The biological foundations of sex. Müllerian excretory duct. Male fetus development Male and female fetal development

Pregnancy Is a physiological process in which a new organism develops in the uterus, which has arisen as a result of fertilization. Pregnancy lasts an average of 40 weeks (10 obstetric months).

In the intrauterine development of a child, two periods are distinguished.:

1. Embryonic (up to 8 weeks of pregnancy inclusive). At this time, the embryo is called an embryo and takes on the characteristics of a person;
2. Fetal (from 9 weeks to the very birth). At this time, the embryo is called the fetus.

The growth of the child, the formation of his organs and systems, proceeds naturally in different periods of intrauterine development, which is subordinated to the genetic code embedded in the germ cells and fixed in the process of human evolution.

Embryo development in the first obstetric month (1-4 weeks)

First week (1-7 days)

Pregnancy starts from the moment fertilization - the fusion of a mature male cell (sperm) and a female egg. This process usually takes place in the ampulla of the fallopian tube. After a few hours, the fertilized egg begins to divide exponentially and descends through the fallopian tube into the uterine cavity (this path takes up to five days).

As a result of division a multicellular organism is obtained, which looks like a blackberry (in Latin "morus"), which is why the embryo at this stage is called morula... Approximately on the 7th day, morula is introduced into the wall of the uterus (implantation). The villi of the outer cells of the embryo are connected to the blood vessels of the uterus, subsequently the placenta is formed from them. Other outer cells of the morula give rise to the development of the umbilical cord and membranes. After a while, various tissues and organs of the fetus will develop from the internal cells.

Information At the time of implantation, a woman may have slight bleeding from the genital tract. Such discharge is physiological and does not require treatment.

Second week (8-14 days)

The outer cells of the morula grow tightly into the lining of the uterus. In the embryo the formation of the umbilical cord, placenta begins, and neural tube, from which the fetal nervous system subsequently develops.

Third week (15-21 days)

The third week of pregnancy is a difficult and important period.... At that time important organs and systems begin to form fetus: the rudiments of the respiratory, digestive, circulatory, nervous and excretory systems appear. In the place where the fetal head will soon appear, a wide plate is formed, which will give rise to the brain. On day 21, the child's heart begins to beat.

Fourth week (22-28 days)

this week the laying of fetal organs continues... The rudiments of the intestines, liver, kidneys and lungs are already present. The heart starts to work more intensively and pumps more blood through the circulatory system.

From the beginning of the fourth week in the embryo body folds appearand appears spinal rudiment (chord).

By the 25th day ends neural tube formation.

By the end of the week (approximately 27-28 days) the muscular system, the spine are formed, which divides the embryo into two symmetrical halves, and the upper and lower limbs.

During this period begins formation of pits on the head, which will later become the eyes of the fetus.

Embryo development in the second obstetric month (5-8 weeks)

Fifth week (29-35 days)

During this period, the embryo weighs about 0.4 grams, length 1.5-2.5 mm.

The formation of the following organs and systems begins:

1. Digestive system: liver and pancreas;
2. Respiratory system: larynx, trachea, lungs;
3. Circulatory system;
4. Reproductive system: precursors of germ cells are formed;
5. Sense organs: The formation of the eyes and inner ear continues;
6. Nervous system: The formation of brain regions begins.

At that time a subtle umbilical cord appears... The formation of limbs continues, the first rudiments of nails appear.

On the face the upper lip and nasal cavities are formed.

Sixth week (36-42 days)

Length embryo during this period is about 4-5 mm.

The sixth week begins placenta formation... At this time, it is just beginning to function, blood circulation between it and the embryo has not yet been formed.

Continues formation of the brain and its divisions... At the sixth week, when performing an encephalogram, it is already possible to record signals from the fetal brain.

Begins the formation of facial muscles... The eyes of the fetus are already more pronounced and uncovered by the eyelids, which are just beginning to form.

In this period, begin change the upper limbs: they lengthen and the rudiments of the hands and fingers appear. The lower limbs remain in their infancy for now.

Changes of important organs occur:

1. Heart... The division into chambers is completed: ventricles and atria;
2. Urinary system... Primary kidneys have formed, the development of the ureters begins;
3. Digestive system... The formation of the sections of the gastrointestinal tract begins: the stomach, small and large intestines. The liver and pancreas by this period practically completed their development;

Seventh week (43-49 days)

The seventh week is significant in that the final the formation of the umbilical cord is completed and the uteroplacental blood circulation is established. Now respiration and nutrition of the fetus will be carried out due to the circulation of blood through the vessels of the umbilical cord and placenta.

The embryo is still bent in an arcuate manner, there is a small tail on the pelvic part of the body. The size of the head is not less than the entire half of the embryo. The length from the crown to the sacrum grows by the end of the week up to 13-15 mm.

Continues upper limb development... The fingers are visible quite clearly, but their separation has not yet occurred. The child begins to perform spontaneous hand movements in response to stimuli.

Okay eyes are formed, already covered with eyelids, which protect them from drying out. The child can open his mouth.

The nasal fold and nose are laid, two paired elevations are formed on the sides of the head, from which they will begin to develop auricles.

Intense development of the brain and its departments.

Eighth week (50-56 days)

The body of the embryo begins to straighten lengthfrom the crown to the coccyx is 15 mm at the beginning of the week and 20-21 mm at 56 days.

Continues formation of important organs and systems: Digestive system, heart, lungs, brain, urinary system, reproductive system (boys develop testicles). The organs of hearing develop.

By the end of the eighth week a child's face becomes familiar to a person: well-defined eyes, covered with eyelids, nose, ears, lip formation ends.

Intensive growth of the head, upper and lower horses is notedossification of the long bones of the arms and legs and the skull develops. The fingers are clearly visible, the skin membrane is no longer between them.

Additionally The eighth week ends with the embryonic period of development and the fetal period begins. The embryo from this time is called the fetus.

Fetal development in the third obstetric month (9-12 weeks)

Ninth week (57-63 days)

At the beginning of the ninth week coccygeal-parietal size the fetus is about 22 mm, by the end of the week - 31 mm.

Is happening improvement of blood vessels of the placenta, which improves uteroplacental blood flow.

The development of the musculoskeletal system continues... The process of ossification begins, the joints of the toes and hands are formed. The fetus begins to make active movements, can squeeze the fingers. The head is lowered, the chin is closely pressed to the chest.

Changes occur in the cardiovascular system... The heart beats up to 150 beats per minute and pumps blood through its own blood vessels. The composition of blood is still very different from that of an adult: it consists only of red blood cells.

Continues further growth and development of the brain, structures of the cerebellum are formed.

The organs of the endocrine system are intensively developingin particular, the adrenal glands, which produce important hormones.

Cartilage tissue is being improved: auricles, laryngeal cartilages, vocal cords are being formed.

Tenth week (64-70 days)

By the end of the tenth week fruit length from the coccyx to the crown is 35-40 mm.

The buttocks begin to develop, the previously existing tail disappears. The fetus is in the uterus in a fairly free position in a bent state.

The development of the nervous system continues... Now the fetus performs not only chaotic movements, but also reflex movements in response to a stimulus. When accidentally touching the walls of the uterus, the child makes movements in response: turns his head, bends or unbends his arms and legs, pushes to the side. The size of the fetus is still very small, and the woman cannot yet feel these movements.

A sucking reflex is formed, the child begins to reflex lips movements.

Diaphragm development ends, which will take an active part in breathing.

Eleventh week (71-77 days)

By the end of this week coccygeal-parietal size the fetus increases to 4-5 cm.

The fetal body remains disproportionate: small torso, large head sizes, long arms and short legs, bent at all joints and pressed to the stomach.

The placenta has already reached sufficient development and copes with its functions: it provides oxygen and nutrients to the fetus and removes carbon dioxide and metabolic products.

Further formation of fetal eyes occurs: at this time, the iris develops, which will further determine the color of the eyes. The eyes are well developed, half-closed for centuries or wide open.

Twelfth week (78-84 days)

Coccygeal-parietal size the fetus is 50-60 mm.

Goes distinctly the development of the genitals in a female or male pattern.

Is happening further improvement of the digestive system.The intestines are extended in length and fit in loops, like in an adult. Its periodic contractions begins - peristalsis. The fetus begins to swallow, swallowing amniotic fluid.

The development and improvement of the fetal nervous system continues... The brain is small in size, but it exactly repeats all the structures of the adult brain. The large hemispheres and other sections are well developed. Reflex movements are improved: the fetus can clench and unclench the fingers into a fist, grabs the thumb and actively sucks it.

In the blood of the fetus not only erythrocytes are already present, but the production of white blood cells - leukocytes - begins.

At this time, the child single respiratory movements begin to be recorded. Before birth, the fetus cannot breathe, its lungs do not function, but it makes rhythmic movements of the chest, imitating breathing.

By the end of the week, the fetus eyebrows and eyelashes appear, the neck is clearly visible.

Fetal development in the fourth obstetric month (13-16 weeks)

13 week (85-91 days)

Coccygeal-parietal size by the end of the week is 70-75 mm. The proportions of the body begin to change: the upper and lower limbs and the trunk are lengthened, the dimensions of the head are no longer so large in relation to the body.

The improvement of the digestive and nervous systems continues. The embryos of milk teeth begin to appear under the upper and lower jaws.

The face is fully formed, the ears, nose and eyes are clearly visible (completely closed by the eyelids).

14 week (92-98 days)

Coccygeal-parietal size by the end of the fourteenth week increases up to 8-9 cm... The proportions of the body continue to change to more familiar proportions. The forehead and nose are well defined on the face, cheeks and chin appear. The first hairs appear on the head (very thin and colorless). The surface of the body is covered with vellus hairs, which retain the lubrication of the skin and thereby perform protective functions.

Improves the musculoskeletal system of the fetus... Bones become stronger. Motor activity is enhanced: the fetus can roll over, bend, make swimming movements.

The development of the kidneys, bladder and ureters ends... The kidneys begin to secrete urine, which mixes with the amniotic fluid.

: Pancreatic cells start to work, producing insulin, and pituitary cells.

Changes in the genitals appear... In boys, the prostate gland is formed, in girls, the ovaries migrate into the pelvic cavity. At the fourteenth week, with a good sensitive ultrasound machine, it is already possible to determine the sex of the child.

Fifteenth week (99-105 days)

Coccygeal-parietal size of the fetus is about 10 cm, fetal weight - 70-75 grams.The head is still quite large, but the growth of arms, legs and trunk begins to outstrip it.

The circulatory system is improved... In a child in the fourth month, it is already possible to determine the blood group and Rh factor. Blood vessels (veins, arteries, capillaries) grow in length, their walls are strengthened.

The production of original feces (meconium) begins. This is due to the ingestion of amniotic fluid, which enters the stomach, then into the intestines and fills it.

Fingers and toes fully formed, an individual pattern appears on them.

Sixteenth week (106-112 days)

The weight of the fetus increases to 100 grams, the coccygeal-parietal size - up to 12 cm.

