The vital activity of the human body is impossible without constant exchange of substances with the external environment. Food contains vital nutrients used by the body as plastic material (for building cells and tissues of the body) and energy (as a source of energy necessary for the functioning of the body).

Water, mineral salts, and vitamins are absorbed by the body in the form in which they are found in food. High-molecular compounds: proteins, fats, carbohydrates cannot be absorbed in the digestive tract without first being broken down into simpler compounds.

The digestive system provides food intake, its mechanical and chemical processing, the movement of “food mass through the digestive canal, the absorption of nutrients and water into the blood and lymphatic channels and the removal of undigested food debris from the body in the form of feces.

Digestion is a set of processes that ensure the mechanical grinding of food and the chemical breakdown of macromolecules of nutrients (polymers) into components suitable for absorption (monomers).

The digestive system includes the gastrointestinal tract, as well as organs that secrete digestive juices (salivary glands, liver, pancreas). The gastrointestinal tract begins with the mouth, includes the oral cavity, esophagus, stomach, small and large intestines, which ends at the anus.

The main role in the chemical processing of food belongs to enzymes(enzymes), which, despite their enormous diversity, have some common properties. Enzymes are characterized by:

High specificity - each of them catalyzes only one reaction or acts on only one type of bond. For example, proteases, or proteolytic enzymes, break down proteins into amino acids (pepsin of the stomach, trypsin, chymotrypsin of the duodenum, etc.); lipases, or lipolytic enzymes, break down fats into glycerol and fatty acids (small intestinal lipases, etc.); Amylases, or glycolytic enzymes, break down carbohydrates into monosaccharides (saliva maltase, amylase, maltase and pancreatic juice lactase).

Digestive enzymes are active only at a certain pH value. For example, gastric pepsin acts only in an acidic environment.

They act in a narrow temperature range (from 36 ° C to 37 ° C); outside this temperature range, their activity decreases, which is accompanied by disruption of the digestive processes.

They are highly active, so they break down a huge amount of organic substances.

Main functions of the digestive system:

1. Secretory– production and secretion of digestive juices (stomach, intestinal), which contain enzymes and other biologically active substances.

2. Motor-evacuation, or propulsion, – ensures grinding and promotion of food masses.

3. Suction– transfer of all final products of digestion, water, salts and vitamins through the mucous membrane from the digestive canal into the blood.

4. Excretory (excretory)– excretion of metabolic products from the body.

5. Incretory– secretion of special hormones by the digestive system.

6. Protective:

a mechanical filter for large antigen molecules, which is provided by the glycocalyx on the apical membrane of enterocytes;

hydrolysis of antigens by enzymes of the digestive system;

The immune system of the gastrointestinal tract is represented by special cells (Peyer's patches) in the small intestine and lymphoid tissue of the appendix, which contain T and B lymphocytes.

DIGESTION IN THE ORAL CAVITY. FUNCTIONS OF SALIVARY GLANDS

In the mouth, the taste properties of food are analyzed, the digestive tract is protected from low-quality nutrients and exogenous microorganisms (saliva contains lysozyme, which has a bactericidal effect, and endonuclease, which has an antiviral effect), grinding, wetting of food with saliva, initial hydrolysis of carbohydrates, formation of a food bolus, irritation of receptors with subsequent stimulation of the activity of not only the glands of the oral cavity, but also the digestive glands of the stomach, pancreas, liver, and duodenum.

Salivary glands. In humans, saliva is produced by 3 pairs of large salivary glands: parotid, sublingual, submandibular, as well as many small glands (labial, buccal, lingual, etc.) scattered in the oral mucosa. Every day, 0.5 - 2 liters of saliva are produced, the pH of which is 5.25 - 7.4.

Important components of saliva are proteins that have bactericidal properties.(lysozyme, which destroys the cell wall of bacteria, as well as immunoglobulins and lactoferrin, which binds iron ions and prevents their capture by bacteria), and enzymes: a-amylase and maltase, which begin the breakdown of carbohydrates.

Saliva begins to be secreted in response to irritation of the receptors of the oral cavity by food, which is an unconditioned stimulus, as well as by the sight, smell of food and the environment (conditioned stimuli). Signals from taste, thermo- and mechanoreceptors of the oral cavity are transmitted to the salivation center of the medulla oblongata, where signals are switched to secretory neurons, the totality of which is located in the region of the nucleus of the facial and glossopharyngeal nerves.

As a result, a complex reflex reaction of salivation occurs. The parasympathetic and sympathetic nerves are involved in the regulation of salivation. When the parasympathetic nerve is activated, the salivary gland releases a larger volume of liquid saliva; when the sympathetic nerve is activated, the volume of saliva is smaller, but it contains more enzymes.

Chewing involves grinding food, moistening it with saliva and forming a food bolus.. During the chewing process, the taste of food is assessed. Then, through swallowing, food enters the stomach. Chewing and swallowing requires the coordinated work of many muscles, the contractions of which regulate and coordinate the chewing and swallowing centers located in the central nervous system.

During swallowing, the entrance to the nasal cavity closes, but the upper and lower esophageal sphincters open, and food enters the stomach. Solid food passes through the esophagus in 3–9 seconds, liquid food in 1–2 seconds.

DIGESTION IN THE STOMACH

Food stays in the stomach for an average of 4-6 hours for chemical and mechanical processing. There are 4 parts in the stomach: the inlet, or cardiac part, the upper part - the bottom (or fornix), the middle largest part - the body of the stomach and the lower part - the antrum, ending with the pyloric sphincter, or pylorus (the opening of the pylorus leads to the duodenum).

The stomach wall consists of three layers: external - serous, middle - muscular and internal - mucous. Contractions of the stomach muscles cause both wave-like (peristaltic) and pendulum-like movements, due to which food is mixed and moves from the entrance to the exit of the stomach.

The gastric mucosa contains numerous glands that produce gastric juice. From the stomach, semi-digested food gruel (chyme) enters the intestines. At the junction of the stomach and intestines there is a pyloric sphincter, which, when contracted, completely separates the stomach cavity from the duodenum.

The mucous membrane of the stomach forms longitudinal, oblique and transverse folds, which straighten when the stomach is filled. Outside the digestion phase, the stomach is in a collapsed state. After 45–90 minutes of rest, periodic contractions of the stomach occur, lasting 20–50 minutes (hungry peristalsis). The capacity of an adult's stomach ranges from 1.5 to 4 liters.

Functions of the stomach:

• food deposit;
• secretory - secretion of gastric juice for food processing;
• motor – for moving and mixing food;
• absorption of certain substances into the blood (water, alcohol);
• excretory – release of some metabolites into the gastric cavity along with gastric juice;
• endocrine - the formation of hormones that regulate the activity of the digestive glands (for example, gastrin);
• protective – bactericidal (most microbes die in the acidic environment of the stomach).

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Composition and properties of gastric juice

Gastric juice is produced by gastric glands, which are located in the fundus (fornix) and body of the stomach. They contain 3 types of cells:

the main ones, which produce a complex of proteolytic enzymes (pepsin A, gastrixin, pepsin B);

lining, which produce hydrochloric acid;

additional, in which mucus is produced (mucin, or mucoid). Thanks to this mucus, the stomach wall is protected from the action of pepsin.

