As you know, after reaching puberty, every girl, and then a woman, happens 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 takes place.
Features of ovulation
The fusion of the spermatozoa with the egg occurs within twelve hours after it enters 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 should 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 common 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 the low temperature, or on the first day of its increase. The most favorable day for the fertilization of an egg is the one when ovulation occurs, or a few days before it begins.
This is due to the fact that spermatozoa 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, there are various and conception calendars.
fertilization mechanism
Fertilization of the egg is a long and complex mechanism during which the union of male and female germ cells takes place. The seminal fluid that enters the female vagina during sexual intercourse contains approximately 60 to 150 million mature spermatozoa. Due to the continuous contraction of the uterus, the seminal fluid is actively captured by it, and therefore the mobile spermatozoa move into the uterine cavity for several minutes, and then reach the far sections of the fallopian tube, where the egg is located.
Despite the fact that there are many male germ cells, they encounter many obstacles in their path (the acidic environment of the vagina, the mucous contents of the cervical canal, and so on), and only one of the fastest spermatozoa will be able to fertilize the egg. True, numerous studies have shown that several spermatozoa can penetrate the egg, but the nucleus with the hereditary information of the egg can connect with the nucleus of only one sperm, resulting in only one embryo. Of course, there are cases when several embryos are obtained during the fertilization process, and as a result, twins are born.
The spermatozoon passes through the strong membranes of the female cell due to the dissolution of the enzymes contained in the acrosomal capsule of its head. Coming into contact with the egg, the capsule ruptures, and an acrosomal filament begins to attach from it to the shells and substances are released that destroy the shell of the egg. Having dissolved a small area, the acrosomal filament penetrates deep into the egg and tightly connects with its internal contents. Then the nucleus and the internal contents of the sperm head are absorbed into the female germ cell.
Changes in the egg
The complete penetration of the spermatozoon into the female reproductive cell starts the process of a significant change 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 underway for the development of the fetus.
The most important and significant events for the unborn child occur within about twelve hours after the penetration of the sperm into the egg. At this time, the nuclei of the male and female cells, which carry all the hereditary information, are combined. 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.
So how does fertilization take place?
Fertilization is the process of fusion of mature germ cells of a man (sperm) and a woman (ovum), resulting in the formation 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 who are 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 germ cell) is the carrier of the X chromosome and no other options. But spermatozoa are formed of two types: either also carriers of the sex X chromosomes, or sex Y chromosomes.
Accordingly, if during fertilization an egg cell merges with a sperm cell that contains the X chromosome, a beautiful daughter will be born, and if the Y chromosome, a boy will be born.
fertilization mechanism
Considering the mechanism of fertilization, first of all, it is necessary to highlight the issue of gamete transport (this is the common name for male and female germ cells - the main characters of fertilization).
How does the movement of spermatozoa through the channels of the female reproductive system
If a normal ejaculation occurs, on average, about 100 million spermatozoa enter the vagina of a woman, and with them such constituent sperm as prostaglandins enter the vagina. They then 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 whole trick is that the vagina is acidic, which is unfavorable for them. But this very cervical mucus has a slightly alkaline environment and, accordingly, contributes to the optimal movement of spermatozoa and, as a result, fertilization. After all, if at the very initial stage a failure occurs, then fertilization will not occur at all.
Immediately at the time of ovulation, under the influence of ovarian estrogenic hormones, the composition of cervical mucus is ideal for fertilization.
In general, due to the appropriate composition of the cervical mucus, spermatozoa 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) spermatozoa will flow up through the channels of the reproductive system.
And already in the upper parts of the female genital tract, a process takes place, called sperm capacitation - this is the acquisition of sperm ability to fertilize. As a result of capacitation, spermatozoa acquire the ability for an acrosomal reaction. In addition, due to capitation, the movements of their tail parts change (they become very mobile).
The finest mechanisms of capacitation are currently not fully understood. But their importance in the process of fertilization is not in doubt. The capacitation time for different spermatozoa is different, which, obviously, is an 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 tissues, which is the main one in the process of fertilization.
