These cells differ significantly between men and women. In men, germ cells or sperm have tail-like projections () and are relatively mobile. Female reproductive cells, called eggs, are immobile and much larger than male gametes. When these cells fuse in a process called fertilization, the resulting cell (zygote) contains a mixture of what is inherited from the father and mother. Human sex organs are produced by the organs of the reproductive system - the gonads. produce sex hormones necessary for the growth and development of primary and secondary reproductive organs and structures.

The structure of human germ cells

Male and female reproductive cells differ greatly in size and shape. Male sperm resemble long, mobile projectiles. These are small cells that consist of a head, middle and tail parts. The head contains a cap-like covering called an acrosome. The acrosome contains enzymes that help the sperm cell penetrate the outer membrane of the egg. located in the head of the sperm. The DNA in the nucleus is tightly packed and the cell does not contain much. The middle part includes several mitochondria that provide energy for. The tail consists of a long projection called a flagellum, which aids in cellular locomotion.

A woman's eggs are one of the largest cells in the body and have a round shape. They are produced in the female ovaries and consist of a nucleus, a large cytoplasmic region, a zona pellucida and a corona radiata. The zona pellucida is a membrane covering that surrounds the eggs. It binds sperm cells and helps in fertilization. The corona radiata is the outer protective layer of follicular cells surrounding the zona pellucida.

Formation of germ cells

Human germ cells are produced through a two-step process of cell division called. Through a series of sequential events, the replicated genetic material in the parent cell is distributed among the four daughter cells. Since these cells have half the number of the parent cell, they are . Human germ cells contain one set of 23 chromosomes.

There are two stages of meiosis: meiosis I and meiosis II. Before meiosis, chromosomes are replicated and exist in the form. At the end of meiosis I, two are formed. The sister chromatids of each chromosome in the daughter cells are still linked. At the end of meiosis II, sister chromatids and four daughter cells are formed. Each cell contains half the chromosomes of its parent cell.

Meiosis is similar to the process of division of non-reproductive cells known as mitosis. produces two daughter cells that are genetically identical and contain the same number of chromosomes as the parent cell. These cells are diploid because they contain two sets of chromosomes. Humans include 23 pairs or 46 chromosomes. When germ cells unite during fertilization, the haploid cell becomes a diploid cell.

The production of sperm is known as spermatogenesis. This process occurs continuously inside the male testicles. Hundreds of millions of sperm must be released for this to happen. The vast majority of sperm do not reach the egg. During oogenesis, or egg development, daughter cells divide unevenly in meiosis. This asymmetric cytokinesis results in the formation of one large egg (oocyte) and smaller cells called polar bodies, which degrade and are not fertilized. After meiosis I, the egg is called a secondary oocyte. The secondary oocyte will complete the second stage of meiosis if the fertilization process begins. Once meiosis II is completed, the cell becomes an egg and can fuse with a sperm cell. When fertilization is complete, the combined sperm and egg become a zygote.

Sex chromosomes

Male sperm in humans and other mammals are heterogametic and contain one of two types of sex chromosomes: X or Y. However, female eggs contain only the X chromosome and are therefore homogametic. Sperm of an individual. If a sperm cell containing an X chromosome fertilizes an egg, the resulting zygote will be XX or female. If the sperm cell contains a Y chromosome, then the resulting zygote will be XY or male.

Helpful information

Sex cells are specialized cells through which the process of sexual reproduction occurs. Female and male germ cells differ from somatic cells (all other cells of the body): they contain half the set of chromosomes. During the process of fertilization, the number of chromosomes is restored. Features of the formation and structure of germ cells ensure their functional specificity.

Female and male reproductive cells: structure

Gametes (sex cells) are characterized by a haploid (single) set of chromosomes. That is, human germ cells contain 23 chromosomes: 22 autosomal and 1 sex chromosome. The types of germ cells (male or female) differ precisely in the sex chromosome: the female germ cell (gamete) contains an X chromosome, the male one contains an X or Y chromosome. During the process of fertilization, the sex of the unborn child depends on the combination of sex chromosomes: XX - female, XY - male.

The structure of germ cells is characterized by incredible structural organization and purposefulness. Male germ cells (spermatozoa), which must be highly mobile in the female reproductive tract, are small cells that lack cytoplasm and consist of a head containing a nucleus with genetic material, and a tail - an organ of movement. Of the cellular elements, they contain only mitochondria, which provide energy for movement, an acrosomal vacuole containing proteolytic enzymes for dissolving the egg membranes, and a proximal centriole. The total length of the sperm is approximately 60 microns, 55 of which are in the tail.