By the end of the sixteenth week, the fetus is already fully formed, he has all the organs and systems. The kidneys are actively working, every hour a small amount of urine is released into the amniotic fluid.

The fetal skin is very thin, subcutaneous adipose tissue is practically absent, therefore blood vessels are visible through the skin. The skin looks bright red, covered with vellus hairs and grease. Eyebrows and eyelashes are well defined. Nails are formed, but they cover only the edge of the nail phalanx.

Mimic muscles are formed, and the fetus begins to "grimace": there is a frown, a semblance of a smile.

Fetal development in the fifth obstetric month (17-20 weeks)

Seventeenth week (113-119 days)

The weight of the fetus is 120-150 grams, the coccygeal-parietal size is 14-15 cm.

The skin remains very thin, but subcutaneous fatty tissue begins to develop under it. The development of milk teeth, which are covered with dentin, continues. Under them, embryos of permanent teeth begin to form.

There is a reaction to sound stimuli... From this week on, we can say for sure that the child began to hear. When strong sharp sounds appear, the fetus begins to actively move.

Fetal position changes... The head is up and is almost vertical. The arms are bent at the elbow joints, the fingers are clenched into a fist almost all the time. From time to time, the baby begins to suck on the thumb.

The heartbeat becomes distinct... From this time on, the doctor can listen to him with a stethoscope.

Eighteenth week (120-126 days)

The child's weight is about 200 grams, the length is up to 20 cm.

The formation of the sleep and wakefulness regime begins... Most of the time, the fetus sleeps, the movements stop at this time.

At this time, a woman may already begin to feel the movement of the child,especially with repeated pregnancies. The first movements are felt as gentle jolts. A woman can feel more active movements during excitement, stress, which affects the emotional state of the child. At this time, the norm is about ten episodes of fetal movement per day.

Nineteenth week (127-133 days)

The child's weight increases to 250-300 grams, body length - up to 22-23 cm.The proportions of the body change: the head lags behind in growth from the body, arms and legs begin to lengthen.

Movements become more frequent and palpable... They can be felt not only by the woman herself, but also by other people, putting their hand to the stomach. Primary pregnant women at this time can only begin to feel movements.

The endocrine system is improving: the pancreas, pituitary gland, adrenal glands, sex glands, thyroid and parathyroid glands are actively functioning.

The composition of the blood has changed: in addition to erythrocytes and leukocytes, there are monocytes and lymphocytes in the blood. The spleen begins to take part in hematopoiesis.

Twentieth week (134-140 days)

Body length increases to 23-25 \u200b\u200bcm, weight - up to 340 grams.

The fetal skin is still thin, covered with protective lubricant and vellus hairs that can persist until the very birth. Subcutaneous fatty tissue develops intensively.

Well formed eyes, at twenty weeks, the blink reflex begins to appear.

Improved movement coordination: baby confidently brings a finger to his mouth and begins to suck. Facial expressions are expressed: the fetus can close its eyes, smile, frown.

By this week, all women are already feeling the movement., regardless of the number of pregnancies. The activity of movements changes during the day. When stimuli appear (loud sounds, stuffy room), the child begins to move very violently and actively.

Fetal development in the sixth obstetric month (21-24 weeks)

Twenty-first week (141-147 days)

Body weight grows up to 380 grams, fetal length - up to 27 cm.

The subcutaneous tissue layer increases... The skin of the fetus is wrinkled, with many folds.

Fetal movements are becoming more active and tangible. The fetus moves freely in the uterine cavity: lies downside down or buttocks, across the uterus. Can pull the umbilical cord, push off with hands and feet from the walls of the uterus.

Sleep and wakefulness changes... Now the fetus spends less time in sleep (16-20 hours).

Twenty-second week (148-154 days)

At 22 weeks, the size of the fetus increases to 28 cm, weight - up to 450-500 grams. The dimensions of the head become proportional to the body and limbs. The legs are almost always bent.

The fetal spine is fully formed: it has all the vertebrae, ligaments and joints. The process of strengthening bones continues.

Improves the nervous system of the fetus: the brain already contains all the nerve cells (neurons) and has a mass of about 100 grams. The child begins to take an interest in his body: he feels his face, arms, legs, tilts his head, brings his fingers to his mouth.

The size of the heart increases significantly, the functional capabilities of the cardiovascular system are improved.

Twenty-third week (155-161 days)

The body length of the fetus is 28-30 cm, weight is about 500 grams... Pigment begins to synthesize in the skin, resulting in the skin acquiring a bright red color. The subcutaneous fat is still quite thin, as a result, the child looks very thin and wrinkled. The lubricant covers the entire skin, and is more abundant in the folds of the body (elbow, axillary, inguinal, and other folds).

The development of internal genital organs continues: in boys - the scrotum, in girls - the ovaries.

Respiratory rate increases up to 50-60 times per minute.

Swallowing reflex is still well developed: the child constantly swallows amniotic fluid with particles of protective skin lubricant. The liquid part of the amniotic fluid is absorbed into the bloodstream, a thick green-black substance (meconium) remains in the intestine. Normally, the intestines should not be emptied before the baby is born. Sometimes the swallowing of water causes hiccups in the fetus, the woman can feel it in the form of rhythmic movements for several minutes.

Twenty-fourth week (162-168 days)

By the end of this week, the weight of the fetus increases to 600 grams, body length - up to 30-32 cm.

The movements become more powerful and clear... The fetus takes up almost all the place in the uterus, but it can still change position and turn over. Muscles are growing strongly.

By the end of the sixth month, the child has well-developed sense organs.Vision begins to function. If a bright light hits a woman's belly, the fetus begins to turn away, tightly squeezes the eyelids. Hearing is well developed. The fetus detects pleasant and unpleasant sounds for itself and reacts to them in different ways. With pleasant sounds, the child behaves calmly, his movements become calm and measured. With unpleasant sounds, it begins to freeze or, conversely, moves very actively.

An emotional bond is established between mother and child... If a woman experiences negative emotions (fear, anxiety, melancholy), the child begins to experience similar feelings.

Fetal development in the seventh obstetric month (25-28 weeks)

Twenty-fifth week (169-175 days)

The length of the fetus is 30-34 cm, body weight increases to 650-700 grams. The skin becomes elastic, the number and severity of folds decreases due to the accumulation of subcutaneous fatty tissue. The skin remains thin with many capillaries giving it a red coloration.

The face looks familiar to humans: well-defined eyes, eyelids, eyebrows, eyelashes, cheeks, auricles. The cartilage of the ears is still thin and soft, their curves and curls are not fully formed.

Bone marrow develops intensively, which takes on a major role in hematopoiesis. The strengthening of the bones of the fetus continues.

Important processes occur in lung maturation: small elements of lung tissue (alveoli) are formed. Before the baby is born, they are without air and resemble deflated balls, which unfold only after the first cry of the newborn. From the 25th week, the alveoli begin to produce a special substance (surfactant), which is necessary to maintain their shape.

Twenty-sixth week (176-182 days)

Fruit length is about 35 cm, weight increases to 750-760 grams.The growth of muscle tissue and subcutaneous fat continues. Bones are strengthened and the development of permanent teeth continues.

The formation of genitals continues... In boys, the testicles begin to descend into the scrotum (the process lasts 3-4 weeks). In girls, the formation of the external genital organs and the vagina is completed.

The senses are improved... The child develops a sense of odors (sense of smell).

Twenty-seventh week (183-189 days)

Weight increases to 850 grams, body length - up to 37 cm.

The organs of the endocrine system are actively functioningparticularly the pancreas, pituitary and thyroid glands.

The fetus is active enough, makes various movements freely inside the uterus.

From the twenty-seventh week of the child individual metabolism begins to form.

Twenty-eighth week (190-196 days)

The child's weight increases to 950 grams, body length - 38 cm.

By this age the fetus becomes practically viable... In the absence of organ pathology, a child with good care and treatment can survive.

Subcutaneous fat continues to accumulate... The skin is still red, vellus hair begins to gradually fall out, remaining only on the back and shoulders. Eyebrows, eyelashes, hair on the head become darker. The child begins to open his eyes frequently. The cartilage of the nose and ears remains soft. The nails have not yet reached the edge of the nail phalanx.

This week starts over actively functioning one of the cerebral hemispheres. If the right hemisphere becomes active, then the child becomes left-handed, if the left, then right-handedness develops.

Fetal development in the eighth month (29-32 weeks)

Twenty-ninth week (197-203 days)

The weight of the fetus is about 1200 grams, the growth increases to 39 cm.

The child has grown up enough and takes up almost all the place in the uterus. Movements become less chaotic. Movements are manifested in the form of periodic jolts with legs and arms. The fetus begins to occupy a definite position in the uterus: with the head or buttocks down.

All organ systems continue to improve... The kidneys excrete up to 500 ml of urine per day. The load of the cardiovascular system increases. Fetal circulation is still significantly different from that of a newborn.

Thirty week (204-210 days)

Body weight increases to 1300-1350 grams, growth remains about the same - about 38-39 cm.

Subcutaneous fatty tissue constantly accumulates,skin folds are straightened. The child adapts to the lack of space and takes a certain position: folds, arms and legs crossed. The skin is still brightly colored, the amount of lubricant and vellus hair is reduced.

Alveoli development and surfactant production continues... The lungs prepare for the birth of the baby and the beginning of breathing.

The development of the head brain, the number of convolutions and the area of \u200b\u200bthe cortex increases.

Thirty-first week (211-217 days)

The child's weight is about 1500-1700 grams, the height increases to 40 cm.

The child's sleep and wakefulness patterns change... Sleep still takes a long time, at this time there is no fetal motor activity. During wakefulness, the child actively moves and pushes.

Eyes fully formed... During sleep, the child closes his eyes, while awake, the eyes are open, and occasionally the child blinks. The color of the iris in all children is the same (blue), then after birth it begins to change. The fetus reacts to bright light by constricting or dilating the pupil.

The size of the brain increases... Now its volume is about 25% of the brain volume of an adult.

Thirty-second week (218-224 days)

The child is about 42 cm tall and weighs 1700-1800 grams.

The accumulation of subcutaneous fat continues, in this connection, the skin becomes lighter, there are practically no folds left on it.

Internal organs are improved: the organs of the endocrine system intensively secrete hormones, surfactant accumulates in the lungs.

The fetus produces a special hormone, which promotes the formation of estrogen in the mother's body, as a result, the mammary glands begin to prepare for milk production.

Fetal development in the ninth month (33-36 weeks)

Thirty third week (225-231 days)

The weight of the fetus increases to 1900-2000 grams, the growth is about 43-44 cm.

The skin becomes lighter and smoother, the layer of adipose tissue increases. Fluffy hair is increasingly wiped away, the layer of protective lubricant, on the contrary, increases. Nails grow to the edge of the nail phalanx.

The child becomes more and more cramped in the uterine cavity, so his movements become more rare, but strong. The position of the fetus is fixed (with the head or buttocks down), the probability that the child will turn over after this period is extremely small.

