Features of the digestive system in children. Children's digestive organs

Young children (especially newborns) have a number of morphological features common to all parts of the gastrointestinal tract: 1) thin, delicate, dry, easily damaged mucous membrane; 2) richly vascularized submucosal layer, consisting mainly of loose fiber; 3) underdeveloped elastic and muscle tissue; 4) low secretory function of the glandular tissue, which separates a small amount of digestive juices with a low content of enzymes. These features make it difficult to digest food if the latter is not appropriate for the age of the child, reduce the barrier function of the gastrointestinal tract and lead to frequent illnesses, create the prerequisites for a general systemic reaction to any pathological effect and require very careful and careful care of the mucous membranes.

Oral cavity. In a newborn and a child in the first months of life, the oral cavity has a number of features that ensure the act of sucking. These include: a relatively small volume of the oral cavity and big tongue, good development of the muscles of the mouth and cheeks, roller-like duplication of the mucous membrane of the gums and transverse folds on the mucous membrane of the lips, fatty bodies (lumps of Bish) in the thickness of the cheeks, characterized by significant elasticity due to the predominance of solid fatty acids in them. The salivary glands are underdeveloped. However, insufficient salivation is mainly due to the immaturity of the nerve centers that regulate it. As they mature, the amount of saliva increases, and therefore, at the age of 3-4 months, the child often has the so-called physiological salivation due to the automatism of swallowing it that has not yet been developed.

Esophagus. In young children, the esophagus is funnel-shaped. Its length in newborns is 10 cm, in children 1 year old - 12 cm, 10 years old - 18 cm, diameter - 7 - 8, 10 and 12-15 mm, respectively, which must be taken into account when carrying out a number of medical and diagnostic procedures.

Stomach. In infants, the stomach is horizontal, with the pyloric portion near the midline and the lesser curvature facing posteriorly. As the child begins to walk, the axis of the stomach becomes more vertical. By the age of 7-11, it is located in the same way as in adults (Fig. 10-12). The capacity of the stomach in newborns is 30 - 35 ml, by the age of 1 it increases to 250 - 300 ml, by the age of 8 it reaches 1000 ml. Cardiac sphincter at infants it is very poorly developed, and the pyloric one functions satisfactorily. This contributes to the regurgitation often observed at this age, especially when the stomach is distended due to swallowing air during sucking ("physiological aerophagy"). In the gastric mucosa of young children, there are fewer glands than in adults. And although some of them begin to function even in utero, in general, the secretory apparatus of the stomach in children of the first year of life is underdeveloped and its functional abilities are low. The composition of gastric juice in children is the same as in adults (hydrochloric acid, lactic acid, pepsin, rennet, lipase, sodium chloride), but the acidity and enzyme activity are much lower (Table 3), which not only affects digestion, but also defines a low barrier function stomach. This makes it absolutely necessary to carefully observe the sanitary and hygienic regime during feeding of children (breast toilet, clean hands, proper expression of milk, sterility of nipples and bottles). IN last years it has been established that the bactericidal properties of gastric juice are provided by lysozyme produced by the cells of the superficial epithelium of the stomach.

As can be seen from Table. 3, acidity indicators fluctuate significantly, which is explained by the individual characteristics of the formation of gastric secretion and the age of the child.

Determination of acidity is carried out by the fractional method using as an irritant 7% cabbage broth, meat broth, 0.1 % histamine or pentagastrin solution. The main active enzyme of gastric juice is chymosin (rennet, labenzyme), which provides the first phase of digestion - curdling of milk. Pepsin (in the presence of hydrochloric acid) and lipase continue the hydrolysis of proteins and fats of curdled milk. However, the importance of gastric juice lipase in the digestion of fats is small due to its extremely low content in it and low activity. This deficiency is filled with lipase, which is found in women's milk, as well as in the pancreatic juice of the child. Therefore, in infants who receive only cow's milk, fats in the stomach do not break down. The maturation of the secretory apparatus of the stomach occurs earlier and more intensively in formula-fed children, which is associated with the body's adaptation to more indigestible food. Functional state and enzymatic activity depend on many factors: the composition of the ingredients and their quantity, the child's emotional tone, his physical activity, and his general condition. It is well known that fats suppress gastric secretion, while proteins stimulate it. Depressed mood, fever, intoxication are accompanied by a sharp decrease in appetite, i.e., a decrease in the secretion of gastric juice. Absorption in the stomach is insignificant and mainly concerns substances such as salts, water, glucose, and only partially - protein breakdown products. Motility of the stomach in children of the first months of life is slowed down, peristalsis is sluggish, the gas bubble is enlarged. The timing of the evacuation of food from the stomach depends on the nature of feeding. So, women's milk lingers in the stomach for 2-3 hours, cow's - for a longer time (3-4 hours and even up to 5 hours, depending on the buffer properties of milk), which indicates the difficulties of digesting the latter and the need to switch to more rare feedings.

Pancreas. In a newborn, the pancreas is small (length 5-6 cm, by the age of 10 it is three times larger), located deep in the abdominal cavity, at the level of the X thoracic vertebra, in subsequent age periods - at the level of the I lumbar vertebra. It is richly vascularized, intensive growth and differentiation of its structure continues up to 14 years. The capsule of the organ is less dense than in adults, consists of fine-fibred structures, and therefore, in children with inflammatory edema of the pancreas, its compression is rarely observed. The excretory ducts of the gland are wide, which provides good drainage. Close contact with the stomach, the root of the mesentery, the solar plexus and the common bile duct, with which the pancreas in most cases has a common outlet to the duodenum, often leads to a friendly reaction from the organs of this zone with a wide irradiation of pain.

The pancreas in children, as in adults, has external and intrasecretory functions. The exocrine function is to produce pancreatic juice. It contains albumins, globulins, trace elements and electrolytes, as well as a large set of enzymes necessary for digestion of food, including proteolytic (trypsin, chymopsin, elastase, etc.), lipolytic (lipase, phospholipase A and B, etc.) and amylolytic (a- and (beta-amylase, maltase, lactase, etc.). The rhythm of pancreatic secretion is regulated by neuro-reflex and humoral mechanisms. Secretin, which stimulates the separation of the liquid part of pancreatic juice and bicarbonates, and pancreozymin, enhances the secretion of enzymes along with other hormones (cholecystokinin, hepatokinin, etc.) produced by the mucosa of the duodenum and jejunum under the influence of hydrochloric acid.The secretory activity of the gland reaches the level of adult secretion by the age of 5. The total volume of secreted juice and its composition depend on the amount and the nature of the food eaten.The intrasecretory function of the pancreas is carried out by the synthesis of hormones (insulin, glucagon, lipocaine) involved in the regulation of carbohydrate and fat metabolism.

Liver. In children, the liver is relatively large, its weight in newborns is 4-6% of body weight (in adults - 3%). The liver parenchyma is poorly differentiated, the lobulation of the structure is revealed only by the end of the first year of life, it is full-blooded, as a result of which it rapidly increases in size with various pathologies, especially with infectious diseases and intoxications. By the age of 8, the morphological and histological structure of the liver is the same as in adults.

The liver performs various and very important functions: 1) produces bile, which is involved in intestinal digestion, stimulates the motor activity of the intestine and sanitizes its contents; 2) stores nutrients, mainly excess glycogen; 3) performs a barrier function, protecting the body from exogenous and endogenous pathogenic substances, toxins, poisons, and takes part in the metabolism of medicinal substances; 4) participates in the metabolism and conversion of vitamins A, D, C, B12, K; 5) during the period prenatal development is a hematopoietic organ.

The functionality of the liver in young children is relatively low. Its enzymatic system is especially untenable in newborns. In particular, the metabolism of indirect bilirubin released during hemolysis of erythrocytes is incomplete, resulting in physiological jaundice.

Gallbladder. In newborns, the gallbladder is located deep in the thickness of the liver and has a spindle shape, its length is about 3 cm.

it acquires a pear-shaped shape by 6-7 months and reaches the edge of the liver by 2 years.

The bile of children differs in composition from the bile of adults. It is poor in bile acids, cholesterol and salts, but rich in water, mucin, pigments, and in the neonatal period, in addition, urea. A characteristic and favorable feature of the bile of a child is the predominance of taurocholic acid over glycocholic acid, since taurocholic acid enhances the bactericidal effect of bile, and also accelerates the separation of pancreatic juice. Bile emulsifies fats, dissolves fatty acids, improves peristalsis.

