Digestion. Nervous and humoral regulation of gastric juice secretion The separation of digestive juices is regulated by the mechanism

Food intolerance due to a deficiency of digestive enzymes This type of food intolerance is especially common among gastroenterologists. Deficiency of digestive proteolytic enzymes and hydrochloric acid develops in patients with diseases

Operations and Dressing Department (OBO) The OBO is deployed by the forces of an operating and dressing platoon, has 5 surgeons on its staff. In the department, in addition to qualified surgical care, they are carried out in close cooperation with the department of anesthesiology and resuscitation

Department of Anesthesiology and Resuscitation The department is designed to bring the wounded out of shock, prepare them for surgery or evacuation to the hospital base. In the conditions of OMedb, recovery from shock should be complete and final and is carried out in all the wounded,

During the day, up to 5-6 liters of digestive juices are secreted into the gastrointestinal tract of a person. Saliva - 1 liter, gastric juice - 1.5 - 2, bile - 0.75 - 1, pancreatic juice - 0.7 - 0.8, intestinal juice - 2 liters. Only about 150 milliliters are excreted out of the intestines! All this mass of the aqueous solution is absorbed, as indicated in the "Large Intestine" section. If the absorption process is disturbed in it, loose stools appear.

Each section of the gastrointestinal tract, as we now know, performs its own unique function. These departments are isolated from each other by special valves. This isolation is necessary, since each section has its own pH of the medium. Thus, the pH of the environment in the oral cavity is alkaline, in the stomach it is acidic (outside the period of digestion, mucus of a neutral or slightly alkaline reaction is separated), in the duodenum during digestion it is neutral, bile and pancreatic juice, which have an alkaline reaction, are also secreted here to neutralize acidity coming from the stomach. In the period between meals, the medium in the small intestine is slightly alkaline, and in the large intestine it is slightly acidic.

In each of the departments, the time spent by food is also specific. Depending on the type, food is in the mouth from a few seconds to minutes, in the stomach from 2 to 4 hours, in the small intestine 4 - 5, and in the large intestine - 12 - 18 hours.

The occupancy of the gastrointestinal tract by microorganisms is also different and specific. So, in the oral cavity there are a large number of microorganisms, in the stomach there are very few of them, in the small intestine during the period when there is no food, they are few, during the period of digestion they multiply rapidly, in the large intestine they are present in enormous quantities.

In general, the very activity of bacteria in the small and large intestines is interconnected. The microflora is distributed both along the intestine and from the center of the intestine to the wall. That is, one type of microorganisms lives in the center of the intestinal cavity, and another near the wall; one species lives in the region of the duodenum, another species lives in the lean one, a third one even lower, and so on.

In addition, we must remember that the intestinal microflora must be strictly

specific, because it was developed and fixed during evolution.

Thus, digestive juices, microorganisms and food create an enteral (internal) environment in the body, which is part of the human ecology. The enteral environment of the body is something in between (buffer environment) between the external (air, soil - that is, what surrounds us) and internal (blood, interstitial fluid) environments.

From the above, it becomes obvious that both the buffer and the internal environment of the body primarily depend on the incoming food (external environment).

Now it is necessary to consider other important features that occur during digestion depending on various kinds of food.

SYMBIOUS DIGESTION

In the previous sections, we have already discussed the role of bacteria inhabiting

gastrointestinal tract during digestion. Let's consider this question in more detail.

According to the views of the recent past, the bacterial flora was considered undesirable and, to a certain extent, harmful. But the studies of academician A.M. Ugolev and other scientists established the opposite - the bacterial flora is not only not harmful, but also necessary for the normal development of the physiological functions of the body.

As a result of evolution, a symbiotic relationship has developed between

the host organism and the bacteria inhabiting its gastrointestinal tract. Between them, there is an exchange of metabolites (waste products), which include nutrients, various inorganic components, stimulants, inhibitors, hormones and other physiologically active substances. The bacterial flora serves as a kind of trophostat - it provides the necessary nutritional ratio of substances in the gastrointestinal tract, destroying some of the excess food components and forming the missing products. Not without reason, in some animals (mainly herbivores), the mass of bacterial flora can be 1/7 of the animal's body weight.

The flow of bacterial metabolites consists of several components:

1 - nutrients modified by microflora;

2 - waste products of bacteria;

3 - ballast substances modified by bacterial flora;

4 - consumption of the bacterial flora itself by the host organism.

These four streams have:

1. Useful substances (vitamins, essential amino acids, etc.).

2. Substances that are currently considered neither useful nor harmful to the body (indifferent) in the development of science.

3. Toxic substances.

Comparison of non-microbial animals with those inhabited by normal microflora showed that non-microbial animals have a number of defects and should be characterized as inferior.

Therefore, maintaining a normal bacterial flora in the body becomes one of the main tasks of optimizing nutrition, optimizing people's lives.

Currently, dysbacterioses are the cause of many diseases and affect almost everyone.

OTHER CHARACTERISTICS OF THE DIGESTIVE SYSTEM

The initial nutritional efficiency of the human body can be judged

according to this fact: each intestinal cell is able to provide food substances (plastic and energy) to 103 - 105 other cells of the body.

