Gastric juice: composition, enzymes, acidity. Gastric juice: what it consists of and why it is needed

51. Properties and composition of intestinal juice. regulation of intestinal secretion.

intestinal juice- hazy alkaline liquid, rich in enzymes and mucus impurities, epithelial cells, cholesterol crystals, microbes (small amount) and salts (0.2% sodium carbonate and 0.7% sodium chloride). The glandular apparatus of the small intestine is its entire mucous membrane. Up to 2.5 liters of intestinal juice is excreted per day in a person.

The content of enzymes is low. Intestinal enzymes that break down different substances, the following: erepsin - polypeptides and peptones to amino acids, catapepsins - proteins in a slightly acidic environment (in the distal part of the small intestine and large intestine, where, under the influence of bacteria, a weak acidic environment), lipase - fats for glycerol and higher fatty acids, amylase - polysaccharides (except fiber) and dextrins to disaccharides, maltase - maltose for two glucose molecules, invertase - cane sugar, nuclease - complex proteins (nucleins), lactase acting on milk sugar and splitting it into glucose and galactose, alkaline phosphatase, hydrolyzing orthophosphoric acid monoesters in an alkaline environment, acid phosphatase, which has the same effect, but exhibits its activity in an acidic environment, etc.

The secretion of intestinal juice includes two processes: the separation of the liquid and dense parts of the juice. The ratio between them varies depending on the strength and type of irritation of the mucous membrane of the small intestine.

The liquid part is a yellowish alkaline liquid. It is formed by a secret, solutions of inorganic and organic substances transported from the blood, and partially by the contents of the destroyed cells of the intestinal epithelium. The liquid part of the juice contains about 20 g/l of dry matter. Among the inorganic substances (about 10 g/l) are chlorides, bicarbonates and phosphates of sodium, potassium, and calcium. The pH of the juice is 7.2-7.5, with increased secretion it reaches 8.6. The organic substances of the liquid part of the juice are represented by mucus, proteins, amino acids, urea and other metabolic products.

The dense part of the juice is a yellowish-gray mass that looks like mucous lumps and includes undestroyed epithelial cells, their fragments and mucus - the secret of goblet cells has a higher enzymatic activity than liquid part juice.

In the mucous membrane of the small intestine, there is a continuous change in the layer of cells of the surface epithelium. Complete renewal of these cells in humans takes 1-4-6 days. Such a high rate of formation and rejection of cells provides a sufficiently large number of them in the intestinal juice (in humans, about 250 g of epitheliocytes are rejected per day).

Mucus forms a protective layer that prevents excessive mechanical and chemical effects of chyme on the intestinal mucosa. In mucus, the activity of digestive enzymes is high.

The dense part of the juice has a much greater enzymatic activity than the liquid part. The main part of the enzymes is synthesized in the intestinal mucosa, but some of them are transported from the blood. There are more than 20 different enzymes in the intestinal juice that are involved in digestion.

regulation of intestinal secretion.

Eating, local mechanical and chemical irritation of the intestine enhance the secretion of its glands with the help of cholinergic and peptidergic mechanisms.

In the regulation of intestinal secretion, local mechanisms play a leading role. Mechanical irritation of the mucous membrane of the small intestine causes an increase in the release of the liquid part of the juice. Chemical stimulants of the secretion of the small intestine are the products of digestion of proteins, fats, pancreatic juice, hydrochloric and other acids. The local action of the products of digestion of nutrients causes the separation of intestinal juice rich in enzymes.

The act of eating does not significantly affect intestinal secretion, at the same time, there are data on the inhibitory effects on it of irritation of the antrum of the stomach, modulating effects of the central nervous system, on the stimulating effect on the secretion of cholinomimetic substances and the inhibitory effect of anticholinergic and sympathomimetic substances. Stimulate intestinal secretion of GIP, VIP, motilin, inhibits somatostatin. The hormones enterocrinin and duocrinin, produced in the mucous membrane of the small intestine, stimulate the secretion of intestinal crypts (Lieberkün's glands) and duodenal (Brunner's) glands, respectively. These hormones have not been isolated in purified form.

Lesson topic: "The effect of intestinal juice on food"

Grade:8

The purpose of the lesson: to form knowledge about the internal structure of the thin and thick sectionsintestines, their functional activity; the role of the large intestine in digestion: the importance of the regulation of digestion

During the classes:

1. Organizational moment. (1-2 min)

Greeting children. Checking if all students are in the class. Set to work.

2.Updating knowledge. (5-7 min)

In the last lesson, we talked about digestion in the stomach, about complex reflex and neurohumoral juice secretion, about the composition of gastric juice. Now we will check what you have learned on this topic.

Solve the crossword "Digestion in the stomach"

Crossword questions:

1. Juice secretion caused by the act of eating

2. Separation of gastric juice due to mechanical irritation of the gastric mucosa.

3. Nerves through which excitation is transmitted from the central nervous system to the glands of the stomach during neurohumoral sap secretion.

4. Environment, activating the action of gastric juice enzymes.

5. Acid, which is part of the gastric juice.

6. An enzyme that easily breaks down the proteins of meat and eggs.

7. A special hormone produced in the gastric mucosa.

8. Bulky expansion digestive tract.

9. Stomach juice, odorless and colorless.

10. An enzyme that causes curdling of milk in the stomach.
Additional questions:

Describe the structure of the stomach.

How is the secretion of gastric juice regulated?

Composition of gastric juice.