At rest (“on an empty stomach”), approximately 20–50 ml of gastric juice, pH 5.0, can be extracted from the human stomach. The total amount of gastric juice secreted in a person during a normal diet is 1.5 - 2.5 liters per day. The pH of active gastric juice is 0.8 - 1.5, because it contains approximately 0.5% HCl.

The role of HCl. Increases the release of pepsinogens by the main cells, promotes the conversion of pepsinogens into pepsins, creates an optimal environment (pH) for the activity of proteases (pepsins), causes swelling and denaturation of food proteins, which ensures increased breakdown of proteins, and also promotes the death of microbes.

Castle factor. Food contains vitamin B12, necessary for the formation of red blood cells, the so-called extrinsic Castle factor. But it can only be absorbed into the blood if there is intrinsic Castle factor in the stomach. This is a gastromucoprotein, which includes a peptide that is cleaved from pepsinogen when it is converted into pepsin, and a mucoid that is secreted by accessory cells of the stomach. When the secretory activity of the stomach decreases, the production of Castle factor also decreases and, accordingly, the absorption of vitamin B12 decreases, as a result of which gastritis with decreased secretion of gastric juice is usually accompanied by anemia.

Phases of gastric secretion:

1. Complex reflex, or brain, lasting 1.5 - 2 hours, during which the secretion of gastric juice occurs under the influence of all factors accompanying food intake. In this case, conditioned reflexes that arise from the sight, smell of food, and surroundings are combined with unconditioned reflexes that occur during chewing and swallowing. The juice released under the influence of the sight and smell of food, chewing and swallowing is called “appetizing” or “fiery”. It prepares the stomach for food intake.

2. Gastric, or neurohumoral, the phase in which secretion stimuli arise in the stomach itself: secretion increases with stretching of the stomach (mechanical stimulation) and with the action of extractive substances of food and protein hydrolysis products on its mucosa (chemical stimulation). The main hormone in activating gastric secretion in the second phase is gastrin. The production of gastrin and histamine also occurs under the influence of local reflexes of the metasympathetic nervous system.

Humoral regulation begins 40–50 minutes after the start of the brain phase. In addition to the activating influence of the hormones gastrin and histamine, activation of the secretion of gastric juice occurs under the influence of chemical components - extractive substances of the food itself, primarily meat, fish, and vegetables. When cooking foods, they turn into decoctions, broths, are quickly absorbed into the blood and activate the digestive system.

These substances primarily include free amino acids, vitamins, biostimulants, and a set of mineral and organic salts. Fat initially inhibits secretion and slows down the evacuation of chyme from the stomach into the duodenum, but then it stimulates the activity of the digestive glands. Therefore, with increased gastric secretion, decoctions, broths, and cabbage juice are not recommended.

Gastric secretion increases most strongly under the influence of protein foods and can last up to 6-8 hours; it changes most weakly under the influence of bread (no more than 1 hour). When a person is on a carbohydrate diet for a long time, the acidity and digestive power of gastric juice decrease.

3. Intestinal phase. In the intestinal phase, the secretion of gastric juice is inhibited. It develops during the passage of chyme from the stomach to the duodenum. When an acidic food bolus enters the duodenum, hormones that suppress gastric secretion - secretin, cholecystokinin and others - begin to be produced. The amount of gastric juice is reduced by 90%.

DIGESTION IN THE SMALL INTESTINE

The small intestine is the longest part of the digestive tract, 2.5 to 5 meters long. The small intestine is divided into three sections: duodenum, jejunum and ileum. Absorption of the breakdown products of nutrients occurs in the small intestine. The mucous membrane of the small intestine forms circular folds, the surface of which is covered with numerous outgrowths - intestinal villi 0.2 - 1.2 mm long, which increase the absorption surface of the intestine.

Each villus includes an arteriole and a lymphatic capillary (lacteal sinus), and venules emerge. In the villus, arterioles divide into capillaries, which merge to form venules. Arterioles, capillaries and venules in the villi are located around the lacteal sinus. Intestinal glands are located deep in the mucous membrane and produce intestinal juice. The mucous membrane of the small intestine contains numerous single and group lymph nodes that perform a protective function.

The intestinal phase is the most active phase of nutrient digestion. In the small intestine, the acidic contents of the stomach are mixed with the alkaline secretions of the pancreas, intestinal glands and liver and the breakdown of nutrients into final products absorbed into the blood occurs, as well as the movement of food mass towards the large intestine and the release of metabolites.

The entire length of the digestive tube is covered with mucous membrane, containing glandular cells that secrete various components of digestive juice. Digestive juices consist of water, inorganic and organic substances. Organic substances are mainly proteins (enzymes) - hydrolases that help break down large molecules into small ones: glycolytic enzymes break down carbohydrates into monosaccharides, proteolytic enzymes break down oligopeptides into amino acids, lipolytic enzymes break down fats into glycerol and fatty acids.

The activity of these enzymes is very dependent on the temperature and pH of the environment., as well as the presence or absence of their inhibitors (so that, for example, they do not digest the stomach wall). The secretory activity of the digestive glands, the composition and properties of the secreted secretion depend on the diet and diet.

In the small intestine, cavity digestion occurs, as well as digestion in the area of ​​the brush border of enterocytes(cells of the mucous membrane) of the intestine - parietal digestion (A.M. Ugolev, 1964). Parietal, or contact, digestion occurs only in the small intestines when chyme comes into contact with their wall. Enterocytes are equipped with mucus-covered villi, the space between which is filled with a thick substance (glycocalyx), which contains threads of glycoproteins.

They, together with mucus, are able to adsorb digestive enzymes from the juice of the pancreas and intestinal glands, while their concentration reaches high values, and the decomposition of complex organic molecules into simple ones is more efficient.

The amount of digestive juices produced by all digestive glands is 6-8 liters per day. Most of them are reabsorbed in the intestines. Absorption is the physiological process of transferring substances from the lumen of the digestive canal into the blood and lymph. The total amount of liquid absorbed daily in the digestive system is 8 - 9 liters (approximately 1.5 liters from food, the rest is fluid secreted by the glands of the digestive system).

The mouth absorbs some water, glucose and some medications. Water, alcohol, some salts and monosaccharides are absorbed in the stomach. The main section of the gastrointestinal tract where salts, vitamins and nutrients are absorbed is the small intestine. The high absorption rate is ensured by the presence of folds along its entire length, as a result of which the absorption surface increases three times, as well as the presence of villi on the epithelial cells, due to which the absorption surface increases by 600 times. Inside each villi there is a dense network of capillaries, and their walls have large pores (45 - 65 nm), through which even fairly large molecules can penetrate.

Contractions of the wall of the small intestine ensure the movement of chyme in the distal direction, mixing it with digestive juices. These contractions occur as a result of coordinated contraction of the smooth muscle cells of the outer longitudinal and inner circular layers. Types of motility of the small intestine: rhythmic segmentation, pendulum movements, peristaltic and tonic contractions.

The regulation of contractions is carried out mainly by local reflex mechanisms with the participation of the nerve plexuses of the intestinal wall, but under the control of the central nervous system (for example, with strong negative emotions, a sharp activation of intestinal motility can occur, which will lead to the development of “nervous diarrhea”). When the parasympathetic fibers of the vagus nerve are excited, intestinal motility increases, and when the sympathetic nerves are excited, it is inhibited.

