Artificial insemination - types and description of methods (IV, IV, artificial insemination), indications (infertility, diseases), contraindications and complications, requirements for a sperm donor. reviews and prices of procedures in clinics

Fertilization - This is the process of fusion of germ cells. As a result of fertilization, a diploid cell is formed - a zygote, this is the initial stage of the development of a new organism. Fertilization is preceded by the release of reproductive products, i.e. insemination. There are two types of insemination:

1) external. Sexual products are released into the external environment (in many freshwater and marine animals);

2) internal. The male secretes sexual products into the female's reproductive tract (in mammals, humans).

Fertilization consists of three successive stages: the rapprochement of gametes, activation of the egg, fusion of gametes (syngamy), and acrosomal reaction.

Gamete convergence

It is caused by a combination of factors that increase the likelihood of gametes meeting: sexual activity of males and females, coordinated in time, appropriate sexual behavior, excess sperm production, large egg sizes. The leading factor is the release of gamones by gametes (specific substances that promote the rapprochement and fusion of germ cells). The egg releases gynogamones, which determine the directional movement of sperm towards it (chemotaxis), and the sperm secrete androgamones.

For mammals, the length of time gametes stay in the female genital tract is also important. This is necessary for sperm to acquire fertilizing ability (so-called capacitation occurs, i.e., the ability to undergo an acrosomal reaction).

Acrosome reaction

The acrosome reaction is the release of proteolytic enzymes (mainly hyaluronidase) that are contained in the acrosome of the sperm. Under their influence, the membranes of the egg dissolve in the place of greatest accumulation of sperm. Outside is a section of the cytoplasm of the egg (the so-called fertilization tubercle), to which only one of the sperm attaches. After this, the plasma membranes of the egg and sperm merge, a cytoplasmic bridge is formed, and the cytoplasms of both germ cells merge. Next, the nucleus and centriole of the sperm penetrate into the cytoplasm of the egg, and its membrane is integrated into the membrane of the egg. The tail part of the sperm is separated and resorbed, without playing any significant role in the further development of the embryo.

Activation of the egg

Activation of the egg occurs naturally as a result of its contact with the sperm. Takes place cortical reactiontion, which protects the egg from polyspermy, i.e. penetration of more than one sperm into it. It lies in the fact that detachment and hardening of the vitelline membrane occurs under the influence of specific enzymes released from the cortical granules.

Metabolism changes in the egg, the need for oxygen increases, and active synthesis of nutrients begins. The activation of the egg ends with the beginning of the translational stage of protein biosynthesis (since m-RNA, t-RNA, ribosomes and energy in the form of macroergs were stored in oogenesis).

Fusion of gametes

In most mammals, at the time the egg meets the sperm, it is in metaphase II, since the process of meiosis in it is blocked by a specific factor. In three genera of mammals (horses, dogs and foxes), the block occurs at the stage diakinesis. This block is removed only after the sperm nucleus penetrates the egg. While meiosis completes in the egg, the nucleus of the sperm that penetrates it takes on a different appearance - first an interphase and then a prophase nucleus. The sperm nucleus turns into the male pronucleus: the amount of DNA in it doubles, the set of chromosomes in it corresponds to n2c (contains a haploid set of reduplicated chromosomes).

After completion of meiosis, the nucleus turns into the female pronucleus and also contains an amount of hereditary material corresponding to n2c.

Both pronuclei undergo complex movements within the future zygote, come closer and merge, forming a synkaryon (contains a diploid set of chromosomes) with a common metaphase plate. Then a common membrane is formed and a zygote appears. The first mitotic division of the zygote leads to the formation of the first two embryonic cells (blastomeres), each of which carries a diploid set of chromosomes 2n2c.

Fertilization of an egg is an amazing process that has been studied by specialists around the world for many years. We know all the stages that sex cells go through before and after the cherished meeting. At the moment of fertilization, something new is formed from the parent cells, combining genetic information from the mother and father. This microscopic unique cell is destined to become a full-fledged person in the future.

