The effect of chromium on spermatogenesis and oogenesis. Oogenesis is the process of formation of eggs. Spermatogenesis and oogenesis. You have serious problems with potency

1. Breeding phase- the first stage of oogenesis. The fetal ovary has in the parenchyma many small round primary germ cells - rudimentary, or germinal, epithelial cells. Primary cells divide quite actively by mitosis. As a result, oogonia accumulate in the cortex of the ovary. Oogonia are cells that actively accumulate nutrients such as proteins, fats and glucose. They differ from their predecessors in their larger size, but in terms of genetic composition they are completely identical and, naturally, diploid.

2. Growth phase- this stage occurs in the ovaries shortly before the birth of a girl. With the participation of oogonia, the last mitosis of these cells occurs, which results in the formation of first-order oocytes. The size of the cells decreases as the cytoplasm of the oogonia is evenly distributed between the daughter cells. But the daughter cells quickly enlarge to be ready to begin their own division. The diploid nuclei of these cells, as well as the protoplasm, will enter prophase. However, prophase first-order oocytes face little difficulty; they are surrounded by a granulosa membrane, congealing in the form of a primordial follicle. They are preserved for a long time. Moreover, out of 2 million primordial follicles embedded in the girl’s ovaries, only 400-450 oocytes will receive further development.

3. Further, during the development of the female body, menstruation comes. The current phase, which began 20 days before the described moment, is called maturation phases. One of the primordial follicles is suddenly given the green light. It begins to increase in size (now we call it the primary follicle), and the oocyte located in it “wakes up” and immediately joins the division that was interrupted, for example, 11 years ago. But this time the division will be meiotic. The first division of meiosis will lead to the formation of a second-order haploid oocyte, which has absorbed almost all the nutritious cytoplasm of the mother cell, and a non-viable first polar body. The second-order oocyte, hiding in the egg-bearing mound and washed by the fluid of an already mature follicle, enters the second division of meiosis, where at the metaphase stage it is overtaken by ovulation. He is destined to die in fallopian tube, without completing the entire path of oogenesis. But things may turn out differently for a young woman. If conception occurs in the fallopian tube, then the second division will reach its end with the formation of first a binucleate egg, and then a mononuclear diploid zygote. A second polar body is formed as a by-product and quickly dissolves.

Female gametogenesis is partly similar to male gametogenesis, but has interesting distinctive features.

1. They differ in terms of “start”. Spermatogenesis starts in puberty, that is, in a 10-12 year old boy. In contrast, oogenesis begins long before the birth of a girl, and ends with the final stage of only a few cells during their fertilization. Most of the egg precursors do not survive to the final stages.

2. During gametogenesis in girls and boys, there is a difference in the life span of cells. Male gametes mature within 74-75 days, developing from germinal epithelium to sperm. Their lifespan varies from 100 to 110 days, starting from the first stages of spermatogenesis. But the release of an egg at the moment of ovulation is the result of a 15-, 25-, or even 40-year wait in the ovary.

3. The quantitative indicators of the processes are also very different. In men with successfully realized sexuality, hundreds of billions of sperm are released throughout their lives. In women, from the first menstruation to the onset of menopause, only 400-450 cells pass through the maturation and “preparation” phases in the ovary.

Cells are called gametogenesis. It is divided into spermatogenesis and oogenesis. Formation begins in the uterine period, during sex differentiation, and continues until the end of reproductive age. Sex cells are secreted by special glands - gonads. In humans and animals, female gametes develop in the ovaries, and male gametes in the testes.

The process of ovogenesis and its features

The development of female germ cells takes quite a long time. The process begins in the cortex of the primary ovarian follicles. Completion is observed after ovulation in the oviduct. Oogenesis is a three-phase process, including the stages of reproduction, growth and development.

Reproduction phase and growth phase

At the first stage of oogenesis, multiple mitotic divisions occur in the cells of the ovarian wall. As a result, a large number of diploid oogonia are formed. In the human body, gonadal reproduction begins during embryogenesis and stops by the third year of life.

The growth period is characterized by an increase in the nucleus and cytoplasm in cells. Substances necessary for subsequent division processes accumulate, and chromosomes double. At this phase, oogonia transform into first-order oocytes. They grow in the ovary and store nutrients. Each oocyte is surrounded by epithelial cells. It forms a vesicle - a follicle.

Oogenesis is a long process. Features of the maturation phase

The maturation phase has a number of features. Prophase of meiosis I occurs during embryonic development, and the remaining stages occur after the organism reaches sexual maturity. Each month, one follicle matures in one of the ovaries. At this stage, the first meiotic division ends, a large secondary oocyte and a small body are formed. These structures enter the second phase of meiosis. At the metaphase stage of meiosis II, ovulation occurs - the oocyte leaves the ovary and ends up in abdominal cavity and passes into the oviduct.

