Anatomical and physiological features of the respiratory system in young children. Features of the structure and development of the respiratory system in children

The beginning of the formation of the tracheopulmonary system begins at the 3-4th week of embryonic development. Already by the 5th-6th week of embryonic development, branching of the second order appears and the formation of three lobes of the right lung and two lobes of the left lung is predetermined. During this period, the trunk of the pulmonary artery is formed, which grows into the lungs along the course of the primary bronchi.

In the embryo at the 6th-8th week of development, the main arterial and venous collectors of the lungs are formed. Within 3 months, the bronchial tree grows, segmental and subsegmental bronchi appear.

During the 11-12th week of development, there are already areas of lung tissue. They, together with segmental bronchi, arteries and veins, form the embryonic lung segments.

Between the 4th and 6th months there is a rapid growth of the pulmonary vasculature.

In fetuses at 7 months, the lung tissue acquires the features of a porous canal structure, the future air spaces are filled with fluid, which is secreted by the cells lining the bronchi.

At 8-9 months of the intrauterine period, further development of the functional units of the lungs occurs.

The birth of a child requires the immediate functioning of the lungs, during this period, with the onset of breathing, significant changes in the airways, especially the respiratory section of the lungs, occur. The formation of the respiratory surface in individual sections of the lungs occurs unevenly. The condition and readiness of the surfactant film lining the lung surface is of great importance for the expansion of the respiratory apparatus of the lungs. Violation of the surface tension of the surfactant system leads to serious illnesses in a young child.

In the first months of life, the child retains the ratio of the length and width of the airways, as in the fetus, when the trachea and bronchi are shorter and wider than in adults, and the small bronchi are narrower.

The pleura covering the lungs in a newborn child is thicker, looser, contains villi, outgrowths, especially in the interlobar grooves. Pathological foci appear in these areas. The lungs for the birth of a child are prepared to perform the function of respiration, but individual components are at the stage of development, the formation and maturation of the alveoli is rapidly proceeding, the small lumen of the muscular arteries is being reconstructed and the barrier function is being eliminated.

After three months of age, period II is distinguished.

1. a period of intensive growth of the lung lobes (from 3 months to 3 years).
2. final differentiation of the entire bronchopulmonary system (from 3 to 7 years).

Intensive growth of the trachea and bronchi occurs in the 1st-2nd year of life, which slows down in subsequent years, and small bronchi grow intensively, the branching angles of the bronchi also increase. The diameter of the alveoli increases, and the respiratory surface of the lungs doubles with age. In children up to 8 months, the diameter of the alveoli is 0.06 mm, at 2 years - 0.12 mm, at 6 years - 0.2 mm, at 12 years - 0.25 mm.

In the first years of life, growth and differentiation of elements of the lung tissue and blood vessels occur. The ratio of share volumes in individual segments is leveled out. Already at the age of 6-7 years, the lungs are a formed organ and are indistinguishable in comparison with the lungs of adults.

Features of the child's respiratory tract

The respiratory tract is divided into upper ones, which include the nose, paranasal sinuses, pharynx, Eustachian tubes, and lower ones, which include the larynx, trachea, bronchi.

The main function of respiration is to conduct air into the lungs, clean it from dust particles, protect the lungs from the harmful effects of bacteria, viruses, and foreign particles. In addition, the respiratory tract warms and humidifies the inhaled air.

The lungs are represented by small sacs that contain air. They connect with each other. The main function of the lungs is to absorb oxygen from atmospheric air and release gases into the atmosphere, primarily carbon dioxide.

Breathing mechanism. When inhaling, the diaphragm and chest muscles contract. Exhalation at an older age occurs passively under the influence of the elastic traction of the lungs. With obstruction of the bronchi, emphysema, as well as in newborns, active inspiration takes place.

Normally, respiration is established with such a frequency at which the volume of respiration is performed due to the minimum energy expenditure of the respiratory muscles. In newborns, the respiratory rate is 30-40, in adults - 16-20 per minute.

The main carrier of oxygen is hemoglobin. In the pulmonary capillaries, oxygen binds to hemoglobin to form oxyhemoglobin. In newborns, fetal hemoglobin predominates. On the first day of life, it is contained in the body about 70%, by the end of the 2nd week - 50%. Fetal hemoglobin has the property of easily binding oxygen and difficult to give it to the tissues. This helps the child in the presence of oxygen starvation.

The transport of carbon dioxide occurs in a dissolved form, the saturation of the blood with oxygen affects the content of carbon dioxide.

The respiratory function is closely related to the pulmonary circulation. This is a complex process.

During breathing, its autoregulation is noted. When the lung is stretched during inhalation, the inspiratory center is inhibited, and during exhalation, exhalation is stimulated. Deep breathing or forced inflation of the lungs leads to reflex expansion of the bronchi and increases the tone of the respiratory muscles. With the collapse and compression of the lungs, the bronchi narrow.

The respiratory center is located in the medulla oblongata, from where commands are sent to the respiratory muscles. The bronchi lengthen during inhalation, and shorten and narrow during exhalation.

The relationship between the functions of respiration and blood circulation is manifested from the moment the lungs expand at the first breath of a newborn, when both the alveoli and blood vessels expand.

Respiratory problems in children can lead to impaired respiratory function and respiratory failure.

Features of the structure of the child's nose

In young children, the nasal passages are short, the nose is flattened due to an underdeveloped facial skeleton. The nasal passages are narrower, the shells are thickened. The nasal passages are finally formed only by 4 years. The nasal cavity is relatively small. The mucous membrane is very loose, well supplied with blood vessels. The inflammatory process leads to the development of edema and reduction due to this lumen of the nasal passages. Often there is stagnation of mucus in the nasal passages. It can dry out, forming crusts.

When closing the nasal passages, shortness of breath may occur, the child during this period cannot suckle the breast, worries, throws the breast, remains hungry. Children, due to the difficulty of nasal breathing, begin to breathe through the mouth, their heating of the incoming air is disturbed and their tendency to catarrhal diseases increases.

If nasal breathing is disturbed, there is a lack of odor discrimination. This leads to a violation of appetite, as well as a violation of the idea of ​​​​the external environment. Breathing through the nose is physiological, breathing through the mouth is a symptom of a disease of the nose.

Accessory cavities of the nose. The paranasal cavities, or sinuses as they are called, are confined spaces filled with air. The maxillary (maxillary) sinuses are formed by the age of 7. Ethmoid - by the age of 12, the frontal is fully formed by the age of 19.

Features of the lacrimal canal. The lacrimal canal is shorter than in adults, its valves are not sufficiently developed, and the outlet is close to the corner of the eyelids. In connection with these features, the infection quickly gets from the nose into the conjunctival sac.

Features of the pharynxchild

The pharynx in young children is relatively wide, the palatine tonsils are poorly developed, which explains the rare diseases of angina in the first year of life. Completely tonsils develop by 4-5 years. By the end of the first year of life, the tonsil tissue becomes hyperplastic. But its barrier function at this age is very low. The overgrown tonsil tissue can be susceptible to infection, so diseases such as tonsillitis, adenoiditis occur.