But in addition to the kinetic activity of spermatozoa, an important role in their transport (and, as a result, in fertilization) is played by 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, with regard to the movement of spermatozoa through the fallopian tubes, 2 phases are distinguished here. The first is short (on the order of several minutes): they quickly enter the tube ampoule.
And the second one is longer, in this phase they slowly move to the place of fertilization. By the way, in this phase, the significance of previously deposited spermatozoa (in the crypts of the cervix) is recognized, they continuously compensate for their counterparts leaving the abdominal cavity, maintaining the required level of spermatozoa in the ampullar part of the fallopian tube.
Here it is appropriate to mention the life span of spermatozoa in the female genital tract. After all, it plays a major role in the process of fertilization. Many authors claim that their viability is several days (up to 5). But after all, the preservation of the ability to move does not yet speak of the ability of fertilization. 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 place of fertilization is a rather complicated process, but what can we say about the transport of the egg, which, moreover, is motionless in itself.
How does egg transport occur?
Fortunately, the egg does not have such a long way to go. In its initial transport, the main role belongs to such factors as: "capture" of its fibriae of the fallopian tube (on 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 is in the cavity of the fallopian tube, you see, this happens much faster. But she not only finds herself in the place of fertilization faster, she also loses her ability to fertilize faster.
Remember, spermatozoa are capable of fertilization for an average of 2 days, and an egg for 24 hours.
Interestingly, in our age of high technology, you can observe the process of ovulation and even fix it on film.
How is the fertilization of the egg
And so here it is! How fertilization occurs: an egg that has entered the ampulla of the fallopian tube is immediately surrounded by a bunch of spermatozoa, and here the carriers of both X-chromosomes and Y-chromosomes.
Under the microscope, X-chromosome carriers are larger than their Y-chromosome-bearing counterparts.
Spermatozoa begin to penetrate into the cells of the radiant crown (This process occurs due to the presence of special enzymes, both in the head of the spermatozoa 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 impermeable to other male germ cells).
In the case of penetration of "extra" spermatozoa into the egg, the normal course of fertilization - development is disturbed, and the embryo inevitably dies.
Meanwhile, the following happens inside the egg: the chromosomes of the zygote enter the first mitotic division (it 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 the genetic information of both parents.
Initially, crushing is synchronous (from 2 blastomeres, 4 are obtained, etc.). Thus, after 96 hours, after the fusion of the nuclei of the 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 the development of the embryo.
And here the implantation of the fetal egg occurs (it lasts about 2 days). The blastocyst usually implants in the anterior or posterior wall of the uterus.
Following implantation, the blastocyst begins to sink into the modified functional layer of the endometrium - into the decidua.
The decidua is divided into several sections, from one of them the maternal part of the placenta is subsequently formed (placentation begins from the 3rd week of pregnancy).
But more on that in other articles.
I hope you understand: how fertilization occurs.
Fertilization mechanisms
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. In this phase, distant interactions between germ cells are carried out. The second phase begins with the fact that the sperm is attached 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 penetration of the sperm into the egg and ends with the unification of the nuclei of the male and female germ cells. This phase characterizes the interaction within the egg.
Distant interactions between sex cells
Distant interactions are provided by a number of non-specific factors, among which a special place belongs to chemicals that are produced by germ cells. It is known that germ cells secrete gamones or gamete hormones. The gammons that are produced by the eggs are called gynogamones, and the spermatozoa are called androgamones. Female germ cells distinguish two groups of gamons: gynogamons I and gynogamons II, which affect the physiology of male germ cells. Spermatozoa produce androgamones I and II.
Some of these chemicals are designed to make it more likely for a sperm to meet an egg. It is known that the movement of the sperm to the egg is carried out through chemotaxis - the movement of sperm along the concentration gradient of certain chemicals released by the egg. Chemotaxis has been reliably shown for many groups of animals, especially invertebrates: molluscs, echinoderms, and hemichordates. Chemotactic factors are isolated from sea urchin eggs: in some species it is a peptide consisting of ten amino acids, and is called spearact, in other species, the peptide consists of fourteen amino acids and is called reactive. When extracts of these substances are added to sea water, spermatozoa of the corresponding species begin to move up the concentration gradient.
