Male and female sex cells have. Features of the structure and movement of the sperm. The concept of parthenogenesis
The female and male reproductive cells, called "gametes" from the Greek "marriage", have half the genetic set and are responsible for the reproduction of organisms, the fusion of which forms a zygote, a diploid cell from which the cells of a new organism come. A person has a set of 23 chromosomes, 22 of which are called autosomes and one is a sex chromosome. This sex chromosome is designated X in females and either X or Y in males.
male reproductive cells
Spermatozoa, male sex cells, are highly mobile and microscopic in size. Their structure is determined by the head, which carries information about the man, the neck and tail, which is responsible for movement. Perhaps the most important part of the spermatozoon, the head, is filled with condensed chromatin. On average, the size of spermatozoa that are constantly produced in the testicles is 50–70 microns, and the average weight of one testicle of an adult is from 20 to 30 g. Interestingly, with a length of 60 microns, only 5 microns are allocated to the lobe of the head.
The testicles are located in the scrotum, which is a skin-muscular formation and consisting of a large number of seminiferous tubules. Among these tubules are interstitial cells responsible for the synthesis of sex hormones. Spermatozoa are formed in the seminiferous tubules and then pass through the large canal, through the epididymis, the vas deferens, after which they are excreted through the abdominal cavity into the urethra. As a result, the completion of this path is the penis, which is the external male genital organ.
An erection is the process of filling with blood the spongy tissue located inside the male genital organ. During the eruption of sperm, called ejaculation, spermatozoa end up in the female genital tract. can occur if at this moment there is a mature egg. During each ejaculation, up to 300 million sperm cells are normally released, which is approximately 1-6 ml of sperm, while the speed of sperm movement is equal to 3.5 mm per minute.
Nutrition and activation of the movement function of spermatozoa is provided by the secret of paired gonads. On average, sperm activity lasts about 48 hours in the cervix and about 2.5 hours inside the vagina.
female reproductive cells
Female sex cells begin to actively develop at the age of about 12 years, but for each woman this figure is individual. In most cases, one germ cell, called an egg, matures monthly, however, exceptions to this rule are also known. I must say that the egg is deprived of the ability to move independently. It carries a fairly large amount of information, including hair color, eyes, height, etc.
The size of the egg is usually from 100 to 200 microns and consists of a rounded nucleus and cytoplasm. The maturation process begins in the ovaries every 24 to 28 days, which is the woman's monthly cycle. An ovocyte of the 1st order, surrounded by a membrane and a crown of follicular cells, up to 4 thousand, leaves the ovary at the time and enters the fallopian tube. Moving along it, it finally matures, forming an already full-fledged egg, the so-called ovocyte of the 2nd order. In total, the nucleus of the egg contains 23 chromosomes, one of which is the sex X chromosome.
If the egg is not fertilized within 12-24 hours after ovulation, it dies.
Hello, Doctor! My name is Anastasia. I was interested in the question: what is the name of the male germ cell? I've heard the term gamete, but I think it's also used for female cells.
Expert Answer
Hello Anastasia! The term "gamete" that you used is correct, only it refers to germ cells in general, in men and women, as well as in animals. A gamete is a cell that has a set of chromosomes and is involved in reproduction. As for the name of the male reproductive cell, the answer is obvious. Sex cells are cells whose combination gives rise to a new organism. Probably, after this sentence, you yourself guessed that in men it is a spermatozoon. and in women, the egg.
Many mistakenly say that the male germ cell is testosterone. It should be noted that testosterone is a male sex hormone responsible for the development of genital organs and secondary sexual characteristics (facial hair, for example). And although it is considered a male hormone, some of it is also produced in women. This is a normal and even necessary phenomenon if the testosterone in the body of a woman does not exceed the norm. Typically, men have more than 10 times more testosterone in their blood than women. However, if the male sex hormone is present in women, then the germ cells, spermatozoa, are only in men. Therefore, it is so important not to confuse the name of male germ cells with hormones.
In the process of fertilization, the sex cells of the paternal and maternal organism participate. Just as the physiology of men and women as a whole differs, the structure of male germ cells and female gametes is not the same. The name of male germ cells - spermatozoa - combines two Greek roots meaning "seed" and "life" and explains their function: without their participation, reproduction is impossible. The structural features of male germ cells are explained by their role in the process of fertilization.
The goal of each spermatozoon is to be the first to reach the egg (female germ cell) and break through its membrane inside. Therefore, each spermatozoon is equipped with a means for rapid movement - a tail, thanks to the vibrating movements of which the male germ cells move very quickly. in this it is completely opposite - they do not have the ability to move and overcome only 10 cm of the way along the oviduct to the place of meeting with the spermatozoon.
The structure of the male reproductive cell - sperm
The male germ cell resembles a tadpole in appearance: each spermatozoon consists of a head, tail and neck. The function of the tail is clear - it provides the ability to move. The head is a kind of container in which each spermatozoon carries the most valuable cargo - genetic information packed into chromosomes.
Ordinary cells of the human body have 46 pairs of chromosomes, and germ cells (both male and female) carry only half the set of chromosomes. Of the 23 pairs of chromosomes in a sperm cell, there is one pair of special sex chromosomes that will ultimately determine what gender the baby will be born to. Sex chromosomes can be of the X or Y type, if a spermatozoon carrying the X chromosome was involved in the process of fertilization, then a girl will be born as a result, a boy will be born on the Y chromosome. The spermatozoon and the egg, when combined, form a complete set of chromosomes, while the Y chromosome can contain only the spermatozoon.