The normal functioning of the gastrointestinal tract is associated with

its continuous regeneration. In it, the epithelium is most rapidly exfoliated. Thus, the renewal time of the duodenal epithelium is 1.8 days, 2.3% per hour; skinny - 3 days, 1.5% per hour; thin 3 - 6 days, 1.4 - 0.7% per hour. The glycocalyx is updated most quickly - in 4 - 10 hours. This renewal of the glycocalyx creates the effect of constant cleaning of the pores of the brush border. Hence, frequent meals, perhaps, exfoliate the intestinal epithelium faster. In general, the time for complete renewal of the intestinal epithelium in humans ranges from 6 to 14 days.

Here, in particular, is one of the answers to the question: why abstinence from food for the above period contributes to scarring of ulcers of the gastrointestinal tract.

Now, knowing the "technology" of the gastrointestinal tract, we should act in accordance with it. And if there were deviations before, then they will gradually level out, and then the gastrointestinal tract will work normally. So here are some practical tips:

Consume fluids before meals.

From the section on enzymes, we know that digestive juices containing them are excreted on food. If you drink any liquid (milk, compote, just water, etc.), then dilute and wash these enzymes into the lower parts of the gastrointestinal tract. As a result, food will lie in the stomach until the body synthesizes and secretes new ones, or slips unprocessed by gastric juices into the underlying sections, where it undergoes decay and bacterial decomposition, followed by absorption of these products into the bloodstream. Your vitality will be spent on synthesizing an additional portion of enzymes and on neutralizing the products of decay from undigested food. There is an overstrain of the secretory apparatus of the stomach, duodenum. Instead of the normal 700 - 800 milliliters of gastric juice with a concentration of 0.4 - 0.5 percent. hydrochloric acid you will need to secrete 1.5 - 2 times more! Therefore, over time, indigestion, low acidity, gastritis and other disorders develop in the stomach.

In addition, the liquid quickly passes into the following departments, which perform their function and have their own pH of the medium. This environment also changes arbitrarily, the protective layer of mucus is washed off, and now there is an ulcerative process in the duodenum and other disorders in this department.

DRINK LIQUIDS (water, juices, compote, tea, etc.) BEFORE MEAL, FOR 10 - 15 MINUTES.

Do not drink anything for an hour or two after eating. Depending on the type of food is in the stomach 2 - 3 hours, and in the small intestine 4 - 5 hours. After about 2 to 4 hours, the digestive process is only gaining momentum in the small intestine. Digestion and absorption of nutrients occurs in certain areas of the small intestine.

The drunk liquid will instantly slip through the stomach and not only dilute the digestive juices of the small intestine, but also wash away the nutrients past the “fields” of their assimilation. As a result, you will again get nothing, but you will feed the putrefactive bacteria.

The pancreas, liver, as well as the glands located in the very small intestine, will be forced to synthesize a new portion of the secret, depleting the body's resources and overstraining at the same time.

AFTER CARBOHYDRATE FOOD (cereals, bread, etc.) YOU CAN DRINK AFTER 3 HOURS, AND AFTER PROTEIN FOOD (meat, fish, etc.) - AFTER 4 - 5 HOURS.

If there is (especially at the beginning of the transition to proper nutrition) an acute desire to quench your thirst, then rinse your mouth and do 2-3

small throat. With the transition to proper nutrition, you will no longer be thirsty.

Chew food thoroughly.

This makes it possible to drive blood through the salivary glands, cleanse

it from toxins and other unnecessary substances. The enzyme lysozyme neutralizes their harmful effects.

The high alkalinity of saliva contributes to maintaining the normal acid-base balance of the body.

The act of chewing increases peristalsis. If the food is poorly ground, then

both abdominal and parietal digestion suffer from this, and in the large intestine these large food particles become available to microorganisms, rot and form "blockages" of fecal stones.

In general, the ancient sages already noticed the effect of fluid intake. Here is what is written in "Chzhud-shih": "If you drink before meals, during meals and after, then the body will be normal, respectively, it will become obese or lose weight." CHEW THOROUGHLY AND DO NOT DRINK ANYTHING.

Do not eat when emotionally abnormal.

Fatigue, pain, fear, grief, anxiety, depression, anger, inflammation, fever, etc. lead to the fact that the digestive juices cease to stand out and the normal movement (peristalsis) of the digestive tract slows down or stops altogether. Earlier it was pointed out that the secretion of juice in the stomach refers to easily inhibited acts. In addition, during emotional outbursts, adrenaline is released, which causes polarization of membranes on the digestive cells of the thin

intestines, and this turns off our porous "catalyst" - the glycocalyx. Food taken in this state is not digested, rots, ferments - hence diarrhea or a feeling of discomfort.

Based on this, adhere to the following recommendations:

a) jokes, laughter at the table contribute to relaxation and calm.

May peace and joy reign at the table. This should be the main rule in life. After all, at this time you are building your body and health;

b) if you experience pain, fever, inflammation, then skip meals - skip as many meals as necessary for this condition to pass;

c) if you experience emotional stress - skip one or more meals until you calm down;

d) if you are tired, then rest a little before eating. There is nothing better than a little rest or relaxation to restore the vitality of a tired person.

Do not take too cold and too hot food, as well as unfamiliar and unusual in large quantities.

Digestive enzymes are active only at our body temperature. If the food is cold or hot, then they will begin their full effect only when the food becomes normal, i.e. takes on body temperature. It is especially harmful to eat cold dishes and drinks: they “extinguish” the digestive “fire”.

