Sexual culture is part of general culture.

The second pattern is the change in the relationship between the biological and the social, their role in the development of sexuality.

The first of which is phasing.

For all stages of psychosexual development, as well as for each stage of stage III, there are general patterns,

As a result of an increased tendency to fantasize and delays in the realization of libido caused by social factors, women are more susceptible to deviations in psychosexual development.

The continuity and interconnection of stages (stages), as well as their violations, represents the third pattern of psychosexual development, and at each stage (stage) of the formation of sexuality there are the makings of the next one.

It is as if a chain of stages is formed(stages), and the loss of any of them for one reason or another distorts the course of subsequent ones and, ultimately, the formation of all sexuality.

Absence or disruption of early stages psychosexual development lead to gross deformations affecting the core of the personality, which, by analogy with psychopathy, can be called “nuclear”.

The division of psychosexual development into stages is arbitrary, since sexual identity, gender role and psychosexual orientations are closely interrelated and are dynamic structures that change not only in the process of their formation, but also throughout subsequent life, although the foundations of all components of sexuality are laid during their formation.

The concepts of “Sex education” and “Sex education”.

Sex education, a system of medical and pedagogical measures to instill in parents, children, adolescents and youth the correct attitude towards gender issues.

The purpose of P. v. - to promote the harmonious development of the younger generation, increase sexological knowledge, the full formation of reproductive function, a sense of responsibility for the health and well-being of the future wife (husband), children, i.e. strengthening marriage and family.

Therefore, P. v. is associated with complex medical, pedagogical and social problems, where physiological, hygienic, pedagogical, moral, ethical and aesthetic aspects are closely intertwined.

For many centuries, the interpretation of questions of P. v. determined by traditions sanctified by religion. Only in the 20th century. Attempts at a scientific approach to the problems of P. v. began; in the 2nd half of the 20th century. interest in them is becoming widespread not only from specialist teachers, sexologists, etc., but also from the public and government agencies. This is due, in particular, to the spread among the youth of many capitalist countries of views that deny any restrictions and moral norms in sexual life (“one sexual morality - free love”), to the increase in sexually transmitted diseases, abortions and childbirth among minors, etc. d.

In many countries (USA, Sweden, Germany, East Germany, etc.), predominantly sex education is carried out - detailed familiarization of children and adolescents (starting from senior preschool and primary school age) with anatomical, physiological, sexological, hygienic and other information related to issues gender and sexuality.

In the USSR P. v. includes sexuality education at a later stage (from the 8th grade of secondary school).

Principles of P.v. follow from the general principles of educational work:

It is carried out as an integral part of the general complex of educational activities in the family, preschool institutions, schools, youth organizations, etc.

Based on a unified approach on the part of parents, teachers and educators, and medical workers;

It has a differentiated - in accordance with the gender, age and degree of preparedness of the child (parents) - and a phased (successive) nature; implies a combination with a favorable moral atmosphere and hygienic conditions.

In P. v. Several stages are conventionally distinguished.

At the age of 2-3, a child develops an awareness of belonging to a certain gender, an understanding of the differences in the body structure of a boy and a girl, and questions like “Where did I come from?” These observations and questions are a consequence of the natural process of learning about the world around us; they do not yet have a sexual nature. It is recommended to answer them in a form accessible to the child, briefly, without excessive detail (for example, descriptions of the structure and function of the genital organs), since the latter can arouse the child’s interest in sexual details that he was not aware of and, naturally, did not ask.

Because, as a rule, a more accurate answer to the question “Where do babies come from?” the child strives to receive only at the age of 5-7, and the question about the role of the father in his birth begins to arise in the child at the age of 6-8 (P. Neubert), until this time children are quite satisfied with formal answers like: “I gave birth to you in maternity hospital”, “You grew in my tummy”, etc. You can give examples from the life of animals, but you should not evade the answer or resort to fairy tales about “cabbage”, “storks”, “bazaar”, etc. The embarrassment of elders, their refusal to answer a question or a soon exposed lie causes the child’s distrust of them, heightened interest in the mysterious side of life and the need to satisfy curiosity with the help of more “informed” older comrades.