The success of fertilization depends on many factors. This process is preceded by hundreds of others, no less important. Conception will not occur if the process of maturation and movement of germ cells: sperm and eggs is disrupted.

Advancement of sperm to the egg

From the moment of ejaculation until the germ cells meet, 3 to 6 hours pass. Sperm are constantly moving, moving towards the point of contact with the egg. The female body is designed in such a way that a man’s reproductive cells encounter many obstacles along the way, intended by nature as a protective mechanism. In this way, weak sperm are eliminated, which are potentially dangerous and not suitable for the formation of a new life.

During one sexual act, up to 300 million sperm enter the vagina, but only one will reach the target. Millions of male reproductive cells die on the way to the egg and directly next to it. Most of the cells flow out along with the sperm almost immediately after ejaculation. A huge number of sperm die in the vagina and cervical mucus of the cervix. A certain number of sperm get stuck in the folds of the cervix, but they become a reserve in case the first group of cells does not reach.

Notably, these stuck sperm are the cause of pregnancy before ovulation. Everyone knows that fertilization becomes possible only after ovulation, but there is a chance of getting pregnant on any day of the cycle. When sexual intercourse occurs before the egg is released, these stuck sperm wait until ovulation and continue on their way to the reproductive cell. Sperm can remain “alive” for up to 7 days, so the risk of pregnancy remains before and after ovulation.

Since sperm are not familiar to the woman’s immune system, it mistakes them for foreign elements and destroys them. If a woman’s immune system is overactive, we can talk about immunological incompatibility, which can cause infertility in a couple.

Sperm that survive the immune attack move into the fallopian tubes. Contact with the slightly alkaline mucus of the cervical canal provokes an increase in sperm activity, they begin to move faster. Muscle contractions help sperm move inside the uterus. One part goes into the fallopian tube, and the other goes into the uterine tube, where the egg is located. In the tube, sperm must resist the flow of fluid, and some cells are retained by the villi of the mucous membrane.

At this stage, reactions are triggered in the upper parts of the tract that provoke capacitation (ripening) of sperm. Certain biochemicals are responsible for this. Due to capacitation, the membrane of the sperm head changes, preparing for penetration into the egg. Sperm become hyperactive.

Maturation and advancement of the egg

Regardless of the length of a particular woman’s cycle, ovulation occurs 14 days before menstruation. With a standard cycle lasting 27-28 days, the release of the egg from the follicle occurs in the middle. It is noteworthy that the length of the cycle varies from woman to woman and can reach 45 days or more. For this reason, experts recommend calculating the day of ovulation based on the expected onset of menstruation. You need to count two weeks from this date.

Terms of fertilization:

1. 14 days before menstruation, the egg is released from the follicle. Ovulation occurs. During this period, the risk of becoming pregnant is greatest.
2. Within 12-24 hours after ovulation, a sperm can fertilize an egg. This period is called the fertile window. One day after ovulation, the egg dies, but this time can be shortened depending on many factors.
3. If sexual intercourse occurs after the egg leaves the follicle, fertilization requires only 1-2 hours. During this time, sperm travel 17-20 cm from the vagina to the fallopian tubes, taking into account all obstacles.
4. If intercourse occurs before ovulation, fertilization is possible within a week. It is noteworthy that sperm with the Y chromosome are faster, but live 1-2 days, and cells with the X chromosome are slow, but can withstand the negative influence of the environment for a week. Many methods of conceiving a child of a certain gender are based on this fact.

Ovulation is a small explosion of the follicle. The egg and the fluid in which the oocyte matured enter the abdominal cavity. The “fringe” of the fallopian tubes includes ciliated epithelium, which unidirectionally propels the egg towards exit from the ovary. These cilia are activated by estrogen, hormones released by the ovaries after ovulation.

During this period, the egg is surrounded by cumulus cells, which form the corona radiata. This crown contains follicular cells and is the secondary shell of the egg. It becomes an obstacle for the sperm during direct fertilization.

How do germ cells unite?

