Fiery fertilization. Fertilization. The essence of double fertilization. Where and how does the fertilization process occur?

Pollination is the process of transferring pollen from the pistil to the pistil. There are two types of pollination: self-pollination and cross-pollination. Self-pollination is the process of transferring pollen from a bisexual flower to the primrose of the same or another flower, but of the same individual. Some plants (barley, oats, millet, some wheat, rapeseed) are cut down even when the flowers have not opened. When cross-pollination occurs, the flower files of one individual are transferred to the flower files of another individual. This is the main type of pollination of flowering plants (apple tree, willow, cucumbers, etc.).

Cross-pollination occurs naturally (by insects, birds, wind, water) and artificially (by humans) in ways.

Vitrozapilnye plants have flowers without nectaries, small, inconspicuous, with a simplified, non-colorful perianth. Large pilae on long stamen filaments protrude far from the perianth, the pistils are open, with large pipules. A lot of pollen is produced, it is small, light, with a smooth surface. Vitrograss plants often grow in open places, forming thickets of one type (reed, feather grass, flat grass). A significant number of glassweed plants bloom in early spring, when the leaves begin to bloom (hazel, alder, birch, etc.).

The overwhelming majority of pocritus-blue plants, distributed in different climatic zones, belong to the entomophilous, or coma-hosing, plants. The perianth (usually the corolla) of entomophilous plants is brightly colored and clearly visible against the green background of the leaves. Flowers are solitary or collected in inflorescence. The pellets of coma-grass plants are smaller than those of vitrozapil plants and produce less pollen: the pollen is large, sticky, with a tuberous or knobby surface. At the bottom of the wreath of many flowers, nectaries are formed, in which a fragrant sweet juice is produced - nectar, the secretion of which stops after fertilization. There are a number of other signs designed to attract insects. This indicates that the evolution of plants and their plants proceeded in parallel. This is the so-called conjugating evolution (coevolution).

Cross-pollination ensures the exchange of genes, maintains high heterozygosity of populations, provides material for natural selection and stores persistent offspring - carriers of the most favorable ratio of genes.

Artificial pollination is widely used to increase yields and breed new plant varieties. At the same time, different methods are used to transfer pollen to the pistil. Yes, from corn, which has unisexual flowers, pollen is collected by shaking the panicle tips of the male flowers into paper bags.

Then the collected pollen is transferred to the female flowers with a brush.

To artificially pollinate a sunflower, put a glove on your hand, use it to remove pollen from one plant and transfer it to another. You can do this by pressing two baskets against each other.

To develop new varieties of plants with bisexual flowers, preparation for artificial pollination is necessary. First of all, the files are removed from the flowers of the plant chosen as the mother plant while still in the bud and these flowers are protected with gauze or paper bags from the nail file being damaged. After 2-3 days, when the bud opens, pollen of a different variety is applied to the pistil with a clean, dry brush, a soft piece of rubber, etc.

Double fertilization. After pollination, the process of fertilization occurs - the fusion of a male reproductive cell with a female one. The pollen that has fallen on the surface of the primordium continues its development (pollen begins to germinate in the pilae), which outwardly turns out to be swelling, the formation of a pollen tube, the walls of which consist of intini and pass through the pores in the exini. The formation of a pollen tube is stimulated by substances that are secreted by the pollen in response to related pollen that has fallen on it. The pollen tube passes through the lush tissue of the style in a short time and penetrates through the micropyle to the embryo sac. Many pollen tubes germinate at the same time, but only one fuses with the embryo sac. Two sperm cells, which were formed from the generative cell as a result of the mitotic process, pass into the pollen tube, which was formed from the vegetative cell. In some cases, sperm can form while still in the pellet. At the point of contact of the pollen tube with the embryo sac, the walls of the embryo sac become slimy and the pollen tube passes inward. When the egg reaches the egg, the pollen tube ruptures and two sperm cells emerge from it. One of the sperm fuses with the egg, forming a diploid zygote, from which the embryo of a new plant organism develops. The second sperm fuses with the secondary (diploid) nucleus, resulting in the formation of a triploid cell, which gives rise to the endosperm, a supply of nutrients for the embryo.