Stage 2 Children of primary school age are taught general moral, ethical and hygienic rules that are important for normal sexual development. An essential role, as at other stages of P. century, is played by the organization of a rational regimen and nutrition. In preschool and primary school age, a child can fall in love (usually with an older, usually handsome or strong person), tries to be closer to his loved one, caress him, and care for him. In such cases, you should not focus your attention on this falling in love; you should try to switch the child’s attention to new games, reading and other activities - the falling in love will go away on its own. As at other stages of parenting, positive examples of correct relationships between parents and other adults are important.

The period of puberty corresponds to the 3rd stage of P. century. As a rule, this period is not accompanied by health problems; Increased fatigue, irritability, and decreased attention may be observed. The task of parents is to provide the child with the necessary information about the physiological characteristics of the growing organism and teach him the appropriate special rules of hygiene. First of all, parents need to prepare the girl for the appearance of menstruation (see Menstrual cycle) - according to surveys, 70% of girls learn about this from their mothers; boy - to wet dreams. It is necessary to teach girls the rules of a special toilet, keeping a menstrual diary, talk about clothing, nutrition, regime during these periods, etc. Boys should also be taught that wet dreams are a natural phenomenon and that they require basic hygiene. A persistent but tactful fight against the abuse of masturbation, which is not uncommon at this time, is necessary, which should not take the form of intimidation with its “terrible” consequences.

The main task of the 4th and 5th stages of P. century.(respectively, adolescents of high school age and boys and girls who have graduated from school) - coverage of issues of gender relations as a complex moral, social and hygienic problem, presentation of the basics of hygiene of sexual life, prevention of sexually transmitted diseases and abortions, moral and ethical issues and marriage hygiene.

Beginning with puberty, adolescents seek and affirm their ideals; They are very critical, easily enter into conflicts with adults, often overestimate their own moral merits or, conversely, suffer from their imaginary shortcomings. The main motive for the behavior of an awakening woman gradually becomes the desire to please others, then the male representatives, the desire for empathy, love and affection. To attract attention, girls try to improve their appearance with fashionable hairstyles, clothes, and cosmetics. At the same time, interest in more accurate information about the “secrets” of love is growing. Young men assert their “I” under the motto “I can do anything as an adult” (including smoking, drinking alcoholic beverages, etc.), and begin to look closely at girls. Often, former attachments to friends (for girls) and comrades (for boys) gradually fade into the background. Young people strive to suppress unclear desires within themselves, but do not know how to do this, do not know how to find themselves in the company of peers of the opposite sex, and often seek help and support from adults, but only if they are tactful. Advice from parents and teachers regarding behavior is accepted with gratitude, unless it is of the nature of an imperative or prohibition (in which case the prohibition is openly or secretly violated). An adult’s ability to see beauty (in nature, art, work, people), to make himself pleasant to others, to treat others with respect and care attracts the attention of a young person and influences him.

Mechanisms of fertilization

The process of fertilization in animals can be divided into three phases. The first phase is characterized by the approach of the sperm to the egg before their contact. During this phase, distant interactions between germ cells take place. The second phase begins with the sperm attaching to the surface of the egg. At this time, contact interactions between germ cells are observed. The third phase of the fertilization process begins after the sperm penetrates the egg and ends with the union of the nuclei of the male and female germ cells. This phase characterizes the interaction within the egg.

Distant interactions between germ cells

Distant interactions are ensured by a number of nonspecific factors, among which a special place belongs to chemical substances produced by germ cells. It is known that reproductive cells secrete gamones or gamete hormones. Gamones produced by eggs are called gynogamons, and those produced by spermatozoa are called androgamones. Female germ cells distinguish two groups of gamones: gynogamons I and gynogamons II, which influence the physiology of male germ cells. Spermatozoa produce androgamones I and II.

Some of these chemicals are designed to increase the likelihood of a sperm meeting an egg. It is known that the movement of sperm to the egg is carried out through chemotaxis - the movement of sperm along the concentration gradient of certain chemicals secreted by the egg. Chemotaxis has been reliably shown for many groups of animals, especially invertebrates: mollusks, echinoderms and hemichordates. Chemotactic factors have been isolated from the eggs of sea urchins: in some species it is a peptide consisting of ten amino acids and is called speract, in other species it is a peptide consisting of fourteen amino acids and is called resact. When extracts of these substances are added to seawater, sperm of the corresponding species begin to move up their concentration gradient.

In the movement of mammalian spermatozoa along the upper parts of the oviduct, the phenomenon of rheotaxis is essential - the ability to move against the oncoming flow of oviduct fluid.