3. Learning new material. (20 min)

So, in the last lessons, you studied digestion in the mouth and stomach. Further, the food bolus enters the longest section - the intestines.

What goals do you think we can set for ourselves today?

As you know, there are special digestive glands throughout the entire alimentary canal. Knowing this, what else can we learn in the lesson?

(- You can find out how the digestive glands affect digestion.)

The purpose of the lesson: to study the processes occurring in the intestines, the role of glands in digestion and understand what absorption is and how it occurs.

Let's open notebooks, write down the chilo and the topic of our lesson "the effect of digestive juice on food."

Food gruel from the stomach in small portions enters the longest part of the digestive tract - the intestines, consisting of the small and large intestines.

Through a special route duodenum pancreatic (pancreatic juice) drains. It is colorless, transparent, has a slightly alkaline reaction and contains all the enzymes that break down proteins, fats and carbohydrates. Pancreatic juice trypsin breaks down proteins into amino acids, lipase breaks down fats into glycerol and fatty acids, amylase breaks down carbohydrates into monosaccharides. An important role in this process is played by bile secreted by the liver. Bile does not break down fats, but creates an alkaline environment in the duodenum, emulsifies, loosens the fat into small droplets, and this enhances the action of the lipase enzyme.

Pancreas It is the second largest gland in the digestive tract. The gland is greyish-red in color and extends transversely from the duodenum to the spleen.

Consists of 2 types of cells: some cells secrete digestive juice,

others are hormones that regulate the metabolism of carbohydrates and fats. For a day at

a person separates about 1.5-2 liters. pancreatic juice.

Nervous and humoral regulation of sap secretion.

Working outjuicepancreas begins under the influence of conditioned and unconditioned reflexes. In preparation for eating and the beginning of the absorption of food through the vagus nervenerve impulses are sent to the organs. But most of juice is produced under the influence of special hormones after the food from the stomach enters the duodenum.

Pancreatic juice is slightly alkaline.

It gets here along a special channelbile juice produced by the liver.

Liver - are called "chemical laboratory", "food warehouse", "dispatcher of the body." What is the basis of these expressions?

Liver - the largest human gland, red-brown in color. its mass reaches 1.5 kg. It is located in abdominal cavity under the diaphragm on the right, only a small part of it comes to the left of the midline. The name "liver" comes from the Russian words "bake", "bake". The liver has highest temperature from all organs of our body.

Functions of the liver.

Takes part not only in the process of digestion.

It also performs one of the vital functions - the neutralization of toxic substances entering the bloodstream from the digestive organs. Many bacteria that are harmful to the body die in the liver.

If there is a lot of glucose in the blood, then part of it is delayed. If it is poor, then on the contrary, it is enriched. The liver stores carbohydrates in the formglycogen - animal starch.

The liver serves as a storehouse of vitamins and is enriched with them especially in summer and autumn.

One of essential functions liver and the synthesis of plasma proteins - albumin and fibrinogen, as well as prothrombin.

The liver produces bile, which passes through the bile duct into the duodenum. Excess bile is collected in the gallbladder and can be used when there is increased digestion in the duodenum.

The formation of bile in the liver cells occurs continuously, but its release into the duodenum occurs only 5-10 minutes after a meal and lasts 6-8 hours. The daily secretion of bile is about 1 liter. Bile does not contain enzymes.

What then is the meaning of bile?

The value of bile:

Thanks to its action, the digestion of fats is facilitated;

It increases the activity of enzymes;

Increases the solubility of fatty acids;

Enhances bowel movement;

Delays putrefactive processes in the intestines.

intestinal juice.

Enzymes are involved in the breakdown of proteins, carbohydrates, fats

intestinal juice, which is produced by the glands of the mucous membrane of the small intestine, is secreted up to 2 liters per day. intestinal juice.

This is where digestion products are absorbed.

The small intestine is the central section of the digestive tract, where the processes of digestion end and the products of digestion are intensively absorbed into the blood.

This is facilitated by adaptations of the small intestine, which, on the one hand, should slow down the movement of food masses through this section (for better digestion), on the other hand, to increase the surface of the mucous membrane of the small intestine.

The length of the human intestine is on average 5-6 meters. The intestines of an adult are 4 times longer than the body, and in a child 6 times. The longer the intestine, the longer the food stays in it (therefore, it is better digested and absorbed). In addition, the peristaltic movements of the small intestine contribute to the optimal mixing of the contents of the intestine with digestive juices and an increase in the time spent in it. small intestine up to 80% of dietary proteins and almost 100% of fats and carbohydrates are digested.

The wall of the small intestine is formed by:

Mucous membrane, submucosal tissue, muscle and serous membranes. The mucous membrane of the small intestine forms folds covered with villi.

On the mucous membrane of the small intestine in 1 sq. cm, there are up to 2500 villi.

The length of the villi is up to 1 mm.

Digestion in the small intestine occurs in three stages:

1) abdominal digestion;

What do you think is the definition of this concept?

2) parietal or membrane digestion.

This phenomenon was discovered by the Russian scientist A.M. Ugolev. What is important, parietal digestion takes place on the same surface of the small intestine, which has the function of absorption. Parietal digestion takes place on the very surface of the intestinal mucosa. Particles that penetrate into the spaces between the villi are digested. Larger particles remain in the intestinal cavity, where they are exposed to the action of digestive juices. This mechanism of digestion contributes to the most complete digestion of food.

