Parting

Ovogenesis is the process of egg formation. spermatogenesis and ovogenesis. Spermatogenesis and oogenesis comparison of features Comparative characteristics of cells at different stages of spermatogenesis

MINISTRY OF EDUCATION AND SCIENCE OF THE RUSSIAN FEDERATION

FSBEI HPE "Penza State University"

medical institute

Department of Clinical Morphology and Forensic Medicine with a course of oncology.

Coursework by discipline

"Histology, Cytology, Embryology".

Spermatogenesis and oogenesis. Similarities and differences"

Completed: Art. gr. 12ll6 IzyavlevaO.V.

Checked by: assistant Yunyashina Yu.V.

Introduction

spermatogenesis

Comparison of spermatogenesis and oogenesis

Conclusion

Bibliography

Introduction

Reproduction or reproduction, the function inherent in all living beings to reproduce their own kind. Unlike all other vital functions of the body, reproduction is not aimed at maintaining the life of an individual, but at preserving its genes in offspring and procreation - thereby preserving the gene pool of a population, species, family, etc. In the course of evolution, different groups of organisms have developed - in many cases independently - different ways and strategies of reproduction, and the fact that these groups have survived and exist proves the effectiveness of different ways of carrying out this process.

With sexual reproduction, offspring usually have two parents. Each parent produces sex cells. Sex cells, or gametes, have a half or haploid set of chromosomes and arise as a result of meiosis. Thus, a gamete (from the Greek gamete - wife, gametes - husband) is a mature reproductive cell containing a haploid set of chromosomes and capable of merging with a similar cell of the opposite sex to form a zygote, while the number of chromosomes becomes diploid. In a diploid set, each chromosome has a paired (homologous) chromosome. One of the homologous chromosomes comes from the father, the other from the mother. The female gamete is called the egg, the male gamete is called the sperm. The process of formation and development of gametes in the gonads has a common name - gametogenesis. All other cells that are not directly involved in the formation of gametes are called somatic cells. Gametogenesis is a broad term that refers to the gradual "creation" of highly specialized cells capable of giving rise to a new organism.

Primary germ cells - gonocytes are descendants of embryonic totipotent cells present in the blastoderm of the embryo during the formation of the primary strip. They appear before the gonad and exist independently of it. Then they enter the posterior extraembryonic endoderm, migrating into the intestinal wall and into the surrounding mesenchyme, and then move to the dorsal mesenterium to the anlage of the gonad. Before development, the gonads actively move in the body with currents of fluids. Once near the gonad, the gonocytes approach it in an amoeboid way, attracted by a proteinaceous factor secreted by the gonad. Penetrating into the gland (ovaries in females, testes in males), germ cells are located in males in the brain, and in females in the cortical layer of the gonads. In the future, the germ cells before their maturation are in the gonads. The gonads of the embryo initially contain a relatively small number of primary germ cells that populated them. But once in the gonads, germ cells begin to divide vigorously, and their number increases dramatically. Cells divide mitotically. Mitosis ensures the transfer to two daughter cells of exactly the same sets of chromosomes containing hereditary information.

1. Spermatogenesis

In the male reproductive system, spermatogenesis occurs in the sex glands (gonads), represented by a paired organ - the testicles, which perform two important functions: - generative (formation of male germ cells); - endocrine (synthesis of male sex hormones).

These functions are interrelated, although they are provided by various structural components of the body.

Spermatogenesis includes four periods: -reproduction; -growth; - maturation; -formations.

breeding period. Spermatogenic cells are represented by spermatogonia. These are small rounded diploid cells located on the basement membrane of the seminiferous convoluted tubules. There are two types of spermatogonia: A and B. Type A is represented by light and dark slightly flattened cells with a light nucleus. Dark spermatogonia - non-dividing, resting cells, are considered stem cells; light spermatogonia - cells dividing by mitosis. Some of them support the population of cambial cells, others - in the course of successive divisions become type B spermatogonia. The latter have a pear-shaped shape, a large rounded nucleus and a centrally located nucleolus. Spermatogonia are replenished by division (complete mitosis) of stem cells of the male gonad. At a certain moment, the daughter cell (derived stem cell) divides incompletely, leaving a bridge that connects the daughter cells, and enters the path of spermatogenesis. Syncytial communication, on the one hand, ensures the synchronism of the existence of cells of the clone, on the other hand (due to the mass character) - the heterogeneity and polymorphism of its constituent cells and thus high viability. The divisions of the gonias are differentiating. In the process of such mitotic divisions, the daughter cells do not fully grow to the original ones and become smaller, and as a result, they prepare the gonia to enter meiosis. The period of mitotic differentiating spermatogenesis ends with the creation of "secondary" spermatogonia, and brings the cells of the clone to the meiotic period of spermatogenesis. Cells that have completed division and entered the period of growth and maturation are called primary spermatocytes (first-order spermatocytes).

