Sex glands and sex cells. The human body develops from a fertilized egg, which is formed as a result of the fusion of two cells: male - sperm and female - egg (Fig. 131). Sex cells are formed in the sex glands.
A child is born with sex-specific sex glands and genital organs - internal and external.
Female reproductive organs
The sex gland of a woman is ovary. This is a paired female sex gland, located at the upper entrance to the small pelvis on both sides of the uterus (Fig. 132).
The ovary consists of two layers - cortical and cerebral. In the cortical layer, egg cells are formed. The medulla is made up of connective tissue containing blood vessels and nerves.
In the ovary, eggs are produced - female germ cells, from which a new organism develops as a result of fertilization.
In the ovary, sex hormones are produced, on which not only the activity of the genital organs of a woman depends, but also the normal activity of everything female body.
Rice. 131. sex cells:
A - sperm; B - egg; 1 - the head of the spermatozoon; 2 - middle or connecting department; 3 - sperm tail; 4 - follicular cells surrounding the egg; 5 - the nucleus of the egg cell.
Its appendage adjoins the posterior edge of the testicle, from which the vas deferens 45-50 mm long extends. To the headepididymis from the testicle passes 10-12 very thin efferent tubules. Semen is carried out of the testicle through these tubules. In the seminiferous tubules of the testis, with the onset of puberty, the rudiments of germ cells - spermatoblasts - begin to divide, as a result of which male germ cells are formed from them - spermatozoa, or gummies(Fig. 131). The zhivchik consists of a head, a middle part and a tail, the contractions of which ensure the movement of spermatozoa. The speed of movement of the gum is about 2-3 mm per minute. The final maturation and accumulation of sperm occurs in the epididymis. Male gonads, unlike female, produce sperm continuously.
Since the maturation of the body of a young man, many millions of spermatozoa are born in the convoluted tubules of the testicles per day. At one time, about 500 million or more of them can be thrown out. Mature gums in the male body can live for about a month, then they grow old and disappear.
During sexual arousal, the spermatozoa accumulated in the epididymis, together with the secretion of the epididymis, move along the vas deferens to the seminal vesicles. The secret of the appendages thins the environment, providing greater sperm motility, and in addition, it nourishes the sperm not only inside the seminal vesicle, but also during the eruption of the seed. During sexual arousal, the secret of the prostate gland is simultaneously produced, which covers the urethra on both sides when it exits the bladder. The secret of the gland activates sperm motility.
At the moment of greatest sexual arousal, first the secretions of the prostate gland are ejected into the posterior urethra, then the spermatozoa, and finally the secretions of the seminal vesicles. The secret of the prostate gland and seminal vesicles, mixing with spermatozoa, forms sperm. With each sexual intercourse, 1-b cm 3 of sperm is released. Sperm erupts through the external opening of the urethra, which opens at the glans penis.
The skin of the penis at the base of the head forms a fold - the foreskin. On the inner surface of it are sebaceous glands of various sizes, the secret of which is involved in the formation of a whitish lubricant.
, pregnancy, childbirth
most often occurs in the expansion of the female oviduct. Spermatozoa, which have poured out with sperm into the vagina, due to their exceptional activity and mobility, move into the uterine cavity, pass it to the oviductsand in one of them they meet with a mature egg. Here, a sperm cell (one of many) is introduced into the egg and fertilizes it.
A fertilized egg with a fluid current moves along the oviduct to the uterus, turning into a lump of cells surrounded by a membrane equipped with villi.
The developing fertilized egg continues its movement to the uterus, where it enters approximately 3-6 days after fertilization. In the uterus, already prepared by ovarian hormones, the villi of the fertilized egg are introduced into the swollen mucous membrane, which grows strongly and soon closes over the fertilized egg. If the egg is fertilized rena and the embryo in the uterus develops normally, stops. The corpus luteum will not disappear within 5-6 months. It grows and with its increasing hormonal influence promotes the growth and further attachment of the egg, and also prevents the maturation of eggs in the ovary.
Rice.134. The position of the baby in the womb:
1-bladder; 2 - placenta, or child's place; 3 - rectum; four - vagina.
At the point of attachment gestational sac to the wall of the uterus is formed placenta, or a child's place (Fig. 134).
The formation of the placenta ends by the end of the third month of pregnancy, and in the future it only increases in size.
Placenta- the organ through which the fetus is connected with the mother's body. Through it, the fetus is nourished, its respiratory and excretory functions are carried out. Many protective bodies (antibodies) pass through the placenta from the mother to the fetus.
Nutritious and come through the umbilical cord, which connects the fetus to the mother's organisms. It looks like a cord 50-60 cm long, 1.5-2 cm thick. The umbilical cord begins in the navel of the fetus and ends in the placenta.
The fetus, which develops in the uterus, is located in special membranes that form, as it were, a bag filled with amniotic fluid. These waters enable the fetus to move freely in the bag, develop, and protect it from accidental injuries.
The shells in which developing fetus, is called afterbirth.
A normal pregnancy lasts 9 months. During this time, a child weighing about 3 kg or more and 50-52 cm tall develops from a fertilized egg of microscopic size.
Pregnancy ends with childbirth. As a result of the hard work of the muscles of the uterus, the child is pushed into the small pelvis, then the abdominal muscles contract, and the child is born.
Mother and child are still connected by a pulsating umbilical cord. The doctor or midwife first ties the umbilical cord near the newborn's abdomen and then cuts it. In a child, the placental is replaced by the pulmonary, pulmonary occurs. Shortly after the birth of the child, the afterbirth comes out of the uterine cavity.
Now the child will feed on mother's milk for almost a year. Breast milk contains proteins, fats, sugar and everything necessary for the growth and development of the child, including vitamins, enzymes that protect against diseases (antibodies).
A few weeks (and sometimes months) after childbirth, the maturation of eggs in the ovary resumes, as evidenced by the onset of menstruation. The woman again becomes capable of conceiving a child.
Post-embryonic human development
age periodization. For a number of signs, all life path man from conception to the natural end can be divided into periods, or stages. There are no clearly defined boundaries between these periods, they are largely conditional.
Several factors have been proposed as criteria for age periodization. Some researchers take the maturation of the gonads and the intensity of body growth as the basis for periodization, others take the time of the appearance and change of teeth, and still others take the degree of development of the central nervous system. The most common is the periodization of children with the allocation of the neonatal period, toddler, preschool and school age. This division reflects the existing system of children's institutions.
It must be assumed that a truly scientific classification cannot be based on any one attribute. In each individual period of life, a set of signs comes to the fore (type of nutrition, motor activity, puberty, etc.). The most appropriate for the organization of work on the education and upbringing of children is such a division of the development of the child into periods in which the complex of its anatomical and physiological characteristics and conditions of life, upbringing and education is taken as the basis.
In modern science there is still no unified classification of periods of growth and development and their age limits. The Symposium on the Problem of Age Periodization in Moscow (1965) recommended the following age periodization, which is not accepted by all researchers:
1) newborn - 1 - 10 days;
2) infancy - 10 days - 1 year;
3) early childhood - 1-3 years;
4) the first childhood -4 - 7 years;
5) the second childhood - 8 - 12 years old boys,
8-11 years old girls;
6) adolescence - 13-16 years old boys,
12-15 years old girls;
7) youthful age - 17-21 years old young men,
16-20 years old girls;
8) mature age, I period - 22-35 years old men,
22-35 years old women; mature age, II period - 36-60 years old men,
36-55 years old women;
9) old age - 61 -74 years old men,
56-74 years old women;
10) senile age - 75-90 years;
11) centenarians - 90 years and above.