If the ovary has several seed germs, then in each of them the process described above occurs, which was discovered by the Russian cytologist and plant embryologist S. G. Navashin in 1898 and called double fertilization.

In unicellular plants with asexual reproduction, ontogenesis begins with the appearance of the organism as a result of division of the mother cell and ends with a new division. In sexual reproduction, it begins with the formation of a zygote and ends with the next division or the formation of a new zygote.

In multicellular plants, ontogeny can occur in different ways. An example of such diversity is flowering plants, whose structure is the most complex. In plants that reproduce sexually, ontogeny begins with the development of the zygote. A characteristic feature of ontogenesis is the presence of sexual (gametophyte) and asexual (sporophyte) generations. The sporophyte is formed from the zygote, the gametophyte from the spore. Haploid spores are formed on sporophytes in sporangia, which ensure the reproduction of spore plants. Spores of terrestrial plants can be functionally the same (Riznosporov plants) or different (Rhiznosporov plants). Small spores are called microspores, large ones are called megaspores. The male gametophyte develops from the microspore, and the female gametophyte from the megaspore. In flowering plants, the sporophyte predominates, the gametophyte is reduced. During the development of the sporophyte in higher seed plants, as a result of successive divisions of the zygote from a homogeneous forming tissue in the process of differentiation and specialization of cells, a seed embryo with a germinal root, stem and bud is formed.

The fertilization process usually occurs in the ampulla of the fallopian tube. Occasionally, the place of fusion of the egg and sperm becomes the “sea of ​​love” - the pouch of Douglas (rectumuterine cavity) of the abdominal cavity. The oocyte, surrounded by follicular cells, is captured due to the sliding movements of the tubal fimbriae along the surface of the ovary. Follicular cells maintain contact with the oocyte for some time, providing it with nutrition and facilitating the movement of the tube's cilia. Later, the bulk of the follicular cells are removed from the surface of the transparent membrane by a flow of tubular fluid.

When male and female germ cells come into contact, the sperm first sticks to the oocyte, and then quickly penetrates the transparent membrane, and the sperm’s own energy is sufficient for this. After the sperm penetrates the egg, meiosis ends with the expulsion of the second polar body. In this case, the transparent membrane becomes impermeable to the second sperm.

The movement of the fertilized egg from the fimbriae to the isthmus of the ampulla can occur within several minutes or hours and is caused by segmental contractions of the tubal muscles, vibrations of the cilia and the flow of tubal fluid.

The motility of the tube is determined by the level of estrogen, progesterone, and prostaglandins.

It is believed that the advancement of the egg into the uterus occurs as follows: estradiol stimulates the synthesis of nFF2a, which leads to blocking of the isthmus of the tube at the time of ovulation; under the influence of progesterone in the early luteal phase, PGE2 promotes relaxation of this section and the opening of the uterine tubal sphincter. At the same time, the continued increase in the secretion of PGR2a stimulates rhythmic contractions of the internal longitudinal layer of muscles, which drive the fertilized egg into the uterus. The duration of this process is on average 3-5 days.

In parallel with changes in the contractility of the fallopian tubes, the microcirculation of their muscular walls, which is of great importance in normal physiology, undergoes dynamic transformations. During the proliferation phase, afferent arterioles and shunts open moderately, and the diameter of efferent venules and afferent lymphatic sinuses narrows. By the time of ovulation, the afferent arterioles expand, the shunts narrow, and the venules open. The state of the vascular bed stabilizes at the early stage of the secretory phase, and then returns to the period of the onset of menstruation.

