Gastric juice: composition, enzymes, acidity. Digestive system: how everything works What does gastric juice look like

They differ in variety, however, the function of absorption of the liquid and the components dissolved in it is especially distinguished. The glands of the small intestine are active participants in this process.

The small intestine immediately follows the stomach. The organ is quite long, the dimensions vary from 2 to 4.5 meters.

Functionally speaking, the small intestine is central to the digestive process. It is here that the final breakdown of all nutritional components occurs.

Not the last role is played by other participants - intestinal juice, bile, pancreatic juice.

The inner wall of the intestine is protected by a mucous membrane and is equipped with countless microvilli, due to the functioning of which the suction surface increases by 30 times.

Between the villi, along the entire inner surface of the small intestine, there are the mouths of many glands through which the secretion of intestinal juice occurs. In the small intestine cavity, acidic chyme and alkaline secretions of the pancreas, intestinal glands and liver are mixed. Read more about the role of villi in digestion.

intestinal juice

The formation of this substance is nothing but the result of the work of the Brunner and Lieberkühn glands. Not the last role in such a process is assigned to the entire mucous membrane of the small intestine. The juice is a cloudy, viscous liquid.

If the salivary, gastric and pancreatic glands retain their integrity during the secretion of digestive juice, then dead cells of the glands will be needed to form intestinal juice.

Food is able to activate the secretion of both the pancreas and other intestinal glands already at the stage of entry into the oral cavity and pharynx.

The role of bile in the process of digestion

The bile entering the duodenum takes care of creating the necessary conditions in order to activate the enzyme base of the pancreas (primarily liposes). The role of acids produced by bile is to emulsify fats, reduce the surface tension of fat droplets. This creates the necessary conditions for the formation of fine particles, the absorption of which can occur without prior hydrolysis. In addition, the contact of fats and lipolytic enzymes increases. The importance of bile in the digestive process is difficult to overestimate.

Thanks to bile in this intestinal section, the absorption of higher fatty acids that do not dissolve in water, cholesterol, calcium salts and fat-soluble vitamins - D, E, K, A is carried out.
In addition, bile acids act as enhancers of hydrolysis and absorption of proteins and carbohydrates.
Bile is an excellent stimulator of intestinal microvilli function. The result of this effect is an increase in the rate of absorption of substances in the intestinal section.
Takes an active part in membrane digestion. This is done by creating comfortable conditions for the fixation of enzymes on the surface of the small intestine.
The role of bile is the function of an important stimulant of the secretion of the pancreas, juice of the small intestine, gastric mucus. Together with enzymes, it participates in small intestine digestion.
Bile does not allow the processes of decay to develop, its bacteriostatic effect on the microflora of the small intestine is noted.

In one day, about 0.7-1.0 liters of this substance is formed in the human body. The composition of bile is rich in bilirubin, cholesterol, inorganic salts, fatty acids and neutral fats, lecithin.

Secrets of the glands of the small intestine and their importance in the digestion of food

The volume of intestinal juice formed in a person in 24 hours reaches 2.5 liters. This product is the result of the active work of the cells of the entire small intestine. At the basis of the formation of intestinal juice, the death of gland cells is noted. Simultaneously with death and rejection, their constant formation takes place.

In the process of digestion of food by the small intestine, three links can be distinguished.

Abdominal digestion.

At this stage, there is an effect on food that has been pre-treated with enzymes in the stomach. Digestion occurs due to secrets and their enzymes entering the small intestine. Digestion is possible due to the participation of pancreatic secretion, bile, intestinal juice.

Membrane digestion (parietal).

At this stage of digestion, enzymes of different origin are active. Some of them come from the small intestine cavity, some are located on the membranes of the microvilli. There is an intermediate and final stage of splitting of substances.

Absorption of end products of cleavage.

In cases of abdominal and parietal digestion, one cannot do without the direct intervention of pancreatic enzymes and intestinal juice. Be sure to have bile. Pancreatic juice enters the duodenum through special tubules. Features of its composition are determined by the volume and quality of food.

The small intestine plays an important role in the process of digestion. In this department, nutrients continue to be processed into soluble compounds.

