Biological basis of sex. Müllerian excretory duct. Fetal development according to male pattern Development according to male and female pattern

Pregnancy- This is a physiological process in which a new organism develops in the uterus, resulting from 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 acquires the features characteristic of a person;
2. Fetal(from 9 weeks to birth). At this time, the embryo is called a fetus.

The growth of a child, the formation of his organs and systems proceeds naturally in different periods of intrauterine development, which is subject 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 occurs 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 journey takes up to five days).

As a result of division a multicellular organism, which looks like a blackberry (in Latin "morus"), which is why the embryo at this stage is called morula. Approximately on the 7th day, the 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 some time, various tissues and organs of the fetus will develop from the internal cells.

Information At the time of implantation, a woman may have small bloody issues from the genital tract. Such secretions are physiological and do not require treatment.

Second week (8-14 days)

The outer cells of the morula grow tightly into the lining of the uterus. At the fetus the formation of the umbilical cord, placenta, as well as 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 beginnings 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 baby's heart begins to beat.

Fourth week (22-28 days)

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

From the beginning of the fourth week in the embryo body wrinkles appear, and appears rudiment of the spine(chord).

Ends by day 25 neural tube formation.

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

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

Development of the embryo 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: eye and inner ear formation continues;
6. Nervous system: the formation of brain regions begins.

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

On the face formed upper lip and nasal cavities.

Sixth week (36-42 days)

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

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

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

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

During this period, they begin upper limbs change: they lengthen and the rudiments of hands and fingers appear. The lower limbs are still in their infancy.

Changes in important organs:

1. A 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 departments begins gastrointestinal tract: stomach, small and large intestines. By this period, the liver and pancreas had 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 uteroplacental circulation is established. Now the breathing 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 at least 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 development upper limbs . The fingers are clearly visible, but their separation from each other has not yet occurred. The child begins to perform spontaneous hand movements in response to stimuli.

Good eyes formed, already covered with eyelids that protect them from drying out. The child can open his mouth.

There is a laying of the nasal fold and nose, two paired elevations are formed on the sides of the head, from which they will begin to develop ear shells.

Intensive development of the brain and its parts.

Eighth week (50-56 days)

The body of the embryo begins to straighten, length from the crown of the head to the coccyx is 15 mm at the beginning of the week and 20-21 mm on day 56.

Continues formation of important organs and systems Key words: digestive system, heart, lungs, brain, urinary system, reproductive system (boys develop testicles). The organs of hearing are developing.

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

Intensive growth of the head, upper and lower horses is noted. particularities, ossification of the long bones of the arms and legs and the skull develops. Fingers are clearly visible, there is no skin membrane between them.

Additionally The eighth week ends the embryonic period of development and begins the fetal. 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 fetus is about 22 mm, by the end of the week - 31 mm.

going on improvement of the vessels of the placenta which improves uteroplacental blood flow.

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 fingers. The head is lowered, the chin is closely pressed to the chest.

Changes occur in the cardiovascular system. The heart makes up to 150 beats per minute and pumps blood through its blood vessels. The composition of blood is still very different from the blood 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 developing in particular, the adrenal glands, which produce important hormones.

Improved cartilage tissue: auricles, cartilages of the larynx, vocal cords are being formed.

Tenth week (64-70 days)

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

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

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

The sucking reflex develops, the child begins reflex movements of the lips.

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

Eleventh week (71-77 days)

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

The body of the fetus remains disproportionate: small body big sizes heads, 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 the fetal eye occurs: at this time, the iris develops, which will later determine the color of the eyes. The eyes are well developed, semi-lidded or wide open.

Twelfth week (78-84 days)

Coccygeal-parietal size fetus is 50-60 mm.

Goes distinctly the development of the genital organs according to the female or male type.

going on further improvement digestive system. The intestines are elongated and fit in loops, as in an adult. Its periodic contractions begin - peristalsis. The fetus begins to make swallowing movements, swallowing amniotic fluid.

The development and improvement of the fetal nervous system continues. The brain is small, but exactly repeats all the structures of the brain of an adult. The cerebral hemispheres and other departments are well developed. Reflex movements are improved: the fetus can squeeze and unclench its 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 register. 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 weeks (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 torso lengthen, the size of the head is no longer so large in relation to the body.

Improvement of the digestive and nervous systems continues. Germs of milk teeth begin to appear under the upper and lower jaws.

The face is fully formed, clearly visible auricles, nose and eyes (completely closed for centuries).

14 weeks (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 ones. The forehead, nose, cheeks and chin are well defined on the face. The first hair appears on the head (very thin and colorless). The surface of the body is covered with fluffy hairs, which retain the lubrication of the skin and thus perform protective functions.

Improving the musculoskeletal system of the fetus. Bones become stronger. Increased motor activity: the fetus can roll over, bend, make swimming movements.

Completed kidney development Bladder and ureters. The kidneys begin to excrete urine, which mixes with the amniotic fluid.

: pancreatic cells begin to work, producing insulin, and pituitary cells.

There are changes in the genitals. 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, fruit weight - 70-75 grams. The head still remains quite large, but the growth of the arms, legs and torso begins to outpace it.

Improves the circulatory system. In a child in the fourth month, it is already possible to determine the blood type and Rh factor. Blood vessels (veins, arteries, capillaries) grow in length, their walls become stronger.

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.

Fully formed fingers and toes, they have an individual pattern.

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 work actively, every hour a small amount of urine is released into the amniotic fluid.

Fetal skin is very thin, subcutaneous fatty tissue is practically absent, so blood vessels are visible through the skin. The skin looks bright red, covered with downy 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": a frown of eyebrows is observed, 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 under it, subcutaneous fatty tissue begins to develop. The development of milk teeth, which are covered with dentin, continues. Under them, the germs of permanent teeth begin to form.

Reaction to sound stimuli. From this week, you can say for sure that the child began to hear. When strong sharp sounds appear, the fetus begins to move actively.

Fetal position changes. The head is raised and is almost vertical. The arms are bent at the elbow joints, the fingers are clenched into a fist almost all the time. Periodically, the child begins to suck his thumb.

Becomes distinct heartbeat. From now on, the doctor can listen to him with a stethoscope.

Eighteenth week (120-126 days)

The weight of the child is about 200 grams, length - up to 20 cm.

The formation of sleep and wakefulness begins. Most of the time the fetus sleeps, movements stop for 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 weight of the child increases to 250-300 grams, body length - up to 22-23 cm. The proportions of the body change: the head lags behind the body in growth, arms and legs begin to lengthen.

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

Improves the endocrine system: the pancreas, pituitary, adrenals, 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 ​​cm, weight - up to 340 grams.

Fetal skin is still thin, covered with a protective lubricant and fluffy hairs that can persist until the very birth. Intensively develops subcutaneous adipose tissue.

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

Improved movement coordination: the child confidently brings his finger to his mouth and begins to suck it. Expressed facial expressions: the fetus can close his eyes, smile, frown.