Fusion of gametes

Direct fertilization occurs in the fallopian tube, closer to the ovary. This stage of the journey is reached by dozens of sperm out of hundreds of millions: the strongest, hardiest and most active sperm. Only one fertilizes the egg, and the rest help it penetrate inside the cell and die.

The most active ones penetrate through the corona radiata and attach to receptors on the outer - pellucid - membrane of the egg. Sperm secrete proteolytic enzymes that dissolve the protein coat. This weakens the protective layer of the egg so that a single sperm can penetrate.

The outer shell protects the inner membrane. The sperm that reaches this membrane first attaches itself to it, and the sex cells fuse in a matter of minutes. The “absorption” of sperm by the egg triggers a chain of reactions that cause changes in its membrane. Other sperm can no longer attach; in addition, the egg secretes substances to repel them. Having merged with the first sperm, the egg becomes impenetrable to others.

As soon as the sperm has penetrated the egg, mechanisms are launched in the woman’s body that notify other systems about fertilization. The functioning of the organs is reorganized in such a way as to preserve the vital activity of the embryo. Since the body may begin to mistake the fertilized egg for a foreign formation, the immune system weakens and cannot cause rejection of the fetus.

Formation of a new genome

In sperm, genetic information is tightly packed. It begins to open only inside the egg, and a pronucleus is formed around it - the precursor of the zygote nucleus. In the pronucleus, the genetic material is rearranged to form 23 chromosomes. It is noteworthy that the genetic material from the mother finishes forming only during the process of fertilization.

Microtubules bring the two pronuclei closer together. Sets of chromosomes combine to form a unique genetic code. It contains information about hundreds of characteristics that a future person will have: from eye color to character traits. These characteristics depend largely on hereditary information passed down from generation to generation, but unique “blocks” are also created.

Fertilization of an egg in stages

1. Sperm “attack” the egg. They hit it with their tails to cause it to spin.
2. A sperm penetrates inside the egg.
3. The fusion of paternal and maternal chromosomes, the formation of a new genetic program. After this, the fertilized egg is called a zygote.
4. 30 hours after fertilization, the division of the zygote begins. The new cells are called blastomeres.
5. On the first day after the zygote is divided into two, then divided into four blastomeres.
6. On the third day there are eight blastomeres.
7. The fourth day is marked by the division of the zygote into sixteen cells. From this time on, the embryo is called a morula.
8. Crushing continues, but liquid forms inside the morula. A blastocyst is formed - the last stage of embryo development before moving into the uterus and implantation.
9. At this stage, the fertilization process is completed, but a full-fledged pregnancy has not yet occurred. Then the zygote moves through the fallopian tubes into the uterus, implants and begins to develop until birth.

After the fertilized egg passes into the uterus, the division process ends and its introduction into the endometrium begins. The place of attachment of the embryo determines the position of the child in the abdomen: when implanted along the back wall, women have a small stomach, and when implanted along the front wall, it is larger.

The introduction of an embryo into the endometrium triggers many biochemical processes, so a woman may experience nausea during this period, a fever and headaches. A specific sign of implantation is bleeding, indicating damage to the walls of the uterus.

How does pregnancy begin?

The first week after fertilization, the zygote is located in the fallopian tubes. On the seventh day, it begins to descend into the uterus and looks for a place to attach. In a healthy woman at this stage, the endometrium of the uterus is thickened, so the zygote is easily fixed without a significant risk of rejection. Insufficient endometrial thickness often causes female infertility.

During the period of movement from the fallopian tubes to the uterus, the egg takes nutrients from the corpus luteum, so the lifestyle of the expectant mother does not play an important role at this stage. However, after the zygote attaches to the endometrium, the situation changes: the pregnant woman must reconsider her lifestyle and nutrition, because now the development of the fetus depends entirely on her behavior. It is important to maintain a normal mental and physical state.

The zygote burrows into the endometrium and implantation begins. This process takes approximately 40 hours: cells divide, penetrate into the mucosa, and then grow. Blood vessels are actively formed, which in the future will turn into the placenta. The embryonic nodule begins to form the body, and the surface cells are the parts that are needed for the development of the fetus (amniotic sac, placenta, umbilical cord). The completion of implantation marks the beginning of the pregnancy period, that is, bearing a child.