Anton Palaznikov

Gastroenterologist, therapist

Work experience more than 7 years.

Professional skills: diagnosis and treatment of diseases of the gastrointestinal tract and biliary system.

The mucosa of the small intestine contains Lieberkün's glands, which produce intestinal digestive juice.

intestinal juice- a colorless liquid, which, when settling, is divided into two layers: the lower one, containing mucous lumps, and the upper one, a liquid transparent layer. Mucous lumps consist of the secret of goblet glands and desquamated epithelial cells, on which up to 70-80% of enzymes are adsorbed. Intestinal juice has proteolytic, lipolytic and amylolytic activity.

Enteropeptidase (enterokinase) is produced in the initial part of the small intestine. It hydrolyzes trypsinogen and procarboxypeptidase, converting them into active enzymes. Its action on other proteins is limited due to its high specificity.

Aminopeptidase, aminotpripeptidase and other intestinal peptidases cleave mainly peptides formed as a result of the action of pepsin and trypsin. Peptidases break down peptides into free amino acids.

Intestinal juice does not hydrolyze native proteins, with the exception of casein. Alkaline phosphatase is involved in the cleavage of phosphatides from various compounds and the phosphorylation of carbohydrates, amino acids and lipids, ensuring their transport through cell membranes. Alkaline phosphatase is present in almost all tissues of the body, but in the epithelial cells of the villi of the small intestine it is 30-40 times more than in the liver or pancreas.

The intestinal juice contains all the enzymes that act on carbohydrates. But the activity of enzymes that break down disaccharides is especially high: glucosidase, fructofuronidase, galactosidase.

Intestinal lipase breaks down fats, but its content in intestinal juice is negligible. Phospholipase acts on ester bonds in phospholipids, splitting them into fatty acids, glycerol and phosphates. In contrast to the enzymes of gastric or pancreatic juice, intestinal juice enzymes act on the products of intermediate hydrolysis of nutrients. Thus, intestinal juice peptidases do not act on native proteins or high-molecular products of their decomposition, but decompose peptides of low molecular weight to individual amino acids.

The main stimulating factor in the regulation of the formation and secretion of intestinal juice is the food slurry itself - chyme. Probably, the neuro-reflex regulation of the secretion of intestinal juice is carried out due to the nerve plexuses (Meissner and Auerbach) located in the intestinal wall. Sympathetic and parasympathetic regulation is carried out through the celiac and vagus nerves. Humoral regulation of juice secretion in the small intestine is carried out by excitatory (vasoactive intestinal polypeptide, enterokinin, cholecystokinin, gastrin) and inhibitory (gastric inhibitory polypeptide, secretin) hormones.

Gastric juice is a solution containing several digestive enzymes, hydrochloric acid solution and mucus. It is produced by the inner walls of the stomach, penetrated by many glands. The work of their constituent cells is aimed at maintaining a certain level of secretion, creating an acidic environment that facilitates the breakdown of nutrients. It is very important that all the "details" of this mechanism work smoothly.

What is gastric juice?

The secret of the glands located in the gastric mucosa is a clear, colorless, odorless liquid, with flakes of mucus. The value of its acidity characterizes the hydrogen index (pH). Measurements show that the pH in the presence of food is 1.6-2, i.e. the liquid in the stomach is highly acidic. The lack of nutrients leads to alkalization of the contents due to bicarbonates to pH = 8 (the maximum possible indicator). A number of diseases of the stomach is accompanied by an increase in acidity to values of 1-0.9.

The digestive juice secreted by the glands is complex in composition. The most important components - hydrochloric acid, gastric juice enzymes and mucus - are produced by different cells of the inner lining of the organ. In addition to the compounds listed above, the liquid contains the hormone gastrin, other molecules of organic compounds, and minerals. The stomach of an adult produces an average of 2 liters of digestive juice.

What is the role of pepsin and lipase?