After the sperm passes through the protective membranes of the egg and comes into contact with its plasma membrane, contact interactions between the germ cells begin, which will lead to the penetration of the sperm into the cytoplasm of the egg.

Contact interactions between germ cells

Contact of the sperm with the egg membrane leads to the activation of the germ cells. The activation reaction is associated with complex morphological, biochemical and physicochemical changes in germ cells. Activation of the male germ cell is primarily associated with the acrosomal reaction, and the female one with the cortical reaction.

Acrosome reaction characterized by rapid changes in the acrosomal apparatus of the sperm head, accompanied by the release of spermolysins contained in it and the ejection of the acrosomal filament towards the surface of the egg.

Let us consider the general scheme of the acrosomal reaction in representatives of different groups of marine invertebrates - echinoderms, annelids, bivalves, gastro-breathers, etc.

At the top of the sperm head, the plasma membrane and the adjacent part of the acrosomal vesicle membrane dissolve (lyse). The free edges of both membranes merge into a single membrane. Spermolysins are released from the exposed acrosome into the environment and lead to the dissolution of the egg membranes at the site of contact with the sperm. After this, the inner membrane of the acrosmal apparatus protrudes outward and forms an outgrowth in the form of a tube (acrosomal filament). The acrosomal filament elongates, passes through the loosened area of ​​the additional egg membranes and comes into contact with the plasma membrane of the egg. In the area of ​​contact of the acrosomal filament with the surface of the egg, the plasma membranes merge and the contents of the acrosomal tube (filament) connect with the cytoplasm of the egg. As a result of membrane fusion, a cytoplasmic bridge is formed. A little later, the nucleus and centriole of the sperm will pass through the cytoplasmic bridge into the cytoplasm of the egg. The acrosome reaction ends with the insertion of the sperm membrane into the egg membrane. From this moment on, the sperm and egg are already a single cell (Fig. 7, 8, 9.).

Fig.7. Acrosome reaction of sperm: A - B - fusion of the outer membrane of the acrosome and the sperm membrane. Effusion of the contents of the acrosomal vesicle; 1 - acrosome membrane; 2 - sperm membrane; 3 - globular actin; 4 - acrosome enzymes; D - E - actin polymerization and formation of an acrosomal extension; 5 - bindin; 6 - acrosome growth; 7 - actin microfilaments; 8 - sperm nucleus. (according to Golichenkov)

Despite the general similarity of the acrosomal reaction, there are certain differences between them in these animals. Thus, in echinoderms, unlike worms and mollusks, the acrosomal apparatus does not contain lytic enzymes. In most animals studied, one acrosomal filament is formed, and in some worms several such filaments are formed.

Fig.8. Sequence of the acrosomal reaction in the sea urchin.(according to Golichenkov)

During fertilization in vertebrates, an acrosome reaction also occurs. In lower vertebrates (lamreys and sturgeons), it is in many ways similar to the axomal reaction of the sperm of invertebrate animals.

Fig.9. Scheme of the processes occurring during the interaction of the membranes of the egg and sperm during fertilization (according to Gilbert).

In shark fish, reptiles and birds, whose eggs are covered with dense shells, the union of gametes occurs before these shells are formed. In these animals, the acrosome continues to fulfill its original role and is well developed.

The acrosome response in mammals differs from that in invertebrates and lower vertebrates. In mammalian sperm, the acrosomal reaction occurs without the formation of an acrosomal outgrowth. Approaching the surface of the egg, the sperm fuses with its plasma membrane through the lateral surface of the head.

In insects and higher fish, the union of germ cells occurs after dense additional egg membranes are completely formed. In these cases, the sperm penetrates the egg through micropillar canals and the union of gametes occurs without the participation of an acrosome.

Egg activation. Cortical reaction. After the male reproductive cell attaches to the surface of the egg and its acrosomal filament comes into contact with the surface of the ooplasm, activation of the egg occurs. Activation of the egg is associated with complex changes in various aspects of its activity. The most striking external manifestation of activation is changes in the surface layer of the ooplasm, called the cortical reaction (Fig. 10).

Fig. 10. Cortical response in a sea urchin egg A-approximation of the sperm to the egg; B-D - successive stages of cortical reaction; shows a wave of release of the contents of cortical granules, spreading from the site of sperm penetration, separation of the membrane and the formation of the perivitelline space, the formation of the hyaline layer; gs-hyaline layer; Jo-yolk shell kg-cortical granule; oo-fertilization membrane PM-plasma membrane; pp-perivitelline space filled with perivitelline fluid (according to Ginzburg).

