HUMAN REPRODUCTION
a physiological function necessary for the preservation of humans as a biological species. The process of reproduction in humans begins with conception (fertilization), i.e. from the moment of penetration of the male reproductive cell (sperm) into the female reproductive cell (egg, or ovum). The fusion of the nuclei of these two cells is the beginning of the formation of a new individual. A human embryo develops in a woman's uterus during pregnancy, which lasts 265-270 days. At the end of this period, the uterus begins to spontaneously contract rhythmically, contractions become stronger and more frequent; the amniotic sac (fetal sac) ruptures and, finally, the mature fetus is “expelled” through the vagina - a child is born. Soon the placenta (afterbirth) also leaves. The entire process, starting with uterine contractions and ending with the expulsion of the fetus and placenta, is called childbirth.
See also
PREGNANCY AND CHILDREN;
HUMAN EMBRYOLOGY. In more than 98% of cases, during conception, only one egg is fertilized, which causes the development of one fetus. Twins (twins) develop in 1.5% of cases. About one in 7,500 pregnancies result in triplets.
See also MULTIPLE BIRTH. Only biologically mature individuals have the ability to reproduce. During puberty (puberty), a physiological restructuring of the body occurs, manifested in physical and chemical changes that mark the onset of biological maturity. During this period, the girl’s fat deposits around the pelvis and hips increase, the mammary glands grow and become round, and hair growth develops on the external genitalia and armpits. Soon after the appearance of these so-called secondary sexual characteristics, the menstrual cycle is established. Boys' physique changes noticeably during puberty; the amount of fat on the stomach and hips decreases, the shoulders become wider, the timbre of the voice decreases, and hair appears on the body and face. Spermatogenesis (production of sperm) in boys begins somewhat later than menstruation in girls.
REPRODUCTIVE SYSTEM OF WOMEN
Reproductive organs. The female internal reproductive organs include the ovaries, fallopian tubes, uterus, and vagina.

FEMALE REPRODUCTIVE ORGANS IN SECTION (side view): ovaries, fallopian tubes, uterus and vagina. All of them are held in place by ligaments and are located in the cavity formed by the pelvic bones. The ovaries have two functions: they produce eggs and secrete female sex hormones that regulate the menstrual cycle and maintain female sexual characteristics. The function of the fallopian tubes is to carry the egg from the ovary to the uterus; in addition, this is where fertilization occurs. The muscular hollow organ of the uterus serves as a “cradle” in which the fetus develops. The fertilized egg is implanted into the wall of the uterus, which stretches as the fetus grows and develops. The lower part of the uterus is its cervix. It protrudes into the vagina, which at its end (vestibule) opens outwards, providing communication between the female genital organs and the external environment. Pregnancy ends with spontaneous rhythmic contractions of the uterus and expulsion of the fetus through the vagina.

The ovaries - two glandular organs weighing 2-3.5 g each - are located behind the uterus on both sides. In a newborn girl, each ovary contains an estimated 700,000 immature eggs. All of them are enclosed in small round transparent sacs - follicles. The latter ripen one by one, increasing in size. The mature follicle, also called the Graafian vesicle, ruptures, releasing the egg. This process is called ovulation. The egg then enters the fallopian tube. Typically, during the entire reproductive period of life, approximately 400 eggs capable of fertilization are released from the ovaries. Ovulation occurs monthly (about halfway through menstrual cycle). The burst follicle sinks into the thickness of the ovary, is overgrown with scar connective tissue and turns into a temporary endocrine gland - the so-called. corpus luteum, which produces the hormone progesterone. The fallopian tubes, like the ovaries, are paired formations. Each of them extends from the ovary and connects to the uterus (from two different sides). The length of the pipes is approximately 8 cm; they bend slightly. The lumen of the tubes passes into the uterine cavity. The walls of the tubes contain inner and outer layers of smooth muscle fibers, which constantly contract rhythmically, which ensures the wave-like movements of the tubes. The inside walls of the tubes are lined with a thin membrane containing ciliated (ciliated) cells. Once the egg enters the tube, these cells, along with muscle contractions of the walls, ensure its movement into the uterine cavity. The uterus is a hollow muscular organ located in the pelvic abdominal cavity. Its dimensions are approximately 8-5-2.5 cm. Pipes enter into it from above, and from below its cavity communicates with the vagina. The main part of the uterus is called the body. The non-pregnant uterus has only a slit-like cavity. The lower part of the uterus, the cervix, is about 2.5 cm long, protruding into the vagina, into which a cavity called the cervical canal opens. When a fertilized egg enters the uterus, it is immersed in its wall, where it develops throughout pregnancy. The vagina is a hollow cylindrical formation 7-9 cm long. It is connected to the cervix along its circumference and extends to the external genitalia. Its main functions are the outflow of menstrual blood, the reception of the male genital organ and male seed during copulation, and the provision of passage for the newborn fetus. In virgins, the external entrance to the vagina is partially closed by a fold of tissue in the shape of a crescent, hymen. This fold usually leaves enough space for the flow of menstrual blood; After the first copulation, the vaginal opening widens.
Mammary glands. Full-fledged (mature) milk in women usually appears approximately 4-5 days after birth. When a baby suckles at the breast, an additional powerful reflex stimulus arises for the glands to produce milk (lactation).
See also MASTRY GLAND. The menstrual cycle is established soon after the onset of puberty under the influence of hormones produced by the endocrine glands. In the early stages of puberty, pituitary hormones initiate the activity of the ovaries, triggering a complex of processes occurring in female body from puberty to menopause, i.e. for approximately 35 years. The pituitary gland cyclically secretes three hormones that are involved in the process of reproduction. The first - follicle-stimulating hormone - determines the development and maturation of the follicle; the second - luteinizing hormone - stimulates the synthesis of sex hormones in the follicles and initiates ovulation; the third - prolactin - prepares the mammary glands for lactation. Under the influence of the first two hormones, the follicle grows, its cells divide, and a large fluid-filled cavity is formed in it, in which the oocyte is located (see also EMBRYOLOGY). The growth and activity of follicular cells is accompanied by the secretion of estrogens, or female sex hormones. These hormones can be found both in follicular fluid and in the blood. The term estrogen comes from the Greek oistros ("fury") and is used to refer to a group of compounds that can cause estrus ("estrus" in animals). Estrogens are present not only in the human body, but also in other mammals. Luteinizing hormone stimulates the follicle to rupture and release the egg. After this, the follicle cells undergo significant changes, and a new structure develops from them - the corpus luteum. Under the influence of luteinizing hormone, it, in turn, produces the hormone progesterone. Progesterone inhibits the secretory activity of the pituitary gland and changes the state of the mucous membrane (endometrium) of the uterus, preparing it to receive a fertilized egg, which must penetrate (implantate) into the wall of the uterus for subsequent development. As a result, the wall of the uterus thickens significantly, its mucous membrane, containing a lot of glycogen and rich in blood vessels, creates favorable conditions for the development of the embryo. The coordinated action of estrogens and progesterone ensures the formation of the environment necessary for the survival of the embryo and the maintenance of pregnancy. The pituitary gland stimulates ovarian activity approximately every four weeks (ovulatory cycle). If fertilization does not occur, most of the mucous membrane, along with the blood, is rejected and enters the vagina through the cervix. Such cyclically repeating spotting called menstruation. For most women, bleeding occurs approximately every 27-30 days and lasts 3-5 days. The entire cycle that ends with the shedding of the uterine lining is called the menstrual cycle. It is regularly repeated throughout the reproductive period of a woman’s life. The first periods after puberty may be irregular, and in many cases they are not preceded by ovulation. Menstrual cycles without ovulation, often found in young girls, are called anovulatory. Menstruation is not at all the release of “spoiled” blood. In fact, the discharge contains very small amounts of blood mixed with mucus and tissue from the lining of the uterus. The amount of blood lost during menstruation is different women varies, but on average does not exceed 5-8 tablespoons. Sometimes minor bleeding occurs in the middle of the cycle, which is often accompanied by mild abdominal pain, characteristic of ovulation. Such pains are called mittelschmerz (German: “middle pains”). Pain experienced during menstruation is called dysmenorrhea. Typically, dysmenorrhea occurs at the very beginning of menstruation and lasts 1-2 days.

