Intestinal juice, its composition and significance. Digestion in the intestine

A food lump chewed and soaked in saliva, in which the chemical transformations of starch have partially begun, is directed to its root by movements of the tongue, and then swallowed. Further processing of food occurs in the stomach.

In the stomach, food lingers from 4 to 11 hours and is mainly subjected to chemical processing with the help of gastric juice. Gastric juice is produced by numerous glands that are located in its mucous membrane. About 100 gastric glands are located on each square millimeter of the mucosa.

There are three types of cells in the stomach: main- produce gastric enzymes lining- produce hydrochloric acid additional in which mucus is produced.

The capacity of the stomach changes with age. In the first month after birth, it reaches 90-100 ml (at birth, the capacity of the stomach is only 7 ml). Further increase in the capacity of the stomach is slow. By the end of the first year of life, it is 0.3 liters, at the age of 4 to 7 years - 0.9 liters, at 9-12 years old - about 1.5 liters. The capacity of the stomach of an adult is 2-2.5 liters.

The mucus produced by the cells of the gastric mucosa protects it from mechanical and chemical damage. Hydrochloric acid not only performs digestive function, but also has the ability to have a detrimental effect on bacteria that enter the stomach, that is, it performs a protective function.

Method for studying the secretion of gastric glands

The imposition of a gastric fistula on an animal makes it possible at any time to receive the contents of the stomach from the opening of the fistula tube. To do this, it is enough to open the animal under anesthesia abdominal cavity and through the incision in the wall of the stomach, insert a metal or plastic fistula tube(fig. 48) and strengthen it with seams. The second end of the fistula tube is left on the surface of the abdomen and closed with a cork outside the experiment. But in this case it is impossible to obtain pure gastric juice, since it is mixed in the stomach with food and saliva. Moreover, this method cannot study the features of the separation of gastric juice into different nutrients.

In an effort to avoid these shortcomings, I. P. Pavlov proposed to supplement the operation of applying a gastric fistula with a transection of the esophagus. During this operation, esophagotomy- the edges of the cut esophagus are sewn into the skin wound on the neck. A few days after such an operation, the animal can eat food for hours, but the food does not enter the stomach. At the same time, pure gastric juice flows from the fistula of the stomach (Fig. 49). This so-called imaginary feeding. With imaginary feeding, you can get large quantities pure gastric juice, which is used in medicinal purposes. The animal is fed with food that is introduced into the stomach through a fistula tube or poured into the lower esophagus. With imaginary feeding, pure gastric juice is obtained, it is possible to study its features and quantity when taken different food. However, this method does not make it possible to study gastric secretion when food is in the stomach.

I.P. Pavlov proposed a new operation - a small one was cut out of a large stomach isolated ventricle. The incision on the large stomach was made so as not to damage the nerves (Fig. 50). The edges of the cut flap are sutured, a small ventricle is formed, and sutures are also applied to the edges of the large stomach incision. As a result of the operation, two stomachs are created: a large one, in which food is digested in the usual way, and a small, isolated one, into which food never enters. But due to the fact that during the operation of isolating the ventricle, the nerves and blood supply are preserved in it, the nature of the secretion of juice in such a ventricle is the same as in the large stomach. And since food never enters the isolated ventricle (Fig. 51), the juice secreted by the glands of the small ventricle is clean, has no impurities, and it can be studied qualitative composition and quantity.

Composition and properties of gastric juice

To study the composition and properties of gastric juice, do the following experiments.

Experience 19

Buy natural gastric juice at the pharmacy. In case of its absence, you can use pepsin (yellowish powder), which can also be purchased at a pharmacy. Dissolve 1 g of pepsin in 500 ml of weak hydrochloric acid (0.2%).

Neutralize part of the gastric juice by adding a few drops of a 10% sodium hydroxide solution to it, shake it thoroughly and determine the reaction using litmus paper. It is necessary to achieve complete neutralization of the juice.

Prepare a solution egg white. To do this, take two raw chicken eggs, separate the protein from the yolk. Pour the whites into a glass and add 200 ml of water. Add half a teaspoon table salt(for better protein dissolution). Filter this cloudy liquid through thin layer cotton wool placed in a funnel. The liquid obtained after filtration is the protein solution.