This week, all women feel the movements regardless of the number of pregnancies. Movement activity changes throughout the day. When irritants 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 become more and more active and tangible. The fetus moves freely in the uterine cavity: lies down with its head or buttocks, across the uterus. It can pull the umbilical cord, push off with hands and feet from the walls of the uterus.

Changes in sleep and wake patterns. Now the fetus spends less time sleeping (16-20 hours).

Twenty-second week (148-154 days)

At week 22, the size of the fetus increases to 28 cm, weight - up to 450-500 grams. The size of the head becomes proportional to the trunk and limbs. The legs are almost all the time in a bent state.

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

Improvement of the fetal nervous system: 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.

Significantly enlarged heart, are being improved functionality of cardio-vascular system.

Twenty-third week (155-161 days)

The body length of the fetus is 28-30 cm, weight - about 500 grams. The pigment begins to be synthesized in the skin, as a result, the skin acquires a bright red color. The subcutaneous fatty tissue is still quite thin, as a result, the child looks very thin and wrinkled. Lubrication covers the entire skin, is more abundant in the folds of the body (elbow, axillary, inguinal, and other folds).

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

Increased respiratory rate up to 50-60 times per minute.

The swallowing reflex is still well developed: the child constantly swallows amniotic fluid with particles of a protective lubricant of the skin. The liquid part of the amniotic fluid is absorbed into the blood, a thick green-black substance (meconium) remains in the intestines. Normally, the intestines should not be emptied until the baby is born. Sometimes swallowing water causes hiccups in the fetus, a 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 are getting stronger and clearer. The fetus occupies almost the entire place in the uterus, but can still change position and roll over. Muscles grow strongly.

By the end of the sixth month, the child has well-developed sense organs. Vision begins to function. If a bright light falls on the woman's stomach, the fetus begins to turn away, tightly closes the eyelids. Hearing is well developed. The fetus determines for itself pleasant and unpleasant sounds 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, longing), 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 a large number of capillaries, giving it a red color.

The face has a familiar human appearance: eyes, eyelids, eyebrows, eyelashes, cheeks, auricles are well expressed. The cartilages of the ears are still thin and soft, their curves and curls are not fully formed.

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

There are important processes in the maturation of the lungs: small elements of lung tissue (alveoli) are formed. Before the birth of the child, they are without air and resemble deflated balloons, which straighten out only after the first cry of the newborn. From the 25th week, the alveoli begin to produce a special substance (surfactant) necessary to maintain their shape.

Twenty-sixth week (176-182 days)

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

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

Improved sense organs. The child develops a sense of smell (smell).

Twenty-seventh week (183-189 days)

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

Organs of the endocrine system are actively functioning in particular the pancreas, pituitary gland and thyroid gland.

The fetus is quite active, 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 weight of the child 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 adipose tissue continues to accumulate. The skin is still red in color, 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 cartilages of the nose and ears remain soft. The nails do not yet reach the edge of the nail phalanx.

This week starts over active functioning of one of the hemispheres of the brain. 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, growth increases to 39 cm.

The child has already grown enough and takes up almost all the space in the uterus. The movements are not so chaotic. The movements are manifested in the form of periodic pushes with the legs and arms. The fetus begins to take a definite position in the uterus: head or buttocks down.

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

Thirtieth week (204-210 days)

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

Constant accumulation of subcutaneous adipose tissue, skin folds are straightened. The child adapts to the lack of space and assumes a certain position: curled up, arms and legs crossed. The skin still has a bright color, the amount of lubrication and vellus hair is reduced.

Continues development of alveoli and production of surfactant. The lungs prepare for the birth of the baby and the start of breathing.

The development of the brain continues brain, the number of convolutions and the area of ​​the cortex increase.

Thirty-first week (211-217 days)

The weight of the child is about 1500-1700 grams, growth increases to 40 cm.

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

Fully formed eyes. During sleep, the child closes his eyes, during wakefulness, the eyes are open, periodically 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 constriction or dilation of the pupil.

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

Thirty-second week (218-224 days)

The height of the child is about 42 cm, weight - 1700-1800 grams.

Continued accumulation of subcutaneous fat, in connection with which, the skin becomes lighter, there are practically no folds on it.

are being improved internal organs : 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 the production of milk.

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, growth is about 43-44 cm.

Skin becomes brighter and smoother, the layer of adipose tissue increases. Vellus hair is more and more wiped, the layer of protective lubricant, on the contrary, increases. The nails grow to the edge of the nail phalanx.

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

The work of internal organs is improving: the mass of the heart increases, the formation of the alveoli is almost completed, the tone of the blood vessels increases, the brain is fully formed.

Thirty-fourth week (232-238 days)

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

The baby is now in 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 childbirth.

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

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

Baby swallows amniotic fluid all the time, thereby stimulating the gastrointestinal tract and the functioning of the kidneys, 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 is 2200-2700 grams. Height increases to 46 cm.

All the 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 depart 6-7 hours after childbirth.

Thirty-sixth week (246-252 days)

The weight of the child varies greatly and can range from 2000 to 3000 grams, height - within 46-48 cm

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

The baby takes a certain position in the uterus: more often he 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 height of the child increases to 48-49 cm, the weight can fluctuate significantly. The skin has become lighter and thicker, the fat layer increases by 14-15 grams per day every day.

Cartilages of the nose and ears become tighter and more elastic.

Fully formed and mature lungs, the alveoli contain the necessary amount of surfactant for the breath of the newborn.

Completion of the digestive system: In the stomach and intestines, there are contractions necessary to push food through (peristalsis).

Thirty-eighth week (260-266 days)

The weight and height of the child varies greatly.

The fetus is fully mature and ready to be born. Outwardly, the child looks like a full-term newborn. The skin is light, fatty tissue is sufficiently developed, vellus hair is practically absent.

Thirty-ninth week (267-273 days)

Usually two weeks before delivery fetus starts to drop clinging to the bones of the pelvis. The child has already reached full maturity. The placenta begins to gradually grow old and metabolic processes worsen in it.

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

Well developed sense organs: the child picks up 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 neonatal born. The child is completely ready for childbirth. Weight can vary significantly: from 250 to 4000 and above 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.