The acrosomal vacuole of the male germ cell contains the following enzymes:

When sperm emerge from the testicle, they are still morphologically immature; they acquire the ability to fertilize and motility in the vas deferens. In addition, male germ cells contain a number of specific antigens, the inactivation of which also occurs in the vas deferens.

The female reproductive cell (ovum) is a large, immobile cell. It contains a large supply of trophic substances that are necessary for the early development of the embryo. In addition, for the formation of blastomeres (the first generations of embryonic cells), the egg contains a sufficient number of cytoplasmic structures. The human egg is oligolecial, meaning it does not contain much yolk.

A feature of the germ cells of higher placentals, including humans, is that a mature germ cell does not exist in isolation, it is always in close contact with the surrounding somatic cells that create the membrane. The complex of the female reproductive cell with somatic membranes is called the ovarian follicle, or ovosomatic histion.

Formation of germ cells. Fertilization

The process of development of germ cells is very complex and multi-stage. Primary gametes (sex cells) in the embryonic period are laid far from the gonads, and then during development, with a current of moving fluids, they are transferred to the gonad area. Already in the gonads their further formation occurs. During further embryonic development, surrounding cells and tissues do not influence the process of direct formation of gametes, and no acquired human characteristics are inherited.

Formation of female germ cells (ovogenesis)

The formation and maturation of female germ cells occurs in follicles located in the ovarian tissue. Primordial follicles move into the ovarian tissue during embryogenesis. A distinctive feature is that female reproductive cells are formed in large numbers in the ovarian tissue; by the time of birth, their number is about two million. A larger number of cells are resorbed, and by the time of puberty there are approximately 300 thousand oocytes. Female germ cells are formed only in the embryonic period, and before puberty only their final structural formation occurs. That is why absolutely all the negative factors that a woman encounters during her life are reflected in the state of her gametes. The influence of alcohol on reproductive cells at any period of life has an extremely negative effect, and its consequences persist forever. New germ cells in women are not formed during life, only their maturation occurs.

During reproductive age, several follicles mature each menstrual cycle. By the time of ovulation (the period when a mature reproductive cell emerges from the follicle), there is a finally formed dominant follicle. It increases in size, and by the time of ovulation, the cavity with the follicle in the ovary, filled with liquid (graphic vesicle), reaches 2 cm in diameter.

When the follicle matures, the cells surrounding it produce hormones - estrogens. Just before ovulation, their concentration increases significantly, resulting in the release of luteinizing hormone. In this case, the follicle ruptures, and the egg, ready for fertilization, is released into the abdominal cavity, from where it then enters the fallopian tubes.

Development of male germ cells (spermatohegesis)

The male reproductive cell is formed in a completely different way. At the time of birth, the gonads contain rudimentary, unformed male reproductive cells. The process of their final formation begins with puberty. A distinctive feature of the formation of male germ cells is that each cell is formed in approximately 75 days, and not from the moment of birth, like female cells.

The process of sperm formation occurs in the convoluted seminiferous tubules. Spermatogonia (the precursors of mature male germ cells) are located on the basement membrane, where they undergo stages of mitotic division. As a result of mitosis, two types of cells are formed. Spermatogonia A retain the ability to further divide by mitosis and give rise to the same cells, while spermatogonia B are evacuated from the membrane and are able to divide only by meiosis. It is after the first meiosis that cells with a single set of chromosomes are formed, which in 75 days finally mature and are ready for fertilization of the egg.

Sex cells: fertilization

The fusion of two sex cells is called fertilization. The fertilization process ends with the formation of a zygote. The sex cells of a woman and a man have a haploid (single) set of chromosomes, and when they merge, the diploid (double) set of chromosomes characteristic of the human body is restored. In this case, the unique genetic information of the maternal and paternal organisms is combined. The formed zygote has the property of typotolerance - it is capable of giving rise to a variety of cells and tissues of the future organism.

The process of fertilization of the egg occurs in the fallopian tube. The sperm, with the help of acrosomal enzymes, destroys the membranes of the egg (corona radiata, zona pellucida), and the process of fusion of its plasma membrane with the membrane of the egg occurs. After this, the head of the sperm penetrates into the cytoplasm of the egg. When the genetic material of the sperm has penetrated the egg, the fertilization process ends, resulting in the formation of a unique new single-cell system, giving rise to a new organism.