Take six tubes, number them and pour 1-2 ml of protein solution into each tube. By heating each test tube over the flame of an alcohol bulb, you will get a coagulated protein. This forms white flakes of insoluble protein. Place all test tubes in a beaker with cold water. After 10-15 minutes, add 2-3 ml of water into test tube No. 1, and 2-3 ml of acidic gastric juice into test tube No. 2. Place both test tubes in a glass of water heated to 37-38°C. After 10 minutes, remove the test tubes from warm water and note what changes have occurred in them.

Now pour acidic gastric juice into test tube No. 3, pre-boiled gastric juice into test tube No. 4, and neutralized gastric juice into test tube No. 5. Place test tubes No. 3, 4, 5 in a glass of hot water (water temperature 37-38°C). Pour acidic gastric juice into test tube No. 6. Immerse this tube in a glass with ice, snow or cold water.

After 15-20 minutes, note what changes have occurred with the protein in test tubes, No. 3, 4, 5, 6.

Separation of gastric juice into various nutrients

Acidic gastric juice is separated by the glands of the stomach only during digestion. When the stomach is empty, its glands are at rest. The reaction of the contents of the stomach outside of digestion is alkaline, which is due to the release of mucus of an alkaline reaction.

The separation of gastric juice begins a few minutes after eating and lasts for hours. The quantity and composition of digestive juices depend on the nature of the food, its chemical composition(Fig. 52).

Meat consists mainly of proteins, bread mainly of carbohydrates, milk contains a significant amount of proteins, fats and carbohydrates. Accordingly, meat is allocated for 7-8 hours the largest number juice, sour and with a significant content of enzymes. Less juice is separated on bread than on meat, the duration of juice secretion is 10-11 hours. The juice separated on bread is rich in enzymes. Juice secretion to milk lasts 6 hours, the largest amount of juice is separated in the 3rd and 4th hours. Inhibition of juice secretion to milk in the first hours is associated with the presence of fat. Fatty food suppresses gastric secretion, and the digestive power of gastric juice decreases. Rational combination of various food products allows you to maintain enough high level juice secretion for a long time.

Mechanism of secretion of gastric juice

In order for the gastric juice to begin to separate, it is not at all necessary that food enter the stomach; it is enough that it enters the oral cavity. This can best be seen when imaginary feeding the dog.

The separation of gastric juice in response to irritation of the taste buds of the oral cavity occurs reflexively. It's innate unconditioned reflex. Food entering the oral cavity irritates the endings of the taste nerves located in the mucous membrane of the mouth and on the tongue. The excitation that has arisen here is carried to the medulla oblongata, from where it reaches the gastric glands through the secretory nerves, and although food does not enter the stomach during imaginary feeding, pure gastric juice flows from the stomach through the opening of the fistula tube.

The secretory nerve for the gastric glands is the vagus nerve. If the vagus nerves are cut, then imaginary feeding will no longer cause the separation of gastric juice.

Sympathetic fibers also approach the gastric glands. Irritation in special conditions the end of the cut sympathetic nerve causes a slight secretion of juice. However, sympathetic nerves great importance in the regulation of the accumulation of enzymes in the secretory cells of the stomach.

Only the integrity of both nerves - both the vagus and the sympathetic - ensures normal sap secretion.

The separation of gastric juice begins not only when food irritates the receptors of the oral cavity. Cooking, talking about food, the sight and smell of it cause the secretion of acidic, enzyme-rich gastric juice. This occurs as a result of the implementation of a conditioned reflex to food. Thanks to conditioned reflexes, the juice begins to separate some time before the start of the meal. I. P. Pavlov called this juice appetizing or fuse. Appetizing juice prepares the stomach in advance for the digestion of food and is important condition its normal operation.

Usually the act of eating always begins with the action of the sight and smell of food, conditioned stimuli for the gastric glands. The food that follows this into the oral cavity acts as an unconditioned stimulus, stimulating the taste buds of the oral mucosa.

The secretion of juice caused by the act of eating is complex reflex phase gastric secretion. It is called complex reflex because during this phase, gastric juice is separated due to a complex of unconditioned and conditioned reflexes.