From the moment of birth to death, specific features of the structure, biochemical processes, functions of the body as a whole and its individual systems are noted in the human body, which change at different periods of its life. These changes are due to hereditary factors that to a certain extent determine the stages of growth and development. However, education and upbringing, nutrition and hygienic living conditions, communication of the child with other people through speech, sports and labor activity and other factors that make up the essence of human social life.
human life econtinuous process of development. start walking and further development motor function, the first words of the child and the development of speech function, the transformation of the child into a teenager during puberty, the continuous development of the central nervous system, the complication of reflex activity - these are just examples of the huge number of continuous changes in the body.
Rice. 135. Change in body proportions with age
The growth and development of the organism and its individual organs occurs unevenly, heterochronously. The uneven growth of the body in length, individual organs and tissues, the mass of the child is accompanied by a number of age-related changes. There is also a change inportions of the child's body (Fig. 135). A newborn differs from an adult in relatively short limbs, a large torso and a large head. Newborn head height is 1/4 body length, in a child of two years - 1/5, six years - 1/6, 12 years - 1/7 and in adults - 1/8. With age, the growth of the head slows down, and the growth of the limbs increases. Before the onset of puberty, there are no gender differences in body proportions, and in puberty (puberty), in young men, the limbs become longer, the torso is shorter, and the pelvis is narrower than in girls.
One can notice three periods of different proportions between the length and width of the body: from 4 to 6 years, from 6 to 15 years and from 15 years to adulthood. If in the prepubertal period the overall height increases due to the growth of the legs, in the pubertal period - due to the growth of the torso.
The uneven growth of the body in length is manifested as follows: in the first year of life, growth increases by 25 cm and reaches 75 cm. In the second year, the growth rate slows down - it increases only by 10 cm. In subsequent years, up to 6-7 years, the growth rate decrease even more. By the beginning of primary school age, growth increases by 7-10 cm per year, and at the age of 8-10 years up to 3-5 cm. During puberty, growth rates increase again, the annual increase is 5-10 cm. Girls have the greatest increase in growth in connection with puberty, it is noted at the age of 12, in boys - at 15 years. By this period, the boys are catching up, and then overtaking the girls in growth.
Growth is mostly completed by the age of 19 for girls and by 20 for boys.
From the neonatal period to reaching adulthood, body length increases 3.5 times, body length - 3 times, arm length - 4 times, leg length - 5 times.
Uneven growth is an adaptation developed by evolution. The rapid growth of the body in length in the first year of life is associated with an increase in body weight, and a slowdown in growth in subsequent years is due to the manifestation of active processes of differentiation of organs, tissues, cells, and functional systems.
It should be borne in mind that development leads to morphological and functional changes, and growth leads to an increase in the mass of tissues, organs and the whole body. In the normal development of the child, both these processes are closely interrelated. However, periods of intense growth may not coincide with periods of intense differentiation.
Increased differentiation causes growth retardation. An increase in the mass of the head and spinal cord basically ends by the age of 8-10, almost reaching the mass of an adult, while the functional improvement of the nervous system continues for a long time.
The maturation of the motor analyzer and the innervation apparatus of the muscles begins at the age of 13-14, passing through a number of stages of improving the motor function. At the same time, at the age of 15-18, further intensive growth and differentiation of muscle tissue occurs. The uneven development of the cardiovascular system manifests itself as follows: from birth to two years, it grows intensively, and the histological differentiation changes slightly; from 2 to 6 years, growth change and differentiation are slowed down, both processes proceed moderately; from 7 to 10 years, the size and volume of the heart increase, and there are no significant structural changes in the muscle; from 11-13 years old again begins to grow intensively, the finest differentiation occurs in the cellular elements. Uneven development is accompanied by growth retardation.
Weight. The greatest weight gain occurs in the first year of life. By the end of the first year of life, body weight triples and reaches 9-10 kg. By the end of the second year, it reaches 12-13 kg. In the future, the mass per year is added by 2 kg. With the onset of puberty, weight gain in girls reaches 4-5 kg, and by the age of 14-15 - 5-8 kg, then the annual weight gain is again 2 kg. In boys, from the age of 13-14, the weight gain is 7-8 kg per year. In the future, in boys, as in girls, the rate of weight gain slows down. The mass of boys and girls up to 10 years old is almost the same. From the age of 15, the mass of boys begins to exceed the mass of girls, and this lead remains throughout the rest of their lives.
The formation of the human body continues after birth (postnatal period) and ends by the age of 22-25. During periods of body growth, the mass and surface of the body increase, which is due to the development of tissues, organs and individual parts of the body. At the same time, the functions of organs and systems develop. Each period is characterized by its own characteristics. There are several schemes of periodization of human development. The most common of them are given in Table. 2.1.
Table 2.1
Age periods of ontogenetic development
|
Main title |
Other names |
|
|
Intrauterine development (antenatal, prenatal ontogeny) |
||
|
Embryonic period |
embryo development |
|
|
fetal period |
Fetal development |
|
|
Extrauterine development |
Postnatal ontogeny |
|
|
Neonatal period |
neonatal period |
Birth to 4 weeks |
|
Breast age |
Infancy |
4 weeks - 1 year |
|
Early childhood |
toddler age |
|
|
First childhood |
Before school age |
|
|
Second childhood |
Adolescence, primary school age |
Boys 8-12 years old, girls 8-11 years old |
|
Adolescence |
Puberty, senior school age |
Boys 13-16 years old, girls 12-15 years old |
|
adolescence |
||
|
Mature age |
Maturity |
|
|
Maturity |
Men 22-35 years old, women 21-35 years old |
|
|
Men 36-60 years old, women 36-55 years old |
||
|
Elderly age |
||
|
Senile age |
||
|
centenarians |
90 years and older |
|
This scheme takes into account not only the morphological and physiological characteristics of a person, but also social factors focused on the system of institutions associated with the education of children and the retirement of an adult.
The growth and development of an organism includes the processes during which an adult individual develops from a fertilized egg. Growth - this is an increase in the size of the body and its parts; under the term " development» understand the various functional changes that occur as a result of the growth and improvement of the structure of organs. An increase in the mass and surface of the body is due to the development of tissues (cells and intercellular substance), organs and individual parts of the body. Growth and development is not just an increase in body weight, but also the formation of various body functions. At this time, a significant part of the physiological parameters approaches the level characteristic of an adult. So, for example, the activity of digestive enzymes increases, the sense organs are improved and nervous system develop protective mechanisms against infection, etc.
The growth and development of the body, its organs and systems from the moment of birth to the onset of maturity proceed heterochronously: periods of growth acceleration alternate with its slowdown. Those organs or their systems that are necessary for the body at this stage of development grow and develop faster. So, at the time of birth, a newborn's nutrition system is formed with liquid food - milk (at the same time, the development of a functional system of nutrition with solid food is delayed). In the process of growth and development, physiological functions adapt to the characteristics of the existence of the organism, i.e. its individual adaptation to environmental conditions occurs.
Achieving maturity is a long process. Among the higher mammals, a person has the longest childhood, during which the development of the brain and the formation of mental functions - speech, thinking, consciousness; This requires communication with other people. The development of a child is influenced by nutrition, care, climatic and geographical factors, family, school, objects around him, people (children and adults), life events, etc. All this is important not only for the physical development of the child, but also extremely important for the mental development adequate to his age. A child needs not only a favorable environment in the family, children's team, but also the love of the people closest to him - parents, friends. For him, both excessive attention and abandonment are equally harmful.
The phenomenon has a positive effect on the growth and development of the organism. heterosis(gr. heterosis- transformation), or "hybrid power", which manifests itself in a greater body length, accelerated development, longer life expectancy and a longer reproductive period, and greater resistance to infections. The reasons for the successful combination of genes and their interaction, mainly in first-generation hybrids, have not yet been established. It is known that heterosis is especially common in people whose parents belong to different nationalities and were geographically separated before marriage. From this it is clear that at the present time, when the improvement of means of communication makes it possible to overcome geographical isolation, heterosis begins to play a particularly important role in the evolutionary development of human society.
In related marriages, the opposite phenomenon often occurs: children are poorly developed physically, prone to infectious diseases, hereditary disorders are often manifested, a short life expectancy is characteristic.