When a sperm penetrates the egg, the enzymes released from it modify the membrane in such a way that other sperm can no longer destroy it and penetrate inside the egg. This process takes only a few minutes. Only one sperm takes part in the fertilization process. In extremely rare cases, when two sperm penetrate the egg, a triploid embryo is formed, but it is not viable and dies within a few days.

After fertilization, the zygote stage lasts about 30 hours. Next, crushing begins. This is the process of mitotic division of the zygote, as a result of which the number of its cells increases, but the overall size remains the same. At this stage, the cells are called blastomeres. After 3 days, when all the formed cells are identical in determination and size, the stage of their differentiation begins. On day 5 of development, the embryo is a blastocyst, which consists of approximately 200 cells. A blastocyst is a hollow ball of cells (trophoblast cells) containing embryoblast cells. If there are two embryoblasts in a blastocyst, identical twins are formed from such an embryo.

During this entire period, the embryo migrates through the fallopian tube into the uterine cavity. This process occurs under the influence of the movements of the villi on the surface of the fallopian tubes. When the embryo reaches the uterine cavity, implantation occurs. In this case, the blastocyst loses the zona pellucida (this process is called hatching) and, with the help of special processes, sinks into the endometrium. This process is regulated by close chemical and physical connections between the endometrium and blastocyst. Trophoblast cells produce human chorionic gonadotropin, which stimulates the production of progesterone by the cells of the corpus luteum, as a result of which menstruation does not occur.

It is precisely this complexly organized process of development of germ cells that ensures the extraordinary phenomenon in which a new, unique organism is formed from two small cells with a set of unique genetic information - a new person.

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Male reproductive cells are called sperm. They are formed in the convoluted tubules of the testicles from cells called spermatogonia. The function of the sperm is to fertilize the female reproductive cell (egg)

The length of the sperm is about 0.05-0.07 mm, and it can only be seen through a microscope. The sperm consists of a head, body and tail (flagellum). Thanks to the presence of a flagellum, sperm are able to move independently. During movement, they usually rotate around their axis. In the head of the sperm there are chromosomes that contain genetic information, and acrosomes - the chemical storage of the male reproductive cell (enzymes that help penetrate the egg). The body of the sperm contains an energy component that ensures contractions of the flagellum.

The semen ejaculated during sexual intercourse contains approximately 300,000,000 to 500,000,000 sperm. However, only 1 sperm is enough for fertilization to occur - the process of transferring genetic material from the father's body to the egg.

A - Head, neck, tail
B - Mitochondria, microtubules, plasma membrane

The fertilizing sperm is always responsible for the sex of the embryo. All sperm have a set of 23 chromosomes, which are located in the head. Each sperm carries a Y or X chromosome, which, when the egg is fertilized, determines the sex of the unborn child. If the egg is fertilized by a sperm that carries a Y chromosome, then the sex of the unborn child will be male, and if the sperm has an X chromosome, it will be female. Since eggs contain only X chromosomes, the sex of the unborn child depends solely on the man.

The concept of “sperm” must be distinguished from the concept of “sperm”. Sperm (seminal fluid), produced by the male gonads, consists of sperm, seminal vesicle fluid, prostate secretion and a small number of epithelial cells of the urethra. Sperm make up on average only 3% of seminal fluid.

Sperm development cycle

The process of sperm development is called spermatogenesis. The duration of sperm development from the moment of formation to its full maturation is 2-2.5 months. That is why, in order to conceive a healthy child, it is recommended to abstain from taking alcohol, drugs and toxic substances during this time period.

Initially, through numerous divisions in the testicular tubules, the male reproductive cell, called at this stage a spermatid, receives a certain chromosome set. Motility is very important for sperm, which is necessary for them to reach the egg and penetrate inside. They are endowed with this property when passing through the epididymis. Sperm develop a tail, a motor apparatus, a head and a cap (acrosome), in which enzymes are concentrated to dissolve the egg membranes along the way. This is how full-fledged sperm are formed.

Next, they are located in the epididymis until it becomes possible to fertilize the egg. If sperm “stay” too long, they will grow old and will not be able to fulfill their sacred mission. The most optimal sperm composition for fertilization occurs when sexual activity occurs at intervals of two days.