Amnion or amniotic sac is a sac of colorless amniotic fluid. They are needed to protect the fragile fetus from pressure from the walls of the uterus, temperature fluctuations, noise and external shocks. In addition, amniotic fluid supports metabolism.

The placenta is a unique organ. It provides the fetus with everything necessary for growth, development and life. At a certain stage, the placenta performs the functions of the lungs, kidneys and digestion, and also produces hormones and other elements necessary for the full development of the child. It transports fresh maternal blood into the umbilical vein and removes metabolic waste from the fetal arteries. The placenta is a kind of filter that protects the fetus from harmful microorganisms and substances. The umbilical cord connects the fetus and the placenta. Blood flows back and forth through the vessels inside it.

3 stages of pregnancy

Pregnancy is divided into three stages: the formation of the body and organs to support the life support of the fetus, the adjustment of body systems, and preparation for birth. Despite the fact that pregnancy lasts 9 months, in medicine this period is counted by weeks. From conception to the appearance of a new life, approximately 40 weeks pass, which is equal to 10 lunar months (based on the 28 days of the cycle). Therefore, the pregnancy calendar consists of 10 months. It is easier to track changes occurring in a pregnant woman’s body using this calendar. A pregnant woman knows exactly what week she needs to take tests and undergo an ultrasound.

How to increase your chances of successful conception

The most favorable period for conception is two days after ovulation. However, if you take into account the viability of sperm for 5 days, active sex should begin 3-4 days before ovulation. The sperm will already be “waiting” for the egg in the abdominal cavity and fallopian tubes.

You can accurately determine the day of ovulation by basal temperature, but you need to rely on such a calendar only after 6 months of regular measurements. In laboratory conditions, ovulation can be determined by urine and saliva.

If a woman’s menstrual cycle is a standard 28 days, for successful conception you need to have sex on days 10-18 of the cycle (preferably every other day when the first day of the cycle is the day of menstruation). You shouldn’t be too pedantic about conception; the main thing in this matter is pleasure and relaxation.

Despite the fact that frequent ejaculations reduce the volume of seminal fluid, regular sex is the key to good sperm motility. Therefore, for successful fertilization, it is enough to have sex every other day. Daily intercourse guarantees conception by 25%, while one sexual intercourse per week reduces the chances to 10%.

A woman can increase the likelihood of conception if she lies on her side or raises her pelvis immediately after sex. However, you need to take into account the peculiarities of the structure of the uterus: when it is bent, it is better to lie on your stomach, slightly bending over, and with a bicornuate form, raise the pelvis. The main thing is that sperm does not leak out of the vagina. After intercourse, you should not use hygiene products or douche, as this can change the pH of the vagina and affect sperm.

If partners have difficulty conceiving, you can go to the clinic and, using diagnostic equipment, accurately track the maturation of the follicle and the time of release of the egg. Harmless and painless ultrasound diagnostics are suitable for these purposes.

You need to understand that fertilization of an egg is not pregnancy. We can talk about successful conception only after the embryo reaches the uterus and goes deeper into the endometrium. A week passes from fertilization of the egg to pregnancy. This time is needed for mechanisms to be activated that do not allow a zygote with the wrong set of chromosomes to implant. This is possible, but most often “broken” zygotes die before or immediately after implantation. They come out along with menstrual flow, so the woman does not even know what processes took place in her body. Such phenomena, as a rule, are not called a lost pregnancy.

The problem of fertilization is one of the most pressing today. Many couples, when thinking about children, try to understand the smallest details of the process. In this article we will discuss in detail what fertilization is in simple words and how the process occurs in human biology.

What is it

During sexual intercourse, the man's seed penetrates the woman's womb, where the gametes (male and female reproductive cells) meet to merge into one. The result of this fusion is called fertilization. An educated zygote carries all the genetic information from both parents.