Intestines. In children, the intestines are relatively longer than in adults (in an infant, it exceeds the length of the body by 6 times, in adults, by 4 times), but its absolute length varies individually within wide limits. The caecum and appendix are mobile, the latter is often located atypically, thereby making it difficult to diagnose inflammation. The sigmoid colon is relatively longer than in adults, and in some children even forms loops, which contributes to the development of primary constipation. With age, these anatomical features disappear. Due to the weak fixation of the mucous and submucosal membranes of the rectum, it may prolapse with persistent constipation and tenesmus in debilitated children. The mesentery is longer and easily stretchable, and therefore torsion, intussusception, etc., easily occur. The omentum in children under 5 years of age is short, so the possibility of localizing peritonitis in a limited area of ​​​​the abdominal cavity is almost excluded. Of the histological features, it should be noted the good severity of the villi and the abundance of small lymphatic follicles.

All intestinal functions (digestive, absorption, barrier and motor) in children differ from those of adults. The process of digestion, which begins in the mouth and stomach, continues in the small intestine under the influence of pancreatic juice and bile secreted into the duodenum, as well as intestinal juice. The intestinal secretory apparatus is generally formed at the time of the birth of the child, and even in the smallest children, the same enzymes are determined in the intestinal juice as in adults (enterokinase, alkaline phosphatase, erepsin, lipase, amylase, maltase, lactase, nuclease), but significantly less active. Only mucus is secreted in the large intestine. Under the influence of intestinal enzymes, mainly the pancreas, there is a breakdown of proteins, fats and carbohydrates. The process of digestion of fats is especially intense due to the low activity of lipolytic enzymes.

In children who are on breastfeeding, lipids emulsified by bile are broken down by 50% under the influence of breast milk lipase. Digestion of carbohydrates occurs in the small intestine parietal under the influence of pancreatic juice amylase and 6 disaccharidases localized in the brush border of enterocytes. In healthy children, only a small part of the sugars is not subjected to enzymatic breakdown and is converted in the large intestine to lactic acid by bacterial decomposition (fermentation). The processes of putrefaction in the intestines of healthy infants do not occur. Hydrolysis products formed as a result of cavitary and parietal digestion are absorbed mainly in the small intestine: glucose and amino acids into the blood, glycerol and fatty acids into the lymph. In this case, both passive mechanisms (diffusion, osmosis) and active transport with the help of carrier substances play a role.

The structural features of the intestinal wall and its large area determine in young children a higher absorption capacity than in adults and, at the same time, an insufficient barrier function due to the high permeability of the mucous membrane for toxins, microbes and other pathogenic factors. The constituent components of human milk are most easily absorbed, the protein and fats of which in newborns are partially absorbed unsplit.

The motor (motor) function of the intestines is carried out in children very energetically due to pendulum movements that mix food, and peristaltic, moving food to the exit. Active motility is reflected in the frequency of bowel movements. In infants, defecation occurs reflexively, in the first 2 weeks of life up to 3-6 times a day, then less often, by the end of the first year of life it becomes an arbitrary act. In the first 2 to 3 days after birth, the baby excretes meconium (original feces) of a greenish-black color. It consists of bile, epithelial cells, mucus, enzymes, swallowed amniotic fluid. The stools of healthy newborns who are on breastfeeding, have a mushy texture, golden- yellow coloration, sour smell. In older children, the chair is decorated, 1-2 times a day.

Microflora. During fetal development, the intestines of the fetus are sterile. Its colonization by microorganisms occurs first during the passage of the mother's birth canal, then through the mouth when children come into contact with surrounding objects. The stomach and duodenum contain a meager bacterial flora. In the small and especially the large intestine, it becomes more diverse, the number of microbes increases; microbial flora depends mainly on the type of feeding of the child. When feeding with mother's milk, the main flora is B. bifidum, the growth of which is promoted by (betta-lactose of human milk. When complementary foods are introduced into the diet or the child is transferred to feeding with cow's milk, gram-negative Escherichia coli, which is a conditionally pathogenic microorganism, predominates in the intestine. therefore, dyspepsia is more often observed in formula-fed children.According to modern concepts, the normal intestinal flora performs three main functions: 1) creating an immunological barrier; 2) final digestion of food residues and digestive enzymes; 3) synthesis of vitamins and enzymes. The normal composition of the intestinal microflora (eubiosis) is easily disturbed under the influence of infection, improper diet, as well as the irrational use of antibacterial agents and other drugs, leading to a state of intestinal dysbacteriosis.

SEMIOTICS OF DIGESTIVE LESIONS

Diseases of the digestive system in children of preschool and school age are 79.3 cases per 1000 children. Specific gravity functional disorders of the digestive system decreases with age in children, and at the same time the frequency of organic diseases increases. For the diagnosis of diseases of the digestive system importance has an analysis of complaints, knowledge and consideration of the anatomical and physiological characteristics of the child's gastrointestinal tract.

ANATOMICAL AND PHYSIOLOGICAL FEATURES OF THE GASTROINTESTINAL TRACT IN CHILDREN

The formation of the digestive organs begins from the 3-4th week of the embryonic period, when the primary intestine is formed from the endodermal plate. At the front end of it, a mouth opening appears on the 4th week, and a little later, at the opposite end, anus. The intestine quickly lengthens, and from the 5th week of the embryonic period, the intestinal tube is delimited into two sections, which are the basis for the formation of the small and large intestines. During this period, the stomach begins to stand out - as an extension of the primary intestine. At the same time, the mucous, muscular and serous membranes of the gastrointestinal tract are being formed, in which blood and lymphatic vessels, nerve plexuses, and endocrine cells are formed.

In the first weeks of pregnancy, the endocrine apparatus of the gastrointestinal tract is laid in the fetus and the production of regulatory peptides begins. In the process of intrauterine development, the number of endocrine cells increases, the content of regulatory peptides in them increases (gastrin, secretin, motilin, gastric inhibitory peptide (GIP), vasoactive intestinal peptide (VIP), enteroglukzhagon, somatostatin, neurotensin, etc.). At the same time, the reactivity of target organs with respect to regulatory peptides increases. In prenatal period peripheral and central mechanisms of nervous regulation of the activity of the gastrointestinal tract are laid.

In the fetus gastrointestinal tract begins to function already at the 16-20th week intrauterine life. By this time, the swallowing reflex is expressed, amylase is found in the salivary glands, pepsinogen in the stomach, and secretin in the small intestine. Normal fetus swallows a large number of amniotic fluid, the individual components of which are hydrolyzed in the intestine and absorbed. The undigested part of the contents of the stomach and intestines goes to the formation of meconium.

During intrauterine development, before implantation of the embryo into the uterine wall, its nutrition occurs at the expense of reserves in the cytoplasm of the egg. The embryo feeds on the secrets of the uterine mucosa and the material of the yolk sac (histotrophic type of nutrition). Since the formation of the placenta, hemotrophic (transplacental) nutrition, provided by transport, is of primary importance. nutrients from the mother's blood to the fetus through the placenta. It plays a leading role until the birth of a child.

From 4-5 months of intrauterine development, the activity of the digestive organs begins and, together with hemotrophic, amniotrophic nutrition occurs. The daily amount of liquid absorbed by the fetus in recent months pregnancy can reach more than 1 liter. The fetus absorbs amniotic fluid containing nutrients (proteins, amino acids, glucose, vitamins, hormones, salts, etc.) and hydrolyzing enzymes. Some enzymes enter the amniotic fluid from the fetus with saliva and urine, the second source is the placenta, the third source is the mother's body (enzymes through the placenta and bypassing it can enter the amniotic fluid from the blood of a pregnant woman).

Part of the nutrients are absorbed from the gastrointestinal tract without prior hydrolysis (glucose, amino acids, some dimers, oligomers and even polymers), since the intestinal tube of the fetus has a high permeability, fetal enterocytes are capable of pinocytosis. This is important to consider when organizing the nutrition of a pregnant woman in order to prevent allergic diseases. Some of the nutrients of the amniotic fluid are digested by its own enzymes, that is, the autolytic type of digestion plays an important role in the amniotic nutrition of the fetus. Amniotrophic nutrition of the type of own abdominal digestion can be carried out from the 2nd half of pregnancy, when pepsinogen and lipase are secreted by the cells of the stomach and pancreas of the fetus, although their level is low. Amniotrophic nutrition and the corresponding digestion are important not only for the supply of nutrients to the blood of the fetus, but also as a preparation of the digestive organs for lactotrophic nutrition.

In newborns and children in the first months of life, the oral cavity is relatively small, the tongue is large, the muscles of the mouth and cheeks are well developed, in the thickness of the cheeks there are fatty bodies (Bish's lumps), which are distinguished by considerable elasticity due to the predominance of solid (saturated) fatty acids in them. These features provide full breast sucking. The mucous membrane of the oral cavity is tender, dryish, rich in blood vessels(easily hurt). The salivary glands are poorly developed, produce little saliva (submandibular, sublingual glands function to a greater extent in infants, in children after a year and adults - parotid). The salivary glands begin to function actively by the 3-4th month of life, but even at the age of 1 year, the volume of saliva (150 ml) is 1/10 of the amount in an adult. The enzymatic activity of saliva at an early age is 1/3-1/2 of its activity in adults, but it reaches the level of adults within 1-2 years. Although the enzymatic activity of saliva at an early age is low, its action on milk contributes to its curdling in the stomach with the formation of small flakes, which facilitates the hydrolysis of casein. Hypersalivation at 3-4 months of age is due to teething, saliva may flow from the mouth due to the inability of children to swallow it. The reaction of saliva in children of the first year of life is neutral or slightly acidic - this may contribute to the development of thrush of the oral mucosa when improper care for her. At an early age, saliva contains a low content of lysozyme, secretory immunoglobulin A, which determines its low bactericidal activity and the need to comply with proper care behind the mouth.

