SPERMATOGENESIS
generative function, or spermatogenesis, consists of 4 stages: 1) reproduction; 2) growth; 3) maturation; 4) formation, or spermiogenesis.
1st stage - reproduction. In the process of the 1st stage, mitotic division of spermatogonia occurs. Among spermatogonia, type A stem cells are distinguished - dark, reserve, non-dividing; type A semi-stem cells are light, rapidly dividing, their nuclei contain more loose chromatin and well-defined nucleoli. By dividing light A-cells, differentiating type A and B cells are formed. Type B cells are distinguished by somewhat larger nuclei and coarser clumps of chromatin.
Differentiating cells appear in the form of chains of syncytium, or clones, i.e., cells begin to divide, but do not move away from each other, as they are interconnected by cytoplasmic bridges. Then these chains of spermatogonial syncytium, or clones, pass through the slightly opening zone of tight contacts to the adluminal part and enter the 2nd stage - the growth stage. From this point on, they are called spermatocytes of the 1st order.
growth stage. This stage consists of 5 phases: 1) leptotenes: - 2) synaptenes; 3) pachytenes; 4) diplotenes; 5) diakinesis.
Leptotena characterized by the fact that the chromosomes of spermatocytes are subjected to spermatization and become visible like thin threads.
Synapten or zygoten is that homologous chromosomes combine in pairs (conjugate), forming bivalents, in which crossover (crossing over) and gene exchange occur between chromosomes.
Pachytene characterized by the fact that the chromosomes of bivalents undergo further spiralization, thickening, and shortening.
Diploten lies in the fact that the chromosomes of the bivalents and the chromatids of the chromosomes begin to diverge, gaps appear between them, but they remain connected to each other in the area of the decussation.
diakinesis characterized by further spiralization of bivalent chromosomes and the formation of tetrads. From each bivalent, one tetrad is formed, consisting of 4 chromatids, or monads. A total of 23 tetrads are formed.
maturation stage. The maturation stage includes 2 divisions (1st division of maturation and 2nd division of maturation).
The division of maturation begins with metaphase. In the spermatocyte of the 1st order, the tetrads line up in the plane of the equator in such a way that one half (dyad) of the tetrad faces one pole of the cell, and the other half, the other. After this, anaphase begins, during which the dyads diverge towards the poles of the cell. Then comes the telophase, as a result of which 2 new cells are formed, called spermatocytes of the 2nd order. Each spermatocyte of the 2nd order contains 23 dyads (a diploid set of chromosomes).
The division of maturation also begins with a metaphase, in which in the spermatocyte of the 2nd order, the dyads line up in the plane of the equator in such a way that one half of the dyad (monad, or chromatid) faces one pole of the cell, the other - to the other. During anaphase, the chromatids diverge towards the poles of the 2nd order spermatocyte. As a result of telophase, from each spermatocyte of the 2nd order, 2 spermatids are formed, each of which contains a haploid set of chromosomes.
Formation stage . During the formation stage, or spermiogenesis, the spermatids are immersed in the recesses of the sustentocytes. On that pole of the nucleus of the spermatid, which faces the sustentocyte, there is the Gylgi complex.
and the opposite pole is the cell center, consisting of 2 centrioles.
The Golgi complex is transformed into a dense granule, which, growing, covers the anterior half of the nucleus. This hat is called acroblastoma and characteristic of early rmatids. In the center of the acroblast of the late spermatid, a dense body is formed, which is called acrosome. IN acrosome contains firtilization enzymes (fertov b1, involved in fertilization). Among these enzymes, there are 2 main enzymes: hyaluronidase and trypsin.
One of the centrioles of the cell center located! at the opposite pole, adjacent to the nucleus and is called! proximal. The second centriole is called the distal centriole. I The distal centriole is divided into 2 rings: proximal ^! and distal. The flagellum I (flagellum) begins from the proximal ring. The distal ring is also displaced in the image. J is the border between the intermediate and main section of the harness-| ka. The main section of the tail (flagellum) ends with a terminal section.
During the formation stage, a significant part of the cytoplasm is shed and remains only in the form of a thin layer covering the head, where the nucleus is located, and the tail.
Mitochondria are displaced to the region of the intermediate part of the tail, located between the two rings of the distal centriole.
Therefore, the formation phase is the transformation of the spermatid into a spermatozoon. The entire process of spermatogenesis ends with the individualization of spermatozoa, i.e., their transformation into independent motile cells, while the spermatogonia were connected by cytoplasmic bridges and constituted syncytium.
Thus, the formed spermatozoon consists of a head, including the nucleus, acroblast and acrosome, and a tail. The tail includes 4 sections: 1) connecting section (neck), located between the proximal centriole and the proximal ring of the distal centriole; 2) intermediate department - I department, located between the proximal and distal! centriole rings; 3) the main section, starting from the distal ring of the distal centriole, which ends with 4) the terminal section.
In the central part of the flagellum, an axial filament passes, consisting of 9 pairs of peripheral and 1 pair of central microtubules.
duration of spermatogenesis. The period from the moment of division of spermatogonia to the formation of a spermatozoon is days. For the full maturation of the sperm, another 15 days are needed. Thus, spermatogenesis lasts 75 days.