The bones of the skull 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 week of pregnancy - Video

In the process of human embryonic development, the general patterns of development and stages characteristic of vertebrates are preserved. At the same time, features appear that distinguish the development of man from the development of other representatives of vertebrates; knowledge of these features is necessary for the doctor. The process of intrauterine development of the human embryo lasts an average of 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 the birth of a child). By the end of the embryonic period, the laying of the main embryonic rudiments of tissues and organs ends, and the embryo acquires the main features characteristic of a person. By the 9th week of development (the beginning of the 3rd month), the length of the embryo is 40 mm, and the weight is about 5 g. In the course of human embryology, studied at the Department of Histology and Embryology, the main attention is early stages (initial and embryonic periods), when the formation of a zygote, crushing, gastrulation, the formation of the 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 a person are formed during the entire active sexual period in large quantities. The duration of development of mature spermatozoa from ancestral cells - spermatogonia - is about 72 days. A detailed description of the processes of spermatogenesis is given in Chapter XXII. The formed spermatozoon has a size of about 70 microns and consists of heads and tail(see fig. 23). The human sperm nucleus contains 23 chromosomes, one of which is the sex chromosome (X or V), the rest are autosomes. Among sperm, 50% contain an X chromosome and 50% a Y chromosome. It has been shown that the mass of the X chromosome is greater than the mass of the Y chromosome; therefore, spermatozoa 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 spermatozoa. To ensure fertilization, the total number of spermatozoa in semen should be at least 150 million, and their concentration in 1 ml should be 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 of spermatozoa, under optimal conditions, they can reach the uterine cavity in 30 minutes - 1 hour, and after 1 1/2 -2 hours they can be in the distal (ampullar) part of the fallopian tube, where they meet with the egg and fertilization. Sperm retain their fertilizing capacity for up to 2 days.

female reproductive cells. The formation of female germ cells (ovogenesis) takes place in the ovaries cyclically, while during the ovarian cycle, as a rule, one oocyte of the 1st order is formed every 24-28 days (see Chapter XXII). The 1st order oocyte released from the ovary during ovulation has a diameter of about 130 microns and is surrounded by a dense shiny area, or membrane and 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. This is where the maturation of the germ cell ends. At the same time, as a result of the second division of maturation, an oocyte of the 2nd order (ovum) is formed, which loses centrioles and thus the ability to divide. The nucleus of a human egg contains 23 chromosomes; one of them is the sex X chromosome.

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

Embryogenesis

Fertilization

Fertilization occurs in the ampulla of the oviduct. The optimal conditions for the interaction of sperm with the egg are usually created within 12 hours after ovulation. During insemination, numerous sperm cells approach the egg and come into contact with its membrane. The egg begins to make rotational movements around its axis at a speed of 4 rotations per minute. These movements are due to the influence of the beating of the sperm flagella and last about 12 hours. In the process of interaction between the male and female germ cells, a number of changes occur in them. Sperm are characterized by capacitation and acrosomal reaction. Capacitation is a process of sperm activation that occurs in the oviduct under the influence of the mucous secretion of its glandular cells. In the mechanisms of capacitation, hormonal factors are of great importance, primarily progesterone (the hormone of the corpus luteum), which activates the secretion of the glandular cells of the oviducts. After capacitation, an acrosomal reaction follows, in which enzymes, hyaluronidase and trypsin, are released from spermatozoa, which play an important role in the process of fertilization. Hyaluronidase breaks down the hyaluronic acid contained in the shiny zone. Trypsin cleaves the 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 egg, and the dissolution of the zona pellucida occur. In the ovum, the cytolemma in the area of ​​sperm attachment forms an elevating tubercle, where one spermatozoon enters, while due to the cortical reaction (see above), a dense shell is formed - fertilization shell, preventing the entry of other sperm and the phenomenon of polyspermy. The nuclei of the female and male germ cells turn into pronuclei, are approaching, the stage is coming synkarion. A zygote appears and by the end of the 1st day after fertilization, crushing begins.

The sex of the unborn child is determined by the combination of sex chromosomes in the zygote. If the egg is fertilized by a spermatozoon with the sex chromosome X, then the resulting diploid set of chromosomes (there are 46 in humans) contains two X chromosomes characteristic of the female body. When fertilized by a sperm with a Y sex chromosome, the zygote produces a combination of XY sex chromosomes, 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 spermatozoa with 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, identified different kinds developmental pathologies due to an abnormal karyotype. The reason for such anomalies is most often the non-disjunction in anaphase of the halves of the sex chromosomes during the process of meiosis of the female germ cells. As a result, two chromosomes get into one cell and a set of sex chromosomes is formed. XX, and in none hit the other. 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 are X chromosomes (type XXX)- superfemale type, 2) OU karyotype (45 chromosomes) - non-viable; 3) karyotype XXY(47 chromosomes) - a male body with a number of disorders - reduced male gonads, no spermatogenesis, enlarged mammary glands (Klinefelter's syndrome); 4) XO type (45 chromosomes) - female body with a number of changes - short stature, underdevelopment of the genital organs (ovary, uterus, oviducts), absence of menstruation and secondary sexual characteristics (Turner's syndrome).

Splitting up

Cleavage 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 muscles 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 nutrition of the embryo is carried out due to the small reserves of yolk in the egg and, possibly, the contents of the fallopian tube.

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

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

The blastocyst stays 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 the increase in the number of blastomeres to 107 cells and the volume of fluid due to increased absorption of the secretion of the uterine glands by the trophoblast, as well as the active production of fluid by the trophoblast itself. The embryoblast is located in the form of a bundle 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 the 5th to the 7th day), the embryo passes the stage of a free blastocyst. During this period, changes occur in the trophoblast and embryoblast associated with the preparation for the introduction of the embryo into the wall of the uterus - implantation.

The blastocyst is covered by the fertilization membrane. In the trophoblast, the number of lysosomes increases, in which enzymes accumulate, ensuring the destruction (lysis) of uterine tissues and thereby contributing to the introduction of the embryo into the thickness of the uterine mucosa. Outgrowths appearing in the trophoblast destroy the fertilization membrane. germinal nodule flattens and turns into germinal shield, 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 uterine wall - begins 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 (sticking) and invasion (penetration). In the first stage, the trophoblast attaches to the uterine mucosa and two layers begin to differentiate in it - cytotrophoblast and symplastotrophoblast, or Plasmodiotrophoblast. During the second stage, the symplastotrophoblast, producing proteolytic enzymes, destroys the uterine mucosa. At the same time, the emerging trophoblast villi, penetrating into the uterus, sequentially destroy its epithelium, then the underlying connective tissue and vessel walls, and the trophoblast comes into direct contact with the blood of the maternal vessels. Formed implantation fossa, in which areas of hemorrhages 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 nourished directly from maternal blood (hematotrophic type of nutrition). From the mother's blood, the fetus receives not only all the nutrients, but also the oxygen necessary for breathing. At the same time, in the uterine mucosa, the formation of glycogen-rich connective tissue cells is enhanced. decidual cells. After the embryo is completely immersed in the implantation fossa, the hole formed in the uterine mucosa is filled with blood and tissue destruction products of the uterine mucosa. Subsequently, the mucosal defect is covered by a regenerating epithelium.

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

gastrulation

Gastrulation in humans occurs in two phases. The first phase precedes implantation or takes place during it, that is, it takes place on the 7th day, and the second phase begins only on the 14th-15th day. In the period between these phases, extra-embryonic organs are actively formed, providing the necessary conditions for the development of the embryo.