ROLE OF THE LIVER AND PANCREAS IN DIGESTION

The liver participates in digestion by secreting bile. Bile is produced by liver cells constantly, and enters the duodenum through the common bile duct only when there is food in it. When digestion stops, bile accumulates in the gallbladder, where, as a result of water absorption, the concentration of bile increases 7 to 8 times.

Bile secreted into the duodenum does not contain enzymes, but only participates in the emulsification of fats (for more successful action of lipases). It produces 0.5 - 1 liter per day. Bile contains bile acids, bile pigments, cholesterol, and many enzymes. Bile pigments (bilirubin, biliverdin), which are breakdown products of hemoglobin, give bile a golden yellow color. Bile is secreted into the duodenum 3 to 12 minutes after the start of eating.

Functions of bile:

• neutralizes acidic chyme coming from the stomach;
• activates pancreatic juice lipase;
• emulsifies fats, making them easier to digest;
• stimulates intestinal motility.

Yolks, milk, meat, and bread increase the secretion of bile. Cholecystokinin stimulates contractions of the gallbladder and the release of bile into the duodenum.

Glycogen is constantly synthesized and consumed in the liver– a polysaccharide, which is a polymer of glucose. Adrenaline and glucagon increase the breakdown of glycogen and the flow of glucose from the liver into the blood. In addition, the liver neutralizes harmful substances that enter the body from the outside or formed during the digestion of food, thanks to the activity of powerful enzyme systems for hydroxylation and neutralization of foreign and toxic substances.

The pancreas is a mixed secretion gland., consists of endocrine and exocrine sections. The endocrine section (cells of the islets of Langerhans) secretes hormones directly into the blood. In the exocrine section (80% of the total volume of the pancreas), pancreatic juice is produced, which contains digestive enzymes, water, bicarbonates, electrolytes, and through special excretory ducts enters the duodenum synchronously with the secretion of bile, since they have a common sphincter with the gallbladder duct .

1.5 - 2.0 liters of pancreatic juice are produced per day, pH 7.5 - 8.8 (due to HCO3-), to neutralize the acidic contents of the stomach and create an alkaline pH, at which pancreatic enzymes work better, hydrolyzing all types of nutrients substances (proteins, fats, carbohydrates, nucleic acids).

Proteases (trypsinogen, chymotrypsinogen, etc.) are produced in an inactive form. To prevent self-digestion, the same cells that secrete trypsinogen simultaneously produce a trypsin inhibitor, so in the pancreas itself, trypsin and other protein breakdown enzymes are inactive. Activation of trypsinogen occurs only in the cavity of the duodenum, and active trypsin, in addition to protein hydrolysis, causes activation of other enzymes of pancreatic juice. Pancreatic juice also contains enzymes that break down carbohydrates (α-amylase) and fats (lipases).

DIGESTION IN THE LARGE INTESTINE

Intestines

The large intestine consists of the cecum, colon and rectum. A vermiform appendix (appendix) extends from the lower wall of the cecum, the walls of which contain many lymphoid cells, due to which it plays an important role in immune reactions.

In the colon, the final absorption of essential nutrients occurs, the release of metabolites and heavy metal salts, the accumulation of dehydrated intestinal contents and their removal from the body. An adult produces and excretes 150-250 g of feces per day. It is in the large intestine that the main volume of water is absorbed (5 - 7 liters per day).

Contractions of the large intestine occur mainly in the form of slow pendulum-like and peristaltic movements, which ensures maximum absorption of water and other components into the blood. Motility (peristalsis) of the large intestine increases during eating, as food passes through the esophagus, stomach, and duodenum.

Inhibitory influences are carried out from the rectum, irritation of the receptors of which reduces the motor activity of the colon. Eating foods rich in dietary fiber (cellulose, pectin, lignin) increases the amount of feces and speeds up its movement through the intestines.

Microflora of the colon. The last sections of the large intestine contain many microorganisms, primarily bacilli of the genus Bifidus and Bacteroides. They participate in the destruction of enzymes supplied with chyme from the small intestine, the synthesis of vitamins, and the metabolism of proteins, phospholipids, fatty acids, and cholesterol. The protective function of bacteria is that the intestinal microflora in the host body acts as a constant stimulus for the development of natural immunity.

In addition, normal intestinal bacteria act as antagonists towards pathogenic microbes and inhibit their reproduction. The activity of the intestinal microflora can be disrupted after prolonged use of antibiotics, as a result of which bacteria die, but yeast and fungi begin to develop. Intestinal microbes synthesize vitamins K, B12, E, B6, as well as other biologically active substances, support fermentation processes and reduce putrefaction processes.

REGULATION OF THE ACTIVITY OF DIGESTIVE ORGANS

Regulation of the activity of the gastrointestinal tract is carried out with the help of central and local nervous and hormonal influences. Central nervous influences are most characteristic of the salivary glands, to a lesser extent in the stomach, and local nervous mechanisms play a significant role in the small and large intestines.

The central level of regulation is carried out in the structures of the medulla oblongata and brain stem, the totality of which forms the food center. The food center coordinates the activity of the digestive system, i.e. regulates contractions of the walls of the gastrointestinal tract and the secretion of digestive juices, and also regulates eating behavior in general. Purposeful eating behavior is formed with the participation of the hypothalamus, limbic system and cerebral cortex.

Reflex mechanisms play an important role in regulating the digestive process. They were studied in detail by Academician I.P. Pavlov, who developed methods of chronic experimentation that made it possible to obtain the pure juice necessary for analysis at any time during the digestion process. He showed that the secretion of digestive juices is largely associated with the process of eating. The basal secretion of digestive juices is very small. For example, on an empty stomach, approximately 20 ml of gastric juice is secreted, and during digestion - 1200 - 1500 ml.

Reflex regulation of digestion is carried out using conditioned and unconditioned digestive reflexes.

Conditioned food reflexes are developed in the process of individual life and arise from the sight, smell of food, time, sounds and surroundings. Unconditioned food reflexes originate from the receptors of the oral cavity, pharynx, esophagus and the stomach itself when food arrives and play a major role in the second phase of gastric secretion.

The conditioned reflex mechanism is the only one in the regulation of salivation and is important for the initial secretion of the stomach and pancreas, triggering their activity (“ignition” juice). This mechanism is observed during phase I of gastric secretion. The intensity of juice secretion during phase I depends on appetite.

Nervous regulation of gastric secretion is carried out by the autonomic nervous system through the parasympathetic (vagus nerve) and sympathetic nerves. Through the neurons of the vagus nerve, gastric secretion is activated, and the sympathetic nerves have an inhibitory effect.

The local mechanism for regulating digestion is carried out with the help of peripheral ganglia located in the walls of the gastrointestinal tract. The local mechanism is important in the regulation of intestinal secretion. It activates the secretion of digestive juices only in response to the entry of chyme into the small intestine.

A huge role in the regulation of secretory processes in the digestive system is played by hormones, which are produced by cells located in various parts of the digestive system itself and act through the blood or through extracellular fluid on neighboring cells. Gastrin, secretin, cholecystokinin (pancreozymin), motilin, etc. act through the blood. Somatostatin, VIP (vasoactive intestinal polypeptide), substance P, endorphins, etc. act on neighboring cells.

The main place of release of hormones of the digestive system is the initial section of the small intestine. There are about 30 of them in total. The release of these hormones occurs under the action of chemical components from the food mass in the lumen of the digestive tube on the cells of the diffuse endocrine system, as well as under the action of acetylcholine, which is a mediator of the vagus nerve, and some regulatory peptides.