The Eustachian tubes open into the nasopharynx and connect it to the middle ear. If the infection travels from the nasopharynx to the middle ear, inflammation of the middle ear occurs.

Features of the larynxchild

The larynx in children is funnel-shaped and is a continuation of the pharynx. In children, it is located higher than in adults, it has a narrowing in the area of ​​the cricoid cartilage, where the subglottic space is located. The glottis is formed by the vocal cords. They are short and thin, this is due to the high sonorous voice of the child. The diameter of the larynx in a newborn in the region of the subglottic space is 4 mm, at 5–7 years old it is 6–7 mm, by the age of 14 it is 1 cm. layer, which can lead to severe respiratory problems.

In boys older than 3 years, the thyroid cartilages form a sharper angle; from the age of 10, a typical male larynx is formed.

Features of the tracheachild

The trachea is a continuation of the larynx. It is wide and short, the framework of the trachea consists of 14-16 cartilaginous rings, which are connected by a fibrous membrane instead of an elastic end plate in adults. The presence of a large number of muscle fibers in the membrane contributes to a change in its lumen.

Anatomically, the trachea of ​​a newborn is at the level of the IV cervical vertebra, and in an adult it is at the level of the VI-VII cervical vertebra. In children, it gradually descends, as does its bifurcation, which is located in a newborn at the level of the III thoracic vertebra, in children of 12 years old - at the level of the V-VI thoracic vertebra.

In the process of physiological respiration, the lumen of the trachea changes. During coughing, it decreases by 1/3 of its transverse and longitudinal dimensions. The mucous membrane of the trachea is rich in glands that secrete a secret that covers the surface of the trachea with a layer 5 microns thick.

The ciliated epithelium promotes the movement of mucus at a speed of 10-15 mm / min in the direction from the inside to the outside.

Features of the trachea in children contribute to the development of its inflammation - tracheitis, which is accompanied by a rough, low-pitched cough, reminiscent of a cough "like a barrel".

Features of the bronchial tree of a child

The bronchi in children are formed by birth. Their mucous membrane is richly supplied with blood vessels, covered with a layer of mucus, which moves at a speed of 0.25-1 cm / min. A feature of the bronchi in children is that the elastic and muscle fibers are poorly developed.

The bronchial tree branches to the bronchi of the 21st order. With age, the number of branches and their distribution remain constant. The dimensions of the bronchi change intensively in the first year of life and during puberty. They are based on cartilaginous semirings in early childhood. Bronchial cartilage is very elastic, pliable, soft and easily displaced. The right bronchus is wider than the left and is a continuation of the trachea, so foreign bodies are more often found in it.

After the birth of a child, a cylindrical epithelium with a ciliated apparatus is formed in the bronchi. With hyperemia of the bronchi and their edema, their lumen sharply decreases (up to its complete closure).

The underdevelopment of the respiratory muscles contributes to a weak cough impulse in a small child, which can lead to blockage of the small bronchi with mucus, and this, in turn, leads to infection of the lung tissue, a violation of the cleansing drainage function of the bronchi.

With age, as the bronchi grow, the appearance of wide lumen of the bronchi, the production of a less viscous secret by the bronchial glands, acute diseases of the bronchopulmonary system are less common compared to children of an earlier age.

Lung Featuresin children

The lungs in children, as in adults, are divided into lobes, lobes into segments. The lungs have a lobed structure, the segments in the lungs are separated from each other by narrow grooves and partitions made of connective tissue. The main structural unit is the alveoli. Their number in a newborn is 3 times less than in an adult. Alveoli begin to develop from 4-6 weeks of age, their formation occurs up to 8 years. After 8 years, the lungs in children increase due to the linear size, in parallel, the respiratory surface of the lungs increases.

In the development of the lungs, the following periods can be distinguished:

1) from birth to 2 years, when there is an intensive growth of the alveoli;

2) from 2 to 5 years, when elastic tissue develops intensively, bronchi with perebronchial inclusions of lung tissue are formed;

3) from 5 to 7 years, the functional abilities of the lungs are finally formed;

4) from 7 to 12 years, when there is a further increase in lung mass due to the maturation of lung tissue.

Anatomically, the right lung consists of three lobes (upper, middle and lower). By the age of 2, the sizes of individual lobes correspond to each other, as in an adult.

In addition to the lobar, segmental division is distinguished in the lungs, 10 segments are distinguished in the right lung, and 9 in the left.

The main function of the lungs is breathing. It is believed that 10,000 liters of air pass through the lungs every day. Oxygen absorbed from the inhaled air ensures the functioning of many organs and systems; the lungs take part in all types of metabolism.

The respiratory function of the lungs is carried out with the help of a biologically active substance - a surfactant, which also has a bactericidal effect, preventing fluid from entering the pulmonary alveoli.

With the help of the lungs, waste gases are removed from the body.

A feature of the lungs in children is the immaturity of the alveoli, they have a small volume. This is compensated by increased breathing: the younger the child, the more shallow his breathing. The respiratory rate in a newborn is 60, in a teenager it is already 16-18 respiratory movements per 1 minute. The development of the lungs is completed by the age of 20.

A wide variety of diseases can interfere with the vital function of breathing in children. Due to the characteristics of aeration, drainage function and evacuation of secretions from the lungs, the inflammatory process is often localized in the lower lobe. This occurs in the supine state in infants due to insufficient drainage function. Paravisceral pneumonia often occurs in the second segment of the upper lobe, as well as in the basal-posterior segment of the lower lobe. The middle lobe of the right lung may often be affected.

The following studies are of the greatest diagnostic value: x-ray, bronchological, determination of blood gas composition, blood pH, examination of the function of external respiration, examination of bronchial secretions, and computed tomography.

According to the frequency of breathing, its ratio with the pulse, the presence or absence of respiratory failure is judged (see Table 14).

By the end of the 3rd - at the beginning of the 4th week of embryonic development, a protrusion of the wall of the anterior intestine appears, from which the larynx, trachea, bronchi and lungs are formed. This protrusion grows rapidly, a flask-shaped extension appears at the caudal end, which divides into the right and left parts at the 4th week. (future right and left lungs). Each part is further divided into smaller branches (future shares). The resulting protrusions grow into the surrounding mesenchyme, continuing to divide and again forming spherical extensions at their ends - bronchial rudiments of ever smaller caliber. Formed in the 6th week lobar bronchi, on the 8th-10th - segmental bronchi. Formation begins from the 16th week respiratory bronchioles. Thus, by the 16th week, the bronchial tree is mainly formed. This is the so-called glandular stage of lung development. From the 16th week, the formation of a lumen in the bronchi begins (stage of recanalization), and from the 24th - the formation of future acini (alveolar stage), does not end by birth, the formation of alveoli continues in the postnatal period. By the time of birth, there are about 70 million primary alveoli in the lungs of the fetus. Formation of the cartilaginous framework of the trachea and bronchi begins from the 10th week, from the 13th week the formation of glands in the bronchi begins, contributing to the formation of the lumen. Blood vessels are formed from the mesenchyme at the 20th week, and motor neurons - from the 15th week. The vascularization of the lungs is especially fast at the 26-28th week. Lymphatic vessels are formed on the 9-10th week, first in the region of the root of the lung. By birth, they are fully formed.