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

The extraembryonic mesoderm is involved in the formation of the anlages of the amniotic (together with the ectoderm) and vitelline (together with the endoderm) vesicles. The edges of the epiblast grow along the mesodermal anlage and form amniotic sac, the bottom of which is facing the endoderm. Reproducing cells of the endoderm form by the 13-14th day yolk vesicle. In humans, the yolk sac contains virtually 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 that faces deep into the wall of the uterus, adjacent to each other amniotic sac and yolk vesicle. This part is attached to the chorion with amniotic, or germinal, legs, formed by extra-embryonic mesoderm. The adjacent bottom of the amniotic sac and the roof of the yolk sac form embryonic shield. The thickened bottom of the amniotic vesicle is an epiblast, and the rest of its wall is extraembryonic ectoderm. The roof of the yolk vesicle is formed by the hypoblast, and its wall outside the shield is 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 continues until the 17th day of development. It becomes possible only after the described processes of the formation of extra-embryonic organs and the establishment of a hematotrophic type of nutrition. In the epiblast, the 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 line, corresponding in its potency to the lateral lips of the blastopore, and the primary nodule is an analogue of the dorsal lip. The fossa, located at the top 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, shifts through the dorsal lip into the space between the bottom of the amniotic vesicle and the roof of the yolk sac, giving notochordal branch. At the same time, the cellular material of the primary streak lays down in the form mesodermal wings to 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 germ also belongs to the same time. allantois. Starting from the 15th day, a small finger-like outgrowth, the 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 extra-embryonic organs is completed.

On the 17th day, the laying of the rudiments of axial organs continues. At this stage, all three germ layers are visible. As part of the ectoderm, cellular elements are arranged in several layers. From the zone of the head nodule, a massive eviction of cells is observed, which, located between the ecto- and endoderm, form the rudiment of the notochord. The walls of the amniotic sac and the yolk sac are two-layered for the most part. In the wall of the yolk sac, the formation of blood islands and primary blood vessels occurs.

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 villi of the chorion. The outer germ layer at the head end is formed by a single layer of cells, the highest along the medial axis of the embryo. When passing into the ectoderm of the amniotic vesicle, its cells are flattened. In the anterior cranial region, the primary streak and 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 single-layer epithelium (of endodermal and ectodermal origin, respectively) and visceral exocelomic mesoderm.

Feeding and respiration of the embryo occurs through allantochorion. Primary villi are bathed in maternal blood.

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

Separation of the body of the embryo from the extra-embryonic (provisional) organs occurs through the formation trunk fold, which is quite clearly expressed on the 20th day. The embryo is increasingly separated from the yolk sac until it is associated with a stalk, and the intestinal tube is formed.

Differentiation of germinal primordia

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

chordal process - provisional organ - resolves.

Mesoderm differentiation begins on the 20th day of embryogenesis. The dorsal sections of the mesodermal sheets are divided into dense segments lying on the sides of the chord - somites. The process of segmentation of the dorsal mesoderm and the formation of somites begins in the head of the embryo and rapidly spreads caudally. On the 22nd day of development, the embryo has 7 pairs of segments, on the 25th - 14, on the 30th - 30, and on the 35th day - 43-44 pairs. Unlike somites, the ventral mesoderm (splanchnotome) not segmented, but split into two leaves - visceral and parietal. A small section of the mesoderm that connects the somites with the splanchnotome is divided into segments - segmented pedicles (nephrogonotome). At the posterior end of the embryo, segmentation of these divisions does not occur. Here, instead of segmental legs, there is a non-segmented nephrogenic rudiment (nephrogenic strand).

In the process of differentiation of the mesoderm from the dermatome and sclerotome, an embryonic rudiment of connective tissue arises - mesenchyme. Other germ layers also take part 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 section of the intestinal tube also takes part in the formation of the mesenchyme.

endoderm differentiation. Isolation of the intestinal endoderm begins with the appearance of the trunk fold. The latter, deepening, separates the germinal endoderm of the future intestine from the extraembryonic endoderm of the yolk sac. In the posterior part of the embryo, the resulting intestine also includes that part of the endoderm from which the endodermal outgrowth of the allantois arises. At the beginning of the 4th week, an ectodermal invagination is formed at the anterior end of the embryo - mouth cavity. 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 stratified epithelium of the anterior part of the digestive tube and its derivatives subsequently develops. The mesenchyme of the intestinal tube is transformed into connective tissue and smooth muscles.

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

Extra-embryonic human organs

Chorion

The villous growths of the trophoblast, later called the chorion, consist of two structural components - the epithelium and the extra-embryonic mesenchyme. The mucous membrane in the part that after implantation will become part of the placenta - the main falling-away membrane, grows stronger than in other areas - the parietal falling-away membrane and the bag falling-away membrane that separates the embryo from the uterine cavity . In the future, this difference appears more and more clearly, and the villi in the region of the parietal and bursal membranes disappear altogether, and in the region of the main falling away membrane they are replaced by highly branched secondary villi, the stroma of which forms a connective tissue with blood vessels. From this point on, the chorion is divided into two sections - branchy and smooth. In the area where the branched chorion is located, the placenta is formed. Due to the main falling off shell, the maternal part is formed

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

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

Child's place, or placenta

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

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

In the placenta there are germinal, or fetal, part and maternal, or uterine. The fetal part is represented by a branched chorion and the amniotic membrane adhering to it, and the maternal part is a modified basal part of the endometrium.

The development of the placenta begins on the 3rd week, when vessels begin to grow into the secondary (epithelial-mesenchymal villi) and form tertiary villi. On the 6-8th week, macrophages, fibroblasts, and collagen fibers differentiate around the vessels. In the differentiation of fibroblasts and the synthesis of collagen, vitamins C and A play an important role, without sufficient intake of which in the body of a pregnant woman, the strength of the bond between the embryo and the mother's body is broken 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 main substance creates the most favorable conditions for the metabolism between the tissues of the mother and fetus. The main substance of the connective tissue of the chorion 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 uterine mucosa and the change of histiotrophic nutrition to hematotrophic occur. This means that the villi of the chorion are washed by the blood of the mother, which has poured out from the destroyed vessels of the endometrium into the lacunae.

The embryonic, or fetal, part of the placenta by the end of the 3rd month is represented by branching chorion plate, consisting of fibrous (collagenous) connective tissue covered with cyto- and syncytiotrophoblast. Branching chorionic villi (stem, or anchor, villi) well developed only on 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.

The chorionic epithelium, or cytotrophoblast, in the early stages of development is represented by a single-layer epithelium with oval nuclei. These cells reproduce by mitosis. Of these, a syncytiotrophoblast develops - a multinuclear structure covering the reducing cytotrophoblast. The syncytiotrophoblast contains a large number of various proteolytic and oxidative enzymes [ATPase, alkaline and acid phosphatases, 5-nucleotidase, DPN-diaphorase, glucose-6-phosphate dehydrogenase (G-6-PDH), a-GPDH, succinate dehydrogenase -SDH, cytochrome oxidase - CO, monoamine oxidase - MAO, non-specific esterases, LDH, NAD and NADP-diaphorases, etc. - only about 60], which is associated with its role in metabolic processes between the mother and fetus. Pinocytic vesicles, lysosomes, and other organelles are found in the cytotrophoblast and syncytium. Starting from the 2nd month, the chorionic epithelium becomes thinner and gradually replaced by syncytiotrophoblast. During this period, the syncytiotrophoblast exceeds the cytotrophoblast in thickness, on the 9-10th week the syncytium becomes thinner, and the number of nuclei in it increases. Numerous microvilli in the form of a brush border appear on the surface of the syncytium facing the lacunae.