Main hormones of the digestive system:

1. Gastrin is formed in the accessory cells of the pyloric part of the stomach and activates the main cells of the stomach, producing pepsinogen, and the parietal cells, producing hydrochloric acid, thereby enhancing the secretion of pepsinogen and activating its conversion into the active form - pepsin. In addition, gastrin promotes the formation of histamine, which in turn also stimulates the production of hydrochloric acid.

2. Secretin is formed in the wall of the duodenum under the influence of hydrochloric acid coming from the stomach with chyme. Secretin inhibits the secretion of gastric juice, but activates the production of pancreatic juice (but not enzymes, but only water and bicarbonates) and enhances the effect of cholecystokinin on the pancreas.

3. Cholecystokinin, or pancreozymin, is released under the influence of food digestion products entering the duodenum. It increases the secretion of pancreatic enzymes and causes contractions of the gallbladder. Both secretin and cholecystokinin are capable of inhibiting gastric secretion and motility.

4. Endorphins. They inhibit the secretion of pancreatic enzymes, but increase the release of gastrin.

5. Motilin enhances the motor activity of the gastrointestinal tract.

Some hormones can be released very quickly, helping to create a feeling of fullness already at the table.

APPETITE. HUNGER. SATURATION

Hunger is a subjective feeling of food need that organizes human behavior in searching for and consuming food. The feeling of hunger manifests itself in the form of burning and pain in the epigastric region, nausea, weakness, dizziness, hungry peristalsis of the stomach and intestines. The emotional feeling of hunger is associated with the activation of limbic structures and the cerebral cortex.

The central regulation of the feeling of hunger is carried out thanks to the activity of the food center, which consists of two main parts: the hunger center and the satiety center, located in the lateral (lateral) and central nuclei of the hypothalamus, respectively.

Activation of the hunger center occurs as a result of a flow of impulses from chemoreceptors that respond to a decrease in the blood levels of glucose, amino acids, fatty acids, triglycerides, glycolytic products, or from the mechanoreceptors of the stomach, excited during its hungry peristalsis. A decrease in blood temperature can also contribute to feelings of hunger.

Activation of the saturation center can occur even before the products of nutrient hydrolysis enter the blood from the gastrointestinal tract, on the basis of which sensory saturation (primary) and metabolic (secondary) are distinguished. Sensory saturation occurs as a result of irritation of the receptors of the mouth and stomach by incoming food, as well as as a result of conditioned reflex reactions in response to the sight and smell of food. Metabolic saturation occurs much later (1.5 - 2 hours after eating), when the products of the breakdown of nutrients enter the blood.

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Appetite is a feeling of need for food, formed as a result of excitation of neurons in the cerebral cortex and limbic system. Appetite helps organize the digestive system, improves digestion and absorption of nutrients. Appetite disorders manifest themselves as decreased appetite (anorexia) or increased appetite (bulimia). Long-term conscious restriction of food consumption can lead not only to metabolic disorders, but also to pathological changes in appetite, up to a complete refusal to eat. published

The human digestive system occupies one of the honorable places in the arsenal of knowledge of a personal trainer, solely for the reason that in sports in general and in fitness in particular, almost any result depends on diet. Gaining muscle mass, losing weight, or keeping it off largely depends on what kind of “fuel” you put into your digestive system. The better the fuel, the better the result will be, but the goal now is to understand exactly how this system is structured and works and what its functions are.

The digestive system is designed to provide the body with nutrients and components and remove residual digestive products from it. Food entering the body is first crushed by the teeth in the oral cavity, then through the esophagus it enters the stomach, where it is digested, then in the small intestine, under the influence of enzymes, the digestive products break down into individual components, and in the large intestine, feces (residual digestive products) are formed. , which is ultimately subject to evacuation from the body.

The structure of the digestive system

The human digestive system includes the organs of the gastrointestinal tract, as well as auxiliary organs, such as the salivary glands, pancreas, gall bladder, liver and more. The digestive system is conventionally divided into three sections. The anterior section, which includes the organs of the oral cavity, pharynx and esophagus. This department carries out food grinding, in other words, mechanical processing. The middle section includes the stomach, small and large intestines, pancreas and liver. Here the chemical processing of food, the absorption of nutritional components and the formation of residual digestive products occur. The posterior section includes the caudal part of the rectum and removes feces from the body.

Structure of the human digestive system: 1- Oral cavity; 2- Palate; 3- Tongue; 4- Language; 5- Teeth; 6- Salivary glands; 7- Sublingual gland; 8- Submandibular gland; 9- Parotid gland; 10- Pharynx; 11- Esophagus; 12- Liver; 13- Gallbladder; 14- Common bile duct; 15- Stomach; 16- Pancreas; 17- Pancreatic duct; 18- Small intestine; 19- Duodenum; 20- Jejunum; 21- Ileum; 22- Appendix; 23- Large intestine; 24- Transverse colon; 25- Ascending colon; 26- Cecum; 27- Descending colon; 28- Sigmoid colon; 29- Rectum; 30- Anal opening.

Gastrointestinal tract

The average length of the digestive canal in an adult is approximately 9-10 meters. It contains the following sections: oral cavity (teeth, tongue, salivary glands), pharynx, esophagus, stomach, small and large intestine.

• Oral cavity- an opening through which food enters the body. On the outside it is surrounded by lips, and inside it there are teeth, tongue and salivary glands. It is inside the oral cavity that food is crushed by the teeth, moistened with saliva from the glands and pushed into the throat by the tongue.
• Pharynx– a digestive tube connecting the oral cavity and the esophagus. Its length is approximately 10-12 cm. Inside the pharynx, the respiratory and digestive tracts intersect, therefore, to prevent food from entering the lungs during swallowing, the epiglottis blocks the entrance to the larynx.
• Esophagus- an element of the digestive tract, a muscular tube through which food from the pharynx enters the stomach. Its length is approximately 25-30 cm. Its function is to actively push crushed food to the stomach, without any additional mixing or pushing.
• Stomach- a muscular organ located in the left hypochondrium. It acts as a reservoir for ingested food, produces biologically active components, digests and absorbs food. The volume of the stomach ranges from 500 ml to 1 liter, and in some cases up to 4 liters.
• Small intestine– part of the digestive tract located between the stomach and large intestine. Enzymes are produced here, which, in conjunction with enzymes of the pancreas and gall bladder, break down digestive products into individual components.
• Colon- the closing element of the digestive tract, in which water is absorbed and feces are formed. The walls of the intestine are lined with mucous membrane to facilitate the passage of residual digestive products out of the body.

Structure of the stomach: 1- Esophagus; 2- Cardiac sphincter; 3- Fundus of the stomach; 4- Body of the stomach; 5- Greater curvature; 6- Folds of the mucous membrane; 7- Pyloric sphincter; 8- Duodenum.

Auxiliary organs

The process of digesting food occurs with the participation of a number of enzymes that are contained in the juice of some large glands. In the oral cavity there are ducts of the salivary glands, which secrete saliva and moisten both the oral cavity and food with it to facilitate its passage through the esophagus. Also in the oral cavity, with the participation of salivary enzymes, the digestion of carbohydrates begins. Pancreatic juice and bile are secreted into the duodenum. Pancreatic juice contains bicarbonates and a number of enzymes such as trypsin, chymotrypsin, lipase, pancreatic amylase and more. Bile accumulates in the gallbladder before entering the intestines, and bile enzymes allow fats to be separated into small fractions, which accelerates their breakdown by the enzyme lipase.