MENSTRUAL CYCLE. The diagram shows the main morphological and physiological changes that form the menstrual cycle. They affect three organs: 1) the pituitary gland, an endocrine gland located at the base of the brain; the pituitary gland secretes hormones that regulate and coordinate the entire cycle; 2) ovaries, which produce eggs and secrete female sex hormones; 3) the uterus, a muscular organ whose mucous membrane (endometrium), abundantly supplied with blood, creates an environment for the development of a fertilized egg. If the egg remains unfertilized, the mucous membrane is rejected, which is the source of menstrual bleeding. All the processes and time intervals depicted in the diagram vary among different women and even among the same woman in different months, depending on her physical and psychological state. FSH (follicle stimulating hormone) is secreted by the anterior pituitary gland into the blood around the 5th day of the cycle. Under its influence, the follicle containing the egg matures in the ovary. Ovarian hormones, estrogens, stimulate the development of the spongy lining of the uterus, the endometrium. As the level of estrogen in the blood increases, the secretion of FSH by the pituitary gland decreases and, approximately on the 10th day of the cycle, the secretion of LH (luteinizing hormone) increases. Under the influence of LH, a fully mature follicle ruptures, releasing the egg. This process, called ovulation, usually occurs on the 14th day of the cycle. Soon after ovulation, the pituitary gland begins to actively secrete a third hormone, prolactin, which affects the condition of the mammary glands. In the ovaries, the opened follicle turns into a large corpus luteum, which almost immediately begins to produce large amounts of estrogen and then progesterone. Estrogens cause the growth of the endometrium, rich in blood vessels, and progesterone causes the development and secretory activity of the glands contained in the mucosa. An increase in the level of progesterone in the blood inhibits the production of LH and FSH. If fertilization does not occur, the corpus luteum undergoes reverse development and the secretion of progesterone decreases sharply. In the absence of sufficient progesterone, the endometrium is shed, which leads to the onset of menstruation. It is believed that the decrease in progesterone levels resolves the secretion of FSH by the pituitary gland and thereby initiates the next cycle.

Pregnancy. In most cases, the release of the egg from the follicle occurs approximately in the middle of the menstrual cycle, i.e. 10-15 days after the first day of the previous menstruation. Within 4 days, the egg moves through the fallopian tube. Conception, i.e. Fertilization of an egg by a sperm occurs in the upper part of the tube. This is where the development of the fertilized egg begins. Then it gradually descends through the tube into the uterine cavity, where it remains free for 3-4 days, and then penetrates the wall of the uterus, and from it the embryo and structures such as the placenta, umbilical cord, etc. develop. Pregnancy is accompanied by many physical and physiological changes in the body. Menstruation stops, the size and weight of the uterus sharply increase, and the mammary glands swell, preparing for lactation. During pregnancy, the volume of circulating blood exceeds the original by 50%, which significantly increases the work of the heart. In general, the pregnancy period is a difficult physical activity. Pregnancy ends with the expulsion of the fetus through the vagina. After childbirth, after about 6 weeks, the size of the uterus returns to its original size.
Menopause. The term "menopause" is made up of the Greek words meno ("monthly") and pausis ("cessation"). Thus, menopause means the cessation of menstruation. The entire period of decline of sexual functions, including menopause, is called menopause. Menstruation stops after surgical removal both ovaries, produced in some diseases. Exposure of the ovaries to ionizing radiation can also lead to cessation of their activity and menopause. About 90% of women stop menstruating between the ages of 45 and 50. This can happen abruptly or gradually over many months, when menstruation becomes irregular, the intervals between them increase, the bleeding periods themselves gradually shorten and the amount of blood lost decreases. Sometimes menopause occurs in women under 40 years of age. Equally rare are women with regular menstruation at 55 years of age. Any bleeding from the vagina that occurs after menopause requires immediate medical attention.
Symptoms of menopause. During the period of cessation of menstruation or immediately before it, many women develop a complex set of symptoms that together constitute the so-called. menopausal syndrome. It consists of various combinations of the following symptoms: “hot flashes” (sudden redness or a feeling of heat in the neck and head), headaches, dizziness, irritability, mental instability and joint pain. Most women complain only of hot flashes, which can occur several times a day and are usually more severe at night. Approximately 15% of women do not feel anything, noting only the cessation of menstruation, and remain in excellent health. Many women have misconceptions about what to expect during menopause and menopause. They are worried about the possibility of loss of sexual attractiveness or sudden cessation of sexual activity. Some fear mental illness or general decline. These fears are based primarily on rumors rather than medical facts.
REPRODUCTIVE SYSTEM OF MEN
The reproductive function in men is reduced to the production of a sufficient number of sperm that have normal motility and are capable of fertilizing mature eggs. Male genital organs include the testes (testes) with their ducts, the penis, and an auxiliary organ - the prostate gland.