Enzymes of gastric juice act as surface-active catalysts for chemical reactions. With the participation of these compounds, complex reactions occur, as a result of which macromolecules of nutrients break down. Pepsin is an enzyme that hydrolyzes proteins into oligopeptides. Another proteolytic enzyme in gastric juice is gastrixin. It has been proven that there are different forms of pepsin that "adjust" to the structural features of different protein macromolecules.

Albumins and globulins are well digested by gastric juice, connective tissue proteins are less hydrolyzed. The composition of gastric juice is not too saturated with lipases. A small amount of an enzyme that breaks down milk fats is produced by the pyloric glands. Products of lipid hydrolysis, the two main constituents of their macromolecules are glycerol and fatty acids.

hydrochloric acid in the stomach

In the parietal cell elements of the fundic glands, gastric acid is produced - hydrochloric acid (HCl). The concentration of this substance is 160 millimoles per liter.

The role of HCl in digestion:

Liquefies the substances that form the food lump, prepares for hydrolysis.
Creates an acidic environment in which the enzymes of the gastric juice are more active.
Acts as an antiseptic, disinfects gastric juice.
Activates hormones and pancreatic enzymes.
Maintains the required pH.

Acidity of gastric juice

In solutions of hydrochloric acid, there are not molecules of a substance, but H + and Cl - ions. The acidic properties of any compound are due to the presence of hydrogen protons, while the alkaline properties are due to the presence of hydroxyl groups. Usually, the concentration of H + ions in gastric juice reaches about 0.4-0.5%.

Acidity is a very important characteristic of gastric juice. The rate of its release and properties are different, which was proved 125 years ago in the experiments of the Russian physiologist I.P. Pavlov. The secretion of juice by the stomach occurs in connection with food intake, at the sight of products, their smells, and the mention of dishes.

An unpleasant taste can slow down and completely stop the release of digestive fluid. The acidity of gastric juice rises or falls in certain diseases of the stomach, gallbladder and liver. This indicator is also influenced by human experiences, nervous shocks. A decrease and increase in the secretory activity of the stomach may be accompanied by pain in the upper abdomen.

The role of mucous substances

Mucus is produced by additional superficial cells of the walls of the stomach.
The role of this component of the digestive juice is to neutralize the acidic contents, protect the shell of the digestive organ from the damaging effects of pepsin and hydrogen ions from the composition of hydrochloric acid. The mucous substance makes the gastric juice more viscous, it better envelops the food lump. Other properties of slime:

contains bicarbonates, giving an alkaline reaction;
envelops the mucous wall of the stomach;
has digestive properties;
regulates acidity.

Neutralization of sour taste and caustic properties of gastric contents

The composition of gastric juice includes bicarbonate anions HCO 3 -. They are secreted as a result of the work of the surface cells of the digestive glands. Neutralization of acidic content occurs according to the equation: H + + HCO 3 - \u003d CO 2 + H 2 O.

Bicarbonates bind hydrogen ions at the surface of the gastric mucosa, as well as at the walls of the duodenum. The concentration of HCO 3 - in the gastric contents is maintained at 45 millimoles per liter.

"Internal factor"

A special role in the metabolism of vitamin B 12 belongs to one of the components of gastric juice - the Castle factor. This enzyme activates cobalamins in food, which is necessary for absorption by the walls of the small intestine. The blood is saturated with cyanocobalamin and other forms of vitamin B 12, transports biologically active substances to the bone marrow, where red blood cells are formed.

Features of digestion in the stomach

The breakdown of nutrients begins even in the oral cavity, where, under the action of amylase and maltase, polysaccharide molecules, in particular starch, break down into dextrins. Then the food bolus passes through the esophagus and enters the stomach. The digestive juice secreted by its walls contributes to the digestion of about 35-40% of carbohydrates. The action of saliva enzymes, active in an alkaline environment, is terminated due to the acidic reaction of the contents. If this well-established mechanism is violated, conditions and diseases arise, many of which are accompanied by a feeling of heaviness and pain in the stomach, belching, and heartburn.

Digestion is the destruction of macromolecules of carbohydrates, proteins and lipids (hydrolysis). The change in nutrients in the stomach takes about 5 hours. The mechanical processing of food started in the oral cavity, its liquefaction by gastric juice continues. Proteins undergo denaturation, which facilitates further digestion.