After fertilization, the formation of the zygote begins, in it the synthesis of hCG occurs, the biological activity of which imitates the activity of LH and FSH. By the time the morula reaches the uterine cavity, the amount of hCG that is necessary to prevent lysis of the corpus luteum is synthesized.

On the 5-6th day after fertilization, the morula turns into a blastocyst, which sheds the zona pellucida and, surrounded by a single-layer trophoblast, gradually sinks into the endometrium. Completion of this process, i.e. Complete immersion of the fertilized egg into the mucous membrane of the uterus occurs on the 7th day, while the proteolytic enzymes of the trophoblast destroy the small capillaries of the endometrium and the trophoblast outgrowths are immersed in the gaps.

Podzolkova N.M., Glazkova O.L.

"Fertilization" and others

The birth of a child is the result of thousands of incredible processes occurring inside a woman. A loving mother wants to know everything she can about her baby. For this reason, many future parents are interested in how fertilization occurs.

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Fertilization of the egg

Nature has decreed that a woman can usually become pregnant in the middle of the cycle, when the well-known ovulation occurs. Unlike sperm, an egg can survive in a woman’s natural environment for 12 to 36 hours. If she does not meet the male seed, she dies and leaves the female body through menstrual bleeding.

Hidden here is the answer to the question of how long after ovulation the egg is fertilized. If ovulation has just passed, the egg has escaped from its “nest”, and sperm are already waiting or on the way, fertilization can take place in a matter of hours.

What you've been waiting for for so long

It also happens that during one ovulation, not one egg matures, but two or even three. How does fertilization of the egg occur in this case? Everything happens as usual, only as a result two or three babies are born at once.

Let's look at how fertilization of an egg occurs point by point.

1. After ejaculation, sperm travel a long, winding path towards the egg. If we take the average speed of a male seed, it takes about 3-6 hours to reach its target. Only one sperm will participate in the fertilization process, and the rest are destined to die.
2. Pushing hard, the sperm breaks through the coating of the female egg. At this moment, the entire body is informed that fertilization occurred a moment earlier. This very signal contributes to some restructuring of the female body, designed to preserve any valuable pregnancy.
3. Now that we have figured out how fertilization of an egg occurs in humans, we can see what happens next. Each of the two parent cells contains one half of the set of chromosomes. As a result, the parent cells unite and form a new, perfect cell, with all the genetic data, known as a zygote. The genetic code of the neoplasm is completely unique.
4. Over the course of seven days, the zygote develops inside the fallopian tube, and then begins its journey to the uterus, “looking for a cozy place” where it will develop over the next nine months.
5. Further, moving away from the place where fertilization occurs, the egg takes with it the corpus luteum as food. For this reason, in the first week, lifestyle does not affect the development process in any way.
6. Having found a cozy place, the embryo “buries itself” in the wall of the uterus. This period of development, which lasts no more than 40 hours, is called implantation.
7. The outer cells begin to divide and join with the lining of the uterus. At the site of the branches, microscopic vessels are formed, which later form the placenta - the environment within which the baby grows, feeding and developing, until birth.
8. The body of the future baby is formed from the embryonic nodule. But the above-mentioned placenta, amniotic sac and umbilical cord are formed from the surface cells necessary to ensure development and safe existence. To better understand how egg fertilization occurs, you can watch the video.

Basal temperature

Measuring basal temperature is perhaps the classic method of determining the day of ovulation. Charts of this temperature are usually made by women planning to give birth to a child. But how does basal temperature change after ovulation if long-awaited fertilization has occurred?

If a woman is pregnant, her basal temperature rises to 37 degrees. This allows you to identify the possible situation even before your period is missed. Of course, it is much more effective to get tested, but since hCG is produced only after implantation of an already fertilized egg, it must be done at least a week after sexual intercourse. Well, when you don’t want to wait, measuring your basal temperature will help.

After fertilization occurs, and the body receives a signal about the beginning of the process of fetal maturation, active production of progesterone begins. It is the beneficial effect of this hormone on the development of the embryo that increases the basal temperature to 37.0-37.1 degrees.