3) Absorption is the process of entry of various substances through the layer of villus cells into the blood and lymph. Absorption is of great importance, this is the way our body gets everything necessary substances. The absorption process takes place in the villi.

Their wall consists of a single layer of epithelium. Each villus contains blood and lymph vessels. Smooth muscle cells are laid along the villus, which contract during digestion, and the contents of their blood and lymphatic vessels squeezed out and goes into the general circulation of blood and lymph. The villi contract 4 to 6 times per minute.

Each villus, in turn, is covered with finger-like outgrowths - microvilli.

So, if you hold a piece of sugar under your tongue for a long time, it will dissolve and begin to be absorbed. However, food in the mouth is a short time and fails to be absorbed. Alcohol is well absorbed in the stomach, partially glucose, in the large intestine - water and some salts.

Proteins are absorbed in the form of water-soluble amino acids. Carbohydrates are absorbed into the blood in the form of glucose. This process is most intense in upper section intestines. Carbohydrates are absorbed slowly in the large intestine.

Fatty acids and glycerol penetrate the cells of the villi of the small intestine, where they form fats characteristic of human body. They are absorbed into the lymph, so the lymph flowing from the intestines has a milky color.

Water absorption begins in the stomach and continues most intensively in the intestines. Water is also absorbed into the blood. mineral salts absorbed into the blood in dissolved form.

From the small intestines, the unabsorbed part of the food passes into the initial section of the large intestine -blind gut. The mucous membrane of the large intestine does not have villi, its cells secrete mucus. The large intestine contains a rich bacterial flora that causes the fermentation of carbohydrates and putrefaction of proteins. As a result of microbial fermentation, vegetable fiber is broken down, which is not affected by the enzymes of digestive juices, therefore it is not absorbed in the small intestines and enters the large intestine unchanged. Under the influence of putrefactive bacteria, unabsorbed amino acids and other products of protein digestion are destroyed. In this case, gases and toxic substances are formed, which, being absorbed into the blood, can cause poisoning of the body. These substances are detoxified in the liver.

The large intestine predominantly absorbs water (up to 4 liters per day), as well as glucose and some drugs. Less than 130-150 g of feces remain from the food gruel, which includes mucus, the remains of the dead epithelium of the mucous membrane, cholesterol, products of changes in bile pigments, giving the feces a characteristic color, undigested residues food, a large number of bacteria.

The movement of food residues in the large intestine occurs due to the contraction of its walls. Feces accumulate inrectum. defecation (intestinal emptying) is a reflex process that occurs on irritation of the receptors of the rectal mucosa with feces when a certain pressure is reached on its walls. The center of defecation is located in the sacrum

department spinal cord. The act of defecation is also subordinate to the cerebral cortex, which causes an arbitrary delay in defecation.

3. Consolidation of the material covered.

And now to check how you learned the material studied. Determine what substances are formed as a result of the digestion of proteins, fats, carbohydrates. Fill the table:

Table: Organic Nutrients

squirrels

fats

carbohydrates

Substances formed during digestion

Answer the following questions:

1) What is the importance of the liver and pancreas in digestion

2) What are the stages of digestion in the small intestine?

3) Explain the mechanism of peristaltic movements of the walls of the small intestine?

4) What is the significance of the appendix?

5) Where is the defecation center located?

5. Homework.

Paragraph 46, pp. 171-174

Answer the questions

Table "Establish correspondence" in writing.

Pancreatic juice is the secret by which food is digested. The composition of the pancreatic juice contains enzymes that break down the fats, proteins and carbohydrates contained in the foods consumed into simpler components. They are involved in further metabolic biochemical reactions occurring in the body. During the day, the human pancreas (PZh) is able to produce 1.5-2 liters of pancreatic juice.

What does the pancreas secrete?

The pancreas is one of the main organs of the endocrine and digestive systems. of this organ makes it indispensable, and the structure of tissues leads to the fact that any impact on the gland leads to their damage. The exocrine (external secretory) function of the pancreas is that special cells secrete digestive juice at each meal, due to which it is digested. Endocrine activity of the gland - involved in the main metabolic processes in the body. One of them is the metabolism of carbohydrates, which occurs with the participation of several pancreatic hormones.

Where is pancreas juice formed and where does it go?

The parenchyma of the pancreas consists of glandular tissue. Its main components are lobules (acini) and islets of Langerhans. They provide external and intrasecretory function organ. are located between the acini, their number is much smaller, and their greater number is located in the tail of the pancreas. They make up 1-3% of the total pancreas. In the cells of the islets, hormones are synthesized, which immediately enter the bloodstream.

The exocrine part has a complex alveolar-tubular structure and secretes about 30 enzymes. The bulk of the parenchyma consists of lobules that look like vesicles or tubules, separated from each other by delicate connective tissue septa. They pass:

• capillaries braiding the acinus with a dense network;
• lymphatic vessels;
• nervous elements;
• outflow duct.

Each acinus consists of 6-8 cells. The secret produced by them enters the cavity of the lobule, from there into the primary pancreatic duct. Several acini combine into lobes, which in turn form larger segments of several lobes.

The small ducts of the lobules merge into a larger excretory canal of the lobe and segment, which flows into the main - - duct. It stretches through the entire gland from tail to head, gradually expanding from 2 mm to 5 mm. In the head part of the pancreas, an additional duct, the santorini, flows into the Wirsung canal (not in every person), the resulting duct connects with the common duct of the gallbladder. Through this so-called ampulla and Vater papilla, the contents enter the lumen of the duodenum.