It should be noted that spermatogenesis in the convoluted seminiferous tubules proceeds in waves, i.e., in one place it only begins, and here only dividing spermatogonia are visible; in another place spermatocytes of the 1st and 2nd orders already appear; in the 3rd, spermatids are formed, therefore the species "
permatogonia and spermatids; in the 4th they begin to form us from I spermatozoa, therefore, here, in addition to spermatogonia, there are spermatids and spermatozoa. The process of spermatogenesis is adversely affected by
flaw food, vitamins. Especially detrimental is the effect of radioactive radiation and high ambient temperature. In this case, the cells located in the adluminal part of the convoluted seminiferous tubules (spermatozoa, spermatids, spermatocytes) die, stick together into giant balls that float in the liquid of these tubules. Only thanks to the preserved spermatogonia located in the basal part of the seminiferous tubules, spermatogenesis can resume.
High temperature suppressive spermatogenesis, is body temperature. Therefore, if the boy's testicle from the abdominal cavity did not descend into the scrotum (this is called cryptorchidism), where the temperature is lower than body temperature, then after growing up such a child will be a barren man. Therefore, the pediatric surgeon must operatively lower the testicle into the scrotum, where the temperature is 34 ° C and below. Tkkaya temperature is most favorable for spermatogenesis. Therefore, all males are "armed" with scrotums.
Ovogenesis.
Development of the female reproductive system consists of 2 phases: 1) indifferent and 2) differentiated.
2nd phase begins on the 7-8th week of embryogenesis. At this time, the reduction (disappearance) of the mesonephric ducts occurs. At the same time, the epithelium of the fallopian tubes develops from the upper ends of the paramesonephric ducts, and the epithelium and glands of the uterus and the primary epithelial lining of the vagina, which is later replaced by the ectodermal epithelium, develop from the lower ends of these ducts joined together. The connective and smooth muscle tissues of the fallopian tubes (oviducts) and uterus develop from the mesenchyme, and the mesothelium of the serous membrane of the oviducts and uterus develops from the visceral leaf of the splanchnotome.
The growing mesenchyme destroys the ends of the sex cords. The sex cords continue to grow into the primary kidney throughout the entire embryonic period and during the first year of the girl's life, that is, until the albuginea is formed around the ovarian RH.
Sex cords consist of coelomic epithelial cells - which later differentiate into folliculocytes - and gonocytes from which ovogonia develop. In the process of further development, the proliferating mesenchyme divides the filamentous cords into islands, each of which consists of an ogonium and a follicular epithelium. From each such follicle, one follicle develops, including 10 and a layer of flattened follicular cells.
At the 3-4th month of embryogenesis, ovogonia enter a period of small growth and turn into oocytes of the 1st order. By the end of embryogenesis, 350,000-400,000 follicles are formed, consisting of future germ cells and folliculocytes. 95% of the follicles contain oocytes of the 1st order at the leptotene stage, the remaining follicles contain ovogonia.
In the process of growth, many of the oocytes die before birth and turn into atretic bodies.
The structure of the ovaries. The ovary is covered with peritoneum on the outside. Under the peritoneum is a protein membrane, consisting of connective tissue. Inward from the albuginea is the cortex (cortex ovarii). In the center of the ovary is the medulla, consisting of loose connective tissue, in which the largest arteries and veins of this organ pass, having a tortuous course. Sometimes there are remnants of the renal tubules of the primary kidney, which indicates the development of the ovarian medulla from the primary kidney.
cortex ovaries includes: 1) follicles; 2) atretic bodies; 3) periodically - corpus luteum; 4) white bodies.
Follicles of the cortex depending on the stage of development and structure, they are divided into: 1) primordial; 2) primary; 3) secondary; 4) tertiary (bubbly follicles, graafian vesicles, mature follicles).
Primordial follicles- the smallest, are presented in the greatest quantity. They consist of a 1st order oocyte at the diplotene stage, surrounded by a single layer of flattened follicular cells.
Primary follicles(folliculus primarius) are characterized by the fact that the oocyte of the 1st order grows in this follicle. At the same time, it is surrounded by one or two layers of cubic or prismatic follicular cells. The basal part of these cells lies on the basement membrane. Microvilli extend from the apical and lateral surfaces of follicular epitheliocytes. The villi of the apical part penetrate into the cytoplasm of the oocyte of the 1st order. Through these villi, nutrients and other substances enter the oocyte of the 1st order, ensuring its growth and development. Around the oocyte of the 1st order, another shell is formed (the 1st shell is the ovolemma, or cytolemma), which is called the brilliant zone (zona pellucida). It consists of glycosaminoglycans, mucoproteins and proteins
the stretching zone is formed due to the functional activity of both the oocyte and folliculocytes. The follicle cells have a well-developed synthetic apparatus, which synthesizes the products necessary for the growth and development of the oocyte. Due to the growth of the oocyte and the increase in the volume and proliferation of primary follicular cells. llIK ula increase and the size of the follicle itself. Therefore, the connective tissue surrounding the follicle becomes denser, and the connective tissue membrane of the follicle begins to form.