Growth period. During meiosis, complex changes in the nuclei take place, preparing the cell for the transition to the haploid state. First-order spermatocytes significantly increase in volume and become the largest spermatogenic cells, the DNA content in the nuclei doubles (2n4c). They separate from the basement membrane of the tubules and move towards the lumen of the tubule. Spermatocytes of the first order immediately enter the prophase of the first division of meiosis, the duration is about 22 days. In the prophase of meiosis I, the spermatocyte grows, and therefore such cells are also called auxocytes, that is, growing. Thus, the largest cells of spermatogenesis are spermatocytes of the first order, preparing for the first division of maturation.

Ripening period. In males, the first reduction division of meiosis ends with the formation of two second-order spermatocytes, or secondary spermatocytes. These are cells smaller than the primary ones, which are located closer to the lumen of the tubules. The second equational division ends with the appearance of 4 haploid cells - spermatids.

The period of formation (spermiogenesis). During this period, spermatids are transformed into mature germ cells - spermatozoa (sperm). During the period of formation, only structural changes in cells occur, since their chromosome set does not change, remaining haploid. At the beginning of spermatogenesis, the cells are still connected to each other by cytoplasmic bridges and continue to be part of the syncytial clone. Structural changes in spermatids are:

compaction of chromatin (due to the replacement of histones with non-histone proteins), a decrease in the nucleus, the acquisition of a pear-shaped shape:

the formation of an acrosome - a flat membrane sac containing a number of lipic enzymes necessary for fertilization. The acrosome is a derivative of the Golgi complex, which initially forms acrosomal granules, which, merging, form a bubble adjacent to the future front surface of the nucleus and gradually spreading over it in the form of a cap;

the formation of the flagellum by the distal centriole, which forms the axoneme of the tail (after the movement of both centrioles to the posterior pole of the nucleus); the proximal centriole is located in the depression of the nuclear envelope;

the formation of special elements of the cytoskeleton occurs as the tail is formed and includes the appearance of 9 longitudinally lying segmented columns around the centrioles (connecting section), which are connected in detail with 9 dense fibers located along the periphery of pairs of axonemal microtubules (intermediate section). In the main section, a fibrous sheath is formed, formed by longitudinal columns connected by ribs;

change in the shape and location of mitochondria, which, from elongated and diffusely scattered throughout the cytoplasm: spermatids, become spiral and focus around dense fibers in the emerging intermediate section, closely adjacent to each other;

removal of excess cytoplasm containing organelles and lipid inclusions from the developing sperm in the form of the so-called residual bodies, which are released into the lumen of the tubule.

A feature of spermatogenesis is the formation of functional syncytium, which unites clones of spermatogenic cells involved in this process. Intercellular connections of spermatogenic cells ensure their synchronous development, nutrient transfer and intercellular exchange of gene expression products. (Fig. 1)

Fig.1. Scheme of spermatogenesis processes.

Spermatogenesis in humans lasts 64-74 days, starting at puberty and continuing throughout life. After 50 years, its intensity decreases significantly. A person produces about 250 million sperm every day. Spermatogenesis normally proceeds at a temperature 3 degrees below body temperature (temperature in the scrotum). It is suppressed by an increase in temperature (wearing excessively warm clothes), cryptorchidism (undescended testicle into the scrotum) and pressure on it from surrounding tissues in the peritoneal cavity and inguinal canal.

2. Oogenesis

Eggs are the female gametes of animals and higher plants. As a rule, eggs are haploid cells, but may have a different ploidy in polyploid organisms. The human egg is about 150 microns in diameter.

The cytoplasm of the eggs (ooplasm) contains inclusions of nutrients - the yolk. Oocytes are produced as a result of oogenesis. After fertilization, the fertilized egg (zygote) develops into an embryo. In parthenogenesis, an embryo and then a new organism develops from an unfertilized egg.

The human egg was first described in 1827 by Baer. This increased interest in the study of the processes of gamete formation and fertilization.

The ovum differs from the sperm in:

overwhelming real estate;

respectively, a characteristic more or less spherical shape;

the presence of a variety of protective and shell-sources of nutrients;

the absence of functional organelles or formations inherent in the spermatozoon: a tail, a specialized mitochondrial complex, an acrosome, etc.;

genetic information (sex chromosomes - XX).

features of education and development, as well as life time;

a much smaller number of them in the body (during life, about 400 eggs are formed in the female body, while hundreds of millions of spermatozoa in the male).

a supply of nutrients for the development of the future embryo, localized in the cytoplasm;

significantly larger (a human egg is 85,000 times larger than a spermatozoon).

The process of development of female germ cells is called oogenesis. Gonocytes infiltrate the rudiment of the female genital gonad, and all further development of the female germ cells occurs in it. Once in the ovary, the gonocytes become oogonia. There is no formation period in this process.

The process of oogenesis consists of three periods: -reproduction; -growth; -ripening.