If the fusion of the egg with the sperm occurs, then further maturation of the oocyte begins. As a result of the completion of meiosis II, a mature ovotide egg and a second polar body are formed.

Oogenesis is a complex multi-stage process, as a result of which cells with a haploid chromosome set are formed from a diploid gamete: one mature egg and three polar bodies.

The egg is spherical in shape and large in size. Its diameter in mammals and humans varies from 0.110 to 0.140 mm. In terms of volume, the egg is 10-20 thousand times larger than the sperm and 2 times longer.

The maturation phase using the example of the human body

Maturation begins at 12-13 years of age, during puberty. The gonads contain multiple follicles that contain oocytes. Under the influence of follicle-stimulating hormone, one after another they begin to develop, reaching the size of a pea. As the eggs inside these vesicles grow, they reach the lumen of the ovary. As a result, the most viable follicle is isolated here, and the rest are reduced. This usually happens on the 10th day from the start of menstruation. The follicle remaining on the surface of the ovary and the Graafian vesicle continue to grow. Having reached maximum development, the formation bursts, and the mature egg is released into the oviduct.

Ovulation occurs. Under the influence of lutein-forming hormone, the burst graafian vesicle changes - now it is the corpus luteum. The cells that make up its wall acquire a yellow tint due to the fat it contains. They occupy the area where the egg was previously located. The corpus luteum produces the hormone progesterone, the action of which is aimed at preparing the uterine mucosa for fertilization.

If the meeting of the egg and sperm does not occur, after a few days regeneration and reduction begins corpus luteum. In the absence of progesterone, the uterine mucosa is destroyed and rejected. This process is characterized by bleeding from the vagina lasting 2-7 days (menstruation).

The process of spermatogenesis and its features

Oogenesis and spermatogenesis are similar to each other, the difference is that the maturation of male gametes occurs in 4 stages.

Spermatogenesis is the formation and formation of male germ cells - sperm. It begins from the moment of sexual differentiation and develops intensively during the period of maturity of the organism.

At the stage of reproduction, multiple mitotic cell divisions begin in the testes, resulting in the formation of numerous spermatogonia with a diploid set of chromosomes. The developmental phase in men begins at puberty and lasts almost the entire life.

At the growth stage, the cells are called 1st order spermatocytes. They gradually increase in size due to the accumulation of nutrients, doubling of DNA and chromosomes.

The maturation phase is characterized by two successive meiotic divisions. As a result, from each primary spermatocyte 4 spermatids with a haploid chromosome set are formed.

Features of the development of male gonads

The maturation phase is characteristic only of spermatogenesis. Its essence lies in the fact that spermatids acquire the structure and motor function characteristic of sperm.

The process of spermatogenesis from the division of the original cell to the release of the sperm into the epididymis is 35-55 days. Up to 7 billion sperm mature in the gonad per day. Male gonads retain their mobility for 2-3 months, and their ability to fertilize for more than 30 days. The formation of sperm directly depends on the state of the body, nutrition and external conditions. Their viability may decrease under the influence of unfavorable factors, poor diet, and internal disorders.

Spermatogenesis and oogenesis are critical processes, which are responsible for the reproduction, development and prolongation of the race of all living beings.

The main function of every person on our planet is the reproduction of their own offspring. Life is impossible without reproduction, and therefore every living creature has the ability to reproduce. In order to begin the process of reproduction, it is necessary that the man and woman have mature gametes. The process of gamete formation is called gametogenesis. In this case, the production of gametes in men is called spermatogenesis, and in women - oogenesis.

Oogenesis and spermatogenesis: the maturation process

The process of preparing gametes for fertilization begins in the gonads, in men this organ is represented by testicles, and in women by ovaries. In general, gametogenesis in both sexes is similar during the first three stages. However, after this part, the maturation period acquires its own characteristics in both sexes.

Already at the first stages of male and female gametogenesis, one can distinguish their own characteristics, for example, male gametes - spermatozoa - are always produced much more than female ones - eggs. In addition, male gametes develop over a longer period than female gametes.

A feature of oogenesis is the pronounced growth of germ cells. From one cell four new ones are formed, which are called spermatids. In this case, of all four cells, only one becomes an egg, and all the rest become polar bodies. Another feature of sperm is that they have a well-defined shape, which cannot be said about eggs.