The sperm begins to move at the moment of ejaculation (ejaculation). The egg is still a long way off, and the path passes through the uterus and the main part of the fallopian tube. After capacitation (ripening and preparing the sperm for fertilization in the female genital tract), it sheds the acrosomal cap to identify the egg and dissolve its membranes for entry. Having pierced the shell of the egg, the sperm inserts the head and body inside and loses the tail. If the cap is not shed, then fertilization does not occur.

For fertilization, many sperm gather around the egg, but after one of them penetrates the membranes, the egg is blocked. At first, a block appears due to a change in electrical potential, and then due to chemical and structural changes. A new membrane forms around the egg, preventing it from being fertilized by another sperm.

The nuclei of the sperm and egg, now called the male and female pronucleus, come together, merge and begin to actively divide. A zygote is formed - a fertilized egg, the first cell of a new organism. A week later, this zygote enters the uterus and in its cavity is fixed to the wall: pregnancy occurs.

To move 1 cm, the sperm must wag its tail at least 800 times

The formation of sperm in the rank begins after he reaches puberty and then continues until death. It has been established that even after eighty years, most men have viable sperm in their semen. Thus, Indian farmer Ramjit Raghava entered the Guinness Book of Records by becoming a father for the first time at the age of ninety-four.

Male reproductive cells (sperm)

When studying male germ cells, one should understand the structure of flagellated (scourge-shaped) spermatozoa, which are the predominant form of spermatozoa, and for comparison, become familiar with the morphology of flagellated (non-scourge-shaped) spermatozoa. It is necessary to pay attention to such physiological characteristics as their mobility, life expectancy, dependence of activity on the environment, etc.

Male germ cells differ significantly in structure and physiological properties from female germ cells. Sperm are much smaller than eggs. The male reproductive cells of a crocodile are 20 microns long, a sparrow is 200 microns, a guinea pig is 100 microns, a bull is 65 microns, and in humans, on average, 50 microns. Sperm are more numerous than eggs. Their number in animals is measured in millions. For example, in a person, 1 cm 3 of sperm contains 60 million sperm. Mature sperm are actively motile cells.

Among the male germ cells of various groups of animals, two significantly different types of sperm are distinguished: flagellated (flagellate) and flagellate (non-flagellate). Flagellated spermatozoa are the predominant form (Fig. 4).

Fig.4. Shapes of human and animal sperm. 1 - person; 2 - tritone; 3 - crayfish; 4 - guinea pig; 5 - pigs; 6 - bull; 7 - rooster; 8 - branched cancer; 9 - tenth cancer; 10 - horse roundworm; 11 - pinworms (according to Golichenkov).

Flagellar spermatozoa, even in animals of very distant species, are built according to the same pattern, which is probably explained by the similarity of their functional purpose throughout the animal world.

A flagellar spermatozoon has four sections: head, neck, middle part, and tail (flagellum). All parts of the sperm are covered on the outside by a common plasma membrane.

The head of the sperm has a different shape in different classes of animals: in newts the head has the shape of a crochet hook, in passerine birds it is corkscrew-shaped, in mammals it is oval in front and pear-shaped on the side. Most of the sperm head is occupied by the nucleus. In the cytoplasm of the anterior part of the head there is an acrosomal apparatus, which plays an important role in the dissolution of the egg membranes. Spermolysins, substances related to proteolytic enzymes, are concentrated in the acrosome (Fig. 5).

Fig.5. Diagram of the structure of mammalian sperm, which depicts structures identified using an electron microscope and indicates the functions they perform (according to Aleksandrovskaya)

The neck is the short, narrower part of the sperm. There are two centrioles in the neck: proximal (anterior), adjacent to the nucleus, and distal (posterior), which connects to the axial filament of the tail.

The middle part of the sperm consists of an axial filament and the surrounding cytoplasm. The cytoplasm contains a large number of mitochondria, which are located one after another in the form of a spirally twisted thread. Mitochondria generate the energy necessary for the movement of the male reproductive cell.

The tail section (flagellum) of the sperm consists of an axial filament, which is covered with a thin layer of cytoplasm. The axial filament of the flagellum is represented by 2 central and 9 peripheral pairs of fibrils, which stretch without significant changes along the entire length of the sperm tail - from the neck almost to the tip (Fig. 6).

Fig.6. Electron microscopic structure of sperm: 1 - head; 2 - neck; 3 - axial thread; 4 - mitochondria; 5 - plasmalemma. (according to Aleksandrovskaya).

Thus, the general organization of sperm and its sections are adapted to perform specific functions inherent in this cell. Such functions are: a) ensuring a meeting with the female reproductive cell; b) encouraging the egg to develop; c) transfer of paternal hereditary material into it.