Did you know? In terms of its effect on the body, sexual intercourse is compared to intense physical activity. During sex, the heart rate increases, muscles contract, body temperature rises and toxins are eliminated (along with sweat), fats and calories are burned (100 kcal for a man, 69 kcal for a woman) - data provided by the University of Montreal.

How does fertilization occur?

The process of merging male and female cells can occur naturally and... The second option helps couples who have problems with childbearing and gives them a chance to become parents.

Natural

Let's look at how the process of egg fertilization occurs day by day.

1st day: . A mature female cell leaves the follicle, it is picked up and advanced to meet the male cell of the villi, which cover the surface of the fallopian tubes.

2nd. Having gone a long way and reaching the shell of the egg, it secretes a special enzyme that dissolves part of the protective shell and forms a passage for the sperm. Penetrating into a female cell, the sperm discards its tail as unnecessary (the information is stored in its head). Literally within half an hour after penetration, two cells merge, forming a single zygote. At this point, the fertilization process is completed, and the process of embryo formation begins. The zygote actively divides every 12-16 hours.

4th day after conception: the embryo is formed, now it needs to reach the uterus through the tubes and gain a foothold there.

5th. The embryo has reached the uterine cavity and for some time will look for the most convenient place for itself.

On days 6-7 after fertilization, pregnancy can be suspected by vaginal discharge, which is called and classified as an early symptom. The discharge is caused by the actions of the embryo - in order to attach itself to the wall of the uterus, it literally bites into its endometrium, touching the vessels. The process of attachment, that is, implantation, takes approximately two days.

10th day. Changes occur in the lining of the uterus, and tissue of the future placenta begins to form. At the same time, the established embryo releases the pregnancy hormone into the maternal blood, to which tests react.

After a positive reaction confirming pregnancy, the doctor observes the process of its development day by day. The entire period of waiting for childbirth is divided into trimesters according to the processes occurring during the three-month period.

Artificial

It is not always possible to get pregnant naturally; artificial insemination comes to the rescue. The method depends on the cause of infertility; today there are three types of procedures:

The simplest type of fertilization and the closest to natural is AI. Before the procedure begins, the couple undergoes mandatory examinations: (women) and (men).

Before the process itself, sperm with the highest activity are collected. Next, the male seed is introduced into the uterine cavity through a catheter, where sperm repeat the path intended by nature, moving through the tubes, they find and fertilize the egg. AI efficiency is up to 20.5%.

Before the procedure, the following mandatory examinations are required:

• (urine, blood, hormones),
• spermogram,
• smears and blood samples for sexually transmitted infections,
• and condition .

Let's look at how fertilization of an egg occurs during IVF in a woman. The woman receives a course of injections that stimulate the maturation of full-fledged female cells, which are then removed (under anesthesia).

Male semen (pre-selected strong and mobile sperm) is placed in an environment close to natural conditions. Male and female cells are mixed and the result is awaited. After a successful fusion, the strongest zygotes are selected for embryo cultivation. Two or three viable embryos are transferred to the woman's uterus, where they take root and develop as in a normal pregnancy. The effectiveness of the method is up to 30%.

The ICSI procedure requires the same tests and studies as for IVF. Specialists study the activity of sperm under a powerful microscope, select the most active one and use a needle to insert it into the female cell (pre-treated with a special composition that dissolves its membrane). The success of this method is estimated at 30%.

Basic rules for successful fertilization

Many factors influence the successful fusion of male and female cells. Perhaps the most important thing is to calculate the ovulation period or, in simple words, the day on which fertilization occurs. The fact is that the egg is viable for only a few hours, while sperm live for about three days; they need a day to pass into the fallopian tube. Therefore, it is preferable to plan conception a day or two before ovulation. Regular sex life of a couple increases the chances of conception; it also has a positive effect on sperm activity.

Did you know? The scientific journals “EurekAlert” and “Nano Letters” published a description of the development of IIN scientists in Dresden. Nanotechnologists have invented so-called spermbots - roughly speaking, a micromotor that wraps around the sperm flagellum and delivers it to the female cell. Such a device can help many couples who want to have children.