secondary follicles(folliculus secundarius) are characterized by the fact that the 1st order oocyte stops growing. Around this oocyte there are many follicular cells forming several layers, which together make up the granular layer (stratum granulosum folliculi). Follicular cells secrete follicular fluid containing estrogen, the female sex hormone. Droplets of follicular fluid accumulate and form the cavity of the follicle (cavum folliculi). As the cavity fills with follicular fluid (liquor follicularis). its size increases. In this case, a part of the follicular cells adjacent to the oocyte of the 1st order is pushed to one of the poles of the follicle and is an oviparous tubercle (cumulus oophorus). From the layer of follicular cells adjacent to the oocyte of the 1st order, processes extend, penetrating into the oocyte. This layer of follicular cells with their processes is called the radiant crown (corona radiata). The radiant crown is the 3rd shell of the 1st order oocyte.
Follicular cells The granular layer of the follicle performs the following functions: barrier, trophic, the formation of follicular fluid and the production of estrogens.
Theca follicle- this is the follicle sheath, formed from the connective tissue surrounding the secondary follicle, and called theca (theca folliculi). The theca consists of the outer theca (theca externa) and the inner theca (theca interna). The outer theca is denser, the inner is loose. Numerous blood vessels originate in the internal Theca, around which are located interstitial cells that secrete the male sex hormone - testosterone. This osterone enters through the basement membrane into the granules and the follicle layer, where it undergoes aromatization, turning into estrogen.
The secondary follicle rapidly increases in size, I due to the proliferation of cells of the granular layer and the growth of the cavity of the follicle.
Tertiary follicles(folliculus tertiarius) is characterized. are even larger and continue to grow due to further reproduction of follicular cells and an increase in the volume of the follicle cavity. Oocyte of the 1st order. And in this follicle it is surrounded by 3 membranes: 1) ovolemma; 2) a brilliant zone; 3) a radiant crown. As a result, pro I of the upcoming growth of the tertiary follicle, its diameter is d 0. ■ reaches 2-3 cm. At the same time, the egg-bearing tubercle shifts to the peripheral pole. An overgrown tertiary follicle-D-cool protrudes the ovarian albuginea, and this protrusion rises above its surface. Ultimately, the theca of the follicle and the ovarian albuginea rupture, and the oocyte is ejected into the abdominal cavity. This I process is called ovulation.
After ovulation, at the site of the bursting tertiary folly-I, the kula develops yellow body. After the involution of the corpus luteum, the body remains in its place white body.
Not all secondary and primary follicles reach maturity. Most of them die and turn into atre-K tic bodies, or follicles
Functions of the ovary. The ovary performs 2 functions: 1) generative (ovogenesis) and 2) endocrine (secretion of sex hormones).
Generative function (ovogenesis). Ovogenesis consists of 3 stages: 1) reproduction; 2) growth; 3) maturation.
breeding stage begins and ends in the embryonic period. Reproduction is carried out by mitotic division of ovogons.
growth stage consists of small and large growth-1 that. Small growth begins in the embryonic period. As a result of this growth, oocytes of the 1st order at the stage! leptotenes are converted into oocytes of the 1st order at the diplotene stage. Small growth ends at puberty. It is at this time that oocytes of the 1st order at the diplotene stage form a pool (accumulation) of oocytes. For small growth, stimulation of the pituitary gland with follitropin is not required.
After puberty, under the influence of pituitary follitropin, a large growth of oocytes of the 1st order occurs. At the same time, not all oocytes immediately enter a period of large
ST a, but only a relatively small part of them (3-30). A period of great growth lasts 12-14 days. As a result of Rb1C growth, one of the follicles is the first to turn into a tertiary follicle, within which the 1st division of maturation occurs.
ripening stage consists of 2 divisions: the 1st and 2nd divisions of maturation.
The 1st division of maturation is carried out in the cavity of the triple follicle. During the 1st division, the 1st stage oocyte divides into the 2nd order oocyte and the directional body. The 2nd order oocyte includes almost the entire cytoplasm with organelles and inclusions, the nucleus, which includes 23 dyads (46 monads - chromatids) and all 3 shells (ovolemma, brilliant zone and radiant crown). The reduction (direction) body includes a small part of the cytoplasm and 46 chromatids. After this, the wall of the follicle breaks and the oocyte of the 2nd order is released into the abdominal cavity (ovulation), from where this oocyte enters the fallopian tube.
The 2nd division of maturation occurs after fertilization of the 2nd order oocyte in the fallopian tube, during which it divides into a mature egg and a directional body. The composition of the egg includes the entire cytoplasm with organelles and the nucleus containing 23 chromosomes. The directional body contains a small portion of the cytoplasm and 23 chromosomes.
