The role of pancreatic juice in digestion. Gastric Juice Where is Digestive Juice Made?

intestinal juice- It is a colorless liquid, slightly alkaline, containing about 3% dry matter.

Secretion of intestinal juice

Throughout the intestine, starting from the pyloric opening, there are many small glands of various types that secrete intestinal juice. Some of them of the alveolar structure - Brunner's glands - are located only in the duodenum, others - tubular Lieberkün - throughout the intestine.

During starvation, intestinal juice is secreted a little, while eating, the secretion of juice increases. Particularly increases the separation of juice with mechanical irritation of the intestinal walls with food. Intestinal juice secretion also increases under the influence of certain chemicals: products of food digestion, extracts from certain organs.

Composition of intestinal juice

In the intestinal juice there are enzymes that decompose all nutrients: into carbohydrates - amylase, invertase, lactase, maltase, phosphatase; on proteins - erepsin; for fats - lipase.

Erepsin

The protein enzyme erepsin turned out to be a complex of various peptidases. It quickly and completely decomposes protein products formed under the action of pepsin and trypsin.

Lipase

Intestinal juice lipase breaks down fats in a general way.

carbohydrate enzymes

The amount of carbohydrate enzymes in the intestinal juice depends on the type of food. This indicates that the composition of food affects the activity of cells that produce enzymes. So, for example, with food devoid of milk, there is no lactase in the intestinal juice, but it appears in it when fed with milk. In suckers, lactase is a constant component of the intestinal juice, gradually disappearing when the animal passes to another kind of food. The same was noted for the enzyme invertase, which decomposes cane sugar. Intestinal amylase and maltase are always present in the intestinal juice. material from the site

Intestinal juice can be obtained from a Tiri Vell fistula. For its formation, a segment of the intestine is isolated, which maintains a vascular and nervous connection with the rest of the intestine through the mesentery. Both ends of this segment are sutured into the skin wound, and the integrity of the intestine is restored by suturing (Fig. 26). However, only the sap of the Lieberkühn glands can be obtained from the Tiri-Vell fistula, since the Brunner glands take up so little space (in the dog) that it is impossible to make a separate fistula to obtain pure Brunner sap.

Gastric juice is a complex digestive juice produced by the gastric mucosa. Everyone knows that food enters the stomach through the mouth. Next comes the process of its processing. Mechanical processing of food is provided by the motor activity of the stomach, and chemical processing is carried out due to the enzymes of gastric juice. After the chemical processing of food has been completed, liquid or semi-liquid chyme is formed along with gastric juice mixed with it.

The stomach performs the following functions: motor, secretory, absorptive excretory and endocrine. The gastric juice of a healthy person is colorless and almost odorless. Its yellowish or green color indicates that the juice contains impurities of bile and pathological doudenogastric reflux. If brown or red color prevails, then this indicates the presence of blood clots in it. An unpleasant and rotten smell indicates that there are serious problems with the evacuation of gastric contents into the duodenum. A healthy person should always have a small amount of mucus. Noticeable excesses in gastric juice tell us about inflammation of the gastric mucosa.

With a healthy lifestyle, there is no lactic acid in the gastric juice. In general, it is formed in the body during pathological processes, such as: pyloric stenosis with a delay in the evacuation of food from the stomach, the absence of hydrochloric acid, a cancerous process, etc. You should also know that the body of an adult should contain about two liters of gastric juice.

Composition of gastric juice

Gastric juice is acidic. It consists of dry residue in the amount of 1% and 99% water. The dry residue is represented by organic and inorganic substances.

The main component of gastric juice is hydrochloric acid, which is associated with proteins.

Hydrochloric acid performs several functions:

activates pepsinogens and converts to pepsins;
promotes denaturation and swelling of proteins in the stomach;
contributes to the favorable evacuation of food from the stomach;
excites pancreatic secretion.

In addition to all this, the composition of gastric juice includes inorganic substances, such as: bicarbonates, chlorides, sodium, potassium, phosphates, sulfates, magnesium, etc. Organic substances include proteolytic enzymes, which play a major role among pepsins. Under the influence of hydrochloric acid, they are activated. Gastric juice also contains non-proteolytic enzymes. Gastric lipase is inactive and breaks down only emulsified fats. Hydrolysis of carbohydrates continues in the stomach under the influence of salivary enzymes. The composition of organic substances includes lysozyme, which provides the bacterial property of gastric juice. Gastric mucus contains mucin, which protects the gastric mucosa from chemical and mechanical irritations from self-digestion. Due to this, gastromucoprotein is produced. It is also called nothing more than the “Castle internal factor”. Only in its presence is it possible to form a complex with vitamin B12, which is involved in erythropoiesis. Gastric juice contains urea, amino acids and uric acid.

The composition of gastric juice must be known not only to doctors and other specialists, but also to ordinary people. Nowadays, diseases of the stomach are quite common, which occur as a result of malnutrition and lifestyle. If you are faced with one of them, then be sure to go to the clinic for a consultation.

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 cavity 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 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 transparent 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 lump of food, 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 contributes to the complete digestion of 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 at different times of secretion, has an unequal digestion power. 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 secreted 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 can have a different composition and quantity in diseases of the liver, blood, stomach, gallbladder, intestines, etc. Its study is the most important diagnostic method 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 a nervous basis. 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 a medicine for 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.

Stomach is a sac-like extension of the digestive tract. Its projection on the anterior surface of the abdominal wall corresponds to the epigastric region and partially extends into the left hypochondrium. In the stomach, the following sections are distinguished: the upper - the bottom, the large central - the body, the lower distal - the 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 the amount of 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 are 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. The 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 various types of 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 egg protein hydrolysis. 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 less important role in the process of gastric digestion and breaks down mainly gelatin. The ability of gastric juice enzymes to break down proteins at different values 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 a protein contained in the 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.

The composition of gastric juice also includes 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). In 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 the red bone marrow, namely for the proper maturation of precursor cells of red blood cells.

The lack of vitamin B 12 in the internal environment of the body, associated with a violation of its absorption due to a lack of internal factor Castle, is observed when part of the stomach is removed, atrophic gastritis and leads to the development of a serious disease - B 12 deficiency 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 a high content of 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 by conditioned reflexes that accompany food intake). 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 the 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 of the vagus nerves, nerve impulses reach the gastric mucosa and excite 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 the lining marks of the stomach, providing 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 of 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.

With prolonged use of predominantly carbohydrate foods (bread, vegetables), the secretion of gastric juice decreases, with the use of food 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 of the secretory function of the 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 spices.

Intestinal phase of gastric secretion- stimulation of secretion, which occurs when contents from the stomach enter the intestine, is determined by reflex influences that occur when the receptors of the duodenum are irritated, and by humoral influences caused by the absorbed products of food breakdown. 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 intestinal mechano- and chemoreceptors 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 of the digestive tract wall, 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. Meat broth, cabbage broth, various chemicals (synthetic analog of gastrin pentagastrin or histamine) are used as stimulants.

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. In a 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 with 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. With the contraction of the smooth muscles of 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 is reduced. 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 affected by the physicochemical properties of food. Food containing carbohydrates leaves the stomach the fastest, then protein food, while fatty foods stay in the stomach for a longer 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 cause an increase in motor activity of the 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 a defensive reaction, with the help of which the body is freed from toxic and poisonous substances that have entered the 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 the receptors of the mucous membrane of the root of the tongue, pharynx, stomach, and 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 of the vestibular apparatus (during driving, sea travel), under the action of certain medicinal substances on the vomiting center.