• Salivary glands divided into small and large. Small ones are located in the oral mucosa and are classified by location (buccal, labial, lingual, molar and palatal) or by the nature of the discharge products (serous, mucous, mixed). The sizes of the glands vary from 1 to 5 mm. The most numerous among them are the labial and palatal glands. The major salivary glands are divided into three pairs: parotid, submandibular and sublingual.
• Pancreas- an organ of the digestive system that secretes pancreatic juice, which contains digestive enzymes necessary for the digestion of proteins, fats and carbohydrates. The main pancreatic substance of duct cells contains bicarbonate anions that can neutralize the acidity of residual digestive products. The islet apparatus of the pancreas also produces the hormones insulin, glucagon, and somatostatin.
• Gallbladder acts as a reservoir for bile produced by the liver. It is located on the lower surface of the liver and is anatomically part of it. The accumulated bile is released into the small intestine to ensure normal digestion. Since in the process of digestion itself, bile is not needed all the time, but only periodically, the gallbladder doses its supply with the help of bile ducts and valves.
• Liver- one of the few unpaired organs in the human body that performs many vital functions. It also participates in the digestive processes. Provides the body's needs for glucose, transforms various energy sources (free fatty acids, amino acids, glycerin, lactic acid) into glucose. The liver also plays an important role in neutralizing toxins that enter the body with food.

Structure of the liver: 1- Right lobe of the liver; 2- Hepatic vein; 3- Aperture; 4- Left lobe of the liver; 5- Hepatic artery; 6- Portal vein; 7- Common bile duct; 8- Gallbladder. I- Path of blood to the heart; II- Path of blood from the heart; III- Path of blood from the intestines; IV- The path of bile to the intestines.

Functions of the digestive system

All functions of the human digestive system are divided into 4 categories:

• Mechanical. Involves chopping and pushing food;
• Secretory. Production of enzymes, digestive juices, saliva and bile;
• Suction. Absorption of proteins, fats, carbohydrates, vitamins, minerals and water;
• Highlighting. Removing the remains of digestive products from the body.

In the oral cavity, with the help of teeth, tongue and the secretion product of the salivary glands, during chewing, primary processing of food occurs, which consists of grinding it, mixing it and moistening it with saliva. Further, during the process of swallowing, food in the form of a lump descends through the esophagus into the stomach, where it is further chemically and mechanically processed. In the stomach, food accumulates and mixes with gastric juice, which contains acid, enzymes and breakdown proteins. Next, food in the form of chyme (liquid contents of the stomach) enters in small portions into the small intestine, where its chemical processing continues with the help of bile and secretion products of the pancreas and intestinal glands. Here, in the small intestine, nutrients are absorbed into the blood. Those food components that are not absorbed move further into the large intestine, where they undergo breakdown under the influence of bacteria. In the colon, water is also absorbed, and then feces are formed from residual digestive products that have not been digested or absorbed. The latter are removed from the body through the anus during defecation.

Structure of the pancreas: 1- Accessory duct of the pancreas; 2- Main pancreatic duct; 3- Tail of the pancreas; 4- Body of the pancreas; 5- Neck of the pancreas; 6- Uncinate process; 7- Papilla of Vater; 8- Lesser papilla; 9- Common bile duct.

Conclusion

The human digestive system is of exceptional importance in fitness and bodybuilding, but of course it is not limited to them. Any intake of nutrients into the body, such as proteins, fats, carbohydrates, vitamins, minerals and more, occurs precisely through the digestive system. Achieving any muscle gain or weight loss results also depends on your digestive system. Its structure allows us to understand which way food goes, what functions the digestive organs perform, what is absorbed and what is excreted from the body, and so on. Not only your athletic performance, but, by and large, your overall health depends on the health of your digestive system.

The liver consists of two lobes: its right lobe is located in the right hypochondrium, the left - in the epigastric region, that is, under the sternum.

Liver functions

Barrier function

In lower animals (molluscs), the primary epithelial elements of the liver form, as it were, cellular cases around the small branches of the intestine, so that all substances from the intestines can enter the bloodstream only through the cells of this case. During the evolutionary development of animals, this conglomerate of liver cells is separated into a separate organ, which, however, is closely connected with the intestine through the portal vein.

Thanks to this arrangement, the liver acts as a barrier through which everything that is absorbed from the intestines passes. In this regard, the liver performs very important functions in the body.

Actually, the barrier function of the liver is that it retains and does not allow certain toxic substances that accidentally enter the body (mercury, lead, etc.) to pass into the bloodstream. Toxic substances contained in food absorbed from the gastrointestinal tract enter the liver through a vein and are neutralized by its cells.

It neutralizes toxic substances formed in the large intestines during the decay of proteins (phenol, indole). In the liver, slightly toxic and easily soluble compounds are formed from these substances, which are easily excreted from the body.

Metabolic function

The liver plays a major role in carbohydrate metabolism. It synthesizes glycogen from glucose. A large amount of glycogen can be deposited in liver cells (over 10% of the weight of the liver). The liver can also synthesize glycogen from volatile fatty acids (in ruminants), from lactic acid, and even from glycerol (for example, in hibernating animals).

The insulin-secreting function of the pancreas is of particular importance, since its disruption leads to the development of diabetes mellitus, which is widespread. In a healthy person, the blood sugar level is 80-120 mg%, and with diabetes, its level can increase to 150-250 mg% or more.

With normal blood sugar levels, it is not excreted in the urine; in other words, there is no sugar in the urine of a healthy person. When the blood sugar level increases above 140-150 mg%, it begins to be excreted in the urine. Patients experience constant thirst and drink a lot of water. Due to the fact that the carbohydrates of the food taken, without being absorbed by cells and tissues, are excreted in the urine, the patient quickly feels hungry and is forced to eat frequently. Otherwise, the fats of the subcutaneous tissue accumulated by the body in the form of reserves, and even proteins and fats in the composition of cells and tissues, undergoing decay, are converted into glucose and pass into the blood, and from there they are excreted with urine. As a result of this, the patient loses weight, has general weakness, and decreased ability to work.

The digestive glands include: salivary glands, stomach glands, liver, pancreas and intestinal glands.

The glands whose ducts open into the oral cavity include the minor and major salivary glands. Minor salivary glands: labial

(glandulae labiates), buccal ( glandulae buccales), molar ( glandulae molares), palatal ( glandulae palatinae), lingual ( glandulae linguales)- located in the thickness of the mucous membrane lining the oral cavity. The paired major salivary glands are located outside the oral cavity, but their ducts open into it. These glands include the parotid, sublingual and submandibular glands.

Parotid gland (glandula parotidea) has a conical shape. The base of the gland faces outward, and the apex enters the maxillary fossa. At the top, the gland reaches the zygomatic arch and the external auditory canal, at the back - the mastoid process of the temporal bone, and at the bottom - the angle of the lower jaw. Excretory duct ( ductus parotideus) passes below the zygomatic arch along the outer surface of the masticatory muscle, then pierces the buccal muscle and opens into the vestibule of the mouth with a hole at the level of the second upper molar.