The esophagus in young children has a funnel-shaped form. Its length in newborns is 10 cm, with age it increases, while the diameter of the esophagus becomes larger. At the age of up to a year, the physiological narrowing of the esophagus is weakly expressed, especially in the area of ​​the cardial part of the stomach, which contributes to frequent regurgitation food in children of the 1st year of life.

The stomach in infants is located horizontally, its bottom and cardia are poorly developed, which explains the tendency of children of the first year of life to regurgitation and vomiting. As the child begins to walk, the axis of the stomach becomes more vertical, and by 7-11 years it is located in the same way as in an adult. The capacity of the stomach in a newborn is 30-35 ml, by the year it increases to 250-300 ml, by the age of 8 it reaches 1000 ml. The secretory apparatus of the stomach in children of the 1st year of life is not sufficiently developed, they have fewer glands in the gastric mucosa than in adults, and their functional abilities are low. Although the composition of gastric juice in children is the same as in adults (hydrochloric acid, lactic acid, pepsin, rennet, lipase), but the acidity and enzymatic activity are lower, which determines the low barrier function of the stomach and the pH of gastric juice (4-5, in adults 1.5-2.2). In this regard, proteins are not sufficiently cleaved in the stomach by pepsin, they are cleaved mainly by cathepsins and gastrixin produced by the gastric mucosa, their optimum action is at pH 4-5. Gastric lipase (produced by the pyloric region of the stomach) breaks down into acidic environment together with lipase of human milk to half of the fats of human milk. These features must be taken into account when prescribing various types of nutrition to a child. With age, the secretory activity of the stomach increases. Motility of the stomach in children of the first months of life is slowed down, peristalsis is sluggish. The timing of the evacuation of food from the stomach depends on the nature of feeding. Women's milk lingers in the stomach for 2-3 hours, cow's - 3-4 hours, which indicates the difficulties of digesting the latter.

The intestines in children are relatively longer than in adults. The caecum is mobile due to the long mesentery, therefore, the appendix can be located in the right iliac region, shift to the small pelvis and to the left half of the abdomen, which creates difficulties in diagnosing appendicitis in young children. The sigmoid colon is relatively long, which predisposes to constipation in children, especially if the mother's milk contains increased amount fat. The rectum in children in the first months of life is also long, with weak fixation of the mucous and submucosal layers, and therefore, with tenesmus and persistent constipation, it may prolapse through the anus. The mesentery is longer and more easily distensible, which can lead to torsion, intussusception, and other pathological processes. The weakness of the ileocecal valve also contributes to the occurrence of intussusception in young children. A feature of the intestines in children is better development circular muscles than longitudinal, which predisposes to intestinal spasms and intestinal colic. A feature of the digestive organs in children is also the weak development of the lesser and greater omentum, and this leads to the fact that the infectious process in the abdominal cavity (appendicitis, etc.) often leads to diffuse peritonitis.

The secretory apparatus of the intestine by the time of the birth of the child is generally formed, the intestinal juice contains the same enzymes as in adults (enterokinase, alkaline phosphatase, lipase, erypsin, amylase, maltase, lactase, nuclease, etc.), but their activity low. Under the influence of intestinal enzymes, mainly the pancreas, there is a breakdown of proteins, fats and carbohydrates. However, the pH of duodenal juice in young children is slightly acidic or neutral, so the breakdown of protein by trypsin is limited (for trypsin, the optimal pH is alkaline). Especially intense is the process of digestion of fats due to the low activity of lipolytic enzymes. In children who are breastfed, lipids emulsified by bile are cleaved by 50% under the influence of maternal milk lipase. Digestion of carbohydrates occurs in the small intestine under the influence of pancreatic amylase and intestinal juice disaccharidases. The processes of putrefaction in the intestines do not occur in healthy infants. The structural features of the intestinal wall and its large area determine in young children a higher absorption capacity than in adults and, at the same time, an insufficient barrier function due to the high permeability of the mucous membrane for toxins and microbes.

The motor function of the gastrointestinal tract in young children also has a number of features. The peristaltic wave of the esophagus and the mechanical irritation of its lower section with a food lump cause a reflex opening of the entrance to the stomach. Motility of the stomach consists of peristalsis (rhythmic waves of contraction from the cardiac section to the pylorus), peristoles (resistance exerted by the walls of the stomach to the tensile action of food) and fluctuations in the tone of the stomach wall, which appears 2-3 hours after eating. The motility of the small intestine includes pendulum movement (rhythmic oscillations that mix intestinal contents with intestinal secretions and create favorable conditions for absorption), fluctuations in the tone of the intestinal wall and peristalsis (worm-like movements along the intestine that promote the promotion of food). Pendulum and peristaltic movements are also noted in the large intestine, and antiperistalsis in the proximal sections, which contributes to the formation of fecal masses. The time of passage of food gruel through the intestines in children is shorter than in adults: in newborns - from 4 to 18 hours, in older ones - about a day. It should be noted that with artificial feeding, this period is extended. The act of defecation in infants occurs reflexively without the participation of a volitional moment, and only by the end of the first year of life does defecation become arbitrary.

A newborn in the first hours and days of life allocates the original feces, or meconium, in the form of a thick mass of dark olive color, odorless. In the future, the feces of a healthy infant are yellow in color, sour reaction and sour smell, and their consistency is mushy. At an older age, the chair becomes decorated. Stool frequency in infants - from 1 to 4-5 times a day, in older children - 1 time per day.

The intestines of a child in the first hours of life are almost free from bacteria. In the future, the gastrointestinal tract is populated by microflora. In the oral cavity of an infant, staphylococci, streptococci, pneumococci, Escherichia coli and some other bacteria can be found. E. coli, bifidobacteria, lactic acid bacilli, etc. appear in the feces. With artificial and mixed feeding, the phase of bacterial infection occurs faster. Gut bacteria contribute to the processes of enzymatic digestion of food. With natural feeding, bifidobacteria, lactic acid bacilli predominate, and in a smaller amount - Escherichia coli. Feces are light yellow with a sour smell, ointment. With artificial and mixed feeding, due to the predominance of decay processes in the feces, there are a lot of Escherichia coli, fermentative flora (bifidoflora, lactic acid bacilli) is present in a smaller amount.

Significant structural and functional differences in the digestive organs of children compared with those of adults are observed only in the first years of life. Morphofunctional features digestive system depend to a large extent on the type of food and the composition of the food. Adequate food for children of the first year of life, especially the first 4 months, is mother's milk. By the time of the birth of the child, the secretory apparatus of the digestive tract is formed according to milk feeding. The number of secretory cells and enzymatic activity of digestive juices are insignificant. In infants, in addition to parietal, intracellular and abdominal digestion, which are not active enough (especially abdominal), there is also autolytic digestion due to human milk enzymes. By the end of the first year of life, with the start of complementary foods and the transition to definitive nutrition, the formation of one's own digestive mechanisms is accelerated. Complementary feeding at 5-6 months ensures the further development of the digestive glands and their adaptation to the nature of the food.

Digestion in the mouth children of different ages is carried out with the help of mechanical and chemical processing of food. Since teething begins only from the 6th month of life after birth, chewing until this process is completed (up to 1.5-2 years) is ineffective. The mucous membrane of the oral cavity in children of the first 3–4 months. life is relatively dry, due to the underdevelopment of the salivary glands and the deficiency of saliva. The functional activity of the salivary glands begins to increase at the age of 1.5–2 months. in 3-4-month-old children, saliva often flows out of the mouth due to the immaturity of the regulation of salivation and swallowing of saliva (physiological salivation). The most intensive growth and development of the salivary glands occurs between the ages of 4 months. and 2 years. By the age of 7, a child produces as much saliva as an adult.

The salivary glands of the newborn secrete very little saliva, from 4-6 months. secretion increases significantly, which is associated with the start of complementary foods: mixed nutrition with thicker food is a stronger irritant of the salivary glands. The secretion of saliva in newborns outside the periods of feeding is very low, while sucking it increases to 0.4 ml / min.

The glands during this period develop rapidly and by the age of 2 years are close in structure to those of adults. Children under 1 year old - 1.5 years old cannot swallow saliva, so they experience salivation. During suckling, saliva wets the nipple and provides a seal, making sucking more effective. The role of saliva is that it is a sealant oral cavity the child, providing, as it were, gluing the nipple to the oral mucosa, which creates the vacuum necessary for sucking. Saliva, mixed with milk, promotes the formation of looser casein flakes in the stomach.