The formation of acini which began from the 24th week, does not end by birth, and their formation continues in the postnatal period.

By birth, the airways (larynx, trachea, bronchi, and acini) are filled with fluid, which is a secretion product of airway cells. It contains a small amount of protein and has a low viscosity, which facilitates its rapid absorption immediately after birth, from the moment breathing is established.

Surfactant, the layer of which (0.1-0.3 microns) covers the alveoli, begins to be synthesized at the end of fetal development. Methyl- and phosphocholine transferase are involved in the synthesis of surfactant. Methyltransferase begins to form from the 22-24th week of intrauterine development, and its activity progressively increases towards birth. Phosphocholine transferase usually matures only by the 35th week of gestation. A deficiency in the surfactant system underlies respiratory distress syndrome, which is more common in preterm infants, clinically manifesting as severe respiratory distress.

The above information on embryogenesis suggests that congenital tracheal stenosis and lung agenesis are the result of developmental disorders at very early stages of embryogenesis. Congenital lung cysts are also a consequence of a malformation of the bronchi and accumulation of secretions in the alveoli.

The part of the foregut from which the lungs originate later turns into the esophagus. If the correct process of embryogenesis is violated, a message remains between the primary intestinal tube (esophagus) and the grooved protrusion (trachea) - esophageal-tracheal fistulas. Although this pathological condition is rare in newborns, if it is present, their fate depends on the time of diagnosis and the speed of providing the necessary medical care. A newborn with such a developmental defect in the first hours looks quite normal and breathes freely. However, at the first attempt to feed, due to the ingress of milk from the esophagus into the trachea, asphyxia occurs - the child turns blue, a large number of wheezing is heard in the lungs, an infection quickly joins. Treatment of such a malformation is only operational and should be carried out immediately after the diagnosis is established. A delay in treatment causes severe, sometimes irreversible, organic changes in the lung tissue due to the constant ingestion of food and gastric contents into the trachea.

It is customary to distinguish upper(nose, throat) medium(larynx, trachea, lobar, segmental bronchi) and lower(bronchioles and alveoli) airways. Knowledge of the structure and function of the various parts of the respiratory system is of great importance for understanding the characteristics of respiratory lesions in children.

upper respiratory tract.Nose in a newborn it is relatively small, its cavities are poorly developed, the nasal passages are narrow (up to 1 mm). The lower nasal passage is absent. The cartilages of the nose are very soft. The mucous membrane of the nose is delicate, rich in blood and lymphatic vessels. By the age of 4, the lower nasal passage is formed. As the facial bones (upper jaw) increase and teeth erupt, the length and width of the nasal passages increase. In newborns, the cavernous part of the submucosal tissue of the nose is underdeveloped, which develops only by 8-9 years. This explains the relative rarity of nosebleeds in children 1 year old. Due to the insufficient development of the cavernous tissue in young children, the inhaled air is slightly warmed, and therefore children cannot be taken outside at temperatures below -10 ° C. A wide nasolacrimal duct with underdeveloped valves contributes to the transition of inflammation from the nose to the mucous membrane of the eyes. Due to the narrowness of the nasal passages and the abundant blood supply to the mucous membrane, the appearance of even a slight inflammation of the nasal mucosa causes difficulty in breathing through the nose in young children. Breathing through the mouth in children of the first six months of life is almost impossible, since a large tongue pushes the epiglottis backwards.

Although the paranasal sinuses begin to form in utero, they are underdeveloped at birth (Table 1).

Table 1

Development of the paranasal sinuses (sinuses) of the nose

These features explain the rarity of diseases such as sinusitis, frontal sinusitis, ethmoiditis, polysinusitis (a disease of all sinuses) in early childhood. When breathing through the nose, air passes with greater resistance than when breathing through the mouth, therefore, during nasal breathing, the work of the respiratory muscles increases and breathing becomes deeper. Atmospheric air passing through the nose is warmed, humidified and purified. The warming of the air is the greater, the lower the outside temperature. So, for example, the air temperature when passing through the nose at the level of the larynx is only 2 ... 3 ° C lower than body temperature. In the nose, the inhaled air is purified, and foreign bodies larger than 5-6 microns in size are captured in the nasal cavity (smaller particles penetrate into the underlying sections). 0.5-1 l of mucus per day is released into the nasal cavity, which moves in the posterior 2/3 of the nasal cavity at a speed of 8-10 mm/min, and in the anterior third - 1-2 mm/min. Every 10 minutes a new layer of mucus passes, which contains bactericidal substances (lysozyme, complement, etc.), secretory immunoglobulin A.

Pharynx the newborn is narrow and small. The lymphopharyngeal ring is poorly developed. Both palatine tonsils in newborns normally do not go out from behind the arches of the soft palate into the pharyngeal cavity. In the second year of life, hyperplasia of the lymphoid tissue is observed, and the tonsils protrude from behind the anterior arches. Crypts in the tonsils are poorly developed, therefore, although there are tonsillitis in children under one year old, they are less common than in older children. By the age of 4-10 years, the tonsils are already well developed and can easily hypertrophy. The tonsils are similar in structure and function to the lymph nodes.

The tonsils are, as it were, a filter for microorganisms, but with frequent inflammatory processes, a focus of chronic infection can form in them. At the same time, they gradually increase, hypertrophy - chronic tonsillitis develops, which can occur with general intoxication and cause sensitization of the body.

Nasopharyngeal tonsils can increase - these are the so-called adenoid vegetations that disrupt normal nasal breathing, and also, being a significant receptor field, can cause allergization, intoxication of the body, etc. Children with adenoids are inattentive, which affects their studies at school. In addition, adenoids contribute to the formation of malocclusion.

Among the lesions of the upper respiratory tract in children, rhinitis and tonsillitis are most often observed.

middle and lower respiratory tract.Larynx by the birth of a child, it has a funnel-shaped shape, its cartilages are tender and pliable. The glottis is narrow and located high - at the level of the IV cervical vertebra (in adults - at the level of the VII cervical vertebra). The cross-sectional area of ​​the airway under the vocal folds is on average 25 mm, and the length of the vocal folds is 4-4.5 mm. The mucous membrane is tender, rich in blood and lymphatic vessels. Elastic tissue is poorly developed. Up to 3 years, the shape of the larynx is the same in boys and girls. After 3 years, the angle of connection of the thyroid plates in boys becomes sharper, which becomes especially noticeable by the age of 7; by the age of 10 in boys, the larynx is similar to that of an adult male.

Glottis remains narrow up to 6-7 years. True vocal folds in young children are shorter than in older ones (this is why they have a high voice); From the age of 12, the vocal folds of boys become longer than those of girls. The peculiarity of the structure of the larynx in young children explains the frequency of its defeat. (laryngitis), and are often accompanied by difficulty breathing - groats.