Around the main pancreatic and common bile ducts and their common ampulla there is a significant amount of smooth muscle fibers that form. It regulates the entry into the lumen of the duodenum required amount pancreatic juice and bile.

In general, the segmental structure of the pancreas resembles a tree, the number of segments individually varies from 8 to 18. They can be large, wide (a sparsely branched variant of the main duct) or narrow, more branched and numerous (densely branched duct). In the pancreas, there are 8 orders of structural units that form such a tree-like structure: starting with a small acinus and ending with the largest segment (which are from 8 to 18), the duct of which flows into the Wirsungs.

Acini cells synthesize, in addition to enzymes, which are proteins by chemical composition, a certain amount of other proteins. Ductal and central acinar cells produce water, electrolytes, and mucus.

The pancreatic juice is a clear liquid with an alkaline environment, which is provided by bicarbonates. They carry out the neutralization and alkalization coming from the stomach food bolus- chyme. This is necessary because the stomach produces hydrochloric acid. Due to its secretion, gastric juice has an acidic reaction.

Enzymes of pancreatic juice

The digestive properties of the pancreas are provided. They are important integral part produced juice and are represented by:

• amylase;
• lipase;
• proteases.

Food, its quality and quantity consumed have a direct impact on:

• on the properties and ratio of enzymes in pancreatic juice;
• on the volume or amount of secretion that the pancreas can produce;
• on the activity of the enzymes produced.

The function of pancreatic juice is the direct participation of enzymes in digestion. Their excretion is influenced by the presence of bile acids.

All pancreatic enzymes in structure and function are 3 main groups:

• lipase - converts fats into their components (fatty acids and monoglycerides);
• protease - breaks down proteins into their original peptides and amino acids;
• amylase - acts on carbohydrates with the formation of oligo- and monosaccharides.

AT active form lipase and α-amylase are formed in the pancreas - they are immediately included in biochemical reactions involving carbohydrates and fats.

All proteases are produced exclusively as proenzymes. They can be activated in the lumen of the small intestine with the participation of enterokinase (enteropeptidase) - an enzyme synthesized in the parietal cells of the duodenum and named by I.P. Pavlov's "enzyme of enzymes". It becomes active in the presence of bile acids. Thanks to this mechanism, the pancreatic tissue is protected from autolysis (self-digestion) by its own proteases produced by it.

Amylolytic enzymes

The purpose of amylolytic enzymes is to participate in the breakdown of carbohydrates. The action of the amylase of the same name is aimed at the transformation of large molecules into their constituent parts - oligosaccharides. Amylases α and β are secreted into active state; they break down starch and glycogen into disaccharides. The further mechanism consists in the breakdown of these substances to glucose - the main source of energy, which is already entering the blood. This is possible due to the enzymatic composition of the group. It includes:

• maltase;
• lactase;
• invertase.

The biochemistry of the process is that each of these enzymes can regulate certain reactions: for example, lactase breaks down milk sugar - lactose.

Proteolytic Enzymes

According to their biochemical reactions, proteases belong to hydrolases: they are involved in the cleavage of peptide bonds in protein molecules. Their hydrolytic effect is similar in exoproteases produced by the pancreas itself (carboxypeptidase) and in endoproteases.

Functions of proteolytic enzymes:

• trypsin converts protein into peptides;
• carboxypeptidase converts peptides into amino acids;
• elastase acts on proteins and elastin.

As mentioned, the proteases in the composition of the juice are inactive (trypsin and chymotrypsin are excreted as trypsinogen and chymotrypsinogen). Trypsin is converted to an active enzyme by enterokinase in the lumen of the small intestine, and chymotrypsinogen by trypsin. In the future, with the participation of trypsin, the structure of other enzymes also changes - they are activated.

The cells of the pancreas also produce a trypsin inhibitor, which prevents them from being digested by this enzyme, which is formed from trypsinogen. Trypsin cleaves peptide bonds, in the formation of which the carboxyl groups of arginine and lysine are involved, and chymotrypsin complements its action by cleaving peptide bonds involving cyclic amino acids.

Lipolytic Enzymes

Lipase acts on fats by first converting them into glycerol and fatty acids, since they cannot enter the vessels due to the size and structure of their molecule. Cholesterase also belongs to the group of lipolytic enzymes. Lipase is water-soluble and acts on fats only at the water-fat interface. It is excreted in an already active form (has no proenzyme) and significantly increases its effect on fats in the presence of calcium and bile acids.

The reaction of the environment to the intake of juice

It is very important that the pH of the pancreatic juice is 7.5 - 8.5. This, as stated, corresponds to an alkaline reaction. The physiology of digestion boils down to the fact that the chemical processing of the food bolus begins in the oral cavity, under the influence of saliva enzymes, and continues in the stomach. After being in his aggressive acid environment chyme enters the lumen of the small intestine. In order not to damage the duodenal mucosa and not deactivate the enzymes, it is necessary to neutralize the acid residues. This is due to the alkalization of incoming food with the help of pancreatic juice.

The effect of food on enzyme production

Enzymes that are synthesized as inactive compounds (such as trypsinogen) are activated upon entry into the small intestine due to duodenal contents. They begin to be released as soon as food enters the duodenum. This process continues for 12 hours. What matters is the food consumed, which affects the enzymatic composition of the juice. The largest amount of pancreatic juice is produced for the incoming carbohydrate food. In its composition, enzymes from the amylase group prevail. But for bread and bakery products stands out maximum amount pancreatic secretion, when used meat products- less. A minimal volume of juice is produced in response to dairy products. If the bread is cut into a thick piece and swallowed in large quantities, poorly chewed, this affects the state of the pancreas - its work is enhanced.

