Physiology of the digestive system. Physiology of the digestive system

PHYSIOLOGY OF DIGESTION

Digestion is a physiological process consisting in the transformation of feed nutrients from complex chemical compounds into simpler ones, available for absorption by the body. In the process of performing various work, the body constantly expends energy. Energy recovery. The biological resources are provided by the intake of nutrients into the body - proteins, carbohydrates and fats, as well as water, vitamins, mineral salts, etc. Most proteins, fats and carbohydrates are high-molecular compounds that cannot be absorbed from the alimentary canal into the blood and lymph without prior preparation. absorbed by the cells and tissues of the body. In the alimentary canal, they undergo physical, chemical, biological influences and turn into low-molecular, water-soluble, easily absorbed substances.

Eating is conditioned by a special feeling - the feeling of hunger. Hunger (food deprivation) as a physiological state (in contrast to hunger as a pathological process) is an expression of the body's need for nutrients. This condition occurs due to a decrease in the content of nutrients in the depot and circulating blood. In the state of hunger, a strong excitation of the digestive tract occurs, its secretory and motor functions increase, the behavioral reaction of animals to search for food changes, the feeding behavior in hungry animals is due to the excitation of neurons in various parts of the central nervous system. The totality of these neurons Pavlov called the food center. This center forms and regulates eating behavior aimed at searching for food, determines the totality of all complex reflex reactions that ensure finding, obtaining, testing and capturing food.

The food center is a complex hypothalamic-limbic-reticulocortical complex, the leading section of which is represented by the lateral nuclei of the hypothalamus. When these nuclei are destroyed, food is refused (aphagia), and their irritation increases food intake (hyperphagia).

In a hungry animal, to which blood was transfused from a well-fed animal, there is an inhibition of reflexes for obtaining and eating food. Various substances are known that cause a state of full and hungry blood. Depending on the type and chemical nature of these substances, several theories have been proposed to explain the feeling of hunger. According to the metabolic theory, the intermediate products of the Krebs cycle, formed during the breakdown of all nutrients, circulating in the blood, determine the degree of nutritional excitability of animals. A biologically active substance isolated from the mucous membrane of the duodenum, arenterin, was found, which regulates appetite. Inhibits appetite cystokinine - pancreozymin. In the regulation of specific appetite, the taste analyzer and its higher department in the cerebral cortex play an important role.

Basic types of digestion. There are three main types of digestion: intracellular, extracellular and membrane. In poorly organized representatives of the animal world, for example, in protozoa, intracellular digestion is carried out. There are special areas on the cell membrane from which pinocytic vesicles or the so-called phagocytic vacuoles are formed. With the help of these formations, a unicellular organism captures food material and digests it with its own enzymes.

In the body of mammals, intracellular digestion is characteristic only of leukocytes - blood phagocytes. In higher animals, digestion occurs in the organ system called the digestive tract, which performs a complex function - extracellular digestion.

Digestion of nutrients by enzymes localized on the structures of the cell membrane, mucous membranes of the stomach and intestines, spatially occupying an intermediate position between intracellular and extracellular digestion, is called membrane or parietal digestion.

The main functions of the digestive organs are secretory, motor (motor), absorption and excretory (excretory).

secretory function. Digestive glands produce and secrete juices into the digestive canal: salivary glands - saliva, stomach glands - gastric juice and mucus, pancreas - pancreatic juice, intestinal glands - intestinal juice and mucus, liver - bile.

Digestive juices, or, as they are also called, secrets, moisten the food and, due to the presence of enzymes in them, contribute to the chemical transformation of proteins, fats and carbohydrates.

motor function. The muscles of the digestive organs, due to their powerful contractile properties, contribute to the intake of food, its movement through the digestive canal and mixing.

suction function. It is performed by the mucous membrane of individual sections of the alimentary canal: it ensures the passage of water and the split parts of food into the blood and lymph.

excretory function. The mucous membrane of the gastrointestinal tract, liver, pancreas and salivary glands secrete their secrets into the cavity of the alimentary canal. Through the digestive canal, the internal environment of the body is connected to the environment.

The role of enzymes in digestion. Enzymes are biological catalysts, accelerators of food digestion. According to their chemical nature, they belong to proteins, according to their physical nature, to colloidal substances. Enzymes are produced by the cells of the digestive glands mostly in the form of proenzymes of the precursors of enzymes that do not have activity. Proenzymes become active only when exposed to a number of physical and chemical activators, different for each of them. For example, the proenzyme peusinogen, produced by the glands of the stomach, is converted into its active form - pepsin - under the influence of hydrochloric (hydrochloric) acid of gastric juice.

Digestive enzymes are specific, that is, each of them has a catalytic effect only on certain substances. The activity of one or another enzyme is manifested in a certain reaction of the environment - acidic or neutral. IP Pavlov found that the enzyme pepsin loses its effect in an alkaline medium, but restores it in an acidic medium. Enzymes are also sensitive to changes in the temperature of the environment: with a slight increase in temperature, the action of enzymes is intensified, and when heated above 60 ° C, it is completely lost. They are less sensitive to low temperatures - their action is somewhat weakened, but it is reversible when the optimum temperature of the environment is restored. For the biological action of enzymes in the animal body, the optimum temperature is 36-40 °C. Enzyme activity also depends on the concentration of individual nutrients in the substrate. Enzymes are hydrolases - they break down chemicals in feed by adding H and OH ions. Enzymes that break down carbohydrates are called amylolytic enzymes, or amylases; proteins (proteins) - proteolytic, or proteases; fats - lipolytic, or lipases.

Methods for studying the functions of the digestive system. The Pavlovian method is considered the most perfect and objective method for studying the function of the digestive organs. In pre-Pavlovian times, the physiology of digestion was studied in primitive ways. To get an idea of ​​the changes in food in the digestive tract, it is necessary to take the contents from its various parts. R. A. Réaumur (XVII-XVIII centuries), to obtain gastric juice, injected hollow metal tubes with holes through the oral cavity into the animal, after filling them with nutrient material (in dogs, birds and sheep). Then, after 14-30 hours, the animals were killed and the metal tubes were removed to study their contents. L. Spalanzani filled the same tubes not with food material, but with sponges, from which he subsequently squeezed out the liquid mass. Often, to study changes in food, the contents of the digestive tract of slaughtered animals were compared with the given food (W. Ellenberger and others). V. A. Basov and N. Blondlot performed a gastric fistula operation in dogs a little later, but they could not isolate a pure secret of the gastric glands, since the contents of the stomach were mixed with saliva and ingested water. A pure secret was obtained as a result of the classical fistula technique developed by IP Pavlov, which made it possible to establish the main patterns in the activity of the digestive organs. Pavlov and his colleagues, using surgical techniques on previously prepared healthy animals (mainly dogs), developed methods for removing the duct of the digestive glands (salivary, pancreas, etc.), obtaining an artificial opening (fistula) of the esophagus, intestines. After recovery, the operated animals served as objects for studying the function of the digestive organs for a long time. Pavlov called this method the method of chronic experiments. At present, the fistula technique has been greatly improved and is widely used to study the digestive and metabolic processes in farm animals.

In addition, to study the functions of the mucosa of various departments, a histochemical method is used, which can be used to establish the presence of certain enzymes. To register various aspects of the contractile and electrical activity of the walls of the alimentary canal, radiotelemetric, radiographic and other methods are used.

DIGESTION IN THE MOUTH

Digestion in the oral cavity consists of three stages: food intake, proper oral digestion and swallowing.

Feed and fluid intake. Before accepting any food, the animal evaluates it with the help of sight and smell. Then, with the help of receptors in the oral cavity, it selects suitable food, leaving inedible impurities.

With a free choice and assessment of the palatability of feed, solutions of various food and rejected substances, two successive phases of feeding behavior appear in ruminants. The first is the phase of testing the quality of food and drink, and the second is the phase of taking food and drinking and rejecting them. Milk, glucose, solutions of hydrochloric and acetic acids in the testing phase and especially in the phase of the act of drinking increase the number of acts of swallowing, the amplitude and frequency of contractions of the complex stomach. Solutions of sodium bicarbonate and salts of potassium chloride, calcium of high concentration inhibit the manifestation of the first and second phases (K. P. Mikhaltsov, 1973).

Animals capture food with their lips, tongue and teeth. Well-developed musculature of the lips and tongue allows you to make a variety of movements in various directions.

A horse, a sheep, a goat, when eating grain, capture it with their lips, cut the grass with incisors and use their tongue to direct it into the oral cavity. Cows and pigs have less mobile lips, they take food with their tongues. Cows cut grass with a lateral movement of the jaws, when the incisors of the lower jaw come into contact with the dental plate of the intermaxilla. Carnivores capture food with their teeth (sharp incisors and fangs).

The intake of water and liquid feed in different animals is also not the same. Most herbivores drink water, as if sucking it through a small gap in the middle of their lips. Retracted back tongue, parted jaws contribute to the passage of water. Carnivores lap up water and liquid food with their tongues.

Chewing. Food that has entered the oral cavity is primarily mechanically processed as a result of chewing movements. Chewing is carried out by lateral movements of the lower jaw on one side or the other. In horses, the mouth opening is usually closed when chewing. Horses immediately carefully chew the accepted food. Ruminants only lightly chew it and swallow it. Pigs chew the food thoroughly, crushing the dense parts. Carnivores knead, crush food and quickly swallow without chewing.

Salivation. Saliva is a product of secretion (excretion) of three pairs of salivary glands: sublingual, submandibular and parotid. In addition, the secret of small glands located on the mucous membrane of the side walls of the tongue and cheeks enters the oral cavity.

Liquid saliva, without mucus, is secreted by serous glands, thick saliva containing a large amount of glucoprotein (mucin) is mixed glands. The serous glands are the parotid glands. Mixed glands - sublingual and submandibular, since their parenchyma contains both serous and mucous cells.

To study the activity of the salivary glands, as well as the composition and properties of the secretions (saliva) they secrete, I. P. Pavlov and D. D. Glinsky on dogs developed a technique for applying chronic fistulas of the ducts of the salivary glands (Fig. 24). The essence of this technique is as follows. A piece of the mucous membrane with the excretory duct is cut out, brought to the surface of the cheek and sewn to the skin. After a few days, the wound heals and saliva is released not into the oral cavity, but outward.

Saliva is collected by ciliadrikas suspended from a funnel attached to the cheek.

In farm animals, the excretion of the duct is carried out as follows. A T-shaped cannula is inserted through the skin incision into the prepared duct. In this case, saliva outside of the experiment enters the oral cavity. But this method is applicable only for large animals, for small animals, in most cases, the method of removing the duct is used along with the papilla, which is implanted into the skin flap,

The main regularities of the activity of the salivary glands and their importance in the process of digestion were studied by I. P. Pavlov.

Salivation in dogs occurs periodically only when food or any other irritants enter the oral cavity. The quantity and quality of the separated saliva mainly depend on the type and nature of the food taken and a number of other factors. Long-term consumption of starchy foods causes the appearance of amylolytic enzymes in saliva. The amount of saliva secreted is affected by the degree of moisture and the consistency of the food: soft bread in dogs produces less saliva than crackers; more saliva is secreted when eating meat powder than raw meat. This is due to the fact that more saliva is needed to wet dry food, this situation is also true for cattle, sheep and goats and has been confirmed by numerous experiments.

Salivation in dogs also increases when so-called rejected substances (sand, bitterness, acids, alkalis and other non-food substances) enter the mouth. For example, if you moisten the oral mucosa with a solution of hydrochloric acid, the secretion of saliva increases (salivation).

The composition of the secreted saliva for food and rejected substances is not the same. Saliva, rich in organic substances, especially protein, is secreted for food substances, and the so-called laundering saliva is released for rejection. The latter should be considered as a defensive reaction: through increased salivation, the animal is freed from foreign non-food substances.

Composition and properties of saliva. Saliva is a viscous liquid of slightly alkaline reaction with a density of 1.002-1.012 and contains 99-99.4% water and 0.6-1% solids.

The organic matter of saliva is represented mainly by proteins, especially mucin. Of the inorganic substances in saliva, there are chlorides, sulfates, carbonates of calcium, sodium, potassium, magnesium. Saliva also contains some metabolic products: salts of carbonic acid, urea, etc. Together with saliva, medicinal substances and paints introduced into the body can also be released.

Saliva contains the enzymes amylase and α-glucosidase. Ptyalin acts on polysaccharides (starch), breaking them down to dextrins and malyose α-glucosidase acts on malyose, converting this disaccharide into glucose. Saliva enzymes are active only at a temperature of 37-40 ° C and in a slightly alkaline environment.