In contrast to spermatogenesis, reproduction, growth and partial maturation occur in the ovaries, ending in the oviduct. In addition, the end of the second division of meiosis occurs only as a result of fertilization, and therefore the process of oogenesis does not always reach its end.

breeding period. Diploid cells formed from gonocytes at the 8th week, oogonia (immature germ cells), repeatedly divide mitotically up to 3-4 months of intrauterine development, as a result of which their number increases in both human ovaries, reaching several hundred thousand. With such a supply of germ cells, a girl is born. New germ cells do not appear after birth and there is a massive degeneration of germ cells. After the last division in the reproduction period, the cell enters the prophase of the first division of maturation, and the cell cycle lingers on this for a long time. In prophase I of meiosis, conjugation of chromosomes, the formation of a synaptonemal complex, and crossing over occur, that is, events that determine all further meiotic processes.

Growth period. The oogonia enter a period of growth. They lose the ability to mitotic division and enter prophase I of meiosis. In prophase I of meiosis, conjugation of chromosomes, the formation of a synaptonemal complex, and crossing over occur, that is, events that determine all further meiotic processes.

There are two phases: small and large growth. Before the onset of puberty, a process of small growth takes place, when there is mainly an increase in the size of the nucleus and cytoplasm due to the accumulation of deutoplasmic substances in the form of yolk. During a period of great growth, the accumulation of nutrient material in the cytoplasm occurs, which is brought to the ovary with the blood of the mother's body. The composition of the so-called yolk inclusions includes proteins, fats, fat-like substances. On the chromosomes of the primary oocyte, a large amount of information and transfer RNA is synthesized, as well as substances of a special composition, located under the plasmolemma, forming the cortical layer. The stages of proleptotene, leptoten, zygotene, pachytene, diplotene come in succession. At the zygotenic stage of the prophase of meiosis, the formation of the synaptonemal complex and the conjugation of homologous chromosomes begin. The synaptonemal complex (SC) is a genetically determined three-membered protein structure. On pachytene, conjugation ends with the formation of a bivalent, which achieves an imaginary reduction in the number of chromosomes. This is how a primary oocyte, or first-order oocyte, is formed, initially surrounded by a layer of flat follicular cells (primordial follicle). The volumes of the nucleus and cytoplasm increase proportionally and slightly. At the same time, nuclear-cytoplasmic relations are not violated.

Forming primary follicles, in which a shiny zone appears for the first time, which has the form of a structureless oxyphilic layer between the primary oocyte and follicular cells of a prismatic shape. It performs a number of important functions: -forms a semi-permeable barrier between follicular cells and oocyte; -increases the surface area of contact between them; - provides species-specific fertilization; -provides monospermic fertilization; - protects the early embryo during its movement through the genital tract before implantation.

In the first half of a large growth, the nucleus and cytoplasm intensively increase (cytoplasmic growth). "Lampbrushes" and nucleoli reach their maximum development and actively participate in RNA synthesis. In the second half of the period of great growth, vitellogenesis (trophoplasmic growth) occurs. In the nucleus, there is a decline in RNA synthesis. Quite often, a karyosphere is formed - a special structure with pores, consisting of elements of membranes and a synaptonemal complex for isolating diplotene chromosomes of the oocyte nucleus from the functional activity of extrachromosomal DNA and nucleoli.

At the end of a period of great growth, the “lamp brushes” lose their loops and are greatly shortened. The stage of diakinesis begins, after which the metaphase plate of the first division of maturation is formed. The nucleoli function for a short time or do not develop at all, and the karyosphere is formed early. Nuclear-cytoplasmic ratios decrease.

At the stage of diakinesis, the course of meiosis slows down until it stops completely (meiosis block). The block of meiosis in humans is removed with the onset of puberty. Prophase I can be very long, and a large growth of oocytes capable of ovulation in a person stretches for decades, that is, for the entire reproductive growth.

With each sexual cycle, a group of oocytes enters a period of great growth, but not all of them develop to the end, since most of them stop growing and die. Only one of them (very rarely several oocytes) passes to the next period of oogenesis - maturation.

Ripening period. With the accumulation of the necessary substances in the cytoplasm of the primary oocyte, the prophase is completed, and then the remaining phases of the first reduction division of maturation. As a result, two diploid, but unequal-sized cells are formed. In one of them, a large cell, called a second-order oocyte, or a secondary oocyte, almost all the accumulated substances necessary for further development remain. The other, small in size, has very little cytoplasm, and therefore is called a reduction or directional body. The formation of a secondary oocyte in a woman coincides with the moment of ovulation, when after the rupture of a mature follicle (Graafian vesicle), which usually occurs on the 14th day of the ovarian-menstrual cycle, the germ cell leaves the follicle. Following this, a second-order secondary oocyte at the metaphase stage of the second division of meiosis, surrounded by a transparent zone and follicular cells of the radiant crown, enters the funnel of the fallopian tube. (Fig.2, 3.)