Testicles (testes, testicles) are oval-shaped paired glands; each of them weighs 10-14 g and is suspended in the scrotum on the spermatic cord. The testicle consists of a large number of seminiferous tubules, which, merging, form the epididymis - epididymis. This is an oblong body adjacent to the top of each testicle. The testicles secrete male sex hormones, androgens, and produce sperm containing male reproductive cells - sperm. Spermatozoa are small, very motile cells, consisting of a head carrying a nucleus, a neck, a body and a flagellum or tail (see SPERM). They develop from special cells in thin convoluted seminiferous tubules. Maturing spermatozoa (so-called spermatocytes) move from these tubules into larger ducts that flow into spiral tubes (efferent, or excretory, tubules). From these, spermatocytes enter the epididymis, where their transformation into sperm is completed. The epididymis contains a duct that opens into the vas deferens of the testicle, which, connecting with the seminal vesicle, forms the ejaculatory (ejaculatory) duct of the prostate gland. At the moment of orgasm, sperm, together with the fluid produced by the cells of the prostate gland, vas deferens, seminal vesicle and mucous glands, are released from the seminal vesicle into the ejaculatory duct and then into the urethra of the penis. Normally, the volume of ejaculate (semen) is 2.5-3 ml, and each milliliter contains more than 100 million sperm.
Fertilization. Once in the vagina, sperm move into the fallopian tubes in about 6 hours using the movements of the tail, as well as due to the contraction of the vaginal walls. The chaotic movement of millions of sperm in the tubes creates the possibility of their contact with the egg, and if one of them penetrates it, the nuclei of the two cells merge and fertilization is completed.
INFERTILITY
Infertility, or the inability to reproduce, can be due to many reasons. Only in rare cases is it caused by the absence of eggs or sperm.
Female infertility. A woman’s ability to conceive is directly related to her age, general health, stage of the menstrual cycle, as well as her psychological mood and lack of nervous tension. Physiological causes of infertility in women include lack of ovulation, unready endometrium of the uterus, genital tract infections, narrowing or obstruction of the fallopian tubes, and congenital abnormalities of the reproductive organs. Other pathological conditions can lead to infertility if left untreated, including various chronic diseases, nutritional disorders, anemia and endocrine disorders.
Diagnostic tests. Determining the cause of infertility requires a complete medical examination and diagnostic laboratory tests. The patency of the fallopian tubes is checked by blowing them. To assess the condition of the endometrium, a biopsy is performed (removal of a small piece of tissue) followed by microscopic examination. The function of the reproductive organs can be judged by analyzing the level of hormones in the blood.
Male infertility. If the semen sample contains more than 25% abnormal sperm, fertilization is rare. Normally, 3 hours after ejaculation, about 80% of sperm retain sufficient mobility, and after 24 hours only a few of them show sluggish movements. Approximately 10% of men suffer from infertility due to insufficient sperm. Such men usually exhibit one or more of the following defects: a small number of sperm, a large number of abnormal forms, decreased or complete absence of sperm motility, and small ejaculate volume. The cause of infertility (sterility) may be inflammation of the testicles caused by mumps (mumps). If the testicles have not yet descended into the scrotum at the onset of puberty, the cells that make sperm may be permanently damaged. The outflow of seminal fluid and the movement of sperm are hindered by obstruction of the seminal vesicles. Finally, fertility (the ability to reproduce) may be reduced as a result infectious diseases or endocrine disorders.
Diagnostic tests. In semen samples, the total number of sperm, the number of normal forms and their motility, as well as the volume of the ejaculate are determined. A biopsy is performed to examine the testicular tissue and the condition of the tubular cells microscopically. The secretion of hormones can be judged by determining their concentration in the urine.
Psychological (functional) infertility. Fertility is also affected by emotional factors. It is believed that a state of anxiety may be accompanied by a spasm of the tubes, which prevents the passage of the egg and sperm. Overcoming feelings of tension and anxiety in women in many cases creates the conditions for successful conception.
Treatment and research. Much progress has been made in the treatment of infertility. Modern methods of hormonal therapy can stimulate spermatogenesis in men and ovulation in women. With the help of special instruments, it is possible to examine the pelvic organs for diagnostic purposes without surgical intervention, and new microsurgical methods make it possible to restore the patency of pipes and ducts. In vitro fertilization (in vitro fertilization). An outstanding event in the fight against infertility was the birth in 1978 of the first child developed from an egg fertilized outside the mother’s body, i.e. extracorporeally. This test tube child was the daughter of Leslie and Gilbert Brown, born in Oldham (UK). Her birth ended the years research work two British scientists, gynecologist P. Steptoe and physiologist R. Edwards. Due to pathology of the fallopian tubes, the woman could not get pregnant for 9 years. To get around this, eggs taken from her ovary were placed in a test tube, where they were fertilized by adding her husband's sperm, and then incubated in special conditions. When the fertilized eggs began to divide, one of them was transferred to the mother's uterus, where implantation occurred and the natural development of the embryo continued. Born with help caesarean section the child was normal in all respects. After this, in vitro fertilization (literally “in glass”) became widespread. Currently, similar assistance to infertile couples is provided in many clinics in different countries and as a result, thousands of “test tube” children have already appeared.