Saliva, wetting the food, facilitates the process of chewing. In addition, it liquefies the food mass, extracting flavoring substances from it. With the help of mucin, saliva glues and envelops the food and thus facilitates its ingestion. Diastatic enzymes in the feed dissolve in saliva to break down starch.

Saliva regulates acid-base balance, neutralizes stomach acids with alkaline bases. It contains substances that have a bactericidal effect (ingiban and lysozyme). Takes part in thermoregulation of the body. Through salivation, the animal is freed from excess heat energy. Saliva contains kallikrein and parotin, which regulate the blood supply to the salivary glands and change the permeability of cell membranes.

Salivation in animals of various species. Saliva in a horse occurs periodically, only when taking food. More saliva is separated for dry food, much less for green grass and moist food. Since the horse carefully chews the food alternately on one side, then on the other, saliva is also more separated by the glands of the side where the chewing takes place.

With each chewing movement, saliva is sprayed from the fistula of the duct of the parotid gland at a distance of up to 25-30 cm. Apparently, in the horse, mechanical irritation with food is the leading factor causing secretion. Taste stimuli also affect the activity of the salivary glands: when solutions of salt, hydrochloric acid, soda, pepper are introduced into the oral cavity, salivation increases. Secretion also increases when crushed feed is given, the taste of which is more noticeable, and when yeast is added to the feed. The secretion of saliva in a horse is caused not only by feed, but also by rejected substances, just as in a dog.

During the day, the horse separates up to 40 liters of saliva. In the saliva of a horse, 989.2 parts of water account for 2.6 parts of organic substances and 8.2 parts of inorganic; saliva pH 345.

There are few enzymes in the saliva of the horse, but the breakdown of carbohydrates still occurs, mainly due to the enzymes pma, which are active in the slightly alkaline reaction of saliva. The action of saliva and feed enzymes can continue even when feed masses enter the initial and central sections of the stomach, where a slightly alkaline reaction is still maintained.

The process of salivation in ruminants proceeds somewhat differently than in horses, since the food in the oral cavity is not thoroughly chewed. The role of saliva in this case is reduced to wetting the feed, which facilitates the process of swallowing. Saliva has the main effect on digestion in the oral cavity during chewing gum. The parotid gland secretes profusely both during the intake of food and chewing gum, and during periods of rest, and the submandibular secretes saliva periodically.

The activity of the salivary glands is influenced by a number of factors from the side of the proventriculus, especially the scar. With an increase in pressure in the scar, the secretion of the parotid gland increases. The salivary glands are also affected by chemical factors. For example, the introduction of acetic and lactic acids into the scar first inhibits and then enhances salivation.

Cattle produce 90-190 liters of saliva per day, sheep - 6-10 liters of saliva. The amount and composition of saliva produced depends on the type of animal, feed and its consistency. In the saliva of ruminants, organic substances make up 0.3, inorganic - 0.7%; saliva pH 8-9. The high alkalinity of saliva, its concentration contribute to the normalization of biotic processes in the pancreas. The copious amount of saliva entering the rumen neutralizes the acids formed during the fermentation of fiber.

Salivation in pigs occurs periodically, when taking feed. The degree of secretory activity of the salivary glands in them depends on the nature of the food. So, when eating liquid talkers, saliva is almost not produced. The nature and method of preparation of food affect not only the amount of saliva, but also its quality. Up to 15 liters of saliva is secreted per day in a pig, and about half of it is secreted by the parotid salivary gland. Saliva contains 0.42% dry matter, of which 57.5 is organic matter, and 42.5% is inorganic; pH 8.1-8.47. The saliva of pigs has a pronounced amylolytic activity. It contains the enzymes ptyalin and malyase. The enzymatic activity of saliva can be preserved in separate portions of the contents of the stomach up to 5-6 hours.

Regulation of salivation. Salivation is carried out under the influence of unconditioned and conditioned reflexes. This is a complex reflex reaction. Initially, as a result of the capture of food and its entry into the oral cavity, the receptor apparatuses of the mucous membrane of the lips and tongue are excited. The food irritates the nerve endings of the fibers of the trigeminal and glossopharyngeal nerves, as well as the branches (upper laryngeal) of the vagus nerve. Through these centripetal pathways, impulses from the oral cavity reach the medulla oblongata, where the center of salivation is located, then enter the thalamus, hypothalamus, and cerebral cortex. From the salivary center, excitation is transmitted to the glands along the sympathetic and parasympathetic nerves, the latter pass through the glossopharyngeal and facial nerves. The parotid gland is innervated by the glossopharyngeal and ear-temporal branches of the trigeminal nerves. The submandibular and sublingual glands are supplied with a branch of the facial nerve called the chorda tympani. Irritation of the drum string causes active secretion of liquid saliva. When the sympathetic nerve is irritated, a small amount of thick, mucus (sympathetic) saliva is secreted.

Nervous regulation has little effect on the function of the parotid gland in ruminants, since the continuity of its secretion is due to the constant action of chemo- and mechanoreceptors of the proventriculus. The sublingual and submandibular glands secrete periodically.

D
The activity of the salivary center of the medulla oblongata is regulated by the hypothalamus and the cerebral cortex. The participation of the cerebral cortex in the regulation of salivation in dogs was established by IP Pavlov. A conditioned signal, such as a call, was accompanied by giving food.

After several such combinations, the dog salivated at just one call. Pavlov called this salivation conditioned reflex. Conditioned reflexes are also developed in horses, pigs, and ruminants. However, in the latter, a conditioned natural stimulus reduces the secretion of the parotid glands. This is due to the fact that they are constantly excited and continuously secrete.

The center of salivation is affected by many different stimuli - reflex and humoral. Irritation of the receptors of the stomach and intestines can excite or inhibit salivation.

The formation of saliva is a secretory process carried out by the cells of the salivary glands. The secretion process includes the synthesis of the secretion parts of the cell, the formation of the secretion granules, the removal of the secret from the cell and the restoration of its original structure. It is covered with a membrane that forms microvilli, inside it contains the nucleus, mitochondria, the Golgi complex, the endoplasmic reticulum, the surface of the tubules of which is dotted with ribosomes. Through the membrane, water, mineral compounds, amino acids, sugars and other substances selectively enter the cell.

Secretion formation occurs in the tubules of the endoplasmic reticulum. Through their wall, the secret passes into the vacuoles of the Golgi complex, where its final formation takes place (Fig. 25). During rest, the glands are more granular due to the presence of many secretion granules, during and after salivation, the number of granules decreases.

swallowing. This is a complex reflex act. The chewed and moistened food is fed with the movement of the cheeks and tongue in the form of a lump on the back of the tongue. Then the tongue presses it against the soft palate and pushes it first to the root of the tongue, then into the pharynx. The food, irritating the mucous membrane of the pharynx, causes a reflex contraction of the muscles that lift the soft palate, and the root of the tongue presses the epiglottis to the larynx, so when swallowing, the lump does not enter the upper respiratory tract. By contraction of the muscles of the pharynx, the food lump is pushed further to the funnel of the esophagus. Swallowing can be carried out only with direct irritation of the afferent nerve endings of the pharyngeal mucosa with food or saliva. Dry mouth makes swallowing difficult or absent.

The swallowing reflex is carried out as follows. Through the sensitive branches of the trigeminal and glossopharyngeal nerves, excitation is transmitted to the medulla oblongata, where the swallowing center is located. From it, excitation goes back along the efferent (motor) fibers of the trigeminal, glossopharyngeal and vagus nerves, which causes muscle contraction. With loss of sensitivity of the pharyngeal mucosa (transection of afferent nerves or lubrication of the mucosa with cocaine), swallowing does not occur.

The movement of the food coma from the pharynx through the esophagus occurs due to its peristaltic movements, which are caused by the vagus nerve that innervates the esophagus.

Peristalsis of the esophagus is a wave-like contraction, in which there is an alternation of contractions and relaxation of individual sections. Liquid food passes through the esophagus quickly, in a continuous stream, dense - in separate portions. The movement of the esophagus causes a reflex opening of the entrance to the stomach.

DIGESTION IN THE STOMACH

In the stomach, food undergoes mechanical processing and chemical effects of gastric juice. Mechanical processing - mixing, and then moving it to the intestines - is carried out by contractions of the muscles of the stomach. Chemical transformations of food in the stomach occur under the influence of gastric juice.

The process of formation by the glands of the gastric mucosa and its separation into the cavity constitute the secretory function of the stomach. In the monochamber stomach and abomasum of ruminants, the glands are divided into cardial, fundal, and pyloric glands, according to their location.

Most of the glands are located in the fundus and lesser curvature of the stomach. The glands of the bottom occupy 2/3 of the surface of the gastric mucosa and consist of the main, parietal and additional cells. The main cells produce enzymes, the parietal cells produce hydrochloric acid, and the accessory cells produce mucus. The secrets of the main and parietal cells are mixed. The cardiac glands consist of accessory cells, the glands of the pyloric region consist of the main and accessory cells.

Methods for studying gastric secretion. An experimental study of gastric secretion was first started by the Russian surgeon V. A. Basov and the Italian scientist Blondlot (1842), who created an artificial gastric fistula in dogs. However, the Basov fistula method did not make it possible to obtain pure gastric juice, since it was mixed with saliva and food masses.

The technique for obtaining pure gastric juice was developed by I.P. Pavlov and his co-workers. In dogs, a gastric fistula was made and the esophagus was cut. The ends of the cut esophagus were brought out and sutured to the skin. Swallowed food did not enter the stomach, but fell out. During the act of eating, the dog excreted pure gastric juice, despite the fact that the food did not enter the stomach. Pavlov called this method the experience of "imaginary feeding". This method makes it possible to obtain pure gastric juice and proves the presence of reflex influences from the oral cavity. However, it cannot be used to establish the effect of food directly on the glands of the stomach. The latter was studied by the isolated ventricle method. One of the options for the operation of an isolated ventricle was proposed by R. Heidenhain (1878). But this isolated ventricle did not have a nervous connection with the large stomach, its connection was carried out only through the blood vessels. This experience did not reflect reflex influences on the secretory activity of the stomach.

The human and animal organism is an open thermodynamic system that constantly exchanges matter and energy with the environment. The body requires replenishment of energy and building material. It is necessary for work, temperature maintenance, tissue repair. These materials are obtained by humans and animals from the environment in the form of animal or plant origin. In foodstuffs in different ratios of nutrients - proteins, fats. Nutrients are large polymer molecules. Food also contains water, mineral salts, vitamins. And although these substances are not a source of energy, they are very important components for life. Nutrients from foods cannot be absorbed immediately; this requires processing of nutrients in the gastrointestinal tract so that the products of digestion can be used.

The length of the digestive tract is approximately 9 m. The digestive system includes the oral cavity, pharynx, esophagus, stomach, small and large intestines, rectum and anal canal. There are additional organs of the gastrointestinal tract - they include the tongue, teeth, salivary glands, pancreas, liver and gallbladder.

The alimentary canal consists of four layers or membranes.

1. Mucous
2. Submucosal
3. muscular
4. Serous

Each shell performs its own functions.

mucous membrane surrounds the lumen of the alimentary canal and is the main absorptive and secretory surface. The mucosa is covered with a cylindrical epithelium, which is located on its own plate. In a plate there are numerous limf. Nodules and they perform a protective function. Outside, the layer of smooth muscles is the muscular plate of the mucous membrane. Due to the contraction of these muscles, the mucous membrane forms folds. The mucosa also contains goblet cells that produce mucus.

submucosa represented by a layer of connective tissue with a large number of blood vessels. The submucosa contains the glands and the submucosal nerve plexus - plexus jeissner. The submucosal layer provides nutrition to the mucous membrane and autonomic innervation of the glands, smooth muscles of the muscle plate.

Muscular membrane. Consists of 2 layers of smooth muscles. Internal - circular and external - longitudinal. Muscles are arranged in bundles. The muscular membrane is designed to perform a motor function, to mechanically process food and move food along the alimentary canal. In the muscular membrane there is a second plexus - Auerbach. On the plexus cells in the gastrointestinal tract, the fibers of the sympathetic and parasympathetic nerves end. The composition contains sensitive cells - Doggel cells, there are motor cells - the first type, there are inhibitory neurons. The set of elements of the gastrointestinal tract is an integral part of the autonomic nervous system.

Outer serosa- connective tissue and squamous epithelium.

In general, the gastrointestinal tract is intended for the course of digestion processes and the basis of digestion is the hydrolytic process of splitting large molecules into simpler compounds that can be obtained by blood and tissue fluid and delivered to the site. The operation of the digestive system resembles the function of a disassembly conveyor.

stages of digestion.