The physical development of a person is a complex of morphological and functional properties of the body that determine the shape, size, body weight and its structural and mechanical qualities.
Introduction
Signs of physical development are variable. The physical development of a person is the result of the influence of hereditary factors (genotype) and environmental factors, and for a person - the whole complex of social conditions ( phenotype). With age, the value of heredity decreases, the leading role passes to individually acquired features.
The physical development of children and adolescents is associated with growth. Each age period - infancy, childhood, adolescence and youth - is characterized by specific features of the growth of individual parts of the body. In each age period, the child's body has a number of characteristic features unique to this age. Between the body of a child and an adult, there are not only quantitative differences (body size, weight), but, above all, qualitative ones.
Currently, there is an acceleration of human physical development. This phenomenon is called acceleration.
In my work, I will try to briefly characterize each of the main stages of individual development of a person.
The main stages of individual human development
When studying human development, its individual and age characteristics in anatomy and other disciplines, they are guided by scientifically based data on age periodization. The scheme of age periodization of human development, taking into account anatomical, physiological, and social factors, was adopted at the VII Conference on Problems of Age Morphology, Physiology, and Biochemistry (1965). It distinguishes twelve age periods (Table 1). Table 1
Individual development, or development in ontogeny, occurs in all periods of life - from conception to death. In human ontogenesis, two periods are distinguished: before birth (intrauterine, prenatal - from the Greek natos - born) and after birth (extrauterine, postnatal).
Prenatal ontogeny
To understand the individual structural features of the human body, it is necessary to get acquainted with the development of the human body in the prenatal period. The fact is that each person has his own individual characteristics of external appearance and internal structure, the presence of which is determined by two factors. This is heredity, traits inherited from parents, as well as the result of the influence of the external environment in which a person grows, develops, studies, works.
In the intrauterine period, from conception to birth, for 280 days (9 calendar months), the embryo (embryo) is located in the mother's body (from the moment of fertilization to birth). During the first 8 weeks, the main processes of the formation of organs and body parts take place. This period is called the embryonic (embryonic), and the body of the future person is the embryo (embryo). From the age of 9 weeks, when the main external human features begin to appear, the body is called a fetus, and the period is fetal (fetal - from the Greek fetus - fetus).
The development of a new organism begins with the process of fertilization (fusion of sperm and egg), which usually occurs in the fallopian tube. Merged sex cells form a qualitatively new unicellular embryo - a zygote that has all the properties of both germ cells. From this moment, the development of a new (daughter) organism begins.
The optimal conditions for the interaction of sperm and egg are usually created within 12 hours after ovulation. The union of the nucleus of the spermatozoon with the nucleus of the ovum leads to the formation in a unicellular organism (zygote) of a diploid set of chromosomes characteristic of a human being (46). The sex of the unborn child is determined by the combination of chromosomes in the zygote and depends on the father's sex chromosomes. If the egg is fertilized by a sperm with the sex chromosome X, then two X chromosomes appear in the resulting diploid set of chromosomes, which are characteristic of the female body. When fertilized by a sperm with a Y sex chromosome, a combination of XY sex chromosomes is formed in the zygote, which is characteristic of the male body.
The first week of embryo development is the period of crushing (division) of the zygote into daughter cells (Fig. 1). Immediately after fertilization, during the first 3-4 days, the zygote divides and simultaneously moves along the fallopian tube towards the uterine cavity. As a result of division of the zygote, a multicellular vesicle is formed - a blastula with a cavity inside (from the Greek blastula - sprout). The walls of this vesicle are formed by two types of cells: large and small. From the outer layer of small cells, the walls of the vesicle are formed - the trophoblast. Subsequently, trophoblast cells form the outer layer of the membranes of the embryo. Larger dark cells (blastomeres) form a cluster - an embryoblast (embryonic nodule, embryo rudiment), which is located medially from the trophoblast. From this accumulation of cells (embryoblast), the embryo and adjacent extraembryonic structures (except for the trophoblast) develop.
Fig.1. 
A - fertilization: 1 - sperm; 2 - egg; B; C - crushing of the zygote, D - morublastula: 1 - embryoblast; 2 - trophoblast; D - blastocyst: 1-embryoblast; 2 - trophoblast; 3 - amnion cavity; E - blastocyst: 1-embryoblast; 2-amnion cavity; 3 - blastocoel; 4 - embryonic endoderm; 5-amnionitic epithelium - F - I: 1 - ectoderm; 2 - endoderm; 3 - mesoderm.
A small amount of fluid accumulates between the surface layer (trophoblast) and the germinal nodule. By the end of the 1st week of development (6-7th day of pregnancy), the embryo enters the uterus and is introduced (implanted) into its mucous membrane; implantation lasts about 40 hours. The surface cells of the embryo that form the vesicle, the trophoblast (from the Greek trophe - nutrition), secrete an enzyme that loosens the surface layer of the uterine mucosa, which is prepared for the introduction of the embryo into it. The emerging villi (outgrowths) of the trophoblast come into direct contact with the blood vessels of the mother's body. Numerous trophoblast villi increase the surface of its contact with the tissues of the uterine mucosa. The trophoblast turns into a nutrient membrane of the embryo, which is called the villous membrane (chorion). At first, the chorion has villi on all sides, then these villi remain only on the side facing the wall of the uterus. In this place, a new organ develops from the chorion and the uterine mucosa adjacent to it - the placenta (children's place). The placenta is the organ that connects the mother's body with the fetus and provides its nutrition.
The second week of the life of the embryo is the stage when the embryoblast cells are divided into two layers (two plates), from which two vesicles are formed (Fig. 2). From the outer layer of cells adjacent to the trophoblast, an ectoblastic (amniotic) vesicle is formed. An endoblastic (yolk) vesicle is formed from the inner layer of cells (the rudiment of the embryo, the embryoblast). The bookmark ("body") of the embryo is located where the amniotic vesicle is in contact with the yolk sac. During this period, the embryo is a two-layer shield, consisting of two sheets: the outer germinal (ectoderm) and the inner germinal (endoderm).
Fig.2. The position of the embryo and embryonic membranes at different stages of human development: A - 2-3 weeks; B - 4 weeks: 1 - amnion cavity; 2 - the body of the embryo; 3 - yolk sac; 4 - tropholast; B - 6 weeks; D - fetus 4-5 months: 1 - body of the embryo (fetus); 2 - amnion; 3 - yolk sac; 4 - chorion; 5 - umbilical cord.
The ectoderm faces the amniotic sac, and the endoderm is adjacent to the yolk sac. At this stage, the surfaces of the embryo can be determined. The dorsal surface is adjacent to the amniotic vesicle, and the ventral surface to the yolk sac. The trophoblast cavity around the amniotic and vitelline vesicles is loosely filled with strands of cells of the extraembryonic mesenchyme. By the end of the 2nd week, the length of the embryo is only 1.5 mm. During this period, the germinal shield thickens in its posterior (caudal) part. Here, in the future, axial organs (chord, neural tube) begin to develop.
The third week of the life of the embryo is the period of formation of a three-layer shield (embryo). The cells of the outer, ectodermal plate of the germinal shield are displaced towards its posterior end. As a result, a cell ridge (primary streak) is formed, which is elongated in the direction of the longitudinal axis of the embryo. In the head (front) part of the primary strip, cells grow and multiply faster, resulting in a slight elevation - the primary nodule (Hensen's nodule). The location of the primary nodule indicates the cranial (head end) of the body of the embryo.
Rapidly multiplying, the cells of the primary streak and the primary nodule grow to the sides between the ectoderm and endoderm, thus forming the median germ layer - the mesoderm. The cells of the mesoderm located between the sheets of the shield are called the intraembryonic mesoderm, and those that have moved beyond it are called the extraembryonic mesoderm.