The work of internal organs is being improved.: the weight of the heart increases, the formation of alveoli is almost complete, the tone of the blood vessels increases, the brain is fully formed.

Thirty-fourth week (232-238 days)

The child's weight ranges from 2000 to 2500 grams, height is about 44-45 cm.

The child now takes a stable position in the uterus... The bones of the skull are soft and mobile thanks to the fontanelles, which can close only a few months after birth.

Head hair grows intensively and take on a certain color. However, hair color may change after childbirth.

Intensive strengthening of bones is noted, in this regard, the fetus begins to take calcium from the mother's body (a woman at this time may notice the appearance of seizures).

The child constantly swallows amniotic fluid, thereby stimulating the gastrointestinal tract and kidney function, which secrete at least 600 ml of clear urine per day.

Thirty-fifth week (239-245 days)

Every day the child adds 25-35 grams. Weight in this period can vary greatly and by the end of the week it is 2200-2700 grams. Growth increases to 46 cm.

All internal organs of the child continue to improve, preparing the body for the upcoming extrauterine existence.

Fatty tissue is intensively deposited, the child becomes more well-fed. The amount of vellus hair is greatly reduced. The nails have already reached the tips of the nail phalanges.

A sufficient amount of meconium has already accumulated in the intestines of the fetus., which normally should leave within 6-7 hours after childbirth.

Thirty-sixth week (246-252 days)

The weight of the child is very different and can be from 2000 to 3000 grams, height - within 46-48 cm

The fetus already has a well-developed subcutaneous fatty tissue, skin color becomes light, wrinkles and folds disappear completely.

The baby takes a certain position in the uterus: more often it lies upside down (less often, legs or buttocks, in some cases, transversely), the head is bent, the chin is pressed to the chest, arms and legs are pressed to the body.

Skull bones, unlike other bones, remain soft, with cracks (fontanelles), which will allow the baby's head to be more pliable when passing through the birth canal.

All organs and systems are fully developed for the existence of a child outside the womb.

Fetal development in the tenth obstetric month

Thirty-seventh week (254-259 days)

The child's height increases to 48-49 cm, the weight can fluctuate significantly. The skin became lighter and thicker, the fat layer increases by 14-15 grams per day every day.

Cartilage of the nose and auricles become denser and more elastic.

Completely lungs are formed and mature, the alveoli contain the necessary amount of surfactant for the breathing of the newborn.

The maturation of the digestive system has ended: contractions occur in the stomach and intestines, which are necessary to push food (peristalsis).

Thirty-eighth week (260-266 days)

Child's weight and height vary greatly.

The fruit is fully ripe and ready for birth... Outwardly, the baby looks like a full-term newborn. The skin is light, the fatty tissue is sufficiently developed, and vellus hair is practically absent.

Thirty-ninth week (267-273 days)

Typically two weeks before delivery the fruit starts to sinkpressing against the bones of the pelvis. The child has already reached full maturity. The placenta begins to age gradually and metabolic processes deteriorate in it.

The weight of the fetus increases significantly (30-35 grams per day). The proportions of the body completely change: the chest and shoulder girdle are well developed, the rounded abdomen, long limbs.

The senses are well developed: the child catches all sounds, sees bright colors, can focus vision, taste buds are developed.

Fortieth week (274-280 days)

All indicators of fetal development correspond to the newexpected. The baby is completely ready for childbirth. The mass can vary significantly: from 250 to 4000 and more grams.

The uterus begins to contract periodically (), which is manifested by aching pains in the lower abdomen. The cervix opens slightly, and the fetal head is pressed closer to the pelvic cavity.

Skull bones are still soft and pliable, which allows the baby's head to change shape and easier to pass through the birth canal.

Fetal development by weeks of pregnancy - Video

In the process of human embryonic development, general patterns of development and stages that are characteristic of vertebrates are preserved. At the same time, there are features that distinguish human development from the development of other vertebrates; knowledge of these features is necessary for the doctor. The process of intrauterine development of the human embryo lasts on average 280 days (10 lunar months). Human embryonic development can be divided into three periods: initial (1st week of development), embryonic (2-8th week of development), fetal (from the 9th week of development to birth). By the end of the embryonic period, the laying of the main embryonic rudiments of tissues and organs ends and the embryo acquires the basic features characteristic of a person. By the 9th week of development (the beginning of the 3rd month), the embryo is 40 mm long and weighs about 5 g. In the course of human embryology, studied at the Department of Histology and Embryology, the main attention is paid to the characteristics of human germ cells, fertilization and human development on early stages (initial and embryonic periods), when the formation of a zygote, cleavage, gastrulation, the formation of rudiments of axial organs and embryonic membranes, histogenesis and organogenesis, as well as interactions in the mother-fetus system occur. The processes of formation of organ systems in the fetus are discussed in detail in the course of anatomy.

Progenesis

Sex cells

Male reproductive cells. Sperm humans are formed during the entire active sexual period in large quantities. The duration of development of mature spermatozoa from the parent cells - spermatogonia - is about 72 days. A detailed description of the processes of spermatogenesis is given in chapter XXII. The formed sperm is about 70 microns in size and consists of heads and tail (see fig. 23). The nucleus of the human sperm contains 23 chromosomes, one of which is sex (X or V), the rest are autosomes. Among the sperm cells, 50% contain the X chromosome and 50% the Y chromosome. It was shown that the mass of the X chromosome is greater than the mass of the Y chromosome; therefore, sperm containing the X chromosome are less mobile than those containing the Y chromosome.

In humans, the normal volume of ejaculate is about 3 ml; it contains an average of 350 million sperm. To ensure fertilization, the total number of sperm in the sperm must be at least 150 million, and their concentration in 1 ml - at least 60 million. In the genital tract of a woman after copulation, their number decreases in the direction from the vagina to the distal end of the fallopian tube. Due to the high mobility, sperm cells under optimal conditions can reach the uterine cavity after 30 minutes - 1 hour, and after 1 1/2 -2 hours they can be in the distal (ampullary) part of the fallopian tube, where they meet with the egg and fertilize. Sperm retain their fertilizing capacity for up to 2 days.

Female reproductive cells. The formation of female germ cells (oogenesis) occurs in the ovaries cyclically, while during the ovarian cycle every 24-28 days, as a rule, one oocyte of the 1st order is formed (see Chapter XXII). The oocyte of the 1st order released from the ovary during ovulation has a diameter of about 130 microns and is surrounded by a dense a shiny area or membrane, and a crown follicular cells, the number of which reaches 3-4 thousand. It is picked up by the fringes of the fallopian tube (oviduct) and moves along it. Here the maturation of the reproductive cell ends. In this case, as a result of the second division of maturation, an oocyte of the 2nd order (egg cell) is formed, which loses its centrioles and thereby the ability to divide. The nucleus of the human egg cell contains 23 chromosomes; one of them is the sex X chromosome.

Egg females (like mammals) of the secondary isocytal type, contains a small amount of yolk grains, more or less evenly distributed in the ooplasm (Fig. 32, L, B). The human egg cell usually spends its reserve of nutrients within 12-24 hours after ovulation, and then dies if it is not fertilized.

Embryogenesis

Fertilization

Fertilization takes place in the ampullar part of the oviduct. The optimal conditions for the interaction of sperm with an egg are usually created within 12 hours after ovulation. During insemination, numerous sperm come close to the egg and come into contact with its membrane. The ovum begins to rotate around its axis at a speed of 4 rotations per minute. These movements are due to the influence of the beating of sperm flagella and last for about 12 hours. In the process of interaction of male and female germ cells, a number of changes occur in them. Sperm cells are characterized by capacitations and acrosomal reactions. Capacitation is a process of sperm activation that occurs in the oviduct under the influence of the mucous secretion of its glandular cells. Hormonal factors, primarily progesterone (corpus luteum hormone), which activates the secretion of glandular cells of the oviducts, are of great importance in the mechanisms of capacitation. Capacitation is followed by an acrosomal reaction, in which the release of enzymes from the spermatozoa - hyaluronidase and trypsin, which play an important role in the fertilization process. Hyaluronidase breaks down the hyaluronic acid contained in the shiny area. Trypsin breaks down proteins of the cytolemma of the egg and cells of the radiant crown. As a result, dissociation and removal of the cells of the radiant crown, surrounding the ovum, and the dissolution of the shiny zone occur. In the oocyte, the cytolemma in the area of \u200b\u200battachment of the sperm forms an elevating tubercle, which includes one sperm, while due to the cortical reaction (see above) a dense membrane is formed - fertilization shell, preventing the entry of other sperm and the phenomenon of polyspermia. The nuclei of the female and male germ cells turn into pronuclei, approaching, the stage comes syncarion. A zygote appears and by the end of 1 day after fertilization, fragmentation begins.

The sex of the unborn child is determined by the combination of sex chromosomes in the zygote. If an egg is fertilized by a sperm with a sex chromosome X, then the resulting diploid set of chromosomes (a person has 46) contains two X chromosomes, characteristic of the female body. When fertilized with a sperm with a sex chromosome Y, a combination of sex chromosomes XY is formed in the zygote, which is characteristic of the male body. Thus, the sex of the child depends on the sex chromosomes of the father. Since the number of sperm produced with the X and Y chromosomes is the same, the number of newborn girls and boys should be equal. However, due to the greater sensitivity of male embryos to the damaging effects of various factors, the number of newborn boys is slightly less than girls: 103 girls are born per 100 boys.

In medical practice, various types of developmental pathologies caused by an abnormal karyotype have been identified. The reason for such anomalies is most often the nondisjunction in the anaphase of the halves of the sex chromosomes in the process of meiosis of the female germ cells. As a result, two chromosomes fall into one cell and a set of sex chromosomes is formed XX, and in the other does not get one. When such eggs are fertilized by sperm with X or Y-sex chromosomes, the following karyotypes can be formed: 1) with 47 chromosomes, of which 3 chromosomes X (type XXX) - super-female type, 2) OU karyotype (45 chromosomes) - not viable; 3) karyotype XXY (47 chromosomes) - a male body with a number of disorders - male sex glands are reduced, spermatogenesis is absent, mammary glands are enlarged (Klinefelter syndrome); 4) type XO (45 chromosomes) - a female organism with a number of changes - short stature, underdevelopment of the genitals (ovary, uterus, oviducts), absence of menstruation and secondary sexual characteristics (Turner syndrome).

Splitting up

The fragmentation of the human embryo begins by the end of the 1st day and continues for 3-4 days after fertilization, as the embryo moves along the oviduct to the uterus. The movement of the embryo is provided by peristaltic contractions of the musculature of the oviduct, the flickering of the cilia of its epithelium, as well as the movement of the secretion of the glands of the fallopian tube. The embryo is nourished by small reserves of yolk in the egg and, possibly, the contents of the fallopian tube.

The fragmentation of the human zygote is complete, uneven, asynchronous. During the first day, it happens slowly. The first division is completed in 30 hours; in this case, the cleavage furrow passes along the meridian and two blastomeres are formed. The two-blastomere stage is followed by the three-blastomere stage. After 40 hours, 4 cells are formed.