The long-awaited result

It should be noted that the remaining normal temperature after fertilization occurs in the female body indicates a lack of progesterone, and this problem, in turn, is a threat of miscarriage or spontaneous abortion. In this case, you need to consult a doctor for help.

Conceiving a child by day

First, let's figure out where a child is conceived.

1. When the ovulation process has taken place and the egg is released from the ovary, it ends up in the fallopian tube. If sexual intercourse has taken place, sperm will wait for an egg ready for conception inside the fallopian tube.
2. Within a few days after fertilization, the embryo that is created moves down the fallopian tube to the uterus. If development does not proceed correctly or the movement of the embryo is too slow, the embryo can penetrate the mucous membrane of the tubes, and this can lead to an ectopic pregnancy.
3. After about 7 days, the embryo reaches the uterus and looks for a warm place where it plans to settle and continue its development.

It is no less interesting to find out how the long-awaited fertilization of an egg occurs day by day in a person.

Important process

We also invite you to watch a video about how human egg fertilization occurs day by day.

How quickly does the process happen?

Many people are interested in how long it takes for fertilization to occur after unprotected love.

There are several possible answers to this question. Firstly, conception of a child can occur exclusively during ovulation or within 12-36 hours after, no more. If during this time the egg does not meet the sperm, it dies and then leaves the female body.

If sexual intercourse took place during ovulation or 1-2 days before it, the question immediately disappears about what day after sexual intercourse fertilization occurs, since here we are talking more about hours. To reach the goal, male seed needs 3-4 hours. If sexual intercourse took place the day before, the sperm are actively waiting to meet the egg in the fallopian tube, and they need no more than an hour to conceive.

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Fertilization is the process of fusion of germ cells of representatives of different sexes, that is eggs and sperm.

Direct fertilization

As a result of natural sexual intercourse sperm falls into vagina , but its acidic environment does not allow sperm to live for more than 2 hours. But the fastest of them still manage to get to uterus through her neck. The mucus that fills the cervix is ​​a good barrier to dangerous microorganisms, but it can also be the same barrier for sperm. In cases where there is too much such mucus or its consistency is not normal, it may even occur (cervical factor). According to some experts, at least 10 million male germ cells should enter the uterus.

Those sperm that successfully pass through the cervix enter the fallopian tubes , from where they are directed against the direction of fluid flow into ovaries .

Fertilization itself, that is, the fusion of cells, occurs in the fallopian region, which is located in maximum proximity to the ovaries. But here, too, not everything is so simple: in order to merge with the egg, several membranes must be overcome, this process is called "penetration" , it also includes the merger itself. It is the first sperm that reaches the second shell that will most likely merge with the egg.

The surface of the egg and sperm is covered with special receptors that ensure their fusion. After fertilization, some parts of the sperm remain inside the egg. Almost immediately in the latter it begins to arise cortical reaction, which consists in the release of special granules into the external environment, as a result of which not a single sperm will be able to fertilize. This mechanism is called "polyspermy block", it usually starts within a few minutes.

In extremely rare cases, a situation may arise when two male reproductive cells were able to simultaneously penetrate the egg. In this case, it develops triploid embryo, which usually develops with a chromosome disorder. Usually such embryos die within a few days, but there are cases when they are implanted into the uterus, then this. Contrary to popular myth, the simultaneous fusion of an egg with two sperm does not result in the birth of twins.

When the merger occurs, it is formed zygote, that is, single-celled, the first stage of embryo development, which lasts no more than 30 hours. Next, the formation of nuclei begins, the unification of maternal and paternal chromosomes occurs due to complex reactions and biological processes.