Part of the mesoderm cells within the primary nodule grows especially actively forward from the head and tail ends of the embryo, penetrates between the outer and inner sheets and forms a cell strand - the dorsal string (chord). At the end of the 3rd week of development, active cell growth occurs in the anterior part of the outer germ layer - the neural plate is formed. This plate soon bends, forming a longitudinal groove - the neural groove. The edges of the groove thicken, approach and fuse with each other, closing the neural groove into the neural tube. In the future, the entire nervous system develops from the neural tube. The ectoderm closes over the formed neural tube and loses contact with it.
In the same period, a finger-like outgrowth, the alantois, penetrates from the back of the endodermal plate of the germinal shield into the extraembryonic mesenchyme (the so-called amniotic stalk), which does not perform certain functions in humans. In the course of the allantois, blood umbilical (placental) vessels sprout from the embryo to the chorion villi. A cord containing blood vessels that connects the embryo to the extra-embryonic membranes (placenta) forms the ventral stalk.
Thus, by the end of the 3rd week of development, the human embryo looks like a three-layer plate, or a three-layer shield. In the region of the outer germ layer, the neural tube is visible, and deeper - the dorsal string, i.e. axial organs of the human embryo appear. By the end of the third week of development, the length of the embryo is 2-3 mm.
The fourth week of life - the embryo, which has the form of a three-layer shield, begins to bend in the transverse and longitudinal directions. The embryonic shield becomes convex, and its edges are delimited from the amnion surrounding the embryo by a deep furrow - the trunk fold. The body of the embryo from a flat shield turns into a three-dimensional one, the ectoderm covers the body of the embryo from all sides.
From the ectoderm, the nervous system, the epidermis of the skin and its derivatives, the epithelial lining of the oral cavity, the anal part of the rectum, and the vagina are further formed. The mesoderm gives rise to internal organs (except endoderm derivatives), the cardiovascular system, the organs of the musculoskeletal system (bones, joints, muscles), and the skin itself.
The endoderm, which is inside the body of the human embryo, rolls up into a tube and forms the embryonic rudiment of the future intestine. The narrow opening connecting the embryonic intestine with the yolk sac later turns into the umbilical ring. From the endoderm, the epithelium and all the glands of the digestive system and respiratory tract are formed.
The embryonic (primary) intestine is initially closed in front and behind. In the anterior and posterior ends of the body of the embryo, invaginations of the ectoderm appear - the oral fossa (future oral cavity) and anal (anal) fossa. Between the cavity of the primary intestine and the oral fossa there is a two-layer (ectoderm and endoderm) anterior (oropharyngeal) plate (membrane). Between the intestine and the anal fossa there is a cloacal (anal) plate (membrane), also two-layered. The anterior (oropharyngeal) membrane ruptures during the 4th week of development. At the 3rd month, the posterior (anal) membrane breaks.
As a result of bending, the body of the embryo is surrounded by the contents of the amnion - amniotic fluid, which acts as a protective environment that protects the embryo from damage, primarily mechanical (concussion).
The yolk sac lags behind in growth and at the 2nd month of intrauterine development looks like a small sac, and then it is completely reduced (disappears). The ventral stalk lengthens, becomes relatively thin and is later called the umbilical cord.
During the 4th week of development of the embryo, the differentiation of its mesoderm, which began on the 3rd week, continues. The dorsal part of the mesoderm, located on the sides of the chord, forms paired thickened protrusions - somites. Somites are segmented, i.e. divided into metameric regions. Therefore, the dorsal part of the mesoderm is called segmented. Segmentation of somites occurs gradually in the direction from front to back. On the 20th day of development, the 3rd pair of somites is formed, by the 30th day there are already 30 of them, and on the 35th day - 43-44 pairs. The ventral part of the mesoderm is not divided into segments. It forms two plates on each side (non-segmented part of the mesoderm). The medial (visceral) plate is adjacent to the endoderm (primary intestine) and is called the splanchnopleura. The lateral (outer) plate is adjacent to the wall of the body of the embryo, to the ectoderm, and is called the somatopleura.
The epithelial cover of the serous membranes (mesothelium), as well as the lamina propria of the serous membranes and the subserous base, develop from the splanchno- and somatopleura. The mesenchyme of the splanchnopleura also goes to the construction of all layers of the digestive tube, except for the epithelium and glands, which are formed from the endoderm. The space between the plates of the non-segmented part of the mesoderm turns into the body cavity of the embryo, which is subdivided into the peritoneal, pleural and pericardial cavities.
Fig.3. Cross section through the body of the embryo (diagram): 1 - neural tube; 2 - chord; 3 - aorta; 4 - sclerotome; 5 - myotome; 6 - dermatome; 7 - primary intestine; 8 - body cavity (as a whole); 9 - somatopleura; 10 - splanchnopleura.
The mesoderm on the border between the somites and the splanchnopleura forms nephrotomes (segmental legs), from which the tubules of the primary kidney, the sex glands, develop. From the dorsal part of the mesoderm - somites - three rudiments are formed. The anteromedial section of the somites (sclerotome) goes to the construction of skeletal tissue, giving rise to cartilage and bones of the axial skeleton - the spine. Lateral to it lies the myotome, from which the skeletal muscles develop. In the posterolateral part of the somite there is a site - the dermatome, from the tissue of which the connective tissue base of the skin is formed - the dermis.
In the head section on each side of the embryo from the ectoderm on the 4th week, the rudiments of the inner ear (first the auditory pits, then the auditory vesicles) and the future lens of the eye are formed. At the same time, the visceral sections of the head are rebuilt, which form the frontal and maxillary processes around the mouth bay. Behind (caudal) of these processes, the contours of the mandibular and sublingual (hyoid) visceral arches are visible.
Elevations are visible on the anterior surface of the torso of the embryo: cardiac, and behind it - hepatic tubercles. The recess between these tubercles indicates the place of formation of the transverse septum - one of the rudiments of the diaphragm. Caudal to the hepatic tubercle is the ventral stalk, which contains large blood vessels and connects the embryo to the placenta (umbilical cord). The length of the embryo by the end of the 4th week is 4-5 mm.
Fifth to eighth weeks
In the period from the 5th to the 8th week of the life of the embryo, the formation of organs (organogenesis) and tissues (histogenesis) continues. This is the time of early development of the heart and lungs, the complication of the structure of the intestinal tube, the formation of visceral arches, the formation of capsules of the sense organs. The neural tube completely closes and expands in the head region (the future brain). At the age of about 31-32 days (5th week), the length of the embryo is 7.5 mm. At the level of the lower cervical and 1st thoracic segments of the body, fin-like rudiments (buds) of the hands appear. By the 40th day, the rudiments of the legs are formed.
At the 6th week (parietal-coccygeal length of the embryo - 12 - 13 mm), the laying of the outer ear is noticeable, from the end of the 6-7th week - the laying of the fingers, and then the toes.
By the end of the 7th week (the length of the embryo is 19-20 mm), the eyelids begin to form. Thanks to this, the eyes are outlined more clearly. On the 8th week (the length of the embryo is 28-30 mm), the laying of the organs of the embryo ends. From the 9th week, i.e. from the beginning of the 3rd month, the embryo (parietal-coccygeal length 39-41 mm) takes the form of a person and is called a fetus.
third to ninth months
Starting from three months and throughout the entire fetal period, further growth and development of the resulting organs and body parts occur. At the same time, the differentiation of the external genitalia begins. Nails are laid on the fingers. From the end of the 5th month (length 24.3 cm), eyebrows and eyelashes become noticeable. At the 7th month (length 37.1 cm), the eyelids open, fat begins to accumulate in the subcutaneous tissue. On the 10th month (length 51 cm) the fetus is born.