From the very first divisions, two types of blastomeres are formed: “dark” and “light”. “Light” blastomeres split faster and are located in one layer around the “dark” ones, which are in the middle of the embryo. From the surface "light" blastomeres, trophoblast, connecting the embryo with the mother's body and providing it with nutrition. Internal “dark” blastomeres form embryoblast - it forms the body of the embryo and all other extraembryonic organs, except for the trophoblast. Starting from three days, cleavage is faster and on the 4th day the embryo consists of 7-12 blastomeres. After 50-60 hours, morula is formed, and on the 3-4th day the formation begins blastocysts - a hollow bubble filled with liquid (Fig. 33, B).

The blastocyst is in the oviduct for 3 days, after 4-4 "/ 2 days it consists of 58 cells, has a well-developed trophoblast and an embryoblast cell mass located inside. After 5-5" / 2 days, the blastocyst enters the uterus. By this time, it increases in size due to an increase in the number of blastomeres up to 107 cells and the volume of fluid due to the increased absorption of uterine secretions by the trophoblast, as well as the active production of fluid by the trophoblast itself. The embryoblast is located in the form of a nodule of germ cells, which is attached from the inside to the trophoblast at one of the poles of the blastocyst.

Within about 2 days (from 5th to 7th days), the embryo passes the stage of free blastocyst. During this period, changes occur in the trophoblast and embryoblast associated with preparation for the introduction of the embryo into the wall of the uterus - implantation.

The blastocyst is covered with a fertilization membrane. In the trophoblast, the number of lysosomes increases, in which enzymes accumulate, which ensure the destruction (lysis) of the tissues of the uterus and thereby contribute to the introduction of the embryo into the thickness of the uterine mucosa. Outgrowths appearing in the trophoblast destroy the fertilization membrane. Embryonic nodule flattens and turns into germinal scutellum, in which preparation for the first phase of gastrulation begins. Gastrulation is carried out by delamination with the formation of two sheets: external - epiblast and internal - hypoblast (fig. 34).

Implantation (nidation) - the introduction of the embryo into the wall of the uterus - starts from the 7th day after fertilization and lasts about 40 hours. During implantation, the embryo is completely immersed in the tissues of the uterine mucosa. There are two stages of implantation: adhesion (adhesion) and invasion (penetration). In the first stage, the trophoblast attaches to the mucous membrane of the uterus and two layers begin to differentiate in it - cytotrophoblast and symplastotrophoblast, or plasmodiotrophoblast. During the second stage, symplastotrophoblast, by producing proteolytic enzymes, destroys the lining of the uterus. In this case, the forming villi of the trophoblast, penetrating into the uterus, sequentially destroy its epithelium, then the underlying connective tissue and vascular walls, and the trophoblast comes into direct contact with the blood of the maternal vessels. Formed implantation fossa, in which areas of hemorrhage appear around the embryo. The trophoblast initially (the first 2 weeks) consumes the decay products of maternal tissues (histiotrophic type of nutrition), then the embryo is fed directly from the maternal blood (hematotrophic type of nutrition). From the mother's blood, the embryo receives not only all the nutrients, but also the oxygen necessary for breathing. At the same time, the formation of glycogen-rich connective tissue cells is enhanced in the uterine mucosa decidual cells. After the embryo is completely immersed in the implantation fossa, the hole formed in the uterine lining is filled with blood and products of destruction of the uterine lining tissue. Subsequently, the defect of the mucous membrane is covered by the regenerating epithelium.

The implantation period is the first critical period in the development of the embryo. The hematotrophic type of nutrition, replacing the histiotrophic one, is accompanied by a transition to a qualitatively new stage of embryogenesis - to the second phase of gastrulation and the establishment of extraembryonic organs.

Gastrulation

Human gastrulation is carried out in two phases. The first phase precedes the implantation or is in the process of it, i.e., it takes place on the 7th day, and the second phase begins only on the 14-15th day. In the period between these phases, extraembryonic organs are actively formed, providing the necessary conditions for the development of the embryo.

The first phase of gastrulation occurs by delamination, while the cells of the embryoblast are split into two sheets - the outer one - epiblast (includes the material of the ectoderm, neural plate, mesoderm and notochord) facing the trophoblast, and internal - hypoblast (includes the material of the embryonic and extraembryonic endoderm) facing the blastocyst cavity. On the 7th day of development, cells that have evicted from the embryonic shield are found, which are located in the cavity of the blastocyst and form extraembryonic mesoderm (mesenchyme). By the 11th day, it fills the blastocyst cavity. The mesenchyme grows up to the trophoblast and is introduced into it, while the chorion - villous membrane embryo with primary chorionic villi .

The extraembryonic mesoderm is involved in the formation of the buds of the amniotic (together with the ectoderm) and yolk (together with the endoderm) vesicles. The edges of the epiblast grow along the mesodermal anlage and form amniotic vesicle, the bottom of which is facing the endoderm. Reproducing endoderm cells form by the 13-14th day yolk vesicle. In humans, the yolk sac contains practically no yolk, but is filled with serous fluid.

By 13-14 days, the embryo has the following structure. The trophoblast, together with the underlying extraembryonic mesoderm, forms chorion. In the part of the embryo, which faces deep into the wall of the uterus, are located adjacent to each other amniotic vesicle and yolk vesicle. This part is attached to the chorion with amniotic, or embryonic, legs, formed by the extraembryonic mesoderm. Adjacent to each other, the bottom of the amniotic and the roof of the yolk vesicles form embryonic scutellum. The thickened bottom of the amniotic vesicle is the epiblast, and the rest of its wall is extraembryonic ectoderm. The roof of the yolk vesicle is formed by a hypoblast, and its wall outside the scutellum is formed by the extraembryonic endoderm.

Thus, in humans, in the early periods of embryogenesis, the extraembryonic parts are well developed - the chorion, amnion, and yolk sac.

The second phase of gastrulation begins on the 14-15th day and lasts until the 17th day of development. It becomes possible only after the described processes of formation of extra-embryonic organs and the establishment of a hematotrophic type of nutrition. In the epiblast, cells divide intensively and move towards the center and inward, located between the outer and inner germ layers. As a result of the process of immigration of cellular material, primary strip, corresponding in potency to the lateral lips of the blastopore, and the primary nodule is an analogue of the dorsal lip. The fossa, located at the apex of the nodule, gradually deepens and breaks through the ectoderm, turns into a homologue of the neurointestinal canal of the lancelet. The cellular material of the epiblast, located anterior to the primary nodule, is displaced through the dorsal lip into the space between the bottom of the amniotic vesicle and the roof of the yolk, giving chordal process. At the same time, the cellular material of the primary strip lies in the form mesodermal wings in a near-chordal position. The embryo acquires a three-layer structure and almost does not differ from the embryo of birds at a similar stage of embryogenesis.

The appearance of the rudiment also belongs to this time. allantois. Starting from the 15th day, a small finger-like outgrowth - allantois grows into the amniotic leg from the posterior part of the intestinal tube. Thus, by the end of the second phase of gastrulation, the laying of all germ layers and all extraembryonic organs is completed.

On the 17th day, the laying of the primordia of the axial organs continues. All three germ layers are visible at this stage. As part of the ectoderm, cellular elements are arranged in several layers. From the zone of the head nodule, there is a massive expulsion of cells, which, located between the ecto- and endoderm, and form the primordium of the notochord. The walls of the amniotic vesicle and yolk sac are two-layered over a greater extent. In the wall of the yolk sac, islets of blood and primary blood vessels are formed.

The connection of the body of the embryo with the chorion is carried out due to the vessels growing into the wall of the allantois and the chorionic villi. The outer germ layer at the head end is formed by one layer of cells, the highest along the medial axis of the embryo. When passing into the ectoderm of the amniotic vesicle, its cells flatten. In the anterior cranial region, a primary stria and a primary nodule can be seen. The cavity of the fetal bladder is lined with a well-developed outer layer of the mesoderm (somatopleura), which also forms the basis of the chorionic villi. The walls of the yolk sac and amniotic vesicle are lined with unilamellar epithelium (endodermal and ectodermal origin, respectively) and visceral exocoelomic mesoderm.

The nutrition and respiration of the embryo occurs through allantochorion. Primary villi are washed by maternal blood.

Starting from 20-21 days, the body of the embryo is isolated from the extraembryonic organs and the final formation of axial primordia occurs. Changes in the embryo itself are first of all expressed in the differentiation of the mesoderm and the division of its part into somites. Therefore, this period is called somitic, in contrast to the previous, presomite period of laying the axial embryo rudiments.

The separation of the body of the embryo from the extraembryonic (provisional) organs occurs through the formation trunk folds, which on the 20th day is quite clearly expressed. The embryo is more and more separated from the yolk sac until it is associated with a stalk, while the intestinal tube is formed.

Differentiation of embryonic primordia

Differentiation of the ectoderm. Neurulation - the process of formation of a neural tube - proceeds unequally in time in different parts of the embryo. The closure of the neural tube begins in the cervical region, then spreads posteriorly and somewhat more slowly in the cranial direction, where cerebral vesicles are formed. Approximately on the 25th day, the neural tube is completely closed; only two open holes at the front and rear ends communicate with the external environment - front and rear neuropores. Posterior neuropore corresponds neurointestinal canal. After 5-6 days, both neuropores are overgrown. With the closing of the lateral walls of the nerve rollers and the formation of a neural tube, a group of ectodermal cells appears, formed in the area of \u200b\u200bthe junction of the neural and the rest (skin) ectoderm. These cells, initially arranged in longitudinal rows on either side between the neural tube and the superficial ectoderm, form neural crest. Neural crest cells are capable of migration. In the trunk, the migrating cells form two main streams: some migrate in the surface layer, the dermis, and others in the abdominal direction, forming the parasympathetic and sympathetic ganglia and the adrenal medulla. Some of the cells remain in the area of \u200b\u200bthe neural crest, forming ganglion plates, which segmented and give rise to the spinal nodes.

Chordal process - provisional organ - is absorbed.

Differentiation of the mesoderm begins from the 20th day of embryogenesis. The dorsal sections of the mesodermal sheets are divided into dense segments lying on the sides of the notochord - somites. The segmentation of the dorsal mesoderm and the formation of somites begins in the head of the embryo and spreads rapidly in the caudal direction. On the 22nd day of development, the embryo has 7 pairs of segments, on the 25th - 14, on the 30th - 30th and on the 35th day - 43-44 pairs. In contrast to somites, the ventral mesoderm (splanchnot) not segmented, but split into two leaves - visceral and parietal. A small area of \u200b\u200bthe mesoderm connecting the somites with the splanchnotome is divided into segments - segmental legs (nephrogonotome). At the posterior end of the embryo, segmentation of these departments does not occur. Here, instead of segmental legs, an unsegmented nephrogenic anlage is located (nephrogenic cord).