Let us consider the successive stages of the cortical reaction using the example of the most fully studied sea urchin eggs. The cortical reaction begins with the membrane bordering each cortical granule adhering to the plasma membrane of the egg. At this point, the granules open and their contents are poured into the vitelline membrane. The process of secretion of the contents of cortical granules begins from the point of attachment of the sperm and spreads in waves in all directions until it covers the entire surface of the egg. Part of the secreted contents of the cortical granules is hydrated and dissolved, forming perivitelline fluid, which pushes the vitelline membrane away from the plasmalemma of the egg, leading to an increase in the volume of the perivitelline space. Another part of the contents of the cortical granules merges with the vitelline membrane, which thickens and transforms into the fertilization membrane. Some of the cortical granules that do not participate in the formation of the fertilization membrane are transformed into a dense layer called the hyaline layer located above the plasma membrane. Once the fertilization membrane is formed, other sperm are unable to penetrate the ooplasm of the egg.

In recent years, the chemical composition of the contents of cortical granules has been studied. It has been shown that the contents of cortical granules contain the following substances: a) a proteolytic enzyme (actellin delaminase), which breaks the bonds between the cell membrane and the plasma membrane of the egg; b) proteolytic enzyme (sperm receptor hydrolase), which releases sperm deposited on the vitelline membrane; c) a glycoprotein that draws water into the space between the vitelline membrane and the plasma membrane, causing their separation; d) a factor promoting the formation of the fertilization membrane; e) structural protein hyaline, involved in the formation of the hyaline layer.

What is the biological significance of the cortical response?

Firstly, the cortical reaction is the mechanism that protects the egg from the penetration of supernumerary sperm.

Secondly, the perivitelline fluid formed as a result of the cortical reaction serves as a specific environment in which the development of the embryo occurs.

When the egg is activated, other changes in various aspects of its activity are observed.

Firstly, the brake that blocked meiosis is reduced and nuclear transformations continue from the very stage at which they stopped at the time the egg left the ovary.

Secondly, a series of biochemical changes are observed, accompanied by increased carbohydrate metabolism and increased synthesis of lipids and proteins.

Thirdly, the permeability of the cell membrane to sodium and potassium ions increases sharply.

Events that occur in the egg after sperm penetration

After the plasma membrane of the acrosomal filament of the sperm fuses with the plasma membrane of the egg, the sperm loses its motility and its recruitment into the egg occurs due to the action of forces emanating from the activated egg. Usually the sperm is drawn into the ooplasm along with the tail, but sometimes the tail is discarded. However, even in cases where the flagellum penetrates the egg, it is discarded and dissolves.

The highly condensed nucleus of the sperm begins to swell, the chromatin loosens and the nucleus turns into a peculiar structure called the male pronucleus.

Similar changes occur in the nucleus of the egg, resulting in the formation of the female pronucleus. During the formation of pronuclei, DNA replication occurs along chromosomes. Subsequently, the pronuclei begin to move towards the center of the egg. The nuclear membranes surrounding each of the pronuclei are destroyed, the pronuclei come closer together and karyogamy occurs. Karyogamy is the last stage of fertilization. When pronuclei combine, a nucleus with a diploid set of chromosomes is formed. Then the chromosomes take an equatorial position, and the first division of the zygote occurs.

Ooplasmic segregation. After penetration of the sperm, intensive movements of the cytoplasm of the egg (ooplasm) begin. In this case, separation and mixing of various components of the ooplasm occurs, which is referred to as ooplasmic segregation. During this process, the main elements of the spatial organization of the embryo are outlined. Therefore, this stage of development is also called promorphogenesis: it means that at this time, milestones are set for future morphogenetic processes.

Mono- and polyspermy

Penetration of one sperm into the egg is called physiological monospermia. Monospermia is characteristic of all groups of animals with external insemination and many animals with internal insemination (those that, like mammals, have small eggs).

In other animals, for example, in some arthropods (insects), mollusks (class gastropods), chordates (shark-like fish, tailed amphibians, reptiles and birds), a large number of sperm penetrate the egg. This phenomenon is called physiological polyspermy. However, in this case, only the nucleus of one sperm is connected to the nucleus of the egg, while the rest are destroyed (Fig. 11).