Critical periods of ontogeny a
In the process of individual development, there are critical periods when the sensitivity of the developing organism to the effects of damaging factors of the external and internal environment is increased. There are several critical periods of development. These most dangerous periods are:
1) the time of development of germ cells - ovogenesis and spermatogenesis;
2) the moment of fusion of germ cells - fertilization;
3) implantation of the embryo (4-8 days of embryogenesis);
4) formation of rudiments of axial organs (brain and spinal cord, spinal column, primary intestine) and formation of the placenta (3-8 weeks of development);
5) the stage of enhanced brain growth (15-20 weeks);
6) formation of the functional systems of the body and differentiation of the urogenital apparatus (20-24th week of the prenatal period);
7) the moment of the birth of the child and the neonatal period - the transition to extrauterine life; metabolic and functional adaptation;
8) the period of early and first childhood (2 years - 7 years), when the formation of relationships between organs, systems and apparatuses of organs ends;
9) adolescence (puberty - in boys from 13 to 16 years, in girls - from 12 to 15 years).
Simultaneously with the rapid growth of the organs of the reproductive system, emotional activity is activated.
Postnatal ontogeny. Neonatal period
Immediately after birth, there is a period called the neonatal period. The basis for this allocation is the fact that at this time the child is fed with colostrum for 8-10 days. Newborns in the initial period of adaptation to the conditions of extrauterine life are divided according to the level of maturity into full-term and premature. Intrauterine development of full-term babies lasts 39-40 weeks, premature babies - 28-38 weeks. When determining maturity, not only these terms are taken into account, but also the mass (weight) of the body at birth.
Newborns with a body weight of at least 2500 g (with a body length of at least 45 cm) are considered full-term, and newborns with a body weight of less than 2500 g are considered premature. In addition to weight and length, other dimensions are taken into account, for example, chest girth in relation to body length and head circumference in relation to chest circumference. It is believed that the girth of the chest at the level of the nipples should be more than 0.5 body length by 9-10 cm, and the girth of the head - more than the girth of the chest by no more than 1-2 cm.
Breast period
The next period - chest - lasts up to a year. The beginning of this period is associated with the transition to feeding "mature" milk. During the breast period, the greatest intensity of growth is observed, in comparison with all other periods of extrauterine life. Body length increases from birth to a year by 1.5 times, and body weight triples. From 6 months milk teeth begin to erupt. In infancy, uneven body growth is pronounced. In the first half of the year, babies grow faster than in the second. In each month of the first year of life, new indicators of development appear. In the first month, the child begins to smile in response to the appeal of adults, at 4 months. persistently tries to stand on legs (with support), at 6 months. tries to crawl on all fours, at 8 - makes attempts to walk, by the year the child usually walks.
Period early childhood
The period of early childhood lasts from 1 year to 4 years. At the end of the second year of life, teething ends. After 2 years, the absolute and relative values of annual body size increases rapidly decrease.
First childhood period
From the age of 4, the period of the first childhood begins, which ends at the age of 7. Starting from the age of 6, the first permanent teeth appear: the first molar (large molar) and the medial incisor on the lower jaw.
The age from 1 year to 7 years is also called the period of neutral childhood, since boys and girls almost do not differ from each other in size and body shape.
second childhood period
The period of second childhood lasts for boys from 8 to 12 years, for girls - from 8 to 11 years. During this period, sex differences in the size and shape of the body are revealed, and an increased growth of the body in length begins. Growth rates in girls are higher than in boys, since puberty in girls begins on average two years earlier. Increased secretion of sex hormones (especially in girls) causes the development of secondary sexual characteristics. The sequence of appearance of secondary sexual characteristics is fairly constant. In girls, the mammary glands first form, then pubic hair appears, then in the armpits. The uterus and vagina develop simultaneously with the formation of the mammary glands. To a much lesser extent, the process of puberty is expressed in boys. Only towards the end of this period do they begin to accelerate the growth of the testicles, scrotum, and then the penis.
Teenage years
The next period - adolescence - is also called puberty, or puberty. It continues in boys from 13 to 16 years old, in girls - from 12 to 15 years old. At this time, there is a further increase in growth rates - the puberty jump, which applies to all body sizes. The greatest increase in body length in girls occurs between 11 and 12 years, in body weight - between 12 and 13 years. In boys, an increase in length is observed between 13 and 14 years, and an increase in body weight between 14 and 15 years. The growth rate of body length is especially high in boys, as a result of which at the age of 13.5-14 they overtake girls in body length. Due to the increased activity of the hypothalamic-pituitary system, secondary sexual characteristics are formed. In girls, the development of the mammary glands continues, there is growth of hair on the pubis and in the armpits. The most clear indicator of puberty of the female body is the first menstruation.
In adolescence, there is an intensive puberty of boys. By the age of 13, their voice changes (mutates) and pubic hair appears, and at 14, hair appears in the armpits. At the age of 14-15, boys have their first wet dreams (involuntary eruptions of sperm).
In boys, compared with girls, the pubertal period is longer and the pubertal growth spurt is more pronounced.
adolescence
Adolescence lasts for boys from 18 to 21 years old, and for girls - from 17 to 20 years old. During this period, the growth process and the formation of the body basically end, and all the main dimensional features of the body reach the definitive (final) value.
In adolescence, the formation of the reproductive system and the maturation of the reproductive function are completed. The ovulatory cycles in a woman, the rhythm of testosterone secretion and the production of mature sperm in a man are finally established.
Mature, elderly, senile age
In adulthood, the shape and structure of the body change little. Between 30 and 50 years, body length remains constant, and then begins to decrease. In the elderly and senile age, gradual involutive changes in the body occur.
Individual differences in the process of growth and development
Individual differences in the process of growth and development can vary widely. The existence of individual fluctuations in the processes of growth and development served as the basis for the introduction of such a concept as biological age, or developmental age (as opposed to passport age).
The main criteria for biological age are:
1) skeletal maturity - (the order and timing of ossification of the skeleton);
2) dental maturity - (terms of eruption of milk and permanent teeth);
3) the degree of development of secondary sexual characteristics. For each of these biological age criteria - "external" (skin), "dental" and "bone" - rating scales and normative tables have been developed to determine the chronological (passport) age by morphological features.
Factors affecting individual development
Factors affecting individual development (ontogenesis) are divided into hereditary and environmental (influence of the external environment).
The degree of hereditary (genetic) influence is not the same at different stages of growth and development. The influence of hereditary factors on the total body size increases from the period of the newborn (tm) to the second childhood, with a subsequent weakening by the age of 12-15.
The influence of environmental factors on the processes of morphofunctional maturation of the body is clearly seen in the example of the timing of menarche (menstruation). Studies of growth processes in children and adolescents in various geographical areas have shown that climatic factors have almost no effect on growth and development, if living conditions are not extreme. Adaptation to extreme conditions causes such a profound restructuring of the functioning of the whole organism that it cannot but affect the growth processes.
Dimensions and proportions, body weight
Among the body sizes, total (from French total - whole) and partial (from Latin pars - part) are distinguished. Total (general) body dimensions are the main indicators of human physical development. These include body length and weight, as well as chest circumference. Partial (partial) dimensions of the body are terms of the total size and characterize the size of individual parts of the body.
Body sizes are determined during anthropometric surveys of various contingents of the population.
Most anthropometric indicators have significant individual fluctuations. Table 2 shows some average anthropometric indicators in postnatal ontogeny.
The proportions of the body depend on the age and gender of the person (Fig. 4). Body length and its age-related changes, as a rule, are individual. So, for example, differences in the body length of newborns during normal pregnancy are in the range of 49-54 cm. The largest increase in the body length of children is observed in the first year of life and averages 23.5 cm. In the period from 1 to 10 years, this indicator gradually decreases by an average of 10.5 - 5 cm per year. From the age of 9, sex differences in growth rate begin to appear. Body weight from the first days of life until about 25 years of age in most people gradually increases, and then remains unchanged.
Fig. 4 Changes in the proportions of body parts in the process of human growth.