Trachea by the birth of a child is almost fully formed. It has a funnel shape. Its upper edge is located at the level of the IV cervical (in an adult at level VII) vertebra. The bifurcation of the trachea lies higher than in an adult. It can be tentatively defined as the intersection of lines drawn from spinae scapulae to the spine. The mucous membrane of the trachea is delicate and rich in blood vessels. The elastic tissue is poorly developed, and its cartilaginous framework is soft and easily narrows the lumen. With age, the trachea increases both in length and in diameter, however, compared with the growth of the body, the rate of increase in the trachea lags behind, and only from puberty does the increase in its size accelerate.

The diameter of the trachea changes during the respiratory cycle. The lumen of the trachea changes especially significantly during coughing - the longitudinal and transverse dimensions decrease by 1/3. There are many glands in the mucous membrane of the trachea - approximately one gland per 1 mm 2 of the surface. Due to the secretion of the glands, the surface of the trachea is covered with a layer of mucus 5 microns thick, the speed of mucus movement is 10-15 mm / min, which is ensured by the movement of the cilia of the ciliated epithelium (10-35 cilia per 1 micron 2).

Structural features of the trachea in children determine its frequent isolated lesions. (tracheitis), as a combination with damage to the larynx (laryngotracheitis) or bronchi (tracheobronchitis).

Bronchi by the time of birth they are formed quite well. The mucous membrane has a rich blood supply, is covered with a thin layer of mucus, which moves at a speed of 0.25-1 cm / min. In the bronchioles, the movement of mucus is slower (0.15-0.3 cm/min). The right bronchus is, as it were, a continuation of the trachea, it is shorter and somewhat wider than the left.

Muscle and elastic fibers in children of the first year of life are still poorly developed. With age, both the length and the lumen of the bronchi increase. The bronchi grow especially fast in the first year of life, then their growth slows down. During the onset of puberty, their growth rate increases again. By the age of 12-13, the length of the main bronchi doubles, with age the resistance to bronchial collapse increases. In children, acute bronchitis is a manifestation of a respiratory viral infection. Less common is asthmatic bronchitis with respiratory allergies. The tenderness of the structure of the bronchial mucosa, the narrowness of their lumen also explain the relatively frequent occurrence in young children bronchiolitis with a syndrome of complete or partial obstruction.

Lung mass at birth is 50-60 g, which is 1/50 of body weight. In the future, it rapidly increases, and especially intensively during the first 2 months of life and during puberty. It doubles by 6 months, triples by the year of life, increases almost 6 times by 4-5 years, 10 times by 12-13 years and 20 times by 20 years.

In newborns, the lung tissue is less airy and is distinguished by the abundant development of blood vessels and loose connective tissue in the septa of the acini. Elastic tissue is underdeveloped, which explains the relatively easy occurrence of emphysema in various lung diseases. Thus, the ratio of elastin and collagen in the lungs (dry tissue) in children under 8 months is 1: 3.8, while in an adult it is 1: 1.7. By the time a child is born, the actual respiratory part of the lungs (the acinus, where gas exchange between air and blood takes place) is underdeveloped.

Alveoli begin to form from the 4-6th week of life, and their number increases very rapidly during the first year, growing up to 8 years, after which the lungs increase due to the linear size of the alveoli.

According to the increase in the number of alveoli, the respiratory surface also increases, especially significantly during the first year.

This corresponds to the greater need for oxygen in children. By birth, the lumen of the terminal bronchioles is less than 0.1 mm, by the age of 2 it doubles, by the age of 4 it triples, and by the age of 18 it increases by 5 times.

The narrowness of the bronchioles explains the frequent occurrence of lung atelectasis in young children. AI Strukov identified 4 periods in the development of the lungs in children.

In the I period (from birth to 2 years) there is a particularly intensive development of the alveoli.

In the II period (from 2 to 5 years) intensively develop elastic tissue, muscular bronchi with peribronchial and lymphoid tissue included in it. This probably explains the increase in the number of cases of pneumonia with a protracted course and the onset of the formation of chronic pneumonia in children at preschool age.

ATIIIperiod (5-7 years) the final maturation of the structure of the acinus occurs, which explains the more benign course of pneumonia at children of preschool and school age.

In the IV period (7-12 years) there is an increase in the mass of mature lung tissue.

As you know, the right lung consists of three lobes: upper, middle and lower, and the left - of two: upper and lower. The middle lobe of the right lung corresponds to the lingular lobe in the left lung. The development of individual lobes of the lung is uneven. In children of the 1st year of life, the upper lobe of the left lung is worse developed, and the upper and middle lobes of the right lung are almost the same size. Only by the age of 2 do the sizes of individual lobes of the lung correspond to each other, as in adults.

Along with dividing the lungs into lobes in recent years, knowledge of the segmental structure of the lungs has become of great importance, since it explains the features of the localization of lesions and is always taken into account during surgical interventions on the lungs.

As mentioned, the formation of the structure of the lungs occurs depending on the development of the bronchi. After the division of the trachea into the right and left bronchi, each of them is divided into lobar, which are suitable for each lobe of the lung. Then the lobar bronchi are divided into segmental. Each segment has the form of a cone or pyramid with the apex directed towards the root of the lung.

The anatomical and functional features of the segment are determined by the presence of self-ventilation, terminal artery and intersegmental septa made of elastic connective tissue. The segmental bronchus with the corresponding blood vessels occupies a certain area in the lobe of the lung. The segmental structure of the lungs is already well expressed in newborns. In the right lung, 10 segments are distinguished, in the left lung - 9 (Fig. 1).

Rice. one. Segmental structure of the lungs

Upper left and right lobes divided into 3 segments: upper-apical (1), superior posterior(2) and upper anterior(3). Sometimes another additional segment is mentioned - axillary, which is not considered independent.

Middle right lobe is divided into 2 segments: interior(4) located medially, and outer(5), located laterally. In the left lung corresponds to the middle share reed, also consisting of 2 segments - upper lingual(4) and lower lingual (5).

The lower lobe of the right lung is divided into 5 segments: basal-apical (6), basal-medial (7), basal-anterior (8), basal-lateral (9) and basal-posterior (10).

The lower lobe of the left lung is divided into 4 segments: basal-apical (6), basal-anterior (8), basal-lateral (9) and basal-posterior (10).

In children, the pneumonic process is most often localized in certain segments, which is associated with the peculiarities of their aeration, the drainage function of their bronchi, the evacuation of secretions from them and the possibility of infection. Most often, pneumonia is localized in the lower lobe, namely in the basal-apical segment (6). This segment is to a certain extent isolated from the other segments of the lower lobe. Its segmental bronchus arises above the other segmental bronchi and runs at a right angle straight back. This creates conditions for poor drainage, since young children are usually in a prone position for a long time. Along with the defeat of the 6th segment, pneumonia is also often localized in the upper-posterior (2) segment of the upper lobe and the basal-posterior (10) segment of the lower lobe. This explains the frequent form of the so-called paravertebral pneumonia. A special place is occupied by the defeat of the middle lobe - with this localization, pneumonia is acute. There is even a term "middle lobe syndrome".