Strengthening the secretory function of the stomach

Increased gastric juice can inactivate some enzymes, because any system, the process goes only under certain conditions. Hypersecretion is accompanied by both increased sap secretion and increased acidity. These phenomena are provoked by spicy seasonings, certain foods, and alcoholic beverages. Prolonged nervous strain, strong emotions also provoke irritable stomach syndrome. Secretion increases in many diseases of the digestive system, in particular in patients with gastritis and peptic ulcer.

The most common symptoms of high stomach acid are heartburn and vomiting. Normalization of the secretory function occurs when dieting, taking special drugs (Almagel, Ranitidine, Gistak and other drugs). Less common is reduced production of digestive juice, which may be associated with hypovitaminosis, infections, and lesions of the stomach walls.

Ecology of life. Health: The vital activity of the human body is impossible without a constant exchange of substances with the external environment. Food contains vital nutrients used by the body as a plastic material and energy. Water, mineral salts, vitamins are absorbed by the body in the form in which they are found in food.

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

Water, mineral salts, 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 prior splitting to simpler compounds.

The digestive system provides food intake, its mechanical and chemical processing., the promotion 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 residues from the body in the form of feces.

Digestion is a set of processes that provide mechanical grinding of food and chemical breakdown of nutrient macromolecules (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 opening, includes the oral cavity, esophagus, stomach, small and large intestines, which ends with the anus.

The main role in the chemical processing of food belongs to enzymes.(enzymes), which, despite their great 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 (gastric pepsin, trypsin, duodenal chymotrypsin, etc.); lipases, or lipolytic enzymes, break down fats to glycerol and fatty acids (lipases of the small intestine, etc.); amylases, or glycolytic enzymes, break down carbohydrates into monosaccharides (saliva maltase, amylase, maltase, and pancreatic lactase).

Digestive enzymes are active only at a certain pH value. For example, stomach pepsin only works 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 a violation of the digestive processes.

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

Main functions of the digestive system:

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

2. Motor-evacuation, or motor, - provides grinding and promotion of food masses.

3. Suction- the transfer of all end 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. Endocrine- 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 the lymphoid tissue of the appendix, which contains T- and B-lymphocytes.

DIGESTION IN THE MOUTH. FUNCTIONS OF THE SALIVARY GLANDS

In the mouth, the taste properties of food are analyzed, the digestive tract is protected from poor-quality nutrients and exogenous microorganisms (saliva contains lysozyme, which has a bactericidal effect, and endonuclease, which has an antiviral effect), grinding, wetting food with saliva, initial hydrolysis of carbohydrates, formation of a food lump, 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, 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 is formed, the pH of which is 5.25 - 7.4.

Important components of saliva are proteins that have bactericidal properties.(lysozyme, which destroys the bacterial cell wall, as well as immunoglobulins and lactoferrin, which binds iron ions and prevents them from being captured 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 with food, which is an unconditioned stimulus, as well as at the sight, smell of food and the environment (conditioned stimuli). Signals from the taste, thermo- and mechanoreceptors of the oral cavity are transmitted to the center of salivation of the medulla oblongata, where the signals are switched to secretory neurons, the totality of which is located in 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 of the salivary gland is activated, a larger volume of liquid saliva is released, when the sympathetic nerve is activated, the volume of saliva is less, but it contains more enzymes.

Chewing consists in grinding food, wetting it with saliva and forming a food bolus.. In the process of chewing, the taste of food is assessed. Further, with the help of 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. Dense food passes through the esophagus in 3-9 seconds, liquid food in 1-2 seconds.

DIGESTION IN THE STOMACH

Food is retained in the stomach for an average of 4-6 hours for chemical and mechanical processing. In the stomach, 4 parts are distinguished: the entrance, or cardial part, the upper one is the bottom (or arch), the middle largest part is the body of the stomach and the lower one is the antral part, ending with the pyloric sphincter, or pylorus (the pylorus opening leads to the duodenum).