Sucking and swallowing are innate unconditioned reflexes. In healthy and mature newborns, they are already formed by the time of birth. When suckling, the baby's lips tightly grasp the nipple of the breast. The jaws squeeze it, and the communication between the oral cavity and the outside air stops. Negative pressure is created in the child's oral cavity, which is facilitated by the lowering of the lower jaw along with the tongue down and back. Then breast milk enters the rarefied space of the oral cavity.

The larynx in infants is located differently than in adults. The entrance to the larynx is located high above the lower posterior edge of the palatine curtain and is connected to the oral cavity. Food moves to the sides of the protruding larynx, so the baby can breathe and swallow at the same time without interrupting sucking.

Digestion in the stomach.

The shape of the stomach, characteristic of adults, is formed in a child by the age of 8-10 years. The cardiac sphincter is underdeveloped, but the muscular layer of the pylorus is expressed, so regurgitation and vomiting are often observed in infants. The capacity of the stomach of a newborn is 40-50 ml, by the end of the first month 120-140 ml, by the end of the first year 300-400 ml.

In infants, the volume of gastric juice is not large, because. the complex reflex phase of gastric secretion is poorly expressed, the receptor apparatus of the stomach is poorly developed, mechanical and chemical exposure do not have a pronounced stimulating effect on the secretion of glands.

The pH of the gastric contents of a newborn baby ranges from slightly alkaline to slightly acidic. During the first day, the environment in the stomach becomes acidic (pH 4 - 6). The acidity of the gastric juice is created not by HCl (free HCl in the juice is negligible), but by lactic acid. The acidity of the gastric juice is provided by lactic acid until about 4-5 months of age. The intensity of HCl secretion increases by about 2 times with mixed feeding and 2-4 times with the transfer to artificial feeding. Acidification of the stomach environment is also stimulated by its proteolytic enzymes.

First 2 months In the life of a child, fetal pepsin plays the main role in the breakdown of proteins, then pepsin and gastrixin (enzymes of an adult). Fetal pepsin has the ability to curdle milk.

The activity of stomach pepsins for plant proteins is quite high from the 4th month of a child's life, and for animal proteins - from the age of 7 months.

In the slightly acidic environment of the stomach of young infants, proteolytic enzymes are inactive, due to which various milk immunoglobulins are not hydrolyzed and absorbed in the intestine in a native state, providing the proper level of immunity. In the stomach of a newborn, 20-30% of the incoming proteins are digested.

Under the influence of saliva and gastric juice in the presence of calcium ions, caseinogen protein dissolved in milk, lingering in the stomach, turns into insoluble loose flakes, which are then exposed to the action of proteolytic enzymes.

Emulsified milk fats are well split by gastric lipase from the moment the child is born, and this lipase is filtered from the capillaries of the gastric mucosa. The lipase of the saliva of the child and breast milk also participate in this process, the lipase of breast milk is activated by the lipokinase of the gastric juice of the child.

Carbohydrates in milk in the stomach of the child are not broken down, since the gastric juice does not contain the appropriate enzymes, and saliva alpha-amylase does not have this property. In the slightly acidic environment of the stomach, the amylolytic activity of the saliva of the child and mother's milk can be preserved.

The activity of all enzymes of the stomach reaches the norm of adults at the age of 14-15.

Contractions of the stomach in a newborn, continuous, weak, but with age they increase, periodic stomach motility appears on an empty stomach.

Women's milk stays in the stomach for 2-3 hours, the nutritional mixture with cow's milk - 3-4 hours. Regulatory mechanisms are immature, local mechanisms are somewhat better formed. Histamine begins to stimulate the secretion of gastric juice from the end of the first month of life.

Digestion in the duodenum carried out with the help of pancreatic enzymes, the duodenum itself, the action of bile. In the first 2 years of life, the activity of proteases, lipases and amylases of the pancreas and duodenum is low, then it rapidly increases: the activity of proteases reaches maximum level by 3 years, and lipase and amylase - by 9 years of age.

The liver of a newborn and an infant is large, a lot of bile is secreted, but it contains little bile acids, cholesterol and salts. Therefore, with early feeding in infants, fats may not be absorbed enough and appear in the feces of children. Due to the fact that little bilirubin is secreted in newborns with bile, they often develop physiological jaundice.

Digestion in the small intestine. The relative length of the small intestine in a newborn is large: 1 m per 1 kg of body weight, while in adults it is only 10 cm.

The mucous membrane is thin, richly vascularized and has increased permeability, especially in children of the first year of life. Lymphatic vessels are numerous, have a wider lumen than in adults. Lymph flowing from the small intestine does not pass through the liver, and the products of absorption enter directly into the blood.

Enzymatic activity the mucosa of the small intestine is high - membrane digestion predominates. Intracellular digestion also plays an important role in digestion. Intracavitary digestion in newborns is not formed. With age, the role of intracellular digestion decreases, but the role of intracavitary increases. There is a set of enzymes for the final stage of digestion: dipeptidases, nucleases, phosphatases, disaccharases. Proteins and fats of women's milk are digested and absorbed better than cow's milk: women's milk proteins are digested by 90-95%, and cow's - by 60-70%. The peculiarities of protein assimilation in young children include the high development of pinocytosis by epitheliocytes of the intestinal mucosa. As a result, milk proteins in children of the first weeks of life can pass into the blood in an unmodified form, which can lead to the appearance of antibodies to proteins. cow's milk. In children older than a year Proteins undergo hydrolysis to form amino acids.

A newborn baby is able to absorb 85-90% fat female milk. However lactose cow's milk is digested better than women's. Lactose is broken down into glucose and galactose, which are absorbed into the blood. The inclusion of pureed fruits and vegetables in the diet enhances the secretory and motor activity of the small intestine. When switching to definitive nutrition (typical of an adult) in the small intestine, the production of invertase and maltase increases, but the synthesis of lactase decreases

Fermentation in the intestines of infants complements the enzymatic breakdown of food. There is no rotting in the intestines of healthy children in the first months of life.

Suction closely related to parietal digestion and depends on the structure and function of the cells of the surface layer of the mucous membrane of the small intestine.

The peculiarity of the absorption of hydrolysis products in children in early ontogenesis is determined by the peculiarity of food digestion - mainly membrane and intracellular, which facilitates absorption. Absorption is also facilitated by the high permeability of the mucous membrane of the gastrointestinal tract. In children of different years of life, absorption in the stomach is more intense than in adults.

Digestion in the large intestine. The intestines of a newborn contain primordial feces (meconium), which includes the remains of amniotic fluid, bile, exfoliated intestinal epithelium, and thickened mucus. It disappears from the feces within 4-6 days of life. Motor skills in young children are more active, which contributes to frequent bowel movements. In infants, the duration of the passage of food gruel through the intestines is from 4 to 18 hours, and in older children - about a day. High motor activity of the intestine, combined with insufficient fixation of its loops, determines the tendency to intussusception.

Defecation in children of the first months of life is involuntary - 5-7 times a day, by the year it becomes arbitrary and occurs 1-2 times a day.

Microflora of the gastrointestinal tract The intestines of the fetus and newborn are sterile during the first 10-20 hours (aseptic phase). Then colonization of the intestine by microorganisms begins (second phase), and the third phase - stabilization of the microflora - lasts at least 2 weeks. The formation of intestinal microbial biocenosis begins from the first day of life, by the 7–9th day in healthy full-term children, the bacterial flora is usually represented mainly by Bifidobacterium bifidum, Lactobacillus acidophilus

The microflora of the gastrointestinal tract in a newborn child mainly depends on the type of feeding, it performs the same functions as the microflora of an adult. For the distal small intestine and the entire large intestine, the bifidoflora is the main one. Stabilization of microflora in children ends by 7 years of age.

Human milk contains p-lactose, which breaks down more slowly than a-lactose in cow's milk. Therefore, in the case of breastfeeding, part of the undigested p-lactose enters the large intestine, where it undergoes cleavage by the bacterial flora, and thus a normal microflora develops in the large intestine. At early feeding lactose does not enter the large intestine with cow's milk, which can be the cause of dysbacteriosis in children.

Neuroendocrine activity of the gastrointestinal tract.

Regulatory peptides produced by the endocrine apparatus of the gastrointestinal tract in the fetus stimulate the growth and differentiation of mucous membranes. The production of enteral hormones in a newborn increases sharply immediately after the first feeding and increases significantly in the first days. The formation of the intramural nervous apparatus, which regulates the secretory and motor activity of the small intestine, is completed at the age of 4-5 years. In the process of maturation of the central nervous system, its role in the regulation of the activity of the gastrointestinal tract increases. However, the conditioned reflex secretion of digestive juices begins in children already in the first years of life, as in adults, subject to a strict diet - a conditioned reflex for a while, which must be taken into account.