The mid-lateral (4) and mid-anterior (5) segmental bronchi are located in the region of the bronchopulmonary lymph nodes; they have a relatively narrow lumen, considerable length, and depart at a right angle. As a result, the bronchi are easily compressed by enlarged lymph nodes, which suddenly leads to the shutdown of a significant respiratory surface and is the cause of severe respiratory failure.

The respiratory system is a collection of organs consisting of the respiratory tract (nose, pharynx, trachea, bronchi), lungs (bronchial tree, acini), as well as muscle groups that contribute to the contraction and relaxation of the chest. Breathing provides the cells of the body with oxygen, which in turn converts it into carbon dioxide. This process occurs in the pulmonary circulation.

The laying and development of the child's respiratory system begins during the 3rd week of a woman's pregnancy. It is formed from three rudiments:

• Splanchnotome.
• Mesenchyme.
• Epithelium of the foregut.

From the visceral and parietal sheets of the splanchnotome, the mesothelium of the pleura develops. It is represented by a single-layer squamous epithelium (polygonal cells), lining the entire surface of the pulmonary system, separating from other organs. The outer surface of the leaf is covered with microcilia that produce a serous fluid. It is necessary for sliding between the two layers of the pleura during inhalation and exhalation.

From the mesenchyme, namely the germ layer of the mesoderm, cartilage, muscle and connective tissue structures, and blood vessels are formed. From the epithelium of the anterior intestine takes the development of the bronchial tree, lungs, alveoli.

In the intrauterine period, the airways and lungs are filled with fluid, which is removed during childbirth with the first breath, and is also absorbed by the lymphatic system and partially into the blood vessels. Breathing is carried out at the expense of maternal blood, enriched with oxygen, through the umbilical cord.

By the eighth month of gestation, pneumocytes produce a surfactant called surfactant. It lines the inner surface of the alveoli, prevents them from falling off and sticking together, and is located at the air-liquid interface. Protects against harmful agents with the help of immunoglobulins and macrophages. Insufficient secretion or absence of surfactant threatens the development of respiratory distress syndrome.

A feature of the respiratory system in children is its imperfection. The formation and differentiation of tissues, cell structures is carried out in the first years of life and up to seven years.

Structure

Over time, the child's organs adapt to the environment in which he will live, the necessary immune, glandular cells are formed. In a newborn, the respiratory tract, unlike an adult organism, has:

• Narrower opening.
• Short stroke length.
• Many vascular vessels in a limited area of ​​the mucosa.
• Delicate, easily traumatized architectonics of the lining membranes.
• Loose structure of lymphoid tissue.

Upper paths

The baby's nose is small, its passages are narrow and short, so the slightest swelling can lead to obstruction, which makes sucking difficult.

The structure of the upper tract in a child:

1. Two nasal sinuses are developed - the upper and middle ones, the lower one will be formed by the age of four. The cartilage framework is soft and pliable. The mucous membrane has an abundance of blood and lymphatic vessels, and therefore minor manipulation can lead to injury. Nosebleeds are rarely noted - this is due to undeveloped cavernous tissue (it will form by the age of 9). All other cases of blood flow from the nose are considered pathological.
2. The maxillary sinuses, the frontal and ethmoid sinuses are not closed, protrude the mucous membrane, are formed by 2 years, cases of inflammatory lesions are rare. Thus, the shell is more adapted to the purification, humidification of the inhaled air. Full development of all sinuses occurs by the age of 15.
3. The nasolacrimal canal is short, exits in the corner of the eye, close to the nose, which ensures a rapid ascending spread of inflammation from the nose to the lacrimal sac and the development of polyetiologic conjunctivitis.
4. The pharynx is short and narrow, due to which it is quickly infected through the nose. At the level between the oral cavity and the pharynx, there is a Pirogov-Waldeyer nasopharyngeal annular formation, consisting of seven structures. The concentration of lymphoid tissue protects the entrance to the respiratory and digestive organs from infectious agents, dust, allergens. Features of the structure of the ring: poorly formed tonsils, adenoids, they are loose, pliable to settlement in their crypts of inflammatory agents. There are chronic foci of infection, frequent respiratory diseases, tonsillitis, difficulty in nasal breathing. Such children develop neurological disorders, they usually walk with their mouths open and are less amenable to schooling.
5. The epiglottis is scapular, relatively wide and short. During breathing, it lies on the root of the tongue - opens the entrance to the lower paths, during the period of eating - prevents the foreign body from entering the respiratory passages.

lower paths

The larynx of a newborn is located higher than that of an adult individual, due to the muscular frame it is very mobile. It has the form of a funnel with a diameter of 0.4 cm, the narrowing is directed towards the vocal cords. The cords are short, which explains the high timbre of the voice. With a slight edema, during acute respiratory diseases, symptoms of croup, stenosis occur, which is characterized by heavy, wheezing breathing with the inability to perform a full breath. As a result, hypoxia develops. The laryngeal cartilages are rounded, their sharpening in boys takes place by the age of 10-12 years.

The trachea is already formed by the time of birth, is located at the level of the 4th cervical vertebra, is mobile, in the form of a funnel, then acquires a cylindrical appearance. The lumen is significantly narrowed, in contrast to an adult, there are few glandular areas in it. When coughing, it can be reduced by a third. Given the anatomical features, in inflammatory processes, narrowing and the occurrence of a barking cough, symptoms of hypoxia (cyanosis, shortness of breath) are inevitable. The frame of the trachea consists of cartilaginous semirings, muscle structures, connective tissue membrane. Bifurcation at birth is higher than in older children.

The bronchial tree is a continuation of the bifurcation of the trachea, divided into the right and left bronchus. The right one is wider and shorter, the left one is narrower and longer. The ciliated epithelium is well developed, producing physiological mucus that cleanses the bronchial lumen. Mucus cilia moves outward at a speed of up to 0.9 cm per minute.

A feature of the respiratory organs in children is a weak cough impulse, due to poorly developed torso muscles, incomplete myelin coverage of the nerve fibers of the tenth pair of cranial nerves. As a result, infected sputum does not go away, accumulates in the lumen of the bronchi of different calibers and there is a blockage with a thick secret. In the structure of the bronchus there are cartilage rings, with the exception of the terminal sections, which consist only of smooth muscles. When they are irritated, a sharp narrowing of the course may occur - an asthmatic picture appears.

The lungs are airy tissue, their differentiation continues up to 9 years of age, they consist of:

• Shares (right of three, left of two).
• Segments (right - 10, left - 9).
• Dolek.

The bronchioles end in a sac in the baby. With the growth of the child, the lung tissue grows, the sacs turn into alveolar clusters, and the vital capacity indicators increase. Active development from the 5th week of life. At birth, the weight of the paired organ is 60–70 grams, it is well supplied with blood and vascularized by lymph. Thus, it is full-blooded, and not airy as in older age. The important point is that the lungs are not innervated, inflammatory reactions are painless, and in this case, you can miss a serious illness.