Rice. 11. Polyspermy in newt. A-penetration of sperm into the egg at the stage of metaphase of the second division of maturation; B-synchronous changes in seed nuclei, formation of seed stars; The B-female nucleus connects with one of the seminal nuclei; The G-E synkaryon enters mitosis, the supernumerary seminal nuclei are pushed into the vegetative hemisphere and degenerate. The numbers above the image of the eggs indicate the time after sperm penetration at a temperature of 23 o (according to Ginzburg).

With physiological monospermy, there are special mechanisms to protect the egg from polyspermy. The first mechanism is associated with a change in membrane potential. It has been established that in a frog egg, a few seconds after contact with the sperm, the membrane charge changes from -28 to 8 mV and remains positive for 20 minutes. The same changes in membrane potential were found in sea urchin eggs. It turned out that the positive charge of the membrane prevents polyspermy. Another widespread mechanism for protecting the egg from penetration by supernumerary sperm is associated with the formation of the fertilization membrane and perivitelline fluid.

As you know, after reaching puberty, every girl, and then every woman, experiences this once a month. This is a rather complex physiological process during which a mature egg is released from the ovary into the fallopian tube. This is where fertilization occurs.

Features of ovulation

The fusion of sperm with the egg occurs within twelve hours after it exits the fallopian tube. It is not difficult to calculate the time of ovulation, and one of the most reliable methods for determining it is, that is, the temperature in the rectum. This procedure must be carried out daily for several months. The temperature is measured at the same time, early in the morning, without getting up in bed, using the most ordinary thermometer.

If you enter the data into a graph, you can see the maturation curve of your egg. Before the onset of menstruation, the maximum temperature decreases, and the moment of ovulation occurs either on the last day of low temperature or on the first day of its increase. The most favorable day for fertilization of an egg is the one when ovulation occurs, or a few days before it begins.

This is explained by the fact that sperm that have entered the cavity of the fallopian tube remain viable for several days. Knowing the day of ovulation, you can not only conceive a child, but also try. For this purpose, there are various conception calendars.

Mechanism of fertilization

Fertilization of an egg is a long and complex mechanism during which the union of male and female reproductive cells occurs. The seminal fluid, which enters the female vagina during sexual intercourse, contains approximately 60 to 150 million mature sperm. Due to the continuous contraction of the uterus, seminal fluid is actively captured by it, and therefore motile sperm move into the uterine cavity for several minutes, and then reach the distant parts of the fallopian tube, where the egg is located.

Despite the fact that there are many male reproductive cells, they encounter many obstacles on their way (the acidic environment of the vagina, the mucous contents of the cervical canal, and so on), and only one of the fastest sperm can fertilize the egg. True, numerous studies have proven that several sperm can penetrate an egg, but the nucleus with the hereditary information of the egg can connect with the nucleus of only one sperm, resulting in the formation of only one embryo. Of course, there are cases when several embryos are produced during the fertilization process, and as a result twins are born.

The sperm passes through the strong membranes of the female cell due to dissolution by enzymes contained in the acrosomal capsule of its head. Coming into contact with the egg, the capsule ruptures, and from it the acrosomal thread begins to attach to the membranes and substances are released that destroy the membrane of the egg. Having dissolved a small area, the acrosomal thread penetrates deep into the egg and tightly connects with its internal contents. Then the nucleus and internal contents of the sperm head are absorbed into the female reproductive cell.

Changes in the egg

Complete penetration of the sperm into the female reproductive cell starts the process of significant changes in the physiological processes in it. The shells of the egg become much more permeable, which is very important for the active accumulation of nutrients with the help of which the embryo will develop. Proteins, calcium and carbohydrates begin to be more actively produced, the maximum amount of calcium and phosphorus is absorbed - in general, preparations are being made for the development of the fetus.

The most important and significant events for the unborn child occur within about twelve hours after the sperm penetrates the egg. At this time, the nuclei of male and female cells, which carry all the hereditary information, unite. A new cell is formed with a full set of chromosomes, from which an embryo will then develop and eventually a new person will be born.

Fertilization, the initial moment of the emergence of a new genetic individuality, is the process of combining female and male gametes.

As a result of fertilization, a one-cell embryo with a diploid set of chromosomes appears and a chain of events underlying the development of the organism is activated.

The biological significance of fertilization is enormous: being a prerequisite for the development of a new individuality, it is at the same time a condition for the continuation of life and the evolution of the species.