In the process of differentiation of the mesoderm from the dermatome and sclerotome, an embryonic rudiment of connective tissue appears - mesenchyme. Other germ layers are also involved in the formation of the mesenchyme, although it mainly arises from the mesoderm. Part of the mesenchyme develops due to cells of ectodermal origin. The rudiment of the endoderm of the head of the intestinal tube also takes part in the formation of the mesenchyme.

Differentiation of endoderm. Isolation of the intestinal endoderm begins from the moment the trunk folds appear. The latter, deepening, separates the embryonic endoderm of the future gut from the extraembryonic endoderm of the yolk sac. In the posterior part of the embryo, the part of the endoderm from which the endodermal outgrowth of allantois arises is also part of the formed intestine. At the beginning of the 4th week, an ectodermal invagination is formed at the anterior end of the embryo - oral fossa. Deepening, the fossa reaches the anterior end of the intestine and, after breaking through the membrane separating them, turns into the mouth opening of the unborn child.

The intestinal tube is formed initially as part of the endoderm of the yolk sac, then the material of the prechordal plate is included in its anterior section. From the material of the prechordal plate, the multilayer epithelium of the anterior part of the digestive tube and its derivatives develops. The intestinal tube mesenchyme is converted to connective tissue and smooth muscle.

Anatomical formation of organs (organogenesis) occurs in parallel with the processes of histogenesis (tissue formation).

Human extraembryonic organs

Chorion

The villous growths of the trophoblast, later called chorion, consist of two structural components - the epithelium and the extraembryonic mesenchyme. The mucous membrane in the part that, after implantation, will become part of the placenta - the main falling-off membrane, grows more strongly than in other areas - the parietal falling-off membrane and the bag-like falling off membrane, which separates the embryo from the uterine cavity . In the future, this difference becomes more and more pronounced, and the villi in the region of the parietal and bursal membranes disappear altogether, and in the region of the main falling off shell they are replaced by highly branched secondary villi, the stroma of which forms connective tissue with blood vessels. From this moment, the chorion is divided into two sections - branched and smooth ... The placenta is formed in the area of \u200b\u200bthe branchy chorion. Due to the main falling off shell, the mother part is formed

placenta, and due to the branchy chorion, its fetal part. By the age of 3 months, the branched chorion acquires, together with the main decaying membrane, a discoidal shape typical of the formed placenta.

Placentation in humans occurs during the 3-6th week of intrauterine development and coincides with the period of formation of organ rudiments. This period is the second critical in human embryogenesis, since various pathogenic influences at this time most often can cause disturbances.

Baby seat, or placenta

The placenta is an extraembryonic organ, due to which a connection is established between the embryo and the mother's body. The human placenta belongs to the type of discoidal hemochorial villous placentas.

It is an important temporary organ with multiple functions that provides a connection between the fetus and the mother's body. The placenta performs trophic, excretory (for the fetus), endocrine (produces chorial gonadotropin, progesterone, placental lactogen, estrogens, etc.), protective (including immunological protection). However, through the placenta (through hematoplacental barrier) alcohol, narcotic and medicinal substances, nicotine, and many hormones easily penetrate from the mother's blood into the fetal blood.

The placenta is distinguished embryonic, or fertile, part and maternal, or uterine ... The fetal part is represented by a branched chorion and an amniotic membrane adhered to it, and the maternal part is represented by a modified basal part of the endometrium.

The development of the placenta begins at the 3rd week, when vessels begin to grow into the secondary (epitheliomesenchymal villi) and form tertiary villi. At 6-8 weeks, macrophages, fibroblasts, collagen fibers differentiate around the vessels. Vitamins C and A play an important role in the differentiation of fibroblasts and the synthesis of collagen, without sufficient supply of which to the body of a pregnant woman, the strength of the connection between the embryo and the mother's body is disturbed and a threat of spontaneous abortion is created.

In parallel, the activity of hyaluronidase increases, due to which the breakdown of hyaluronic acid molecules occurs.

A decrease in the viscosity of the basic substance creates the most favorable conditions for the metabolism between the tissues of the mother and the fetus. The main substance of the chorionic connective tissue contains a significant amount of hyaluronic and chondroitinsulfuric acids, which are associated with the regulation of placental permeability.

The formation of collagen fibers in the villi coincides in time with an increase in the proteolytic activity of the trophoblastic epithelium ( cytotrophoblast) and its derivative (syncytiotrophoblast).

With the development of the placenta, the destruction of the mucous membrane of the uterus occurs and the change of histiotrophic nutrition to hematotrophic one. This means that the chorionic villi are washed by the mother's blood, which poured out from the destroyed endometrial vessels into the lacunae.

The embryonic, or fetal, part of the placenta by the end of the 3rd month is represented by a branching chorionic plate, consisting of fibrous (collagen) connective tissue covered with cyto- and syncytiotrophoblast. Branching chorionic villi (stem, or anchor, villi) well developed only from the side facing the myometrium. Here they pass through the entire thickness of the placenta and with their tops plunge into the basal part of the destroyed endometrium.

Chorial epithelium, or cytotrophoblast, in the early stages of development is represented by a single-layer epithelium with oval nuclei. These cells multiply mitotic. From them, a syncytiotrophoblast develops - a multinucleated structure covering a reducing cytotrophoblast. The syncytiotrophoblast contains a large number of various proteolytic and oxidative enzymes [ATPases, alkaline and acidic phosphatases, 5-nucleotidases, DPN-diaphorase, glucose-6-phosphate dehydrogenase (G-6-FDG), α-GPDH, succinate dehydrogenase -SDH, cytochrome oxidase - CO, monoamine oxidase - MAO, nonspecific esterases, LDH, NAD and NADP-diaphorase, etc. - only about 60], which is associated with its role in metabolic processes between the body of the mother and the fetus. In the cytotrophoblast and in the syncytium, pinocytic vesicles, lysosomes, and other organelles are detected. Starting from the 2nd month, the chorionic epithelium becomes thinner and is gradually replaced by syncytiotrophoblast. During this period, the syncytiotrophoblast is thicker than the cytotrophoblast, at 9-10 weeks the syncytium becomes thinner, and the number of nuclei in it increases. On the surface of the syncytium, facing the lacunae, numerous microvilli appear in the form of a brush border.

Between the syncytium and the cell trophoblast there are slit-like submicroscopic spaces reaching in places up to the basement membrane of the trophoblast, which creates conditions for the bilateral penetration of trophic substances, hormones, etc. between the syncytium and the stroma of the villi.

In the second half of pregnancy, and especially at the end of it, the trophoblast is severely thinned in places and the villi are covered with a fibrin-like oxyphilic mass, which is, apparently, a product of plasma coagulation and trophoblast decay (“Langhans fibrinoid”).

With increasing gestational age, the number of macrophages and collagen-producing differentiated fibroblasts decreases, and fibrocytes appear. The number of collagen fibers, although increasing, remains small in most villi until the end of pregnancy.

The structural and functional unit of the formed placenta is cotyledon, formed by the stem villi and its secondary and tertiary (terminal) ramifications. The total number of cotyledons in the placenta reaches 200.

The maternal part of the placenta is presented basal lamina and connective tissue septa separating the cotyledons from each other, as well as lacunas, filled with maternal blood. Trophoblastic cells are also found in the places where the stem villi come into contact with the decaying membrane. (peripheral trophoblast).

Already in the early stages of pregnancy, the chorionic villi destroy the outer, that is, the layers closest to the fetus, the layers of the main falling off shell, and in their place are formed filled with maternal blood lacunae, into which the chorionic villi hang freely. The deep, undisturbed parts of the decaying shell, together with the trophoblast, form the basal plate.

Basal layer of the endometrium - connective tissue of the mucous membrane of the uterus, containing decidual cells. These large, glycogen-rich connective tissue cells are located deep in the lining of the uterus. They have clear boundaries, rounded nuclei and oxyphilic cytoplasm. In the basal lamina, more often at the place of attachment of the villi to the maternal part of the placenta, there are accumulations of peripheral cytotrophoblast cells. They resemble decidual cells, but differ in more intense basophilia of the cytoplasm. Amorphous substance (Rohr's fibrinoid) is located on the surface of the basal plate facing the chorionic villi. Trophoblastic cells of the basal lamina, together with fibrinoid, play an essential role in providing immunological homeostasis in the mother-fetus system.

Part of the main falling away membrane, located on the border of the branched and smooth chorion, that is, along the edge of the placental Disc, is not destroyed during the development of the placenta. Adhering tightly to the chorion, it forms a closing plate that prevents the outflow of blood from the lacunae of the placenta.

The blood in the gaps is continuously renewed. It comes from the uterine arteries entering here from the muscular membrane of the uterus. These arteries run along the placental septa and open into lacunae. The maternal blood flows from the placenta through the veins originating from the lacunae in large holes.

The blood of the mother and the blood of the fetus circulates through independent vascular systems and does not mix with each other. Hemochorial barrier, separating both blood flows, it consists of the endothelium of the fetal vessels, the connective tissue surrounding the vessels, the epithelium of the chorionic villi (cytotrophoblast, syncytiotrophoblast), and, in addition, of the fibrinoid, which in places covers the villi outside.

Placenta formation ends at the end of the 3rd month of pregnancy.

The placenta formed by this time ensures the final differentiation and rapid growth of the rudiments of the fetal organs formed in the previous period.

Yolk sac

The yolk sac is formed by the extraembryonic endoderm and the extraembryonic mesoderm; it takes an active part in the nutrition and respiration of the human embryo for a very short time. After the formation of the trunk fold, the yolk sac is associated with the intestine yolk stalk. The yolk sac itself is displaced into the space between the chorionic mesenchyme and the amniotic membrane. Its main role is hematopoietic. As a hematopoietic organ, it functions until the 7-8th week, and then undergoes reverse development. In the umbilical cord, the remainder of the yolk sac is later found in the form of a narrow tube. In the wall of the yolk sac, primary sex cells are formed - gonoblasts, migrating from it with blood to the rudiments of the sex glands.

Amnion

The amnion grows very quickly in size and by the end of the 7th week its connective tissue comes into contact with the connective tissue of the chorion. In this case, the epithelium of the amnion passes to the amniotic leg, which later turns into the umbilical cord, and in the region of the umbilical ring it closes with the ectodermal cover of the skin of the embryo.

The amniotic membrane forms the wall of the reservoir in which the fetus is located. Its main function is the production of amniotic fluid, which provides an environment for the developing organism and protects it from mechanical damage. The epithelium of the amnion, facing its cavity, secretes amniotic fluid, and also takes part in the reabsorption of them . The amniotic fluid creates an aqueous environment necessary for the development of the embryo, maintaining the necessary composition and concentration of salts in the amniotic fluid until the end of pregnancy (see Fig. 37, AND). Amnion also performs a protective function, preventing harmful agents from entering the fetus.