In the movement of mammalian spermatozoa along the upper sections of the oviduct, the phenomenon of rheotaxis is essential - the ability to move against the oncoming flow of the oviduct fluid.
After the spermatozoon passes through the protective membranes of the egg and comes into contact with its plasma membrane, contact interactions between germ cells begin, which will lead to the penetration of the spermatozoon into the cytoplasm of the egg.
Contact interactions between sex cells
The contact of the sperm with the membrane of the egg leads to the activation of germ cells. The activation reaction is associated with complex morphological, biochemical and physicochemical changes in germ cells. The activation of the male germ cell is primarily associated with the acrosomal reaction, and the female - with the cortical reaction.
acrosomal reaction It is 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, entero-respirators, etc.
At the top of the spermatozoon head, the plasma membrane and the part of the membrane of the acrosomal vesicle adjacent to it dissolve (lyse). The free edges of both membranes merge into a single membrane. From the exposed acrosome, spermolysins are released into the environment and lead to the dissolution of the egg membranes at the site of contact with the spermatozoon. After that, 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 accessory 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 fuse and the contents of the acrosomal tubule (filament) are connected to 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 spermatozoon pass through the cytoplasmic bridge into the cytoplasm of the egg. The acrosomal reaction is completed by the incorporation of the sperm cell membrane into the egg cell membrane. From this moment, the spermatozoon and the egg are already a single cell (Fig. 7, 8, 9.).
Fig.7. Acrosomal reaction of the spermatozoon: A - B - fusion of the outer membrane of the acrosome and the membrane of the spermatozoon. Outpouring of the contents of the acrosomal vesicle; 1 - acrosome membrane; 2 - sperm membrane; 3 - globular actin; 4 - acrosome enzymes; D - D - polymerization of actin and the formation of an acrosomal outgrowth; 5 - bindin; 6 - acrosome outgrowth; 7 - actin microfilaments; 8 - sperm nucleus. (according to Golichenkov)
Despite the general similarity of the acrosomal reaction, these animals also have certain differences between them. Thus, in echinoderms, unlike worms and molluscs, the acrosomal apparatus does not contain lytic enzymes. In most of the 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 acrosomal reaction also occurs. In lower vertebrates (lampreys and sturgeons), it is in many respects similar to the acrsom reaction of invertebrate spermatozoa.
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 acrosomal response in mammals differs from that in non-vertebrates and lower vertebrates. In mammalian sperm, the acrosomal reaction proceeds without the formation of an acrosomal outgrowth. Approaching the surface of the egg, the sperm fuses with its plasma membrane on the lateral surface of the head.
In insects and higher fish, the union of germ cells occurs after the dense additional egg shells are completely formed. In these cases, the spermatozoon enters the egg through the micropillar channels and the union of gametes occurs without the participation of the acrosome.
egg activation. cortical reaction. After the male germ cell attaches to the surface of the egg and its acrosomal filament comes into contact with the surface of the ooplasm, the egg is activated. Activation of the egg is associated with complex changes in various aspects of its activity. The most striking external manifestation of activation are changes in the surface layer of the ooplasm, called the cortical reaction (Fig. 10).
Fig.10. Cortical reaction in the egg of a sea urchin A- approaching the sperm to the egg; B-D-successive stages of the cortical reaction; a wave of release of the contents of the cortical granules is shown, propagating from the site of penetration of the sperm, the separation of the membrane and the formation of the perivitelline space, the formation of the hyaline layer; hs-hyaline layer; zho-yolk shell kg-cortical granule; oo-fertilization shell pm-plasmic membrane; pp - perivitelline space filled with perivitelline fluid (according to Ginzburg).