It should be emphasized that fertilization is not a one-time act, but rather a process that takes a more or less long period of time. This is a multi-stage process, which distinguishes the following stages: attraction of sperm by the egg, binding of gametes and, finally, fusion of male and female reproductive cells. In the scientific literature, events associated with the convergence of gametes are sometimes called insemination, distinguishing between external and internal insemination, depending on whether male reproductive cells are released into the environment or into the female genitals. External insemination is typical for animals living in an aquatic environment. Internal insemination is characteristic mainly of terrestrial animals, although it is quite common among inhabitants of the aquatic environment. Insemination can be free, in which all areas of the oocyte are accessible to sperm, but it can also be limited, when there is a dense membrane with a micropyle on the surface of the egg. During internal insemination in a number of animals, male gametes are transferred to females in the form spermatophores, special capsules containing sperm. Spermatophores are first released into the environment and then transferred in one way or another to the female’s reproductive tract.

The connection of gametes determines the possibility karyogamy, or nuclear fusion. Thanks to karyogamy, the union of paternal and maternal chromosomes occurs, leading to the formation of the genome of a new individual. As a result of the fusion of gametes, a diploid zygote appears, the ability for DNA replication is restored, and preparation for cleavage divisions begins. The mechanisms of egg activation for development are relatively autonomous. Their inclusion can be carried out in addition to fertilization, which occurs, for example, during natural or artificial virgin development, or parthenogenesis.

Interest in the problem of fertilization goes far beyond the scope of embryology itself. Gamete fusion is a fruitfully used model for studying the fine molecular and cellular mechanisms of specific cell membrane interactions; to study the molecular basis of metabolic activation and proliferation of somatic cells. It is also of general biological interest that fertilization is a striking and, perhaps, unique example of a complete reversal of cell differentiation. Indeed, highly specialized germ cells are not capable of self-reproduction. They are haploid and cannot divide. However, after fusion they turn into a totipotent cell, which serves as the source of the formation of all cell types inherent in a given organism.

The history of the discovery of fertilization is lost in the mists of time. In any case, in the 18th century, the Italian naturalist Abbot Lazzaro Spallanzani (1729-1799) experimentally proved that fertilization depends on the presence of sperm, and for the first time carried out artificial insemination of frog eggs, mixing them with sperm obtained from the testes. Nevertheless, the meaning of the events occurring in this case remained unclear almost until the last quarter of the 19th century, when Oscar Hertwig (1849-1922) in the late 1870s, studying fertilization in sea urchins, came to the conclusion that the essence of this process is the fusion of nuclei germ cells. Together with the works of the Belgian Eduard van Beneden (1883, roundworm), the German scientist Theodor Boveri (1887, roundworm), and the Swiss zoologist Hermann Fohl (1887, starfish), O. Hertwig’s research laid the foundation for modern ideas about fertilization. It should be emphasized that it was these works that served as a strong basis for the assumption that the nucleus is the bearer of hereditary properties. It was T. Boveri (1862-1915), in a series of brilliant cytological studies, who substantiated the theory of chromosome individuality in the late 1880s and created the basis of cytogenetics.

Soon after the essence of fertilization was elucidated, researchers focused their attention on the mechanisms underlying this process. This area of ​​research remains relevant today. The lead in developing the theory of fertilization belongs to the American researcher Frank Lilly (1862-1915). While studying the properties of “egg water,” that is, sea water in which unfertilized eggs of the sea urchin Arbacia or the polychaete Nereis had been present for some time, Lilly discovered that a substance was released from the eggs that had the ability to glue sperm into lumps. The observed agglutination turned out to be species specific, and Lilly called the agglutination factor secreted by the unfertilized egg the fertilization substance, or fertilizine(from the English fertilization - fertilization). The essence of Lilly's theory of fertilization is the recognition that in the peripheral region of the egg there is fertilisin, which has an affinity for the surface receptors of sperm (sperm antifertilisin). Thanks to this affinity, fertilizin binds, according to Lilly, sperm. However, in order to claim universality and explain not only the mechanism of gamete union, but also the reasons for sperm agglutination, the possibility of preventing polyspermy, the high specificity of the fertilization process, etc., the fertilizin theory needed numerous assumptions, under the yoke of which it eventually died out.