Condition, lifestyle, and bad habits are of no small importance for success. Let's break it down point by point. After using the products, it will take some time for complete recovery. If the drugs were based on hormones, the hormonal balance should be restored. Analgesics and anti-inflammatory drugs have a negative effect on ovulation.

Poor nutrition reduces the likelihood of conception. Sweets in large quantities, fast food, flour and fatty foods increase weight and blood sugar levels. This provokes hormonal imbalance. Caffeine and adherence to vegetarianism have a bad effect on reproductive function; the body needs animal proteins.

Important! It is advisable to normalize excess or underweight with the help of a qualified nutritionist, and not on your own.

Stress is harmful to both men and women, and it equally affects the ability to bear children. You need to be able to relax and avoid provoking situations. Massage, aromatherapy, and a relaxing bath help with this.

Giving up bad habits - alcohol, alcohol - will significantly increase the chances of success. Alcohol and nicotine negatively affect the production of hormones necessary for sperm activity and ovulation; in addition, abuse can provoke pathologies at an early stage of embryo development.

Of course, it is important to monitor your health. Often men and women brush aside seemingly minor ailments, forgetting that the body is a single system. Once every six months, a year, you can and should set aside time to visit a gynecologist, urologist, and take general tests to prevent health problems.

Consciousness plays a key role in successful fertilization and the subsequent birth of a healthy baby. Under the supervision and recommendations of a specialist doctor, future parents will be able to prepare qualitatively, undergo the necessary examinations, and possibly procedures, which will significantly increase the chances of conception.

How did life originate on our planet? You can believe in the big bang theory, the divine principle, or Charles Darwin's teachings about evolution. What is certain is that all species of organisms on Earth continue to exist through reproduction. Which, in turn, is unthinkable without fertilization. What is fertilization, its types and types, meaning and stages, as well as other interesting details, we will consider in this article. [photo1]

The union of two cells of different sexes, male and female, as a result of which the initial stage of a new organism is formed, is fertilization. The male cell (sperm) has a stimulating effect on the female cell (ovum) and causes the beginning of its development. The introduction of a set of paternal chromosomes into the maternal egg reflects the essence of fertilization. Its biological significance lies in the formation of a zygote - a cell that combines the characteristics of both parents in various proportions and combinations. Thus, the hereditary inclinations of the maternal and paternal organisms are combined and reward their offspring with them. This creates many genetic variations that influence the evolutionary process of the species and its natural selection.

Types of fertilization

Having decided what fertilization is, you should understand its types. Depending on the number of organisms involved in the process of sexual reproduction, cross-fertilization and self-fertilization are distinguished. Different individuals take part in cross-fertilization. Its essence is easy to imagine using the example of a flower: pollen from the pistil of one plant is transferred to the stigma of a completely different one. Cross fertilization of plants is called pollination. It directly depends on external factors that contribute to its implementation. Cross fertilization is inherent in all mammals and humans. Self-fertilization is a process in which cells of the same individual take part. Occurs in the animal world in bisexual organisms in which their own female and male cells unite. A striking example is tapeworms. Self-fertilization is also characteristic of non-opening flowers that are capable of self-pollination.

Types of fertilization

Depending on where exactly the fertilization process occurs, there are several types:

• External fertilization.
  It is characteristic of those amphibians, mollusks, fish, and amphibians in which fertilization occurs outside the body of their female. Usually occurs in an aquatic environment, where representatives of male and female individuals deposit their heterosexual cells. Since their meeting directly depends on external factors, organisms produce a huge number of eggs and sperm, from several thousand to several million. Indeed, with the external type of fertilization, most of the germ cells die, and it is this approach that ensures the survival of the species.
• Internal fertilization.
  Occurs in all species of terrestrial animals. Also found in some aquatic species. The meeting and fusion of male and female cells occurs in this case in the female’s body, or more precisely, in her reproductive tract. This ensures the highest probability of fertilization, so much fewer cells of different sexes are needed to participate in the process. Next, the embryo develops in the mother’s body and the possibility of its death is minimized. Animals tend to have few offspring and therefore care for them and exhibit signs of complex parental behavior. To achieve fertilization, a person needs 1 egg and 1 sperm, which, however, can cover a long distance to meet it.
• Double fertilization.
  Found in angiosperms and flowering plants. The process is ensured by the presence of 2 male sperm and 8 female nuclei. One sperm fertilizes the egg, which subsequently forms into an embryo, the other merges with the large nucleus of the central cell and forms the nutrient medium necessary for the formation of a new organism.
• Artificial insemination. This type is widely used in animal husbandry and agriculture, when pre-planned artificial crossing or insemination is used to obtain the required combination of properties. In this way, additional offspring are obtained from an outstanding producer or plant varieties with certain qualities are developed. In humans, artificial insemination is used in the treatment of infertility. It is called extracorporeal, out-of-body, or IVF.
  Its principle is that fertilization of an egg by a sperm occurs outside the female body. Only after the cells have fused into a single, fertilized egg is placed in the uterus. The method of producing a “test tube baby” is gaining immense popularity and gives a chance to become parents to those couples who are unable to conceive a child naturally. Often, in this case, donor male or female germ cells are used.

Some organisms are capable of reproduction without the process of fertilization. Bees, aphids, some birds and amphibians are capable of parthenogenesis. Here, for the development of a cell, the genetic material of only one parent is used and same-sex offspring are produced.
In addition to the above types of fertilization, it is divided into monospermy - when only one sperm penetrates the egg, and polyspermy - in this case, several male ones enter the female cell at the same time. But even in this case, a single-nuclear fusion occurs, while the remaining nuclei are destroyed. The first variant of fertilization affects most representatives of the animal and plant world, while the second is characteristic only of certain groups of animals and certain plant species.

Stages of fertilization

In order for the process of cell fusion to occur, they must go through several stages:

1. The egg and sperm must come closer and begin to interact. This is aided by the ability of the male cell to move only against a substance that the female cell secretes, called chemotaxis. And also rheotaxis, which implies the ability of the sperm to move forward and against the flow of fluid in the fallopian tubes.
2. Cells (or gametes) begin contact interaction. A fairly large number of sperm reach the outer pellucida of the egg. Only the one that manages to be the first to overcome these outer shells by softening the adjacent area attaches to the egg.
3. The sperm penetrates the egg.
4. In the human body, at this stage there is a passive and slow movement of the female egg through the fallopian tube to the uterus. In the body of animals, a fertilized cell begins preparation for fragmentation.

Basic principle of fertilization

Fertilization must occur strictly within the species. This corresponds to a certain number and structure of male and female chromosomes, as well as their chemical affinity. If fertilization of foreign germ cells does occur, the development of the embryo occurs abnormally and, as a rule, leads to the appearance of sterile individuals incapable of childbearing.

The process of the origin of life in humans

The meeting and union of a male sperm and a female egg is the first step in the birth of a new human life. A zygote, a cell formed as a result of this process, combines a set of 46 parental chromosomes containing their entire genetic code. The gender of the unborn child is random, like winning the lottery, but is already determined at this stage. The fertilization process, on the one hand, looks quite simple. In fact, this is a rather complex and multi-stage reaction. Despite the rapid development in the field of reproductive technologies, the process of fertilization still seems to be a kind of miracle, a mystery. Having understood what fertilization is, it is very important to understand what genetic code we, humans, and the inhabitants of our entire planet as a whole will pass on to our descendants.

The birth of a new life is a real miracle. How much must happen for a cell to turn into a person? Knowledge of where this truly unique process begins will be useful when planning pregnancy and expecting a child.

Conditions for fertilization

A girl can become pregnant from the moment her menstruation begins. In each such cycle, processes occur that prepare the woman’s body for conception. We are talking, first of all, about developing the necessary hormones regulating the maturation and ovulation of the egg.