TAKE FOOD AND DRINKS WITH A MODERATE TEMPERATURE.

In our body, there are certain mechanisms of adaptation to food. Depending on the composition of food, the zones of adsorption (absorption) of carbohydrates, proteins, fats and other substances can become larger or smaller.

The most important element in the adaptation of the intestine to the peculiarities of nutrition should be considered a change in the set and properties of enzymes that carry out parietal digestion.

Changes in the structure of the villi, the ultrastructure of the microvilli, and their mutual arrangement in the brush border are important for adapting intestinal functions to various nutritional conditions.

The composition of the intestinal microflora also changes depending on the diet.

Depending on the composition of food, the set of hormones changes dramatically, and, therefore, significant adaptive restructuring of digestive processes is possible already at the level of the intestinal hormonal system (CHS).

The secretory elements of CGS are controlled by both chyme components and blood components (those that are mainly dependent on food).

The restructuring of the CGS affects the nervous system due to feedback, restructuring it. As a result, a person gradually develops natural taste and nutritional needs; body functions are normalized and there is a general recovery.

In addition, it is possible to change and actually changes the character of a person. Already in ancient times, the Hindus, Chinese and other peoples paid attention to this and successfully used food to exert the necessary influence on the character of a person.

INTRODUCING UNFAMILIAR FOOD GRADUALLY

AND INCREASE IT LITTLE LITTLE. This rule is especially important to observe when switching to a fresh plant-based diet.

Eat only when you're hungry.

Let's make a reservation right away: the natural feeling of hunger must be distinguished from the perverted and pathological feeling of "chewing something."

A real feeling of hunger appears only when the food has gone through all the stages of digestion and assimilation. Only then the concentration of nutrients in the blood decreases slightly. These signals are sent to the food center, and you feel a real feeling of hunger.

A false feeling of hunger appears when there are disorders in

work of the gastrointestinal tract. With proper nutrition, this pathological disorder disappears, provided that you have cleansed your body well before.

Another postulate follows from the same point: no “snacks” between meals. Already the ancient sages wrote in "Chzhud-shih": "It is impossible" to eat new food until the old one is digested, because they may turn out to be incompatible and start a quarrel.

If you constantly chew something, then you will not have mucus for

protection of the gastric mucosa and 12 duodenal ulcer. The secretory apparatus will be constantly overloaded, especially cells with intermittent secretion. In addition, it is known that during the digestion of food, desquamation of the epithelium of the mucosa of the gastrointestinal tract occurs.

Naturally, with frequent meals, this process will be much more intense, which will lead to rapid wear of the gastrointestinal tract.

EAT ONLY WHEN YOU HAVE A HEALTHY HUNGER FEELING.

Use symbiotic digestion wisely.

As an example of the negative and positive influence of microflora, we will analyze two cases.

The formation and secretion of gastric juice is controlled by nervous and humoral mechanisms.

The separation of gastric juice occurs in 2 phases:

1) The first phase of secretion reflex secretion:

Definitely a reflex gastric juice is secreted by irritation of the olfactory receptors of the oral cavity, pharynx, esophagus;

conditioned reflex sap secretion occurs when visual, olfactory, auditory receptors are stimulated, i.e. the sight, the smell of food, etc.

The juice separated at the same time, Pavlov called fiery or appetizing - it prepares the stomach to receive food. This was studied in experiments with "imaginary feeding ”, when food is only in the oral cavity, but does not enter the stomach, but falls out through an opening in the esophagus.

2) Second phase of secretion gastric or neurohumoral, is associated with irritation of food receptors of the gastric mucosa: mechanical and chemical irritation → sensory neuron → medulla oblongata → motor neuron → working organ (juice secretion). Starts immediately after eating and lasts 2 hours.

Centers of nervous regulation:

Digestion, salivation,

juice secretion - medulla oblongata;

Hunger and satiety - diencephalon;

Taste area - forebrain

Defecation - spinal cord.

Strong irritants are the products of digestion of proteins (meat, fish, vegetable broths), mineral salts, water. The secretion of gastric juice occurs as long as there is food in the stomach: fatty foods are digested for 7-8 hours, carbohydrate foods are digested much faster.

Humoral phase of regulation : Gastric mucosa secretes hormone into blood gastrin, it enters the glands and occurs activation of secretion of gastric juice and regulation of peristalsis of the stomach and intestines (begins 2 hours after a meal, is carried out by the gastrointestinal tract's own hormones ( histamine, gastrin, secretin)). In addition, the hormones of the anterior pituitary and adrenal cortex contribute to the synthesis of digestive enzymes. sympathetic autonomic nervous system slows down, a parasympathetic – stimulates secretion of digestive juices.

A great merit in the study of the physiology of digestion belongs to Pavlov, who proposed and used the following methods: fistula method; The method of gastric fistula with transection of the esophagus (imaginary feeding); Formation of an "isolated ventricle".

With the help of the first two methods, the existence of the first phase of gastric secretion was proved, the third - the existence of the second phase of secretion.

The fistula of the stomach is displayed on the outer side of the abdominal wall. In experiments on the formation "isolated ventricle" when a small ventricle was surgically separated from the stomach, and a fistula was placed on it with preservation of innervation and blood supply, it was possible to obtain pure gastric juice. This made it possible to find out that the amount and composition of the secreted juice depends on the chemical composition of the food - more juice with the highest content of enzymes is released for protein foods, less for carbohydrates, and even less for fats.