Differences oogenesis from spermatogenesis:
1) during oogenesis, the stage of reproduction begins and ends in the embryonic period, and during spermatogenesis - after puberty;
2) during oogenesis, the growth stage begins in the embryonic period and includes periods of small and large growth, while during spermatogenesis, the growth stage is not divided into periods of large and small growth and proceeds in a sexually mature organism;
3) during oogenesis, the 1st division of maturation occurs in the mature ovarian follicle, the 2nd division - in the fallopian tube, and during spermatogenesis, both divisions from maturation occur in the convoluted seminiferous tubules of the testis;
4) oogenesis includes 3 stages (there is no stage of Formation), asSpermatogenesis consists of 4 hundred and th;
5) as a result of oogenesis, 1 mature egg and 3 directional bodies are formed from one oocyte of the 1st order (the first directional body can divide into 2 new bodies), and during spermatogenesis, 4 spermatozoa are formed from one spermatozoa of the 1st order.
Ovulation. This is the release of a 2nd order oocyte from the tertiary follicle into the abdominal cavity. Ovulation is preceded by 1 hormonal changes in a woman's body. 36 hours before ovulation, the level of estrogen in the blood rises. This, by the principle of negative feedback, suppresses the secretion of follitropin by the pituitary gland. After this, an intensive release of lutropin by the anterior pituitary gland begins. 12 hours before ovulation, the content of lutropin in the blood reaches its maximum level (ovulatory dose). During these 12 hours, hyperemia of the wall of the tertiary follicle occurs, then the content of follicular fluid in the cavity of the follicle increases, intrafollicular pressure increases. This pressure acts on the wall of the follicle, causing it to swell, become infiltrated with leukocytes, and loosen. The activity of the hyaluronidase enzyme increases, which causes the breakdown of hyaluronic acid, which leads to further loosening and weakening of the wall of the tertiary follicle and the ovarian albuginea. Under the influence of increased pressure on the wall! follicle is irritated nerve endings,! which reflexively causes the release of oxytocin, which also takes part in the process of ovulation. As a result of all these factors, a rupture of the wall of the follicle occurs. and ovarian albuginea and the release of a 2nd order oocyte into the abdominal cavity.
In this paper, we propose to highlight the difference between oogenesis and spermatogenesis, to talk about these processes themselves. Of course, we will not disregard the sex cells, we will explain in detail their structure and functions.
Reproduction is the main purpose of all living beings on our planet, it is it that helps to continue the race, that is, our planet will never be empty. On the contrary, now the number of living beings, especially people, is growing in the egg and sperm cells - these are women and men, respectively. It is to them that our article will be devoted. Gametogenesis refers to the process of formation of germ cells. If we are talking about sperm, then it is called spermatogenesis, if about eggs, then oogenesis. You will learn all this in more detail below.
Ovogenesis and spermatogenesis, the difference between which is not critical, are very similar in many of their features, can be called one general term - "gametogenesis". Now about this a little more.
To begin with, let's analyze the concept itself, we can single out two words: "gamete" and "genesis", the latter from Greek can be translated as follows - "origin". That is, literally, the term "gametogenesis" means "the origin of gametes." Gametes are sex cells, in men - spermatozoa, in women - eggs. The gametogenesis itself can also be divided by gender: the gametogenesis that occurs in the body of a man is called spermatogenesis, and in the body of a woman it is called oogenesis. But here we come to the first difference between these processes. Ovogenesis begins even before the birth of a girl, and spermatogenesis occurs in boys who have reached a certain age, usually 12-13 years.
The process of egg formation, that is, oogenesis, occurs even in the womb, while puberty, or rather its first stage, takes about nine years. We offer a little more detail to consider the stages of puberty girls:
As we mentioned earlier, in girls, eggs are formed even in the womb, in boys everything is a little different. Spermatozoa begin their development only when they reach 12-14 years. There are also changes before this stage of puberty:
Upon reaching the age of 12-14, a young man can already begin to have sex, but parents should warn him, because he can already cause an unwanted early pregnancy of his companion. Now let's go directly to the male and female germ cells, consider their structure, stages of formation, similarities and differences.
Let's start with the female germ cells, the characteristics of oogenesis will be discussed by us a little later. To begin with, we propose to consider the structure and functions of the egg.
The egg is a relatively large and immobile cell, its size reaches 170 microns, which is much larger than male germ cells (up to 70 microns). Each of them contains the necessary nutrients, there we will see:
Cells can divide according to the amount of yolk:
From a negligible amount to a very large amount, respectively. If we consider the female egg, then it can be attributed to the alecithal and isolecithal types. That is, there is little yolk in it, which can be explained by the fact that the human embryo quickly switches to a hematotrophic type of nutrition. The isolecithal type means that the yolk is distributed evenly and the nucleus is in the center.
The ovum has the following membranes:
All shells have a protective function, they do not allow more than one sperm to enter the egg, which is necessary for fertilization. All others are blocked.
Now let's highlight the functions of the egg:
Everyone knows that a sperm cell is a male reproductive cell, but how does it work? Let's break this issue down a bit. You can see the appearance of gametes in the photo of this section. In its structure, the following parts can be distinguished:
The head of the spermatozoon is filled with the nucleus, it is she who carries the hereditary information. During fertilization, the egg passes exactly it. The sex of the unborn child depends on the sperm. If he carries the X chromosome, then there will be a girl, if Y, then a boy.
The neck is presented as a slight narrowing in front of the middle part of the sperm, it is this part that is responsible for active movement, otherwise fertilization would be impossible.