1. food intake. It involves taking food into the mouth, chewing food into smaller pieces, moisturizing, forming a food bolus, and swallowing.
2. Digestion of food. In the course of it, further processing and enzymatic breakdown of nutrients are carried out, while proteins are broken down by proteases and into dipeptides and amino acids. Carbohydrates are cleaved by amylase to monosaccharides, and fats are cleaved by lipases and esterases to monoglycerin and fatty acids.
3. The resulting simple compounds are subjected to the following process - product absorption. But not only the breakdown products of nutrients are absorbed, but water, electrolytes, and vitamins are absorbed. During absorption, substances are transferred to the blood and lymph. There is a chemical process in the gastrointestinal tract, as in any production, by-products and wastes arise, which can often be toxic.
4. Excretion- are removed from the body in the form of feces. To carry out the processes of digestion, the digestive system performs motor, secretory, absorption and excretory functions.

The digestive tract is involved in water-salt metabolism, it produces a number of hormones - an endocrine function, has a protective immunological function.

Types of digestion- are subdivided depending on the intake of hydrolytic enzymes and are divided into

1. Own - macroorganism enzymes
2. Symbiotic - due to enzymes that bacteria and protozoa living in the gastrointestinal tract give us
3. Autolytic digestion - due to enzymes that are contained in the foods themselves.

Depending on localization the process of hydrolysis of nutrients digestion is divided into

1. Intracellular

2. Extracellular

Distant or cavity

Contact or wall

Cavitary digestion will occur in the lumen of the gastrointestinal tract, enzymes, on the membrane of microvilli of intestinal epithelial cells. Microvilli are covered with a layer of polysaccharides, form a large catalytic surface, which ensures rapid splitting and rapid absorption.

The value of the work of I.P. Pavlova.

Attempts to study the processes of digestion begin already in the 18th century, for example Reamur tried to get gastric juice by putting a sponge tied with a string into the stomach and got digestive juice. There were attempts to implant glass or metal tubes into the ducts of the glands, but they quickly fell out and an infection joined. The first clinical observations in humans were carried out with gastric injury. In 1842 a Moscow surgeon bass put a fistula on the stomach and closed with a stopper outside the digestive processes. This operation made it possible to obtain gastric juice, but the disadvantage was that it was mixed with food. Later, in Pavlov's laboratory, this operation was supplemented by cutting the esophagus in the neck. Such an experience is called the experience of imaginary feeding, and after feeding, the chewed food is digested.

English physiologist Heidenhain suggested isolating a small ventricle from a large one, this made it possible to obtain pure gastric juice, unmixed with food, but the disadvantage of the operation was that the incision was perpendicular to the greater curvature - it crossed the nerve - the vagus. Only humoral factors could act on the small ventricle.

Pavlov proposed to do it parallel to the greater curvature, the vagus was not cut, it reflected the entire course of digestion in the stomach with the participation of both nervous and humoral factors. I.P. Pavlov set the task of studying the function of the digestive tract as close as possible to normal conditions, and Pavlov develops methods of physiological surgery by performing various operations on animals, which later helped in the study of digestion. Basically, the operations were aimed at the imposition of fistulas.

Fistula- artificial communication of the cavity of the organ or duct of the gland with the environment to obtain the contents and after the operation the animal recovered. This was followed by recovery, long-term nutrition.

In physiology is sharp experiences- once under anesthesia and chronic experience- in conditions as close to normal as possible - with anesthesia, without pain factors - this gives a more complete picture of the function. Pavlov develops fistulas of the salivary glands, small ventricular surgery, esophagotomy, gallbladder and pancreatic duct.

First merit Pavlova in digestion consists in the development of chronic experiments. Further, Ivan Petrovich Pavlov established the dependence of the quality and quantity of secrets on the type of food irritant.

Thirdly- adaptability of glands to nutritional conditions. Pavlov showed the leading role of the nervous mechanism in the regulation of the digestive glands. Pavlov's work in the field of digestion was summarized in his book On the Work of the Most Important Digestive Glands. In 1904, Pavlov was awarded the Nobel Prize. In 1912, Newton University in England, Byron elected Pavlov an honorary doctor of the University of Cambridge, and at the initiation ceremony there was such an episode when Cambridge students let down a toy dog ​​with numerous fistulas.

Physiology of salivation.

Saliva is formed by three pairs of salivary glands - parotid, located between the jaw and ear, submandibular, located under the lower jaw, and sublingual. Small salivary glands - work constantly, unlike large ones.

parotid gland consists only of serous cells with a watery secretion. Submandibular and sublingual glands secrete a mixed secret, tk. include both serous and mucous cells. Secretory unit of the salivary gland salivon, into which the acinus enters, blindly ending in expansion and formed by acinar cells, the acinus then opens into the intercalary duct, which passes into the striated duct. Acinus cells secrete proteins and electrolytes. This is where water comes in. Then, the correction of the content of electrolytes in saliva is carried out by intercalary and striated ducts. The secretory cells are still surrounded by myoepithelial cells capable of contraction, and the myoepithelial cells, by contracting, squeeze out the secret and promote its movement along the duct. The salivary glands receive an abundant blood supply, there are 20 times more beds in them than in other tissues. Therefore, these small-sized organs have a rather powerful secretory function. From 0.5 - 1.2 liters are produced per day. saliva.

Saliva.

• Water - 98.5% - 99%
• Dense residue 1-1.5%.
• Electrolytes - K, HCO3, Na, Cl, I2

Saliva secreted in the ducts is hypotonic compared to plasma. In acini, electrolytes are secreted by secretory cells and they are contained in the same amount as in plasma, but as saliva moves through the ducts, sodium and chloride ions are absorbed, the amount of potassium and bicarbonate ions becomes larger. Saliva is characterized by a predominance of potassium and bicarbonate. The organic composition of saliva represented by enzymes - alpha-amylase (ptyalin), lingual lipase - is produced by glands located at the root of the tongue.

The salivary glands contain kalikrein, mucus, lactoferrin - bind iron and help reduce bacteria, lysozyme glycoproteins, immunoglobulins - A, M, antigens A, B, AB, 0.

Saliva is excreted through the ducts - functions - wetting, the formation of a food lump, swallowing. In the oral cavity - the initial stage of the breakdown of carbohydrates and fats. Complete splitting cannot occur because. short time for food to stay in the food cavity. The optimum action of saliva is a weakly alkaline environment. PH of saliva = 8. Saliva limits the growth of bacteria, promotes healing of injuries, hence the licking of wounds. We need saliva for the normal function of speech.

Enzyme salivary amylase It breaks down starch into maltose and maltotriose. Salivary amylase is similar to pancreatic amylase, which also breaks down carbohydrates into maltose and maltotriose. Maltase and isomaltase break down these substances into glucose.

saliva lipase begins to break down fats and enzymes continue their action in the stomach until the pH value changes.

Regulation of salivation.

The regulation of saliva secretion is carried out by parasympathetic and sympathetic nerves, and at the same time, the salivary glands are regulated only reflexively, since they are not characterized by a humoral mechanism of regulation. Salivary secretion can be carried out with the help of unconditioned reflexes that occur when the oral mucosa is irritated. In this case, there may be food irritants and non-food ones.

Mechanical irritation of the mucous membrane also affects salivation. Salivation can occur on the smell, sight, memory of delicious food. Salivation is formed with nausea.

Inhibition of salivation is observed during sleep, with fatigue, with fear and with dehydration.

The salivary glands receive double innervation from the autonomic nervous system. They are innervated by the parasympathetic and sympathetic divisions. Parasympathetic innervation is carried out by 7 and 9 pairs of nerves. They contain 2 salivary nuclei - the upper -7 and the lower - 9. The seventh pair innervates the submandibular and sublingual glands. 9 pair - parotid gland. In the endings of the parasympathetic nerves, acetylcholine is released, and when acetylcholine acts on the receptors of secretory cells through G-proteins, the secondary messenger inositol-3-phosphate is innervated, and it increases the calcium content inside. This leads to an increase in the secretion of saliva poor in organic composition - water + electrolytes.

The sympathetic nerves reach the salivary glands through the superior cervical sympathetic ganglion. In the endings of postganglionic fibers, norepinephrine is released, i.e. secretory cells of the salivary glands have adrenergic receptors. Norepinephrine causes the activation of adenylate cyclase, followed by the formation of cyclic AMP, and cyclic AMP enhances the formation of protein kinase A, which is necessary for protein synthesis and sympathetic effects on the salivary glands increase secretion.

Saliva with high viscosity with a large amount of organic matter. As an afferent link in the excitation of the salivary glands, this will involve the nerves that provide general sensitivity. Taste sensitivity of the anterior third of the tongue is the facial nerve, the posterior third is the glossopharyngeal. The posterior sections still have innervation from the vagus nerve. Pavlov showed that the secretion of saliva to rejected substances, and the ingress of river sand, acids, and other chemicals, there is a large release of saliva, namely liquid saliva. Salivation also depends on the fragmentation of food. For food substances, a smaller amount of saliva is given, but with a high content of the enzyme.

Physiology of the stomach.

The stomach is a section of the digestive tract, food is delayed from 3 to 10 hours for mechanical and chemical processing. A small amount of food is digested in the stomach, the absorption area is also not large. This is a food storage tank. In the stomach, we allocate the bottom, the body, the pyloric section. The contents of the stomach are limited from the esophagus by the cardiac sphincter. When the pyloric section passes into the duodenum. There is a functional sphincter.

Function of the stomach

1. Deposition of food
2. Secretory
3. Motor
4. Suction
5. excretory function. Promotes the removal of urea, uric acid, creatine, creatinine.
6. Endocrine function - the formation of hormones. The stomach performs a protective function

On the basis of functional features, the mucosa is divided into acid-producing, which is located in the proximal section on the central part of the body, antral mucosa is also isolated, which does not form hydrochloric acid.

Compound- mucous cells that form mucus.

• Parietal cells that produce hydrochloric acid
• Chief cells that produce enzymes
• Endocrine cells that produce the hormone G-cells - gastrin, D-cells - somatostatin.

Glycoprotein - forms a mucous gel, it envelops the wall of the stomach and prevents the action of hydrochloric acid on the mucous membrane. This layer is very important otherwise the violation of the mucous membrane. It is destroyed by nicotine, little mucus is produced in stressful situations, which can lead to gastritis and ulcers.

The glands of the stomach produce pepsinogens, which act on proteins, they are in an inactive form and require hydrochloric acid. Hydrochloric acid is produced by parietal cells, which also produce Castle factor- which is needed for the assimilation of the external factor B12. In the area of ​​the antrum there are no parietal cells, the juice is produced in a slightly alkaline reaction, but the mucous membrane of the antrum is rich in endocrine cells that produce hormones. 4G-1D - ratio.

To study the function of the stomach methods are being studied that impose fistulas - the allocation of a small ventricle (According to Pavlov), and in humans, gastric secretion is studied by probing and receiving gastric juice on an empty stomach without giving food, and then after a test breakfast and the most common breakfast is - a glass of tea without sugar and a slice of bread. Such simple foods are powerful stomach stimulants.

Composition and properties of gastric juice.

At rest in the human stomach (without eating) is 50 ml of basal secretion. It is a mixture of saliva, gastric juice and sometimes reflux from the duodenum. About 2 liters of gastric juice is produced per day. It is a clear opalescent liquid with a density of 1.002-1.007. It has an acidic reaction, since there is hydrochloric acid (0.3-0.5%). pH-0.8-1.5. Hydrochloric acid can be in a free state and bound to a protein. Gastric juice also contains inorganic substances - chlorides, sulfates, phosphates and bicarbonates of sodium, potassium, calcium, magnesium. Organic substances are represented by enzymes. The main enzymes of gastric juice are pepsins (proteases that act on proteins) and lipases.

Pepsin A - pH 1.5-2.0

Gastrixin, pepsin C - pH- 3.2-.3.5

Pepsin B - gelatinase

Renin, pepsin D chymosin.

Lipase, acts on fats

All pepsins are excreted in their inactive form as pepsinogen. Now it is proposed to divide pepsins into groups 1 and 2.

Pepsins 1 are allocated only in the acid-forming part of the gastric mucosa - where there are parietal cells.

Antral part and pyloric part - pepsins are secreted there group 2. Pepsins carry out digestion to intermediate products.

Amylase, which enters with saliva, can break down carbohydrates in the stomach for some time, until the pH changes to an acidic moan.

The main component of gastric juice is water - 99-99.5%.