There are slit-like submicroscopic spaces between the syncytium and the cellular trophoblast, 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 becomes very thin in places and the villi are covered with a fibrin-like oxyphilic mass, which, apparently, is a product of plasma coagulation and trophoblast decay (“Langhans' fibrinoid”).

With an increase in the 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 villus and its secondary and tertiary (final) branches. The total number of cotyledons in the placenta reaches 200.

The maternal part of the placenta is represented basal plate and connective tissue septa that separate cotyledons from each other, as well as gaps, filled with maternal blood. Trophoblast cells are also found at the points of contact between the stem villi and the sheath. (peripheral trophoblast).

Already in the early stages of pregnancy, chorionic villi destroy the outer, i.e., closest to the fetus, layers of the main falling membrane, and in their place are formed filled with maternal blood gaps, into which chorionic villi hang freely. The deep undestroyed parts of the falling off membrane, together with the trophoblast, form the basal plate.

Basal layer of the endometrium- connective tissue of the uterine lining decidual cells. These large, glycogen-rich connective tissue cells are located in the deep layers of the uterine mucosa. They have clear boundaries, rounded nuclei and oxyphilic cytoplasm. In the basal plate, more often at the site of attachment of the villi to the maternal part of the placenta, clusters of peripheral cytotrophoblast cells are found. They resemble decidual cells, but differ in more intense cytoplasmic basophilia. Amorphous substance (Rohr's fibrinoid) located on the surface of the basal plate facing the chorionic villi. The trophoblastic cells of the basal lamina, together with fibrinoid, play an essential role in ensuring immunological homeostasis in the mother-fetus system.

Part of the main falling off shell, located on the border of the branched and smooth chorion, i.e., along the edge of the placental Disc, does not collapse during the development of the placenta. Tightly adhering 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 constantly updated. It comes from the uterine arteries, which enter here from the muscular membrane of the uterus. These arteries run along the placental septa and open into lacunae. Maternal blood flows from the placenta through veins that originate from the lacunae with large holes.

Maternal and fetal blood circulate independently vascular systems and do not mix with each other. hemochorial barrier, separating both blood flows, 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 fibrinoid, which in some places covers the villi from the outside.

The formation of the placenta 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 extra-embryonic endoderm and extra-embryonic mesoderm, 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 connected with the intestine yolk stalk. The yolk sac itself is displaced into the space between the chorion 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 composition of 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 germ cells are formed - gonoblasts, migrating from it with blood to the rudiments of the sex glands.

Amnion

The amnion grows in size very quickly and by the end of the 7th week its connective tissue comes into contact with the connective tissue of the chorion. At the same time, the amnion epithelium passes to the amniotic stalk, which later turns into the umbilical cord, and in the region of the umbilical ring it merges 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 their reabsorption . The amniotic fluid creates the aquatic 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, BUT). Amnion also performs a protective function, preventing harmful agents from entering the fetus.

The epithelium in the early stages is single-layered squamous throughout, formed by large polygonal cells closely adjacent to each other, in which mitosis constantly occurs. On the 3rd month of embryogenesis, the epithelium is transformed into a prismatic one. The epithelium of the placental disc is prismatic, sometimes multi-rowed. On the surface of the epithelium there are microvilli. The cytoplasm always contains small lipid droplets, glycogen grains, 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 cuboidal. In the epithelium of the amnion covering the placental disc, secretion is probably predominant, and in the epithelium of the extraplacental amnion, resorption of amniotic fluid is predominant.

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, linking the amnion to the chorion. In the layer of dense connective tissue, the acellular part lying under the basement membrane and the cellular part can be distinguished. The latter consists of several layers of fibroblasts, between which there is a dense network of thin bundles of collagen and reticular fibers tightly adjacent to each other, 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 a layer of dense connective tissue, connect the amnion with the chorion. This connection is very fragile, and therefore both shells are easy to separate from each other. The main substance of the connective tissue contains many glycosaminoglycans.

Allantois

The allantois is a small finger-like endoderm that grows into the amniotic stalk. In humans, the 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 towards the chorion, the final branches of which lie in the stroma of the villi. On the 2nd month of embryogenesis, allantois is reduced.

umbilical cord

The umbilical cord is formed mainly from the mesenchyme located in the amniotic stalk and yolk stalk. The 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 remnants 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 tissue, called Wharton's jelly, that provides turgor and elasticity of the cord. The amniotic membrane covering the surface of the cord fuses with its gelatinous tissue.

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

Based on the foregoing, the main features early stages development of the human embryo: 1) asynchronous type of complete crushing and the formation of "light" and "dark" blastomeres; 2) early isolation and formation of extra-embryonic 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 the amnion, chorion and weak development of the yolk sac and allantois.

mother-fetus system

The mother-fetus system arises during pregnancy and includes two subsystems - the mother's body and the fetus's body, as well as the placenta, which is the 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, processing it, 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 receive information about the state of the developing fetus. In the endometrium are chemo-, mechano- and thermoreceptors, and in blood vessels baroreceptors. Receptor nerve endings of the free type are especially numerous in the walls of the uterine vein and in the decidua in the area of ​​​​attachment of the placenta. Irritation of the uterine receptors causes changes in the intensity of respiration, the level of blood pressure in the mother's body, aimed at providing 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), as well as hypothalamic endocrine system. An important regulatory function is performed by hormones: sex hormones, thyroxine, corticosteroids, insulin, etc. Thus, during pregnancy, the activity of the mother's adrenal cortex increases and the production of corticosteroids, which are involved in the regulation of fetal metabolism, increases. The placenta produces chorionic gonadotropin, which stimulates the formation of adrenocorticotropic hormone of the pituitary gland, which activates the activity of the adrenal cortex and enhances the secretion of corticosteroids.

Regulatory neuroendocrine apparatus of the mother ensures 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 fetal body perceive signals about changes in the mother's body or their own homeostasis. They are found in the walls of the umbilical arteries and veins, in the mouths of the hepatic veins, in the skin and intestines of the fetus.

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

Regulatory neurohumoral mechanisms of the fetal body are formed in the process of development. The first motor reactions in the fetus appear on 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 increased 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 suffering from diabetes when insulin production is reduced, there is an increase in body weight and an increase in insulin production in the pancreatic islets.

The action of the neurohumoral regulatory systems of the fetus is directed to the actuators - 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 mentioned, 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, human chorionic gonadotropin, placental lactogen, etc. Through the placenta, humoral and nervous connections are made between the mother and the fetus. There are also extraplacental humoral connections through the fetal 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. enter. Normally, foreign substances do not penetrate the mother's body through the placenta. They can begin to penetrate only in conditions of pathology, when the barrier function of the placenta is impaired. An important component of humoral connections are immunological connections that ensure the maintenance of immune homeostasis in the mother-fetus system.