Hormonal imbalances can lead to negative consequences: delayed ovulation, its complete absence, termination of pregnancy, infertility.

During the normal process of egg maturation, ovulation occurs in the middle of the cycle. Egg leaves the follicle and ovary, enters the fallopian tube and moves along it towards the uterus. The internal contents of the egg are protected by a dense protein shell, in which nutrients are also concentrated.

The time for fertilization and conception is limited to 24 hours. If nothing happens during this time, the egg will die.

Sperm before fertilization

In the male body, under the influence of hormones, sperm are formed. Their maturation occurs in the testicle, then they enter the epididymis, after which, moving along the vas deferens, they reach the seminal vesicles and prostate gland. It is in this gland that sperm are mixed with internal secretions. This is how sperm appears. She ends up taking part in the process. fertilization.

During sexual intercourse, about five hundred million sperm enter the female genital tract along with sperm. Along the way, the weakest cells are eliminated, but only hundreds reach the goal. Large screening occurs when moving through the mucus plug in the cervix: only the fastest and most mobile penetrate inside. The advancement process does not end when it enters the woman’s internal genital organs. Purpose spermatozoa is the fallopian tube. This is where fertilization of the egg occurs. Before this, the woman’s immune system destroys another part of the sperm as carriers of foreign genetic material.

The best time for fertilization

A woman's body is best tuned to fertilization on the eve of ovulation. Therefore, for couples planning a pregnancy, it is ideal if sexual contact passes at this time.

On the eve of ovulation, the fallopian tubes are most mobile, the mucus in the cervix thins, and the activity of cellular immunity decreases.

When sexual intercourse occurs two to four days before ovulation, the strongest, healthiest and most tenacious sperm can wait for the egg to mature in one of the sections fallopian tube.

If sexual intercourse took place before ovulation, sperm are already waiting for the egg. In this case, given the speed of sperm movement, there is a possibility that fertilization will occur within an hour after ejaculation.

Otherwise, the chance of conception remains within 24 hours after ovulation. It is not possible to accurately calculate the time of ovulation by day or hour, so fertilization is possible even on the seventh day after sexual intercourse. If this does not happen, the couple planning a pregnancy has to wait for the next cycle.

Fertilization process

So, how does egg fertilization occur in humans? Let us remember that it can only happen during the period of ovulation (about a couple of weeks before the next menstruation).

Fertilization is the fusion of an egg and a sperm. Usually, several male germ cells secrete enzymes go into attack. The outer shell is destroyed. Most often, one of the sperm reaches the goal.

After the union of male and female reproductive cells, a dense membrane is formed around the egg, preventing further penetration of sperm.

The fertilized egg is called a zygote. She begins to move towards the uterus. Most often, its progress through the fallopian tube takes from five to seven days. During this period, active cell division is observed.

A week later, the embryo implants into the wall of the uterus. The production of the hCG hormone begins. Germ receives oxygen and nutrients.

Whether pregnancy occurs is determined by the presence and concentration of the hCG hormone in a woman’s blood.

If pregnancy does not occur

Many couples who have no problems conceiving children find it difficult to understand those for whom having a child, for various reasons, seems like an unattainable dream. Do not panic if pregnancy does not occur on the first (second or third) try. It is believed that the reason to consult a doctor is a one-year period of regular unprotected sexual activity, during which conception has not occurred.

With the modern level of medical development, many couples can be helped: after treatment, they have long-awaited babies. In some cases, with male and female infertility, the only solution is artificial insemination.

The essence of in vitro fertilization, or IVF, is in vitro fertilization. The egg, removed from the body of the expectant mother, is combined with the sperm of the future father artificially, in a test tube. After this, the embryo is placed in an incubator for two to five days. Then the embryo, again artificially, is transferred to the woman’s uterus, where its further development occurs. If it is impossible to obtain an egg or sperm from future parents, donor cells.

Thus, the seemingly simple and natural process of fertilization has many pitfalls. But for the sake of the happiness of the birth of a child, future parents, with the help of the latest advances in medicine, overcome all difficulties and obstacles.