The specific amount of enzymes contained in the juice also depends on the food: 3 times more lipase is produced for fatty foods than proteases for digesting meat. Therefore, with inflammation of the pancreas are prohibited fatty foods: on their splitting, the gland has to synthesize a huge amount of enzymes, which is a significant functional load for the organ and enhances the pathological process.

The foods you eat also affect Chemical properties pancreatic fluid: in response to the intake of meat, more alkaline environment than other dishes.

Regulation of intestinal juice

In short, the secretion of intestinal juice occurs under the influence of mechanical and chemical irritation of the cells of the mucous membranes of the duodenum when the food bolus enters. Only fat leads to the separation of secretions in areas of the intestine remote from the place of its receipt in a reflex way.

Mechanical irritation normally occurs with food masses, the process is accompanied by the release of a large amount of mucus.

Chemical irritants are:

• gastric juice;
• breakdown products of proteins and carbohydrates;
• pancreatic secret.

The pancreatic juice leads to an increase in the amount of enterokinase secreted in the contents of the intestinal secretion. Chemical irritants lead to the release of liquid juice containing few dense substances.

In addition, the cells of the mucous membrane of the human small and large intestines contain the hormone enterocrinin, which stimulates the separation of intestinal juice.

The pancreas secretes important biological fluid- pancreatic juice, without which the normal process of digestion and the intake of nutrients into the body is impossible. With any pathology of the organ and reduced formation of juice, this activity is disturbed. To restore healthy digestion of food, you need to pick up. In severe pancreatitis or other diseases, the patient has to take such drugs for life. The child may suffer as a result of the ducts or the gland itself.

Correction of exocrine disorders is done by a doctor according to the level of lipase. It is an indispensable enzyme and is fully synthesized only by the gland itself. Therefore, the activity of any medication for replacement therapy calculated in lipase units. The dosage and duration of its use depends on the degree of pancreatic insufficiency.

Bibliography

1. Korotko G.F. Secretion of the pancreas. M .: "TriadKh" 2002, p. 223.
2. Poltyrev S.S., Kurtsin I.T. Physiology of digestion. M. Higher school. 1980
3. Rusakov V.I. Fundamentals of private surgery. Rostov University Publishing House 1977
4. Khripkova A.G. age physiology. M. Enlightenment 1978
5. Kalinin A.V. Violation of abdominal digestion and its drug correction. Clinical perspectives of gastroenterology, hepatology. 2001 No. 3, pp. 21–25.

Stomach is a sac-like extension of the digestive tract. Its projection on the anterior surface abdominal wall corresponds to the epigastric region and partially enters left hypochondrium. Secreted in the stomach following departments: upper - bottom, large central - body, lower distal - antrum. The place where the stomach communicates with the esophagus is called the cardiac region. The pyloric sphincter separates the contents of the stomach from the duodenum (Fig. 1).

• depositing food;

• its mechanical and chemical processing;

• gradual evacuation of food contents into the duodenum.

Depending on the chemical composition and quantity food taken it is in the stomach from 3 to 10 hours. At the same time, the food masses are crushed, mixed with gastric juice and liquefied. Nutrients exposed to the action of gastric enzymes.

Composition and properties of gastric juice

Gastric juice is produced by the secretory glands of the gastric mucosa. 2-2.5 liters of gastric juice is produced per day. There are two types of secretory glands in the gastric mucosa.

Rice. 1. Division of the stomach into sections

In the area of ​​the bottom and body of the stomach, acid-producing glands are localized, which occupy approximately 80% of the surface of the gastric mucosa. They are depressions in the mucosa (gastric pits), which are formed by three types of cells: chief cells produce proteolytic enzymes pepsinogens, lining (parietal) - hydrochloric acid and additional (mucoid) - mucus and bicarbonate. In the region of the antrum there are glands that produce a mucous secret.

Pure gastric juice is a colorless transparent liquid. One of the components of gastric juice is hydrochloric acid, so it pH is 1.5 - 1.8. Concentration of hydrochloric acid in gastric juice is 0.3 - 0.5%, pH gastric contents after a meal may be significantly higher than pH pure gastric juice due to its dilution and neutralization by the alkaline components of food. The composition of gastric juice includes inorganic (ions Na +, K +, Ca 2+, CI -, HCO - 3) and organic substances (mucus, end products of metabolism, enzymes). Enzymes are formed by the chief cells of the gastric glands in an inactive form - in the form pepsinogens, which are activated when small peptides are cleaved from them under the influence of hydrochloric acid and turn into pepsins.

Rice. The main components of the secret of the stomach

The main proteolytic enzymes of gastric juice include pepsin A, gastrixin, parapepsin (pepsin B).

Pepsin A breaks down proteins into oligopeptides pH 1,5- 2,0.

Optimal Enzyme pH gastrixin is 3.2-3.5. It is believed that pepsin A and gastrixin act on different kinds proteins, providing 95% of the proteolytic activity of gastric juice.

Gastrixin (pepsin C) - proteolytic enzyme of gastric secretion, showing maximum activity at pH equal to 3.0-3.2. It hydrolyzes hemoglobin more actively than pepsin and is not inferior to pepsin in the rate of hydrolysis. egg white. Pepsin and gastrixin provide 95% of the proteolytic activity of gastric juice. Its amount in gastric secretion is 20-50% of the amount of pepsin.