Due to the anatomical and physiological structure, pathological processes develop in the basal regions, cases of atelectasis and emphysema are not uncommon.

Functional features

The first breath is carried out by reducing oxygen in the blood of the fetus and increasing the level of carbon dioxide, after clamping the umbilical cord, as well as changing the conditions of stay - from warm and humid to cold and dry. Signals along the nerve endings enter the central nervous system, and then to the respiratory center.

Features of the function of the respiratory system in children:

• Air conduction.
• Cleansing, warming, moisturizing.
• Oxygenation and removal of carbon dioxide.
• Protective immune function, synthesis of immunoglobulins.
• Metabolism is the synthesis of enzymes.
• Filtration - dust, blood clots.
• lipid and water metabolism.
• shallow breaths.
• Tachypnea.

In the first year of life, respiratory arrhythmia occurs, which is considered the norm, but its persistence and the occurrence of apnea after one year of age is fraught with respiratory arrest and death.

The frequency of respiratory movements directly depends on the age of the baby - the younger, the more often the breath is taken.

NPV norm:

• Newborn 39–60/minute.
• 1-2 years - 29-35 / min.
• 3-4 years - 23-28 / min.
• 5-6 years - 19-25 / min.
• 10 years - 19-21 / min.
• Adult - 16-21 / min.

Taking into account the peculiarities of the respiratory organs in children, the attentiveness and awareness of parents, timely examination, therapy reduces the risk of transition to the chronic stage of the disease and serious complications.

By the time the child is born, the morphological structure is still imperfect. Intensive growth and differentiation of the respiratory organs continue during the first months and years of life. The formation of the respiratory organs ends on average by the age of 7, and then only their sizes increase. All airways in a child are much smaller and narrower than in an adult. Their features morfol. structures in children of the first years of life are:

1) thin, tender, easily damaged dry mucosa with insufficient development of glands, with reduced production of secretory immunoglobulin A (SIgA) and surfactant deficiency;

2) rich vascularization of the submucosal layer, represented mainly by loose fiber and containing few elastic and connective tissue elements;

3) softness and suppleness of the cartilaginous framework of the lower respiratory tract, the absence of elastic tissue in them and in the lungs.

Nose and nasopharyngeal space . In young children, the nose and nasopharyngeal space are small, short, flattened due to insufficient development of the facial skeleton. The shells are thick, the nasal passages are narrow, the lower one is formed only by 4 years. Cavernous tissue develops by 8-9 years.

Accessory cavities of the nose . By the birth of a child, only the maxillary sinuses are formed; frontal and ethmoid are open protrusions of the mucous membrane, which are formed in the form of cavities only after 2 years, the main sinus is absent. Completely all adnexal cavities of the nose develop by 12-15 years.

Nasolacrimal canal . Short, its valves are underdeveloped, the outlet is located close to the angle of the eyelids, which facilitates the spread of infection from the nose to the conjunctival sac.

Pharynx . In young children, it is relatively wide, the palatine tonsils are clearly visible at birth, but do not protrude due to well-developed arches. Their crypts and vessels are poorly developed, which to some extent explains the rare diseases of angina in the first year of life. By the end of the first year, the lymphoid tissue of the tonsils, including the nasopharyngeal (adenoids), is often hyperplastic, especially in children with diathesis. Their barrier function at this age is low, like that of the lymph nodes. The overgrown lymphoid tissue is colonized by viruses and microbes, foci of infection are formed - adenoiditis and chronic tonsillitis.

thyroid cartilage form an obtuse rounded corner in young children, which after 3 years becomes more acute in boys. From the age of 10, a characteristic male larynx is formed. The true vocal cords in children are shorter than in adults, which explains the height and timbre of a child's voice.

Trachea. In children of the first months of life, it is often funnel-shaped; at an older age, cylindrical and conical forms predominate. Its upper end is located in newborns much higher than in adults (at the level of the IV cervical vertebrae), and gradually descends, as does the level of the tracheal bifurcation (from the III thoracic vertebra in a newborn to V-VI at 12-14 years). The framework of the trachea consists of 14-16 cartilaginous half-rings connected behind by a fibrous membrane (instead of an elastic end plate in adults). The membrane contains many muscle fibers, the contraction or relaxation of which changes the lumen of the organ. The child's trachea is very mobile, which, along with the changing lumen and softness of the cartilage, sometimes leads to its slit-like collapse on exhalation (collapse) and is the cause of expiratory dyspnea or rough snoring breathing (congenital stridor). The symptoms of stridor usually disappear by age 2, when the cartilage becomes denser.

bronchial tree . By the time of birth, the bronchial tree is formed. The dimensions of the bronchi increase intensively in the first year of life and in the pubertal period. They are based on cartilaginous semicircles in early childhood, which do not have a closing elastic plate and are connected by a fibrous membrane containing muscle fibers. Bronchial cartilage is very elastic, soft, springy and easily displaced. The right main bronchus is usually almost a direct continuation of the trachea, so it is in it that foreign bodies are more often found. The bronchi, like the trachea, are lined with multi-row cylindrical epithelium, the ciliated apparatus of which is formed after the birth of a child.

Due to the increase in the thickness of the submucosal layer and mucous membrane by 1 mm, the total area of ​​the lumen of the bronchi of the newborn decreases by 75% (in an adult - by 19%). Active motility of the bronchi is insufficient due to poor development of muscles and ciliated epithelium. Incomplete myelination of the vagus nerve and underdevelopment of the respiratory muscles contribute to the weakness of the cough impulse in a small child; the infected mucus accumulating in the bronchial tree clogs the lumens of the small bronchi, promotes atelectasis and infection of the lung tissue. a functional feature of the bronchial tree of a small child is the insufficient performance of the drainage, cleansing function.

Lungs. In a child, as in adults, the lungs have a segmental structure. The segments are separated from each other by narrow grooves and layers of connective tissue (lobular lung). The main structural unit is the acinus, but its terminal bronchioles end not in a cluster of alveoli, as in an adult, but in a sac (sacculus). From the "lace" edges of the latter, new alveoli are gradually formed, the number of which in a newborn is 3 times less than in an adult. The diameter of each alveolus increases (0.05 mm in a newborn, 0.12 mm at 4-5 years, 0.17 mm by 15 years). In parallel, the vital capacity of the lungs increases. The interstitial tissue in the child's lung is loose, rich in blood vessels, fiber, contains very little connective tissue and elastic fibers. In this regard, the lungs of a child in the first years of life are more full-blooded and less airy than those of an adult. Underdevelopment of the elastic framework of the lungs contributes to both the occurrence of emphysema and atelectasis of the lung tissue.

The tendency to atelectasis is exacerbated by a deficiency of surfactant, a film that regulates alveolar surface tension and is produced by alveolar macrophages. It is this deficiency that causes insufficient expansion of the lungs in preterm infants after birth (physiological atelectasis).