The products of hydrolysis absorbed into the blood and lymph are included in the process of anabolism.

Topic: Age features of the digestive system in children and adolescents

Target classes: after completing the study of the topic, students should know:

age-related structural features, functions of the oral cavity, esophagus, stomach, small intestine, large intestine, pancreas, liver and biliary tract in children;

features of abdominal and parietal digestion in children;

processes of formation of intestinal microbiocenosis in the postnatal period;

some methods for assessing digestion in children (coprogram);

the concept of microbiocenosis and dysbacteriosis;

methods for assessing intestinal microbiocenosis;

Students must be able to:

collect anamnesis, paying attention to the nature of nutrition, appetite, stool;

assess the nature of the stool in children, depending on the age and nature of nutrition;

to palpate the abdomen (superficial and deep);

percussion of the abdomen, the borders of the liver (according to Kurlov and Obraztsov-Strazhesko);

evaluate the results of coprological and microbiological studies.

Brief summary of the material.

Oral cavity represents the initial part of the digestive tract. It is bounded above by the hard and soft palate, below by the diaphragm of the mouth, and on the sides by the cheeks. In infants, the oral cavity has structural features in connection with adaptation to the act of sucking. The dimensions of the oral cavity in a child of the first year of life are relatively small. The alveolar processes of the jaws are underdeveloped, the bulge of the hard palate is weakly expressed, the soft palate is located more horizontally than in an adult. There are no transverse folds on the hard palate of the newborn. The mucous membrane of the oral cavity is delicate, there are many blood vessels in it, so it looks bright red with a slight matte shade. The tongue is relatively large and almost completely fills the oral cavity. The muscles of the tongue and lips are well developed. The tongue has all kinds of papillae, the number of which increases during the first year of life. There are many relatively wide lymphatic capillaries in the body of the tongue. On the gums, a roller-like thickening is noticeable - the gingival membrane, which is a duplication of the mucous membrane. The mucosa of the lips has transverse folding. In the thickness of the cheeks, rather dense fat pads are delimited (due to the refractory fats contained in them), called Bish's lumps. Chewing muscles are well developed. All these features of the oral cavity are important for the act of sucking. The sucking reflex is fully expressed in mature full-term newborns.

Saliva contributes to better sealing of the oral cavity during sucking. The salivary glands in newborns are poorly developed, they are richly vascularized and mature rather quickly. Saliva is important in the digestion of carbohydrates (amylase appears in saliva, first in the parotid, and by the end of the second month in other salivary glands) and the formation of a food bolus, has a bactericidal effect.

Esophagus in a newborn child, it often has a funnel-shaped shape, the expansion of the funnel is turned upwards. Gradually, as the child grows and develops, the shape of the esophagus becomes the same as in an adult, i.e. funnel pointing down. From a practical point of view, it is customary to give norms, taking into account not the true length of the esophagus, but the distance from the dental arches to the inlet of the stomach. This distance increases with age, amounting to a child at the age of one month 16.3 - 19.7 cm, at the age of 1.5-2 years - 22-24.5, by the age of 15-17 reaching the size of an adult - 48-50 cm. The absolute length of the esophagus in newborn children is 10-11 cm, by the end of the 1st year of life it reaches 12 cm, by 5 years -16 cm, by 10 years -18 cm, by 18 years - 22 cm, in an adult it is 25-32 see in infancy the elastic and muscular tissue of the esophagus is poorly developed, there are many blood vessels in the mucous membrane, and the glands are almost completely absent. The cardiac sphincter, which functionally separates the stomach and esophagus, is incomplete in infants, which causes the discharge of contents from the stomach into the esophagus and can lead to regurgitation and vomiting. The formation of the cardiac department is completed by 8 years of age.

Stomach in children of the first months of life it has a horizontal position. His tone is firm. The physiological volume of the stomach is less than the anatomical capacity. The stomach of an infant is distinguished by a relatively weak development of the muscular layer of the cardiac section and the bottom and a well-developed pyloric section. The gastric glands, which mainly produce pepsin (chief cells) and hydrochloric acid (parietal cells), are poorly developed. With the onset of enteral nutrition, the number of glands increases.

Small intestine differs in variability of a form and the sizes at children of early age. The length of the intestine and the location of its sections largely depend on the tone of the intestinal wall and the nature of the food. In young children, in addition to a relatively large overall length, the intestinal loops lie more compactly, since the abdominal cavity in this period is mainly occupied by a relatively large liver, and the small pelvis is not developed. Only after the first year of life, as the small pelvis develops, the location of the loops of the small intestine becomes permanent. The ileum ends with an ileocecal valve consisting of two leaflets and a frenulum. The upper valve is low and long, located obliquely; the lower one is higher and shorter, located vertically. In young children, there is a relative weakness of the ileocecal valve, and therefore the contents of the caecum, the richest in bacterial flora, can be thrown into the ileum, predisposing to dysbiosis. The mucosa of the small intestine has many folds, microvilli, due to which the absorption surface of the intestine increases. Hydrolysis and absorption on the surface of the small intestine mucosa is performed by enterocytes. From the side of the intestinal lumen, the microvilli are covered with a protein-lipoglycoprotein complex - a glycocalyx containing lactase, esterase, alkaline phosphatase, and other enzymes. Hydrolysis and absorption, carried out on the membrane of the "brush border" of enterocytes, is called membrane or parietal digestion. In children of the first months of life, the intensity of abdominal digestion is low. But the enzymes of membrane digestion have high activity. All parts of the small intestine of an infant have a high hydrolytic and absorption capacity. In addition, in children of the first weeks of life, pinocytosis by enterocytes of the intestinal mucosa is relatively highly developed. Milk proteins can pass into the baby's blood unchanged. This can partly explain the frequency of allergic diathesis with early artificial feeding. In breastfed infants, the hydrolysis of nutrients begins even in the oral cavity due to the enzymes of mother's milk - autolytic digestion.

Colon. The development of the large intestine by the birth of a child does not end. The muscular bands of the large intestine in newborns are hardly noticeable, and haustra are absent until 6 months. In children under 4 years of age, the ascending colon is longer than the descending colon. Due to the relatively longer colon and the above features, children may be prone to constipation.

Rectum in children of the first months of life, it is relatively long and, when filled, can occupy the small pelvis. The ampulla of the rectum is almost not developed in the newborn. The anal columns and sinuses are not formed, fatty tissue is not developed, and therefore it is poorly fixed. Therefore, infants should not be potty-trained early.

In newborns liver is one of the largest organs and makes up 4.4% of body weight. It occupies almost half of the volume of the abdominal cavity. In the postnatal period, its growth slows down and lags behind the rate of increase in body weight. In children of the first 6 months of life, the liver protrudes from under the edge of the costal arch at the level of the right nipple line by 2-3 cm, at the age of 1.5-2 years - by 1.5 cm, 3-7 years - by 1.2 cm. The liver is held in a certain position by ligaments and partly by connective tissue located in the extraperitoneal field. Due to the imperfect structure of the ligamentous apparatus, the liver in children is very mobile. The liver is one of the main organs of hematopoiesis in the antenatal period. In a newborn, hematopoietic cells make up about 5% of the volume of the liver, their number decreases with age. The liver deposits blood, it can accumulate up to 6% of all blood, occupying up to 15% of the volume of the liver. It is the largest glandular organ of the digestive system, producing bile. In the structure of the organ, several segments are distinguished, delimited by elements of the fibrous capsule. The lobed structure is revealed by the year. Histologically, by the age of 8, the liver becomes almost the same as in adults. The gallbladder in newborns is spindle-shaped, and in older children it is pear-shaped. At the age of 5 years, its bottom is projected to the right of the midline 1.5-2 cm below the costal arch.

Pancreas is the second largest gland (after the liver) of the gastrointestinal tract, producing the main digestive enzymes. In newborns, it is smooth, similar to a prism, by the age of 5-6 its consistency thickens, the surface becomes bumpy and takes the same shape as in an adult. In newborns, the pancreas is relatively mobile. With age, the formation of connective tissue ligaments limits its mobility.

Functional features of the digestive system.

Enzymatic processing of food in the oral cavity is carried out with the help of enzymes contained in saliva - amylases, peptidases, etc. When feeding with milk, food quickly moves into the stomach and does not have time to undergo enzymatic hydrolysis. The most important for digestion is the amylase enzyme contained in saliva, which breaks down starch into tri- and disaccharides. The activity of salivary enzymes increases significantly between the ages of one and four years. The severity of secretion depends on the nature of the diet. Saliva with artificial feeding is allocated more than with natural feeding. By wetting the mucous membranes, saliva helps to seal the oral cavity during the act of sucking. It also promotes foaming, wetting thick food, which, mixed with saliva, is easier to swallow. Milk mixed with saliva curdles in the stomach into smaller, more delicate flakes. The content of lysozyme in saliva determines its protective, bactericidal effect.