Freezing of embryos. Recently, a modified method has been proposed that has raised a number of ethical and legal issues: freezing fertilized eggs for later use. This technique, developed mainly in Australia, allows a woman to avoid having to undergo repeated egg retrieval procedures if the first attempt at implantation fails. It also makes it possible to implant an embryo into the uterus at the appropriate time in a woman's menstrual cycle. Freezing the embryo (at the very initial stages of development) and then thawing it also allows for successful pregnancy and childbirth.
Egg transfer. In the first half of the 1980s, another promising method of combating infertility was developed, called egg transfer, or in vivo fertilization - literally “in a living” (organism). This method provides artificial insemination a woman who has agreed to become a sperm donor for the future father. After a few days, the fertilized egg, which is a tiny embryo (embryo), is carefully washed out of the donor's uterus and placed in the uterus of the expectant mother, who carries the fetus and gives birth. In January 1984, the first child born after an egg transfer was born in the United States. Egg transfer is a non-surgical procedure; it can be done in a doctor's office without anesthesia. This method can help women who cannot produce eggs or have genetic disorders. It can also be used for tubal obstruction if a woman does not want to undergo the repeated procedures often required for in vitro fertilization. However, a child born in this way does not inherit the genes of the mother who carried him.
See also

Reproduction saves humans as a species from extinction. The male and female reproductive systems produce offspring.

Millions of sperm are produced in the testes (testes) every day. During sexual intercourse, sperm are released through the vas deferens into the vagina.

The ovaries contain a reserve of eggs. One of them is released every month. If she is fertilized by a sperm, then an embryo will develop from her in the uterus. During childbirth, the baby comes out through the vagina.

The reproductive system is activated during puberty, i.e. in adolescence. The male and female reproductive systems are different, but both produce sex cells through meiosis, a special type of cell division that produces sex cells with different sets of genes, causing individual characteristics people. The nucleus of human germ cells contains only 23 chromosomes (gene carriers), i.e. half the set available in all other cells. Eggs are produced in 2 female gonads - the ovaries. The ovaries of a newborn girl already have the entire supply of eggs.

With the onset of puberty in women, 1 egg matures and is released every month. This process is called ovulation. Sperm mature in 2 male gonads – the testes (testes). More than 250 million sperm are produced every day. During sexual intercourse, millions of sperm are released from the man's penis into the woman's vagina. If sexual intercourse took place within 24 hours after ovulation, then one of the sperm floating to the fallopian tubes can penetrate the egg and fertilization will occur. The sperm nucleus (23 chromosomes) will merge with the egg nucleus (23 chromosomes). The combined genetic material (46 chromosomes) will serve as the genetic code for the development of a new organism.

Do you know where babies come from? And I really wanted to find out. You know, at three years old everything is interesting. I come to the kindergarten, and there Lyoshka says that they found him in the cabbage. On Saturday we came to my grandmother's dacha. Cabbage! More than me. I crawled through the whole garden bed and couldn’t find my little sisters or brothers. I decided that they were in mature...

The external female genitalia, or vulva, includes the pubis, labia majora and minora, clitoris, vestibule, Bartholin glands, and hymen. On the anterior side, the vulva is limited by an elevation formed by adipose tissue and covered with hairs. It is called the pubis. Pubic hair grows to the outer edges of the labia majora - two ridges that cover the space between them...

Male genital organs, unlike female ones, are located outside the body cavity and consist of the penis and testicles. The testicles, which perform the same functions as the female ovaries, are located in the scrotum and produce both male reproductive cells - sperm, and the male hormone - testosterone. The testes are a paired male reproductive gland that produces sperm and secretes...

You grow because the number of cells in your body increases. As a result of division, one cell produces two new ones. Where does the very first cell come from, from which all the other cells then appeared? It appears after the union of two germ cells. One such germ cell matures in the female body. It's called an egg. Do you hear a hint in this word...

Compared to eggs or caviar, female eggs are tiny. They gradually mature in a woman’s body in special organs - the ovaries. There are two of them, and they are located in the abdominal cavity. The ovaries are little egg factories. Every month, one or two eggs mature in a woman's ovary. The “production” of eggs begins in adult girls. Little girls have ovaries...

Male reproductive cells are called sperm. They also mature in special organs - the testes, which are located in the leather pouch of the scrotum. Spermatozoa can swim in liquid using a long outgrowth called a tail. The sperm, the male reproductive cell, has an oval head, flattened at the back, and a tail. The sperm develops in the testicle within 75 days and becomes “mature”, reaching a length of 1/20 mm….

If male sperm enter a woman’s body, they will reach the egg on their own. One of the sperm, the most mobile and nimble, will connect with her. This is how the process of fertilization occurs. Moving along the fallopian (uterine) tubes, the fertilized egg divides repeatedly, and a hollow ball consisting of many cells is formed. After 7 days it penetrates the wall of the uterus. This stage...

Pregnancy lasts 6500 hours, or 280 days, or 9 months. This time is necessary for the ripening of the fetus and the birth of a child. Pregnancy is the period between conception and birth of a child. In the first 2 months, the new organism developing in the uterus is called an embryo, and later, when its organs are already functioning, it is called a fetus. The amniotic fluid surrounding the fetus protects it...

The embryo is so small that it cannot take care of itself. Therefore, for nine long months in the body of the expectant mother, he grows and gains strength in a special chamber - the uterus, the walls of which consist of strong muscles. The embryo located in the uterus is surrounded by a thin membrane, inside of which there is liquid. As it moves towards the uterus, the fertilized egg divides many times...

Before birth, the fetus does not breathe. Nutrients and oxygen come to him with the mother's blood. They enter the body of the embryo through a special flexible channel - the umbilical cord. It also removes waste that accumulates in the blood of the unborn child. Normally, approximately 38 weeks after fertilization, the uterus begins to contract. This is how pregnant women begin to experience labor pains...

INTRODUCTION

The ability to reproduce, i.e. producing a new generation of individuals of the same species is one of the main characteristics of living organisms. During the process of reproduction, genetic material is transferred from the parent generation to the next generation, which ensures the reproduction of characteristics not only of one species, but of specific parent individuals. For a species, the meaning of reproduction is to replace those of its representatives who die, which ensures the continuity of the existence of the species; in addition, under suitable conditions, reproduction makes it possible to increase the total number of the species.

Page

Introduction. 1
Reproduction in general. 3-4
Human reproduction and development. 5
Male genital organs. 5-6
Female genital organs. 6-7
The beginning of life (conception). 7-8
Intrauterine development. 8-11
Birth, growth and development of an infant. 12-13
Growth and development of the breast in a child from one year onwards. 14-15

10. Beginning of maturation. 16-19

11. Literature used. 20

REPRODUCTION IN GENERAL

There are two main types of reproduction - asexual and sexual. Asexual reproduction occurs without the formation of gametes and involves only one organism. Asexual reproduction usually produces identical offspring, and the only source of genetic variation is random mutations.