Before we consider the features of spermatogenesis and oogenesis, we propose to single out the main function of spermatozoa - this is the transfer of genetic material to the egg.
Let's start with the formation of the female germ cell, highlight the periods of oogenesis and characterize each of them. So, the phases are distinguished:
Now we can already name the first difference between oogenesis and spermatogenesis: in the first case, the female germ cells (eggs) are born, and in the second - male (spermatozoa). Let's characterize each stage of oogenesis.
At the stage of reproduction, the original cells (germ cells) present in the parenchyma are divided by mitosis. Thus, in the cortical layer of the ovaries there is an accumulation of ovogons. They accumulate:
Now they are very different from their predecessors, the resulting ovogonia are much larger than the primordia, but their genetic composition is identical. It is also important to note that this process occurs even before the birth of a girl, that is, in the womb.
The next stage occurs shortly before the girl is born. This stage is called growth. Now there is a division by mitosis, so the first-order oocytes are formed. Compared to ovogonia, they become smaller, but then quickly increase in size. Now the oocytes are waiting for a slight difficulty, they are captured by the granulosa membrane and stop developing at the stage of the primordial follicle. In total, there are about two million such cells, but only a few of them (about 450) will receive further development.
The third stage (maturation) occurs shortly before the appearance of the first menstruation of a girl. One of the dormant follicles wakes up and continues its development, which stopped about 12-13 years ago.
We have already identified one difference between oogenesis and spermatogenesis (various germ cells develop), from what we have read, we can also highlight the fact that ovogenesis begins even before the birth of a girl, but the process of spermatogenesis begins when she reaches 12-14 years old. We have already identified two differences, then we will once again designate this to consolidate knowledge.
The stages of spermatogenesis are also slightly different from the stages of oogenesis (the presence of another stage). The following stages of spermatogenesis are distinguished:
Here we see the similarity of these processes, the first three stages are the same, only at the stage of maturation ovogenesis ends, and spermatogenesis continues, the stage of formation begins.
You have almost finished reading this article, try it yourself - name the differences between spermatogenesis and oogenesis. Now check how you coped with the task.
The first difference between oogenesis and spermatogenesis is the different start time of the process. In girls, the process of gametogenesis begins during fetal development, in boys - at 12-14 years.
The second difference is that in the process of oogenesis, eggs develop, and spermatogenesis - spermatozoa.
The third difference is the life span of germ cells. The sperm cell lives from one hundred to one hundred and ten days (if we take into account the entire process of spermatogenesis, approximately 74 days), the female germ cell is the result of a long wait in the ovary (from 12 to 40 years).
The fourth difference is quantity. Over the course of a man's life, many hundreds of billions of spermatozoa are born, and approximately 450 eggs go through all the stages of oogenesis.
In the course of writing the article, we identified both similarities and differences between spermatogenesis and oogenesis. Now let's generalize again, denote as a list of similarities of these processes.
1. Sexual reproduction of multicellular organisms. 3
2. Gametogenesis. 4
2.1 Spermatogenesis. 4
2.2 Ovogenesis. five
2.3 Meiosis. 6
List of used literature.. 12
Genetics and related studies of the physiological characteristics of human reproduction have a huge impact on the life of mankind today.
Modern people often do not remember or forget about the past and believe that interest in genetics and related issues has arisen recently. But it can be argued that interest in reproduction is as old as our own species.
Reproduction is the main manifestation of life for any species, even if its representatives are not aware of it.
Mendel discovered the basic laws of heredity at about the same time that other biologists began to study the structure of the cell. Therefore, when the laws of genetics were rediscovered in the 1900s, scientists were already able to understand that the so-called factors must correspond to structures observed in reality - chromosomes. The identification of abstract concepts and real structures is the largest achievement of genetics at an early stage of its development, and it was made mainly due to the study of the nature of sex.
The development of gametes in multicellular animals occurs in the sex glands - gonads (Greek gone - seed). There are two types of germ cells: male (sperm) and female (eggs). Spermatozoa develop in the testes, eggs in the ovaries.
The process of formation of germ cells (gametes) is known collectively as gametogenesis. It is characterized by a number of very important biological processes and proceeds somewhat differently during the maturation of spermatozoa (spermatogenesis) and eggs (ovogenesis).
The testis consists of numerous tubules. A transverse section through the tubule shows that its wall has several layers of cells. They represent successive stages in the development of spermatozoa.
The outer layer is made up of spermatogonia - cells of a rounded shape; they have a relatively large nucleus and a significant amount of cytoplasm. During embryonic development and after birth until puberty, spermatogonia divide by mitosis, thereby increasing the number of these cells and the testis. The period of intensive division of spermatogonia is called the reproduction period. After the onset of puberty, some of the spermatogonia also continue to divide mitotically and form the same cells, but some of the spermatogonia move to the next growth zone, located closer to the lumen of the tubule. Here there is a significant increase in cell size due to an increase in the amount of cytoplasm. At this stage, they are called first-order spermatocides.