Pepsin B plays a lesser role in the process gastric digestion and breaks down gelatin. The ability of gastric enzymes to break down proteins different meaning pH plays an important adaptive role, as it ensures the efficient digestion of proteins in conditions of qualitative and quantitative diversity of food entering the stomach.

Pepsin-B (parapepsin I, gelatinase)- a proteolytic enzyme, activated with the participation of calcium cations, differs from pepsin and gastrixin in a more pronounced gelatinase action (breaks down the protein contained in connective tissue, - gelatin) and a less pronounced effect on hemoglobin. Pepsin A is also isolated, a purified product obtained from the mucous membrane of the stomach of a pig.

Gastric juice also contains a small amount of lipase, which breaks down emulsified fats (triglycerides) into fatty acids and diglycerides at neutral and slightly acidic values pH(5.9-7.9). At infants gastric lipase breaks down more than half of the emulsified fat found in breast milk. In an adult, the activity of gastric lipase is low.

The role of hydrochloric acid in digestion:

• activates pepsinogens of gastric juice, turning them into pepsins;
• creates an acidic environment, optimal for the action of gastric juice enzymes;
• causes swelling and denaturation of food proteins, which facilitates their digestion;
• has a bactericidal effect
• regulates the production of gastric juice (when pH vantral part of the stomach becomes less 3,0 , the secretion of gastric juice begins to slow down);
• has a regulatory effect on gastric motility and the process of evacuation of gastric contents into the duodenum (with a decrease pH in the duodenum there is a temporary inhibition of gastric motility).

Functions of gastric mucus

The mucus that is part of the gastric juice, together with HCO - 3 ions, forms a hydrophobic viscous gel that protects the mucosa from the damaging effects of hydrochloric acid and pepsins.

stomach mucus - component of the contents of the stomach, consisting of glycoproteins and bicarbonate. It plays an important role in protecting the mucous membrane from the damaging effects of hydrochloric acid and gastric secretion enzymes.

The composition of the mucus formed by the glands of the fundus of the stomach includes a special gastromucoprotein, or Castle intrinsic factor, which is necessary for the full absorption of vitamin B 12. It binds to vitamin B 12. entering the stomach as part of food, protects it from destruction and promotes the absorption of this vitamin. Vitamin B 12 is necessary for the normal implementation of hematopoiesis in red bone marrow, namely for the proper maturation of progenitor cells of red blood cells.

Lack of vitamin B 12 internal environment organism, associated with a violation of its absorption due to a lack internal factor Castle, observed when part of the stomach is removed, atrophic gastritis and leads to the development of a serious disease - B 12-deficient anemia.

Phases and mechanisms of regulation of gastric secretion

On an empty stomach, the stomach contains a small amount of gastric juice. Eating causes profuse gastric secretion of acidic gastric juice with high content enzymes. I.P. Pavlov divided the entire period of secretion of gastric juice into three phases:

• complex reflex, or cerebral,

• gastric, or neurohumoral,
• intestinal.

Cerebral (complex reflex) phase of gastric secretion - increased secretion due to food intake, its appearance and smell, effects on the receptors of the mouth and pharynx, acts of chewing and swallowing (stimulated conditioned reflexes accompanying meals). Proven in experiments with imaginary feeding according to I.P. Pavlov (an esophagotomized dog with an isolated stomach that retained innervation), food did not enter the stomach, but abundant gastric secretion was observed.

Complex reflex phase gastric secretion begins even before food enters the oral cavity at the sight of food and preparation for its reception and continues with irritation of taste, tactile, temperature receptors of the oral mucosa. Stimulation of gastric secretion in this phase is carried out conditional and unconditioned reflexes arising as a result of the action of conditioned stimuli (view, smell of food, environment) on the receptors of the sense organs and the unconditioned stimulus (food) on the receptors of the mouth, pharynx, esophagus. Afferent nerve impulses from receptors excite the nuclei of the vagus nerves in the medulla oblongata. Further along the efferent nerve fibers vagus nerve impulses reach the gastric mucosa and stimulate gastric secretion. Transection of the vagus nerves (vagotomy) completely stops the secretion of gastric juice in this phase. The role of unconditioned reflexes in the first phase of gastric secretion is demonstrated by the experience of “imaginary feeding”, proposed by I.P. Pavlov in 1899. The dog was previously subjected to an esophagotomy operation (transection of the esophagus with the removal of the cut ends to the skin surface) and a gastric fistula was applied (artificial communication of the organ cavity with the external environment). When feeding the dog, swallowed food fell out of the cut esophagus and did not enter the stomach. However, 5-10 minutes after the start of imaginary feeding, there was an abundant separation of acidic gastric juice through the gastric fistula.

The gastric juice secreted in the complex reflex phase contains a large amount of enzymes and creates the necessary conditions for normal digestion in the stomach. I.P. Pavlov called this juice “ignition”. Gastric secretion in the complex reflex phase is easily inhibited under the influence of various extraneous stimuli (emotional, painful influences), which negatively affects the digestion process in the stomach. Inhibitory influences are realized upon excitation of sympathetic nerves.

Gastric (neurohumoral) phase of gastric secretion - an increase in secretion caused by the direct action of food (protein hydrolysis products, a number of extractive substances) on the gastric mucosa.

gastric, or neurohumoral, phase gastric secretion begins when food enters the stomach. The regulation of secretion in this phase is carried out as neuro-reflex, and humoral mechanisms.