Genetic variability is beneficial to the species, since it supplies “raw materials” for natural selection, and therefore for evolution. The offspring that are most adapted to their environment will have an advantage in competition with other members of the same species and will have a greater chance of surviving and passing on their genes to the next generation. Thanks to this species they are able to change, i.e. speciation process is possible. Increased variation can be achieved by shifting the genes of two different individuals in a process called genetic recombination, which is an important feature of sexual reproduction; In a primitive form, genetic advice is already found in some bacteria.

SEXUAL REPRODUCTION

In sexual reproduction, offspring are produced by the fusion of genetic material from haploid nuclei. Usually these nuclei are contained in specialized sex cells called gametes; During fertilization, the gametes fuse to form a diploid zygote, which during development produces a mature organism. Gametes are haploid; they contain one set of chromosomes obtained as a result of meiosis; they serve as a link between this generation and the next (during sexual reproduction of flowering plants, not cells, but nuclei, merge, but usually these nuclei are also called gametes).

Meiosis important stage life cycles that include sexual reproduction, as it leads to a halving of the amount of genetic material. Due to this, in a series of generations that reproduce sexually, this number remains constant, although during fertilization it doubles each time. During meiosis, as a result of the random birth of chromosomes (independent distribution) and the exchange of genetic material between homologous chromosomes (crossing over), new combinations of genes appear in one gamete, and such shuffling increases genetic diversity. The fusion of the halogen nuclei contained in gametes is called fertilization or syngamy; it leads to the formation of a diploid zygote, i.e. a cell containing one set of chromosomes from each parent. This combination of two sets of chromosomes in the zygote (genetic recombination) represents the genetic basis of intraspecific variation. The zygote grows and develops into a mature organism of the next generation. Thus, during sexual reproduction in the life cycle, an alternation of diploid and haploid phases occurs, and in different organisms these phases take different forms.

Gametes usually come in two types, male and female, but some primitive organisms produce only one type of gamete. In organisms that produce two types of gametes, they can be produced by male and female parents, respectively, or it may be that the same individual has both male and female reproductive organs. Species in which there are separate male and female individuals are called dioecious; such are most animals and humans.

Parthenogenesis is one of the modifications of sexual reproduction in which the female gamete develops into a new individual without fertilization by the male gamete. Parthenogenetic reproduction occurs in both the animal and plant kingdoms and has the advantage of increasing the rate of reproduction in some cases.

There are two types of parthenogenesis, haploid and diploid, depending on the number of chromosomes in the female gamete.

HUMAN REPRODUCTION AND DEVELOPMENT

MALE GENITAL ORGANS

The male reproductive system consists of paired testes (testes), vas deferens, a number of accessory glands and the penis (penis). The testis is a complex tubular gland, ovoid in shape; it is enclosed in a capsule called the tunica albuginea and consists of approximately a thousand highly convoluted seminiferous tubules embedded in connective tissue containing interstitial (Leydig) cells. Sperm gametes (sperm) are produced in the seminiferous tubules, and interstitial cells produce the male sex hormone testosterone. The testes are located outside the abdominal cavity, in the scrotum, and therefore sperm develop at a temperature that is 2-3 degrees C lower than the temperature of the internal areas of the body. More low temperature The scrotum is determined partly by its position and partly by the choroid plexus formed by the artery and vein of the testis and acting as a countercurrent heat exchanger. Contractions of special muscles move the testes closer or further from the body, depending on the air temperature, to maintain the temperature in the scrotum at a level optimal for sperm production. If a man has reached puberty and the testes have not descended into the scrotum (a condition called cryptorchidism), he remains sterile forever, and in men who wear too tight underpants or take very hot baths, sperm production may be so reduced that it leads to infertility. Only a few mammals, including whales and elephants, have their testes in the abdominal cavity their entire lives.

The seminiferous tubules reach 50 cm in length and 200 microns in diameter and are located in areas called lobules of the testis. Both ends of the tubules are connected to the central region of the testis by the rete testis (rete testis) by short, straight seminiferous tubules. Here sperm is collected in 10 20 efferent tubules; along them it is transferred to the head of the epididymis (epididymyx), where it is concentrated as a result of the reabsorption of fluid secreted by the seminiferous tubules. Sperm mature in the head of the epididymis, after which they travel along a convoluted 5-meter efferent tubule to the base of the epididymis; here they remain for a short time before entering the vas deferens. The vas deferens is a straight tube about 40 cm long, which, together with the artery and vein of the testis, forms the seminal quantum and transports sperm to the urethra (urethra), which passes inside the penis. The relationship between these structures, the male accessory glands and the penis is shown in the figure.

FEMALE GENITAL ORGANS

a physiological function necessary for the preservation of humans as a biological species. The process of reproduction in humans begins with conception (fertilization), i.e. from the moment of penetration of the male reproductive cell (sperm) into the female reproductive cell (egg, or ovum). The fusion of the nuclei of these two cells is the beginning of the formation of a new individual. Soon the placenta (afterbirth) also leaves. The entire process, starting with uterine contractions and ending with the expulsion of the fetus and placenta, is called childbirth.

REPRODUCTIVE SYSTEM OF WOMEN
Reproductive organs. The female internal reproductive organs include the ovaries, fallopian tubes, uterus, and vagina.

FEMALE REPRODUCTIVE ORGANS IN SECTION (side view): ovaries, fallopian tubes, uterus and vagina. All of them are held in place by ligaments and are located in the cavity formed by the pelvic bones. The ovaries have two functions: they produce eggs and secrete female sex hormones that regulate the menstrual cycle and maintain female sexual characteristics. The function of the fallopian tubes is to carry the egg from the ovary to the uterus; in addition, this is where fertilization occurs. The fertilized egg is implanted into the wall of the uterus, which stretches as the fetus grows and develops. The lower part of the uterus is its cervix. It protrudes into the vagina, which at its end (vestibule) opens outwards, providing communication between the female genital organs and the external environment. Pregnancy ends with spontaneous rhythmic contractions of the uterus and expulsion of the fetus through the vagina.