Let us consider the successive stages of the cortical reaction on the example of the most fully studied sea urchin eggs. The cortical reaction begins when the membrane surrounding each cortical granule fuses with the plasma membrane of the egg. At this point, the granules open, and their contents are poured into the yolk membrane. The process of secretion of the contents of the cortical granules begins from the place of attachment of the spermatozoon and spreads in waves in all directions until it covers the entire surface of the egg. Part of the secreted content of the cortical granules is hydrated and dissolved, forming a perivitelline fluid, which pushes the yolk membrane away from the egg plasmolemma, leading to an increase in the volume of the perivitelline space. Another part of the contents of the cortical granules merges with the yolk membrane, which thickens and transforms into the fertilization membrane. Part of the cortical granules that are not involved in the formation of the fertilization membrane turn into a dense layer, called the hyaline layer, located above the plasma membrane. After the fertilization membrane is formed, other spermatozoa are deprived of the opportunity to penetrate the ooplasm of the egg.
In recent years, the chemical composition of the content of cortical granules has been studied. It has been shown that the content of cortical granules contains 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) a proteolytic enzyme (sperm-receptor hydrolase), which releases sperm deposited on the yolk membrane; c) a glycoprotein that draws water into the space between the yolk membrane and the plasma membrane, causing their stratification; d) a factor contributing to 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 reaction?
First, the cortical reaction is the mechanism that protects the egg from the penetration of supernumerary spermatozoa.
Secondly, the perivitelline fluid formed as a result of the cortical reaction serves as a specific environment in which the development of the embryo proceeds.
When the egg is activated, other changes in the most diverse aspects of its activity are also observed.
First, the brake that blocked meiosis is reduced and nuclear transformations continue from the very stage at which they stopped by the time the egg left the ovary.
Secondly, a series of biochemical changes is observed, accompanied by an increase in carbohydrate metabolism, an increase in the synthesis of lipids and proteins.
Thirdly, the permeability of the cell membrane for sodium and potassium ions increases sharply.
Events that occur in the egg after the penetration of the spermatozoon
After the plasma membrane of the acrosomal filament of the sperm fuses with the plasma membrane of the egg, the sperm loses its mobility and is drawn inside the egg due to the action of forces emanating from the activated egg. Usually, the spermatozoon is drawn into the ooplasm along with the tail, but sometimes the tail section is discarded. However, even in those cases when the flagellum penetrates the egg, it is discarded and absorbed.
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 converge and karyogamy occurs. Karyogamy is the last stage of fertilization. When the pronuclei unite, a nucleus with a diploid set of chromosomes is formed. Then the chromosomes occupy the equatorial position, and the first division of the zygote occurs.
Ooplasmic segregation. After the penetration of the spermatozoon, intensive movements of the cytoplasm of the egg (ooplasm) begin. In this case, stratification occurs, the mixing of various components of the ooplasm, which is referred to as ooplasmic segregation. In the course of 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 milestones for future morphogenetic processes are set up at this time.
Mono- and polyspermy
Penetration of one sperm cell into the egg is called physiological monospermia. Monospermy is found in all groups of externally inseminated animals and in many internally inseminated animals (those that, like mammals, have small eggs).
In other animals, for example, in some arthropods (insects), mollusks (gastropods), chordates (shark-like fish, tailed amphibians, reptiles and birds), a large number of sperm enter 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 the newt. A-penetration of sperm into the egg at the stage of metaphase II division of maturation; B-synchronous changes in the seed nuclei, the formation of seed stars; The B-female nucleus connects to one of the seminal nuclei; G - E-syncarion enters mitosis, supernumerary seed nuclei are pushed into the vegetative hemisphere and degenerate. The numbers above the eggs are the time after the penetration of spermatozoa at a temperature of 23 o (according to Ginzburg).
With physiological monospermy, there are special mechanisms for protecting the egg from polyspermy. The first mechanism is associated with a change in the membrane potential. It has been established that in a frog egg, after a few seconds, after contact with a spermatozoon, the membrane charge changes from -28 to 8 mV and remains positive for 20 minutes. Similar changes in membrane potential have been 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 the penetration of supernumerary spermatozoa is associated with the formation of the fertilization membrane and perivitelline fluid.