Submandibular gland (glandula submandibularis) located in the submandibular triangle of the neck at the posterior edge of the mylohyoid muscle, a duct emerges from the gland ( ductus submandibularis), which goes around the posterior edge of this muscle, runs along the medial edge of the sublingual gland and opens on the sublingual papilla.

Sublingual gland (glandula sublingualis) located above the mylohyoid muscle, under the mucous membrane, forming a sublingual fold. Several small ducts emerge from the gland, opening into the oral cavity along the sublingual fold, and a large sublingual duct, which either merges with the duct of the submandibular gland or opens independently next to it on the sublingual papilla.

Development. The salivary glands develop from the epithelium of the oral mucosa by protruding it outward in the form of tubes with a mass of lateral branches of the same structure.

Anomalies. There are no interesting anomalies.

Liver (Ierag)- the largest gland, its weight in humans reaches 1500 g. The liver is located in the abdominal cavity, under the diaphragm, in the right hypochondrium. Its upper border along the right midclavicular line is at the level of the 4th intercostal space. Then the upper border of the liver descends to the 10th intercostal space along the right midaxillary line. On the left, the upper border of the liver gradually descends from the 5th intercostal space along the midthoracic line to the level of attachment of the 8th left costal cartilage to the 7th rib. The lower border of the liver runs along the edge of the costal arch on the right; in the epigastric region, the liver is adjacent to the posterior surface of the anterior abdominal wall. The liver is divided into a larger (right) and smaller (left) lobe and two surfaces - diaphragmatic and visceral. The gallbladder is located on the visceral surface (vesicafellea) (bile reservoir) and porta hepatis (porta hepatis), through which the portal vein, hepatic artery and nerves enter, and the common hepatic duct and lymphatic vessels exit. On the visceral surface of the right lobe there is a square (lobus quadratus) and tailed (lobus caudatus) shares. The liver is fixed to the diaphragm by the falciform ligament (lig.falciforme) and coronary ligament (lig. coronarium), which along the edges forms the right and left triangular ligaments (lig. triangulare dextrum el triangulare sinistrum). Round ligament of the liver (lig. teres hepatis) - overgrown umbilical vein, starts from the umbilicus, passes along the notch of the round ligament (incisura lig. teretis), enters the lower edge of the falciform ligament and then reaches the porta hepatis. The inferior vena cava passes on the posterior surface of the right lobe, to which the venous ligament is attached (lig. venosum) - an overgrown venous duct connecting the fetus's umbilical vein with the inferior vena cava. The liver performs a protective (barrier) function; it neutralizes toxic breakdown products of proteins and toxic substances absorbed from the intestine into the blood, formed as a result of the activity of microbes in the large intestine. Toxic substances in the liver are neutralized and excreted from the body through urine and feces. The liver participates in digestion by secreting bile. Bile is produced by liver cells constantly, and enters the duodenum through the common bile duct only when there is food in it. When digestion stops, bile, passing through the cystic duct, accumulates in the gallbladder, where, as a result of water absorption, the concentration of bile increases 7-8 times.

Gallbladder (vesica fellea) located in a fossa on the visceral surface of the liver. The bottom is highlighted in it (fundus vesicae felleae), body (corpus vesicae felleae) and cervix (collum vesicae felleae), which continues into the cystic duct (ductus cysticus), draining into the common hepatic duct, formed by the confluence of the right and left hepatic ducts (ductus hepaticus dexter et sinister). The common hepatic duct becomes the common bile duct (ductus choledochus), located between the layers of the hepatoduodenal ligament anterior to the portal vein and to the right of the common hepatic artery. The common bile duct passes behind the upper part of the duodenum and the head of the pancreas, pierces the intestinal wall, merges with the pancreatic duct and opens at the apex of the major duodenal papilla.

Development. It is a protrusion of the epithelial layer of the duodenum in the ventral direction. From the very beginning, there are two lobes, each with its own excretory duct. At first, its tubular structure is clearly expressed, later it is smoothed out.

The gallbladder and its duct are formed as a result of protrusion of the bile duct.

Anomalies. The most common is lobulation of the liver, as well as cases of movement of the gallbladder into the left groove of the liver.

Pancreas) is located in the abdominal cavity, behind the stomach at the level of the bodies of the 1st-2nd lumbar vertebrae, going to the left and up to the gate of the spleen. Its mass in an adult is 70-80 g. Its head is distinguished (caputpancreatis), body (corpus pancreatis) and tail (cauda pancreatis). The pancreas is an external and internal secretion gland. As a digestive gland, it produces pancreatic juice, which through the excretory duct (ductus pancreaticus) flows into the lumen of the descending part of the duodenum, opening at its major papilla, having previously connected with the common bile duct.

Development. It is an epithelial outgrowth from the duodenum. It develops from three primordia: the main (paired), ventral one, which remains in connection with the duodenum using the main duct, and the additional, dorsal one, connected to the duodenum by the accessory duct.

Anomalies. There are no interesting anomalies.

One of the main conditions for life is the intake of nutrients into the body, which are continuously consumed by cells in the process of metabolism. For the body, the source of these substances is food. Digestive system ensures the breakdown of nutrients into simple organic compounds(monomers), which enter the internal environment of the body and are used by cells and tissues as plastic and energy material. In addition, the digestive system ensures that the body receives the required amount of water and electrolytes.

Digestive system, or gastrointestinal tract, is a convoluted tube that begins with the mouth and ends at the anus. It also includes a number of organs that ensure the secretion of digestive juices (salivary glands, liver, pancreas).

Digestion is a set of processes during which food is processed in the gastrointestinal tract and the proteins, fats, and carbohydrates contained in it are broken down into monomers and the subsequent absorption of monomers into the internal environment of the body.

Rice. Human digestive system

The digestive system includes:

• the oral cavity with the organs located in it and the adjacent large salivary glands;
• pharynx;
• esophagus;
• stomach;
• small and large intestine;
• pancreas.

The digestive system consists of a digestive tube, the length of which in an adult reaches 7-9 m, and a number of large glands located outside its walls. The distance from the mouth to the anus (in a straight line) is only 70-90 cm. The large difference in size is due to the fact that the digestive system forms many bends and loops.

The oral cavity, pharynx and esophagus, located in the human head, neck and chest cavity, have a relatively straight direction. In the oral cavity, food enters the pharynx, where the digestive and respiratory tracts cross. Then comes the esophagus, through which food mixed with saliva enters the stomach.

In the abdominal cavity there is the final section of the esophagus, stomach, small intestine, cecum, colon, liver, pancreas, and in the pelvic area - the rectum. In the stomach, the food mass is exposed to gastric juice for several hours, liquefied, actively mixed and digested. In the swollen intestine, food continues to be digested with the participation of many enzymes, resulting in the formation of simple compounds that are absorbed into the blood and lymph. Water is absorbed in the colon and feces are formed. Undigested and unsuitable for absorption substances are removed out through the anus.

Salivary glands

The oral mucosa has numerous small and large salivary glands. The large glands include: three pairs of large salivary glands - parotid, submandibular and sublingual. The submandibular and sublingual glands secrete both mucous and watery saliva; they are mixed glands. The parotid salivary glands secrete only mucous saliva. The maximum release, for example, from lemon juice can reach 7-7.5 ml/min. The saliva of humans and most animals contains the enzymes amylase and maltase, due to which a chemical change occurs in food already in the oral cavity.