Fig. 2. Scheme of oogenesis processes.

The second division of meiosis is not always completed, but only if the spermatozoon reaches the surface of the oocyte and penetrates into it. This division is also uneven, as it leads to the formation of an egg from a secondary oocyte, which retains all the substances necessary for the development of a new organism, and a new reduction body.

The cyclical growth and maturation of germ cells in a sexually mature female body is manifested in the fact that 5-20 oocytes are involved in the process of large growth every month, but only one of them will enter the maturation phase, and the rest will die in the process of follicular atresia. In the 5th decade, with the onset of menopause, the development of germ cells stops: in the future, they undergo degenerative changes and disappear from the ovary.

Rice. 3. Stages of human oocyte development:

A - before birth, a small proportion of primordial follicles begin to grow, and these follicles are now called developing. B - After some period of continuous growth, some of the developing follicles accumulate fluid, turning into antral follicles. C - with the onset of puberty once a month, a wave of luteinizing hormone (LH) secreted by the pituitary gland induces one antral follicle to mature: the first-order oocyte located in this follicle completes the first division of meiosis, forming a polar body and turning into a second-order oocyte. G - the second-order oocyte, together with the polar body and part of the surrounding follicular cells, is released at the moment when the follicle ruptures on the surface of the ovary. The oocyte of the second order undergoes the second division of meiosis only if it is fertilized. - primordial follicle; II - developing follicle; III - antral follicle; VI - large antral follicle (Graaf's vesicle); V - erupted follicle; 1 - oocyte of the first order, stopped in prophase I: 2 - follicular cells; 3 - cavity; 4 - oocyte of the first order; 5 - LH level rise; 6 - oocyte of the first order completes the first division of meiosis, turning into a second-order oocyte; 7 - surface of the ovary; 8 - oocyte of the second order; 9 - 1st polar body.

Ovogenesis proceeds with the constant interaction of developing germ cells with epithelial cells in the follicles.

Comparison of spermatogenesis and oogenesis

Oogenesis has a fundamental similarity with spermatogenesis, oogenesis also goes through a series of stages: reproduction, growth and maturation.

Despite this fundamental similarity of genetic processes during spermatogenesis and oogenesis, there are significant differences between them.

First, the formation stage is inherent in spermatogenesis and is absent during oogenesis.

Secondly, the growth stage in oogenesis is longer than in spermatogenesis.

Thirdly, the stage of maturation of oogenesis has its own characteristics, consisting in the uneven divisions of maturation, leading to the release of polar bodies. spermatogenesis oogenesis reproduction

Fourth, in female individuals, the first division of meiosis begins during fetal development, is completed for the first time by the time of puberty, and in the last - on the eve of menopause. In boys, meiosis begins only with the achievement of puberty and persists throughout the entire puberty of a man.

Fifth, the formation of mature germ cells in women occurs cyclically with a period of approximately 28 days, while in men it occurs continuously.

Sixth, unlike spermatogonia, each of which, as a result of meiosis, produces four functionally complete spermatozoa, only one egg is obtained from the oogonium. After the first division of meiosis, most of the cytoplasm leaves one daughter cell, and a small part goes to the second, called the directional body. The same happens during the second division of meiosis. The directional bodies degenerate.

Seventh, the male and female sex cells are very different in structure and function: the spermatozoon is a small mobile cell, very rich in mitochondria, which supply it with energy for movement, while the egg cell is the largest cell in the human body (diameter 150 - 200 microns). ), which contains not only significant reserves of nutrients, but also messenger RNAs that will be used in the early stages of embryo development. The egg is surrounded by follicular cells that feed it and forms a specialized structure - the follicle (Graaf's vesicle).

Eighth, the course of spermatogenesis is more susceptible to the influence of environmental factors than the course of oogenesis, due to differences in the location of the genital organs (testes, as a rule, are located outside the abdominal cavity).

Rice. 4. Comparison of spermatogenesis and oogenesis.

Conclusion

Sexual reproduction is a significant evolutionary acquisition of organisms. On the other hand, it contributes to the reassortment of genes, the emergence of a variety of organisms and increase their competitiveness in a constantly changing environment. Compared to other cells, the function of gametes is unique. They ensure the transfer of hereditary information between individuals of different generations, which saves life in time.

Bibliography

1. Valkov E.I. "General and Medical Embryology". Textbook for medical schools. St. Petersburg "FOLIANT" 2003 Art. 27-34.

indicating the topic right now to find out about the possibility of obtaining a consultation.

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. AT 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 with 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.