Differences between oogenesis and spermatogenesis at different stages

Gametogenesis in males and females develops gradually in several stages. Only the first three stages of spermatogenesis and oogenesis coincide, then differences appear in the process of gamete maturation. The entire process of gamete development can be divided into the following stages:

1. The first stage is the process of reproduction. This process begins in the original cells, which are called spermogonia in men and oogonia in women. From these cells, a large number of new cells are formed by division.
2. The next stage is the growth stage. During this period, the germ cells transformed into spermatocytes and oocytes begin to increase in size. It is important to note that oocytes are much larger in size than spermatocytes because female cells store nutrients. Spermatocytes do not need to accumulate nutritional components, since they require a high degree of motility.
3. Maturation stage accompanied by cell division. Division occurs in two stages, called first and second meiosis. Repeated division of cells implies the appearance of already mature female gametes along with polar bodies and spermatids.
4. Next, male gametes enter the stage of formation, in which still immature spermatids receive their final sperm form. In female germ cells, this stage is absent, so the eggs do not have such a complete form as male gametes.

The main features of spermatogenesis and oogenesis are that the maturation of male germ cells is mainly aimed at multiple divisions, during which a large number of sperm are formed, while maturation in women is characterized by the formation of only one egg.

Characteristics of oogenesis and spermatogenesis

If we consider ovogenesis and spermatogenesis in comparison, we can identify a number of other characteristics that distinguish these two processes. First, gametogenesis in men and women occurs in different gonads, which are called testes in men and ovaries in women. It is in these organs that the production and maturation of gametes occurs.

Sex cells in spermatogenesis are called spermatozoa, and in oogenesis they are called eggs. As you know, for the process of fertilization to occur, it is necessary for the male gamete to enter the female one.

In comparing oogenesis and spermatogenesis, one cannot fail to note the different sizes of gametes of male and female individuals. The egg is much larger than the sperm, since it absorbs many useful and nutrients throughout the entire period. Moreover, after maturation, male gametes become mobile, thanks to which they can easily cross the female reproductive tract. Female gametes remain motionless during the entire time during which the egg is being prepared for fertilization.

Also, the sex cells of men and women differ in shape. Sperm have a complete round shape with a tail, unlike the egg, which has a simple round shape.

If we consider oogenesis and spermatogenesis in the table, we will notice that the stages at which an increase in size, division and full maturation occur in both sexes are the same. The schemes of oogenesis and spermatogenesis are very similar, however, the development of sperm also includes a fourth stage, which consists of final formation.

Another feature of spermatogenesis and oogenesis is the different periods of production of male and female germ cells. Eggs are formed in a woman’s body cyclically, which is what the menstrual cycle is associated with. The formation of a new egg occurs every 21-35 days. At the end of the cycle, the egg dies, this process is accompanied by bleeding. As a result, changes occur in the hormonal background, as a result of which a new process of egg maturation is launched.

In men, the formation of sperm occurs constantly, and the production of gametes occurs throughout the entire period of a man’s maturity. A man produces about 30 million sperm per day. In women, the number of gametes is much smaller. For comparison, over the course of a lifetime, representatives of the fair sex produce about 500 mature germ cells.

Spermatogenesis, unlike oogenesis, is more susceptible to external conditions. This is primarily due to the fact that the gonads, or testes, in men are located outside the abdominal cavity, that is, in the testicles.

In women, the gonads, that is, the ovaries in which the egg is formed, are located more reliably. This is due to the fact that the appearance of eggs in the body future woman begins even before her birth and ends after fertilization.

The growth stage in oogenesis significantly exceeds the similar stage in spermatogenesis, which explains that the egg is much larger in size than sperm. But male gametes compensate for this stage by cell division and the formation of a large number of sperm.

Why is an egg so much larger than a sperm?

As mentioned earlier, during the growth process the egg absorbs all the nutrients and beneficial substances. It is important for sperm to preserve their sperm in order to be able to travel through the female reproductive tract and fertilize an egg in the future. Besides, female gametes nutrients are necessary in order to further nourish the developing fetus.

Differences in the sizes of male and female gametes are also caused by the fact that the lifespan of an egg is much longer than that of sperm. For example, male gametes, under favorable conditions, can exist for only a few days. As for the egg, it exists throughout the entire period of fetal development, until the moment of birth.

Stages of distribution of DNA molecules in germ cells

At the stage of germ cell division, upon closer examination, one can observe the process of chromosome separation. During cell division, all DNA molecules are doubled in their nuclei, after which chromosomes are redistributed, which can be divided into the following stages:

1. Leptotene stage. At this stage, the nucleus and the twisted strands of chromosomes can be distinguished. Paternal and maternal chromosomes are located at a distance.
2. Zygotic. At this stage, chromosomes come into contact and genes are exchanged.
3. Pachytennaya. At this stage, the connection between chromosomes is strengthened in the cell and they twist well with each other.
4. Diplotennaya. This stage is characterized by the doubling of all chromosomes, after which they are separated into two pairs.

