Biological basis of sex. male fetus male fetus

The male gender is the weakest. The complex transformations that the fetus goes through in the womb are likely to increase the vulnerability of boys.

Fortunately, at least one threat to the future existence of men can be removed from the alarm list. The Y chromosome, which has been shrinking for millions of years, seems to have stopped doing that.

But it's too early to have fun. Contrary to popular belief that boys are unparalleledly strong and resilient, males of our species have inherent biological weaknesses that make them more vulnerable to life's hazards than girls, such as environmental pollutants (insecticides, lead, plasticizers) and affecting the brain and hormones. A number of studies have shown that sometimes boys get sick from them, while girls are not harmed at all.

Illustration by Charles Dana Gibson/Life Magazine.

To begin with, men are simply dying out. Nature, recognizing the weakness of the male sex, tried to compensate for quality with quantity: 106 boys were born for every 100 girls throughout human history. (Humans are not unique in this regard: male piglets are more likely to die before birth, so they conceive in greater numbers.) However, in recent decades, in the US, Japan, Canada, and Northern Europe, everywhere, wherever the researchers looked, the number of newborn boys began to decline. Between 1970 and 1990, there were 1.7 fewer boys born in the United States (per 1,000 births) than in previous decades and centuries, while in Japan the figure fell by 3.7.

Boys are more than two-thirds more likely to be born prematurely (before the 37th week of pregnancy) than girls. Despite all the advances in medicine, in the 1970s, boys were 30% more likely than girls to die before their first birthday, while in the middle of the 18th century this figure was only 10%.

If the boy still manages to grow up, new dangers await him. For example, he is more prone to neurological diseases: in the US, there are five times more autistic boys than girls. Boys are more difficult to tolerate poisoning with a small amount of lead, and more often suffer from asthma. The correlation between air pollution and autism is again stronger in boys.

What's the matter? Why has nature placed such a burden on the male sex?

The answer is simple: men's problems begin in the womb. The fetus that is destined to become a man goes through more complex changes in its development.

The nine-month transformation of several cells into a child is a period of increased vulnerability, when many chronic diseases are acquired. In our species, the female gender appears “by default”, this is, as it were, the basic and simplest model. The embryo begins development with female traits (that's why men have nipples). Transformation into a man is fraught with various dangers. When the Y chromosome induces the body of the fetus to produce testosterone around the eighth week, the hermaphrodite brain has to rewire itself, killing the cells of the areas responsible for communication and nurturing the centers of sexual activity and aggression. The relatively simple reproductive system of a woman is exchanged for a more complex male, new tissues appear - the testicles and the prostate gland. Therefore, in order for a man to grow, cells need to divide more often, and with each division, the risk of error increases.

In addition, the combination of XY chromosomes is more vulnerable than XX. In women, if one of the X chromosomes gets damaged, there is always a healthy double at the ready, which cannot be said about men. In addition, the X chromosome has never shortened, it contains more useful genetic information for brain development, regeneration, etc. This is probably why boys become autistic more often.

The immune system of women is stronger than men, because it is supported by estrogen - a hormone that counteracts the antioxidant process and thereby protects and even repairs the brain. Therefore, the male brain is more susceptible to damage. Indeed, autistic boys have lower levels of estrogen and higher testosterone levels.

Hormonal imbalance can be the result of poisoning - for example, with an insecticide. In 2001, the United States banned chlorpyrifos, which had been used for years, because of which boys seemed to be born with a lower IQ, while it affected girls much less frequently. And phthalates, sometimes used in toys, have been linked to increased aggression and attention problems, which are, of course, more common in boys. In addition, these substances feminize the male genital organs.

Boys also appear to be more vulnerable to bisphenol A, which is structurally similar to estrogen. It is used in the production of polycarbonate plastic, thermal paper, food packaging (foil, cans). Boys poisoned by this substance in the womb are more likely to demonstrate hyperactivity, aggressiveness, and anxiety. Women exposed to bisphenol A are more likely to give birth to boys with low levels of thyroid hormones (in girls, the effect is not seen), which direct brain development.