Functions of the stomach:

Mechanical

The process of mechanical processing of food in the digestive canal and the chemical breakdown of nutrients by enzymes into simpler components that are absorbed by the body.

To ensure physical and mental work, growth and development, to cover the energy costs that occur during the implementation of physiological functions, in addition to the continuous supply of oxygen, the body needs a wide variety of chemicals. Their body receives with food, which is based on products of plant, animal and mineral origin. Foods consumed by humans contain nutrients: proteins, fats and carbohydrates, rich in energy released when they are broken down in the body. The body's need for nutrients is determined by the intensity of the energy processes occurring in it.

As a building material, mainly proteins containing the necessary amino acids are used. From them, the body synthesizes its own proteins, peculiar only to it. With their insufficient amount in food, a person develops various pathological conditions. Proteins cannot be replaced by other nutrients, while fats and carbohydrates, within certain limits, can replace each other. Therefore, human food must contain a certain minimum amount of each nutrient. When compiling a diet (composition and quantity of products), it is necessary to take into account not only their energy value, but also their qualitative composition. Human food must necessarily include products of both plant and animal origin.

Many chemicals in food cannot be absorbed as they are in the body. Their careful mechanical and chemical processing is necessary. Mechanical processing consists in grinding, mixing and rubbing food to the state of gruel. Chemical processing is carried out by enzymes that are secreted by the digestive glands. In this case, complex organic substances are broken down into simpler ones and absorbed by the body. The complex processes of mechanical grinding and chemical breakdown of food products occurring in the body are called digestion.

Digestive enzymes act only in a certain chemical environment: some in an acidic environment (pepsin), others in an alkaline environment (trypsin), and others in a neutral one (saliva amylase). The maximum activity of enzymes is observed at a temperature of 37 - 40 °C. At higher temperatures, most enzymes are destroyed, and at low temperatures, their activity is suppressed. Digestive enzymes are strictly specific: each of them acts only on a substance of a certain chemical composition. Three main groups of enzymes are involved in digestion (Table 12.2): proteolytic (proteases) that break down proteins, lipolytic (lipases) that break down fats, and glycolytic (carbohydrases) that break down carbohydrates.

There are three types of digestion:

• extracellular (cavitary) - takes place in the cavity of the gastrointestinal tract.
• membrane (parietal) - occurs at the border of the extra- and intracellular environment, is carried out by enzymes associated with the cell membrane;

  Extracellular and membrane digestion is characteristic of higher animals. Extracellular digestion begins the digestion of nutrients, membrane digestion provides intermediate and final stages of this process.

• intracellular - found in the simplest organisms.

STRUCTURE AND FUNCTIONS OF THE DIGESTIVE ORGANS

In the digestive system, the alimentary canal and the digestive glands that communicate with it through the excretory ducts are distinguished: salivary, gastric, intestinal, pancreatic and liver, located outside the alimentary canal and communicating with it with their ducts. All digestive glands belong to the glands of external secretion (endocrine glands secrete their secret into the blood). For a day, an adult produces up to 8 liters of digestive juice.

The alimentary canal in humans has a length of about 8-10 m and is divided into the following sections: oral cavity, pharynx, esophagus, stomach, small and large intestines, rectum, anus (Fig. 1.). Each department has its own characteristic structural features and is specialized in performing a certain phase of digestion.

The wall of the alimentary canal for most of its length consists of three layers:

• outdoor [show]

  outer layer- serous membrane - formed by connective tissue and mesentery, which separate the alimentary canal from the internal organs.

• middle [show]

  middle layer- muscular membrane - in the upper section (oral cavity, pharynx, upper part of the esophagus) is represented by striated, and in other sections - by smooth muscle tissue. Smooth muscles are located in two layers: outer - longitudinal, inner - circular.

  Due to the contraction of these muscles, food is promoted through the alimentary canal and the substances are mixed with digestive juices.

  In the muscle layer are nerve plexuses, consisting of clusters of nerve cells. They regulate the contraction of smooth muscles and the secretion of the digestive glands.

• internal [show]

  The inner layer consists of mucous and submucosal layers with abundant blood and lymphatic supply. The outer layer of the mucous membrane is represented by the epithelium, the cells of which secrete mucus, which facilitates the movement of the contents through the digestive canal.

  In addition, endocrine cells that produce hormones that are involved in the regulation of motor and secretory activity of the digestive system are diffusely located in the mucous layer of the digestive canal, and there are also many lymph nodes that perform a protective function. They neutralize (partially) pathogens that enter the body with food.

  The submucosal layer has numerous small glands that secrete digestive juices.

Digestion in the mouth. The oral cavity is bounded from above by the hard and soft palate, from below by the maxillohyoid muscle (diaphragm of the mouth), and on the sides by the cheeks. The mouth opening is limited by the lips. An adult has 32 teeth in the oral cavity: 4 incisors, 2 canines, 4 small molars and 6 large molars on each jaw. Teeth are made up of a special substance called dentin, which is a modified bone tissue. Outside they are covered with enamel. Inside the tooth there is a cavity filled with loose connective tissue, which contains nerves and blood vessels. Teeth are designed to grind food, they play a role in the formation of sounds.