KM - the middle line. The numbers on the right show the ratio of body parts in children and adults, the numbers below show the age.
table 2
Length, mass and body surface area in postiatal orthogenesis
Table 2
After the age of 60, body weight usually begins to gradually decrease, mainly as a result of atrophic changes in tissues and a decrease in their water content. The total body weight consists of a number of components: the mass of the skeleton, muscles, fatty tissue, internal organs and skin. In men, the average body weight is 52-75 kg, in women - 47-70 kg.
In the elderly and senile age, characteristic changes are observed not only in the size and weight of the body, but also in its structure; these changes are studied by the special science of gerontology (gerontos - old man). It should be emphasized that an active lifestyle, regular physical education slows down the aging process.
Acceleration
It should be noted that over the past 100-150 years there has been a noticeable acceleration in the somatic development and physiological maturation of children and adolescents - acceleration (from Latin acceleratio - acceleration). Another term for the same trend is "epochal shift". Acceleration is characterized by a complex set of interrelated morphological, physiological, and mental phenomena. To date, morphological indicators of acceleration have been determined.
Thus, the length of the body of children at birth over the past 100-150 years has increased by an average of 0.5-1 cm, and the weight - by 100-300 g. During this time, the mass of the placenta in the mother has also increased. There is also an earlier alignment of the ratios of chest and head girths (between the 2nd and 3rd month of life). Modern one-year-old children are 5 cm longer and 1.5-2 kg heavier than their peers in the 19th century.
The body length of preschool children over the past 100 years has increased by 10-12 cm, and for schoolchildren - by 10-15 cm.
In addition to an increase in body length and weight, acceleration is characterized by an increase in the size of individual parts of the body (segments of limbs, thickness of skin-fat folds, etc.). Thus, the increase in chest girth in relation to the increase in body length was small. The onset of puberty in modern adolescents occurs about two years earlier. The acceleration of development has also affected motor functions. Modern teenagers run faster, jump further from a place, pull themselves up on the crossbar (horizontal bar) more times.
Epochal shift (acceleration) affects all stages of human life, from birth to death. For example, the length of the body of adults also increases, but to a lesser extent than in children and adolescents. So, at the age of 20-25 years, the body length of men increased by an average of 8 cm.
Acceleration covers the entire body, affecting the size of the body, the growth of organs and bones, the maturation of the sex glands and the skeleton. In men, changes in the process of acceleration are more pronounced than in women.
Men and women are distinguished by sexual characteristics. These are primary signs (genital organs) and secondary (for example, the development of pubic hair, the development of the mammary glands, a change in voice, etc.), as well as body features, proportions of body parts.
The proportions of the human body are calculated as a percentage according to the measurement of the longitudinal and transverse dimensions between the boundary points set on various protrusions of the skeleton.
The harmony of body proportions is one of the criteria for assessing the state of human health. With disproportion in the structure of the body, one can think of a violation of growth processes and the causes that caused it (endocrine, chromosomal, etc.). Based on the calculation of body proportions in anatomy, three main types of human physique are distinguished: mesomorphic, brachymorphic, dolichomorphic. The mesomorphic body type (normosthenics) includes people anatomical features which are approaching the average parameters of the norm (taking into account age, gender, etc.). In people of the brachymorphic body type (hypersthenics), transverse dimensions predominate, muscles are well developed, they are not very tall. The heart is located transversely due to the high-standing diaphragm. In hypersthenics, the lungs are shorter and wider, the loops of the small intestine are located mainly horizontally. Persons of dolichomorphic body type (asthenics) are characterized by a predominance of longitudinal dimensions, have relatively longer limbs, poorly developed muscles and a thin layer of subcutaneous fat, and narrow bones. Their diaphragm is lower, so the lungs are longer, and the heart is located almost vertically. Table 3 shows the relative sizes of body parts in people of different body types.
Table 3
Conclusion
What can be the conclusion of the above?
Human growth is uneven. Each part of the body, each organ develops according to its own program. If we compare the growth and development of each of them with a long-distance runner, then it is not difficult to find that during this many years of "running" the leader of the competition is constantly changing. In the first month of embryonic development, the head is in the lead. In a two-month-old fetus, the head is larger than the body. This is understandable: the brain is located in the head, and it is the most important organ that coordinates and organizes the complex work of organs and systems. The development of the heart, blood vessels and liver also begins early.
In a newborn baby, the head reaches half of its final size. Up to 5-7 years of age, there is a rapid increase in body weight and length. At the same time, the arms, legs and torso grow alternately: first, the arms, then the legs, then the torso. The size of the head during this period increases slowly.
At primary school age from 7 to 10 years, growth is slower. If earlier arms and legs grew more quickly, now the torso becomes the leader. It grows evenly, so that the proportions of the body are not violated.
AT adolescence hands grow so intensively that the body does not have time to adapt to their new size, hence some clumsiness and sweeping movements. After that, the legs begin to grow. Only when they reach their final size does the torso join in the growth. First, it grows in height, and only then begins to grow in width. During this period, the physique of a person is finally formed.
If we compare the body parts of a newborn and an adult, it turns out that the size of the head has only doubled, the torso and arms have become three times larger, while the length of the legs has increased five times.
An important indicator of the development of the body is the appearance of menstruation in girls and wet dreams in boys, it indicates the onset of biological maturity.
Along with the growth of the body is its development. Human growth and development different people occur at different times, so anatomists, doctors, physiologists distinguish between calendar age and biological age. Calendar age is calculated from the date of birth, biological age reflects the degree of physical development of the subject. The last one is different for each person. It may happen that people who are at the same biological age may differ by 2-3 years on the calendar, and this is completely normal. Girls tend to develop faster.
Literature
1. Medical scientific and educational journal No. 28 [October 2005]. Section - Lectures. Title of the work - PERIODS OF CHILDHOOD. Author - P.D. Vaganov
2. Vygotsky L.S. Collected works in 6 volumes. Volume 4
3. Vygotsky L.S. article "Problems of age periodization of child development"
4. Obukhova L.F. textbook "Children's (age) psychology". Fundamental and clinical physiology / Ed.A.G. Kamkin and A.A. Kamensky. - M.: "Academy", 2004.
5. Schmidt R., Tews G. Human Physiology: Per. from English. - M.: Mir, 1996.
6. Dragomilov A.G., Mash R.D. Biology: Man. - 2nd ed., revised. - M.: Ventana-Graf, 2004.
7. Sapin. M.R., Bryksina Z.G. Anatomy and physiology of children and adolescents: Proc. allowance for students. ped. universities. - M.: Publishing center "Academy", 2002.
8. Chusov Yu.N. Human Physiology: Proc. allowance for ped. Schools (special No. 1910). - M.: Enlightenment, 1981.
9. Encyclopedia "Round the World"
10. "Rusmedservice"
11. Encyclopedia "Wikipedia"
Studying the topic: "The musculoskeletal system" is an excellent way and an occasion to develop a cognitive interest in the anatomy and physiology of the human body among children who are fond of sports. Especially such types of it as bodybuilding (athleticism), bodybuilding, power sports, athletics, etc.
Modern sport makes quite high demands on the physical fitness of athletes. Training loads in recent years have increased in almost all sports. Trainings and competitions are accompanied by emotional and physical overstrain, which often leads to various disorders in the body - from ordinary pain in the muscles to the development of serious immunodeficiency states.
An athlete who has achieved certain results in his sport, but who lacks just a little bit to win, begins to wonder: what to do? In addition, rumors are often circulated in his environment that "the leaders are using something." As a result, he is faced with a choice: whether or not to use approved pharmacological preparations or nutritional supplements to increase the effectiveness of the training process, or can he decide to use doping drugs? In any case, the choice of an athlete should be influenced by the information he receives about all the pros and cons of the drugs used, as well as the certain amount of knowledge he has acquired from the field of biology and medicine.