Already in the course of early studies of fertilization, the idea of ​​gamons arose - substances that provide activation or blocking of individual stages of fertilization. In accordance with their origin, they distinguished gynogamones, secreted by eggs, and androgamones, produced by male reproductive cells. Thus, it was believed that gynogamon 1, diffusing from the egg, activates the movement of the sperm, overcoming the action of androgamon 1, which inhibits the movement of the sperm. Gynogamon 2 is a synonym for fertilisin, and androgamon 2 is a sperm antifertilisin.

In the fifties of the 20th century, the idea of ​​the interaction of fertilisin with antifertilisin was transformed into the hypothesis of specific phagocytosis. According to this concept, the presence of interacting molecules on the surface of the egg and sperm provides a complementary zipper reaction that allows the sperm to be absorbed into the egg.

Despite a certain speculativeness, these and many other similar hypotheses about the mechanisms of interaction between sperm and eggs played a positive role, revealing, firstly, the existence of a whole family of specific molecules on the surface of interacting gametes and, secondly, initiating systematic research into the nature of these molecules .

The second half of the last century was the heyday of ultrastructural and molecular biological research, which revealed a wide variety of specific forms of cellular interaction during fertilization. It became clear that a universal theory of fertilization, if it could exist, would be only as a set of some of the most general principles for organizing this process.

The specific mechanisms of fertilization depend on many factors. Suffice it to say about the uniqueness of fertilization in animals with external and internal insemination. Obviously, certain differences in the fertilization process are also due to the fact that in different animals the penetration of sperm into the egg occurs at different stages of oogenesis. In many annelids, mollusks, nematodes and crustaceans, sperm penetrates first-order oocytes at the prophase stage. In other annelids, mollusks and insects - at the metaphase stage of the primary oocyte. Many vertebrates are characterized by insemination at the metaphase stage of the secondary oocyte. In some coelenterates and sea urchins, fertilization occurs at the stage of a mature egg after the completion of maturation divisions and the release of directional or reduction bodies. Finally, one cannot help but recall the variety of types of sperm, among which there are flagellar forms and sperm without flagella (for example, amoeboid sperm nematodes), with and without an acrosome, with and without an acrosomal thread. Naturally, in each such case, the specific mechanisms that ensure the subtle interaction between germ cells differ.

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So how does fertilization occur?

Fertilization is the process of fusion of mature sex cells of a man (sperm) and a woman (egg), resulting in the appearance of a zygote (it contains the genetic information of both parents).

In this article I will not dwell on how the maturation of germ cells occurs, so as not to overload you with information; for those interested, read here: sperm, egg.

Let's talk directly about how fertilization occurs.

I will only draw your attention to the fact that the factor that determines the sex of the child is sperm. The fact is that the egg (female reproductive cell) is the carrier of the X chromosome and no other options. But spermatozoa are formed of two types: either also carriers of sex X chromosomes, or sex Y chromosomes.

Accordingly, if during fertilization the fusion of an egg with a sperm that contains an X chromosome occurs, a beautiful daughter will be born, and if the Y chromosome is present, a boy will be born.

Mechanism of fertilization

When considering the mechanism of fertilization, first of all, it is necessary to highlight the issue of gamete transport (this is the general name for male and female germ cells - the main characters of fertilization).

How do sperm move through the canals of a woman’s reproductive system?

If normal ejaculation occurs, on average about 100 million sperm enter the woman’s vagina, and along with them sperm components such as prostaglandins enter the vagina. They play a special role in the process of fertilization: they activate the contractile activity of the uterus and fallopian tubes, and under the influence of contraction of the muscles of the uterus, cervical mucus is released from the cervical canal, without which further movement of male gametes would be impossible. The trick is that the vagina has an acidic environment, which is unfavorable for them. But this very cervical mucus has a slightly alkaline environment and, accordingly, contributes to the optimal movement of sperm and, as a result, fertilization. After all, if a failure occurs at the very initial stage, then fertilization will not occur at all.

Immediately at the time of ovulation, under the influence of estrogen hormones from the ovaries, the composition of cervical mucus is ideal for fertilization.

In general, due to the appropriate composition of cervical mucus, sperm enter the uterus. At the same time, some of them may linger in the crypts of the cervix, this is a kind of sperm reserve, from which in the future (if necessary) sperm will flow up the canals of the reproductive system.