The oral cavity is lined with a mucous membrane. The ducts of three pairs of salivary glands open into it - parotid, sublingual and submandibular. In the oral cavity is the tongue, which is a muscular organ covered with a mucous membrane, on which there are small numerous papillae containing taste buds. At the tip of the tongue there are receptors that perceive sweet taste, on the root of the tongue - bitter, on the lateral surfaces - sour and salty. With the help of the tongue, food is mixed during chewing and pushed through when swallowing. Language is the organ of human speech.

The region of transition of the oral cavity into the pharynx is designated as a pharynx. On the sides of it are accumulations of lymphoid tissue - the tonsils. The lymphocytes contained in them play a protective role in the fight against microorganisms. The pharynx is a muscular tube in which nasal, oral and laryngeal parts are distinguished. The last two connect the oral cavity with the esophagus. The length of the esophagus is about 25 cm. Its mucosa forms longitudinal folds that facilitate the passage of fluid. No food changes occur in the esophagus.

Digestion in the stomach. The stomach is the most expanded section of the alimentary canal, having the shape of an inverted chemical vessel - a retort. It is located in the abdominal cavity. The initial part of the stomach, connected to the esophagus, is called the cardial, located to the left of the esophagus and raised upwards from the place of their connection, is designated as the fundus of the stomach, and the descending middle part is referred to as the body. Smoothly narrowing, the stomach passes into the small intestine. This outlet section of the stomach is called the pyloric. The lateral edges of the stomach are curved. The left convex edge is called the greater curvature, and the right concave edge is called the lesser curvature of the stomach. The capacity of the stomach in an adult is about 2 liters.

The size and shape of the stomach changes depending on the amount of food taken and the degree of contraction of the muscles of its walls. In places where the esophagus passes into the stomach and the stomach into the intestines, there are sphincters (compressors) that regulate the movement of food. The mucous membrane of the stomach forms longitudinal folds, significantly increasing its surface. The thickness of the mucous membrane contains a large number of tubular glands that produce gastric juice. The glands consist of secretory cells of several types: the main ones, which produce the enzyme pepsin, the parietal cells - hydrochloric acid, the mucous membranes - mucus, and the endocrine cells - hormones.

Digestion in the intestine. The small intestine is the longest part of the alimentary canal, 5-6 m long in an adult. It contains the duodenum, jejunum and ileum. The duodenum is horseshoe-shaped and is the shortest part of the small intestine (about 30 cm). The excretory ducts of the liver and pancreas open into the cavity of the duodenum.

The boundary between the jejunum and ileum is not clearly defined. These sections of the intestine form numerous bends - loops of the intestines and are suspended throughout the mesentery to the posterior abdominal wall. The mucous membrane of the small intestine forms circular folds, its surface is covered with villi, which are a specialized absorption apparatus. Inside the villi are an artery, vein, lymphatic vessel.

The surface of each villus is covered with a single layer of cylindrical epithelium. Each epithelial cell of the villus has outgrowths of the apical membrane - microvilli (3-4 thousand). Circular folds, villi and microvilli increase the surface of the intestinal mucosa (Fig. 2). These structures facilitate the final stages of digestion and the absorption of digested products.

Between the villi, the mucous membrane of the small intestine is permeated with a huge number of mouths of tubular glands that secrete intestinal juice and a number of hormones that provide various functions of the digestive system.

The pancreas is oblong in shape and is located on the back wall of the abdominal cavity under the stomach. Three sections are distinguished in the gland: head, body and tail. The head of the gland is surrounded by the duodenum, its caudal part is adjacent to the spleen. Through the thickness of the entire gland passes its main duct, which opens into the duodenum. The pancreas contains two types of cells: some cells secrete digestive juice, others secrete special hormones that regulate carbohydrate metabolism. Therefore, it belongs to the glands of mixed secretion.

The liver is a large digestive gland, its mass in an adult reaches 1.8 kg. It is located in the upper part of the abdominal cavity, on the right under the diaphragm. The anterior surface of the liver is convex, while the lower surface is concave. The liver consists of two lobes - right (large) and left. On the lower surface of the right lobe are the so-called gates of the liver, through which the hepatic artery, portal vein and the corresponding nerves enter it; here is the gallbladder. The functional unit of the liver is the lobule, which consists of a vein located in the center of the lobule and rows of liver cells radially diverging from it. The product of the liver cells - bile - through special bile capillaries enters the biliary system, including the bile ducts and gallbladder, and then into the duodenum. Bile is stored in the gallbladder between meals and released into the intestines during active digestion. In addition to the formation of bile, the liver takes an active part in the metabolism of proteins and carbohydrates, in the synthesis of a number of substances important for the body (glycogen, vitamin A), and influences the processes of hematopoiesis and blood clotting. The liver performs a protective function. Many toxic substances brought with blood from the gastrointestinal tract are neutralized in it, and then excreted by the kidneys. This function is so important that with a complete shutdown of the liver (for example, in case of injury), a person immediately dies.

The last section of the alimentary canal is the large intestine. Its length is about 1.5 m, and its diameter is 2-3 times the diameter of the small intestine. The large intestine is located on the anterior wall of the abdominal cavity and surrounds the small intestine in the form of a rim. It is subdivided into the cecum, sigmoid and rectum.

A characteristic feature of the structure of the large intestine is the presence of swellings formed by the mucous and muscular membranes. Unlike the small intestine, the mucous membrane of the large intestine does not contain circular folds and villi, there are few digestive glands in it and they consist mainly of mucous cells. The abundance of mucus promotes the movement of denser food residues through the large intestine.