The third period in the development of male gametes is called the maturation period. During this period, two rapidly advancing divisions occur one after the other. From each first-order spermatocide, two second-order spermatocytes are first formed, and then four spermatids, which are oval in shape and much smaller in size. Cell division during the maturation period is accompanied by a rearrangement of the chromosome apparatus (meiosis occurs). Spermatids move to the zone closest to the lumen of the tubules, where spermatozoa are formed from them.
In most wild animals, spermatogenesis occurs only at certain times of the year. In the intervals between them in the tubules of the testes contains only spermatogonia. But in humans and most domestic animals, spermatogenesis occurs throughout the year.
The phases of oogenesis are comparable to those of spermatogenesis. In this process, there is also a period of reproduction, when ovogonia intensively divide - small cells with a relatively large nucleus and a small amount of cytoplasm. In mammals and humans, this period ends before birth. The oocytes of the first order formed by this time remain unchanged for many years. With the onset of puberty, periodically individual oocytes enter a period of growth. Oocytes increase, yolk, fat, pigments accumulate in them. Complex morphological biochemical transformations take place in the cytoplasm of a cell in its organelles and membranes. Each oocyte is surrounded by small follicular cells that provide its nutrition.
Then comes the period of maturation, during which two successive divisions occur associated with the transformation of the chromosome apparatus (meiosis). In addition, these divisions are accompanied by an uneven division of the cytoplasm between daughter cells. When a first-order oocyte divides, one large cell is formed - a second-order oocyte, containing almost the entire cytoplasm, and a small cell, called the polar, or reduction body.
At the second division of maturation, the cytoplasm is again unevenly distributed. One large ovotida and a second reduction body are formed. At this time, the first reduction body can also divide into two cells. Thus, one ovotid and three reduction bodies are formed from one first-order oocyte.
Further, an egg is formed from the ovotida, and the reduction bodies dissolve or remain on the surface of the egg, but do not take part in further development. The uneven distribution of the cytoplasm provides the egg with a significant amount of cytoplasm and nutrients that will be required in the future for the development of the embryo.
In mammals and humans, periods of reproduction and growth of egg cells take place in follicles. The follicle is filled with fluid and contains an egg. During ovulation, the wall of the follicle bursts, the egg enters the abdominal cavity, and then, as a rule, into the oviducts (fallopian tubes). The period of maturation of egg cells takes place in the tubes, and fertilization takes place here.
In many animals, ovogenesis and maturation of eggs occur only in certain seasons of the year. In women, one egg usually matures monthly, and for the entire period of puberty, about 400 eggs.
In the nuclei of immature germ cells, as well as the nuclei of somatic cells, all chromosomes are paired, the set of chromosomes is double (2 n), diploid. In the process of maturation of germ cells, reduction division (meiosis) occurs, in which the number of chromosomes decreases, becomes single (n), haploid. Meiosis (from the Greek meiosis - reduction) occurs during gametogenesis. This process takes place during two successive divisions of the maturation period, called the first and second meiotic divisions, respectively. Each of these divisions has phases similar to mitosis.
Schematically, these phases can be depicted as follows:
Interphase I
Prophase I
Meiosis Division I Prometophase I
Metaphase I
Anaphase I
Telophase I
Interphase II - in - Prophase II
therokinesis Metaphase II
Division II Anaphase II
Telophase II
In interphase I (apparently, even during the period of growth), the amount of chromosomal material is doubled by reduplication of DNA molecules.
Of all the phases, prophase I is the longest and most complex in terms of the processes occurring in it. It distinguishes 5 successive stages. Leptonema - a stage of long, thin, weakly spiralized chromosomes, on which thickenings - chromomeres are visible. Zygonema is the stage of the pairing of homologous chromosomes, in which the chromomeres of one homologous chromosome are accurately applied to the corresponding chromomeres of the other (this phenomenon is called conjugation, or synapsis). Pachinema is the stage of thick filaments. Homologous chromosomes are connected in pairs - bivalents. The number of bivalents corresponds to the haploid set of chromosomes. At this stage, each of the chromosomes included in the bivalent already consists of two chromatids, so each bivalent includes four chromatids. At this time, the conjugating chromosomes intertwine, which leads to the exchange of parts of the chromosomes (the so-called crossover, or crossing-over). Diplonema - the stage when homologous chromosomes begin to repel each other, but in a number of areas where crossing over occurs, they continue to be still connected. Diakinesis is the stage at which the repulsion of homologous chromosomes continues, but they still remain connected into bivalents by their ends, forming characteristic shapes - rings and crosses. At this stage, the chromosomes are maximally spiralized, shortened and thickened. Immediately after diakinesis, the nuclear envelope dissolves.
In prometaphase I, chromosome spiralization reaches its greatest extent. They move around the equator.
In metaphase I, bivalents are located along the equator, so that the centromeres of homologous chromosomes face opposite poles and repel each other.
In anaphase I, it is not the chromatids that begin to diverge towards the poles, but the whole homologous chromosomes of each pair, since, unlike mitosis, the centromere does not divide and the chromatids do not separate. This is the first meiotic division fundamentally different from mitosis. Division ends in telophase I.
Thus, during the first meiotic division, homologous chromosomes separate. Each daughter cell already contains a haploid number of chromosomes, but the DNA content is still equal to their diploid set. Following a short interphase during which DNA synthesis does not occur, cells enter the second meiotic division.