Despite the fact that the body of the mother and fetus are genetically foreign in terms of protein composition, immunological conflict usually does not occur. This is ensured by a number of mechanisms, among which the following are of significant importance: 1 - proteins synthesized by syncytiotrophoblast, which inhibit the immune response of the mother's 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 the pericellular fibrinoid of the placenta, charged in the same way as the lymphocytes of the washing blood, is negative; 4 - proteolytic properties of the trophoblast also contribute to the inactivation of foreign proteins. Amniotic waters also take part in the immune defense, containing 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 case of an incompatible pregnancy.

A certain relationship between the homologous organs of the mother and the fetus is shown: the defeat of any organ of the mother leads to a violation of the development of the organ of the same name in the fetus. In an animal experiment, it has been established that the blood serum of an animal from which a part of an organ has been removed stimulates proliferation in the organ of the same name. However, the mechanisms of this phenomenon are not well understood.

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

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

In human ontogenesis, several critical ones can be distinguished. 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) development of axial rudiments of organs and formation of the placenta (3-8 weeks of development); 5) the stage of enhanced brain growth (15-20 weeks); 6) formation of the main functional systems of the body and differentiation of the reproductive apparatus (weeks 20-24); 7) birth; 8) neonatal period (up to 1 year); 9) puberty (11-16 years).

Violations of sexual development in boys are associated with pathology of the secretion or action of androgens. Clinical picture depends on the age at which the problem started.

Modern means for self-defense is an impressive list of items that differ in the principles of action. The most popular are those that do not require a license or permission to purchase and use. AT online store Tesakov.com, You can buy self-defense products without a license.

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

Stages of formation:

• intrauterine;
• prepubertal;
• pubertal.

prenatal period

The intrauterine 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 influences further ontogeny. In humans, the XY set determines the male sex. Up to 5-6 weeks, female and male embryos develop in the same way. Primary germ cells have the ability to differentiate both in one way and in another way up to the 7th week of pregnancy. Before this period, two internal ducts are laid: wolf (mesonephric) and mullerian (paramesonephric). The primary gonad up to 7 weeks is indifferent (indistinguishable in boys and girls). It consists of a cortex and a medulla.

After 6 weeks of development, sexual 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, causing it to transform into a male pattern.

Testicular embryogenesis:

• the formation of sex cords from the cortical substance of the primary gonad;
• the appearance of Leydig and Sertoli cells;
• the formation of convoluted seminiferous tubules from sex cords;
• the formation of the albuginea from the cortical substance.

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

At the 9th week of intrauterine development, the influence of the chromosomal and gonadal sex affects the genital ducts. Anti-Müllerian factor causes atrophy of the paramesonephric 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 epididymis, seminal vesicles, vas deferens and ejaculatory ducts are formed in the fetus. Primary germ cells are transformed into spermatogonia.

At the intrauterine stage, a great influence belongs to dihydrotestosterone. This hormone is produced 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.

• guide ligament defects;
• gonadal dysgenesis;
• hypogonadism in the prenatal period;
• immaturity of the femoral-genital nerve;
• anatomical barriers to the movement of the testicle;
• weakening of the tone of the muscles of the abdominal wall;
• violation of the synthesis and action of testosterone.

prepubertal period

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

puberty

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

Male sex steroids:

• enhance the growth of internal and external genital organs;
• affect the development of 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 and the formation of mature spermatozoa begins.

Normal onset of sexual development and definition of its delay

Puberty in boys starts with an increase. Average age the appearance of this symptom - 11 years.

Table 1 - Average values ​​of 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 occurs in less than 2 years);
• slow (formation takes 5 or more years).

The normal sequence of signs of puberty at puberty is:

1. testicular enlargement (10-11 years);
2. penis enlargement (10-11 years);
3. development of the prostate, an increase in the size of the larynx (11-12 years);
4. a significant increase in the testicles and penis (12-14 years);
5. pubic hair female type(12-13 years old);
6. nodulation in the area of ​​the mammary glands, (13-14 years old);
7. beginning of voice mutation (13-14 years old);
8. the appearance of hair in the armpits, on the face (14-15 years);
9. pigmentation of the skin of the scrotum, first ejaculation (14-15 years);
10. maturation of spermatozoa (15-16 years);
11. male-type pubic hair (16-17 years old);
12. stop the growth of the bones of the skeleton (after 17 years).

The stage of puberty is assessed according to Tanner.

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

Retarded puberty in boys

Delayed sexual development is determined if the boy has a testicular volume of less than 4 ml by the age of 14, 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 may be due to:

• constitutional features (family);
• violations of the hypothalamic-pituitary regulation ();
• primary insufficiency of testicular tissue ();
• 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 causes of delayed sexual development.

Family forms of delayed sexual development can be corrected with the help of. Anabolic steroids are prescribed to adolescents with this form of the disease to prevent short stature.

In secondary hypogonadism, gonadotropins and gonadorelin are used in the treatment. This therapy is the prevention of infertility in the future. The use of hormones of 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.

Precocious puberty in boys

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

Causes

Precocious puberty is divided into:

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

True precocious 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 tumors of the adrenal glands).

False precocious puberty is usually not accompanied by activation of spermatogenesis (except in cases of familial testosterone toxicosis).

Causes of false precocious puberty:

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

Diagnostics

Examination for signs of precocious puberty includes:

• collection of anamnesis;
• general inspection;
• examination of the genital organs;
• hormone tests (LH, FSH, testosterone, TSH,);
• samples with gonadoliberin;
• bone age study;
• skull x-ray, brain tomography, etc.

Treatment

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

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

Endocrinologist Tsvetkova I. G.

Add a comment

Kelly. Fundamentals of modern sexology. Ed. Peter

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

The development of gender and social approaches to it. Part 1

The development of gender and social approaches to it. Part 3

The development of gender and social approaches to it. Part 4

The development of gender and social approaches to it. Part 5

Hormones and fetal development. The gonads of the fetus, whose chromosomes are programmed to form female characteristics, will automatically develop into ovaries. However, if the gonads are programmed to develop in a male pattern, another process is required for the formation of the testicles, controlled SRY genome normally located in Y -chromosome. A significant amount of research evidence pointed to the existence of a substance called H-Y - an antigen that helps the development of the germinal gonads into testicles, and this substance was eventually isolated ( Pennisi, 1995).

When the testicles are formed, they also begin to produce two hormones. Testosterone ensures the transformation of the wolf ducts into the internal genital organs of a man.SRY - gene activates the testicles of the embryo to produce anti-Müllerian hormone, which inhibits the transformation of the 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-type embryo is sometimes referred to as the Adam principle. It has also been suggested that the complex genetic and biochemical interactions that must be realized to do this may well make the male developmental pathway somewhat more vulnerable to changes and complications in the environment. For example, cases of mental retardation, learning disabilities, some forms of speech pathology, and variant sexual behavior are known to be more common in men than in women ( Reinisch & Sanders, 1992).