Spermatogenesis and ovogenesis are a prelude to fulfilling the main purpose of a person - procreation. At the initial stage, the formation and maturation of sperm and eggs should occur. Anatomically and physiologically, the reproductive systems of women and men have characteristic features and are very different from each other. Are there similarities and differences in gametogenesis? What are the differences between spermatogenesis and oogenesis? Comparative characteristics of oogenesis and spermatogenesis will help answer these questions.

gamete formation

Representatives of mammals are characterized by sexual dimorphism - the division of gametes into female eggs and male spermatozoa. Their differences are due to the difference in the tasks facing the male and female. The somatic cell structures in the human body divide mitotically as soon as they reach the stage of maturity. Sexual, on the other hand, go through several successive stages in their development until they reach maturity in order to participate in fertilization.

The emergence, formation and development of human gametes occurs in the reproductive system. The process by which male spermatozoa are formed is called spermatogenesis, and female spermatozoa are called oogenesis or oogenesis. Male gametogenesis occurs in the seminiferous tubules. Women's are formed in the ovaries. The scheme of oogenesis and spermatogenesis reflects the following stages of development:

Reproduction.
Growth.
Maturation.

A comparison of the intracellular and differential developmental processes that occur at these stages allows us to note some similarities in the individual moments of spermatogenesis, as well as oogenesis. The above scheme shows that during reproduction, spermatocytes and oocytes of the first order are formed as a result of mitosis from spermatogonia and ovogonia. They enter the active phase of meiosis and give rise to a population of spermocytes and oocytes of the second order, which, in turn, go through the next stage of meiosis, during which spermatids and ovotids are formed.

Comparison of processes reveals another feature and similarity - both begin during the development of the fetus. The precursors of germ cells - gonocytes - are formed earlier than the organs of the reproductive system, and are transported to the rudiments of the gonads due to the ability to amoeboid movement. They migrate along the germinal dorsal fold to the place where the gonads are formed.

Female gametes are formed in the ovaries.

When the primary ones are at their destination, they are actively introduced into the medulla of the future testes or the cortical layer in the ovaries. Such features of the similarity of purposeful movement are due to chemotaxis. The rudiments of the gonads synthesize specific substances that "attract" primary spermatocytes and oocytes. Inside the rudiments of the reproductive organs, the formation of spermatogonia and oogonia - stem cells occurs. After each mitotic division, they:

Change shape.
They increase in size.
Become capable of regular, frequent division.

They also enter the first phase of meiosis (prophase). In prophase, primary spermatocytes and oocytes remain until puberty. This is where the similarity ends. Since the tasks of the formation and development of processes are different, each has characteristic features. A comparison of the formation of spermatocytes shows that in men, mitosis begins at puberty, and its development occurs throughout life. Whereas in women, oocytes divide by mitosis only in the period of embryo development. And, despite the fact that the scheme places these stages side by side, in reality they have temporary differences.

growth process

Also, a comparison of the features of the structure and size of spermatocytes and oocytes shows their difference from each other. At the growth stage, the following features of development are noted:

The increase in size is almost 4 times.
Doubling (replication) of DNA.

Female gametes contain a large amount of nutrients.

The scheme reflects not only the similarities and differences in the stage of division, but also shows what happens inside the cellular structure. The scheme makes it possible to compare oogenesis and spermatogenesis at the level of chromosome division. Comparing the internal processes of development that the diagram shows, one can find much more similarities than when analyzing the previous diagram. The difference between a spermatocyte and an oocyte of the first order is also reflected in their size, which is due to the accumulation of more nutrients by female gametes necessary for subsequent divisions. However, comparing their sizes, you can notice one feature - women's sperm are larger than men's. What is the reason for this difference?

Oocytes must provide nutrition for the processes after fertilization, and for spermatocytes, from which spermatozoa will subsequently appear, it is important to maintain mobility, which will be hindered by a large supply. Yes, they have a different lifespan. The sperm remains viable after ejaculation for several days under favorable conditions. And from a fertilized egg, an embryo develops over a long period, which requires a large amount of reserves.

At this stage of gametogenesis, the similarity is that each oocyte and spermatocyte contains a complete set of chromosomes and is diploid. This scheme marks the similarity of processes. The difference lies in differentiation, changes that occur in the cell cytoplasm and nucleus. In the so-called period S, doubling of all DNA molecules occurs. There are several stages of redistribution of hereditary material in the nuclei of germ cells, which are visible when comparing the scheme:

Leptotennaya - at this stage, a formed nucleus and spirally twisted strands of chromosomes are visible. In this case, the paternal and maternal chromosomes do not converge.
Zygotenic - a comparative characteristic of this stage is the convergence of chromosomes and the exchange of genes.
Pachytene - homologous chromosomes twist with each other, form tight spirals and, accordingly, thicken.
Diplomatic - the stage of duplication and separation of two pairs of chromosomes.

The above scheme fully reflects everything that happens in the nucleus during the growth stage. Its completion is marked by the formation of spermatocytes and oocytes of the first order, ready to enter the next stage - maturation.