Prophase II does not last long. During metaphase II, the chromosomes line up at the equator and the centromeres divide. In anaphase II, sister chromatids move toward opposite poles. Division ends in telophase II. After this division, the chromatids that have fallen into the nuclei of daughter cells are called chromosomes.
Reproduction or reproduction of offspring into the world is one of the most important missions of all living beings on our planet. The genetic material is passed from parents to offspring, which allows for quite a long time not to interrupt their genus. Today we will talk in more detail about the continuation of the human race. Consider concepts such as spermatogenesis and oogenesis. Where does the process of reproduction begin? Of course, with the penetration of the male cell into the female. Where do they come from? We are interested in the process of gametogenesis. Ovogenesis is a sequential process of formation of the female germ cell. Spermatogenesis - male formation Today we will analyze what are the similarities and what are the differences between these processes.
We have already mentioned that ovogenesis is the process of reproduction of the female germ cell, which is called the "ovum". We propose to talk a little about why it is needed and what function it performs. Briefly consider the structure of the egg.
As mentioned earlier, the egg is a reproductive cell that has a rounded 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 radiant crown. This shell received such a 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 very tiny cell. In total, a newborn girl has about a million eggs in stock. But over time, many of them die. Until the moment of puberty, only about 300 thousand of them remain, and about 400 of them ovulate. Where is everyone else going? They simply die, never 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.
Ovogenesis is the formation of female germ cells. It should immediately be clarified 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 are:
We can immediately note that the process of oogenesis is not very different from spermatogenesis, you yourself will notice this further.
So, the stages of oogenesis are the following:
The very first stage takes place 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 are very actively dividing, so there is an accumulation of ovogons. They accumulate in the cortical layer. It is ovogonia that accumulate all the necessary nutrients, namely:
How do oogonia differ from germ cells? They get bigger in size. Their similarity lies in the fact that the genetic makeup is the same.
If we briefly consider the second phase, we will see that it also occurs before the birth of a girl. Now, oocytes of the first order are formed from oogonia. The size during division decreases significantly, but the oocytes quickly gain their mass. Further, future eggs are waiting for a long conservation 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.
We learned that in ovogenesis, a female reproductive cell called an ovum is formed. Now we turn to spermatogenesis and the male germ cell. So, for the continuation of the human race, a pair of eggs is needed, which is able to fertilize it. Spermatozoon - this is the necessary half.
There can be many millions of spermatozoa in the male body, unlike eggs in the female body. They consist:
When the spermatozoon has reached the egg, the tail needed for movement disappears. Further, the female germ 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 spermatozoon. 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 and oogenesis are fairly similar processes. The first one has the following steps:
At the stage of reproduction, more than a thousand spermatogonia are formed by dividing each about ten times. During division, they absorb nutrients.
In the process of growth, they greatly increase in size. It is at the stage of growth that the transformation of spermatogonia into spermatocytes of the first order takes place.
At the ripening stage, 2 divisions occur:
During the formation of the spermatids come into contact with the processes of the cell, and sperm are formed. When they complete their formation, they gain mobility.
It is worth noting immediately the first similarity between oogenesis and spermatogenesis - both processes are needed for the formation, maturation and growth of germ cells, male or female. Although there are many similarities in the processes, some differences can be identified.
Another common feature is the almost identical stages of the process (spermatogenesis has one more stage). The general steps are:
The features of these stages have been discussed in detail above. Let's get to the differences.
Let's start with the fact that during oogenesis and spermatogenesis we have a different result, ovogenesis corresponds to such a result as the formation of a female reproductive cell, and spermatogenesis to a male. 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 stage of formation, while ovogenesis 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 lies in the greater number of male germ cells compared to female ones. This can be explained as follows: only one sperm out of about 200 million reaches the egg.
Spermatogenesis and ovogenesis are the basic functions of a person, without which it is impossible to conceive a new life. Both concepts can be combined into one - gametogenesis, which is the process of production and maturation of germ cells in the body.
Spermatogenesis (production of spermatozoa) occurs in the testicles of men, ovogenesis (the maturation of eggs) occurs in the ovaries of women. For both sexes, the function of reproduction is laid down by nature, the tactics of gametogenesis are similar at some stages, but the development of cells occurs in different ways.
Gametes are basic reproductive cells with a set of chromosomes. The scheme of their formation in the male and female body includes three main stages:
Each phase in both sexes has its own similarities and differences. The process of reproduction begins with the division of primary cells: spermatogonia in men, oogonia in women. The male body produces germ cells continuously - from the moment the fetus develops to a very old age, and in the female they are laid during fetal development (from 2 to 5 months of embryo development), the number is fixed at the end of the production phase. This is the first difference between oogenesis and spermatogenesis. The similarity is the formation of precursors of germ cells (gonocytes) in the embryonic period and their migration to the places of future production of germ cells. In both men and women, it is the gonocytes that are the basis for the generation of gametes.