FEMALE REPRODUCTIVE ORGANS IN SECTION (front view). The follicles in which the eggs develop are shown inside the ovary. Every month, one of the follicles ruptures, releasing the egg, after which it turns into a hormone-secreting structure - the corpus luteum. The corpus luteum hormone progesterone prepares the uterus for the implantation of a fertilized egg.

The burst follicle sinks into the thickness of the ovary, is overgrown with scar connective tissue and turns into a temporary endocrine gland - the so-called. corpus luteum, which produces the hormone progesterone. The fallopian tubes, like the ovaries, are paired formations. Each of them extends from the ovary and connects to the uterus (from two different sides). The length of the pipes is approximately 8 cm; they bend slightly. The lumen of the tubes passes into the uterine cavity. The walls of the tubes contain inner and outer layers of smooth muscle fibers, which constantly contract rhythmically, which ensures the wave-like movements of the tubes. The inside walls of the tubes are lined with a thin membrane containing ciliated (ciliated) cells. Once the egg enters the tube, these cells, along with muscle contractions of the walls, ensure its movement into the uterine cavity. The uterus is a hollow muscular organ located in the pelvic abdominal cavity. The tubes enter into it from above, and from below its cavity communicates with the vagina. The main part of the uterus is called the body. The non-pregnant uterus has only a slit-like cavity. The lower part of the uterus, the cervix, is about 2.5 cm long, protruding into the vagina, into which a cavity called the cervical canal opens. When a fertilized egg enters the uterus, it is immersed in its wall, where it develops throughout pregnancy. The vagina is a hollow cylindrical formation 7-9 cm long. It is connected to the cervix along its circumference and extends to the external genitalia. Its main functions are the outflow of menstrual blood, the reception of the male genital organ and male seed during copulation, and the provision of passage for the newborn fetus. In virgins, the external opening to the vagina is partially covered by a crescent-shaped fold of tissue, the hymen. This fold usually leaves enough space for the flow of menstrual blood; After the first copulation, the vaginal opening widens.
Mammary glands. Full-fledged (mature) milk in women usually appears approximately 4-5 days after birth. When a child suckles at the breast, there is an additional powerful reflex stimulus to the glands producing milk (lactation). The menstrual cycle is established shortly after the onset of puberty under the influence of hormones produced by the endocrine glands. In the early stages of puberty, pituitary hormones initiate the activity of the ovaries, triggering a complex of processes that occur in the female body from puberty to menopause, i.e. for approximately 35 years. The pituitary gland cyclically secretes three hormones that are involved in the process of reproduction. The first - follicle-stimulating hormone - determines the development and maturation of the follicle; the second - luteinizing hormone - stimulates the synthesis of sex hormones in the follicles and initiates ovulation; the third - prolactin - prepares the mammary glands for lactation. Under the influence of the first two hormones, the follicle grows, its cells divide, and a large fluid-filled cavity is formed in it, in which the oocyte is located. The growth and activity of follicular cells is accompanied by the secretion of estrogens, or female sex hormones. These hormones can be found both in follicular fluid and in the blood. Estrogens are present not only in the human body, but also in other mammals. Luteinizing hormone stimulates the follicle to rupture and release the egg. After this, the follicle cells undergo significant changes, and a new structure develops from them - the corpus luteum. Under the influence of luteinizing hormone, it, in turn, produces the hormone progesterone. Progesterone inhibits the secretory activity of the pituitary gland and changes the state of the mucous membrane (endometrium) of the uterus, preparing it to receive a fertilized egg, which must penetrate (implantate) into the wall of the uterus for subsequent development. As a result, the wall of the uterus thickens significantly, its mucous membrane, containing a lot of glycogen and rich in blood vessels, creates favorable conditions for the development of the embryo. The coordinated action of estrogens and progesterone ensures the formation of the environment necessary for the survival of the embryo and the maintenance of pregnancy. The pituitary gland stimulates ovarian activity approximately every four weeks (ovulatory cycle). If fertilization does not occur, most of the mucous membrane, along with the blood, is rejected and enters the vagina through the cervix. Such cyclically recurring bleeding is called menstruation. For most women, bleeding occurs approximately every 27-30 days and lasts 3-5 days. The entire cycle that ends with the shedding of the uterine lining is called the menstrual cycle. It is regularly repeated throughout the reproductive period of a woman’s life. The first periods after puberty may be irregular, and in many cases they are not preceded by ovulation. Menstrual cycles without ovulation, often found in young girls, are called anovulatory. Menstruation is not at all the release of “spoiled” blood. In fact, the discharge contains very small amounts of blood mixed with mucus and tissue from the lining of the uterus. The amount of blood lost during menstruation varies from woman to woman, but on average does not exceed 5-8 tablespoons. Sometimes minor bleeding occurs in the middle of the cycle, which is often accompanied by mild abdominal pain.
Pregnancy. In most cases, the release of the egg from the follicle occurs approximately in the middle of the menstrual cycle, i.e. 10-15 days after the first day of the previous menstruation. Within 4 days, the egg moves through the fallopian tube. Conception, i.e. Fertilization of an egg by a sperm occurs in the upper part of the tube. This is where the development of the fertilized egg begins. Then it gradually descends through the tube into the uterine cavity, where it remains free for 3-4 days, and then penetrates the wall of the uterus, and from it the embryo and structures such as the placenta, umbilical cord, etc. develop. Pregnancy is accompanied by many physical and physiological changes in the body. Menstruation stops, the size and weight of the uterus sharply increase, and the mammary glands swell, preparing for lactation. During pregnancy, the volume of circulating blood exceeds the original by 50%, which significantly increases the work of the heart. In general, the pregnancy period is a difficult physical activity. Pregnancy ends with the expulsion of the fetus through the vagina. After childbirth, after about 6 weeks, the size of the uterus returns to its original size.
Menopause. The term "menopause" is made up of the Greek words meno ("monthly") and pausis ("cessation"). Thus, menopause means the cessation of menstruation. The entire period of decline of sexual functions, including menopause, is called menopause. Menstruation also stops after surgical removal of both ovaries, performed for certain diseases. Exposure of the ovaries to ionizing radiation can also lead to cessation of their activity and menopause. About 90% of women stop menstruating between the ages of 45 and 50. This can happen abruptly or gradually over many months, when menstruation becomes irregular, the intervals between them increase, the bleeding periods themselves gradually shorten and the amount of blood lost decreases. Sometimes menopause occurs in women under 40 years of age. Equally rare are women with regular menstruation at 55 years of age. Any bleeding from the vagina that occurs after menopause requires immediate medical attention.
REPRODUCTIVE SYSTEM OF MEN
The reproductive function in men is reduced to the production of a sufficient number of sperm that have normal motility and are capable of fertilizing mature eggs. Male genital organs include the testes (testes) with their ducts, the penis, and an auxiliary organ - the prostate gland.