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

In the mucous membrane of the stomach are numerous glands that produce gastric juice. From the stomach, semi-digested food gruel (chyme) enters the intestines. At the site of the transition of the stomach into the intestines, there is a pyloric sphincter, which, when reduced, completely separates the stomach cavity from the duodenum.

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

Functions of the stomach:

depositing food;
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 into the cavity of the stomach along with gastric juice of some metabolites;
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).

Composition and properties of gastric juice

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

the main ones that 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 by a person during normal nutrition is 1.5 - 2.5 liters per day. The pH of active gastric juice is 0.8 - 1.5, since it contains approximately 0.5% HCl.

The role of HCl. It increases the secretion of pepsinogens by the chief 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 contributes to the death of microbes.

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

Phases of gastric secretion:

1. Complex reflex, or cerebral, lasting 1.5 - 2 hours, in which the secretion of gastric juice occurs under the influence of all the factors that accompany food intake. At the same time, conditioned reflexes arising from the sight, smell of food, and the environment are combined with unconditioned reflexes that occur during chewing and swallowing. Juice released under the influence of the type and smell of food, chewing and swallowing is called "appetizing" or "fire". It prepares the stomach for food intake.

2. Gastric, or neurohumoral, the phase in which secretion stimuli occur in the stomach itself: secretion is enhanced by stretching the stomach (mechanical stimulation) and by the action of extractives of food and protein hydrolysis products on its mucosa (chemical stimulation). The main hormone in the activation of 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 joins 40-50 minutes after the onset of the cerebral phase. In addition to the activating effect of the hormones gastrin and histamine, the activation of gastric juice secretion occurs under the influence of chemical components - extractive substances of the food itself, primarily meat, fish, and vegetables. When cooking food, they turn into decoctions, broths, are quickly absorbed into the bloodstream and activate the activity of the digestive system.

These substances primarily include free amino acids, vitamins, biostimulants, 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, cabbage juice are not recommended.

Most strongly gastric secretion increases under the influence of protein food and can last up to 6-8 hours, it changes least of all under the influence of bread (no more than 1 hour). With a long stay of a person on a carbohydrate diet, the acidity and digestive power of gastric juice decrease.

3. Intestinal phase. In the intestinal phase, inhibition of the secretion of gastric juice occurs. It develops when the chyme passes from the stomach to the duodenum. When an acidic food bolus enters the duodenum, hormones begin to be produced that quench gastric secretion - secretin, cholecystokinin and others. 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. In the small intestine, digestion products are absorbed. 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 suction surface of the intestine.

Arterioles and a lymphatic capillary (milky sinus) enter each villus, and venules exit. In the villus, arterioles divide into capillaries, which merge to form venules. Arterioles, capillaries and venules in the villus are located around the lactiferous sinus. Intestinal glands are located in the thickness of the mucous membrane and produce intestinal juice. The mucous membrane of the small intestine contains numerous single and group lymphatic nodules 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 nutrients are broken down to final products that are absorbed into the blood, as well as the food mass moves towards the large intestine and the release of metabolites.

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

The activity of these enzymes is very dependent on the temperature and pH of the medium., 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 excreted secret depend on the diet and diet.

In the small intestine, cavity digestion occurs, as well as digestion in the zone 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 the 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 glycoprotein filaments.

They, together with mucus, are able to adsorb the digestive enzymes of the pancreatic juice 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 intestine. Absorption is the physiological process of transferring substances from the lumen of the alimentary canal into the blood and lymph. The total amount of fluid absorbed daily in the digestive system is 8-9 liters (approximately 1.5 liters from food, the rest is the fluid secreted by the glands of the digestive system).

Some water, glucose, and some drugs are absorbed in the mouth. 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 villus 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.

Regulation of contractions is carried out mainly by local reflex mechanisms involving 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"). With excitation of the parasympathetic fibers of the vagus nerve, intestinal motility increases, with excitation of the sympathetic nerves, it is inhibited.

THE ROLE OF THE LIVER AND PANCREAS IN DIGESTION

The liver is involved in digestion by secreting bile. Bile is produced by the 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 absorption of water, the concentration of bile increases by 7-8 times.