Sexual culture is part of the general culture.
The second pattern is the change in the ratio of biological and social, their role in the development of sexuality.
The first of which is phase.
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 due to social factors, women are more susceptible to deviations in psychosexual development.
The continuity and interconnection of stages (stages), as well as their violations, is the third regularity of psychosexual development, and at each stage (stage) of the formation of sexuality there are the makings of the next one.
Formed, as it were, a chain of stages(stages), and the loss for one reason or another of any of them distorts the course of subsequent and, as a result, the formation of all sexuality.
Absence or violation 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 conditional, since sexual identity, gender role and psychosexual orientations are closely interconnected. 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.
Concepts "Sex education" and "Sex education".
Sex education, a system of medical and pedagogical measures to educate parents, children, adolescents and youth of the correct attitude towards gender issues.
P.'s purpose in. - to promote the harmonious development of the younger generation, increase sexological knowledge, the full formation of childbearing 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. in. 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 P.'s questions. determined by the traditions consecrated by religion. Only in the 20th century attempts of the scientific approach to problems of P. of century began; in the 2nd half of the 20th century. interest in them is becoming widespread not only on the part of specialist teachers, sexologists, etc., but also on the part of the public and state bodies. This is connected, in particular, with the spread among the youth of many capitalist countries of views that deny any restrictions and moral norms in sexual life ("single sexual morality - free love"), with the growth of venereal diseases, abortions and childbirth among minors, etc. d.
In many countries (USA, Sweden, Germany, East Germany, etc.), sexual education is predominantly carried out - a detailed acquaintance of children and adolescents (starting with senior preschool and primary school ages) with anatomical, physiological, sexological, hygienic, and other information related to issues gender and sex life.
In the USSR, P. century. includes sexuality education at a later stage (starting from the 8th grade of high school).
P.'s principles in. stem 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, medical workers;
It has a differentiated - in accordance with the sex, age and degree of preparedness of the child (parents) - and a phased (successive) character; implies a combination with a favorable moral atmosphere and hygienic conditions.
In P. in. conditionally distinguish several stages.
At the age of 2-3, the child develops a consciousness of belonging to a certain gender, an understanding of the differences in the structure of the body of a boy and a girl, questions like "Where did I come from?" These observations and questions are a consequence of the natural process of cognition of the surrounding world, 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 did not suspect and, naturally, did not ask.
Because, as a rule, a more accurate answer to the question "Where do children come from?" the child seeks to receive only at the age of 5-7, and the question of the role of the father in his birth begins to arise in a child at the age of 6-8 (P. Neubert), until this time, children are quite satisfied with formal answers such as: "I gave birth to you in maternity hospital", "You grew up in my tummy", etc. You can give examples from the life of animals, but you should not evade the answer or resort to tales about "cabbage", "storks", "bazaar", etc. The embarrassment of the elders, their refusal to answer the question or soon exposed lies cause the child's distrust of them, a 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 well as at other stages of P. of century, is played by the organization of a rational mode and food. At preschool and primary school age, a child can fall in love (more often with an older, usually handsome or strong person), tries to be closer to his beloved, caress, care for him. In such cases, one should not fix attention on this falling in love, one should try to switch the child's attention to new games, reading, and other activities - falling in love will pass by itself. As in other stages of P.V., positive examples of correct relationships between parents and other adults are important.
The 3rd stage of P. of century corresponds to the period of puberty. As a rule, this period is not accompanied by health disorders; fatigue, irritability, 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, tell them about clothes, food, regimen during these periods, etc. Boys should also be educated that wet dreams are a natural phenomenon and that they require basic hygiene. A persistent but tactful fight against the abuse of onanism, which is not uncommon at this time, is needed, which should not take the form of intimidation by its "terrible" consequences.