As far as we know today, the development of the female reproductive organs and their entire reproductive system does not depend on the production of any hormone, and this fact has been labeled the “Eve principle”. If a SRY -the gene is missing, so male hormones are not produced, the germinal gonads become ovaries, and the Mullerian ducts become the uterus, fallopian tubes, and part of the vagina. Without testosterone to stimulate their development, the wolffian ducts simply disappear. However, the discovery of the gene DAX -1 in the X chromosome cast doubt on the assumption that the development of the fetus according to the female type occurs in a 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 genitalia and the brain. The development of the male body mainly occurs under the influence of testosterone. Both the ovaries and testicles first develop in the abdomen; then the ovaries will move into the pelvis, and the testicles will descend into the scrotum.

Among many lower mammals, males and females of the same species show predictably different behaviors. Initially, it was assumed that hormones do not have a great influence on the predestination of different 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 formation of the central nervous system, especially the brain, in such a way 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. In many mammals there appears to be 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 takes place. The absence of androgens produced by the testicles leads to the reverse processes: demasculinization and feminization ( Olsen, 1992; Rubinow & Schmidt, 1996).

Deviations in sexual differentiation

Disorder	Cause	Typical manifestations	Predominant gender identity
Consequences of intrauterine androgenization	Hormone therapy during pregnancy	Individuals are genetically female (XX) with an enlarged penis-like clitoris. Usually undergo surgical correction and raised as girls
Effects of exposure to diethylstilbestrol	Prescribing diethylstilbestrol to prevent miscarriage	In boys: less separation of functions between the hemispheres of the brain; decrease in spatial abilities; less self-confidence. In girls; according to unverified data, there may be a masculinizing effect	In boys - masculine with the possibility of developing feminine traits; in girls - indefinite
Congenital adrenal hyperplasia	A genetic disorder in which androgens accumulate in the body	Masculinization of the genitals in genetically female individuals (XX). Even after surgical correction and upbringing, girls show a craving for masculine toys and behavior patterns, as well as more developed spatial abilities.	Any, with a tendency to have some masculine traits
Candrogen insensitivity syndrome	The cells of the body of a genetically male organism are not able to respond normally to testosterone	Genetically boys (XY), are born with female genitalia and are usually raised as girls. During puberty, breasts develop, but menstruation is absent. They tend to show feminine behavior	Feminine
Dihydrotestosterone deficiency syndrome	Lack of an enzyme necessary for the normal development of the male reproductive organs	Genetically boys (XY), are born with genitalia that look more like a man's. During puberty, male secondary sexual characteristics develop. Subsequently, they can live as males	Masculine

exposure to synthetic hormones. Other evidence has shown that fetal exposure to certain sex-like synthetic hormones can lead to behavioral features, which can be considered as characteristic of men or women. 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 prenatally exposed to these hormones have been born with genitalia more like those of men, such as enlarged clitoris. Both men and women exposed to testosterone-like hormones were subsequently observed and compared with control groups. Evidence has been obtained that such exposure leads to greater individualism, independence, self-confidence and aggressiveness than in men and women who were not exposed to synthetic hormones before birth. Calculated according to some psychological scales, "indices of masculinity" 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 a number of years to prevent miscarriages, but there has been evidence that fetal exposure to this substance can lead to changes in brain development. Men who were exposed to such prenatal influences showed less separation of functions between the hemispheres, as well as a decrease in spatial abilities compared to their brothers who avoided such influences. Both of these effects may represent feminization or demasculinization of the fetus, since men in general have a greater separation of functions between the hemispheres and better spatial abilities than women. Boys exposed to diethylstilbestrol have been rated as less confident and less aggressive than control boys in other studies (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 designed to give their genitals a more "feminine" appearance. There is an indication that girls with this syndrome tend to prefer toys and activities that are considered more masculine ( Berebaum & Hines , 1992), behave like boys and perceive themselves as "tomboys" ( Slijper et ai ., 1992) and also display more typically male 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 congenital features caused by hormonal influences, that may have a natural consequence of the preference for playing with toys for boys. In contrast, boys who have experienced reduced levels of androgens during their development appear to exhibit relatively impaired visual orientation abilities.

Research on the impact of such impairments on subsequent behavior is sometimes conflicting, and much work remains to be done to elucidate 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 gonads is necessary for the formation of the male genitalia and the eventual suppression of the female reproductive structures. There is a fairly rare genetic disorder called androgen insensitivity syndrome, in which cells from the developing body of genetic males ( XY ) are not capable of a normal response to testosterone secreted by the fetal testicles. As a result, instead of male organs, normal-looking female genitalia are formed, but the internal female organs remain in an underdeveloped state. During puberty, the 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 as girls from birth, since anatomically they look like girls, and it may well happen that the existence of some disorders is diagnosed only in connection with the absence of menstruation ( Money, 1994).

Studies on some genetic males who were raised as girls and treated like women have shown that such people display traditionally feminine traits, including a preference for housekeeping over a career and playing with dolls as children. Typically, they report wanting a male sexual partner and dreaming of starting a family. The scientists hypothesized that in the case of androgen insensitivity syndrome, the inefficiency of the latter during prenatal development of these genetic males not only leads to the feminization of their genitals, but also prevents any masculinization of their brains. This can create conditions leading to unambiguously feminine 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 feminine traits. There is evidence from a clinical study that girls with this syndrome have difficulty adjusting to their infertility and that a surgical procedure to increase the size of the vagina can lead to feelings of inferiority. Effective psychological support for children with such disorders and their parents is extremely important ( Slijper etal., 1994).

Syndrome of lack of dihydrotestosterone. There is another violation 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 men lack the enzyme dihydrotestosterone, which is necessary for the normal development of male external genitalia in the fetus.

Boys with dihydrotestosterone deficiency syndrome are born with undescended testicles and an underdeveloped penis, which can be mistaken for a clitoris, while the internal genital organs are normally developed. Sometimes there is a partially formed vagina, and the scrotum may be folded in such a way that it resembles the labia. Researchers found 18 genetic males in the Dominican Republic who were misidentified as 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 an increase in muscle mass, a lowering of the timbre of the voice, and an enlarged penis. There was no breast enlargement or development of any other female characteristics. These girls-becoming-boys were subjected to much ridicule in their area. Sixteen of them eventually adopted masculine behavioral patterns and apparently showed sexual interest in women. These facts were explained on the basis of the following hypothesis. Since the fetal gonads of these boys most likely secreted testosterone during fetal development, and the disturbance only affected the formation of the external genitalia, this allowed the children to more easily transition to a male gender identity and a male gender role.

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

Hormonesandbehavior

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 termed male or female behavior, and that opinions about the appropriateness of this or that behavior for girls and boys are shaped by society (Levy & Heller, 1992). We can assume the existence of a multiplication 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 environment, children learn certain roles, and then at 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 effects of chromosomes and hormones in the prenatal period can predetermine the infant's tendency to specific types of behavior and which behavior is innately an integral part of masculinity or femininity.