Spermatogenesis and oogenesis are also similar at the stage of cell growth: female ovogonia and male spermatogonia are transformed into oocytes and spermatocytes of the 1st order. Oocytes are substantially larger than male cells because they store nutrients. In the process of division, the chromosomes that determine the sex of the unborn child diverge into different spermatids (heterogamety), and the female cell contains only one type of chromosome set (homogamety). Intracellular material in the oocyte is distributed unevenly, in contrast to plasma in spermatogonia.
The scheme for the formation of gametes in the male and female body includes three main stages
The maturation stage includes two phases of meiosis, during which more highly developed cells are formed - oocytes and spermatocytes of the 2nd order, and from them - spermatids and eggs. The difference between oogenesis and spermatogenesis in the maturation phase is that one spermatocyte forms 4 spermatids at once, and only one egg and three accompanying bodies, also called polar or reduction bodies, are obtained from an oocyte. This feature is associated with the biological purpose of the female germ cell - providing nutrition for the future organism that will be born in it. The task of male germ cells is high mobility and fertilizing ability. This is necessary to deliver the genetic material to the egg.
Features of spermatogenesis and oogenesis are determined by differences in the localization of gametes during development. All stages of division of male germ cells occur in the convoluted seminiferous tubules located in the testicles. Gradually formed spermatozoa move towards the exit and are deposited in the epididymis, where they become mobile and pass the maturation phase.
In the female body, the sex cell changes locations:
In spermatogenesis, there is a formation stage that is not present in oogenesis. It is at this time that the spermatid becomes a spermatozoon. The process begins at puberty.
Spermatogonia turn into full-fledged male germ cells in about 74 days, which make up the cycle of spermatogenesis. The ovulatory cycle is more complex.
In gametogenesis, spermatogenesis and oogenesis have different goals: for the male reproductive system, it is important to produce as many spermatozoa of equal quality as possible, and for the female, the formation of a mature egg.
Differences between spermatogenesis and oogenesis can be traced to the last stage of the cycle - the release of germ cells for the purpose of fertilization. In men, the process occurs every time an orgasm is achieved during sexual stimulation. Spermatozoa in the seminal fluid pass through the vas deferens, enriching the composition of their nutrient medium with secretion products of various glands (prostate, cooper glands, seminal vesicles).
In women, the process of release of a mature egg is called ovulation and does not depend on external factors. The reproductive system is programmed for certain cycles, during which the hormonal background changes for a while, provoking the release of an egg (2nd order oocyte) from the follicle. If fertilization does not occur, the egg dies.
Comparison of oogenesis and spermatogenesis reflects the table:
| Characteristics | Ovogenesis | spermatogenesis |
| breeding season | Only in the embryonic period | Throughout the life cycle |
| Quantity | From one oocyte - one egg | From one spermatocyte - four spermatozoa |
| Duration | The process (meiosis) occurs in blocks lasting 21-35 days, can be interrupted for a month | Continuous process of meiosis |
| transformation | During growth to meiotic division | During the formation period after meiotic division |
| Nutrients | Are accumulating | Do not accumulate |
| cell type | Individual | Cell structure (syncytial clone) |
Comparative characteristics show that the development of the female cell (the process of oogenesis) goes through a more complex path, being covered at each stage with membranes that subsequently form a follicle (reaches about 1 cm in diameter). Therefore, significantly fewer oocytes are produced: only 500 in a lifetime against 30 million daily produced by male testicles of spermatozoa. This is due to the fact that the period of reproduction of female germ cells ends after the birth of a girl. All cells produced by the body during this time constitute the ovarian reserve. A woman loses one egg every month since puberty. Moreover, many oocytes die during apoptosis, that is, part of the reserve is wasted. Oogenesis also differs from spermatogenesis in that part of the spermatozoa also dies, but this number is compensated.
Often the cause of infertility is the depletion of the ovaries by the age of 35-40.
The ovaries work almost continuously and stop only during periods of pregnancy and lactation. In the modern world, women have much more “idle” cycles than pregnancies. Often the cause of infertility is the depletion of the ovaries by the age of 35-40. When the couple finally decided to have children, it turns out that the supply of eggs is already almost exhausted. When a critical volume is reached, menopause occurs, when the chances of conception are extremely low.
Nature has given eggs more reliable protection from external influences than men, whose spermatogenesis reacts to almost any factors - alcohol, overheating, stress, smoking, physical overload. The quality of each portion of sperm may differ from the previous one. The process of spermatogenesis is continuous and much shorter than oogenesis, so if a man plans to conceive a child, then he has the opportunity to change the spermogram parameters:
In most cases, it is the low characteristics of the spermogram that are the cause of infertility. Unlike spermatogenesis, oogenesis does not give women the opportunity to influence the quality and quantity of their germ cells. But lifestyle during pregnancy plays a big role, since the egg becomes vulnerable in the process of its division and the formation of the embryo.
Knowledge of the features of spermatogenesis and oogenesis will help to correctly assess the chances of conceiving a healthy child. It is impossible to plan your life in advance. Many study, work, waiting for the right moment to conceive a child. For men, the time factor is not as relevant as for women, but over time, the number of Leydig cells decreases, problems with the prostate arise. All this causes infertility, which in many cases can be prevented.
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