An important component is hydrochloric acid. Its functions:

1. It promotes the conversion of the inactive form of pepsinogen into the active form - pepsins.
2. Hydrochloric acid creates an optimal pH value for proteolytic enzymes
3. Causes denaturation and swelling of proteins.
4. The acid has an antibacterial effect and the bacteria that enter the stomach die.
5. Participates in the formation and hormone - gastrin and secretin.
6. Locks up milk
7. Participates in the regulation of the transition of food from the stomach to the 12-colon.

Hydrochloric acid formed in parietal cells. These are rather large pyramidal cells. Inside these cells there is a large number of mitochondria, they contain a system of intracellular tubules and a bubble system in the form of vesicles is closely connected with them. These vesicles bind to the tubular part when activated. A large number of microvilli are formed in the tubule, which increase the surface area.

The formation of hydrochloric acid occurs in the intratubular system of parietal cells.

At the first stage the chloride anion is transported into the lumen of the tubule. Chlorine ions enter through a special chlorine channel. A negative charge is created in the tubule, which attracts intracellular potassium there.

At the next stage there is an exchange of potassium for a hydrogen proton, due to the active transport of hydrogen potassium ATPase. Potassium is exchanged for a proton of hydrogen. With this pump, potassium is driven into the intracellular wall. Carbonic acid is formed inside the cell. It is formed as a result of the interaction of carbon dioxide and water due to carbonic anhydrase. Carbonic acid dissociates into a hydrogen proton and an HCO3 anion. The hydrogen proton is exchanged for potassium, and the HCO3 anion is exchanged for a chloride ion. Chlorine enters the parietal cell, which then goes into the lumen of the tubule.

In parietal cells, there is another mechanism - sodium - potassium atphase, which removes sodium from the cell and returns sodium.

The process of formation of hydrochloric acid is an energy-consuming process. ATP is produced in mitochondria. They can occupy up to 40% of the volume of parietal cells. The concentration of hydrochloric acid in the tubules is very high. pH inside the tubule up to 0.8 - the concentration of hydrochloric acid is 150 mmol per liter. The concentration is 4,000,000 higher than in plasma. The process of formation of hydrochloric acid in the parietal cells is regulated by the influence on the parietal cell of acetylcholine, which is released at the endings of the vagus nerve.

The lining cells have cholinergic receptors and stimulates the formation of HCl.

gastrin receptors and the hormone gastrin also activates the formation of HCl, and this occurs through the activation of membrane proteins and the formation of phospholipase C and inositol-3-phosphate is formed and this stimulates an increase in calcium and the hormonal mechanism starts.

The third type of receptors - histamine receptorsH2 . Histamine is produced in the stomach by enterochromic mast cells. Histamine acts on H2 receptors. Here, the influence is realized through the adenylate cyclase mechanism. Adenylate cyclase is activated and cyclic AMP is formed

Inhibits - somatostatin, which is produced in D cells.

Hydrochloric acid- the main factor of mucosal damage in violation of the protection of the membrane. Treatment of gastritis - suppression of the action of hydrochloric acid. Very widely used histamine antagonists - cimetidine, ranitidine, block H2 receptors and reduce the formation of hydrochloric acid.

Suppression of hydrogen-potassium atphase. A substance was obtained, which is the pharmacological drug omeprazole. It inhibits hydrogen-potassium atphase. This is a very mild action that reduces the production of hydrochloric acid.

Mechanisms of regulation of gastric secretion.

The process of gastric digestion is conditionally divided into 3 phases overlapping each other.

1. Difficult reflex - cerebral

2. Gastric

3. Intestinal

Sometimes the last two are combined into neurohumoral.

Complex-reflex phase. It is caused by the excitation of the gastric glands by a complex of unconditioned and conditioned reflexes associated with food intake. Conditioned reflexes arise when the olfactory, visual, auditory receptors are stimulated, to the sight, smell, and environment. These are conditional signals. They are superimposed by the effect of irritants on the oral cavity, pharynx, esophagus receptors. These are unconditional irritations. It was this phase that Pavlov studied in the experiment of imaginary feeding. The latent period from the start of feeding is 5-10 minutes, that is, the gastric glands are turned on. After the cessation of feeding - secretion lasts 1.5-2 hours if food does not enter the stomach.

The secretory nerves will be the vagus. It is through them that the effect on the parietal cells that produce hydrochloric acid occurs.

Nervus vagus stimulates gastrin cells in the antrum and Gastrin is formed, and D cells, where somatostatin is produced, are inhibited. It was found that the vagus nerve acts on gastrin cells through a mediator, bombesin. This excites the gastrin cells. On D cells that somatostatin produces, it suppresses. In the first phase of gastric secretion - 30% of gastric juice. It has high acidity, digestive power. The purpose of the first phase is to prepare the stomach for the meal. When food enters the stomach, the gastric phase of secretion begins. At the same time, the food content mechanically stretches the walls of the stomach and excites the sensitive endings of the vagus nerves, as well as the sensitive endings, which are formed by the cells of the submucosal plexus. Local reflex arcs appear in the stomach. The Doggel cell (sensitive) forms a receptor in the mucosa and, when irritated, it is excited and transmits excitation to type 1 cells - secretory or motor. There is a local local reflex and the gland begins to work. Type 1 cells are also postganlionars for the vagus nerve. The vagus nerves keep the humoral mechanism under control. Simultaneously with the nervous mechanism, the humoral mechanism begins to work.

humoral mechanism associated with the release of Gastrin G cells. They produce two forms of gastrin - from 17 amino acid residues - "small" gastrin and there is a second form of 34 amino acid residues - large gastrin. Small gastrin has a stronger effect than large gastrin, but the blood contains more large gastrin. Gastrin, which is produced by subgastrin cells and acts on parietal cells, stimulating the formation of HCl. It also acts on parietal cells.

Functions of gastrin - stimulates the secretion of hydrochloric acid, enhances the production of the enzyme, stimulates gastric motility, is necessary for the growth of the gastric mucosa. It also stimulates the secretion of pancreatic juice. The production of gastrin is stimulated not only by nervous factors, but also foods that are formed during the breakdown of food are also stimulants. These include protein breakdown products, alcohol, coffee - caffeinated and decaffeinated. The production of hydrochloric acid depends on ph and when the ph drops below 2x, the production of hydrochloric acid is suppressed. Those. this is due to the fact that a high concentration of hydrochloric acid inhibits the production of gastrin. At the same time, a high concentration of hydrochloric acid activates the production of somatostatin, and it inhibits the production of gastrin. Amino acids and peptides can act directly on the parietal cells and increase the secretion of hydrochloric acid. Proteins, having buffer properties, bind a hydrogen proton and maintain an optimal level of acid formation

Supports gastric secretion intestinal phase. When chyme enters duodenum 12, it affects gastric secretion. 20% of gastric juice is produced in this phase. It produces enterogastrin. Enterooksintin - these hormones are produced under the action of HCl, which comes from the stomach into the duodenum, under the influence of amino acids. If the acidity of the medium in the duodenum is high, then the production of stimulating hormones is suppressed, and enterogastron is produced. One of the varieties will be - GIP - gastro-inhibiting peptide. It inhibits the production of hydrochloric acid and gastrin. The inhibitory substances also include bulbogastron, serotonin and neurotensin. From the 12th side of the duodenum, reflex influences can also occur that excite the vagus nerve and include local nerve plexuses. In general, the separation of gastric juice will depend on the amount of food quality. The amount of gastric juice depends on the residence time of food. In parallel with the increase in the amount of juice, its acidity also increases.

The digestive power of the juice is greater in the first hours. To assess the digestive power of the juice, it is proposed Ment's method. Fatty foods inhibit gastric secretion, so it is not recommended to take fatty foods at the beginning of a meal. Hence, children are never given fish oil before meals. Preliminary intake of fats - reduces the absorption of alcohol from the stomach.

Meat - a protein product, bread - vegetable and milk - mixed.

For meat- the maximum amount of juice is released with a maximum secretion in the second hour. Juice has maximum acidity, fermentation is not high. The rapid increase in secretion is due to strong reflex irritation - sight, smell. Then, after the maximum secretion begins to decline, the decline in secretion is slow. The high content of hydrochloric acid ensures protein denaturation. The final breakdown takes place in the intestines.

Secretion for bread. The maximum is reached by the 1st hour. The rapid increase is associated with a strong reflex stimulus. Having reached the maximum, secretion drops rather quickly, because. there are few humoral stimulants, but the secretion lasts a long time (up to 10 hours). Enzymatic capacity - high - no acidity.

Milk - slow rise of secretion. Weak irritation of receptors. Contain fats, inhibit secretion. The second phase after reaching the maximum is characterized by a uniform decline. Here, the breakdown products of fats are formed, which stimulate secretion. Enzymatic activity is low. It is necessary to consume vegetables, juices and mineral water.

Secretory function of the pancreas.

Chyme that enters the 12th duodenum is exposed to the action of pancreatic juice, bile and intestinal juice.

Pancreas- the largest gland. It has a dual function - intrasecretory - insulin and glucagon and exocrine secretory function, which ensures the production of pancreatic juice.

Pancreatic juice is produced in the gland, in the acinus. Which are lined with transitional cells in 1 row. In these cells there is an active process of formation of enzymes. They have a well-defined endoplasmic reticulum, the Golgi apparatus, and the ducts of the pancreas begin from the acini and form 2 ducts that open into the 12th duodenum. The largest duct Wirsunga duct. It opens along with the common bile duct in the region of Vater's papilla. This is where the sphincter of Oddi is located. Second accessory duct Santorinni opens proximal to the Versung duct. Study - the imposition of fistulas on 1 of the ducts. In humans, it is studied by probing.

In my own way composition of pancreatic juice- transparent colorless liquid of alkaline reaction. The amount is 1-1.5 liters per day, pH 7.8-8.4. The ionic composition of potassium and sodium is the same as in plasma, but there are more bicarbonate ions, and less Cl. In the acinus, the content is the same, but as the juice moves along the ducts, it leads to the fact that the cells of the duct provide the capture of chloride anions and the amount of bicarbonate anions increases. Pancreatic juice is rich in enzyme composition.

Proteolytic enzymes acting on proteins - endopeptidases and exopeptidases. The difference is that endopeptidases act on internal bonds, while exopeptidases cleave off terminal amino acids.

Endopepidases- trypsin, chymotrypsin, elastase

Ectopeptidase- carboxypeptidases and aminopeptidases

Proteolytic enzymes are produced in an inactive form - proenzymes. Activation occurs under the action of enterokinase. It activates trypsin. Trypsin is released in the form of trypsinogen. And the active form of trypsin activates the rest. Enterokinase is an enzyme in the intestinal juice. With blockages in the duct of the gland and with heavy alcohol consumption, activation of pancreatic enzymes inside it may occur. The process of self-digestion of the pancreas begins - acute pancreatitis.

For carbohydrates aminolytic enzymes - alpha-amylase act, breaks down polysaccharides, starch, glycogen, cannot break down cellulo, with the formation of maltoise, maltothiose, and dextrin.

fatty litholytic enzymes - lipase, phospholipase A2, cholesterol. Lipase acts on neutral fats and breaks them down to fatty acids and glycerol, cholesterol esterase acts on cholesterol, and phospholipase on phospholipids.

Enzymes on nucleic acids- ribonuclease, deoxyribonuclease.

Regulation of the pancreas and its secretion.

It is associated with nervous and humoral mechanisms of regulation and the pancreas is switched on in 3 phases.

• Difficult reflex
• gastric
• intestinal

Secretory nerve - nervus vagus, which acts on the production of enzymes in the cell of the acini and on the cells of the ducts. There is no effect of sympathetic nerves on the pancreas, but sympathetic nerves cause a decrease in blood flow, and there is a decrease in secretion.

Of great importance humoral regulation pancreas - the formation of 2 hormones of the mucous membrane. The mucosa contains C cells that produce the hormone secretin and secretin being absorbed into the blood, it acts on the cells of the pancreatic ducts. Stimulates these cells by the action of hydrochloric acid

The 2nd hormone is produced by I cells - cholecystokinin. Unlike secretin, it acts on acinus cells, the amount of juice will be less, but the juice is rich in enzymes and the excitation of type I cells occurs under the action of amino acids and, to a lesser extent, hydrochloric acid. Other hormones act on the pancreas - VIP - has an effect similar to secretin. Gastrin is similar to cholecystokinin. In the complex reflex phase, secretion is released 20% of its volume, 5-10% falls on the gastric, and the rest on the intestinal phase, and so on. the pancreas is at the next stage of exposure to food, the production of gastric juice interacts very closely with the stomach. If gastritis develops, then pancreatitis follows.

Physiology of the liver.