In any sport, strong or enduring muscles are indispensable, and for this you need proteins and carbohydrates, vitamins and minerals. On the market sports nutrition for the athlete, there are many nutritional supplements, and manufacturing companies advertise the miraculous power of their products. However, where big money is being made, the effect is likely to be exaggerated. An athlete is usually “bought” on advertising in the “confession of a champion” style, often the label and products have nothing in common, manufacturers and traders may incorrectly refer to the results of research by scientists, exaggerating the effectiveness of the product or giving false information about the dosage of its components. The name of the manufacturer gives, of course, certain guarantees of quality, but this does not solve all problems.
In this article, we will try to describe the main components of balanced composite formulations that exist on the sports nutrition market and characterize their effect on body functions and performance. But you should start with the physiology of muscles and the age characteristics of the body.
I. Age features of the development of the organism
The formation of the human body continues after birth and ends by the age of 22-25. During periods of growth and development of the body, the mass and surface of the body increase, which is due to the development of tissues, organs and individual parts of the body. At the same time, the functions of organs and systems develop. Each period is characterized by its own characteristics. According to the scheme adopted at the VII All-Union Conference on Problems of Age Morphology, Physiology and Biochemistry (1965), several periods of human development are distinguished (Table 1).
Table 1. Age periods of ontogenetic development
Main title |
Other names |
Age |
Intrauterine development (antenatal, prenatal ontogeny) |
||
Embryonic period |
embryo development |
|
fetal period |
Fetal development |
|
Extrauterine development (postnatal ontogenesis) |
||
neonatal period, or |
neonatal period |
From birth to 4 weeks |
Early childhood |
toddler age |
|
First childhood |
preschool age |
|
Second childhood |
Adolescence, primary school age |
Boys 8-12 years old, |
Adolescence |
puberty, |
Boys 13-16 years old |
adolescence |
||
Mature age - I period |
Maturity | Men aged 22–38, |
Mature age - II period |
Maturity | Men 36–60 years old, |
Elderly age |
||
Senile age |
||
centenarians |
90 years and older |
|
This scheme takes into account not only the morphophysiological characteristics of a person, but also social factors focused on the system of children's institutions associated with the education of children and the retirement of an adult.
The growth and development of the organism include the processes of development of an adult individual from a fertilized egg. Growth is an increase in the size of the body and its parts; the term "development" means various functional changes that occur as a result of the growth and improvement of the structure of organs. An increase in the mass and surface of the body is due to the development of tissues (cells and intercellular substance), organs and individual parts of the body. At the same time, the functions of organs and systems develop. Growth and development is not just an increase in body weight, but also the formation of various functions of the body. At this time, a significant part of the physiological parameters approaches the level characteristic of an adult. For example, the activity of digestive enzymes increases, the sense organs and the nervous system improve, defense mechanisms against infection develop, etc.
The growth of the organism, its organs and systems from the moment of birth to the onset of maturity proceeds heterochronously (from the Greek. heteros- another, chronos– time), i.e. unevenly: periods of acceleration of growth alternate with its slowdown. Those organs or organ systems that are more necessary for the existence of the organism at this stage of development grow and develop faster. So, at the time of birth, a newborn has a nutrition system with liquid food (milk). At the same time, the development of functional systems in which there is no need at a given moment of life is delayed: for example, the development of a functional system of nutrition with solid food. Thus, in the process of growth and development, physiological functions adapt to the characteristics of the existence of the organism, i.e. its individual adaptation to environmental conditions occurs.
Achieving maturity is a long process. Among the higher mammals, a person has the longest childhood, during which the development of the brain and the formation of mental functions - speech, thinking, consciousness. For their normal development, communication with other people is necessary. The development of a child is influenced by nutrition, care, climatic and geographical factors, family, school, yard in which he lives, objects surrounding him, people (children and adults), life events, etc.
The phenomenon of heterosis also has a positive effect on the growth and development of the organism (from the Greek. heteroioses- transformation), or "hybrid power", which manifests itself in a greater body length, accelerated development, greater life expectancy and the duration of the reproductive period, in greater resistance to infections. It is known that heterosis is especially common in people whose parents belong to different nationalities and were geographically separated before marriage.
In related marriages, the opposite phenomenon often occurs: children are poorly developed physically, susceptible to infectious diseases, hereditary disorders often appear, and a short life expectancy is characteristic.
Taking into account the possibility of developmental delay or often occurring, especially in recent decades, advanced development, it is necessary to determine and take into account the biological age of a person. Biological age is called age of development. It reflects the growth, development, maturation, aging of the organism and is determined by its structural, functional and adaptive features.
Biological age can be determined by a number of indicators of morphological maturity:
- the degree of development of secondary sexual characteristics;
- skeletal maturity (the order and timing of ossification of the skeleton);
- dental maturity (terms of eruption of milk and molars).
When assessing biological age, physiological and biochemical parameters (levels of basic and other types of metabolism, characteristics of the cardiovascular, respiratory, neuroendocrine and other systems) and the level of mental development of the individual are also taken into account.
Indicators of physical development
The indicators of physical development include the length and weight of the body, girths (circumferences) of the head and chest. They are called anthropometric indicators. Each age stage is characterized by their specific value.
Throughout the entire period of intrauterine development, as well as childhood, the development of the body is uneven. The upper part of the body is ahead of the lower in growth and development, and the central parts (head and torso) develop faster than the peripheral parts (limbs). During puberty, the limbs grow faster than the head and trunk (Fig. 1).
Rice. 1. The physical development of the child goes in two directions: from the head to the lower limbs - the upper parts of the body develop earlier than the lower ones; areas of the body located closer to the center develop earlier than peripheral areas
Age-related changes in body length. The growth and development of a person is most intensive in the first year of life. Average length the body of newborn girls is 52.2 cm, boys - 52.6 cm; in the first year of life, it increases by 25 cm. In the second year of life, it increases by 10–15 cm, in the third year of life, by 8 cm. Then, up to 6 years, the annual increase in body length is 4–5 cm.
An increase in body length at the age of 6–7 years by 8–10 cm received the name half-height(or I growth) jump. During puberty (11-14 years) occurs growth (II growth), or pubertal, jump. The length of the body at the same time increases during the first year immediately by 11–12 cm, and in the last year by 6–7 cm. During growth, the proportions of the body change, which is clearly seen in the ratio of the sizes of the head and torso. In a newborn, this ratio is 1: 4, while in an adult it is 1: 8 (Fig. 2).
Rice. 2. Changes in body proportions with age in girls and boys and growth spurts in girls and boys
The increase in body length and weight during each year occurs cyclically. Thus, the increase in body length occurs most intensively in the summer months, while the increase in weight mainly occurs in the autumn period.
Age-related changes in body weight. The body weight of newborn girls is on average 3.4 kg, boys - 3.5 kg. Immediately after birth, the weight of a newborn decreases by about 200 g, and then begins to increase rapidly: in the first month of life, it increases by 600 g, in the second and third - by 800 g, and in each subsequent (up to one year) monthly increase by 50 g less than the previous month. The initial body weight of the child by 4-4.5 months. approximately doubles, and by the year triples and is 10.3 kg for boys and 9.8 kg for girls. In the first year of life, the increase is 6–7 kg, in the second year it is 2–3 kg, in the next three years it is 1.5–2.0 kg, and in the 6th and 7th years of life it increases again. The peak rate of body weight gain in girls occurs at 13 years of age (5.0–5.5 kg per year) and in boys at 15 years of age (5.5–6.5 kg per year).
The circumference (girth) of the chest in a newborn is 34-36 cm. For the first year, the increase is 11-13 cm, for the second - 3-3.5, for the third - 2-2.5 cm. By 6 years, the circumference reaches 58 cm (56.9 cm for girls and 59.1 cm for boys). The maximum increase in this indicator falls on the puberty period, and throughout the entire period, girls lag behind boys in the growth of the chest circumference.