Pleural cavity . In a child, it is easily extensible due to the weak attachment of the parietal sheets. The visceral pleura, especially in newborns, is relatively thick, loose, folded, contains villi, outgrowths, most pronounced in the sinuses, interlobar grooves.

lung root . It consists of large bronchi, vessels and lymph nodes (tracheobronchial, bifurcation, bronchopulmonary and around large vessels). Their structure and function are similar to peripheral lymph nodes. They easily respond to the introduction of infection. The thymus gland (thymus) is also placed in the mediastinum, which is large at birth and normally gradually decreases during the first two years of life.

Diaphragm. In connection with the characteristics of the chest, the diaphragm plays a large role in the mechanism of breathing in a small child, ensuring the depth of inspiration. The weakness of its contractions partly explains the extremely shallow breathing of a newborn. The main functions physiological features respiratory organs are: superficial nature of breathing; physiological shortness of breath (tachypnea), often irregular breathing rhythm; tension of gas exchange processes and easy onset of respiratory failure.

1. The depth of breathing, the absolute and relative volumes of one respiratory act in a child is much less than in an adult. When crying, the volume of breathing increases by 2-5 times. The absolute value of the minute volume of breathing is less than that of an adult, and the relative value (per 1 kg of body weight) is much larger.

2. The frequency of breathing is the greater, the younger the child, compensates for the small volume of each respiratory act and provides oxygen to the child's body. Rhythm instability and short (for 3-5 minutes) respiratory arrest (apnea) in newborns and preterm infants are associated with incomplete differentiation of the respiratory center and its hypoxia. Oxygen inhalations usually eliminate the respiratory arrhythmia in these children.

3. Gas exchange in children is carried out more vigorously than in adults, due to the rich vascularization of the lungs, blood flow velocity, and high diffusion capacity. At the same time, the function of external respiration in a small child is disturbed very quickly due to insufficient lung excursions and expansion of the alveoli.

The respiratory rate of a newborn child is 40 - 60 per 1 min, one-year-old - 30 -35, 5 - 6 years old - 20 -25, 10 years old - 18 - 20, adult - 15 - 16 per 1 min.

Percussion tone in a healthy child of the first years of life is usually high, clear, with a slightly boxy tone. When crying, it can change - to a distinct tympanitis on maximum inspiration and shortening on exhalation.

Hearing normal breath sounds depend on age: up to a year in a healthy child, breathing is weakened vesicular due to its superficial nature; at the age of 2 - 7 years, puerile (children's) breathing is heard, more distinct, with a relatively louder and longer (1/2 of inhalation) exhalation. In school-age children and adolescents, breathing is the same as in adults - vesicular.

The leading role in the origin of this syndrome is given to the deficiency of surfactant - a surfactant that lines the inside of the alveoli and prevents their collapse. The synthesis of surfactant changes in prematurely born children, and various adverse effects on the fetus, leading to hypoxia and hemodynamic disorders in the lungs, also affect. There is evidence of the participation of prostaglandins E in the pathogenesis of respiratory distress syndrome. These biologically active substances indirectly reduce the synthesis of surfactant, have a vasopressor effect on the vessels of the lungs, prevent the closure of the arterial duct and normalize blood circulation in the lungs.

The development of the respiratory organs begins at the 3rd week of embryonic development and continues for a long time after the birth of the child. At the 3rd week of embryogenesis, a protrusion appears from the cervical endodermal tube, which grows rapidly, and a flask-shaped expansion appears on its caudal section. On the 4th week, it is divided into right and left parts - the future right and left lungs - each of which branches like a tree. The resulting protrusions grow into the surrounding mesenchyme, continuing to divide, at their ends spherical extensions appear - the rudiments of the bronchi - of an increasingly small caliber. On the 6th week lobar bronchi are formed, on the 8th-10th - segmental. The number of airways typical for an adult is formed by the end of the 16th week of fetal development. From this endodermal rudiment, the epithelium of the lungs and respiratory tract is formed. Smooth muscle fibers and cartilage of the bronchi are formed from the mesodermal mesenchyme (the formation of the cartilaginous framework of the trachea and bronchi begins from the 10th week of fetal development). This is the so-called pseudoglandular stage of lung development. A greater number of bronchi approach the lower lobes of the lungs, the airways of which are longer than those of the upper ones.

The canalicular phase (recanalization) - weeks 16-26 - is characterized by the formation of a lumen in the bronchi, continued development and vascularization of the future respiratory sections of the lung. The final phase (alveolar) - the period of alveolar formation - begins from the 24th week, does not end at birth, the formation of alveoli continues in the postnatal period. By the time of birth, there are about 70 million primary alveoli in the lungs of the fetus.

The respiratory organs in children are relatively smaller and are characterized by incomplete anatomical and histological development. The nose of a young child is relatively small, the nasal passages are narrow, and the lower nasal passage is absent. The mucous membrane of the nose is delicate, relatively dry, rich in blood vessels. Due to the narrowness of the nasal passages and the abundant blood supply to their mucous membrane, even a slight inflammation causes difficulty in breathing through the nose in young children. Breathing through the mouth in children of the first six months of life is impossible, since a large tongue pushes the epiglottis backwards. Particularly narrow in young children is the exit from the nose - the choana, which is often the cause of a long-term violation of their nasal breathing.

The paranasal sinuses in young children are very poorly developed or completely absent. As the facial bones (upper jaw) increase in size and teeth erupt, the length and width of the nasal passages and the volume of the paranasal sinuses increase. By the age of 2, the frontal sinus appears, the maxillary cavity increases in volume. By the age of 4, the lower nasal passage appears. These features explain the rarity of diseases such as sinusitis, frontal sinusitis, ethmoiditis, in early childhood. Due to the insufficient development of cavernous tissue in young children, the inhaled air is slightly warmed, and therefore children cannot be taken outside at temperatures below -10 ° C. Cavernous tissue develops well by 8-9 years, this explains the relative rarity of nosebleeds in children of the 1st year of life. A wide nasolacrimal duct with underdeveloped valves contributes to the transition of inflammation from the nose to the mucous membrane of the eyes. Passing through the nose, atmospheric air is warmed, humidified and purified. 0.5-1 l of mucus per day is secreted into the nasal cavity. Every 10 minutes, a new layer of mucus passes through the nasopharynx, which contains bactericidal substances (lysozyme, complement, etc.), secretory immunoglobulin A.

The pharynx in children is relatively narrow and has a more vertical direction than in adults. The lymphopharyngeal ring in newborns is poorly developed. The pharyngeal tonsils become visible only by the end of the 1st year of life. Therefore, sore throats in children under 1 year old are less common than in older children. By the age of 4-10 years, the tonsils are already well developed, and their hypertrophy can easily occur. In puberty, the tonsils begin to undergo reverse development. The tonsils are, as it were, a filter for microbes, but with frequent inflammatory processes, a focus of chronic infection can form in them, causing general intoxication and sensitization of the body.

The growth of adenoids (nasopharyngeal tonsil) is most pronounced in children with constitutional anomalies, in particular with lymphatic-hypoplastic diathesis. With a significant increase in adenoids - 1.5-2nd degree - they are removed, since nasal breathing is disturbed in children (children breathe through their mouths - the air is not cleaned and warmed by the nose, and therefore they often suffer from colds), the shape of the face changes (adenoid face), children become distracted (mouth breathing distracts attention), their academic performance worsens. When breathing through the mouth, posture is also disturbed, adenoids contribute to the formation of malocclusion.