Splitting up

When the egg is fertilized, it begins its movement towards the uterus due to contractions of the muscles of the tube. The next process after the formation of the zygote is the process of crushing - miotic division , the size of the embryo does not increase, the cells divide, but only become smaller. The size of the embryo at this stage does not exceed 130 microns. This process lasts about three days, the cells of the embryo remain the same. They do not interact with each other, and are only together thanks to the shell. If such a shell is damaged, several genetically identical embryos can form, and then they develop identical twins.

At the point of highest pleasure during the loving fusion of two bodies, a miracle occurs - a new life is born. Seminal fluid containing about 3 million sperm is released into the woman’s genital tract. The environment in which sperm are located, in addition to its nutritional properties, also has the unique ability to reduce the acidity of the vagina. Thanks to this, sperm survive quietly in a woman’s body for up to 9 days, patiently waiting for the egg to mature.

In turn, everything in a woman’s body is also adapted for conception: in response to sexual intercourse, another egg is released (therefore, pregnancy can occur on almost any day of the menstrual cycle). The production of the hormone progesterone by the ovaries increases, which prepares the uterine mucosa to receive the embryo.

The process of fertilization and attachment of the egg:
A- release of the egg from the ovary and ejaculation; b- fertilization; V- attachment of the egg to the uterus and its division; G- development of a fertilized egg into an embryo.

Fertilization of the egg occurs in the fallopian tube (Fig. b). A mature egg is surrounded by many sperm, each of which strives to penetrate it, but only one (in rare cases, two or three) succeeds. The head of the sperm enters the egg, and its tail, having fulfilled its function of ensuring movement, disappears. At this point, the surface of the egg changes, preventing access to other sperm.

This is where the real miracle begins - the birth of a new life - the division of a single cell with two nuclei, formed as a result of the fusion of a sperm and an egg. In the process of dividing into 2-4-8-16-32-64 cells, the embryo moves towards the uterus, where it arrives 11-12 days after conception.

During this period, the embryo is divided into two unequal parts: a large one, from which the body of the unborn child is formed, and a smaller one, which forms the placenta - the organ of respiration, blood circulation, excretion and nutrition of the embryo. This last part of the fertilized egg attaches to the uterus and deepens into its mucous membrane by 3-4 cm. Individual cells drill through the mucous membrane, reaching contact with the vessels of the uterus. In this way, the blood vessels of the placenta are connected to the blood vessels of the mother.

Boy or girl?

The sex of the conceived baby is determined at the moment of fertilization and depends on which sperm is in the egg - a female or male carrier. When two cells, male and female, merge, the embryo inherits genes (certain properties): from the mother - from her egg, from the father - from the sperm.

I am often asked the question whether it is possible to plan the gender of the future baby. There is an opinion that if sexual intercourse was before ovulation, then there will be a girl, and if after ovulation, then it will be a boy. Or, if you eat certain foods during pregnancy, then a child of the desired gender will be born. In fact, this method of gender planning is nothing more than “grandmother’s invention.”

Planning the sex of a child is a very difficult and expensive process; It is impossible to do this at home. Sex can only be planned through artificial insemination, electron microscopy of sperm, or determination of sex chromosomes: X or Y. In other situations, everything depends only on chance.

It is also stupid to assume that it is the woman who is to blame for the fact that only girls or boys are born. Modern science has long proven that the gender of children is influenced only by men.

The laws of heredity were first precisely formulated by Gregor Mendel at the end of the 19th century. The carriers of heredity in plants, animals and people are the so-called hereditary bodies chromosomes. Each human cell contains 46 chromosomes: 44 normal and 2 sex chromosomes.

Human chromosome diagram:

Woman = 44+XX;
Male = 44+XY.

When the sperm penetrates the egg, an important division occurs, as a result of which half of the chromosomes are discarded:

Ovum 44+XX (after division 22+X);
Sperm 44+XY (after division 22+X or 22+Y).

The process of fertilization and sex determination occurs as follows:

Egg + Sperm
(22+X) + (22+X) = 44+XX(girl fetus);
(22+X) + (22+Y) = 44+XY(boy embryo).