The liver is the largest organ. The weight of an adult is 2.5% of the total body weight. For 1 minute, the liver receives 1350 ml of blood and this is 27% of the minute volume. The liver receives both arterial and venous blood.

1. Arterial blood flow - 400 ml per minute. Arterial blood enters through the hepatic artery.

2. Venous blood flow - 1500 ml per minute. Venous blood enters through the portal vein from the stomach, small intestine, pancreas, spleen, and partly the large intestine. It is through the portal vein that nutrients and vitamins from the digestive tract enter. The liver captures these substances and then distributes them to other organs.

An important role of the liver belongs to carbon metabolism. It maintains blood sugar levels by being a depot of glycogen. Regulates the content of lipids in the blood and especially the low density lipoproteins that it secretes. An important role in the protein department. All plasma proteins are made in the liver.

The liver performs a neutralizing function in relation to toxic substances and drugs.

It performs a secretory function - the formation of bile by the liver and the excretion of bile pigments, cholesterol, and medicinal substances. Carries out endocrine function.

The functional unit of the liver is hepatic lobule, which is built from hepatic beams formed by hepatocytes. In the center of the hepatic lobule is the central vein, into which blood flows from the sinusoids. Collects blood from capillaries of a portal vein and capillaries of a hepatic artery. The central veins, merging with each other, gradually form the venous system of outflow of blood from the liver. And the blood from the liver flows through the hepatic vein, which flows into the inferior vena cava. In the hepatic beams, upon contact of neighboring hepatocytes, bile ducts. They are separated from the intercellular fluid by tight junctions, which prevents the mixing of bile and extracellular fluid. The bile formed by hepatocytes enters the tubules, which gradually merge to form the system of intrahepatic bile ducts. It eventually enters the gallbladder or through the common duct into the duodenum. The common bile duct connects to Persungov pancreatic duct and together with it opens at the top Vaterova pacifier. There is a sphincter at the exit of the common bile duct. Oddy, which regulate the flow of bile into the 12th duodenum.

Sinusoids are formed by endothelial cells that lie on the basement membrane, around - perisinusoidal space - space Disse. This space separates sinusoids and hepatocytes. Hepatocyte membranes form numerous folds, villi, and they protrude into the peresinusoidal space. These villi increase the area of ​​contact with the peresophageal fluid. Weak expression of the basement membrane, sinusoid endothelial cells contain large pores. The structure resembles a sieve. Pores pass substances from 100 to 500 nm in diameter.

The amount of proteins in the peresinusoidal space will be greater than in plasma. There are macrocytes of the macrophage system. These cells, through endocytosis, ensure the removal of bacteria, damaged erythrocytes, and immune complexes. Some sinusoid cells in the cytoplasm may contain droplets of fat - cells Ito. They contain vitamin A. These cells are associated with collagen fibers, their properties are close to fibroblasts. They develop with cirrhosis of the liver.

Production of bile by hepatocytes - the liver produces 600-120 ml of bile per day. Bile performs 2 important functions -

1. It is necessary for the digestion and absorption of fats. Due to the presence of bile acids - bile emulsifies fat and turns it into small droplets. The process will promote a better action of lipases, for better breakdown into fats and bile acids. Bile is necessary for the transport and absorption of cleavage products.

2. Excretory function. It removes bilirubin and cholesterol. The secretion of bile occurs in 2 stages. Primary bile is formed in hepatocytes, it contains bile salts, bile pigments, cholesterol, phospholipids and proteins, electrolytes, which are identical in content to plasma electrolytes, except bicarbonate anion, which is more in bile. This is what gives the alkaline reaction. This bile comes from hepatocytes to the bile ducts. At the next stage, bile moves along the interlobular, lobar duct, then to the hepatic and common bile duct. As bile progresses, ductal epithelial cells secrete sodium and bicarbonate anions. This is essentially a secondary secretion. The volume of bile in the ducts can increase by 100%. Secretin increases bicarbonate secretion to neutralize hydrochloric acid from the stomach.

Outside of digestion, bile is stored in the gallbladder, where it enters through the cystic duct.

Secretion of bile acids.

Liver cells secrete 0.6 acids and their salts. Bile acids are formed in the liver from cholesterol, which enters the body either with food, or can be synthesized by hepatocytes during salt metabolism. When carboxyl and hydroxyl groups are added to the steroid nucleus, primary bile acids

ü Holevaya

ü Chenodeoxycholic

They combine with glycine, but to a lesser extent with taurine. This leads to the formation of glycocholic or taurocholic acids. When interacting with cations, sodium and potassium salts are formed. Primary bile acids enter the intestines and in the intestines, intestinal bacteria convert them into secondary bile acids

• Deoxycholic
• Litocholic

Bile salts are more ion-forming than the acids themselves. Bile salts are polar compounds, which reduces their penetration through the cell membrane. Therefore, absorption will decrease. By combining with phospholipids and monoglycerides, bile acids contribute to the emulsion of fats, increase the activity of lipase and convert the products of fat hydrolysis into soluble compounds. Since bile salts contain hydrophilic and hydrophobic groups, they take part in the formation with cholesterols, phospholipids and monoglycerides to form cylindrical discs, which will be water-soluble micelles. It is in such complexes that these products pass through the brush border of enterocytes. Up to 95% of bile salts and acids are reabsorbed in the intestine. 5% will be excreted in the feces.

Absorbed bile acids and their salts combine in the blood with high-density lipoproteins. Through the portal vein, they again enter the liver, where 80% are again captured from the blood by hepatocytes. Thanks to this mechanism, a reserve of bile acids and their salts is created in the body, which ranges from 2 to 4 g. There, the enterohepatic cycle of bile acids takes place, which promotes the absorption of lipids in the intestine. For people who do not eat much, this turnover occurs 3-5 times a day, and for people who eat a lot of food, such a cycle can increase up to 14-16 times a day.

Inflammatory conditions of the small intestine mucosa reduce the absorption of bile salts, which impairs the absorption of fats.

Cholesterol - 1.6-8, mmol/l

Phospholipids - 0.3-11 mmol / l

Cholesterol is considered as a by-product. Cholesterol is practically insoluble in pure water, but when combined with bile salts in micelles, it turns into a water-soluble compound. In some pathological conditions, cholesterol precipitates, calcium is deposited in it, and this causes the formation of gallstones. Gallstone disease is a fairly common disease.

• The formation of bile salts is facilitated by excessive absorption of water in the gallbladder.
• Excessive absorption of bile acids from bile.
• Increase in cholesterol in bile.
• Inflammatory processes in the gallbladder mucosa

The capacity of the gallbladder is 30-60 ml. For 12 hours in the gallbladder it can accumulate up to 450 ml of bile and this happens due to the process of concentration, while water, sodium and chloride ions, other electrolytes are absorbed and usually the bile is concentrated in the bladder 5 times, but the maximum concentration is 12-20 times. Approximately half of the soluble compounds in gallbladder bile are bile salts, and high concentrations of bilirubin, cholesterol and leucitin are also achieved here, but the electrolyte composition is identical to plasma. The emptying of the gallbladder occurs during the digestion of food and especially fat.

The process of emptying the gallbladder is associated with the hormone cholecystokinin. It relaxes the sphincter Oddy and helps to relax the muscles of the bladder itself. Peristaltic contractions of the bladder then go to the cystic duct, the common bile duct, which leads to the removal of bile from the bladder into the duodenum. The excretory function of the liver is associated with the excretion of bile pigments.

Bilirubin.

Monocyte is a macrophage system in the spleen, bone marrow, and liver. 8 g of hemoglobin breaks down per day. When hemoglobin breaks down, 2-valent iron is split off from it, which combines with protein and is deposited in reserve. From 8 g Hemoglobin => biliverdin => bilirubin (300 mg per day) The norm of bilirubin in the blood serum is 3-20 μmol / l. Above - jaundice, staining of the sclera and mucous membranes of the oral cavity.

Bilirubin binds to a transport protein blood albumin. This is indirect bilirubin. Bilirubin from blood plasma is captured by hepatocytes and in hepatocytes bilirubin combines with glucuronic acid. Bilirubin glucuronil is formed. This form enters the bile ducts. And already in the bile this form gives direct bilirubin. It enters the intestine through the bile duct system. In the intestine, intestinal bacteria split off glucuronic acid and convert bilirubin into urobilinogen. Part of it undergoes oxidation in the intestines and enters the feces and is already called stercobilin. The other part will be absorbed and enter the bloodstream. From the blood it is captured by hepatocytes and again enters the bile, but some will be filtered in the kidneys. Urobilinogen enters the urine.

Prehepatic (hemolytic) jaundice caused by a massive breakdown of red blood cells as a result of the Rh conflict, the entry into the blood of substances that cause the destruction of red blood cell membranes and some other diseases. With this form of jaundice, the content of indirect bilirubin in the blood is increased, the content of stercobilin in the urine is increased, bilirubin is absent, and the content of stercobilin in the feces is increased.

Hepatic (parenchymal) jaundice caused by damage to liver cells during infections and intoxications. With this form of jaundice, the content of indirect and direct bilirubin is increased in the blood, the content of urobilin is increased in the urine, bilirubin is present, and the content of stercobilin in the feces is reduced.

Subhepatic (obstructive) jaundice caused by a violation of the outflow of bile, for example, when the bile duct is blocked by a stone. With this form of jaundice, the content of direct bilirubin (sometimes indirect) is increased in the blood, there is no stercobilin in the urine, bilirubin is present, and the content of stercobilin in the feces is reduced.

Regulation of bile formation.

Regulation is based on feedback mechanisms based on the level of concentration of bile salts. The content in the blood determines the activity of hepatocytes in the production of bile. Outside the period of digestion, the concentration of bile acids decreases and this is a signal for increased formation of hepatocytes. The excretion into the duct will decrease. After eating, there is an increase in the content of bile acids in the blood, which, on the one hand, inhibits the formation in hepatocytes, but at the same time enhances the release of bile acids in the tubules.

Cholecystokinin is produced under the action of fatty and amino acids and causes bladder contraction and sphincter relaxation - i.e. stimulation of bladder emptying. Secretin, which is released by the action of hydrochloric acid on C cells, enhances tubular secretion and increases the content of bicarbonate.

Gastrin affects hepatocytes and enhances secretory processes. Indirectly, gastrin increases the content of hydrochloric acid, which then increases the content of secretin.

Steroid hormones- Estrogens and some androgens inhibit the formation of bile. The mucosa of the small intestine produces motilin- It promotes the contraction of the gallbladder and the excretion of bile.

Influence of the nervous system- through the vagus nerve - enhances bile formation and the vagus nerve contributes to the contraction of the gallbladder. Sympathetic influences are inhibitory in nature and cause relaxation of the gallbladder.

Intestinal digestion.

In the small intestine - the final digestion and absorption of the products of digestion. The small intestine receives 9 liters daily. Liquids. We absorb 2 liters of water with food, and 7 liters come from the secretory function of the gastrointestinal tract, and of this amount, only 1-2 liters will enter the large intestine. The length of the small intestine to the ileocecal sphincter is 2.85 m. The corpse is 7 m.

The mucous membrane of the small intestine forms folds that increase the surface by 3 times. 20-40 villi per 1 sq. mm. This increases the area of ​​the mucosa by 8-10 times, and each villus is covered with epitheliocytes, endotheliocytes, containing microvilli. These are cylindrical cells, on the surface of which there are microvilli. From 1.5 to 3000 on 1 cell.

The length of the villi is 0.5-1 mm. The presence of microvilli increases the area of ​​the mucosa and it reaches 500 sq.m. Each villus contains a blindly ending capillary, a feeding arteriole approaches the villus, which breaks up into capillaries that pass at the top into venous capillaries and produce blood outflow through the venules. The blood flow is venous and arterial in opposite directions. Rotary-countercurrent systems. At the same time, a large amount of oxygen passes from arterial to venous blood without reaching the top of the villus. It is very easy to create conditions under which the tops of the villi will receive less oxygen. This can lead to the death of these areas.

glandular apparatus - Bruner's glands in the duodenum. Liberty glands in the jejunum and ileum. There are goblet cells that produce mucus. The glands of the 12th duodenum resemble the glands of the pyloric part of the stomach and they secrete a mucous secret for mechanical and chemical irritation.

Them regulation takes place under the influence vagus nerves and hormones especially secretin. The mucous secretion protects the duodenum from the action of hydrochloric acid. The sympathetic system reduces the production of mucus. When we experience striving, we have an easy opportunity to get a duodenal ulcer. By reducing the protective properties.