The bile secreted into the duodenum does not contain enzymes, but only participates in the emulsification of fats (for a 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 products of the breakdown of hemoglobin, give bile a golden yellow color. Bile is secreted into the duodenum 3-12 minutes after the start of the meal.

Functions of bile:

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

Increase the secretion of bile yolks, milk, meat, bread. Cholecystokinin stimulates contractions of the gallbladder and secretion of bile into the duodenum.

Glycogen is constantly synthesized and consumed in the liver A polysaccharide 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 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 department (cells of the islets of Langerhans) releases 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 enters the duodenum synchronously with the release of bile through special excretory ducts, since they have a common sphincter with the gallbladder duct .

1.5 - 2.0 liters of pancreatic juice is 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 cleavage enzymes are inactive. Trypsinogen activation occurs only in the duodenal cavity, and active trypsin, in addition to protein hydrolysis, causes the activation of other pancreatic juice enzymes. 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 caecum, colon and rectum. From the lower wall of the caecum, a appendix (appendix) departs, in the walls of which there are many lymphoid cells, due to which it plays an important role in immune reactions.

In the large intestine, the final absorption of the necessary nutrients, the release of metabolites and salts of heavy metals, the accumulation of dehydrated intestinal contents and its removal from the body take place. 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).

Large intestine contractions occur mainly in the form of slow pendulum and peristaltic movements, which ensures maximum absorption of water and other components into the blood. Motility (peristalsis) of the colon increases during eating, the passage of food through the esophagus, stomach, duodenum.

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

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

In addition, normal intestinal bacteria act as antagonists in relation to 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 the 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 decay processes.

REGULATION OF THE ACTIVITY OF THE DIGESTIVE ORGANS

The regulation of the activity of the gastrointestinal tract is carried out with the help of central and local nervous, as well as hormonal influences. Central nervous influences are most characteristic of the salivary glands, to a lesser extent of 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 the contractions of the walls of the gastrointestinal tract and the secretion of digestive juices, and also regulates eating behavior in general terms. Purposeful eating behavior is formed with the participation of the hypothalamus, the limbic system and the cerebral cortex.

Reflex mechanisms play an important role in the regulation of the digestive process. They were studied in detail by academician I.P. Pavlov, having developed methods of a chronic experiment, which make it possible to obtain the pure juice necessary for analysis at any moment of 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, about 20 ml of gastric juice is released on an empty stomach, and 1200-1500 ml is released during digestion.

Reflex regulation of digestion is carried out with the help of conditioned and unconditioned digestive reflexes.

Conditioned food reflexes are developed in the process of individual life and arise at the sight, smell of food, time, sounds and environment. Unconditioned food reflexes originate from the receptors of the oral cavity, pharynx, esophagus and the stomach itself when food enters 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.

The 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 of regulation of 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 that are produced by cells located in various parts of the digestive system itself and act through the blood or through the 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 site of secretion of the 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 when chemical components from the food mass in the lumen of the digestive tube act on the cells of the diffuse endocrine system, as well as under the action of acetylcholine, which is a vagus nerve mediator, and some regulatory peptides.

The main hormones of the digestive system:

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

2. Secretin formed in the wall of the duodenum under the action 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 inhibit 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 satiety already at the table.

APPETITE. HUNGER. SATURATION

Hunger is a subjective sensation of food need, which organizes human behavior in the search for and consumption of 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 sensation 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 due to the activity of the food center, which consists of two main parts: the center of hunger and the center of saturation, located in the lateral (lateral) and central nuclei of the hypothalamus, respectively.

The activation of the hunger center occurs as a result of the flow of impulses from chemoreceptors that respond to a decrease in the content of glucose, amino acids, fatty acids, triglycerides, glycolysis products in the blood, or from mechanoreceptors of the stomach that are excited during its hungry peristalsis. A decrease in blood temperature can also contribute to the feeling of hunger.

The activation of the saturation center can occur even before the products of hydrolysis of nutrients 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 with incoming food, as well as as a result of conditioned reflex reactions in response to the appearance and smell of food. Metabolic saturation occurs much later (1.5 - 2 hours after a meal), when the breakdown products of nutrients enter the bloodstream.