The epithelium in the early stages is monolayer flat throughout, formed by large polygonal cells closely adjacent to each other, in which mitosis constantly occurs. At the 3rd month of embryogenesis, the epithelium is transformed into prismatic. The epithelium of the placental disc is prismatic, in places multi-row. There are microvilli on the surface of the epithelium. The cytoplasm always contains small drops of lipids, grains of glycogen and glycosaminoglycans. In the apical parts of the cells there are vacuoles of various sizes, the contents of which are released into the amnion cavity. The epithelium of the extraplacental amnion is cubic. In the epithelium of the amnion, which covers the placental disc, there is probably predominantly secretion, and in the epithelium of the extraplacental amnion, predominantly resorption of amniotic fluid takes place.

In the stroma of the amniotic membrane, there are basement membrane, a layer of dense connective tissue and a spongy layer of loose connective tissue, connecting the amnion with the chorion. In the layer of dense connective tissue, one can distinguish the cell-free part lying under the basement membrane and the cellular part. The latter consists of several layers of fibroblasts, between which there is a dense network of tightly adjacent thin bundles of collagen and reticular fibers, forming an irregular lattice oriented parallel to the surface of the shell.

The spongy layer is formed by very loose ("mucous") connective tissue. Rare bundles of collagen fibers, which are a continuation of those that lie in the layer of dense connective tissue, connect the amnion with the chorion. This bond is very fragile, and therefore both shells can be easily separated from each other. There are many glycosaminoglycans in the main substance of the connective tissue.

Allantois

Allantois is a small finger-like endoderm that grows into the amniotic pedicle. In humans, allantois does not reach great development, but its importance in providing nutrition and respiration of the embryo is still great, since vessels grow along it to the chorion, the final ramifications of which lie in the stroma of the villi. At the 2nd month of embryogenesis, allantois is reduced.

Umbilical cord

The umbilical cord is formed mainly from the mesenchyme located in the amniotic pedicle and yolk stalk. Allantois and the vessels growing along it also take part in its formation. From the surface, all these formations are surrounded by an amniotic membrane. The yolk stalk and allantois are rapidly reduced, and only their remains are found in the umbilical cord of the newborn.

The formed umbilical cord is an elastic connective tissue formation in which two umbilical arteries and umbilical vein. It is formed by a typical gelatinous (mucous) tissue, which contains a huge amount of hyaluronic acid. It is this fabric, called Wharton's jelly, that provides the turgor and elasticity of the cord. The amniotic membrane covering the surface of the cord grows together with its gelatinous tissue.

The value of this fabric is extremely great. It protects the umbilical vessels from compression, thereby ensuring a continuous supply of nutrients and oxygen to the embryo. Along with this, the gelatinous tissue prevents the penetration of harmful agents from the placenta to the embryo by the extravascular route and thus performs a protective function.

Based on the foregoing, the main features of the early stages of development of the human embryo can be noted: 1) the asynchronous type of complete cleavage and the formation of “light” and “dark” blastomeres; 2) early isolation and formation of extraembryonic organs; 3) early formation of the amniotic vesicle and the absence of amniotic folds; 4) the presence of two phases of gastrulation - delamination and immigration, during which the development of provisional organs also occurs; 5) interstitial type of implantation; 6) strong development of amnion, chorion and poor development of the yolk sac and allantois.

Mother-fetus system

The mother-fetus system arises during pregnancy and includes two subsystems - the mother's organism and the fetus's organism, as well as the placenta, which is the connecting link between them.

The interaction between the mother's body and the fetus's body is provided primarily by neurohumoral mechanisms. At the same time, the following mechanisms are distinguished in both subsystems: receptor, perceiving information, regulatory, carrying out its processing, and executive.

The receptor mechanisms of the mother's body are located in the uterus in the form of sensitive nerve endings, which are the first to perceive information about the state of the developing fetus. The endometrium contains chemo-, mechano- and thermoreceptors, and in the blood vessels - baroreceptors. Free-type receptor nerve endings are especially numerous in the walls of the uterine vein and in the decidua in the region of attachment of the placenta. Irritation of uterine receptors causes changes in the intensity of respiration, the level of blood pressure in the mother's body, aimed at ensuring normal conditions for the developing fetus.

The regulatory mechanisms of the mother's body include parts of the central nervous system (temporal lobe of the brain, hypothalamus, mesencephalic reticular formation), and hypothalamoendocrine system. An important regulatory function is performed by hormones: sex hormones, thyroxine, corticosteroids, insulin, etc. Thus, during pregnancy there is an increase in the activity of the adrenal cortex of the mother and an increase in the production of corticosteroids, which are involved in the regulation of fetal metabolism. In the placenta, chorionic gonadotropin is produced, which stimulates the formation of the adreno-corticotropic hormone of the pituitary gland, which activates the activity of the adrenal cortex and enhances the secretion of corticosteroids.

Regulatory neuroendocrine devices of the mother ensure the preservation of pregnancy, the necessary level of functioning of the heart, blood vessels, hematopoietic organs, liver and the optimal level of metabolism, gases, depending on the needs of the fetus.

The receptor mechanisms of the fetus' body perceive signals about changes in the mother's body or its own homeostasis. They are found in the walls of the umbilical arteries and veins, in the orifices of the hepatic veins, in the skin and intestines of the fetus.

Irritation of these receptors leads to a change in the fetal heart rate, blood flow rate in its vessels, affects the blood sugar content, etc.

The regulatory neurohumoral mechanisms of the fetus are formed during development. The first motor reactions in the fetus appear in the 2-3rd month of development, which indicates the maturation of the nerve centers. The mechanisms regulating gas homeostasis are formed at the end of the second trimester of embryogenesis. The beginning of the functioning of the central endocrine gland - the pituitary gland - is noted at the 3rd month of development. The synthesis of corticosteroids in the adrenal glands of the fetus begins in the second half of pregnancy and increases with its growth. The fetus has enhanced insulin synthesis, which is necessary to ensure its growth associated with carbohydrate and energy metabolism. It should be noted that in newborns born to mothers with diabetes mellitus, when the production of insulin is reduced, there is an increase in body weight and an increase in insulin production in the islets of the pancreas.

The action of the neurohumoral regulatory systems of the fetus is aimed at the executive mechanisms - the organs of the fetus, which provide a change in the intensity of respiration, cardiovascular activity, muscle activity, etc. and determine the change in the level of gas exchange, metabolism, thermoregulation and other functions.

As already indicated, in providing connections in the mother-fetus system, a particularly important role is played by placenta, which is able not only to accumulate, but also to synthesize the substances necessary for the development of the fetus. The placenta performs endocrine functions, producing a number of hormones: progesterone, estrogen, chorionic gonadotropin, placental lactogen, etc. Through the placenta Humoral and nerve connections are carried out between the mother and the fetus. There are also extraplacental humoral connections through the membranes and amniotic fluid.

The humoral communication channel is the most extensive and informative. Through it, oxygen and carbon dioxide, proteins, carbohydrates, vitamins, electrolytes, hormones, antibodies, etc. are supplied. Normally, foreign substances do not penetrate from the mother's body through the placenta. They can begin to penetrate only under pathological conditions, when the barrier function of the placenta is impaired. An important component of humoral connections are immunological connections that maintain immune homeostasis in the mother-fetus system.

Despite the fact that the body of the mother and the fetus is genetically foreign in the composition of proteins, an immunological conflict usually does not occur. This is ensured by a number of mechanisms, among which the following are essential: 1 - proteins synthesized by syncytiotrophoblast that inhibit the immune response of the maternal organism; 2 - chorionic gonadotropin and placental lactogen, which are in high concentration on the surface of the syncytiotrophoblast, take part in the suppression of maternal lymphocytes; 3-immunomasking effect of glycoproteins of pericellular fibrinoid placenta, charged in the same way as lymphocytes of the washing blood, is negative; 4 - the proteolytic properties of trophoblast also contribute to the inactivation of foreign proteins. The amniotic waters, which contain antibodies that block antigens A and B, characteristic of the blood of a pregnant woman, and do not allow them into the blood of the fetus in the event of an incompatible pregnancy, also take part in the immune defense.

A definite relationship between the homologous organs of the mother and the fetus is shown: damage to any organ of the mother leads to a violation of the development of the organ of the same name of the fetus. In an experiment on animals, it was found that the blood serum of an animal from which a part of an organ was removed stimulates proliferation in the organ of the same name. However, the mechanisms of this phenomenon have not been sufficiently studied.

Nerve connections include the placental and extraplacental channels: placental (in the fetus - interoreceptive) - irritation of the baro- and chemoreceptors in the vessels of the placenta and umbilical cord, and extraplacental (in the fetus - exteroreceptive) - the entry into the central nervous system of the mother, irritation associated with the growth of the fetus, etc. The presence of nerve connections in the mother - fetus system is confirmed by data on the innervation of the placenta, the high content of acetylcholine in it, the delay in fetal development in the denervated uterine horn of experimental animals, etc.

In the process of formation of the mother-fetus system, there are a number of critical periods, the most important for the establishment of interaction between the two systems, aimed at creating optimal conditions for the development of the fetus.

Several critical ones can be distinguished in human ontogenesis. periods of development: in progenesis, embryogenesis and postnatal life. These include: 1) the development of germ cells, ovogenesis and spermatogenesis; 2) fertilization; 3) implantation (7-8 days of embryogenesis); 4) the development of axial organ rudiments and the formation of the placenta (3-8th week of development); 5) stage of increased brain growth (15-20th week); 6) the formation of the main functional systems of the body and the differentiation of the reproductive apparatus (20-24th week); 7) birth; 8) neonatal period (up to 1 year); 9) puberty (11-16 years old).

Disorders of sexual development in boys are associated with the pathology of the secretion or action of androgens. The clinical picture depends on the age at which the problem occurred.

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The formation of the male reproductive system goes on continuously until the end of adolescence. Doctors distinguish 3 stages of genital differentiation. Each of them has its own dominant influences and a certain physiological meaning.

Formation stages:

• intrauterine;
• pre-pubertal;
• pubertal.

Intrauterine period

The prenatal period begins with conception and ends with the birth of a child. At the time of fertilization of the egg, the chromosomal sex of the child is determined. The obtained genetic information remains unchanged and affects further ontogenesis. In humans, the XY set determines the male gender. Until 5-6 weeks, female and male embryos develop in the same way. Primary germ cells have the ability to differentiate according to one or another variant up to 7 weeks of gestation. Before this period, two internal ducts are laid: wolffian (mesonephral) and muller (paramesonephral). Primary gonad up to 7 weeks old is indifferent (indistinguishable in boys and girls). It consists of the cortex and medulla.

After 6 weeks of development, sex differences appear in differentiation. Their occurrence is due to the influence of the SKY gene, which is located on the short arm of the Y chromosome. This gene encodes a specific "male membrane protein" H-Y antigen (testicular development factor). The antigen affects the cells of the primary indifferent gonad, makes it transform in the male pattern.

Testicular embryogenesis:

• the formation of genital cords from the cortex of the primary gonad;
• the emergence of Leydig and Sertoli cells;
• the formation of convoluted seminiferous tubules from genital cords;
• the formation of the tunica albuginea from the cortex.