To summarize, we can say that spermatogenesis and oogenesis are two processes aimed at the production of germ cells, which have their similarities and differences, due to the peculiarities of the structure of male and female organisms.

Reproduction or reproduction of offspring into the world is one of the most important purposes of all living beings on our planet. Genetic material is passed from parents to offspring, which allows for quite a long time without interrupting one’s family line. Today we will talk in more detail about the continuation of the human race. Let's consider concepts such as spermatogenesis and oogenesis. Where does the reproduction process begin? Of course, with the penetration of a male cell into a female one. Where do they come from? We are interested in the process of gametogenesis. Oogenesis is the sequential process of formation of the female reproductive cell. Spermatogenesis is the formation of men. Today we will look at the similarities and differences between these processes.

Egg

We have already mentioned that ovogenesis is the process of reproduction of the female reproductive cell, which is called the “egg”. We suggest we talk a little about why it is needed and what function it performs. Let's briefly look at the structure of the egg.

As mentioned earlier, the egg is sex cell, having a round shape. It necessarily contains all the necessary nutrients, because its main function is to ensure the development of the body from the moment of fertilization. Like any other cell, the egg contains a nucleus in the very center. Around the nucleus with a haploid set of chromosomes is the cytoplasm. The egg also has an upper protective layer - the corona radiata. This shell received this name due to the fact that it consists of a large number of small villi.

Near the nucleus, as a result of meiosis, another small body is formed; this formation is a cell of very tiny sizes. In total, a newborn girl has approximately a million eggs in reserve. But over time, many of them die. There are only about 300 thousand of them left before puberty, and about 400 of them undergo ovulation. Where does everyone else go? They simply die without having time to ripen.

We propose to discuss the process itself called “ovogenesis”. This is the maturation of those same female germ cells. Let's get started right now.

Oogenesis

Oogenesis is the formation of female germ cells. It’s worth clarifying right away that in mammals it begins even before birth, that is, in utero. Before we list and characterize all the stages of oogenesis, we highlight the main purpose of this process. So, the functions:

• a haploid set of chromosomes must be formed in the nucleus of the egg;
• satisfaction of the zygote in the availability of nutrients.

We can immediately note that the process of oogenesis is not very different from spermatogenesis, you will notice this yourself later.

So, the stages of oogenesis are the following:

• reproduction;
• height;
• maturation.

The very first stage occurs in the womb. The girl already has a large number of primary germ cells, which at this stage can be called rudiments or embryos. These future eggs divide very actively, which is how oogonia accumulate. They accumulate in the cortex. It is the oogonia that accumulates all the necessary nutrients, namely:

• protein;
• fats;
• glucose.

How do oogonia differ from germ cells? They become larger in size. Their similarity lies in the fact that the genetic composition is the same.

If we briefly consider the second phase, we will see that it also occurs before the birth of a girl. Now first-order oocytes are formed from oogonia. The size decreases significantly during division, but the oocytes quickly gain mass. Next, the future eggs will undergo long-term preservation in the form of prophase oocytes. Now there are about two million of them, and only about 400 oocytes will receive further development.

The last stage occurs after a large amount of time (about 11-12 years, and sometimes more). At this phase, one of the preserved oocytes suddenly begins its further development. The result will be the arrival of menstruation.

Sperm

We learned that during oogenesis, a female reproductive cell called an egg is formed. Now we move on to spermatogenesis and the male reproductive cell. So, for the continuation of the human race, a pair is needed for an egg that is capable of fertilizing it. The sperm is the necessary half.

There can be many millions of sperm in the male body, unlike eggs in female body. They consist of:

• from the head;
• necks;
• middle part;
• filamentous tail.

When the sperm reaches the egg, the tail needed for movement disappears. Further, the female reproductive cell allows only the head of the sperm to enter, since it carries the genetic material. As you know, the shell of the egg is quite strong, so there is an acrosome on the head of the sperm. It contains a special substance that can dissolve the shell. The size of one male reproductive cell is only 0.05 millimeters, so in order to see it, you need a powerful microscope.

Spermatogenesis

Spermatogenesis and oogenesis are quite similar processes. The first consists of the following stages:

• reproduction;
• height;
• maturation;
• formation.

During the reproduction stage, more than a thousand spermatogonia are formed by dividing each about ten times. As they divide, they absorb nutrients.