Newborns and infants have morphological and functional immaturity of the secretory apparatus of the stomach, which is manifested by a low volume of secretion of the gastric glands and the qualitative characteristics of gastric juice. In children of the first months of life, there is an almost complete absence of hydrochloric acid in gastric juice; pH is mainly determined by the hydrogen ions of not hydrochloric, but lactic acid (Table 27). The gastric glands of a newborn synthesize several isoforms of pepsin, of which the largest amount is fetal pepsin, which exhibits maximum activity at pH 3.5. At the same time, its effect on proteins, including curdling, is 1.5 times stronger than that of pepsin itself.

The digestive organs of the child have a number of morphological and physiological features. These features are most pronounced in young children, in whom the digestive apparatus is adapted mainly for the assimilation of breast milk, the digestion of which requires the least amount of enzymes.

In a newborn and infants, the oral cavity is absolutely small. The lips of newborns are thick, on their inner surface there are transverse ridges. The circular muscle of the mouth is well formed. The cheeks of newborns and young children are rounded and convex due to the presence between the skin and the well-developed buccal muscle of a rounded fat body (Bish's fat lumps), which, starting from 4 summer age gradually atrophied. The hard palate is flat, its mucous membrane forms slightly pronounced transverse folds, and is poor in glands. The soft palate is relatively short, located almost horizontally. The palatine curtain does not touch the posterior pharyngeal wall, which allows the child to breathe during sucking. With the appearance of milk teeth, a significant increase in the size of the alveolar processes of the jaws occurs, and the arch of the hard palate rises, as it were. The tongue of newborns is short, wide, thick and inactive; clearly defined papillae are visible on the mucous membrane. The tongue occupies the entire oral cavity - when the oral cavity is closed, it comes into contact with the cheeks and hard palate, protrudes forward between the jaws in the vestibule of the mouth. The mucous membrane of the oral cavity in children, especially at an early age, is thin and easily vulnerable, which must be taken into account when treating the oral cavity. The mucous membrane of the bottom of the oral cavity forms a noticeable fold, which is covered with a large number of villi. A protrusion in the form of a roller is also present on the mucous membrane of the cheeks in the gap between the upper and lower jaws. In addition, there are transverse folds (rollers) on the hard palate, and roller-like thickenings on the gums. These formations provide sealing of the oral cavity during sucking. On the mucous membrane in the region of the hard palate along the midline in newborns there are Bohn's nodules - yellowish formations - retention cysts of the salivary glands, which disappear by the end of the first month of life. The mucous membrane of the oral cavity in children of the first 3-4 months of life is relatively dry, which is due to the insufficient development of the salivary glands and the deficiency of saliva. The salivary glands (parotid, submandibular, sublingual, small glands of the oral mucosa) in the newborn can be characterized by low secretory activity and secrete a small amount of thick, viscous saliva necessary for gluing the lips and sealing the oral cavity during sucking. The functional activity of the salivary glands begins to increase at the age of 1.5-2 months; in 3-4-month-old children, saliva often flows out of the mouth due to the immaturity of the regulation of salivation and swallowing of saliva (physiological salivation). The most intensive growth and development of the salivary glands occurs between the ages of 4 months and 2 years. By the age of 7, a child produces as much saliva as an adult. The reaction of saliva in newborns is often neutral or slightly acidic. From the first days of life, saliva contains osamylase and other enzymes that are necessary for the breakdown of starch and glycogen. In newborns, the concentration of amylase in saliva is low; during the first year of life, its content and activity increase significantly and reach a maximum level at 2-7 years.

The pharynx of a newborn is funnel-shaped and bottom edge projected at the level of the intervertebral disc between CVI and CIV. A to adolescence it descends to the CVI-CVII level. The larynx in infants also has a funnel-shaped shape and is located differently than in adults. The entrance to the larynx is located high above the lower back edge of the palatine curtain and is connected with the oral cavity. Food moves to the sides of the protruding larynx, so the baby can immediately breathe and swallow without interrupting sucking.

Sucking and swallowing are already innate unconditioned reflexes. In healthy and mature newborns, they are formed by the time of birth. When suckling, the baby's lips tightly grasp the nipple of the breast. The jaws squeeze it, and the communication between the oral cavity and the outside air stops. Negative pressure is formed in the child's oral cavity, which is facilitated by the lowering of the lower jaw along with the tongue down and back. Further, breast milk enters the rarefied space of the oral cavity. All elements of the masticatory apparatus of a newborn are adapted for the process of breast sucking: the gingival membrane, pronounced palatine transverse folds and fatty bodies in the cheeks. The adaptation of the oral cavity of a newborn to sucking is physiological infantile retrognathia, which later turns into orthognathia. In the process of sucking, the child makes rhythmic movements of the lower jaw from front to back. The absence of the articular tubercle facilitates the sagittal movements of the child's mandible.

The esophagus is a spindle-shaped muscular tube lined from the inside with a mucous membrane. By birth, the esophagus is formed, its length in a newborn is 10-12 cm, at the age of 5 years - 16 cm, and at 15 years old already 19 cm. The ratio between the length of the esophagus and body length remains relatively constant and is approximately 1:5. The width of the esophagus in a newborn is 5-8 mm, at 1 year old - 10-12 mm, by 3-6 years old - 13-15 mm and by 15 years old - 18-19 mm. The dimensions of the esophagus must be taken into account during fibroesophagogastroduodenoscopy (FEGDS), duodenal sounding and gastric lavage. Anatomical narrowing of the esophagus in newborns and children of the first year of life is slightly expressed and is formed with age. The wall of the esophagus in a newborn is thin, the muscular membrane is poorly developed, it grows intensively up to 12-15 years. The mucous membrane of the esophagus in infants is poor in glands. Longitudinal folds appear at the age of 2-2.5 years. The submucosa is well developed, rich in blood vessels. Outside the act of swallowing, the passage of the pharynx into the esophagus is closed. Peristalsis of the esophagus occurs during swallowing movements.

The stomach of a newborn is in the form of a cylinder, a bull horn or a fishhook and is placed high (the inlet of the stomach is at the level of TVIII-TIX, and the opening of the pylorus is at the level of TXI-TXII). As the child grows and develops, the stomach descends, and by the age of 7 years, its inlet (with a vertical position of the body) is projected between TXI and TXII, and the output is between TXII and L. In infants, the stomach is located horizontally, but as soon as the child begins walk, it gradually takes more vertical position. Cardiac part, fundus and pyloric part of the stomach in a newborn are weakly expressed, the pylorus is wide. The entrance part of the stomach is often located above the diaphragm, the angle between the abdominal part of the esophagus and the wall of the fundus of the stomach adjacent to it is poorly expressed, the muscular membrane of the cardial part of the stomach is also poorly developed. Gubarev's valve (a mucosal fold protruding into the esophageal cavity and preventing the return of food) is almost not expressed (it develops by 8-9 months of life), the cardiac sphincter is functionally inferior when the pyloric section of the stomach is functionally well developed already at birth. These features determine the possibility of reflux of the contents of the stomach into the esophagus and the development of peptic lesions of its mucous membrane. In addition, the tendency of children of the first year of life to regurgitation and vomiting is associated with the absence of a tight grasp of the esophagus by the legs of the diaphragm and impaired innervation with increased intragastric pressure. Swallowing air while sucking (aerophagia) also contributes to regurgitation with improper feeding technique, short bridle tongue, greedy sucking, excessively rapid release of milk from the mother's breast. In the first weeks of life, the stomach is located in an oblique frontal plane, completely covered in front by the left lobe of the liver, and therefore the fundus of the stomach in the supine position is located below the antral-pyloric section, therefore, to prevent aspiration after feeding, children should be given an elevated position. By the end of the first year of life, the stomach lengthens, and already in the period from 7 to 11 years, it acquires a shape similar to that of an adult. By the age of 8, the formation of its cardiac part is completed. The anatomical capacity of the stomach of a newborn is 30-35 cubic meters. cm, by the 14th day of life, it increases to 90 cubic meters. see Physiological capacity is less than anatomical, and on the first day of life is only 7-10 ml; by the 4th day after the start of enteral nutrition, it increases to 40-50 ml, and by the 10th day - up to 80 ml. Further, the capacity of the stomach increases monthly by 25 ml and by the end of the first year of life it is 250-300 ml, and by 3 years - 400-600 ml. An intensive increase in the capacity of the stomach begins after 7 years and by 10-12 years is 1300-1500 ml. The muscular membrane of the stomach in a newborn is poorly developed, it reaches its greatest thickness only by the age of 15-20. The mucous membrane of the stomach in a newborn is thick, the folds are high. During the first 3 months of life, the surface of the mucous membrane increases by 3 times, which contributes to better digestion of milk. By the age of 15, the surface of the gastric mucosa increases 10 times. With age, the number of gastric pits increases, into which openings of the gastric glands open. By birth, the gastric glands are morphologically and functionally underdeveloped, their relative number (per 1 kg of body weight) in newborns is 2.5 times less than in adults, but rapidly increases with the onset of enteral nutrition. The secretory apparatus of the stomach in children of the first year of life is underdeveloped, its functional abilities are low. The gastric juice of an infant contains the same components as the gastric juice of an adult: hydrochloric acid, chymosin (curdles milk), pepsins (break down proteins into albumoses and peptones) and lipase (breaks down neutral fats into fatty acids and glycerol). For children in the first weeks of life, a very low concentration of hydrochloric acid in gastric juice and its low total acidity are characteristic. It increases significantly after the introduction of complementary foods, i.e. when switching from lactotrophic nutrition to normal. In parallel with lowering the pH of gastric juice, the activity of carbonic anhydrase, which is involved in the formation of hydrogen ions, increases. In children of the first 2 months of life, the pH value is mainly determined by the hydrogen ions of lactic acid, and subsequently by hydrochloric acid. The synthesis of proteolytic enzymes by the chief cells begins in the antenatal period, but their content and functional activity in newborns are low and gradually increase with age. The leading role in the hydrolysis of proteins in newborns is played by fetal pepsin, which has a higher proteolytic activity. In infants, significant fluctuations in the activity of proteolytic enzymes are indicated depending on the nature of feeding (with artificial feeding, activity indicators are higher). In children of the first year of life (unlike adults), a significant activity of gastric lipase is noted, which ensures the hydrolysis of fats in the absence of bile acids in a neutral environment. Low concentrations of hydrochloric acid and pepsins in the stomach in newborns and infants determine the reduced protective function of gastric juice, but at the same time contribute to the preservation of Ig, which come with mother's milk. In the first months of life, the motor function of the stomach is reduced, peristalsis is sluggish, and the gas bubble is enlarged. The frequency of peristaltic contractions in newborns is the lowest, then it actively increases and after 3 years it stabilizes. By the age of 2, the structural and physiological features of the stomach correspond to those of an adult. In infants, an increase in the tone of the muscles of the stomach in the pyloric region is likely, the maximum manifestation of which is pylorospasm. At an older age, cardiospasm is sometimes observed. The frequency of peristaltic contractions in newborns is the lowest, then it actively increases and stabilizes after 3 years.