Recently, attention has been drawn to the role of the hypothalamus, pituitary gland, and gonads and to their interaction 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 types of behavior occur in some proportion in all people, the threshold for exhibiting a particular type of behavior may be lower in either men or women. This may mean that the combination of prenatal hormonal influences and postnatal factors may lead to more frequent manifestation of one or another behavior in one of the sexes. According to such a hypothesis, the threshold for the manifestation of 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 rely on research that is far from being objective or carefully controlled.

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

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

Factorsinfancy andchildhood

Sex determination at birth. With the exception of cases of birth of children with vaguely expressed genitals, at the birth of babies there is usually no difficulty in determining their sex. A glimpse of 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 launched that will later help shape the gender identity of an adult.

Raising a child as a boy or girl. Most experts believe that boys and girls are treated differently in the process of education, which is called differentiating socialization. In every society men and women are expected to conform to certain prescribed roles, and in every society men and women tend to 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 colors 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 more gently and in a more protective manner, while boys will be treated more harshly, encouraging them to behave independently. There is evidence that physical punishment is more commonly used on boys than on girls.

Nevertheless, reviews of the scientific literature on the topic of differentiating socialization draw different conclusions about the degree 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 dissimilarity in parenting practices towards boys and girls (Jacklin & Reynolds, 1993; Lytton & Romney, 1991).

The idea of ​​the child about his body. As children grow up, they 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 the influences of the people around him and becomes the bearer of a discernible self-concept, including the idea of ​​himself as a boy or girl. Gradually, the child becomes more and more aware of the sex of his body, the presence of male or female genital organs, and defines them as part of his sexual nature. All these factors lead to the development of primary gender identity with t and. In fact, this gender identity is established so early that, with few exceptions, any attempt to re-evaluate the sex (if it was incorrectly determined at birth) turns out to be psychologically very difficult already after 18-20 months of life.

Definitions

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

EFFECTMULTIPLICATIONS - mutually reinforcing combination of hereditary and social factors in the process of human development.

SYKDROMDIHYDROTESTOSTERONE DEFICIENCY - 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 form male secondary sexual characteristics and, as a rule, male behavioral characteristics appear..

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

SYNDROMEANDROGEN INSUFFICIENCY - a condition in a developing fetus in which its cells do not respond to androgens, resulting in the development of female vulva in genetic males ( XY ). In the future, feminization of behavioral characteristics is also observed..

H- Y-ANTIGEN - substance produced in the embryo in the presence of Y-xpo mosomes. Plays an important role in the transformation of the germinal gonads into testicles.

ANTIMULLEROVHORMONE - a hormone secreted by the fetal testicles that prevents the development of female reproductive structures from the Müllerian ducts.

INTRAUTERINE ANDROGENIZATION - a condition in which the use of hormones prescribed during pregnancy causes masculinization of the genital organs of a genetically female ( XX ) of the fetus and possibly affect subsequent behavioral characteristics, even if the child is raised as a girl.

Until now, one has to deal with the myth that initially the human embryo develops along the female path, and only then in future boys, under the influence of androgens, male ones are formed from the female genital organs. This is not true.

Genetic sex determination occurs during fertilization. The Y chromosome is a genetically male determinant (the zygote contains 22 pairs of autosomes + XY sex chromosomes, i.e. 46XY). The karyotype of the zygote is genetically female - 46XX.

Until about the 6-7th week of intrauterine life of the embryo, its gonads develop identically in both men and women. This so-called indifferent stage development of the embryo, when the reproductive system of both sexes develops according to one genetic program.
During the formation of the gonadal sex, the fetus develops male ( Wolfs) and female ( Mullers) ducts. Initially, the development of these ducts begins unipotentially, i.e., regardless of the future sex, and only one of them can develop into a genital tract associated with a specific genetic sex of the fetus. In particular, the wolf duct turns into the structures of the male genital tract, and the mullerian - the female. The simultaneous presence of the Wolffian and Mullerian ducts at this stage is a legacy from our distant hermaphrodite ancestors who lived hundreds of millions of years ago.

Primary germ cells are formed in the wall of the yolk sac and on the 5th week of embryogenesis begin to migrate into the gonadal folds - rudiments indifferent gonads AT indifferent period development of primary gonads in their stromal tissue contains two types of cells. One type of cell at the gonadal stage of sex differentiation develops into the ovarian granulosa cells or into the Sertoli cells of the seminiferous tubules in the testes. The second type of cells at the gonadal stage differentiate into cells of the transparent membrane (theca pellucida) in the ovaries or Leydig cells in the testes.

Embryo male at the 6-7th week of embryonic life after the migration of primary germ cells into the primary gonads in the presence of a Y-chromosome containing SRY gene, differentiation occurs Sertoli cells. In the process of differentiation, Sertoli cells are located around the primary germ cells, as a result, the development of testicular tubules in the primary gonads begins. Differentiation of mesenchymal (stromal) cells of the gonads into interstitial Leydig cells, which will subsequently secrete the male sex hormone testosterone, starts from the 8-9th week and ends at the 10th week of fetal development.
In the female embryo, differentiation of primary gonads into ovaries (determined FOXL2 genome) starts from the 9th week, when the X chromosomes are activated. If the FOXL2 gene fails, the primary gonads will develop into ... testicles!

Development internal male reproductive organs in the fetus occurs under the influence of testosterone. The secretion of testosterone by Leydig cells in the male fetus begins around the 8-9th week of development, under the influence of placental chorionic gonadotropin, the secretion of which is stimulated by growth hormone. Under influence testosterone Wolffian ducts are transformed in their development into the epididymis, vas deferens and seminal vesicles.
The Sertoli cells of the fetal testicles secrete mullerian inhibitory factor(synonym - anti-mullerian hormone) calling regression Müllerian ducts in a male fetus.

In a developing fetus by female type, granulosa cells and tunica pellucidum cells do not secrete anti-Mullerian hormone and testosterone. In the absence of anti-Müllerian hormone, the Müllerian ducts develop into internal female reproductive organs (fallopian tubes, uterus, upper vagina), and at the same time regression wolf ducts due to the lack of testosterone secretion in the fetus.

Differentiation of the external genitalia occurs from the urogenital sinus, genital tubercle, genital folds and genital folds. The development of the external genital organs depends on sex hormones.
In a developing fetus by male type, under influence testosterone the urogenital sinus gives rise to the prostate and bulbourethral glands.
5-alpha reductase catalyzes the conversion of testosterone to dihydrotestosterone. Approximately at the 12th week of intrauterine development, the genital tubercle under the influence dihydrotestosterone differentiates into the penis, the genital folds form the distal urethra, and the genital folds develop into the scrotum.
In a developing fetus by female type, in the absence of androgens, at about the 14th week of intrauterine development, the urogenital sinus develops into the lower part of the vagina, the genital tubercle into the clitoris, and the genital folds and genital folds differentiate into the labia minora and labia majora, respectively. Female sex hormones contribute to the differentiation of the extragonadal organs of the female reproductive system.

As we can see, a fetus with an XY karyotype cannot be considered a female fetus at any stage.