Under the influence of various influences, gastric secretion can be inhibited. It is necessary for the dog to show the cat while eating, how the separation of gastric juice stops in her. Kind of stale food bad smell its sloppy environment, reading while eating lead to inhibition of gastric secretion, which reduces the digestive effect of juices and food is absorbed worse.

The complex reflex separation of gastric juice lasts only 1.5-2 hours. The total duration of gastric secretion is 6-10 hours after a meal. Consequently, the complex reflex phase cannot explain all the regularities in the separation of gastric juice. However, this phase is the starting one and largely determines the nature of further juice separation.

When food enters the stomach, gastric juice continues to be released onto it as long as there is digestible food in the stomach. Due to what mechanisms is gastric juice now separated?

The food that enters the stomach mechanically irritates the receptors located in the gastric mucosa, the excitation is transmitted to the central nervous system and from there it reaches the gastric glands along the vagus nerves. If the vagus nerves are cut, then the mechanical irritation of the walls of the stomach no longer causes juice secretion.

Experiments on dogs, as well as observations on humans in a laboratory led by K. M. Bykov, showed that mechanical irritation of the stomach wall in a dog with pieces of rubber, glass beads, and in a person with a rubber balloon introduced into the stomach cavity can cause quite a strong secretion of juice. In humans, the separation of gastric juice with mechanical irritation of the stomach wall begins after 5-10 minutes, in dogs - a little later. The separation of gastric juice during mechanical irritation of the gastric mucosa is a reflex process, regulated by the nervous system.

Bykov Konstantin Mikhailovich (1886-1959) - a prominent Soviet physiologist, student and collaborator of I.P. Pavlov. Known for his work in the field of physiology and pathology of digestion. He developed a method for obtaining pure gastric juice from a person. K. M. Bykov - the author of the doctrine of the regulatory influence of the cerebral cortex on the work of internal organs.

But not only due to mechanical irritation of the walls of the stomach, juice is separated when food is in the stomach. An important role here belongs to the chemicals circulating in the blood during digestion and humorally stimulating gastric secretion. If a dog is fed meat or milk and at the height of secretion, 200 ml of blood is taken from it and transfused to another dog whose gastric glands are at rest, then after the introduction of blood, the second dog will begin to separate gastric juice. This can be understood as follows: into the blood during digestion from gastrointestinal tract chemicals, products of digestion. They are carried by the blood to the glands of the stomach and stimulate their activity. Particularly active in this regard are the substances contained in meat broth, cabbage broth, decoctions of fish, mushrooms, vegetables.

In addition, under the influence of hydrochloric acid or digestion products in the gastric mucosa, special hormone - gastrin, which is absorbed into the blood and enhances the secretion of the gastric glands.

Separation of gastric juice due to mechanical irritation of the gastric mucosa, as well as due to chemical substances absorbed from the stomach into the blood is neurohumoral phase secretions.

Both phases of gastric secretion - complex reflex and neurohumoral - are interconnected. Thus, the abundant separation of gastric juice in the complex reflex phase leads to accelerated formation and absorption of gastrin, which, in turn, causes an increase in the neurohumoral phase of secretion.

Passage of food from stomach to duodenum

In the stomach, food is also mechanically processed. In the thickness of the walls of the stomach there are smooth muscles, the fibers of which go in three directions: longitudinal, oblique and circular. Contractions of the muscles of the stomach contribute to better mixing of food with digestive juice, and also contribute to the movement of food from the stomach to the intestines.

The contents of the stomach in the form of a food slurry soaked in gastric juice, by movements of the muscles of the stomach, moves to the outlet part of it, which is called pyloric department. On the border of the pyloric part of the stomach and duodenum the circular muscle is located - the constrictor - sphincter. Hydrochloric acid, which is part of the gastric contents, reflexively causes relaxation of the pyloric sphincter; only after that does a portion of the acidic food slurry pass into the duodenum (Fig. 53). Entering the duodenum, hydrochloric acid causes a reflex contraction of the sphincter, therefore, after a portion of gastric contents passes into the intestine, its further intake is delayed for a while. When the food slurry that has entered the intestine is neutralized by the contents of the duodenum, which have alkaline reaction, the sphincter opens and the next portion of food gruel passes from the stomach into the intestine.