The secret of the small intestine formed by enterocytes, which begin their maturation in the crypts. As the enterocyte matures, they begin to move towards the top of the villi. It is in the crypts that the cells actively transport chlorine and bicarbonate anions. These anions create a negative charge that attracts sodium. Osmotic pressure is created, which attracts water. Some pathogenic microbes - dysentery bacillus, cholera vibrio increase the transport of chloride ions. This leads to a large release of fluid in the intestine up to 15 liters per day. Normally 1.8-2 liters per day. Intestinal juice is a colorless liquid, cloudy due to the mucus of epithelial cells, has an alkaline pH of 7.5-8. Intestinal juice enzymes accumulate inside enterocytes and are released along with them when they are rejected.

intestinal juice contains a complex of peptidases, which is called eryxin, which ensures the final breakdown of protein products to amino acids.

4 aminolytic enzymes - sucrase, maltase, isomaltase and lactase. These enzymes break down carbohydrates into monosaccharides. There is intestinal lipase, phospholipase, alkaline phosphatase and enterokinase.

Intestinal juice enzymes.

1. Peptidase complex (erypsin)

2.Amylolytic enzymes- sucrase, maltase, isomaltase, lactase

3. Intestinal lipase

4. Phospholipase

5. Alkaline phosphatase

6. Enterokinase

These enzymes accumulate inside the enterocytes and the latter, as they mature, rise to the top of the villi. At the top of the villus, the rejection of enterocytes occurs. Within 2-5 days, the intestinal epithelium is completely replaced by new cells. Enzymes can enter the intestinal cavity - abdominal digestion, the other part is fixed on the membranes of microvilli and provides membranous or parietal digestion.

Enterocytes are covered with a layer glycocalyx- carbon surface, porous. It is a catalyst that promotes the breakdown of nutrients.

The regulation of acid separation occurs under the influence of mechanical and chemical stimuli acting on the cells of the nerve plexuses. Doggel cells.

Humoral substances- (increase secretion) - secretin, cholecystokinin, VIP, motilin and enterocrinin.

Somatostatin inhibits secretion.

In the large intestine Liberty glands, a large number of mucous cells. Mucus and bicarbonate anions predominate.

Parasympathetic Influences- increase mucus secretion. With emotional arousal within 30 minutes, a large amount of secretion is formed in the large intestine, which causes the urge to empty. Under normal conditions, mucus provides protection, gluing of feces and neutralizes acids with the help of bicarbonate anions.

The normal microflora is of great importance for the function of the large intestine. It is non-pathogenic bacteria that take part in the formation of the immunobiological activity of the body - lactobacilli. They help to increase immunity and prevent the development of pathogenic microflora; when taking antibiotics, these bacteria die. The body's defenses are weakened.

Colon bacteria synthesize vitamin K and B vitamins.

Bacterial enzymes break down fiber by microbial fermentation. This process goes with the formation of gas. Bacteria can cause protein putrefaction. At the same time, in the large intestine, poisonous products- indole, skatole, aromatic hydroxy acids, phenol, ammonia and hydrogen sulfide.

Neutralization of toxic products occurs in the liver, where they combine with glucuric acid. Water is absorbed and stool is formed.

The composition of feces includes mucus, the remains of dead epithelium, cholesterol, products of changes in bile pigments - stercobilin and dead bacteria, which account for 30-40%. Fecal masses may contain undigested food debris.

Motor function of the digestive tract.

We need motor function at the 1st stage - absorption of food and chewing, swallowing, movement through the digestive canal. Motility contributes to the mixing of food and secretions of the glands, participates in the processes of absorption. Motility carries out the excretion of the end products of digestion.

The study of the motor function of the gastrointestinal tract is carried out using different methods, but it is widespread balloon cinematography- introduction into the cavity of the digestive canal of a canister connected to a recording device, while measuring the pressure, which reflects motility. Motor function can be observed with fluoroscopy, colonoscopy.

X-ray gastroscopy- a method of registration of electrical potentials arising in the stomach. Under experimental conditions, registration is taken from isolated sections of the intestine, visual observation of motor function. In clinical practice - auscultation - listening in the abdominal cavity.

Chewing- when chewing, food is crushed, frayed. Although this process is voluntary chewing is coordinated by the nerve centers of the brain stem, which ensure the movement of the lower jaw in relation to the upper. When the mouth opens, the proprioceptors of the muscles of the lower jaw are excited and reflexively cause contraction of the masseter, medial pterygoid and temporal muscles, which contributes to the closing of the mouth.

When the mouth is closed, food irritates the receptors of the oral mucosa. Which, when irritated, are sent to twoabdominal muscle and lateral pterygoid that help open the mouth. When the jaw drops, the cycle repeats again. With a decrease in the tone of the masticatory muscles, the lower jaw can drop under the force of gravity.

The muscles of the tongue are involved in the act of chewing.. They place food between the upper and lower teeth.

The main functions of chewing -

Destroy the cellulose shell of fruits and vegetables, promote mixing and wetting of food with saliva, improve contact with taste buds, increase the area of ​​​​contact with digestive enzymes.

Chewing releases odors that act on olfactory receptors. It enhances the pleasure of eating and stimulates gastric secretions. Chewing promotes the formation of a food bolus and its swallowing.

The chewing process changes the act of swallowing. We swallow 600 times a day - 200 swallows with food and drink, 350 without food and another 50 at night.

It's a complex coordinated act . Includes oral, pharyngeal and esophageal phase. Allocate arbitrary phase- until the food bolus hits the root of the tongue. This is an arbitrary phase that we can terminate. When the food bolus hits the root of the tongue, non-voluntary phase of swallowing. The act of swallowing starts from the root of the tongue towards the hard palate. The food bolus moves to the root of the tongue. The palatine curtain rises, as a lump passes through the palatine arches, the nasopharynx closes, the larynx rises - the epiglottis descends, the glottis descends, this prevents food from entering the respiratory tract.

The food bolus goes down the throat. Due to the muscles of the pharynx, the food bolus is moved. At the entrance to the esophagus is the upper esophageal sphincter. When the lump moves, the sphincter relaxes.

Sensory fibers of the trigeminal, glossopharyngeal, facial and vagus nerves take part in the swallowing reflex. It is through these fibers that signals are transmitted to the medulla oblongata. Coordinated muscle contraction is provided by the same nerves + hypoglossal nerve. It is the coordinated contraction of the muscles that directs the food bolus into the esophagus.

With the reduction of the pharynx - relaxation of the upper esophageal sphincter. When a food bolus enters the esophagus, esophageal phase.

In the esophagus there is a circular and longitudinal layer of muscles. Moving the lump with the help of a peristaltic wave, in which the circular muscles are above the food lump, and longitudinal in front. Circular muscles narrow the lumen, while longitudinal muscles expand. The wave moves the food bolus at a speed of 2-6 cm per second.

Solid food passes through the esophagus in 8-9 seconds.

Liquid causes relaxation of the muscles of the esophagus and the liquid flows in a continuous column in 1-2 s. When the food bolus reaches the lower third of the esophagus, it causes relaxation of the lower cardiac sphincter. The cardiac sphincter is in good shape at rest. Pressure - 10-15 mm Hg. Art.

Relaxation occurs reflexively with the participation vagus nerve and mediators that cause relaxation - vaso-intestinal peptide and nitric oxide.

When the sphincter is relaxed, the food bolus passes into the stomach. With the work of the cardiac sphincter, 3 unpleasant disorders occur - achalasia- occurs with sphincter sphincter contraction and weak peristalsis of the esophagus, which leads to expansion of the esophagus. Food stagnates, decays, an unpleasant odor appears. This condition does not develop as often as sphincter insufficiency and reflux condition- Throwing of gastric contents into the esophagus. This leads to irritation of the esophageal mucosa, heartburn appears.

Aerophagia- swallowing air. It is typical for infants. When sucking, air is swallowed. The child cannot be immediately laid horizontally. In an adult, it is observed with a hasty meal.

Outside the period of digestion, smooth muscles are in a state of tetanic contraction. During the act of swallowing, relaxation of the proximal stomach occurs. Together with the opening of the cardiac sphincter, the cardiac section relaxes. Decreased tone - receptive relaxation. Reducing the tone of the muscles of the stomach allows you to accommodate large amounts of food with a minimum pressure of the cavity. Receptive relaxation of the stomach muscles regulated by the vagus nerve.

Involved in relaxation of the stomach muscles choelcystokinin- promotes relaxation. The motor activity of the stomach in the proximal and distal calving on an empty stomach and after eating is expressed differently.

In condition on an empty stomach the contractile activity of the proximal section is weak, rare, and the electrical activity of smooth muscles is not great. Most of the stomach muscles do not contract on an empty stomach, but approximately every 90 minutes a strong contractile activity develops in the middle sections of the stomach, which lasts 3-5 minutes. This periodic motility is called migratory myoelectric complex - MMK, which develops in the middle sections of the stomach and then moves on to the intestines. It is believed that it helps to cleanse the gastrointestinal tract from mucus, exfoliated cells, bacteria. Subjectively, you and I feel the occurrence of these contractions in the form of suction, murmuring in the stomach. These signals increase the feeling of hunger.

The gastrointestinal tract on an empty stomach is characterized by periodic motor activity and is associated with the excitation of the hunger center in the hypothalamus. The level of glucose decreases, the content of calcium increases, choline-like substances appear. All this affects the center of hunger. From it, signals enter the cerebral cortex and then makes us realize that we are hungry. On the descending paths - periodic motility of the gastrointestinal tract. This prolonged activity gives signals that it is time to eat. If we take food in this state, then this complex is replaced by more frequent contractions in the stomach, which originate in the body and do not extend to the pyloric region.

The main type of stomach contraction during digestion is peristaltic contractions - contraction of the circular and longitudinal muscles. In addition to peristaltic, there are tonic contractions.

The main rhythm of peristalsis is 3 contractions per minute. The speed is 0.5-4cm per second. The contents of the stomach move towards the pyloric sphincter. A small part is pushed through the digestive sphincter, but when it reaches the pyloric region, a powerful contraction occurs here, which throws the rest of the contents back into the body. - retropulsation. It plays a very important role in the processes of mixing, grinding the food bolus to smaller particles.

Food particles no more than 2 cubic mm can pass into the duodenum.

The study of myoelectric activity showed that slow electrical waves appear in the smooth muscles of the stomach, which reflect the depolarization and repolarization of the muscles. The waves themselves do not lead to contraction. Contractions occur when the slow wave reaches a critical level of depolarization. An action potential appears at the top of the wave.

The most sensitive section is the middle third of the stomach, where these waves reach the threshold value - pacemakers of the stomach. He creates the main rhythm for us - 3 waves per minute. In the proximal part of the stomach, such changes do not occur. The molecular basis has not been sufficiently studied, but such changes are associated with an increase in the permeability to sodium ions, as well as an increase in the concentration of calcium ions in smooth muscle cells.

Found in the walls of the stomach are not muscle cells that are excited periodically - Kayala cells These cells are associated with smooth muscle. Evacuation of the stomach into the duodenum. Grinding is important. The evacuation is affected by the volume of gastric contents, chemical composition, calorie content and consistency of food, the degree of its acidity. Liquid foods are digested faster than solid foods.

When part of the gastric contents enters the 12th duodenum from the latter, obturator reflex- the pyloric sphincter closes reflexively, further intake from the stomach is not possible, gastric motility is inhibited.

Motility is inhibited when digesting fatty foods. In the stomach, the functional prepyloric sphincter- on the border of the body and the digestive part. There is a union of the digestive department and 12 small intestine.

It is inhibited by the formation of enterogastrons.

The rapid transition of the contents of the stomach into the intestines is accompanied by unpleasant sensations, severe weakness, drowsiness, dizziness. This occurs when the stomach is partially removed.

Motor activity of the small intestine.

The smooth muscles of the small intestine on an empty stomach may also contract due to the appearance of the myoelectric complex. Every 90 minutes. After a meal, the migrating myoelectric complex is replaced by the motility that is characteristic of digestion.

In the small intestine, motor activity in the form of rhythmic segmentation can be observed. Contraction of the circular muscles leads to segmentation of the intestine. There is a change of shrinking segments. Segmentation is necessary for mixing food, if longitudinal contractions are added to the contraction of the circular muscles (narrow the lumen). From the circular muscles - the movement of the contents is mask-like - in different directions

Segmentation occurs approximately every 5 seconds. This is a local process. It captures segments at a distance of 1-4 cm. Peristaltic contractions are also observed in the small intestine, which cause the contents to move towards the ileocecal sphincter. The contraction of the intestine occurs in the form of peristaltic waves that occur every 5 seconds - a multiple of 5 - 5.10.15, 20 seconds.

The contraction in the proximal sections is more frequent, up to 9-12 per minute.