Leydig cells begin to secrete testosterone, and Sertoli - anti-Müllerian factor.

At the 9th week of intrauterine development, the influence of the chromosomal and gonadal sex affects the reproductive ducts. The anti-Müllerian factor causes atrophy of the paramesonephral duct. Without this influence, the uterus, fallopian tubes, and the upper third of the vagina are formed from the duct. The regression factor leaves only rudiments in the male body.

Testosterone stimulates the development of wolf ducts. By the beginning of the 14th week, the fetus has formed the epididymis, seminal vesicles, vas deferens and vas deferens. Primary germ cells are transformed into spermatogonia.

At the prenatal stage, great influence belongs dihydrotestosterone... This hormone is formed from testosterone by the enzyme 5a-reductase. Dihydrotestosterone is involved in the formation of external organs (penis, scrotum).

In the prenatal period, the testicles descend into the scrotum. By birth, this process is completed in 97% of full-term boys and in 79% of premature ones.

• defects of the guiding ligament;
• dysgenesis of the gonads;
• hypogonadism in the prenatal period;
• immaturity of the femoral genital nerve;
• anatomical obstacles to the movement of the testicle;
• weakening of the muscle tone of the abdominal wall;
• violation of the synthesis and action of testosterone.

Pre-pubertal period

The pre-pubertal period is characterized by relative functional rest. In the first months after birth, a child's blood levels can be high (due to the intake of maternal levels). Further, the concentration of FSH and LH, as well as testosterone falls to extremely low values. The pre-pubertal period is called the "juvenile pause". It lasts until the end of prepubertal period.

Puberty

In the pubertal stage, testosterone synthesis is activated in the testicle. First, at the age of 7-8, the boy's blood androgen level rises due to the adrenal glands (adrenarche). Then, at the age of 9-10 years, inhibition decreases in the centers of the hypothalamus responsible for sexual development. This increases the levels of GnRH, LH and FSH. These hormones affect the testicle, increasing testosterone production.

Male sex steroids:

• enhance the growth of internal and external genital organs;
• affect the development of the accessory glands;
• form sexual characteristics (secondary, tertiary);
• enhance the linear growth of the body;
• increase the percentage of muscle tissue;
• affect the distribution of subcutaneous fat.

In puberty, the maturation of germ cells begins and the formation of mature sperm cells.

Normal onset of sexual development and determination of its delay

Boys' puberty starts with an increase. The average age at which this trait appears is 11 years.

Table 1 - Average values \u200b\u200bof testicular volume in different age periods (according to Jockenhovel F., 2004).

The rate of puberty is the rate at which signs of puberty appear.

Possible rates:

• medium (all signs are formed in 2-2.5 years);
• accelerated (formation takes place in less than 2 years);
• slow (formation takes 5 years or more).

The normal sequence of signs of puberty at puberty is:

1. enlarged testicles (10-11 years);
2. penile enlargement (10-11 years old);
3. development of the prostate, an increase in the size of the larynx (11-12 years old);
4. significant enlargement of the testes and penis (12-14 years old);
5. female pubic hair growth (12-13 years old);
6. nodularity in the area of \u200b\u200bthe mammary glands, (13-14 years old);
7. onset of voice mutation (13-14 years old);
8. the appearance of hair in the armpits, on the face (14-15 years old);
9. pigmentation of the skin of the scrotum, the first ejaculation (14-15 years);
10. maturation of sperm (15-16 years);
11. male pubic hair (16-17 years old);
12. stopping the growth of bones of the skeleton (after 17 years).

Puberty is assessed by Tanner.

Table 2 - Estimation of the stage of sexual development according to Tanner.

Delayed puberty in boys

Delayed sexual development is determined if a boy, by the age of 14, has a testicle volume less than 4 ml, there is no growth of the penis in length and an increase in the scrotum. In this case, it is required to start an examination to identify the cause of the pathology.

Causes

Delayed sexual development can be due to:

• constitutional features (family);
• violations of the hypothalamic-pituitary regulation ();
• primary testicular tissue failure ();
• severe somatic pathology.

Diagnostics

• collection of anamnesis;
• assessment of heredity;
• assessment of bone age by radiograph;
• general inspection;
• examination of the external genital organs, assessment of the volume of the testicles and the size of the scrotum;
• hormonal profile (LH, FSH, testosterone, prolactin, TSH);
• tomography of the brain, x-ray of the skull;
• cytogenetic study.

Treatment

Treatment depends on the cause of the delayed puberty.

Family forms of delayed puberty can be corrected with the help. To prevent stunting, adolescents with this form of the disease are prescribed anabolic steroids.

For secondary hypogonadism, gonadotropins and gonadorelin are used in the treatment. This therapy is the prevention of future infertility. The use of hormones in the hypothalamic-pituitary region stimulates the development of the testicles and.

With primary hypogonadism, from the age of 14, boys are prescribed testosterone replacement therapy.

Premature puberty in boys

The appearance of signs of puberty in boys under 9 years of age is considered premature. This condition can lead to social maladjustment. In addition, premature sexual development is one of the reasons for short stature.

Causes

Premature sexual development is divided into:

• true (associated with the work of the hypothalamic-pituitary region);
• false (associated with the autonomous secretion of hormones by the adrenal glands or tumors).

True premature sexual development is complete (there are signs of masculinization and activation of spermatogenesis).

The reason for this condition may be:

• idiopathic;
• associated with diseases of the central nervous system;
• associated with the primary;
• arising against the background of prolonged hyperandrogenism (for example, with adrenal tumors).

False premature sexual development is usually not accompanied by activation of spermatogenesis (except in cases of familial testosterone toxicosis).

Causes of false premature sexual development:

• congenital hyperplasia of the adrenal cortex;
• , testicles;
• cushing's syndrome;
• secreting tumors;
• hyperplasia of Leydig cells (familial testosterone toxicosis);
• androgen treatment;
• isolated premature adrenarche.

Diagnostics

Examination for signs of premature sexual development includes:

• collection of anamnesis;
• general inspection;
• examination of the genitals;
• analyzes of hormones (LH, FSH, testosterone, TSH,);
• samples with gonadoliberin;
• bone age research;
• x-ray of the skull, tomography of the brain, etc.

Treatment

For the treatment of true premature puberty, synthetic analogs of gonadoliberin are used. This drug suppresses the impulse secretion of LH and FSH. If the cause of the disease is a pathology of the central nervous system, then the patient is prescribed appropriate treatment (by a neurologist, neurosurgeon).

Treatment for false precocious puberty depends on the underlying causes. If the pathology is associated with an isolated adrenarche, only observation is carried out. If a hormonally active tumor is found, radical treatment (surgery, radiation therapy) is performed. In cases of congenital hyperplasia of the adrenal cortex, corticosteroid therapy is selected.

Endocrinologist I. G. Tsvetkova

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Kelly. Foundations of modern sexology. Ed. Peter

Translated from English by A. Golubev, K Isupova, S. Komarov, V, Misnik, S. Pankov, S. Rysev, E. Turutina

Gender development and social approaches to it. Part 1

Development of gender and social approaches to it. Part 3

Gender development and social approaches to it. Part 4

Development of gender and social approaches to it. Part 5

Hormones and fetal development. The sex glands of the embryo, whose chromosomes are programmed to form feminine traits, will automatically develop into the ovaries. However, if the gonads are programmed to develop in a male pattern, another process is needed for the formation of the testes, controlled bySry -gen normally located inY -chromosome. A significant amount of research data indicated the existence of a substance calledH - Y -antigen, which helps the conversion of the germinal gonads into testes, and this substance was eventually isolated (Pennisi, 1995).

When the testes are formed, they also start producing two hormones. Testosterone is responsible for the transformation of the wolf ducts into the male genital organs. SRY -gene activates the testicles of the embryo to produce anti-Müllerian hormone, which suppresses the transformation of Müllerian ducts into female genital organs (Haqq et al., 1994; Hunter , 1995). The fact that the presence of these two hormones is necessary for the development of a male embryo is sometimes called the "Adam's principle." It was also assumed that the complex genetic and biochemical interactions that must be realized for this are quite capable of providing a slightly greater vulnerability of the male path of development in relation to changes and complications in the environment. It is known, for example, that cases of mental retardation, learning disabilities, some forms of speech pathology and variant sexual behavior are more common in men than in women (Reinisch & Sanders, 1992).

As far as is known today, the development of the female genital organs and their entire reproductive system does not depend on the production of any hormone, and this fact has received the designation "Eve principle". If Sry The -gene is absent, so male hormones are not produced, the germ glands become ovaries, and the Müllerian ducts become the uterus, fallopian tubes and part of the vagina. Without testosterone to stimulate their development, the wolf ducts simply disappear. Still finding the gene DAX -1 in the X chromosome cast doubt on the assumption that the development of the female fetus occurs in some sense "by default" in the absence of Sry-gene.

From the 10th week of fetal development, sexual differentiation occurs at three different levels - the internal genital organs, the external genital organs and the brain. The development of the male body is mainly influenced by testosterone. Both the ovaries and testes first develop in the abdomen; then the ovaries are mixed into the pelvic region, and the testicles descend into the scrotum.

Among many lower mammals, males and females of the same species exhibit predictably different behaviors. Initially, it was assumed that hormones do not have much influence on the predetermination of the differing behavior of the sexes. The work of William Young (Young , 1961) and other studies have led to the hypothesis that testosterone, present in the embryos of many mammals, affects the structures and pathways of the central nervous system, especially the brain, so that the adult animal exhibits male behavior. If testosterone is absent, adult behavior is typical of females. This phenomenon has been found, for example, in monkeys and rats. Many mammals appear to have a critical period in development and in sexual differentiation when the presence of male hormones exerts this "masculinizing" effect. At the same time, a parallel and independent process of defeminization is taking place. The absence of androgens produced by the testes leads to the reverse processes: demasculinization and feminization (Olsen 1992; Rubinow & Schmidt, 1996).