As they grow, they greatly increase in size. It is at the growth stage that the transformation of spermatogonia into first-order spermatocytes occurs.

At the maturation stage, 2 divisions occur:

• meiosis (as a result we have 2nd order spermatocytes);
• mitosis (spermatid is formed).

During formation, spermatids come into contact with cell processes, and sperm are formed. When they complete their formation, they gain mobility.

Similarities

It is worth immediately noting the first similarity between oogenesis and spermatogenesis - both processes are necessary for the formation, maturation and growth of germ cells, male or female. Although there are many similarities in the processes, some differences can also be identified.

Another common feature is the almost identical stages of the process (spermatogenesis has one more stage). General stages:

• reproduction;
• height;
• maturation.

We discussed the features of these stages in detail above. Let's get down to the differences.

Differences

Let's start with the fact that during oogenesis and spermatogenesis we have different result, oogenesis corresponds to such a result as the formation of a female germ cell, and spermatogenesis - a male one. As you have already noticed, there is one more stage in the process of sperm formation than in the formation of an egg. The former also go through the formation stage, while oogenesis does not need this stage.

The process of oogenesis begins in girls in the womb, and spermatogenesis begins in boys who have reached 12 years of age. This is another difference.

The last difference is the greater number of male reproductive cells compared to female ones. This can be explained this way: only one sperm out of about 200 million reaches the egg.

Spermatogenesis. The process of development of male reproductive cells, ending with the formation of sperm. It flows inside the convoluted seminiferous tubules, which make up more than 90% of the volume of the testicle of an adult sexually mature man.

On the inner wall of the tubules there are 2 types of cells - the earliest spermatogonia, the first cells of spermatogenesis, from which, as a result of successive cell divisions, through a series of stages, mature spermatozoa and nourishing Sertoli cells are gradually formed. Spermatogenesis begins simultaneously with the activity of the testicle under the influence of sex hormones during puberty of a teenager and then proceeds continuously in most men almost until the end of life, has a clear rhythm and uniform intensity.

The time required for the transformation of spermatogonia into sperm takes about 74 - 75 days in humans. In this case, spermatogonia, which are found in the testicles of boys even before the onset of puberty, are of two types: A and B, or dark and light; some of them are stored as spare ones, while others begin to grow and divide. Spermatogonia, containing a double set of chromosomes, divide by mitosis, leading to the emergence of subsequent cells - first-order spermatocytes. Further, as a result of two successive meiotic divisions, 2nd order spermatocytes are formed, and then spermatids are the cells of spermatogenesis, immediately preceding the spermatozoon. With these divisions, the number of chromosomes is reduced by half.

Spermatids do not divide; they enter the final period of spermatogenesis, the period of sperm formation, and after a long differentiation phase they turn into sperm. This occurs through gradual elongation of the cell, changes, and elongation of its shape, as a result of which the cell nucleus of the spermatid forms the head of the sperm, and the membrane and cytoplasm form the neck and tail. In the last phase of development, the sperm heads are closely adjacent to the Sertoli cells, receiving nutrition from them until full maturation. After this, the sperm, already mature, enter the lumen of the testicular tubule and then into the epididymis, where they accumulate.

Oogenesis. The process of development of female gamete germ cells, ending with the formation of eggs. During the woman's menstrual cycle Only one egg matures. The process of oogenesis is fundamentally similar to spermatogenesis and also goes through a number of stages: reproduction, growth and maturation. Eggs are formed in the ovary, developing from immature germ cells - oogonia, containing a diploid number of chromosomes. Oogonia, like spermatogonia, undergo successive mitotic divisions, which are completed by the time of birth of the fetus.

Then comes the period of growth of oogonia, when they are called first-order oocytes. They are surrounded by a single layer of cells - the granulosa membrane - and form the so-called primordial follicles. A female fetus on the eve of birth contains about 2 million of these follicles, but only about 450 of them reach the stage of second-order oocytes and leave the ovary during ovulation. The maturation of an oocyte is accompanied by two successive divisions, leading to a halving of the number of chromosomes in the cell. As a result of the first division of meiosis, a large oocyte of the second order and the first polar body are formed, and after the second division - a mature egg cell capable of fertilization and further development with a haploid set of chromosomes and a second polar body. Polar bodies are small cells that play no role in oogenesis and are eventually destroyed.

Unlike the formation of sperm in men, which begins only during puberty, the formation of eggs in women begins before they are born and is completed for each given egg only after its fertilization. Therefore, any unfavorable environmental factors, starting from the stage intrauterine development girls may result in genetic abnormalities in her offspring.