Thus, the transition of food gruel from the stomach to the intestines is done in portions, gradually. It contributes better processing digestive juices from the contents of the stomach and intestines.

Instruction

The main component of gastric juice is hydrochloric acid. It also includes inorganic (chlorides, bicarbonates, sodium, potassium, phosphates, magnesium, sulfates) and organic substances (proteolytic enzymes). regulation secretory function gastric glands carry out nervous and humoral mechanisms. The process of synthesis of gastric juice is conditionally divided into 3 phases: cephalic (complex reflex), gastric, intestinal.

During the complex reflex phase, the gastric glands are excited by irritation of the olfactory, visual, auditory receptors by the sight and smell of the dish, the perception of the situation associated with eating. Such influences are superimposed by irritation of the receptors of the oral cavity, the esophagus in the process of chewing and swallowing food. As a result, the secretory activity of the gastric glands is launched. Juice that is released under the influence of the type and smell of food, in the process of chewing and swallowing, is called "appetizing" or "fire", it has a high acidity and high proteolytic activity. In this case, the stomach becomes prepared for eating.

The 2nd gastric phase is superimposed on the complex reflex phase of secretion. The vagus nerve and intramural local reflexes take part in its regulation. In this phase, the secretion of juice is associated with a reflex response to the effects of mechanical and chemical irritants on the gastric mucosa. Irritation of the receptors of the gastric mucosa promotes the release of gastrin, which is the most powerful of cell stimulants. At the same time, the content of histamine in the mucous membrane increases, this substance is a key stimulator of the production of hydrochloric acid.

The intestinal phase of secretion of gastric juice occurs when food passes from the stomach to the intestines. The amount of secretion released during this period is no more than 10% of the total volume of gastric juice, it increases in initial period and then starts to decrease. As the duodenum fills up, secretory activity continues to decrease under the influence of peptides that are secreted by the endocrine gastrointestinal glands.

The most effective causative agent of the secretion of gastric juice is protein food. Prolonged leads to an increase in the amount of secretion in response to other food stimuli, as well as an increase in acidity and an increase in the digestive activity of gastric juice. carbohydrate food(for example, bread) is the weakest stimulant of secretion. Among the non-nutritional factors that increase the secretory activity of the gastric glands, the greatest role play stress, rage, irritation. The oppressive influence is longing, fear, depressive states.

Sore throat is a symptom of many various diseases associated not only with the respiratory tract, but also with other human systems and organs, for example, with the stomach. With gastro-food reflux - the reflux of gastric juice into the esophagus - the mucous membranes in the throat are irritated, causing pain. Competent ENT doctors quickly recognize this condition and send patients to be treated by a gastroenterologist.

A sore throat primarily raises suspicions of respiratory diseases. But in some cases, this can be a symptom of a completely different disease associated, for example, with the gastrointestinal tract - this is gastroesophageal reflux.

It seems strange, but in the human body everything is interconnected, and digestive problems can really lead to painful sensations in the throat.

gastrointestinal reflux

If the baby does not get used to the regimen, feed him, however, try to approximately observe 3-hour (or more) intervals between meals. Otherwise, excess breast milk in the gastrointestinal tract can cause bloating and colic.

During breastfeeding child do not be distracted by conversations and TV. Indeed, at this moment there is an invisible contact between the mother and the baby, which forms a close bond. Indifference to the process of feeding or haste can adversely affect the nervous system of the crumbs.

Artificial feeding is essential. From the days, if there is no donor milk, the child is given 40-90 g of an adapted mixture, after 6-8 days the portion is increased to 50-100. The number of feedings is 6 times with an interval of 3.5 hours. This in between is associated with a longer retention of the mixture in the digestive tract.

Advice 4: How to choose the composition of water for the treatment of diseases of the gastrointestinal tract

Water, saturated with mineral salts and ions, is one of the best medicines for various diseases, including diseases of the gastrointestinal tract. But one must also take into account the fact that different mineral water differently affect the work of this body.