Sexual differentiation deviations

Disorder	Cause	Typical manifestations	Prevailing gender identity
The consequences of intrauterine androgenization	Prescribing hormone therapy during pregnancy	Individuals genetically female (XX) with an enlarged penis-like clitoris. Usually undergoes surgery and are raised as girls
Effects of exposure to diethylstilbestrol	Prescribing diethylstilbestrol to prevent miscarriage	In boys: less separation of functions between the cerebral hemispheres; decreased spatial ability; less self-confidence. Girls; according to unverified data, there may be a masculinizing effect	In boys, it is masculine with the possibility of developing feminine traits; girls - undefined
Congenital adrenal hyperplasia	A genetic disorder in which the body accumulates androgens	Masculinization of the genitals in genetically female individuals (XX). Even after surgical correction and education as girls, there is a craving for masculine toys and behavior patterns, as well as more developed spatial abilities.	Anyone with a tendency to have some masculine traits
Candrogen insensitivity syndrome	Genetically male body cells are unable to respond normally to testosterone	Genetically boys (XY) are born with female genitals and are usually raised as girls. During puberty, breasts develop, but menstruation is absent. Typically exhibit feminine behavior	Feminine
Dihydrotestosterone deficiency syndrome	Lack of an enzyme necessary for the normal development of male genital organs	Genetically boys (XY) are born with genitals that look more like male ones. Male secondary sexual characteristics develop during puberty. Subsequently, they can live as males	Masculine

Exposure to synthetic hormones. Other evidence has shown that exposing the fetus to certain synthetic hormones similar to sex can lead to behaviors that can be considered male or female. Large doses of certain types of synthetic progestins, commonly used in the past to treat certain medical conditions during pregnancy, appear to affect the fetus in much the same way as testosterone. Some females who were prenatally exposed to these hormones were born with genitals that were more like males, such as enlarged clits. Both men and women exposed to hormones similar to testosterone were subsequently followed up and compared with control groups. Evidence has been obtained that such exposure leads to the manifestation of greater individualism, independence, self-confidence and aggressiveness than in men and women who were not exposed to synthetic hormones before birth. The "indices of masculinity" calculated according to some psychological scales in such people, as a rule, turn out to be higher (Reinisch & Sanders, 1992).

Another synthetic hormone similar to estrogen is called diethylstilbestrol. It has been widely used for the prevention of miscarriages for a number of years, but there is evidence that exposure of the fetus to this substance can lead to changes in brain development. Men who were exposed to such prenatal stimuli showed less separation of functions between the hemispheres, as well as a decrease in spatial ability, compared to their brothers who avoided such influence. Both of these effects can represent feminization or demasculinization of the fetus, since men in general tend to be more divided between hemispheres and have better spatial abilities than women. Boys exposed to diethylstilbestrol were judged in other studies to be less confident and less aggressive than control boys (Reinisch & Sanders, 1992), A number of studies have also suggested that exposure to diethylstilbestrol in women may lead to masculinization of their features, although much remains unclear as to the effect of this synthetic hormone on women (Hines & Collaer, 1993; LishetaL, 1992).

Congenital adrenal hyperplasia. Sometimes congenital adrenal hyperplasia is called androgenital syndrome. It is a genetic disorder that leads to the accumulation of androgenic hormones in the fetus or infant. Genetic girls born with this disorder often have masculinized genitals and may undergo surgery to make their genitals look more feminine. There is an indication that girls with this syndrome tend to prefer toys and activities that are considered more masculine (Berebaum & Hines , 1992), behave similarly to boys and perceive themselves as "tomboy" (Slijper et ai ., 1992), and also show more typically masculine traits than their sisters (Dittman, Kappes, & Kappes, 1993).

There is also some evidence that the ability for visual orientation in space, which is normally better developed in boys, is increased in girls with congenital adrenal hyperplasia. It has been suggested that it is this circumstance, and not the congenital features caused by hormonal influences, may have a natural consequence of the preference for playing with toys for boys. In contrast, boys who have experienced reduced androgen levels during their development appear to exhibit relatively impaired visual orientation abilities.

Research on the effect of such impairments on subsequent behavior sometimes yields conflicting data, and much work remains to be done to clarify the issue (Hines & Collaer, 1993; Levy & Heller, 1992; Money, 1994).

Androgen insensitivity syndrome. As explained earlier in this chapter, the secretion of hormones by the germinal glands is required for the formation of male genitalia and the eventual suppression of female reproductive structures. There is a rather rare genetic disorder called androgen insensitivity syndrome, in which the cells of the developing organism of genetic males (XY ) are not capable of a normal response to testosterone secreted by the testicles of the fetus. As a result, normal looking female genitals are formed instead of male organs, but the internal female organs remain in an underdeveloped state. During puberty, a female breast is formed. It is also possible to have a short vaginal canal, but since the uterus is absent, menstruation never occurs. These children are brought up from birth as girls, since anatomically they look like that, and it may well happen that the existence of some violations is diagnosed only in connection with the onset of menstruation (Money, 1994).

Studies in some genetic males who were raised as girls and who were treated like women have shown that such people exhibit traditionally feminine traits, including preferring housekeeping to a career and playing with dolls as children. Typically, they report that they want a male sexual partner and dream of starting a family. Scientists have suggested that in the case of androgen insensitivity syndrome, the ineffectiveness of the latter during the intrauterine development of these genetic males not only leads to feminization of their genitals, but also prevents any masculinization of their brains. This can create conditions that lead to unequivocally female behavior in later life (Hines & Collaer, 1993; Money , 1994). Of course, it should be noted that the processes of socialization in the course of raising such children as girls also contribute to the formation of these traditionally female traits. There is evidence from a clinical study that girls with this syndrome have difficulty adapting to their infertility and that a surgical procedure aimed at increasing the size of the vagina can lead to feelings of inferiority. Effective psychological support for children with such disabilities and their parents is extremely important (Slijper etal., 1994).

Dihydrotestosterone deficiency syndrome. There is another disorder that allows us to look at the role of hormones and socialization in the formation of gender identity from a new angle. This is a genetic disorder in which genetic males lack the enzyme dihydrotestosterone, which is necessary for the normal development of male external genital organs in the fetus.

Boys with DHT deficiency syndrome are born with undescended testes and an underdeveloped penis, which can be mistaken for the clitoris, while the internal genitals are normal. Sometimes there is a partially formed vagina, and the scrotum may be folded in such a way that it resembles the labia. Researchers have found 18 genetic males in the Dominican Republic, whose sex was mistakenly female at birth and who were raised as girls (Imperato - McGinleyet al., 1982). During puberty, these children suddenly began to show male secondary sexual characteristics, including increased muscle mass, decreased voice and enlarged penis. There was no breast enlargement or the development of any other female characteristics. These girls-becoming-boys were subjected to a lot of ridicule in their area. Sixteen of them eventually internalized male behavioral patterns and appeared to show sexual interest in women. These facts were explained based on the following hypothesis. Since during the period of intrauterine development, the embryonic gonads of these boys most likely secreted testosterone, and the violation affected only the formation of the external genital organs, this made it easier for children to switch to male gender identity and male gender role.

In other words, testosterone can exert some kind of masculinizing influence in the prenatal period on the formation and properties of the brain. But some dispute this conclusion, suggesting instead that social pressures may well lead to male behavior choices that are more acceptable in terms of traditional cultures. A similar case of congenital DHT deficiency syndrome has been reported in five men in New Guinea. They, too, were raised as girls until they showed masculine characteristics during puberty and began to lead a masculine lifestyle. Since they lived in a society dominated by men, identifying as a man rather than a woman meant an increase in social status (Herdt & Davidson, 1988).

Hormones and behavior

We are just beginning to understand the effects that hormones have on the human brain during the prenatal period. There is no doubt that postnatal learning is a key determinant of much of what is called male or female behavior, and that societal perceptions about the appropriateness of behavior for girls and boys (Levy & heller, 1992). It is possible to assume the existence of a multiplying effect, when biological and social factors act, alternately mutually reinforcing each other as a person matures. At birth, there are relatively few noticeable differences in behavior between the sexes. By interacting more and more with their surroundings, children learn certain roles, and then, during puberty, hormonal factors again cause significant shifts in sexual differentiation, further increasing the difference between women and men. It remains to be seen to what extent the influence of chromosomes and hormones in the prenatal period can predetermine the tendency of the infant to specific types of behavior and what kind of behavior is innate to be an integral part of masculinity or femininity.

Recently, attention has been drawn to the role of the hypothalamus, pituitary, and gonads and their interactions at various stages of development. A number of suggestions have been made that differences in the neuroendocrine system can also influence sexual orientation and behavior (Hines & Collaer, 1993; Swaab & Gofman, 1995; Ward, 1992). No behavior is exclusively male or exclusively female, other than reproductive. Although all behaviors are found in some proportion in all people, the threshold for a particular type of behavior may be lower in either men or women. This could mean that the combination of prenatal hormonal influences and postpartum factors may lead to more frequent manifestations of a particular behavior in one of the sexes. According to this hypothesis, the threshold for displaying aggression, for example, may be lower for men than for women. At the same time, however, there are claims that biological theories about differences in behavior between men and women are based on the results of research, far from being objective or carefully monitored.

It was stated that in reality, the works underlying such theories are in many ways imbued with the corresponding systems of social and political Values, which leads to the emergence of many gender myths (Fausto - Sterling, 1992).

It may be that prenatal factors prepare the conditions for the subsequent formation of gender identity and gender role.

Factors infancy andchildhood

Sex determination at birth. With the exception of babies born with unclear genitals, babies are usually born without difficulty in determining their sex. A quick glance at the genitals is enough to determine whether a newborn is classified as a boy or a girl. As soon as someone announces "Boy!" or "Girl!", social mechanisms are triggered, which will subsequently help the formation of an adult's gender identity.

Raising a child as a boy or girl. Most experts believe that boys and girls are treated differently in the upbringing process, which is called differentiating socialization. In every society, men and women are expected to fulfill certain prescribed roles, and in every society, as a rule, men and women have fairly consistent ideas about these expectations, whether they like them or not (Best & Williams, 1993). For example, immediately after sex determination, pink and blue can be used as a distinguishing feature corresponding to the named sex, and the child will be referred to as "he" or "she". It is also expected that girls will be treated gently and in a more protective manner, and boys will be tougher, encouraging them to behave independently. There is evidence that physical punishment is more often applied to boys than girls.

Nonetheless, reviews of the scientific literature on differential socialization have drawn different conclusions about the extent of differences in the treatment of parents with their sons and daughters. Some analyzes point to significant differences, while others find only minimal evidence of differences in parenting practices for boys and girls (Jacklin & Reynolds, 1993; Lytton & Romney, 1991).

The child's idea of \u200b\u200bhis body. As they grow up, children undergo further socialization and learn behavioral patterns that are considered appropriate for their gender. As the child becomes more and more aware of himself, he begins to respond to influences from the people around him and becomes a bearer of a distinguishable self-concept, including the idea of \u200b\u200bhimself as a boy or girl. Gradually, the child becomes more and more clearly aware of the sex of his body, whether he has male or female genital organs, and defines them as part of his sexual nature. All these factors lead to the development of a primary gender identity with t and. In fact, this gender identity is established so early that, with a few exceptions, any attempt to reassess sex (in the case of its incorrect determination at birth) turns out to be psychologically very difficult after 18-20 months of life.

Definitions

DIFFERENTIATING SOCIALIZATION - differences in attitudes towards boys and girls in the process of their upbringing.

THE EFFECT MULTIPLICATIONS - mutually reinforcing combination of hereditary and social factors in the process of human development.

SIKDROM LACK OF DIHYDROTESTOSTERONE - a condition in which a genetically male organism has underdeveloped genitals and can be defined as a girl at birth. However, during puberty, such people begin to develop male secondary sexual characteristics and, as a rule, male behavioral characteristics appear..

Congenital ADRENAL HYPERPLASIA - a genetic disorder that causes masculinization of genetic women, which also manifests itself in behavior.

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