The main task of the 4th and 5th stages of P. century.(respectively, adolescents of senior school age and young men and women who have graduated from school) - coverage of gender relations as a complex moral, social and hygienic problem, a presentation of the basics of sexual hygiene, prevention of sexually transmitted diseases and abortions, moral and ethical issues and hygiene of marriage.
Beginning with puberty, adolescents seek and assert their ideals; they are very critical, easily come into conflict with adults, often overestimate their own moral merits or, on the contrary, suffer from their imaginary shortcomings. The main motive for the behavior of an awakening woman gradually becomes the desire to please others, then - to representatives of the male sex, the desire for empathy, for 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 everything as an adult" (including smoking, drinking alcoholic beverages, etc.), and begin to look closely at the girls. Often, former attachments to girlfriends (for girls) and comrades (for boys) gradually fade into the background. Young people seek to suppress vague desires in themselves, but do not know how to do this, they do not know how to find themselves in the society of their peers of the opposite sex, they 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 in the nature of an imperative or prohibition (in which case the prohibition is openly or covertly violated). The ability of an adult to see the beautiful (both in nature, art, labor, a person), to make himself pleasing to others, to treat others with respect and care, attracts the attention of a young person and influences him.
Fertilization is a complex mechanism of sequential processes, only with strict observance of the conditions of which you can get the desired pregnancy. So, a woman must have a mature egg, passable fallopian tubes, a sufficient thickness of the uterine mucosa, which must be ready for the attachment of a fertilized egg. After implantation, the female body must provide hormonal support for pregnancy.
A man should have a sufficient number of morphologically normal mobile mature spermatozoa capable of penetrating the uterine cavity, fallopian tube through the cervix and fertilizing the egg.
In women, the sex cells are called eggs, and in men, spermatozoa.
The ovum resembles an ordinary cell, has a rounded shape, includes a nucleus containing DNA (maternal genetic material), cytoplasm and a membrane. The cell is surrounded by the so-called "radiant crown", consisting of protective cells.
The spermatozoon has a fundamentally different structure. This is due to the function it performs: it needs to overcome the distance from the cervix to the ovarian section of the fallopian tube. The spermatozoon has a head (which contains DNA: paternal genetic material), a neck and a tail. On the head of the sperm there is a special structure - the acrosome, which contains enzymes that facilitate the penetration of the sperm into the egg.
The fundamental difference between the female and male organisms is that the supply of eggs in the female body is strictly limited and is laid during the intrauterine development of the girl. When the innate supply of follicles is depleted, a woman loses her reproductive function (menopause). In the male body, the process of sperm formation does not depend on age and is permanent.
The physiological process of fertilization
The process of fertilization is completely dependent on hormonal regulation, the psycho-emotional state of the female body, environmental factors, etc. The menstrual cycle conditionally begins on the first day of menstruation, when the hormonal background “zeroes out”. It is then that the growth of a cohort of follicles begins, from which, by the 5-7th day of the menstrual cycle, one follicle is selected. When the follicle reaches a size of 18-25 mm (usually on the 12-14th day of the menstrual cycle), ovulation occurs.
As a result, the egg is released into the abdominal cavity, from where, with the help of fimbriae (special outgrowths of the fallopian tube), it enters the ovarian section of the fallopian tube, where it meets with spermatozoa, which, in turn, after ejaculation, have come a long way for several hours along the female sexual tract. As a result of this meeting, in the presence of favorable environmental conditions, fertilization occurs.
In the future, the already dividing embryo (zygote - containing maternal and paternal genetic material) makes its way through the fallopian tubes to the uterus due to peristaltic contractions of the walls of the fallopian tubes, the movement of the villi and the capillary flow of fluid. Later, getting into the uterine cavity, the embryo is attached to one of the walls of the uterus, implantation and further development of the embryo occurs.
Conditions necessary for a successful fertilization process:
maturation of the follicle in the ovary, the egg ready for fertilization;
ovulation, sufficient function of the corpus luteum;
normal concentration of high-quality active spermatozoa;
penetration of spermatozoa into the fallopian tubes, their promotion through the female genital tract, the ability to fertilize;
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