Rice. Fig. 2. Scheme of regulation of the activity of gastric lining marks, which provide the secretion of hydrogen ions and the formation of hydrochloric acid

Irritation of mechano-, chemo-, and thermoreceptors of the gastric mucosa with food causes a flow of nerve impulses along afferent nerve fibers and reflexively activates the main and parietal cells of the gastric mucosa (Fig. 2).

It has been experimentally established that vagotomy does not eliminate gastric juice secretion in this phase. This indicates the existence humoral factors that enhance gastric secretion. Such humoral substances are the hormones of the gastrointestinal tract, gastrin and histamine, which are produced by special cells of the gastric mucosa and cause a significant increase in the secretion of mainly hydrochloric acid and, to a lesser extent, stimulate the production of gastric juice enzymes. Gastrin It is produced by G-cells of the antrum of the stomach during its mechanical stretching by incoming food, exposure to protein hydrolysis products (peptides, amino acids), as well as excitation of the vagus nerves. Gastrin enters the bloodstream and acts on parietal cells endocrine way(Fig. 2).

Products histamine carry out special cells of the fundus of the stomach under the influence of gastrin and with excitation of the vagus nerves. Histamine does not enter the bloodstream, but directly stimulates nearby parietal cells (paracrine action), which leads to the release of a large amount of acidic secretion, poor in enzymes and mucin.

The efferent impulse coming through the vagus nerves has both a direct and indirect (through stimulation of the production of gastrin and histamine) effect on an increase in the formation of hydrochloric acid by parietal cells. Enzyme-producing chief cells are activated both by parasympathetic nerves and directly under the influence of hydrochloric acid. The mediator of parasympathetic nerves acetylcholine increases the secretory activity of the gastric glands.

Rice. Formation of hydrochloric acid in the parietal cell

The secretion of the stomach in the gastric phase also depends on the composition of the food taken, the presence of spicy and extractive substances in it, which can significantly enhance gastric secretion. A large number of extractive substances are found in meat broths and vegetable broths.

At long-term use predominantly carbohydrate foods (bread, vegetables), the secretion of gastric juice decreases, while eating foods rich in proteins (meat), it increases. The influence of the type of food on gastric secretion is of practical importance in certain diseases accompanied by a violation secretory function stomach. So, with hypersecretion of gastric juice, food should be soft, enveloping texture, with pronounced buffering properties, should not contain meat extractives, spicy and bitter seasonings.

Intestinal phase of gastric secretion- stimulation of secretion, which occurs when the contents of the stomach enter the intestine, is determined reflex influences, arising from irritation of the receptors of the duodenum, and humoral influences caused by the absorbed products of the breakdown of food. It is enhanced by gastrin, and the intake of acidic food (pH< 4), жира — тормозит.

Intestinal phase gastric secretion begins with the gradual evacuation of food masses from the stomach into the duodenum and is corrective nature. Stimulating and inhibitory influences from the duodenum on the glands of the stomach are realized through neuro-reflex and humoral mechanisms. When the mechano- and chemoreceptors of the intestine are irritated by the products of protein hydrolysis from the stomach, local inhibitory reflexes are triggered, the reflex arc of which closes directly in the neurons of the intermuscular nerve plexus walls of the digestive tract, resulting in inhibition of gastric secretion. However, humoral mechanisms play the most important role in this phase. When the acidic contents of the stomach enter the duodenum and decrease pH its content is less 3,0 mucosal cells produce a hormone secretin that inhibits the production of hydrochloric acid. Similarly, the secretion of gastric juice is affected cholecystokinin, the formation of which in the intestinal mucosa occurs under the influence of hydrolysis products of proteins and fats. However, secretin and cholecystokinin increase the production of pepsinogens. In the stimulation of gastric secretion in the intestinal phase, the products of protein hydrolysis (peptides, amino acids) absorbed into the blood take part, which can directly stimulate the gastric glands or increase the release of gastrin and histamine.

Methods for studying gastric secretion

For the study of gastric secretion in humans, probe and tubeless methods are used. sounding stomach allows you to determine the volume of gastric juice, its acidity, the content of enzymes on an empty stomach and when stimulating gastric secretion. As stimulants use meat broth, cabbage decoction, various chemical substances(synthetic analogue of gastrin pentagastrin or histamine).

Acidity of gastric juice determined to assess the content of hydrochloric acid (HCI) in it and expressed as the number of milliliters of decinormal sodium hydroxide (NaOH), which must be added to neutralize 100 ml of gastric juice. Free acidity of gastric juice reflects the amount of dissociated hydrochloric acid. Total acidity characterizes the total content of free and bound hydrochloric acid and other organic acids. At healthy person on an empty stomach, the total acidity is usually 0-40 titration units (i.e.), free acidity is 0-20 t.u. After submaximal stimulation with histamine, the total acidity is 80-100 tons, free acidity is 60-85 tons.

Special thin probes equipped with sensors are widely used. pH, with which you can register the dynamics of change pH directly in the stomach cavity during the day ( pH meter), which makes it possible to identify factors provoking a decrease in the acidity of gastric contents in patients peptic ulcer. Probeless methods include endoradio sounding method digestive tract, in which a special radio capsule, swallowed by the patient, moves along the digestive tract and transmits signals about the values pH in its various departments.