In distal calving 5 - 8. The regulation of motility of the small intestine is stimulated by the parasympathetic system and suppressed by the sympathetic. Local plexuses that can regulate motility in small areas of the small intestine.

Muscle relaxation - humoral substances involved- VIP, nitric oxide. Serotonin, methionine, gastrin, oxytocin, bile - stimulate motility.

Reflex reactions occur when irritated by the products of digestion of food and mechanical stimuli.

The contents of the small intestine pass into the large intestine through ileocecal sphincter. This sphincter is closed outside the period of digestion. After eating, every 20 - 30 seconds it opens. Up to 15 milliliters of contents from the small intestine enters the blind.

An increase in pressure in the caecum reflexively closes the sphincter. Periodic evacuation of the contents of the small intestine into the large intestine is carried out. Filling of the stomach - causes the opening of the ileocecal sphincter.

The large intestine is different in that the longitudinal muscle fibers do not go in a continuous layer, but in separate ribbons. The large intestine forms a sac-like expansion - gaustra. This is an expansion that is formed by the expansion of smooth muscles and mucous membranes.

In the colon, we observe the same processes, only more slowly. There is segmentation, pendulum-like contractions. Waves can propagate to the rectum and back. The content moves slowly in one direction and then in the other. During the day, forcing peristaltic waves are observed 1-3 times that move the contents to the rectum.

The motorboat is regulated parasympathetic (excite) and sympathetic (inhibit) influences. Blind, transverse, ascending - vagus nerve. Descending, sigmoid and rectus - pelvic nerve. sympathetic- superior and inferior mesenteric ganglion and hypogastric plexus. From humoral stimulants- substance P, tachykinins. VIP, Nitric Oxide - slow down.

The act of defecation.

The rectum is normally empty. Filling of the rectum occurs during the passage and forcing of the wave of peristalsis. When the feces enter the rectum, they cause a distension of more than 25% and a pressure above 18 mm Hg. relaxation of the internal smooth muscle sphincter.

Sensitive receptors inform the central nervous system, causing the urge. It is also controlled by the external sphincter of the rectum - striated muscles, regulated arbitrarily, innervation - pudendal nerve. Contraction of the external sphincter - suppression of the reflex, feces go proximally. If the act is possible, relaxation of both the internal and external sphincter occurs. The longitudinal muscles of the rectum contract, the diaphragm relaxes. The act is facilitated by the contraction of the pectoral muscles, the muscles of the abdominal wall and the muscles lifting the anus.

The concept of physiology can be interpreted as the science of the laws of operation and regulation of a biological system in conditions of health and the presence of diseases. Physiology studies, among other things, the vital activity of individual systems and processes, in a particular case, this is, i.e. the vital activity of the digestive process, the patterns of its work and regulation.

The very concept of digestion means a complex of physical, chemical and physiological processes, as a result of which, in the process, they are split into simple chemical compounds - monomers. Passing through the wall of the gastrointestinal tract, they enter the bloodstream and are absorbed by the body.

The digestive system and the process of digestion in the oral cavity

A group of organs is involved in the process of digestion, which is divided into two large sections: the digestive glands (salivary glands, glands of the liver and pancreas) and the gastrointestinal tract. Digestive enzymes are divided into three main groups: proteases, lipases, and amylases.

Among the functions of the digestive tract, one can note: the promotion of food, the absorption and excretion of undigested food residues from the body.

The process is born. During chewing, the food supplied in the process is crushed and moistened with saliva, which is produced by three pairs of large glands (sublingual, submandibular and parotid) and microscopic glands located in the mouth. Saliva contains the enzymes amylase and maltase, which break down nutrients.

Thus, the process of digestion in the mouth consists in the physical crushing of food, exerting a chemical effect on it and moisturizing it with saliva for ease of swallowing and continuing the digestion process.

Digestion in the stomach

The process begins with the fact that food, crushed and moistened with saliva, passes through the esophagus and enters the organ. Within a few hours, the food bolus experiences mechanical (muscle contraction when moving to the intestines) and chemical effects (gastric juice) inside the organ.

Gastric juice consists of enzymes, hydrochloric acid and mucus. The main role belongs to hydrochloric acid, which activates enzymes, promotes fragmentary cleavage, has a bactericidal effect, destroying a lot of bacteria. The enzyme pepsin in the composition of gastric juice is the main one, splitting proteins. The action of mucus is aimed at preventing mechanical and chemical damage to the shell of the organ.

What composition and amount of gastric juice will depend on the chemical composition and nature of food. The sight and smell of food contributes to the release of the necessary digestive juice.

As the digestion process progresses, food gradually and portionwise moves into the duodenum.

Digestion in the small intestine

The process begins in the cavity of the duodenum, where the food bolus is affected by pancreatic juice, bile and intestinal juice, since it contains the common bile duct and the main pancreatic duct. Inside this organ, proteins are digested into monomers (simple compounds) that are absorbed by the body. Learn more about the three components of chemical exposure in the small intestine.

The composition of pancreatic juice includes the enzyme trypsin, which breaks down proteins, which converts fats into fatty acids and glycerol, the enzyme lipase, as well as amylase and maltase, which break down starch into monosaccharides.

Bile is synthesized by the liver and stored in the gallbladder, from where it enters the duodenum. It activates the lipase enzyme, participates in the absorption of fatty acids, increases the synthesis of pancreatic juice, and activates intestinal motility.

Intestinal juice is produced by special glands in the inner lining of the small intestine. It contains over 20 enzymes.

There are two types of digestion in the intestine and this is its feature:

• cavitary - carried out by enzymes in the cavity of the organ;
• contact or membrane - performed by enzymes that are located on the mucous membrane of the inner surface of the small intestine.

Thus, food substances in the small intestine are actually completely digested, and the end products - monomers are absorbed into the blood. Upon completion of the digestion process, the digested food remains from the small intestine into the large intestine.

Digestion in the large intestine

The process of enzymatic processing of food in the large intestine is rather insignificant. However, in addition to enzymes, obligate microorganisms (bifidobacteria, Escherichia coli, streptococci, lactic acid bacteria) are involved in the process.

Bifidobacteria and lactobacilli are extremely important for the body: they have a beneficial effect on the functioning of the intestines, participate in the breakdown, ensure the quality of protein and mineral metabolism, enhance the body's resistance, and have an antimutagenic and anticarcinogenic effect.

Intermediate products of carbohydrates, fats and proteins are broken down here to monomers. Colon microorganisms produce (groups B, PP, K, E, D, biotin, pantothenic and folic acids), a number of enzymes, amino acids and other substances.

The final stage of the digestion process is the formation of fecal masses, which are 1/3 composed of bacteria, and also contain epithelium, insoluble salts, pigments, mucus, fiber, etc.

Absorption of nutrients

Let's dwell on the process separately. It represents the ultimate goal of the digestion process, when food components are transported from the digestive tract to the internal environment of the body - blood and lymph. Absorption occurs in all parts of the gastrointestinal tract.

Absorption in the mouth is practically not carried out due to the short period (15 - 20 s) of food in the cavity of the organ, but not without exceptions. In the stomach, the absorption process partially covers glucose, a number of amino acids, dissolved alcohol. Absorption in the small intestine is the most extensive, largely due to the structure of the small intestine, which is well adapted to the suction function. Absorption in the large intestine concerns water, salts, vitamins and monomers (fatty acids, monosaccharides, glycerol, amino acids, etc.).

The central nervous system coordinates all nutrient absorption processes. Humoral regulation is also involved.

The process of protein absorption occurs in the form of amino acids and water solutions - 90% in the small intestine, 10% in the large intestine. Absorption of carbohydrates is carried out in the form of various monosaccharides (galactose, fructose, glucose) at different rates. Sodium salts play a role in this. Fats are absorbed in the form of glycerol and fatty acids in the small intestine into the lymph. Water and mineral salts begin to be absorbed in the stomach, but this process proceeds more intensively in the intestines.

Thus, it covers the process of digestion of nutrients in the mouth, in the stomach, in the small and large intestines, as well as the process of absorption.

Digestion- a set of physical, chemical and physiological processes that ensure the processing and transformation of food into simple chemical compounds that can be absorbed by the cells of the body. These processes occur in a certain sequence in all parts of the digestive tract (oral cavity, pharynx, esophagus, stomach, small and large intestines with the participation of the liver and gallbladder, pancreas), which is ensured by regulatory mechanisms of various levels. The sequential chain of processes leading to the breakdown of nutrients into absorbable monomers is called the digestive conveyor.

Depending on the origin of hydrolytic enzymes, digestion is divided into 3 types: proper, symbiotic and autolytic.

own digestion carried out by enzymes synthesized by the glands of a person or animal.

Symbiotic digestion occurs under the influence of enzymes synthesized by the symbionts of the macroorganism (microorganisms) of the digestive tract. This is how fiber is digested in the large intestine.

Autolytic digestion carried out under the influence of enzymes contained in the composition of the food taken. Mother's milk contains the enzymes needed to curdle it.

Depending on the localization of the process of hydrolysis of nutrients, intracellular and extracellular digestion are distinguished.

intracellular digestion is a process of hydrolysis of substances inside the cell by cellular (lysosomal) enzymes. Substances enter the cell by phagocytosis and pinocytosis. Intracellular digestion is characteristic of protozoa. In humans, intracellular digestion occurs in leukocytes and cells of the lymphoreticulo-histiocytic system. In higher animals and humans, digestion is carried out extracellularly.

extracellular digestion divided into distant (cavitary) and contact (parietal, or membrane).

• Distant (cavity) digestion is carried out with the help of enzymes of digestive secrets in the cavities of the gastrointestinal tract at a distance from the place of formation of these enzymes.
• Contact (parietal, or membrane) digestion occurs in the small intestine in the glycocalyx zone, on the surface of microvilli with the participation of enzymes fixed on the cell membrane and ends with absorption - transport of nutrients through the enterocyte into the blood or lymph.

The importance of digestion and its types. Functions of the digestive tract

For the existence of an organism, it is necessary to constantly replenish energy costs and the supply of plastic material that serves to renew cells. This requires the intake of proteins, fats, carbohydrates, minerals, trace elements, vitamins and water from the external environment. There are the following types of digestion:

1. Autolytic. Carried out by enzymes found in the food itself.

2. Symbiotic. Occurs with the help of symbiotic organisms (human intestinal microflora breaks down about 5% of fiber to glucose, in ruminants 70-80%).

3. Own. Carried out by specialized digestive organs.

a. Cavitary - enzymes located in the cavity of the digestive canal.

b. Membrane or parietal - enzymes adsorbed on the membranes of the cells of the digestive canal.

c. Cellular - cell enzymes.

Own digestion is a process of physical and chemical processing of food by specialized organs, as a result of which it turns into substances that can be absorbed in the digestive canal and assimilated by the cells of the body.

The digestive organs perform the following functions:

1. Secretory. It consists in the production of digestive juices necessary for the hydrolysis of food components.

2. Motor and motor. Provides mechanical processing of food, its movement through the digestive canal and the removal of undigested products.

3. Suction. Serves for absorption from the gastrointestinal tract of hydrolysis products.

4. Excretory. Thanks to it, undigested residues and metabolic products are excreted through the gastrointestinal tract.

5. Hormonal. There are cells in the gastrointestinal tract that produce local hormones. They are involved in the regulation of digestion and other physiological processes.

Digestion in the mouth. The composition and physiological significance of saliva

Food processing begins in the mouth. A person has food in it for 15-20 seconds. Here it is crushed, moistened with saliva and turns into a food lump. Absorption of certain substances occurs in the oral cavity. For example, small amounts of glucose and alcohol are absorbed. The ducts of 3 pairs of large salivary glands open into it: parotid, submandibular and sublingual. In addition, there are a large number of small glands in the mucous membrane of the tongue, cheeks and palate. During the day, about 1.5 liters of saliva is produced. saliva pH 5.8-8.0. The osmotic pressure of saliva is lower than that of blood. Saliva contains 99% water and 1% solids. The composition of the dry residue includes:

1. Minerals. Cations of potassium, sodium, calcium, magnesium. Anions of chlorine, rhodonate (SCN-), bicarbonate, phosphate anions.

2. Simple organic substances. Urea, creatinine, glucose.

3. Enzymes: ?-amylase, maltase, kallikrein, lysozyme (muramidase), a small amount of nucleases.

4. Proteins. Immunoglobulins A, some plasma proteins.

5. Mucin, a mucopolysaccharide that gives saliva its mucous properties.

Functions of saliva:

1. She plays a protective role. Saliva wets the oral mucosa, and mucin prevents its mechanical irritation. Lysozyme and rhodonate have an antibacterial effect. Immunoglobulins A and salivary nucleases also provide a protective function. Rejected substances are removed from the oral cavity with saliva. When they enter the mouth, a large amount of liquid saliva is released.