This will be of interest to you:

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

Gastric juice is a digestive juice, which contains a variety of components. It is produced by cells belonging to the gastric mucosa and is, in its pure form, a colorless liquid. What exactly is in the composition of human gastric juice?

Hydrochloric acid

Perhaps the main component that is part of the gastric juice is hydrochloric acid. It is its production that the parietal cells of the fundic glands of the stomach are engaged in. Due to hydrochloric acid, it is possible to maintain a certain limit in relation to the degree of acidity in the stomach. In addition, the presented component creates obstacles for the penetration of pathogenic bacteria into the body, and also prepares food for effective hydrolysis.

It should be noted that the specified component in the composition of gastric juice is characterized by a constant and unchanged concentration, namely 160 mmol per liter. Specialists pay attention to some features associated with this substance: as you know, the digestive process begins in the mouth, and saliva enzymes (maltase, amylase) are involved in the process of splitting polysaccharides. Thus, the food bolus penetrates into the stomach area, where at least 30-40% of carbohydrates are digested with the help of a specific juice.

In addition, under the influence of hydrochloric acid, which is part of the gastric juice, the alkaline environment is transformed into an acidic one, and salivary enzymes are activated.

Of course, without the presented component, the optimal functioning of the gastrointestinal tract is simply impossible.

About what other components of this composition, further.

bicarbonate and mucus

Bicarbonates are a specific component that is needed in the stomach area in order to neutralize hydrochloric acid, which occurs in the surface membrane of the stomach of the mucous type, duodenum 12. It is due to this effect that the mucosa is protected from the harmful effects of acid. Bicarbonates are produced by cells that are part of the superficial accessory group of cells. Their concentration in human gastric juice is 45 mmol per liter.

Next, I would like to draw attention to such an important component as mucus. This is because it allows for ideal protection of the gastric mucosa. Specialists pay attention to the following features associated with the presented component:

it forms a gel layer that is immiscible and its thickness is not more than 0.6 mm;
the gel concentrates bicarbonates, which neutralize, as noted earlier, the acid. This forms the protection of the mucous membrane from the damaging effects of hydrochloric acid, as well as pepsin;
mucus is produced by accessory cells, which, moreover, are superficial. This creates another small protective layer.

Thus, bicarbonates and mucus, each of these components is part of the gastric juice. However, their functioning would be incomplete without hydrochloric acid, as well as some other components that will be presented below.

Other components

The next component of the composition in humans are pepsins. This is also a unique component, because it is with its help that the most rapid and efficient breakdown of proteins is carried out. Modern medicine is aware of several forms of pepsin, each of which, in turn, affects certain categories of the protein component. This component is obtained from pepsinogens, and this happens in the process of penetration into the environment with certain density indicators.

Next, I would like to mention lipase. Despite the fact that this component is found in the gastric juice in an insignificant ratio, the role of this enzyme is no less significant than that of all the others. It is lipase that performs the function related to the initial hydrolysis of fats, namely their splitting into fatty acids and glycerol.

This enzyme is a surface-active catalyst, which is also relevant for other enzymes in the composition of gastric juice.

Another component in the gastric juice is the internal factor of Castle. This is another special enzyme, this feature is explained by the ability to activate the inactive form of vitamin B12 (it is known to enter the human body together with food). Intrinsic factor Castle is produced by the parietal cells of the gastric glands, and therefore is very important for maintaining the optimal state of the gastric juice.

It should be noted that during every 24 hours, at least two liters of the composition are produced in the stomach of a normal adult. Any changes in the color of this composition indicate diseases, certain pathological conditions that deserve the closest attention. One should not neglect those cases when mucus appears in the area of gastric juice, because this indicates inflammatory processes in the area of \u200b\u200bthe gastric mucosa.

Thus, all components in the composition of this component are enzymes and other substances necessary for it. Their presence is a guarantee of 100% well-coordinated work of the gastrointestinal system, the absence of pain and other unpleasant symptoms. That is why experts recommend periodically checking the ratio of this component.

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HOW TO SIGNIFICANTLY REDUCE THE RISK OF CANCER?