Without detracting from any rights of men, it should still be recognized that male weakness is a scientific fact. Perhaps we should think about how to protect the males of our species?

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 bleeding 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) muscular system, spine are formed, 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 upper lip and nasal cavities formed.

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 of the brain and its parts. 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 the sections of the gastrointestinal tract begins: the 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 upper limb development. 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.

The development of the nervous system continues. 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, large head, 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 of the 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.

The development of the kidneys, bladder and ureters is completed. 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, gonads, 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: it 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 improving the functionality of the cardiovascular 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.

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

Biological and social factors influencing gender identification are so closely related that it is difficult to understand them. When a child is born to parents, at the present time it is already known in advance what gender it will be, and if the mother did not know this before childbirth. What would then be her thirst to find out the sex of the baby as soon as possible. This is because parents treat their children differently depending on their gender. Thus, the behavior of mom and dad gives the child an incentive to learn more about himself by identifying himself by gender.

After conception, the process of formation of sexual characteristics in the embryo takes place. Having united, the female and male cells unite their chromosomes, 23 each from the sperm and the egg into a new organism. It turns out a total of 46 chromosomes. The female cell always carries the X chromosome, and the male spermatozoon is either Y or X. Thus, the female code is XX, and the male XY is male.

Further in the development of the embryo, the stage of formation of the gonads takes place. This happens in the sixth week of pregnancy. Until this time, the definition of the fetus is impossible. A male embryo occurs when a male chromosome is present. Here, the H-Y antigen, the antigen responsible for the male genetic code, must necessarily take place. The absence of this antigen indicates that the sex of the child will be female.

The appearance of the genital organs occurs after the stage of formation of the gonads with the help of hormones. This stage begins at 8-9 weeks of gestation. When more testosterone is produced, the sex is defined as male. Both in the female and in the male body there are hormones of both sexes, however, a greater amount of a certain hormone indicates a specific gender.

The process of intrauterine development of the fetus involves the effect of androgens on it (hormones that play a decisive role in the occurrence of secondary sexual characteristics in both one and the other sex, for example, coarseness of the voice, “vegetation” on the face and the whole body. Like all men, increased secretion sweat, elongation of the penis, the formation of the face and skeleton of the body according to the male type, an increase in the size of the prostate and the amount of its secretion). If the androgens did not have a sufficient effect on the fetus, then a girl will be born. In the first period, the laying of the penis occurs. Then comes the creation of the sexual orientation of the brain. There is a stage of formation of the male or female hypothalamus.

Bookmark of external organs

On the seventh week, the organs inherent in a certain sex undergo changes under the influence of sex hormones.
In the female fetus, steroid hormones form the labia, and in the male fetus, the penis. The genital tubercle becomes the penis in men and the clitoris in women.
At the beginning of the 3rd month, there is an opening of the vaginal fissure in girls and an increase in the length of the penis in boys. 11-12 weeks is the period when one sex can be accurately distinguished from the other by sexual characteristics; in a fetus with XY chromosomes, the median suture is overgrown.

Bookmark of internal organs:

1. The initial 6 weeks of pregnancy, the male and female embryo cannot be distinguished;
2. Only after 8 weeks of pregnancy, the testicles of an embryo with sexual characteristics of a boy secrete testosterone and an inhibitor of the Müllerian ducts, leading to the disappearance of the ducts themselves. In the absence of male hormones, the Mullerian ducts (a double canal with a connected distal part, which appears after the end of the second month of embryo development inside the mother from the grooves that perform the delimiting role of the epithelium) begin to transform into female organs. The Wolf ducts (structures in the fetus, subsequently developing into the male genital organs located inside) cease to exist.
3. After 9 months of pregnancy in the female fetus, the Mullerian duct turns into the fallopian tubes, and in the male fetus, the glands pass into the scrotum.

Video how the sex of the child is formed

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 Müllerian 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.