The amylase enzyme converts food starch into a disaccharide, maltose, and the latter, under the action of a second enzyme, maltase, is converted into two glucose molecules. Although salivary enzymes are highly active, complete breakdown of starch in the oral cavity does not occur, since food remains in the mouth for only 15-18 seconds. The saliva reaction is usually slightly alkaline or neutral.

Esophagus

The wall of the esophagus is three-layered. The middle layer consists of developed striated and smooth muscles, during the contraction of which food is pushed into the stomach. Contraction of the esophageal muscles creates peristaltic waves, which, arising in the upper part of the esophagus, spread along the entire length. In this case, the muscles of the upper third of the esophagus are sequentially contracted, and then the smooth muscles in the lower sections. When food passes through the esophagus and stretches it, a reflex opening of the entrance to the stomach occurs.

The stomach is located in the left hypochondrium, in the epigastric region and is an extension of the digestive tube with well-developed muscular walls. Depending on the phase of digestion, its shape may change. The length of an empty stomach is about 18-20 cm, the distance between the walls of the stomach (between the greater and lesser curvature) is 7-8 cm. A moderately filled stomach has a length of 24-26 cm, the greatest distance between the greater and lesser curvature is 10-12 cm. The capacity of the adult stomach person varies depending on the food and liquid taken from 1.5 to 4 liters. The stomach relaxes during the act of swallowing and remains relaxed throughout the meal. After eating, a state of increased tone occurs, which is necessary to begin the process of mechanical processing of food: grinding and mixing the chyme. This process is carried out due to peristaltic waves, which occur approximately 3 times per minute in the area of ​​the esophageal sphincter and propagate at a speed of 1 cm/s towards the exit into the duodenum. At the beginning of the digestion process, these waves are weak, but as digestion in the stomach ends, they increase in both intensity and frequency. As a result, a small portion of chyme is forced to exit the stomach.

The inner surface of the stomach is covered with a mucous membrane that forms a large number of folds. It contains glands that secrete gastric juice. These glands consist of main, accessory and parietal cells. The main cells produce gastric juice enzymes, the parietal cells produce hydrochloric acid, and the accessory cells produce mucoid secretions. The food is gradually saturated with gastric juice, mixed and crushed by contraction of the stomach muscles.

Gastric juice is a clear, colorless liquid that is acidic due to the presence of hydrochloric acid in the stomach. It contains enzymes (proteases) that break down proteins. The main protease is pepsin, which is secreted by cells in an inactive form - pepsinogen. Under the influence of hydrochloric acid, pepsinohep is converted into pepsin, which breaks down proteins into polypeptides of varying complexity. Other proteases have a specific effect on gelatin and milk protein.

Under the influence of lipase, fats are broken down into glycerol and fatty acids. Gastric lipase can only act on emulsified fats. Of all food products, only milk contains emulsified fat, so only it is broken down in the stomach.

In the stomach, the breakdown of starch that began in the oral cavity continues under the influence of salivary enzymes. They act in the stomach until the bolus of food is saturated with acidic gastric juice, since hydrochloric acid stops the action of these enzymes. In humans, a significant part of starch is broken down by salivary ptyalin in the stomach.

Hydrochloric acid plays an important role in gastric digestion, which activates pepsinogen to pepsin; causes swelling of protein molecules, which promotes their enzymatic breakdown, promotes the curdling of milk to casein; has a bactericidal effect.

2-2.5 liters of gastric juice are secreted per day. On an empty stomach, a small amount of it is secreted, containing mainly mucus. After eating, secretion gradually increases and remains at a relatively high level for 4-6 hours.

The composition and amount of gastric juice depend on the amount of food. The greatest amount of gastric juice is secreted for protein foods, less for carbohydrate foods, and even less for fatty foods. Normally, gastric juice has an acidic reaction (pH = 1.5-1.8), which is caused by hydrochloric acid.

Small intestine

The human small intestine starts from the pylorus of the stomach and is divided into the duodenum, jejunum and ileum. The length of the small intestine of an adult reaches 5-6 m. The shortest and widest is the 12-part intestine (25.5-30 cm), the jejunum is 2-2.5 m, the ileum is 2.5-3.5 m. Thickness The small intestine is constantly decreasing along its course. The small intestine forms loops, which are covered in front by the greater omentum, and are limited from above and from the sides by the large intestine. In the small intestine, chemical processing of food and absorption of the products of its breakdown continue. Mechanical mixing occurs and food moves towards the colon.

The wall of the small intestine has a structure typical of the gastrointestinal tract: mucous membrane, submucosal layer, which contains accumulations of lymphoid tissue, glands, nerves, blood and lymphatic vessels, muscular layer, and serous membrane.

The muscular coat consists of two layers - the inner circular and the outer - longitudinal, separated by a layer of loose connective tissue in which nerve plexuses, blood and lymphatic vessels are located. Due to these muscle layers, the intestinal contents are mixed and moved towards the outlet.

A smooth, moist serous membrane facilitates the sliding of the viscera relative to each other.

The glands perform a secretory function. As a result of complex synthetic processes, they produce mucus that protects the mucous membrane from injury and the action of secreted enzymes, as well as various biologically active substances and, first of all, enzymes necessary for digestion.

The mucous membrane of the small intestine forms numerous circular folds, thereby increasing the absorption surface of the mucous membrane. The size and number of folds decreases towards the colon. The surface of the mucous membrane is dotted with intestinal villi and crypts (depressions). Villi (4-5 million) 0.5-1.5 mm long carry out parietal digestion and absorption. Villi are outgrowths of the mucous membrane.

In ensuring the initial stage of digestion, a large role belongs to the processes occurring in the duodenum. On an empty stomach, its contents have a slightly alkaline reaction (pH = 7.2-8.0). When portions of the acidic contents of the stomach pass into the intestine, the reaction of the contents of the duodenum becomes acidic, but then due to the alkaline secretions of the pancreas, small intestine and bile entering the intestine it becomes neutral. In a neutral environment, gastric enzymes stop acting.

In humans, the pH of the contents of the duodenum ranges from 4-8.5. The higher its acidity, the more pancreatic juice, bile and intestinal secretions are released, the evacuation of stomach contents into the duodenum and its contents into the jejunum slows down. As it moves through the duodenum, the food contents are mixed with secretions entering the intestine, the enzymes of which already in the duodenum hydrolyze nutrients.

Pancreatic juice does not enter the duodenum constantly, but only during meals and for some time after that. The amount of juice, its enzymatic composition and the duration of release depend on the quality of the food received. The largest amount of pancreatic juice is secreted into meat, the least into fat. 1.5-2.5 liters of juice are released per day at an average rate of 4.7 ml/min.

The gallbladder duct opens into the lumen of the duodenum. Bile is released 5-10 minutes after eating. Under the influence of bile, all intestinal juice enzymes are activated. Bile enhances intestinal motility, promoting the mixing and movement of food. In the duodenum, 53-63% of carbohydrates and proteins are digested, fats are digested in smaller quantities. In the next section of the digestive tract - the small intestine - further digestion continues, but to a lesser extent than in the duodenum. Basically, the absorption process takes place here. The final breakdown of nutrients occurs on the surface of the small intestine, i.e. on the same surface where suction occurs. This breakdown of nutrients is called parietal or contact digestion, in contrast to cavity digestion, which occurs in the cavity of the digestive canal.