The intestine starts from the pylorus and ends at the anus. Distinguish between small and large intestines. The small intestine is divided into duodenum, jejunum and ileum; large intestine - on the blind, colon (ascending, transverse, descending, sigmoid) and rectum. The relative length of the small intestine in a newborn is large: 1 m per 1 kg of body weight, while in adults it is only 10 cm.

The duodenum of a newborn has an annular shape (bends form later), its beginning and end are located at level L. In children older than 5 months, the upper part of the duodenum is at level TXII; the descending part gradually descends towards the age of 12 to the level of LIMLIV. In young children, the duodenum is very mobile, but by the age of 7, adipose tissue appears around it, which fixes the intestine, reducing its mobility. In the upper part of the duodenum, acidic gastric chyme is alkalized, prepared for the action of enzymes that come from the pancreas and are formed in the intestine, and mixed with bile. The folds of the mucous membrane of the duodenum in newborns are lower than in older children, the duodenal glands are small, less branched than in adults. The duodenum has a regulatory effect on the entire digestive system through hormones that are secreted by the endocrine cells of its mucous membrane.

The small intestine occupies approximately 2/5, and the ileum 3/5 of the length of the small intestine (excluding the duodenum). The ileum terminates in the ileocecal valve (Bauhinian valve). In young children, relative weakness of the ileocecal valve is noted, and therefore the contents of the caecum, which is very rich in bacterial flora, can be thrown into the ileum, causing a high incidence of inflammatory lesions of its terminal section. The small intestine in children occupies a variable position, depending on the degree of its filling, the position of the body, the tone of the intestines and the muscles of the anterior abdominal wall. Compared with adults, the intestinal loops lie more compactly (due to the relatively large sizes liver and underdevelopment of the small pelvis). After 1 year of life, as the pelvis develops, the location of the loops of the small intestine becomes more constant. In the small intestine baby there are relatively many gases, the volume of which gradually decreases until complete disappearance by the age of 7 (adults normally do not have gases in the small intestine). The mucous membrane is thin, richly vascularized and has increased permeability, especially in children of the first year of life. The intestinal glands in children are larger than in adults. Their number increases significantly during the first year of life. All in all histological structure mucous membrane becomes similar to that in adults by 5-7 years. In newborns, single and group lymphoid follicles are present in the thickness of the mucous membrane. Initially, they are scattered throughout the intestine, and later they are grouped mainly in the ileum in the form of group lymphatic follicles (Peyer's patches). Lymphatic vessels are numerous, have a wider lumen than in adults. Lymph flowing from the small intestine does not pass through the liver, and the products of absorption immediately enter the bloodstream. The muscular coat, especially its longitudinal layer, is poorly developed in newborns. The mesentery in newborns and young children is short, increasing significantly in length during the first year of life. In the small intestine, the main stages of the complex process of splitting and absorption of nutrients occur with the combined action of intestinal juice, bile and pancreatic secretions. The breakdown of nutrients with the help of enzymes occurs both in the cavity of the small intestine (abdominal digestion) and directly on the surface of its mucous membrane (parietal, or membrane, digestion, which dominates in infancy in the period dairy nutrition). The secretory apparatus of the small intestine is generally formed by birth. Even in newborns, the same enzymes can be determined in the intestinal juice as in adults (enterokinase, alkaline phosphatase, lipase, amylase, maltase, nuclease), however, their activity is lower and increases with age. The features of protein assimilation in young children include the high development of pinocytosis epithelial cells of the intestinal mucosa, as a result of which milk proteins in children in the first weeks of life can pass into the blood in an unmodified form, which can lead to the appearance of AT to cow's milk proteins. In children older than a year, proteins undergo hydrolysis to form amino acids. Already from the first days of life in a child, all parts of the small intestine have a fairly high hydrolytic activity. Disaccharidases appear in the intestine as early as prenatal period. Maltase activity is quite high at birth and remains so in adults; sucrase activity increases somewhat later. In the first year of life, a direct correlation is noted between the age of the child and the activity of maltase and sucrase. Lactase activity increases rapidly in recent weeks gestation, and after birth, the increase in activity decreases. It remains high throughout the period of breastfeeding, by the age of 4-5 there is a significant decrease in it, it is the smallest in adults. It should be noted that human milk lactose is absorbed more slowly than cow's milk lactose, and partly enters the colon, which contributes to the formation of gram-positive intestinal microflora in breast-fed children. Due to the low activity of lipase, the process of digesting fats is especially intense. Fermentation in the intestines of infants complements the enzymatic breakdown of food. There is no rotting in the intestines of healthy children in the first months of life. Absorption is closely related to parietal digestion and depends on the structure and function of the cells of the surface layer of the small intestine mucosa.

The large intestine in a newborn has an average length of 63 cm. By the end of the first year of life, it lengthens to 83 cm, and then its length is approximately equal to the height of the child. By birth, the colon does not complete its development. The newborn does not have omental processes (they appear on the 2nd year of the child's life), the bands of the colon are slightly outlined, the haustras of the colon are absent (they appear after 6 months). Colon bands, haustra and omental processes are finally formed by the age of 6-7 years.

The mucous membrane of the large intestine in children has a number of features: deepened crypts, flatter epithelium, higher rate of its proliferation. Juice secretion in the colon normal conditions small; however, it sharply increases with mechanical irritation of the mucous membrane.

The rectum in a newborn has the shape of a cylinder, does not have an ampulla (its formation occurs in the first period of childhood) and bends (they form immediately with the sacral and coccygeal bends of the spine), its folds are not expressed. In children of the first months of life, the rectum is relatively long and poorly fixed, because fatty tissue is not developed. The rectum occupies the final position by 2 years. In a newborn, the muscular membrane is poorly developed. Due to the well-developed submucosa and weak fixation of the mucous membrane relative to the submucosa, as well as insufficient development of the sphincter anus in young children, it often occurs. The anus in children is located more dorsally than in adults, at a distance of 20 mm from the coccyx.

The motor function of the intestine (motor) consists of pendulum movements that occur in the small intestine, due to which its contents are mixed, and peristaltic movements that move the chyme towards the large intestine. The colon also has anti-peristaltic movements that thicken and form feces. Motor skills in young children are more active, which contributes to frequent bowel movements. In infants, the duration of the passage of food gruel through the intestines is from 4 to 18 hours, and in older children - about a day. High motor activity of the intestine, combined with insufficient fixation of its loops, determines the tendency to intussusception.