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1. Can cancer be prevented?
The occurrence of a disease such as cancer depends on many factors. No one can be completely safe. But everyone can significantly reduce the chances of a malignant tumor.

2. How does smoking affect the development of cancer?
Absolutely, categorically ban yourself from smoking. This truth is already tired of everyone. But quitting smoking reduces the risk of developing all types of cancer. Smoking is associated with 30% of cancer deaths. In Russia, lung tumors kill more people than tumors of all other organs.
Eliminating tobacco from your life is the best prevention. Even if you smoke not a pack a day, but only half, the risk of lung cancer is already reduced by 27%, as the American Medical Association found.

3. Does excess weight affect the development of cancer?
Keep your eyes on the scales! Extra pounds will affect not only the waist. The American Institute for Cancer Research has found that obesity contributes to the development of tumors in the esophagus, kidneys, and gallbladder. The fact is that adipose tissue serves not only to store energy reserves, it also has a secretory function: fat produces proteins that affect the development of a chronic inflammatory process in the body. And oncological diseases just appear against the background of inflammation. In Russia, 26% of all cancer cases are associated with obesity.

4. Does exercise help reduce the risk of cancer?
Set aside at least half an hour a week for exercise. Sport is on the same level as proper nutrition when it comes to cancer prevention. In the US, a third of all deaths are attributed to the fact that patients did not follow any diet and did not pay attention to physical education. The American Cancer Society recommends exercising 150 minutes a week at a moderate pace or half as much but more vigorously. However, a study published in the journal Nutrition and Cancer in 2010 proves that even 30 minutes is enough to reduce the risk of breast cancer (which affects one in eight women in the world) by 35%.

5.How does alcohol affect cancer cells?
Less alcohol! Alcohol is blamed for causing tumors in the mouth, larynx, liver, rectum, and mammary glands. Ethyl alcohol breaks down in the body to acetaldehyde, which then, under the action of enzymes, turns into acetic acid. Acetaldehyde is the strongest carcinogen. Alcohol is especially harmful to women, as it stimulates the production of estrogen - hormones that affect the growth of breast tissue. Excess estrogen leads to the formation of breast tumors, which means that every extra sip of alcohol increases the risk of getting sick.

6. Which cabbage helps fight cancer?
Love broccoli. Vegetables are not only part of a healthy diet, they also help fight cancer. This is also why recommendations for healthy eating contain the rule: half of the daily diet should be vegetables and fruits. Especially useful are cruciferous vegetables, which contain glucosinolates - substances that, when processed, acquire anti-cancer properties. These vegetables include cabbage: ordinary white cabbage, Brussels sprouts and broccoli.

7. Which organ cancer is affected by red meat?
The more vegetables you eat, the less red meat you put on your plate. Studies have confirmed that people who eat more than 500 grams of red meat per week have a higher risk of developing colon cancer.

8. Which of the proposed remedies protect against skin cancer?
Stock up on sunscreen! Women aged 18-36 are particularly susceptible to melanoma, the deadliest form of skin cancer. In Russia, in just 10 years, the incidence of melanoma has increased by 26%, world statistics show an even greater increase. Both artificial tanning equipment and the sun's rays are blamed for this. The danger can be minimized with a simple tube of sunscreen. A study published in the Journal of Clinical Oncology in 2010 confirmed that people who regularly apply a special cream get melanoma half as often as those who neglect such cosmetics.
The cream should be chosen with a protection factor of SPF 15, applied even in winter and even in cloudy weather (the procedure should turn into the same habit as brushing your teeth), and also do not expose yourself to sunlight from 10 to 16 hours.

9. Do you think stress affects the development of cancer?
By itself, stress does not cause cancer, but it weakens the entire body and creates conditions for the development of this disease. Research has shown that constant worry alters the activity of the immune cells responsible for turning on the fight-and-flight mechanism. As a result, a large amount of cortisol, monocytes and neutrophils, which are responsible for inflammatory processes, constantly circulate in the blood. And as already mentioned, chronic inflammatory processes can lead to the formation of cancer cells.

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