greatest independence, the activity of the organism in the environment.

Old age period.

Growth and development.

The transition of functional systems to the mode of growing up of the body is characterized by the growth of organs and tissues of the body, the establishment of the corresponding proportions of the body. In the process of individual development, several types of growth are distinguished: limited and unlimited; isometric and allometric.

Limited(definite). Growth is confined to certain stages of ontogenesis. Example: insects grow only during molting; in humans, growth stops at the age of 13-15 years. There may be a pubertal growth spurt during puberty.

Unlimited growth is observed in fish, houseplants throughout life, or in perennials.

Isometric growth- growth in which the organ grows at the same rate as the rest of the body. Changes in body size do not accompany a change in its shape. Typical for fish and insects with incomplete transformation (locusts, with the exception of wings and genitals)

Allometric is called the growth in which a given organ grows at the same rate than the rest of the body. The growth of an organism leads to a change in its proportions. They are characteristic of mammals and humans. In almost all animals, the development of reproductive organs is the last thing.

FUNDAMENTALS OF GENETICS.

Genetics- a science that studies the laws of inheritance and variability.

The task of genetics: the study of the problems of storage, transmission, implementation of the variability of hereditary information.

Methods:

1. Hybridological method(crossings) - developed by G. Mendel, is the main one in genetic research. The method makes it possible to reveal the patterns of inheritance of individual traits and properties during sexual reproduction of organisms.

2. Cytogenetic method- allows you to study the karyotype of body cells and identify genomic and chromosomal mutations. Since the advent of this method, the causes of multiple human diseases have been established (village of Downa and others).

3. Genealogical method(pedigrees) - studies of inheritance, of any trait in a person in a number of generations (a pedigree is compiled, family members who have the trait under study are noted)

4. Twin method- they study twins with the same genotypes, one hundred allows you to identify the influence of the environment on the formation of traits.

5. Biochemical method- studies metabolic disorders resulting from gene mutations.

6. Population statistical method- allows you to calculate the frequency of occurrence of genes and genotypes in the population.

Basic concepts.