Instruction

Water saturated with bicarbonate ions and sodium cations reduces the internal environment

They differ in variety, however, the function of absorption of the liquid and the components dissolved in it is especially distinguished. glands small intestine 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, throughout inner surface small intestine, there are 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 for the formation of intestinal juice, dead cells glands.

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 fixing enzymes on the surface of the small intestine.
• The role of bile accounts for the function of an important stimulant of pancreatic secretion, juice 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.

1. Abdominal digestion.

On the this stage there is an effect on food that has passed pre-processing 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.

1. 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.

1. 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.

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 plastic material and energetic. 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., promotion of “food mass through the alimentary canal, absorption nutrients and water into the circulatory 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 at the mouth and includes the oral cavity, esophagus, stomach, small and colon which ends at 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, so they break down great amount 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 in the lymphoid tissue of the appendix, which contain T- and B-lymphocytes.

DIGESTION IN THE MOUTH. FUNCTIONS OF THE SALIVARY GLANDS

In the mouth, the taste properties of food are analyzed, protection digestive tract 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 food bolus, irritation of receptors with subsequent stimulation of the activity of not only the glands of the oral cavity, but also the digestive glands of the stomach, pancreas, liver, 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 taste, thermo- and mechanoreceptors of the oral cavity are transmitted to the center of salivation of the medulla oblongata, where 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. Upon activation of the parasympathetic nerve salivary gland more volume is released liquid saliva, with activation of the sympathetic - 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, an assessment is made palatability food. 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 - 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 - the bottom (or arch), the middle the largest part- the body of the stomach and the lower, - the antral part, ending with the pyloric sphincter, or pylorus, (the opening of the pylorus leads to the duodenum).

The wall of the stomach consists of three layers: external - serous, middle - muscular and internal - mucous. Contractions of the stomach muscles 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, necessary for the formation of red blood cells, the so-called external factor Castle. But it can be absorbed into the blood only if it is present in the stomach. internal factor Castle. 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 decreased secretion gastric juice, as a rule, are 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. Wherein conditioned reflexes, arising from the sight, smell of food, environment, are combined with unconditional, arising from 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 arise 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: duodenal, skinny 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 end 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 digestive enzymes 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. Suction is physiological process transfer of substances from the lumen of the alimentary canal into the blood and lymph. Total The 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).

The mouth absorbs some water, glucose, and some medications. Water, alcohol, some salts and monosaccharides are absorbed in the stomach. The main section of the gastrointestinal tract, where salts, vitamins and nutrients are absorbed, is the small intestine. The high absorption rate is ensured by the presence of folds along its entire length, as a result of which the absorption surface increases three times, as well as the presence of villi on the epithelial cells, due to which the absorption surface increases by 600 times. Inside each 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 nerve plexuses 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. The bile contains bile acids, bile pigments, cholesterol, 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 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 detoxifies harmful substances, which entered the body from the outside or formed during the digestion of food, due 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. AT exocrine department(80% of the total volume of the pancreas) pancreatic juice is produced, which contains digestive enzymes, water, bicarbonates, electrolytes, and according to special excretory ducts enters the duodenum synchronously with the release of bile, since they have a common sphincter with the duct of the gallbladder.

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, activates 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 bottom wall caecum comes out appendix(appendix), 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).

Contractions of the large intestine 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 rich food 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. Protective function bacteria is that 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 to pathogenic microbes and inhibit their reproduction. The activity of the intestinal microflora can be disturbed after long-term use antibiotics, as a result of which bacteria die, but yeasts 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 neural mechanisms play an essential 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 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 the 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 individual life and arise by 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.

an important role in the regulation secretory processes hormones play in the digestive system, which are produced by cells located in various departments 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 is formed in the accessory 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 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.

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Appetite is a feeling of need for food, which is formed as a result of excitation of neurons in the cerebral cortex and the 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). Prolonged conscious restriction of food intake can lead not only to metabolic disorders, but also to pathological changes appetite up to complete failure from food. published

Gastric juice- complex composition digestive juice, generated various cells mucous membrane of the stomach. Pure gastric juice is a colorless, odorless, slightly opalescent liquid with suspended mucus lumps. Contains hydrochloric (hydrochloric) acid, enzymes (pepsin, gastrixin), gastrin hormone, soluble and insoluble mucus, minerals (sodium, potassium and ammonium chlorides, phosphates, sulfates), traces of organic compounds (lactic and acetic acid, as well as urea, glucose, etc.). Has an acid reaction.