In the area of ​​​​the transition of the small intestine to the thick (to the caecum), there is a special valve (flap) that ensures the movement of the intestinal contents in one direction - from the small to the large. In the caecum there is a vermiform process - the appendix, which plays a role in the immune defense of the body. The rectum ends with a sphincter - an annular striated muscle that regulates bowel movements.

In the digestive system, sequential mechanical and chemical processing of food is carried out, specific for each of its departments.

Food enters the oral cavity in the form of solid pieces or liquids of various consistencies. Depending on this, it either immediately enters the throat, or undergoes mechanical and initial chemical processing. The first is carried out by the chewing apparatus - the coordinated work of the masticatory muscles, teeth, lips, palate and tongue. As a result of chewing, food is crushed, ground and mixed with saliva. The enzyme amylase contained in saliva begins the hydrolytic breakdown of carbohydrates. If food lingers in the oral cavity for a long time, then cleavage products are formed - disaccharides. Saliva enzymes are active only in a neutral or slightly alkaline environment. Mucus excreted with saliva neutralizes acidic foods that have entered the mouth. Saliva lysozyme has a detrimental effect on many microorganisms contained in food.

The mechanism of separation of saliva is reflex. When food comes into contact with the receptors of the oral cavity, they are excited, which is transmitted through the sensory nerves to the medulla oblongata, where the center of salivation is located, and from it the signal goes to the salivary glands. These are unconditioned salivary reflexes. The salivary glands begin to secrete their secret not only when the receptors of the oral cavity are irritated by food products, but also at the sight, smell of food, and sounds associated with eating. These are conditioned salivary reflexes. Saliva glues food particles into a lump and makes it slippery, facilitating passage through the pharynx and esophagus, preventing damage to the mucous membrane of these organs by food particles. The composition and amount of saliva may vary depending on the physical properties of the food. During the day, a person secretes up to two liters of saliva.

The formed food bolus moves to the pharynx by the movement of the tongue and cheeks and causes irritation of the receptors of the root of the tongue, palate and posterior pharyngeal wall. The resulting excitation along the afferent nerve fibers is transmitted to the medulla oblongata - to the center of swallowing, and from there - to the muscles of the oral cavity, pharynx, larynx, esophagus. Due to the contraction of these muscles, the food bolus is pushed into the pharynx, bypassing the respiratory tract (nasopharynx, larynx). Then, by contraction of the muscles of the pharynx, the food bolus moves into the open opening of the esophagus, from where, through its peristaltic movements, it moves to the stomach.

The food entering the cavity of the stomach causes contractions of its muscles and an increase in the secretion of gastric juice. Food mixes with gastric juice and turns into a liquid slurry - chyme. Up to 3 liters of juice is secreted per day in an adult. Its main components involved in the breakdown of nutrients are enzymes - pepsin, lipase and hydrochloric acid. Pepsin breaks down complex proteins into simple ones, which undergo further chemical changes in the gut. It acts only in an acidic environment, which is provided by the presence in the stomach of hydrochloric acid secreted by parietal cells. Gastric lipase only breaks down emulsified milk fat. Carbohydrates in the stomach cavity are not digested. An important component of gastric juice is mucus (mucin). It protects the stomach wall from mechanical and chemical damage and the digestive action of pepsin.

After 3-4 hours of treatment in the stomach, chyme begins to enter the small intestine in small portions. The movement of food into the intestines is carried out by strong contractions of the pyloric part of the stomach. The rate of gastric emptying depends on the volume, composition and consistency of the food taken. Liquids pass into the intestines immediately after entering the stomach, and poorly chewed and fatty foods linger in the stomach for up to 4 hours or more.

The complex process of stomach digestion is regulated by nervous and humoral mechanisms. The secretion of gastric juice begins even before eating (conditioned reflexes). So, cooking, talking about food, the sight and smell of it cause the release of not only saliva, but also gastric juice. Such previously secreted gastric juice is called appetizing or ignition. It prepares the stomach for the digestion of food and is an important condition for its normal functioning.

Eating is accompanied by mechanical irritation of the receptors of the oral cavity, pharynx, esophagus and stomach. This leads to increased gastric secretion (unconditioned reflexes). The centers of secretory reflexes are located in the medulla oblongata and diencephalon, in the hypothalamus. From them, impulses travel through the vagus nerves to the gastric glands.

In addition to reflex (nervous) mechanisms, humoral factors are involved in the regulation of gastric secretion. The gastric mucosa produces the hormone gastrin, which stimulates the secretion of hydrochloric acid and, to a small extent, the release of pepsin. Gastrin is released in response to food entering the stomach. With an increase in the secretion of hydrochloric acid, the release of gastrin is inhibited and thus self-regulation of gastric secretion is carried out.

Stimulants of gastric secretion include histamine, which is formed in the gastric mucosa. Many nutrients and their cleavage products, which enter the bloodstream when they are absorbed in the small intestine, have a juice effect. Depending on the factors that stimulate the secretion of gastric juice, several phases are distinguished: cerebral (nervous), gastric (nerve-humoral) and intestinal (humoral).

The breakdown of nutrients is completed in the small intestine. It digests most of the carbohydrates, proteins and fats. Both extracellular and membrane digestion is carried out here, in which bile and enzymes formed by the intestinal glands and pancreas participate.