Age-related changes in body proportions. In a newborn, the length of the head is 1/4 of the total body length, in a 2-year-old - 1/5, in a 6-year-old - 1/6, and in an adult - 1/8. In newborns, the length of the upper and lower extremities approximately the same and is 1/3 of the body length. By the age of 7, the legs lengthen from 18 cm to 62.0–63.0 cm. By the age of 7, the length of the arms increases to 52.0–54.0 cm. The length of the body changes much less: by the age of 8, it becomes equal to 36.9 cm .
Over the entire period of development, the length of the lower limbs increases 5 times, the arms - 4 times, and the trunk - 3 times.
Age-related changes in indicators of physical development of boys and girls. Changes in indicators of physical development that occur in different periods of growth of the body are not the same in intensity. The greatest increase in all indicators is noted in the first year of a child's life. In girls, the maximum changes in most indicators of physical development are noted in earlier periods than in boys. So, in girls they are registered at 7, 9, 11 and 13 years old, in boys at 8, 10 and 12 years old. The growth rate increases especially intensively during puberty (for girls - at 11-13 years old, and for boys - at 12-14 years old). The growth of the body in length ends in girls at 16-17 years old, in boys at 18-19 years old.
To be continued
In humans, germ cells are formed in special organs - the gonads (in the ovaries in women and in the testes in men).
The female sex cell - the egg - is haploid, large, round, immobile.
In the process of embryogenesis, about 400 thousand primary germ cells are laid in the female body, their reproduction stops at the time of birth and they turn into first-order oocytes. Each oocyte is surrounded by epithelial cells and forms an egg vesicle. (follicle). Only a small part of the oocytes of a woman's ovary matures and gives rise to eggs. This process begins at the age of 12-13 and ends at the age of 50-53. As the oocyte grows, the follicular epithelium grows, a cavity with liquid appears in it - a Graaffian bubble. The rupture of the mature follicle and the release of the egg from the ovary is called ovulation. It occurs on average once every 29 days. Usually one egg cell matures alternately in one or the other ovary. The formation of an oocyte of the second order occurs in the fallopian tube. Here, the egg is fertilized by the sperm.
The male sex cell - the spermatozoon - is formed in the testes during spermatogenesis. The nucleus with a haploid set of chromosomes is located in the head of the spermatozoon. The secretions of the pituitary gland, ovaries, testes and other endocrine glands influence the formation of germ cells.
During fertilization, the egg and sperm fuse to form a diploid zygote.
The process of crushing the zygote takes place within 3-4 days, when the zygote moves along the fallopian tube to the uterus. The resulting blastomeres form morulu, and then a single-layer embryo - blastula; a cavity is distinguished in it - blastocoel and the wall blastoderm. As a result of crushing of superficially located blastomeres, a shell is formed that participates in the nutrition of the embryo - trophoblast, and the central blastomeres form embryoblast, an embryo develops from it. Consequently, the formed germinal vesicle includes the trophoblast surrounding the cavity with liquid, and the embryoblast - the germinal nodule lying in the cavity.
In the second week, gastrulation occurs and the trophoblast sinks into the wall of the uterus: in a seven-day-old embryo, the ectoderm forms an amniotic vesicle. From the embryo, which has the shape of a shield, cells are evicted into the cavity of the blastula and fill it. Together with the trophoblast, these cells form chorion. Subsequently, embryonic membranes develop - amnion and yolk sac. The yolk sac functions as a hematopoietic organ. The derivative of the yolk sac is the primary bladder - allantois. Subsequently, the amnion overgrows the embryo and forms an aqueous shell of the fetus, protecting it from damage and creating a homogeneous liquid medium here. The part of the chorion facing the wall of the uterus has villi, grows into its tissues and forms a child's place, or placenta, through which the fetus feeds. The blood vessels of the fetus and mother intertwine in the placenta. Nutrients, oxygen are absorbed from the blood of the mother's body and decay products are released.
After the birth of a child, his body grows and develops up to 20-23 years. The development process is divided into four periods: 1) chest, during which the child eats a highly valuable product - mother's milk, which contains all the necessary substances for development; 2) nursery - from one to three years; 3) preschool - three to seven years; four) school - from seven to 17 years - the period of formation of the basic physical, mental and moral qualities of a person.
| Development periods | Structural features | Physiological features | |
| Embryonic | Zygote | fertilized ovum. It carries a diploid set of chromosomes: one set is from the egg, the other is from the sperm. Each pair of chromium is homologous | Fertilization occurs in the oviduct, where the sperm enters as a result of sexual intercourse. The oviduct connects the ovary (female) gonad) with the uterus, where the further development of the embryo occurs |
| Blastula | The first stage of embryonic development. Represents a single-layered multicellular vesicle | Formed in the oviduct as a result of crushing (mitotic division without subsequent cell growth) of the zygote | |
| gastrula | The second stage of embryonic development. having two germ layers: ectoderm and endoderm; then the mesoderm appears. All organ systems are formed from these three leaves. | The blastula moves into the uterus and is introduced into its wall, after which the gastrula is formed from it. On the side of the gastrula where it is in contact with the wall of the uterus, embryonic membranes (placenta, bladder) are formed, on the opposite side - the embryo | |
| Fetus | Passes through all stages of embryonic development, similar to the stages of development of vertebrates; the bladder is filled with a watery liquid, the placenta with its villi is introduced into the walls of the uterus; The umbilical cord connects the placenta to the fetus. The fetus has one circulation | Features of embryonic development (gill slits, tail), as well as hairline indicate common origin all chordates and confirm the position of the biogenetic law. By 9 months, the fetus completely acquires all the features of the human body. Developing in the aquatic environment, it is protected from impacts and moves freely. It receives oxygen through the placenta through the umbilical vein. and nutrients, through the umbilical artery, venous blood returns to the mother's body |
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| Postpartum | Newborn | The newborn has a disproportionate body structure - a very large head and short legs and arms. The bones of the skull are not fused, between them there are skin films - fontanelles; pelvic bones not fused, spine without bends | Non-fused bones go behind each other, reduce the volume of the head and body, which helps the birth of a child. When the umbilical cord is ligated, an excess of CO2 is created in the blood, which has a humoral effect on the respiratory center of the medulla oblongata and, as a result, the first reflex movement occurs - a cry and a breath. Then the next innate reflex appears - sucking |
| Thoracic (up to 12 months) | The child masters the movements - raises his head, lies on his stomach, gets up - this contributes to the formation of curves of the spine: cervical, thoracic, lumbar. Milk teeth appear | Muscles are formed in the child, movements become diverse, the skeleton is strengthened, and there is a need to walk. In the first period - feeding with breast milk containing all the necessary nutrients, then supplementing with food containing vitamins. Higher nervous activity- First words spoken | |
| Nursery (1-3 years) | The proportions of the body change in the child: the head becomes relatively smaller, the limbs lengthen. The brain develops more pronounced furrows and convolutions | An independent organism, switches to eating regular food. The fontanelles in the skull are overgrown. Expressed emotions, articulate speech. Requires constant medical supervision and care for a fragile body | |
| Preschool (3-7 years old) | Milk teeth are replaced by permanent ones. Differences in the cells of the cerebral cortex are clearly revealed | coordinated movements. Speech associated with thinking. Conditioned reflex centers of speech and writing are formed | |
| School (7-17 years old) | Enhanced development of the musculoskeletal system, enhanced growth of the body, which ends by the age of 20-25. After 10 years, the pelvic bones fuse. In accordance with the structural features of the body, children, adolescents and youthful periods of development are distinguished. | At the age of 13-15 years, the restructuring of the body begins in connection with puberty, the activity and structure of the cerebral cortex, the functions of the endocrine glands change. This causes psychological (the predominance of excitation over inhibition), physiological (menstrual cycle) and physical changes in the body. Secondary sexual characteristics appear: in girls, the shape of the body, the timbre of the voice change; in boys - body proportions, physical development intensifies, voice breaks, facial hair appears. However, complete formation ends by the age of 20-25. | |