MALE REPRODUCTIVE ORGANS include the testicles (testes) with their ducts, the prostate gland and the penis with the urethra (urethra). Each testicle is an oval-shaped gland, consisting of thin convoluted tubules and suspended in the scrotum on the spermatic cord. The testes produce sperm and secrete male sex hormones, which are necessary both for the functioning of the male reproductive system and for the development and maintenance of secondary sexual characteristics. Sperm maturation occurs in the epididymis, an adnexal structure that also consists of convoluted tubules and is adjacent to the upper part of the testicle. Sperm rise through a duct called the vas deferens (located in the spermatic cord) and enter the seminal vesicle, where they accumulate; here they mix with seminal fluid, secreted mainly by the prostate gland. The seminal vesicle opens into the urethra, through which sperm is released.

Ticket 12

Respiratory system

a set of organs and anatomical formations that ensure the movement of air from the atmosphere to the pulmonary alveoli and back (inhalation-exhalation respiratory cycles) and gas exchange between the air entering the lungs and the blood. Schematic representation of D. s. human - The respiratory organs themselves are the lungs (Lungs) and the respiratory tract: upper (nose (paranasal sinuses) , Paranasal sinuses , pharynx (Pharynx)) and lower (Larynx) , Trachea , Bronchi , including the terminal, or terminal, bronchioles). The abundant blood supply of the respiratory tract and the liquid secretion of the glands of their epithelium are important for maintaining the necessary parameters of temperature and humidity of the air penetrating into the lungs from the atmosphere. The airways end with the transition of the terminal bronchioles into the respiratory ones (respiratory bronchioles, the branches of which form acini - the functional-anatomical unit of the respiratory parenchyma of the lung. The respiratory system also includes the chest and respiratory muscles, the activity of which ensures stretching of the lungs with the formation of the inhalation and exhalation phases and changes in pressure in the pleural cavity, respiratory center, peripheral nerves and receptors involved in the regulation of respiration (Respiration) .

The main ones include the diaphragm, external and internal intercostal muscles and abdominal muscles, which ensure the respiratory act during quiet breathing. Inhalation occurs due to an increase in negative pressure in the cavity chest due to an increase in its volume with lowering of the diaphragm, raising of the ribs and expansion of the intercostal spaces as a result of contraction of the diaphragm and external intercostal muscles. The relaxation of these muscles creates the conditions for exhalation, which occurs partly passively (under the influence of the elastic traction of the stretched lungs and due to the lowering of the ribs under the weight of the chest wall), partly due to the contraction of the internal intercostal muscles and abdominal muscles. With difficulty and increased breathing, auxiliary muscles (neck, as well as almost all muscles of the torso) can participate in the respiratory act. Thus, with increased inhalation, the sternocleidomastoid muscles, latissimus dorsi, serratus posterior superior, pectoralis major and minor, scalenes, trapezius and other muscles contract; with increased exhalation - the lower serratus posterior, iliocostal muscles (lower parts), transverse thoracic muscle, rectus abdominis, quadratus lumborum muscles. The participation of auxiliary muscles in the act of breathing at rest is observed in some types of shortness of breath (Dyspnea) .

The main function of D. s. - ensuring gas exchange between the blood and the external environment in accordance with the needs of the body, which are determined by the intensity of metabolism and differ significantly in states of rest and physical work. Under basal metabolic conditions in healthy adults, the respiratory rate is 12-16 per 1 min the diaphragm is set high, displacing air from the alveoli.

At physical activity increase in gas exchange in D. s. Normally, it is ensured by a decrease in the level of the diaphragm with an increase in the volume of alveolar air, expansion of the lumen of the bronchi, and therefore the resistance to air flow decreases. In addition, during physical activity, the depth and frequency of breathing increase in such an optimal ratio that ensures ventilation of the increased volume of the alveoli with an adequately increased minute volume of breathing with a minimal increase in the work of the respiratory muscles. With pathology leading to impaired airway patency, limited breathing depth, impaired diffusion of gases in the lungs, as well as respiratory regulation disorders, respiratory failure develops , manifested by increased work of the respiratory muscles and (or) various gas exchange disorders.

For normal activity of D. s. and maintaining sterility in the space of the pulmonary alveoli, the ability of the respiratory organs to self-cleanse from microbes and dust particles entering the respiratory tract from the atmosphere is important. In addition to the peristalsis of the small bronchi, the drainage function is normally provided by the mechanism of mucociliary transport. The backup mechanism for drainage of the respiratory tract is Cough .

Human respiratory system (above - sagittal section of the nasal cavity, mouth and larynx): 1 - nasal cavity; 2 - oral cavity; 3 - larynx; 4 - trachea; 5 - left main bronchus; 6 - left lung; 7 - right lung; 8 - segmental bronchi; 9 - right pulmonary arteries; 10 - right pulmonary veins; 11 - right main bronchus; 12 - pharynx; 13 - nasopharyngeal passage.

Excretory system

1. Introduction. 1

2. Reproduction in general. 3-4

3. Human reproduction and development. 5

4. Male genital organs. 5-6

5. Female genital organs. 6-7

6. The beginning of life (conception). 7-8

7. Intrauterine development. 8-11

8. Birth, growth and development of an infant. 12-13

9. Growth and development of the breast in a child from one year onwards. 14-15

10. Beginning of maturation. 16-19

11. Literature used. 20

REPRODUCTION IN GENERAL

There are two main types of reproduction - asexual and sexual. Asexual reproduction occurs without the formation of gametes and involves only one organism. Asexual reproduction usually produces identical offspring, and the only source of genetic variation is random mutations.