Liver cells secrete bile continuously, but it is released into the duodenum only with food intake. Bile contains bile acids, bile pigments, and many other substances. The pigment bilirubin determines the light yellow color of bile in humans. Bile acids aid in the digestion and absorption of fats. Bile, due to its inherent alkaline reaction, neutralizes the acidic contents entering the duodenum from the stomach and thereby stops the action of pepsin, and also creates favorable conditions for the action of intestinal and pancreatic enzymes. Fat droplets under the influence of bile are converted into a finely dispersed emulsion, and then split by lipase to glycerol and fatty acids that can penetrate the intestinal mucosa. If bile is not secreted into the intestines (blockage of the bile duct), then fats are not absorbed by the body and are excreted with feces.

Enzymes produced by the pancreas and secreted into the duodenum are able to break down proteins, fats and carbohydrates. During the day, a person produces up to 2 liters of pancreatic juice. The main enzymes contained in it are trypsin, chymotrypsin, lipase, amylase and glucosidase. Most enzymes are produced by the pancreas in an inactive state. Their activation is carried out in the cavity of the duodenum. So, trypsin and chymotrypsin in the composition of pancreatic juice are in the form of inactive trypsinogen and chymotrypsinogen and pass into the active form in the small intestine: the first under the action of the enterokinase enzyme, the second - trypsin. Trypsin and chymotrypsin break down proteins into polypeptides and peptides. Intestinal juice dipeptidases break down dipeptides into amino acids. Lipase hydrolyses bile emulsified fats into glycerol and fatty acids. Under the action of amylase and glucosidase, most carbohydrates are broken down to glucose. Effective absorption of nutrients in the small intestine is facilitated by its large surface, the presence of multiple folds, villi and microvilli of the mucous membrane. Villi are specialized organs of absorption. By contracting, they contribute to the contact of the mucosal surface with chyme, as well as the outflow of blood and lymph, saturated with nutrients. When relaxing from the intestinal cavity, fluid again enters their vessels. During the day, up to 10 liters of liquid are absorbed in the small intestine, of which 7-8 liters are digestive juices.

Most of the substances formed during the digestion of food and water are absorbed in the small intestine. Undigested food remains in the large intestine, which continues the absorption of water, minerals and vitamins. Numerous bacteria contained in the large intestine are essential for the decomposition of undigested food residues. Some of them are able to break down the cellulose of plant foods, others - to destroy the unabsorbed products of the digestion of proteins and carbohydrates. In the process of fermentation and decay of food residues, toxic substances are formed. When they enter the bloodstream, they are neutralized in the liver. Intensive absorption of water in the large intestine contributes to the reduction and compaction of chyme - the formation of feces that are removed from the body during the act of defecation.

Food hygiene

Human nutrition should be organized taking into account the laws of the digestive system. You should always follow the rules of food hygiene.

1. Try to stick to certain meal times. This contributes to the formation of conditioned juice reflexes and better digestion of ingested food and significant preliminary juice secretion.
2. Food should be deliciously prepared and beautifully presented. The sight, the smell of the food served, the table setting excite the appetite, increase the secretion of digestive juices.
3. Food should be taken slowly, chewing well. Chopped food is digested faster.
4. Food temperature should not be higher than 50-60 °C and lower than 8-10 °C. Hot and cold foods irritate the mucous membranes of the mouth and esophagus.
5. Food should be prepared from good quality products so as not to cause food poisoning.
6. Try to eat raw fruits and vegetables regularly. They contain many vitamins and fiber, which stimulates the motor work of the intestines.
7. Raw vegetables and fruits must be washed before eating with boiled water and protected from contamination by flies - carriers of pathogenic microbes.
8. Strictly follow the rules of personal hygiene (wash hands before eating, after contact with animals, after visiting the toilet, etc.).

THE TEACHING OF I. P. PAVLOV ABOUT DIGESTION

Study of the activity of the salivary glands. Saliva is secreted into the oral cavity through the ducts of three pairs of large salivary glands and from many small glands located on the surface of the tongue and in the mucous membrane of the palate and cheeks. To study the function of the salivary glands, Ivan Petrovich Pavlov suggested using in dogs the operation of exposing the opening of the excretory duct of one of the salivary glands to the surface of the skin of the cheek. After the dog has recovered from the operation, saliva is collected, its composition is examined and its amount is measured.

So I. P. Pavlov found that salivation occurs reflexively, as a result of irritation of the nerve (sensory) receptors of the oral mucosa by food. Excitation is transmitted to the center of salivation, located in the medulla oblongata, from where it is sent along the centrifugal nerves to the salivary glands, which intensively secrete saliva. This is an unconditioned reflex separation of saliva.

IP Pavlov discovered that saliva can also be released when the dog only sees food or smells it. These reflexes discovered by IP Pavlov were called conditioned reflexes, since they are caused by conditions that precede the emergence of an unconditioned salivary reflex.

The study of digestion in the stomach, the regulation of the secretion of gastric juice and its composition at various stages of the digestive processes became possible thanks to the research methods developed by IP Pavlov. He improved the method of applying a gastric fistula in a dog. A cannula (fistula) made of stainless metal is inserted into the formed opening of the stomach, which is brought out and fixed on the surface of the abdominal wall. Through the fistula tube, you can take the contents of the stomach for examination. However, pure gastric juice cannot be obtained by this method.