The structure of male germ cells is such that in the head of the spermatozoon, in its front part, there is an acrosome, which provides its “penetrating ability”. The enzymes that this cell organelle secretes allow the spermatozoon to penetrate the dense membrane of the egg.
The neck of the male germ cell has a complex "stuffing". It contains organelles (structural elements) of the cell, which are responsible for its viability and activity. Protoplasm is also located here - it is she who will ensure the possibility of cell division, which is formed in the process of fertilization.
When fertilization occurs, the nuclei of the germ cells unite and a zygote is formed, giving rise to a new human life. , which leads to the impossibility of fertilization in a natural way, requires specialized treatment. In case the result remains negative, future parents turn to.
Progenesis - formation, development and maturation of male and female germ cells.
sex cells- gametes, unlike somatic, have a haploid set of chromosomes. All gamete chromosomes, with the exception of one sex chromosome, are called autosomes, sexual gonosome.
male reproductive cells have X or Y sex chromosomes.
female reproductive cells only H.
Differentiated gametes have a low level of metabolism and are not capable of reproduction.
male reproductive cells
male reproductive cells - spermatozoa (sperms) develop into very few thousand millions. They are small in size (in humans, about 70 microns), have the ability to actively move at a speed of 30-50 microns / sec. The spermatozoon has a flagellar shape.
¨The process of formation and maturation of spermatozoa - spermatogenesis.
The structure of the sperm
The spermatozoon consists of two parts: 1) 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 in the nucleus of 22 autosomes and 1 sex chromosome (gonosomes). Depending on which sex chromosome the X or Y sperm nucleus has, they are divided into two types:
1) androspermia - contain Y - chromosomes,
2) gynecospermia - contain X - chromosomes.
¨The kernel is characterized by a high content nucleoprotamines and nucleohistones. The anterior part of the nucleus is covered with a flat sac that forms case sperm. On the anterior pole of the cap is located acrosome(from Greek acros - top; soma - body). Both formations (sheath and acrosome) are derivatives of the Golgi complex.
acrosome contains a set of enzymes, among which an important place belongs to hyaluronidase and proteases(trypsin), which are able to dissolve the membranes of the egg.
The head is covered with a cell membrane on the outside.
Tail(feagellum) sperm consists of:
a) the connecting part (neck) formed by two centioles - proximal and distal, the axial thread (axoneme) originates from the distal;
b) the intermediate part formed by two central and 9 pairs of peripheral microtubules surrounded by mitochondria in a spiral (mitochondrial sheath);
c) the main part, which in structure resembles an eyelash. Surrounded by a thin fibrillar sheath;
d) the terminal part, which contains single contractile filaments.
Like the head, the tail is covered with a cell membrane.
Functions of spermatozoa
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 stimuli - 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 slightly alkaline environment.
female reproductive cells
female reproductive cells - eggs (oocytes). Formed in the ovaries. Quantity - for the entire life of a person and a mammal, several hundred mature. Amphibians and fish can have several tens of thousands.
Egg has a spherical shape, sizes vary from a few microns to a few cm. Characteristic of the eggs is a large volume of cytoplasm and the presence of yolk. In addition, the eggs do not have the ability to move independently.
These cells are significantly different in men and women. In men, germ cells or spermatozoa have tail-like outgrowths () and are relatively mobile. The 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 those 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 sex cells are very different from each other in size and shape. Male spermatozoa resemble long, moving 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 includes enzymes that help the sperm cell to penetrate the outer shell of the egg. located in the head of the spermatozoon. The DNA in the nucleus is densely packed and the cell does not contain much. The middle part includes several mitochondria that provide energy for. The tail section consists of a long outgrowth called the flagellum, which aids in cellular locomotion.
The female eggs are one of the largest cells in the body and are round in shape. They are produced in the female ovaries and consist of a nucleus, a large cytoplasmic region, a zona pellucida, and a radiant crown. The zona pellucida is the membrane covering that surrounds the oocytes. It binds sperm cells and helps in fertilization. The radiant crown is the outer protective layer of follicular cells surrounding the zona pellucida.
The formation of germ cells
Human germ cells are produced through a two-step process of cell division called. Through a series of successive 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. Prior to meiosis, chromosomes replicate and exist as . At the end of meiosis I, two are formed. The sister chromatids of each chromosome are still connected in daughter cells. At the end of meiosis II, sister chromatids and four daughter cells are produced. Each cell contains half of the chromosomes from the parent cell.
Meiosis is similar to the process of non-sex cell division 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 have two sets of chromosomes. Humans have 23 pairs or 46 chromosomes. When germ cells combine during fertilization, the haploid cells become a diploid cell.
The production of spermatozoa is known as spermatogenesis. This process takes place continuously inside the male testicles. Hundreds of millions of sperm must be released for this to happen. The vast majority of spermatozoa do not reach the egg. During oogenesis, or egg development, the daughter cells divide unevenly during meiosis. This asymmetric cytokinesis results in the formation of one large egg (oocyte) and smaller cells called polar bodies, which degrade and fail to fertilize. 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 spermatozoa 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. The spermatozoon 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.