The main components of gastric juice: - Hydrochloric acid

Parietal cells of the fundic (synonymous with the main) glands of the stomach secrete hydrochloric acid, the most important component of gastric juice. Its main functions: maintaining a certain level of acidity in the stomach, which ensures the conversion of pepsinogen into pepsin, preventing penetration into the body pathogenic bacteria and microbes, contributing to the swelling of the protein components of food, preparing it for hydrolysis. Hydrochloric acid produced by parietal cells has a constant concentration of 160 mmol/L.

Bicarbonates

HCO3 bicarbonates - necessary to neutralize hydrochloric acid at the surface of the gastric and duodenal mucosa in order to protect the mucosa from acid exposure. Produced by superficial accessory (mucoid) cells. The concentration of bicarbonates in gastric juice is 45 mmol/l.

Pepsinogen and pepsin

Pepsin is the main enzyme that breaks down proteins. There are several isoforms of pepsin, each of which affects a different class of proteins. Pepsins are obtained from pepsinogens when the latter enter an environment with a certain acidity. The main cells of the fundic glands are responsible for the production of pepsinogens in the stomach.

Slime

Slime - the most important factor protection of the gastric mucosa. The mucus forms an immiscible gel layer, about 0.6 mm thick, concentrating bicarbonates that neutralize acid and thus protect the mucosa from the damaging effects of hydrochloric acid and pepsin. Produced by superficial accessory cells.

Castle's intrinsic factor

Intrinsic factor Castle is an enzyme that converts the inactive form of vitamin B12, supplied with food, into an active, digestible form. It is secreted by the parietal cells of the fundic glands of the stomach.

The chemical composition of gastric juice

The main chemical components of gastric juice: - water (995 g/l); - chlorides (5-6 g/l); - sulfates (10 mg/l); - phosphates (10-60 mg/l); - bicarbonates (0-1.2 g/l) of sodium, potassium, calcium, magnesium; - ammonia (20-80 mg/l).

Volume of production of gastric juice

About 2 liters of gastric juice is produced in the stomach of an adult per day. Basal (that is, at rest, not stimulated by food, chemical stimulants, etc.) secretion in men is (in women, 25-30% less): - gastric juice - 80-100 ml / h; - hydrochloric acid - 2.5-5.0 mmol/h; - pepsin - 20-35 mg/h. The maximum production of hydrochloric acid in men is 22-29 mmol / h, in women - 16-21 mmol / h.

Physical properties of gastric juice

Gastric juice is practically colorless and odorless. Greenish or yellowish color indicates the presence of bile impurities and pathological duodenogastric reflux. The red or brown hue may be due to blood impurities. Unpleasant putrid smell usually a consequence serious problems with the evacuation of gastric contents into the intestines. Normally, gastric juice contains only a small amount of mucus. A noticeable amount of mucus in the gastric juice indicates inflammation of the gastric mucosa.

Examination of gastric juice

The study of the acidity of gastric juice is carried out using intragastric pH-metry. Fractional probing, which was previously common, during which gastric juice was previously pumped out with a gastric or duodenal probe, today has no more than historical significance. A decrease in the content and especially the absence of hydrochloric acid in the gastric juice (achilia, hypochlorhydria) indicates, as a rule, the presence of chronic gastritis. A decrease in gastric secretion, especially hydrochloric acid, is characteristic of gastric cancer.

For duodenal ulcer ( peptic ulcer) there is an increase in the secretory activity of the gastric glands, the formation of hydrochloric acid is most enhanced. The amount and composition of gastric juice can change in diseases of the heart, lungs, skin, endocrine diseases (diabetes, thyrotoxicosis), diseases hematopoietic system. Yes, for pernicious anemia characteristically complete absence secretion of hydrochloric acid. An increase in the secretion of gastric juice can be observed in individuals with increased excitability of the parasympathetic part of the autonomic nervous system, with prolonged smoking.