Genetic variability is beneficial to the species, since it supplies “raw materials” for natural selection, and therefore for evolution. The offspring that are most adapted to their environment will have an advantage in competition with other members of the same species and will have a greater chance of surviving and passing on their genes to the next generation. Thanks to this species they are able to change, i.e. speciation process is possible. Increased variation can be achieved by shifting the genes of two different individuals, a process called genetic recombination, which is an important feature of sexual reproduction; In a primitive form, genetic advice is already found in some bacteria.

SEXUAL REPRODUCTION

In sexual reproduction, offspring are produced by the fusion of genetic material from haploid nuclei. Usually these nuclei are contained in specialized germ cells - gametes; During fertilization, the gametes fuse to form a diploid zygote, which during development produces a mature organism. Gametes are haploid - they contain one set of chromosomes resulting from meiosis; they serve as a link between this generation and the next (during sexual reproduction of flowering plants, not cells, but nuclei, merge, but usually these nuclei are also called gametes).

Meiosis is an important stage in life cycles involving sexual reproduction, as it leads to a reduction in the amount of genetic material by half. Due to this, in a series of generations that reproduce sexually, this number remains constant, although during fertilization it doubles each time. During meiosis, as a result of the random birth of chromosomes (independent distribution) and the exchange of genetic material between homologous chromosomes (crossing over), new combinations of genes appear in one gamete, and such shuffling increases genetic diversity. The fusion of the halogen nuclei contained in gametes is called fertilization or syngamy; it leads to the formation of a diploid zygote, i.e. a cell containing one set of chromosomes from each parent. This combination of two sets of chromosomes in the zygote (genetic recombination) represents the genetic basis of intraspecific variation. The zygote grows and develops into a mature organism of the next generation. Thus, during sexual reproduction in the life cycle, an alternation of diploid and haploid phases occurs, and in different organisms these phases take different forms.

There are two types of parthenogenesis - haploid and diploid, depending on the number of chromosomes in the female gamete.

HUMAN REPRODUCTION AND DEVELOPMENT

MALE GENITAL ORGANS

The male reproductive system consists of paired testes (testes), vas deferens, a number of accessory glands and the penis (penis). The testis is a complex tubular gland of an ovoid shape; it is enclosed in a capsule - the tunica albuginea - and consists of approximately a thousand highly convoluted seminiferous tubules, immersed in connective tissue that contains interstitial (Leydig) cells. In the seminiferous tubules, gametes are formed - sperm (spermatozoa), and interstitial cells produce the male sex hormone testosterone. The testes are located outside the abdominal cavity, in the scrotum, and therefore sperm develop at a temperature that is 2-3 degrees C lower than the temperature of the internal areas of the body. The cooler temperature of the scrotum is partly determined by its position and partly by the choroid plexus formed by the artery and vein of the testis, which acts as a countercurrent heat exchanger. Contractions of special muscles move the testes closer or further from the body, depending on the air temperature, to maintain the temperature in the scrotum at a level optimal for sperm production. If a man has reached puberty and the testes have not descended into the scrotum (a condition called cryptorchidism), he remains sterile forever, and in men who wear too tight underpants or take very hot baths, sperm production may be so reduced that it leads to infertility. Only a few mammals, including whales and elephants, have their testes in the abdominal cavity their entire lives.

The seminiferous tubules reach 50 cm in length and 200 microns in diameter and are located in areas called lobules of the testis. Both ends of the tubules are connected to the central region of the testis - the rete testis - short straight seminiferous tubules. Here the sperm is collected in 10 - 20 efferent tubules; along them it is transferred to the head of the epididymis (epididymyx), where it is concentrated as a result of the reabsorption of fluid secreted by the seminiferous tubules. Sperm mature in the head of the epididymis, after which they travel along a convoluted 5-meter efferent tubule to the base of the epididymis; here they remain for a short time before entering the vas deferens. The vas deferens is a straight tube about 40 cm long, which, together with the artery and vein of the testis, forms the seminal quantum and transfers sperm to the urethra (urethra), which passes inside the penis. The relationship between these structures, the male accessory glands and the penis is shown in the figure.

FEMALE GENITAL ORGANS

The role of a woman in the process of reproduction is much greater than that of a man, and it involves interactions between the pituitary gland, ovaries, uterus and fetus. The female reproductive system consists of paired ovaries and fallopian tubes, the uterus, vagina and external genitalia. The ovaries are attached to the wall of the abdominal cavity by a fold of peritoneum and perform two functions: they produce female gametes and secrete female sex hormones. The ovary is almond-shaped, consists of an outer cortex and an inner medulla, and is enclosed in a connective tissue membrane called the tunica albuginea. The outer layer of the cortex consists of rudimentary epithelial cells from which gametes are formed. The cortex is formed by developing follicles, and the medulla is formed by stroma containing connective tissue, blood vessels and mature follicles.

The fallopian tube is a muscular tube about 12 cm long through which female gametes leave the ovary and enter the uterus.

The opening of the fallopian tube ends in an extension, the edge of which forms a fimbria, approaching the ovary during ovulation. The lumen of the fallopian tube is lined with ciliated epithelium; The movement of female gametes to the uterus is facilitated by peristaltic movements of the muscular wall of the fallopian tube.

The uterus is a thick-walled potato sack approximately 7.5 cm long and 5 cm wide, consisting of three layers. The outer layer is called the serosa. Beneath it is the thickest middle layer - the myometrium; it is formed by bundles of smooth muscle cells that are sensitive to oxytocin during childbirth. The inner layer - the endometrium - is soft and smooth; it consists of epithelial cells, simple tubular glands and spiral arterioles that supply the cells with blood. During pregnancy, the uterine cavity can increase 500 times - from 10 cm. up to 5000 cm3 The lower entrance to the uterus is the cervix, which connects the uterus to the vagina. Vagina. The entrance to the vagina, the external opening of the urethra and the clitoris are covered by two folds of skin - the labia majora and minora, forming the vulva. The clitoris is a small formation capable of erection, homologous to the male penis. In the walls of the vulva there are Bartholin's glands, which secrete mucus during sexual arousal, which moisturizes the vagina during intercourse.