Maturation

A feature of maturation is the miyotic division of spermatocytes and oocytes. In this case, 4 cells are formed from one gamete. Spermatogonia divides in half, forming a second-order spermatocyte with a haploid (half) set of chromosomes. The second stage gives the formation of two equivalent spermatids. In accordance with the above diagram, it can be seen that 1 diploid spermatocyte forms 4 haploid spermatids in 2 divisions.

The chromosomes responsible for sex (X and Y) diverge into different spermatids, which determines the peculiarities of the heterogamety of the male material. Comparison of oogenesis at maturation shows that female cells are homogametic, that is, they contain only XX chromosomes. This is the lack of similarity of fission processes. Otherwise, a comparison of these developmental processes shows their complete similarity.

The difference between spermatogenesis and oogenesis during maturation is that the spermatogonium cytoplasm is divided equally, and during the division of the primary oocyte, an uneven redistribution of intracellular material occurs. The scheme of oogenesis clearly shows that a large cell is formed - a secondary oocyte - and a smaller one - a reduction body. The secondary oocyte migrates into the fallopian tube, where the second phase of meiosis of ovogenesis occurs. It ends after the introduction of the sperm into the cell, with the formation of an ovotida. The egg is again divided into 2 daughter cells. The diagram shows how, as a result of division:

The main part of the cytoplasm goes into the egg.
Smaller - in the guide.

Female cells contain only XX chromosomes.

As a result of two stages of reduction division, 1 mature egg and 3 small bodies are formed. This is one of the differences and features of the development of oogenesis and spermatogenesis. If a feature of spermatogenesis is the focus on increasing the number of equivalent spermatozoa, then a characteristic feature of the development of oogenesis is the formation of one mature egg. A comparison of the features of oogenesis and spermatogenesis shows that the difference can be traced in the tasks of gametes and, in particular, in the course of the maturation period.

The features and difference between oogenesis and spermatogenesis do not end with this comparison, since there is another period in spermatogenesis that is not in oogenesis. This is the stage of formation of sexually mature spermatozoa. A comparison scheme of the device, size and number resulting from a number of germ cell divisions shows how different they are. Comparison of the features of the number of sex gametes shows:

In a man, 1 cm3 of ejaculate contains about 100 million spermatozoa.
In a woman, by the beginning of puberty, about 300 thousand oocytes of the first order are formed in the follicles.

Comparing these numbers shows how much more male gametes are formed. This happens all the time, until old age. In women during puberty, most of the eggs die, and about 500 remain. A feature of their development is that the cell, as a result of meiosis, is covered with membranes, between which nutrient fluid accumulates, forming a follicle. A mature follicle reaches a diameter of 1 cm.

In spermatogenesis, there is one more period of maturation than in oogenesis.

Analysis of the stages of gametogenesis

Comparison of spermatogenesis with oogenesis indicates that there are much fewer similarities between them than differences, which is also indicated by the diagram. Oogenesis and spermatogenesis can be summarized briefly in a summary table that clearly shows the similarities and differences between spermatogenesis and oogenesis:

Comparison
Place of education	testicles
		Oocytes

Mobility comparison	Actively mobile	motionless
	"Spoon-shaped" with a flagellum	oval
Deposition of nutrient fluid	Do not accumulate	Accumulate
Type of division during the breeding season	Mitosis results in the development of sperm cells.	Mitosis results in the development of oocytes.
Characteristics of the growth phase	Increase in cell volume	Increase in cell volume
Characteristics of the ripening stage	During meiosis, spermatids are produced	Meiosis develops oocytes
Total number of phases

Comparing the similarities and differences between spermatogenesis and oogenesis are as follows:

The phases that female gametes and sperm go through are largely the same, except for an additional phase of sperm formation (having certain features), in which they acquire a characteristic shape and form a motor apparatus.
A comparison of the division phase of gametes of the first order indicates differences, since 4 germ cells develop from a spermatocyte, and 1 mature egg cell develops from an oocyte.
Comparison of oogenesis shows the cyclical nature of egg production. The cycle is 20-34 days. If the egg is not fertilized, then it dies, and the resulting substances trigger the maturation of a new egg. Spermatozoa are constantly being formed.
There are differences in the number of germ cells. About 30 million spermatozoa are produced per day in a man as a result of spermatogenesis. A woman has no more than 500 eggs in her entire life.
If we compare the duration of the reproduction stage, it turns out that it also has its own characteristics - during oogenesis, it ends immediately after the birth of the girl, and reproduction during spermatogenesis goes on throughout the entire period of life.
Comparison of growth stages indicates differences in time in different types of gametogenesis - spermatogenesis is shorter.
During mitosis or meiosis at the stage of maturation of oogenesis, an uneven redistribution of cellular contents occurs.
Comparison of the degree of influence of external factors on gamete formation has the following features - spermatogenesis is most susceptible to such an influence, since the genital organs in which it occurs are outside the body cavity.