The Eustachian tubes in young children are wide, and with the horizontal position of the child, the pathological process from the nasopharynx easily spreads to the middle ear, causing the development of otitis media.

The larynx in young children has a funnel-shaped shape (later - cylindrical) and is located slightly higher than in adults (at the level of the 4th cervical vertebra in a child and the 6th cervical vertebra in an adult). The larynx is relatively longer and narrower than in adults, its cartilages are very pliable. False vocal cords and mucous membrane are delicate, rich in blood and lymphatic vessels, elastic tissue is poorly developed. The glottis in children is narrow. The vocal cords in young children are shorter than in older children, so they have a high voice. From the age of 12, the vocal cords in boys become longer than in girls. These features of the larynx explain the easy development of stenotic phenomena in children even with moderate inflammatory changes in the mucous membrane of the larynx. The increased neuromuscular excitability of a small child is also of great importance. Hoarseness of voice, often noted in young children after a cry, often depends not on inflammation, but on weakness of the easily fatiguable muscles of the vocal cords.

The trachea in newborns is funnel-shaped, its lumen is narrow, the posterior wall has a wider fibrous part, the walls are more pliable, the cartilages are soft, easily compressed. Its mucous membrane is delicate, rich in blood vessels and dryish due to insufficient development of the mucous glands, the elastic tissue is poorly developed. The secretion of the glands provides a layer of mucus on the surface of the trachea with a thickness of 5 microns, the speed of which is 10--15 mm / min (provided by cilia - 10--30 cilia per 1 micron 2). The growth of the trachea occurs in parallel with the growth of the trunk, most intensively - in the 1st year of life and in the pubertal period. Features of the structure of the trachea in children lead to inflammatory processes in the easy occurrence of stenotic phenomena, determine frequent isolated (tracheitis), combined with lesions of the larynx (laryngotracheitis) or bronchi (tracheobronchitis) lesions. In addition, due to the mobility of the trachea, its displacement may occur during a unilateral process (exudate, tumor).

The bronchi are fairly well formed at birth. Bronchial growth is intense in the 1st year of life and in the pubertal period. Their mucous membrane is richly vascularized, covered with a layer of mucus, which moves at a speed of 3-10 mm/min, slower in the bronchioles - 2-3 mm/min. The right bronchus is, as it were, a continuation of the trachea, it is shorter and wider than the left. This explains the frequent entry of a foreign body into the right main bronchus. The bronchi are narrow, their cartilages are soft. Muscle and elastic fibers in children of the 1st year of life are still not sufficiently developed. The tenderness of the bronchial mucosa, the narrowness of their lumen explain the frequent occurrence in young children of bronchiolitis with a syndrome of complete or partial obstruction.

The lungs in newborns weigh about 50 g, by 6 months their mass doubles, by the year it triples, by the age of 12 it increases 10 times, by the age of 20 - 20 times. Pulmonary fissures are poorly expressed. In newborns, lung tissue is less airy, with abundant development of blood vessels and connective tissue in the septa of the acini and an insufficient amount of elastic tissue. The latter circumstance explains the relatively easy occurrence of emphysema in various lung diseases. The weak development of elastic tissue partly explains the tendency of young children to atelectasis, which is also facilitated by insufficient excursion of the chest, narrowness of the bronchi. This is also facilitated by insufficient production of surfactant, especially in premature babies. Atelectasis occurs especially easily in the posterior lower sections of the lungs, since these sections are especially poorly ventilated due to the fact that the child lies on his back almost all the time, and blood stasis easily occurs. The acini are not well differentiated. In the process of postnatal development, alveolar ducts with typical alveoli are formed. Their number increases rapidly during the 1st year and continues to increase up to 8 years. This leads to an increase in the respiratory surface. The number of alveoli in newborns (24 million) is 10-12 times, and their diameter (0.05 mm) is 3-4 times less than in adults (0.2-0.25 mm). The amount of blood flowing through the lungs per unit time is greater in children than in adults, which creates the most favorable conditions for gas exchange in them.

The formation of the structure of the lungs occurs depending on the development of the bronchi. After the division of the trachea into the right and left main bronchi, each of them is divided into lobar bronchi, which are suitable for each lobe of the lung. Then the lobar bronchi are divided into segmental. Each segment has independent ventilation, a terminal artery and intersegmental septa made of elastic connective tissue. The segmental structure of the lungs is already well expressed in newborns. In the right lung, 10 segments are distinguished, in the left - 9. The upper left and right lobes are divided into three segments - 1, 2 and 3, the middle right lobe - into two segments - 4 and 5. In the left lung, the middle lobe corresponds to the lingual, also consisting of two segments - the 4th and 5th. The lower lobe of the right lung is divided into five segments - 6, 7, 8, 9 and 10th, the left lung - into four segments - 6, 8, 9 and 10th. In children, the pneumonic process is most often localized in certain segments (6, 2, 10, 4, 5th), which is associated with the characteristics of aeration, drainage function of the bronchi, evacuation of secretions from them and possible infection.

External respiration, that is, the exchange of gases between atmospheric air and the blood of the capillaries of the lungs, is carried out by simple diffusion of gases through the alveolar-capillary membrane due to the difference in the partial pressure of oxygen in the inhaled air and venous blood flowing through the pulmonary artery into the lungs from the right ventricle. Compared with adults, young children have pronounced differences in external respiration due to the development of acini, numerous anastomoses between the bronchial and pulmonary arteries, and capillaries.

The depth of breathing in children is much less than in adults. This is due to the small mass of the lungs and the structural features of the chest. The chest in children of the 1st year of life is, as it were, in a state of inspiration due to the fact that its anteroposterior size is approximately equal to the lateral one, the ribs depart from the spine at almost a right angle. This determines the diaphragmatic nature of breathing at this age. An overcrowded stomach, bloating of the intestines limit the mobility of the chest. With age, it gradually passes from the inspiratory position to the normal one, which is a prerequisite for the development of chest type of breathing.

The need for oxygen in children is much higher than in adults. So, in children of the 1st year of life, the need for oxygen per 1 kg of body weight is about 8 ml / min, in adults - 4.5 ml / min. The superficial nature of breathing in children is compensated by a high respiratory rate (in a newborn - 40--60 breaths per 1 min, at the age of 1 year - 30--35, 5 years - 25, 10 years - 20, in adults - 16-18 breaths in 1 min), participation in respiration of most of the lungs. Due to the greater frequency, the minute volume of breathing per 1 kg of body weight is twice as high in young children than in adults. The vital capacity of the lungs (VC), that is, the amount of air (in milliliters) that is maximally exhaled after a maximal inspiration, is significantly lower in children compared to adults. VC increases in parallel with the growth of the volume of the alveoli.

Thus, the anatomical and functional features of the respiratory system in children create the prerequisites for a milder respiratory disorder than in adults.