The external genital organs are laid in the same way in embryos of both sexes in the region of the cloacal membrane, which is the ventral wall of the cloaca. A spur-shaped protrusion of the coelom (urorectal fold) divides the cloaca into two sections: dorsal (anlage of the rectum) and ventral (more extensive primary urogenital sinus). With an embryo length of 15 mm, the urorectal fold reaches the cloacal membrane, divides it into anal and genitourinary parts, forming the primary perineum. From this point on, the development of the intestines and the genitourinary system occurs in isolation.

There is no consensus on the timing of laying the external genitalia.. According to some authors, this occurs on the 5th week with an embryo length of 13-15 mm; according to others - on the 6th; still others attribute their appearance to the 7th week of embryonic life. Differentiated, sex-appropriate development of the external genital organs begins at the end of the 3rd month of the embryonic period. In the male fetus, this process is carried out for a period of 9-10 weeks under the control of embryonic androgens. In female fetuses, feminization of the external genitalia is observed from the 17th to 18th week of pregnancy.

external genitalia of the examined embryos and fetuses (8-10 weeks of pregnancy), the sex of which was determined by the histological picture of the gonads, consist of labioscrotal folds and the genital tubercle.

The urethral groove runs on the dorsal surface of the genital tubercle. Its edges in the form of thin low plates close the primary urogenital opening of a slit-like form, which was formed after the opening of the urogenital membrane. The narrow laying of the primary perineum separates the urogenital fissure from the anus. The base of the genital tubercle covers the arcuate labioscrotal folds (genital folds). The fetuses of both sexes at this stage have an identical structure of the external genitalia, which we, like previous researchers, classify as neutral, indifferent.

In the second half of the prefetal period (11-13 weeks of pregnancy), the nature of the external genitalia in the female fetus remains unchanged. Only at the pudendal tubercle does the direction change slightly: from vertical it becomes dorsocaudal.

At the stage of 14-16 weeks, the ratio of the parts of the external genitalia remains the same. Increasing in size, they do not undergo morphological changes. The genital tubercle (clitoris), due to the significant predominance of longitudinal dimensions over transverse ones, looks especially large. While maintaining a dorsocaudal direction, it sharply protrudes from the underdeveloped labia majora, which remain narrow (1–2 mm) and flat, expressed only in the upper 2/3 of their length. The ratio of the length of the clitoris to its thickness is 3:5. Anogenital distance is 3 mm.

The period of 17 - 19 weeks is characterized by significant shaping processes that give the external genital organs of the fetus specifically female features. There is a rapid development of the labia majora. Passing from the front into the pubic tubercle, and from behind converging at an acute angle into the posterior commissure, they close the pudendal fissure. The clitoris, due to an increase in transverse dimensions, becomes relatively shorter, the small labia formed from the edges of the urethral fissure close over the clitoris in the form of a foreskin.

Along with morphological changes, there is a rapid growth of all components of the vulva, except for the clitoris.

At subsequent stages of intrauterine development, a uniform increase in the size of the external genitalia is observed, proportional to the overall growth of the fetus.

The length of the large shameful lips, as a rule, is equal to the length of the genital slit and reaches 35-36 mm by the time of the onset of childbirth. The older the fetus, the more elastic and fuller they close the genital gap.

Small shameful lips for a period of 17-18 weeks, they are thin skin folds up to 4 mm long (1/3 of the length of the labia majora). This ratio is maintained up to 23 weeks; then the growth rate of the small pudendal lips exceeds that of the large ones, and in a full-term fetus, the small lips are 2/3 of the length of the large ones. In an immature fetus, small shameful lips protrude from the gaping genital slit, and by the onset of urgent delivery, they are usually completely covered by large ones. There may be an unexpressed asymmetry in the size of the right and left lips, both large and small.

The clitoris undergoes interesting changes. With the growth of the fetus, it becomes wider, almost without increasing in length: by the 23-24th week, the ratio of its length to width is already less than 2, and in a full-term fetus it approaches 1.

The vestibule of the vagina until the 19th-20th week retains a pronounced funnel-shaped shape, covered with a smooth shiny membrane. In its depths, a barely protruding border of the hymen is determined.