Thus, if we analyze gametogenesis in detail, then spermatogenesis, ovogenesis have more differences than similarities, which is due to the difference in the tasks that are assigned to the eggs and spermatozoa during sexual demorphism.

Many couples want to know as much as possible about their bodies when planning a pregnancy. It is especially important for conception to take into account the natural cycles of maturation of the sex gametes, since they play the main role in the birth of a child. We will try to tell you what oogenesis and spermatogenesis are and how these processes are controlled.

Hematogenesis is the process of formation of germ cells by the male and female body. It is necessary, since sexual reproduction is impossible without a sperm and an egg. Since the formation of male and female gametes have a different direction, it is customary to consider the process of spermatogenesis and oogenesis separately.

spermatogenesis

How often sperm is renewed can be judged by the duration of maturation of one sperm - from 73 to 75 days. However, new cells are produced constantly, because the number of spermatozoa after ejaculation is fully restored after 3 days. During this period, there are 4 stages of spermatogenesis:

Reproduction. The beginning of spermatogenesis begins with the division of the so-called primary cells. As a result of the first division, 2 types of cells appear, the first of which is necessary for the further production of spermatogonia with a diploid set of chromosomes, and the second, with further division, passes into the next stage of gamete development.
Growth period. For the subsequent formation of a spermatozoon in the spermatocyte, active metabolic processes begin, the synthesis of proteins and enzymes, and the doubling of the chromosome set.
Maturation. The second type of cells is obtained after the reduction division of the first order spermatocyte. This stage is characterized by 2 stages of meiosis. As a result of the first stage, spermatocytes of the second order are obtained, containing a 23-chromosomal set. After the second division of the spermatocyte, 4 spermatids with a haploid set of chromosomes are formed. Half of the spermatids resulting from meiosis contain an X or Y chromosome. The X chromosome is responsible for the formation of the female fetus, while the Y chromosome is responsible for the male principle.
Formation. After meiosis, the transition from spermatid to spermatozoon begins, for which it is necessary to go through several phases of maturation. At the end of spermiogenesis, the immature gamete turns into sperm.

What is important to know about oogenesis

The female gamete in most cases is formed about 14-18 days from the primary cells laid down during the prenatal development. The future egg is located in specific cells called follicles, which protect and nourish the oocyte. It is important to understand that during this time, 1-2 gametes normally mature. The entire process of egg maturation is divided into 3 periods:

Division. This stage is carried out only in the period of intrauterine development. As a result of mitotic division, about 1 million oogonia are laid in the female body. Oocytes, having completed the division phase by the time of the birth of a girl, pass into prophase I of meiosis, which lasts until the onset of puberty.
Growth. In total, 2 stages of gamete growth are distinguished. The first preparatory stage - previtellogenesis - is characterized by a proportional increase in all structural units of the gamete and RNA is actively produced. The second stage of growth, when follicles are released - vitellogenesis - is characterized by a high frequency of growth of the cytoplasm of the cell, while the nucleus does not increase much. As the oocyte grows, the follicle also matures.
Maturation. The stage is characterized by two divisions of meiosis, as a result of the first of them, mature follicles burst and release a second-order oocyte. It is interesting that as a result of the first division, the so-called irregular bodies containing the Y chromosome are eliminated by the body. The egg completes its maturation after fertilization.

For a clearer understanding, it is necessary to visually consider the process of sperm formation and chromosome distribution. Scheme of spermatogenesis:

It is important to understand how the follicle develops. Oogenesis scheme:

What hormones regulate gametogenesis

Hormonal regulation of spermatogenesis and oogenesis is carried out under the influence of hormones secreted by the sex glands and the hypothalamic-pituitary part of the brain. The mechanism of triggering the reproductive system begins with the production of releasing hormone by the hypothalamus, which causes a response in the pituitary gland - it secretes LH and FSH. It is under the influence of FSH that spermatogonia and oogonia begin the process of transformation from the primary stage of development to the secondary.

In men, spermatogenesis is initiated by testosterone, which is released under the influence of LH. It affects the division, growth and maturation of sperm. The second important hormone is FSH. It attaches to the plasma membrane receptors of Sertoli cells, which accelerate the maturation of spermatozoa and the multiplication of nutrients in the cells.

In the female body, oogenesis is regulated by the ovarian hormone estrogen. They are produced by the walls of the follicle, which, due to feedback from the hypothalamic-pituitary part of the brain, grow under the influence of FSH. When a critical amount of estrogen accumulates in the body, LH is released and the oocyte is released.

How cells behave after gametogenesis

Features of spermatogenesis and oogenesis include the development of the gamete after it has been formed. The oocyte completes all stages of division after fertilization of the egg. After release, it is sent through the fallopian tubes to meet the sperm.

After the maturation of germ cells in the body of a man, spermatozoa move to the vas deferens. There they are combined with the seminal fluid, which ensures their vitality, nourishes and protects from external factors.