In some animals, sperm do not have flagella and are called flagellaless (non-flagellate). These sperm have a wide variety of shapes: round, thread-like, biconcave, sometimes of a very unusual type (Fig. 6).

The viability and mobility of sperm in water is limited in time. In sea water they lose mobility after a few hours, and in fresh water, as a rule, after a few minutes. In animals with internal fertilization, male reproductive cells retain their viability somewhat longer: in a pig - 22 - 30 hours, in a sheep - 30 - 36 hours, in cattle - 25 - 30 hours, in the female reproductive tract the life expectancy of sperm varies from 2 to 4 days.

In some animal species, sperm remain viable in the female genital tract for a long time. For example, in some bats, insemination occurs in the fall, but throughout the animals' winter hibernation, the sperm remain dormant. Fertilization occurs only the following spring. In chickens, sperm are stored for 3 weeks. In many insects, sperm are stored for a long time. For example, in bees, male reproductive cells are preserved for several years.

There have been and still are many misconceptions regarding sperm motility and their fertilizing ability. It was believed that the fertilizing ability of the sperm is maintained until it loses the ability to move. It is now known that motility will persist much longer than the ability to fertilize. Thus, rabbit sperm lose their ability to fertilize after a 30-hour stay in the female’s genital tract, while they can maintain motility for more than two days. Human sperm retain the ability to fertilize for 1 - 2 days, and they retain motility for up to 4 days.

Progenesis - formation, development and maturation of male and female reproductive cells.

Sex cells- gametes, unlike somatic ones, have a haploid set of chromosomes. All chromosomes of gametes, with the exception of one sex chromosome, are called autosomes, sexual gonosoma.

Male reproductive cells have sex chromosomes X or Y.

Female reproductive cells only X.

Differentiated gametes have a low level of metabolism and are not capable of reproduction.

Male reproductive cells

Male reproductive cells - spermatozoa (sperm cells) develop into several thousand millions. They are small in size (about 70 microns in humans) and have the ability to actively move at a speed of 30-50 microns/sec. The sperm has a flagellated shape.

¨The process of formation and maturation of sperm - spermatogenesis.

Structure of sperm

The sperm consists of two parts: 1) the head; 2) tail.

Head The spermatozoon (caput spermatozoidi) contains a small dense nucleus with a haploid set of chromosomes. Humans are characterized by the presence of 22 autosomes and 1 sex chromosome (gonosome) in the nucleus. Depending on which sex chromosome the sperm nucleus has, X or Y, they are divided into two types:

1) androspermia - contain Y chromosomes,

2) gynecospermia - contain X chromosomes.

¨The core is characterized by a high content nucleoprotamines And nucleohistones. The anterior part of the nucleus is covered with a flat sac, which forms cover sperm. On the anterior pole of the cap there is acrosome(from Greek acros - top; soma - body). Both formations (cap and acrosome) are derivatives of the Golgi complex.

Acrosome contains a set of enzymes, among which an important place belongs hyaluronidase And proteases(trypsin), which are capable of dissolving the membranes of the egg.

The outside of the head is covered with a cell membrane.

Tail(feagellum) sperm consists of:

a) the connecting part (neck) formed by two centioles - proximal and distal, from the distal one the axial thread (axoneme) originates;

b) the intermediate part formed by two central and 9 pairs of peripheral microtubules surrounded in a spiral by mitochondria (mitochondrial sheath);

c) the main part, which in structure resembles an eyelash. Surrounded by a fine fibrillar sheath;

d) the terminal part, which contains single contractile filaments.

Just like the head, the tail is covered with a cell membrane.

Functions of sperm

1. Fertilization of the egg. With the help of the tail, the sperm is able to move in a certain direction, which is determined by specific substances secreted by the egg - gynogamons.

2. React to chemical irritants - chemotaxis.

3. Can move against the flow of liquid - rheotaxis.

4. Retain the ability to fertilize under optimal conditions for 36-88 hours.

5. Optimal conditions are a slightly alkaline environment.

Female reproductive cells

Female reproductive cells - eggs (ovocytes). Formed in the ovaries. Quantity - several hundred mature over the lifetime of a human or a mammal. Amphibians and fish can have several tens of thousands.

Egg has a spherical shape, sizes range from several microns to several cm. Characteristic of eggs is a large volume of cytoplasm and the presence of a yolk. In addition, eggs do not have the ability to move independently.