Already by the 24-25th week, the vestibule is significantly flattened, and the hymen becomes available for measurement. Until 28-30 weeks, the hymen is often circular, and its opening has the shape of a collapsed longitudinal slit. The width of the hymen border reaches 2-3 mm.

After 30 weeks, there is a predominant growth of the lower semicircle of the hymen, a wedge-shaped protrusion is often found along the midline. At this level, the width of the lower part of the hymen is 5-7 mm. Its upper semicircle retains its former width, as a result of which the hole takes the form of a transverse crescent-shaped slot.

Timing of feminization of the external genitalia and endocrine activity of the fetal adrenal glands. In fetuses of 8-14 weeks, the fetal adrenal cortex is represented by a wide germinal zone with a narrow layer of undifferentiated cells of the definitive zone. Up to 11 weeks of pregnancy in the cells of the internal germinal zone, there is a high activity of acid and alkaline phosphatases and esterases. RNA is found in significant amounts in both zones. The content of lipids in the fetal zone is low; they are absent in the definitive cortex.

In fetuses of 12-14 weeks, the enzymatic activity and RNA content in the adrenal glands are reduced; the accumulation of lipids in the inner zone begins.

The stage of 15-17 weeks is characterized by differentiation of the definitive cortex according to the bundle type, which is accompanied by a further decrease in enzyme activity and a decrease in RNA in the cytoplasm.

Lipid deposits appear and rapidly grow in the cells of the outer zone. Their content in this zone remains high until the end of the antenatal period.

At 27-28 weeks, a glomerular zone is formed under the capsule of the gland.

By 34-35 weeks, there is an increase in the enzymatic activity of the adrenal cortex in parallel with an increase in cytoplasmic RNA, reaching a maximum level in the second half of intrauterine development.

Non-keto lipids of the definitive cortex are considered as C18 steroids: estradiol or estriol. In the second half of pregnancy, the level of estradiol in maternal and fetal blood is the same, while estriol in the fetus is 10 times higher than in the mother. Therefore, it is legitimate to consider C18-steroids of the outer zone of the fetal adrenal cortex as estriol responsible for the feminization of the female external genitalia in the antenatal period of ontogenesis.

In fetuses of 17-19 weeks, there is a rapid accumulation of lipids in the definitive zone of the adrenal cortex, and the external genitalia undergo feminization. By this time, there is a noticeable increase in the size of the fetal adrenal glands, their size exceeds (at this stage of development) the size of the internal genitalia of the fetus.

In the last stages of intrauterine life, the lipid content in the outer zone of the adrenal cortex remains high; in the external genitalia, feminization is completed and all parts of the vulva grow, except for the clitoris. Consequently, following the differentiation of the definitive fetal adrenal cortex in female fetuses, feminization and rapid growth of the external genitalia occur.

The development of the external genitalia of the fetus in the pathological course of pregnancy. Unfavorable conditions of intrauterine existence can disrupt the timing of morphogenesis. The state of the vulva in this case depends on the time and duration of the action of pathological factors. With long-term preservation of pathological conditions in 14.1% of cases, a lag (for a period of 2 to 17 weeks) in the development of the external genitalia was revealed. The short action of the damaging factor in 0.9% of cases contributes to earlier feminization of the genitals. Violation of the terms of morphogenesis of the vulva during the pathological course of pregnancy can be associated with a violation of steroidogenesis in the fetal adrenal glands, which manifests itself in a change in the accumulation of lipids in the definitive cortex.

Particularly noteworthy are cases of violations of the morphogenesis of the female external genitalia with prolonged use (during pregnancy) of large doses of progesterone.

In one of these cases, pregnancy from 4 weeks was complicated by the threat of termination. Progesterone treatment was performed at 8, 13, 16 and 18 weeks. On the 22nd week there was a spontaneous miscarriage. There is masculinization of the external genitalia of the female fetus.

It should be emphasized that the tissues of the genitals of the embryo and fetus are highly sensitive to the action of steroid hormones. Long-term use in the fetal period and in high doses of exogenous progesterone can disrupt fetal adrenal steroidogenesis, causing the production of excessive amounts of androgenic steroids responsible for masculinization of the external genitalia.