Motor function of the stomach and mechanisms of its regulation

The motor function of the stomach is carried out by the smooth muscles of its wall. Directly when eating, the stomach relaxes (adaptive food relaxation), which allows it to deposit food and contain a significant amount of it (up to 3 liters) without a significant change in pressure in its cavity. When reducing smooth muscle In the stomach, food is mixed with gastric juice, as well as grinding and homogenization of the contents, which end in the formation of a homogeneous liquid mass (chyme). Portioned evacuation of chyme from the stomach into the duodenum occurs when the smooth muscle cells of the antrum of the stomach contract and the pyloric sphincter relaxes. The intake of a portion of acidic chyme from the stomach into the duodenum lowers the pH of the intestinal contents, leads to excitation of the mechano- and chemoreceptors of the duodenal mucosa and causes reflex inhibition of chyme evacuation (local inhibitory gastrointestinal reflex). In this case, the antrum of the stomach relaxes, and the pyloric sphincter contracts. The next portion of chyme enters the duodenum after the previous portion is digested and the value pH its contents are restored.

The rate of evacuation of chyme from the stomach into the duodenum is influenced by physiochemical properties food. The food containing carbohydrates leaves the stomach the fastest, then - protein food, while fatty food stays in the stomach for more long time(up to 8-10 hours). Acidic food undergoes slower evacuation from the stomach compared to neutral or alkaline food.

Gastric motility is regulated neuro-reflex and humoral mechanisms. Parasympathetic vagus nerves increase the motility of the stomach: increase the rhythm and strength of contractions, the speed of peristalsis. With excitation of the sympathetic nerves, inhibition of the motor function of the stomach is observed. The hormone gastrin and serotonin increase motor activity stomach, while secretin and cholecystokinin inhibit gastric motility.

Vomiting is a reflex motor act, as a result of which the contents of the stomach are ejected through the esophagus into the oral cavity and enter the external environment. This is provided by contraction of the muscular membrane of the stomach, muscles of the anterior abdominal wall and diaphragm and relaxation of the lower esophageal sphincter. Vomiting is often defensive reaction, with the help of which the body is freed from toxic and poisonous substances trapped in gastrointestinal tract. However, it can occur with various diseases of the digestive tract, intoxication, and infections. Vomiting occurs reflexively when the vomiting center of the medulla oblongata is stimulated by afferent nerve impulses from receptors of the mucous membrane of the root of the tongue, pharynx, stomach, intestines. Usually the act of vomiting is preceded by a feeling of nausea and increased salivation. Excitation of the vomiting center with subsequent vomiting can occur when the olfactory and taste receptors are irritated by substances that cause a feeling of disgust, receptors vestibular apparatus(when driving a car, sea travel), under the action of some medicinal substances to the vomiting center.

The mucous surface of the stomach has many folds, elongated longitudinally, and elevations (gastric fields), on which there are a large number of pits. In these recesses, gastric juice is secreted. It is produced by the glands of the mucous surface of the organ, looks like a colorless clear liquid and has a sour taste.

Cells of the glands of the stomach are divided into three groups: main, additional and parietal. Each of them produces different components that are included in the gastric juice. The composition of the main cells is enzymes that help to decompose food substances into simpler, more easily digestible ones. Pepsin, for example, breaks down proteins, and lipase breaks down fats.

Parietal cells are produced without which the necessary acidic environment cannot form in the stomach cavity. Its concentration does not exceed 0.5%. A huge role in digestion also belongs to hydrochloric acid. It is she who helps to soften many substances of the food lump, makes the enzymes of gastric juice active, and destroys microorganisms. Hydrochloric acid is involved in the formation of digestive hormones. It also stimulates the production of enzymes. Such a concept as "acidity" determines the amount of juice. She is not always the same. Acidity depends on how quickly the juice is released and whether it is neutralized by mucus, which has an alkaline reaction, its level changes with diseases of the digestive system.

Viscosity, which has gastric juice, gives it the mucus produced by additional cells. It makes the hydrochloric acid neutral, thereby reducing the juice. Also, this mucus promotes complete digestion. nutrients, protects the mucous membrane from irritation and damage.

In addition to the components listed above, gastric juice contains many inorganic and organic substances, including the Castle factor - a special substance, without which it is impossible to absorb vitamin B 12 in the small intestine, which is necessary for the full maturation of red blood cells in the bone marrow.

Gastric juice secreted in different time secretion, has an unequal power of digestion. This was established by IP Pavlov. He stated that secretion does not continue continuously: when the process of digestion does not occur, no juice is released into the stomach cavity. It is produced only in connection with the reception of food. The secretion of gastric juice can provoke not only food that has entered the stomach or tongue. Even the smell of her, talking about her is the reason for his formation.

Gastric juice may different composition and quantity in diseases of the liver, blood, stomach, gallbladder, intestines, etc. His study - essential method diagnostics used in modern medicine. It is carried out using a gastric tube, which is inserted directly into the stomach, sometimes on an empty stomach, sometimes after taking a preparatory breakfast, consisting of special irritants. The extracted content is then analyzed. Modern probes have sensors that respond to temperature, pressure and acidity in the organ.

The quality and quantity of it can also change under the influence of experiences, on nervous ground. Therefore, sometimes it is necessary to conduct repeated analyzes of gastric juice in order to clarify the diagnosis.

It is known that in medical practice it is used as medicinal product with diseases of the stomach, which are accompanied by insufficient secretion of juice or a small amount of hydrochloric acid in it. Use it only as directed by a doctor. The gastric juice prescribed for this purpose can be both natural and artificial.