During the first hours of life, meconium (original feces) is passed - a dark green sticky mass with a pH of about 6.0. Meconium consists of desquamated epithelium, mucus, remnants of amniotic fluid, bile pigments, etc. On the 2-3rd day of life, feces are mixed with meconium, and from the 5th day, feces take on a characteristic appearance for a newborn. In children of the first month of life, defecation usually occurs after each feeding - 5-7 times a day, in children from the 2nd month of life - 3-6 times, in 1 year - 1-2 times. With mixed and artificial feeding, defecation is more rare. Feces in children who are breastfed, mushy, yellow color, sour reaction and sour smell; with artificial feeding, the feces have a thicker consistency (putty-like), lighter, sometimes with a grayish tint, neutral or even alkaline, more pungent odor. The golden yellow color of feces in the first months of a child's life is due to the presence of bilirubin, greenish - biliverdin. In infants, defecation occurs reflexively, without the participation of the will. From the end of the first year of life, a healthy child is gradually accustomed to the fact that defecation becomes an arbitrary act.

The microflora of the gastrointestinal tract is involved in digestion, prevents the development of pathogenic flora in the intestine, synthesizes a number of vitamins, takes part in the inactivation of physiologically active substances and enzymes, affects the rate of renewal of enterocytes, enterohepatic circulation of bile acids, etc. The intestines of the fetus and newborn are sterile during the first 10- 20 hours (aseptic phase). Then colonization of the intestine by microorganisms begins (second phase), and the third phase - stabilization of the microflora - lasts at least 2 weeks. The formation of intestinal microbial biocenosis begins from the first day of life, by the 7th-9th day in healthy full-term children, the bacterial flora is usually represented mainly by Bifidobacteriumbifidum, Lactobacillusacidophilus. With natural feeding, bifidum prevails among the intestinal microflora, with artificial feeding, acidophilus, bifidum and enterococci are present in almost equal amounts. The transition to nutrition, which is typical for adults, is accompanied by a change in the composition of the intestinal microflora.

The pancreas is a parenchymal organ of external and internal secretion. In newborns, it is small in size: its mass is about 23 g, and its length is 4-5 cm. Already by 6 months, the mass of the gland doubles, by 1 year it increases 4 times, and by 10 years - 10 times. In a newborn, the pancreas is located deep in the abdominal cavity at the level of TX, that is, higher than in an adult. Due to weak fixation to back wall in the abdominal cavity of a newborn, it is more mobile. In infants and older children, the pancreas is at the LN level. Iron grows more intensively in the first 3 years and in puberty. By birth and in the first months of life, the pancreas is not sufficiently differentiated, abundantly vascularized and poor in connective tissue. At an early age, the surface of the pancreas is smooth, and by the age of 10-12, tuberosity appears, which is due to the isolation of the boundaries of the lobules. The lobes and lobules of the pancreas in children are smaller and few in number. The endocrine part of the pancreas is more developed at birth than the exocrine part. Pancreatic juice contains enzymes that provide hydrolysis of proteins, fats and carbohydrates, as well as bicarbonates, which create the alkaline environment necessary for their activation. In newborns, a small volume of pancreatic juice is secreted after stimulation, amylase activity and bicarbonate capacity are low. Amylase activity from birth to 1 year increases several times. When switching to a normal diet, in which more than half of the calorie requirement is covered by carbohydrates, amylase activity increases rapidly and reaches maximum values ​​​​by 6-9 years. The activity of pancreatic lipase in newborns is low, which determines the significant role of salivary gland lipase, gastric juice and breast milk lipase in the hydrolysis of fat. The activity of duodenal content lipase increases by the end of the first year of life, reaching the level of an adult by the age of 12. The proteolytic activity of the secret of the pancreas in children during the first months of life is quite high, it reaches a maximum at the age of 4-6 years. The type of feeding has a significant effect on the activity of the pancreas: with artificial feeding, the activity of enzymes in the duodenal juice is 4-5 times higher than with natural feeding.

The liver at the time of birth is one of the largest organs and occupies 1/3-1/2 of the volume of the abdominal cavity, its lower edge protrudes significantly from under the hypochondrium, and the right lobe can even touch the iliac crest. In newborns, the mass of the liver is more than 4% of body weight, and in adults - 2%. In the postnatal period, the liver continues to grow, but more slowly than body weight: the initial mass of the liver doubles by 8-10 months and triples by 2-3 years. Due to the different rate of increase in the mass of the liver and body in children from 1 to 3 years of age, the edge of the liver comes out from under the right hypochondrium and is easily palpated 1-3 cm below the costal arch along the midclavicular line. From the age of 7, the lower edge of the liver does not come out from under the costal arch and is not palpable in a calm position; in the midline does not go beyond the upper third of the distance from the umbilicus to the xiphoid process. The formation of liver lobules begins in the fetus, but by the time of birth, the liver lobules are not clearly demarcated. Their final differentiation is completed in the postnatal period. The lobulated structure is revealed only by the end of the first year of life. The branches of the hepatic veins are located in compact groups and do not intersperse with the branches of the portal vein. The liver is plethoric, as a result of which it rapidly increases with infections and intoxications, circulatory disorders. The fibrous capsule of the liver is thin. About 5% of the volume of the liver in newborns is accounted for by hematopoietic cells, then their number rapidly decreases. In the composition of the liver, the newborn has more water, but less protein, fat and glycogen. By the age of 8, the morphological and histological structure of the liver becomes the same as in adults.

The formation of bile begins already in the prenatal period, but bile formation at an early age is slowed down. With age, the ability of the gallbladder to concentrate bile increases. The concentration of bile acids in the hepatic bile in children of the first year of life is significant, especially in the first days after birth, which leads to the frequent development of subhepatic cholestasis (bile thickening syndrome) in newborns. By the age of 4-10, the concentration of bile acids decreases, and in adults it increases again. The neonatal period is characterized by the immaturity of all stages of the hepato-intestinal circulation of bile acids: insufficiency of their uptake by hepatocytes, excretion through the tubular membrane, slowing of bile flow, dyscholia due to a decrease in the synthesis of secondary bile acids in the intestine and a low level of their reabsorption in the intestine. Children produce more atypical, less hydrophobic, and less toxic fatty acids than adults. The accumulation of fatty acids in the intrahepatic bile ducts determines the increased permeability of intercellular junctions and the increased content of bile components in the blood. The bile of a child in the first months of life contains less cholesterol and salts, and this determines the rarity of the formation of stones. In newborns, fatty acids combine mainly with taurine (in adults - with glycine). Taurine conjugates are more soluble in water and less toxic. Undoubtedly higher bile content of taurocholic acid, which has a bactericidal effect, determines the rarity of the development of bacterial inflammation of the biliary tract in children of the first year of life. Enzymatic systems of the liver, which provide adequate metabolism of various substances, are not mature enough at birth. Artificial feeding stimulates their earlier development, but leads to their disproportion. After birth, the child's albumin synthesis decreases, which leads to a decrease in the albumin-globulin ratio in the blood. In children, transamination of amino acids occurs in the liver much more actively: at birth, the activity of aminotransferases in the child's blood is 2 times higher than in the mother's blood. Along with this, the processes of transamination are not mature enough, and the number of essential acids for children is greater than for adults. So, in adults there are 8 of them, children under 5-7 years old need additional histidine, and children in the first 4 weeks of life also need cysteine. The urea-forming function of the liver is formed by the age of 3-4 months; before that, children have a high excretion of ammonia in the urine at a low concentration of urea. Children of the first year of life are resistant to ketoacidosis, although they receive a diet rich in fat, and at the age of 2-12 years, on the contrary, they are prone to it. In a newborn, the content of cholesterol and its esters in the blood is significantly lower than in the mother. After the start of breastfeeding for 3-4 months, hypercholesterolemia is noted. For the next 5 years, the concentration of cholesterol in children remains lower than in adults. In newborns in the first days of life, insufficient activity of glucuronyl transferase is noted, with the participation of which conjugation of bilirubin with glucuronic acid and the formation of water-soluble "direct" bilirubin occur. Difficulty in bilirubin excretion is main reason physiological jaundice newborns. The liver performs a barrier function, neutralizes endogenous and exogenous harmful substances, including toxins that come from the intestines, and takes part in the metabolism of drugs. In young children, the neutralizing function of the liver is not sufficiently developed. The gallbladder in newborns is usually hidden by the liver, its shape can be different. Its dimensions increase with age, and by the age of 10-12 years, the length increases by about 2 times. The rate of excretion of gallbladder bile in newborns is 6 times less than in adults. .

Thus, the age characteristics of the digestive system inherent in children necessitate separate cooking in the first year of life, up to 1.5 years, from 1.5 to 3 years and from 3 to 7 years. The food that the body of a child at the age of 5-7 years is able to process is not suitable for children of the first year of life. Age-related features of the motor function of the stomach and intestines of children determine the features of diets in different age periods.