And already in the upper parts of the woman’s reproductive tract, a process occurs called sperm capacitation - this is the acquisition by sperm of the ability to fertilize. As a result of capacitation, sperm acquire the ability to undergo an acrosomal reaction. In addition, due to capitation, the movements of their tail parts change (they become very mobile).

The subtle mechanisms of capacitation are currently not fully understood. But their importance in the fertilization process is beyond doubt. The capacitation time is different for different sperm, which is obviously a very important factor for the fertilization process.

By the way, after capacitation they live less than before it. At the same time, capacitated male germ cells have increased activity and, as a result, an increased ability to penetrate tissue, which is the main thing in the process of fertilization.

But in addition to the kinetic activity of sperm, a significant role in their transport (and, as a consequence, in fertilization) is played by the contraction of the smooth muscles of the uterus and fallopian tubes, and in addition, the movement of microvilli of the ciliated epithelium of the endocervix and the flow of fluid in the lumen of the fallopian tube.

By the way, regarding the movement of sperm through the fallopian tubes, there are 2 phases. The first is short (about a few minutes): they quickly enter the tube ampoule.

And the second is longer; during this phase they slowly move towards the site of fertilization. By the way, during this phase the importance of previously deposited spermatozoa (in the crypts of the cervix) is learned; they continuously replace their counterparts leaving the abdominal cavity, maintaining the required level of spermatozoa in the ampullary part of the fallopian tube.

Here it is advisable to mention the life expectancy of sperm in the female genital tract. After all, this plays a major role in the process of fertilization. Many authors claim that their viability is several days (up to 5). But the preservation of the ability to move does not indicate the ability to fertilize. Under favorable conditions (if the sperm is in the cervical mucus), the ability to fertilize remains up to 2 days from the moment of ejaculation.

In general, the transport of male germ cells to the site of fertilization is a rather complex process, but what about the transport of the egg, which is also immobile in itself.

How does egg transport occur?

Fortunately, the egg does not have such a long journey ahead. In its initial transport, the main role belongs to such factors as: its “capture” by the fibria of the fallopian tube (from the side where ovulation occurred), and the flow of follicular fluid (appears when the follicle ruptures).

Thus, within a few minutes after the rupture of the follicle, the egg ends up in the cavity of the fallopian tube; you must admit, this happens much faster. But she not only finds herself at the site of fertilization faster, she also loses her ability to fertilize faster.

Remember, sperm are capable of fertilization on average 2 days, and an egg 24 hours.

Interestingly, in our age of high technology, you can observe the ovulation process and even record it on film.

How does egg fertilization occur?

And so here it is! How does fertilization occur: an egg entering the ampullary section of the fallopian tube is immediately surrounded by a bunch of sperm, and these are carriers of both X-chromosomes and Y-chromosomes.

Under a microscope, X chromosome carriers are larger than their Y chromosome carriers.

Sperm begin to penetrate into the cells of the corona radiata (This process occurs due to the presence of special enzymes, both in the head of the sperm and in the tubal fluid). Many try to penetrate, but only one of them succeeds. And immediately after the penetration of one of them, a cortical reaction of the egg occurs. The essence of this reaction is that cortical granules are released from the egg, which attach to the material of its shell and change its properties (it becomes impenetrable to other male germ cells).

If “extra” sperm penetrate the egg, the normal course of fertilization and development is disrupted, and the embryo inevitably dies.

Meanwhile, the following happens inside the egg: the chromosomes of the zygote enter the first mitotic division (this occurs 24 hours after the start of fertilization). The nucleus of a fertilized egg has a diploid set of chromosomes (46) - the new organism is a carrier of genetic information from both parents.

Initially, fragmentation is synchronous (from 2 blastomeres 4 are obtained, etc.). Thus, 96 hours after the fusion of the nuclei of male and female germ cells, the embryo consists of 16-32 blastomeres (this is the morula stage). And it is at this stage, due to the contractile activity of the fallopian tube, that the fertilized egg (zygote) enters the uterus (within 4 days). Read more about embryo development.

And here the implantation of the fertilized egg occurs (lasts about 2 days). Typically, the blastocyst is implanted in the area of ​​the anterior or posterior wall of the uterus.

Following implantation, the blastocyst begins to submerge into the modified functional layer of the endometrium - into the decidua.

The decidua is divided into several sections, from one of which the maternal part of the placenta is subsequently formed (Placentation begins in the 3rd week of pregnancy).

But more on that in other articles.

I hope it has become clear to you how fertilization occurs.