To study the role of the nervous system in the regulation of the activity of the stomach, IP Pavlov developed another special method, which made it possible to obtain pure gastric juice. IP Pavlov combined the imposition of a fistula on the stomach with the transection of the esophagus. When eating, swallowed food falls out through the opening of the esophagus without entering the stomach. With such imaginary feeding, as a result of food irritation of the nerve receptors of the oral mucosa, gastric juice is reflexively released in the stomach.

The secretion of gastric juice can also be caused by a conditioned reflex - the type of food or any stimulus that is combined with food. I. P. Pavlov called gastric juice secreted by conditioned reflex before eating "appetizing" juice. This first complex-reflex phase of gastric secretion lasts about 2 hours, and food is digested in the stomach for 4-8 hours. Therefore, the complex-reflex phase cannot explain all the regularities in the separation of gastric juice. In order to clarify these questions, it was necessary to study the effect of food on the secretion of the gastric glands. IP Pavlov brilliantly solved this problem by developing the operation of the small ventricle. During this operation, a flap is cut out from the fundus of the stomach, without completely separating it from the stomach and preserving all blood vessels and nerves suitable for it. The mucous membrane is cut and sutured so as to restore the integrity of the large stomach and form a small ventricle in the form of a sac, the cavity of which is isolated from the large stomach, and the open end is brought to the abdominal wall. In this way, two stomachs are created: a large one, in which food is digested in the usual way, and a small, isolated ventricle, into which food does not enter.

With the entry of food into the stomach, the second - gastric, or neurohumoral, phase of gastric secretion begins. Food entering the stomach mechanically irritates the nerve receptors of its mucous membrane. Their excitation causes an increased reflex secretion of gastric juice. In addition, during digestion, chemicals enter the bloodstream - food breakdown products, physiologically active substances (histamine, the hormone gastrin, etc.), which are brought by the blood to the glands of the digestive system and enhance secretory activity.

Currently, painless methods for studying digestion have been developed, which are widely used in humans. So, the probing method - the introduction of a rubber tube-probe into the cavity of the stomach and duodenum - allows you to get gastric and intestinal juices; X-ray method - image of the digestive organs; endoscopy - the introduction of optical instruments - makes it possible to examine the cavity of the digestive canal; with the help of radio pills - miniature radio transmitters swallowed by the patient, changes in the chemical composition of food, temperature and pressure in various parts of the stomach and intestines are studied.

The human stomach is a hollow muscular organ that digests food that has entered it. Here, the regulation of the secretion of gastric juice for the digestion of food occurs.

The secret is released when food enters the stomach to destroy pathogenic bacteria and is a kind of antiseptic.

The regulatory system functions by sending hormones and the central nervous system electrical signals.

Special glands located in the inner shell of the organ produce secretory fluid, mucus. The latter serves as a protective layer covering its walls.

Selection phases

Neurohumoral regulation in the body is carried out by the central nervous system together with humoral factors - hormones in the blood, plasma, and tissue fluid.

Three phases of regulation of gastric acid secretion are also distinguished, such as:

• complex reflex;
• gastric;
• intestinal.

The primary impulse for the glands is the sight and smell of food. Visual, olfactory sensors excite the nerve fibers of the oral cavity, larynx, and digestive organs involved in this process.

Complex reflex

The initial component of the phase begins with the production of a secret due to the flow of nerve impulses of olfactory, visual, auditory images to the brain regions. This increases the excitability of neurons, which activate the work of the endocrine glands.

Impulses of the oral cavity, larynx, esophagus are transmitted through sensory fibers to the brain, from there they follow to the endocrine glands.

These actions cause an increased separation of gastric juice, which has a high acidity, a greater ability to break down proteins.

gastric

The course of the complex reflex phase gives an impetus to the neurohumoral phase. In this case, the regulation of gastric juice secretion is due to the participation of the vagus cranial nerve, local intramural reflexes.

Its release begins when various mechanical, chemical pathogens of fibers enter the inner shell.

They are food, organic substances released from it, hydrochloric acid, saline, amino acids, hormones.

Excitation of the sensitive fibers of the inner shell activates the flow of centripetal impulses to the brain.

The produced reaction is accompanied by an increase in the mobility of the cranial nerve, impulses directed through it to the secretory cells.

Exit from the sensitive endings of mediators of nervous excitation causes the release of gastrin - a hormone that stimulates the release of hydrochloric acid, gastrointestinal juices.

intestinal

When oxidized food passes to the intestines, secretion production first increases, and then sharply decreases. The first is due to the production of gastrin by cells of an endocrine nature.

A decrease in the alkaline environment provokes the appearance of hormonal substances - secretin and enterogastrin, produced by the intestines.

The composition and properties of intestinal juice are determined by more than 20 biocatalysts that have a beneficial effect on digestion, such as:

• proteolytic - enterokinase;
• nuclease - for cleavage of nucleic acids;
• sucrase - synthesis of glucose, fructose;
• lipase - functions of splitting fatty acids, etc.

Thus, there is a regulation of the secretion of intestinal juice.

Conclusion

The cerebral cortex plays an important role in the regulation of nutrition and digestion. With the help of its departments, neurohumoral regulation of the separation of gastric juice is carried out before and during meals.

The food center of the brain regulates the contractile, excretory, and absorption functions of the digestive system.