In the small intestine, the most intense absorption occurs 1-2 hours after eating. The absorption of monosaccharides, alcohol, water and mineral salts occurs not only in the small intestine, but also in the stomach, although to a much lesser extent than in the small intestine.

Colon

The large intestine is the final part of the human digestive tract and consists of several sections. Its beginning is considered to be the cecum, at the border of which with the ascending section the small intestine flows into the large intestine.

The large intestine is divided into the cecum with appendix, ascending colon, transverse colon, descending colon, sigmoid colon and rectum. Its length ranges from 1.5-2 m, its width reaches 7 cm, then the large intestine gradually decreases to 4 cm at the descending colon.

The contents of the small intestine pass into the large intestine through a narrow slit-like opening located almost horizontally. At the point where the small intestine flows into the large intestine there is a complex anatomical device - a valve equipped with a muscular circular sphincter and two “lips”. This valve, which closes the hole, has the shape of a funnel, with its narrow part facing the lumen of the cecum. The valve opens periodically, allowing contents to pass in small portions into the colon. When the pressure in the cecum increases (during mixing and moving food), the “lips” of the valve close, and access from the small intestine to the large intestine is stopped. Thus, the valve prevents the contents of the large intestine from flowing back into the small intestine. The length and width of the cecum are approximately equal (7-8 cm). A vermiform appendix (appendix) extends from the lower wall of the cecum. Its lymphoid tissue is the structure of the immune system. The cecum directly passes into the ascending colon, then the transverse colon, descending colon, sigmoid colon and rectum, which ends in the anus (anus). The length of the rectum is 14.5-18.7 cm. In front, the rectum with its wall is adjacent in men to the seminal vesicles, vas deferens and the section of the bottom of the bladder lying between them, even lower - to the prostate gland; in women, the rectum borders in front with the posterior wall of the vagina along its entire length.

The entire process of digestion in an adult lasts 1-3 days, of which the longest time is spent on food residues remaining in the large intestine. Its motility provides a reservoir function - accumulation of contents, absorption of a number of substances from it, mainly water, its promotion, formation of feces and their removal (defecation).

In a healthy person, the food mass begins to enter the large intestine 3-3.5 hours after ingestion, which fills within 24 hours and is completely emptied within 48-72 hours.

In the large intestine, glucose, vitamins, amino acids produced by bacteria in the intestinal cavity, up to 95% of water and electrolytes are absorbed.

The contents of the cecum undergo small and long movements, first in one direction or the other, due to slow contractions of the intestine. The colon is characterized by contractions of several types: small and large pendular, peristaltic and antiperistaltic, propulsive. The first four types of contractions ensure mixing of the intestinal contents and increasing pressure in its cavity, which helps thicken the contents by absorbing water. Strong propulsive contractions occur 3-4 times a day and push intestinal contents towards the sigmoid colon. Wave-like contractions of the sigmoid colon mix feces into the rectum, the distension of which causes nerve impulses that are transmitted along the nerves to the center of defecation in the spinal cord. From there, impulses are sent to the anal sphincter. The sphincter relaxes and contracts voluntarily. The defecation center in children of the first years of life is not controlled by the cerebral cortex.

Microflora in the digestive tract and its function

The large intestine is richly populated by microflora. The macroorganism and its microflora constitute a single dynamic system. The dynamism of the endoecological microbial biocenosis of the digestive tract is determined by the number of microorganisms entering it (about 1 billion microbes are ingested orally per day in humans), the intensity of their reproduction and death in the digestive tract and the removal of microbes from it in feces (a person normally excretes 10 per day per day). 12 -10 14 microorganisms).

Each section of the digestive tract has a characteristic number and set of microorganisms. Their number in the oral cavity, despite the bactericidal properties of saliva, is large (I0 7 -10 8 per 1 ml of oral fluid). The contents of the stomach of a healthy person on an empty stomach are often sterile due to the bactericidal properties of pancreatic juice. The contents of the colon contain the maximum number of bacteria, and 1 g of feces of a healthy person contains 10 billion or more microorganisms.

The composition and number of microorganisms in the digestive tract depends on endogenous and exogenous factors. The first includes the influence of the mucous membrane of the digestive canal, its secretions, motility and the microorganisms themselves. The second includes the nature of nutrition, environmental factors, and the use of antibacterial drugs. Exogenous factors influence directly and indirectly through endogenous factors. For example, the intake of this or that food changes the secretory and motor activity of the digestive tract, which shapes its microflora.

Normal microflora - eubiosis - performs a number of important functions for the macroorganism. Its participation in the formation of the body’s immunobiological reactivity is extremely important. Eubiosis protects macroorganism from the introduction and reproduction of pathogenic microorganisms in it. Disturbance of the normal microflora during illness or as a result of long-term administration of antibacterial drugs often entails complications caused by the rapid proliferation of yeast, staphylococcus, Proteus and other microorganisms in the intestines.

Intestinal microflora synthesizes vitamins K and group B, which partially cover the body's need for them. Microflora also synthesizes other substances important for the body.

Bacterial enzymes break down cellulose, hemicellulose and pectins undigested in the small intestine, and the resulting products are absorbed from the intestine and included in the body's metabolism.

Thus, the normal intestinal microflora not only participates in the final link of digestive processes and has a protective function, but also produces a number of important vitamins, amino acids, enzymes, hormones and other nutrients.

Some authors distinguish heat-generating, energy-generating and stimulating functions of the large intestine. In particular, G.P. Malakhov notes that microorganisms living in the large intestine, during their development, release energy in the form of heat, which warms the venous blood and adjacent internal organs. And according to various sources, from 10-20 billion to 17 trillion microbes are formed in the intestines during the day.

Like all living things, microbes have a glow around them - bioplasm, which charges the water and electrolytes absorbed in the large intestine. It is known that electrolytes are one of the best batteries and energy carriers. These energy-rich electrolytes, together with the blood and lymph flow, are carried throughout the body and give their high energy potential to all cells of the body.

Our body has special systems that are stimulated by various environmental influences. Through mechanical stimulation of the sole of the foot, all vital organs are stimulated; through sound vibrations, special zones on the auricle are stimulated, connected with the entire body, light stimulation through the iris of the eye also stimulates the entire body and diagnostics are carried out using the iris, and on the skin there are certain areas that are connected with internal organs, the so-called Zakharyin zones. Geza.

The large intestine has a special system through which it stimulates the entire body. Each section of the large intestine stimulates a different organ. When the intestinal diverticulum is filled with food gruel, microorganisms begin to rapidly multiply in it, releasing energy in the form of bioplasma, which has a stimulating effect on this area, and through it on the organ associated with this area. If this area is clogged with fecal stones, then there is no stimulation, and the function of this organ begins to slowly fade, then the development of a specific pathology. Especially often, fecal deposits form in the folds of the large intestine, where the movement of feces slows down (the place of transition of the small intestine to the large intestine, the ascending bend, the descending bend, the bend of the sigmoid colon). The junction of the small intestine and the large intestine stimulates the nasopharyngeal mucosa; ascending bend - thyroid gland, liver, kidneys, gall bladder; descending - bronchi, spleen, pancreas, flexures of the sigmoid colon - ovaries, bladder, genitals.