Comparison of spermatogenesis and oogenesis

Differences between spermatogenesis and oogenesis, first of all, can be found in the process of maturation of germ cells. The most noticeable difference is in the structure and size of spermatocytes and oocytes. The size of an oocyte of the II order reaches a gigantic size compared to sperm, since female cells need more nutrients for the normal development of the embryo.

It is important to know that meiosis in spermatozoa ends before insemination, and in women after fertilization of the egg.

Within 1 day, more than 25 million sperm mature in the testicles, while in the female body, about 400 gametes mature in a lifetime. The quality of the female gamete does not depend on external factors, but internal cycles and hormonal levels influence oocytes. In men, gametogenesis continues until the end of life.

Outcome

Ovogenesis and spermatogenesis, regardless of their colossal differences, are aimed at achieving a common goal - the conception of a child. But since male and female cells perform different functions and are secreted by different systems, their development has its own characteristics.

Spermatozoa mature within 75 days and determine the sex of the unborn child. Sperm renewal occurs within 3 days, while the oocyte matures 1 time in 26-34 days. The egg is responsible for the normal development of the fetus, because its formation is much more complicated and longer. What is the difference between male and female sex cells?

Primordial sex cells can be found at the fourth week of development outside the embryo in the endoderm of the yolk sac. From there, they migrate during the sixth week to the sex ridges and combine with somatic cells to form primitive gonads, which soon differentiate into testes or ovaries, depending on the composition of the zygote's sex chromosomes (XY or XX).

Both during and during oogenesis, meiotic division occurs, however, there are important differences in its details and timing, which can have clinical and genetic consequences for the offspring. Female meiosis begins early during embryonic development in a limited number of cells. In contrast, male meiosis occurs continuously in many cells throughout a male's adult life.

study directly meiosis person is very difficult. In women, the main stages of meiosis occur in the ovaries of the fetus, in oocytes before ovulation and after fertilization. Although cells after fertilization can be studied in vitro, access to earlier steps is limited.

Get testicular material for the study of male meiosis is less difficult, since testicular biopsy is included in the examination of many men attending fertility clinics. A lot of information has been obtained about the cytogenetic, biochemical and molecular mechanisms of normal meiosis and the causes and consequences of meiotic disorders.

spermatogenesis

spermatozoa formed in the seminiferous tubules of the testicles after puberty. The tubules are filled with spermatogonia at different stages of differentiation. These cells originate from primary germ cells as a result of a long series of mitoses. The last cell type in the sequence of spermatogenesis are the primary spermatocytes, which enter the first division of meiosis, forming two haploid secondary spermatocytes.

Secondary spermatocytes quickly pass the second division of meiosis, forming two spermatids, which, without further division, mature into spermatozoa. In humans, this process takes about 64 days. Huge numbers of spermatozoa are formed, usually about 200 million per ejaculation, and during a lifetime about 1012, which requires many hundreds of previous mitoses.

Ovogenesis

Unlike spermatogenesis, which begins at puberty and continues throughout life, oogenesis begins during the prenatal period. The ovum develops from oogonia, cells in the ovarian cortex derived from primordial germ cells in about 20 mitoses. Each oogonium is the central cell in the developing follicle.

About third In the first month of intrauterine development, the ovogons of the embryo begin to form primary oocytes, most of which enter the prophase of the first division of meiosis. The process of oogenesis is not synchronized, and both its early and final stages coexist in the fetal ovaries. At the time of the girl's birth, there are several million oocytes, but they are mostly degraded.

Ripen and ovulate eventually only about 400 eggs. Primary oocytes practically complete the prophase of the first division of meiosis by the time of birth, and those that do not undergo degeneration remain in this phase for quite a long time, until ovulation during the menstrual cycle.

With the onset of sexual maturity individual follicles about once a month begin to grow, mature and ovulate. Before ovulation, the oocyte quickly completes the division of meiosis I in such a way that one descendant cell becomes a secondary oocyte (or egg) containing almost the entire cytoplasm with organelles, and the second turns into the first directional (polar) body.

The second division begins quickly meiosis, during ovulation, it reaches the metaphase stage, where the division process stops, ending in the event of fertilization.

Fertilization in humans

Fertilization of the egg usually occurs in the fallopian tubes within about a day after ovulation. Although there may be many sperm around the egg, the entry of the first sperm into the egg sets off a chain of biochemical events that prevent the entry of other sperm.

Behind fertilization This is followed by the completion of the second division of meiosis with the formation of the second polar body. The chromosomes of a fertilized egg and sperm form pronuclei surrounded by a nuclear membrane. Shortly after fertilization, the chromosomes of the zygote double and divide by mitosis, forming two diploid daughter cells. This is the first mitosis in a series of cleavages that initiates the development of the embryo.

While development starts with education zygotes(conception), in clinical medicine, the onset and duration of pregnancy is usually calculated from the start of the last menstrual cycle, approximately 14 days before conception.