2. Saliva wets food and dissolves some of its components.

3. It promotes the adhesion of food particles, the formation of a food bolus and its swallowing (swallowing experience).

4. Saliva contains digestive enzymes that carry out the initial hydrolysis of carbohydrates, α-amylase breaks down starch to dextrins. It is active only in alkaline and neutral environments. Maltase hydrolyses the disaccharides maltose and sucrose to glucose.

5. Without the dissolution of dry food substances by saliva, the perception of taste is impossible.

6. Saliva provides mineralization of the teeth, because. contains phosphorus and calcium, i.e. performs a trophic function.

7. Excretory. With saliva, a small amount of protein metabolism products is excreted - urea, uric acid, creatinine, as well as salts of heavy metals.

Mechanism of saliva formation and regulation of salivation

In the glandular cells of the acini of the salivary glands are secretory granules. They carry out the synthesis of enzymes and mucin. The resulting primary secret exits the cells into the ducts. There it is diluted with water and saturated with minerals. The parotid glands are mainly formed by serous cells and produce a liquid serous secretion, and the sublingual glands by mucous membranes, which secrete saliva rich in mucin. Submandibular produce mixed serous-mucous saliva.

The regulation of salivation is predominantly carried out by nervous mechanisms. Outside of digestion, small glands mainly function. During the digestive period, the secretion of saliva increases significantly. The regulation of digestive secretion is carried out by conditioned and unconditional reflex mechanisms. Unconditional reflex salivation occurs when initially tactile, and then temperature and taste receptors of the oral cavity are stimulated. But the main role is played by taste. Nerve impulses from them along the afferent nerve fibers of the lingual, glossopharyngeal and upper laryngeal nerves enter the salivary center of the medulla oblongata. It is located in the region of the nuclei of the facial and glossopharyngeal nerves. From the center, impulses go along the efferent nerves to the salivary glands. To the parotid gland, efferent parasympathetic fibers go from the lower salivary nucleus as part of the Jacobson's nerve, and then the ear-temporal nerves. Parasympathetic nerves innervating the serous cells of the submandibular and sublingual glands start from the superior salivary nucleus, go as part of the facial nerve, and then the tympanic string. The sympathetic nerves innervating the glands come from the salivary nuclei of the II-VI thoracic segments, interrupt in the cervical ganglion, and then their postganglionic fibers go to the mucous cells. Therefore, irritation of the parasympathetic nerves leads to the release of a large amount of liquid saliva, and the sympathetic - a small amount of mucous. Conditioned reflex salivation begins earlier than unconditioned reflex. It arises on the smell, type of food, sounds preceding feeding. The conditioned reflex mechanisms of secretion are provided by the cerebral cortex, which stimulates the center of salivation through descending pathways.

A small contribution to the regulation of salivation is made by humoral factors. In particular, it is stimulated by acetylcholine and histamine, and thyroxine inhibits it. Kallikrein, produced by the salivary glands, stimulates the formation of bradykinin from plasma kininogens. It dilates the vessels of the glands and enhances the secretion of saliva.

Salivation in the experiment is investigated by imposing a fistula of the salivary duct, i.e. its removal to the skin of the cheek. In the clinic, pure saliva is collected using a Lappgi-Krasnogorsky capsule, which is attached to the exit of the excretory duct of the gland. The conductivity of the ducts of the glands is used using sialography. This is an X-ray examination of the ducts filled with the contrast agent ndolipol. The excretory function of the glands is studied by means of radiosialography. This is a recording of the secretion of radioactive iodine by the glands.

Chewing serves for the mechanical processing of food, i.e. its biting, crushing and grinding. When chewing, food is wetted with saliva, and a food bolus is formed from it. Chewing occurs due to the complex coordination of muscle contractions that provide movement of the teeth, tongue, cheeks and floor of the mouth. Chewing is examined using electromyography of masticatory muscles and mastication. This is a recording of chewing movements. On the masticogram, 5 phases of the masticatory period can be distinguished:

1. Resting phase.

2. Introduction of food into the mouth.

3. Initial crushing.

4. The main phase of chewing

5. Formation of a food bolus and swallowing.

The total duration of the chewing period is 15-30 seconds.

The strength of the masticatory muscles is examined using gnathodynamometry, their tonusmiotonometry, the effectiveness of chewing - chewing tests.

Chewing is a complex reflex act, i.e. it is carried out by unconditioned and conditioned reflex mechanisms. Unconditional reflex consists in the fact that the mechanoreceptors of periodontal teeth and oral mucosa are irritated by food. From them, impulses along the afferent fibers of the trigeminal, glossopharyngeal and upper laryngeal nerves enter the chewing center of the medulla oblongata. Through the efferent fibers of the trigeminal, facial and hypoglossal nerves, impulses go to the masticatory muscles, carrying out unconscious concerted contractions. Conditioned reflex influences allow you to arbitrarily regulate the chewing act.

swallowing

Swallowing is a complex reflex act that begins arbitrarily. The formed food bolus moves to the back of the tongue, the tongue is pressed against the hard palate and moves to the root of the tongue. Here it irritates the mechanoreceptors of the root of the tongue and palatine arches. From them, along the afferent nerves, impulses go to the swallowing center of the medulla oblongata. From it, along the efferent fibers of the hypoglossal, trigeminal, glossopharyngeal and vagus nerves, they enter the muscles of the oral cavity, pharynx, larynx, and esophagus. The soft palate reflexively rises and closes the entrance to the nasopharynx. At the same time, the larynx rises and the epiglottis descends, closing the entrance to the larynx. The food bolus is pushed into the expanded pharynx. This ends the oropharyngeal phase of swallowing. Then the esophagus is pulled up and its upper sphincter relaxes. The esophageal phase begins. The food bolus moves along the esophagus due to its peristalsis. The circular muscles of the esophagus contract above the food bolus and relax below it. The wave of contraction-relaxation extends to the stomach. This process is called primary peristalsis. When a food bolus approaches the stomach, the lower esophageal or cardiac sphincter relaxes, passing the bolus into the stomach. Outside of swallowing, it is closed and serves to prevent the reflux of gastric contents into the esophagus. If the food bolus gets stuck in the esophagus, then secondary peristalsis begins from its location, which is identical in mechanisms to the primary one. Solid food moves through the esophagus for 8-9 seconds. Liquid drains passively, without peristalsis, in 1-2 seconds. Swallowing disorders are called dysphagia. They occur with violations in the center of swallowing (rabies), innervation of the esophagus or muscle spasms. A decrease in the tone of the cardiac sphincter leads to a reflex, i.e. reflux of stomach contents into the esophagus (heartburn). If its tone, on the contrary, is increased, food accumulates in the esophagus. This phenomenon is called achalasia.

In the clinic, swallowing is examined fluoroscopically, by swallowing a suspension of barium sulfate (radiocontrast substance).

Digestion in the stomach

The stomach performs the following functions:

1. Depositor. Food stays in the stomach for several hours.

2. Secretory. The cells of its mucosa produce gastric juice.

3. Motor. It provides mixing and movement of food masses into the intestines.

4. Suction. It absorbs a small amount of water, glucose, amino acids, alcohols.

5. Excretory. With gastric juice, some metabolic products (urea, creatinine and salts of heavy metals) are excreted into the alimentary canal.

6. Endocrine or hormonal. In the gastric mucosa there are cells that produce gastrointestinal hormones - gastrin, histamine, motilin.

7. Protective. The stomach is a barrier to pathogenic microflora, as well as harmful nutrients (vomiting).

Composition and properties of gastric juice. The meaning of its components

1.5-2.5 liters of juice is formed per day. Outside of digestion, only 10-15 ml of juice per hour is secreted. Such juice has a neutral reaction and consists of water, mucin and electrolytes. When eating, the amount of juice formed increases by 500-1200 ml. The juice produced in this case is a colorless transparent liquid of a strongly acidic reaction, since it contains 0.5% hydrochloric acid. The pH of the digestive juice is 0.9-2.5. It contains 98.5% water and 1.5% solids. Of these, 1.1% are inorganic substances, and 0.4% are organic. The inorganic part of the dry residue contains cations of potassium, sodium, magnesium and anions of chlorine, phosphoric and sulfuric acids. Organic substances are represented by urea, creatinine, uric acid, enzymes and mucus.

Enzymes of gastric juice include peptidases, lipase, lysozyme. Pepsins are peptidases. It is a complex of several enzymes that break down proteins. Pepsins hydrolyze peptide bonds in a protein molecule with the formation of products of their incomplete cleavage - peptones and polypeptidosis. Pepsins are synthesized by the chief cells of the mucosa in an inactive form, in the form of pepsinogens. The hydrochloric acid of the juice cleaves off the protein that inhibits their activity. They become active enzymes. Pepsin A is active at pH=1.2-2.0. Pepsin C, gastrixin at pH=3.0-3.5. These two enzymes break down short chain proteins. Pepsin B, parapepsin is active at pH=3.0-3.5. It breaks down connective tissue proteins. Pepsin D, hydrolyzes milk protein - casein. Pepsins A, B, and D are mainly synthesized in the antrum. Gastriksin is formed in all parts of the stomach. Digestion of proteins is most active in the mucosal layer of mucus, since enzymes and hydrochloric acid are concentrated there. Gastric lipase breaks down emulsified milk fats. In an adult, its value is not great. In children, it hydrolyzes up to 50% of milk fat. Lysozyme destroys microorganisms that have entered the stomach.

Hydrochloric acid is formed in parietal cells through the following processes.

1. The transition of bicarbonate anions into the blood in exchange for hydrogen cations. The process of formation of bicarbonate anions in parietal cells occurs with the participation of carbonic anhydrase. As a result of such an exchange, alkalosis occurs at the height of secretion.

2. Due to the active transport of protons into these cells.

3. With the help of active transport of chloride anions in them.

Hydrochloric acid dissolved in gastric juice is called free. Found in association with proteins determines the bound acidity of the juice. All acidic juice products provide its overall acidity.

Value of Hydrochloric Acid Juice:

1. Activates pepsinogen.

2. Creates an optimal reaction environment for the action of pepsins.

3. Causes denaturation and loosening of proteins, providing access for pepsins to protein molecules.

4. Promotes curdling of milk, i.e. formation from dissolved caseinogen, insoluble casein.

5. Has an antibacterial effect.

6. Stimulates gastric motility and secretion of gastric glands.

7. Promotes the production of gastrointestinal hormones in the duodenum.

Mucus is produced by accessory cells. Mucin forms a membrane tightly adjacent to the mucosa. Thus, it protects its cells from mechanical damage and the digestive action of the juice. Mucus accumulates some vitamins (groups B and C), and also contains the internal factor of Castle. This gastromucoprotide is necessary for the absorption of vitamin B12, which ensures normal erythropoiesis.

Food coming from the oral cavity is located in the stomach in layers and is not mixed for 1-2 hours. Therefore, in the inner layers, the digestion of carbohydrates continues under the action of saliva enzymes.

Regulation of gastric secretion

Digestive secretion is regulated by neurohumoral mechanisms. Three phases are distinguished in it: complex reflex, gastric and intestinal. The complex reflex is divided into conditioned reflex and unconditional reflex periods. Conditioned reflex begins from the moment when the smell, type of food, sounds preceding feeding cause excitation of the olfactory, visual and auditory sensory systems. As a result, the so-called ignition gastric juice is produced. It has high acidity and great proteolytic activity. After food enters the oral cavity, the unconditioned reflex period begins. It irritates the tactile, temperature and taste buds of the mouth, pharynx and esophagus. Nerve impulses from them come to the center of regulation of gastric secretion of the medulla oblongata. From it, impulses along the efferent fibers of the vagus go to the gastric glands, stimulating their activity. Thus, in the first phase, the regulation of secretion is carried out by the bulbar secretion center, the hypothalamus, the limbic system and the cerebral cortex.

The gastric phase of secretion begins from the moment the food bolus enters the stomach. Basically, its regulation is provided by neurohumoral mechanisms. The food lump that has entered the stomach, as well as the released ignition juice, irritates the receptors of the gastric mucosa. Nerve impulses from them go to the bulbar center of gastric secretion, and from it through the vagus to the glandular cells, supporting secretion. At the same time, impulses are sent to the G-cells of the mucosa, which begin to produce the hormone gastrin. Basically, G-cells are concentrated in the anus of the stomach. Gastrin is the most powerful stimulant of hydrochloric acid secretion. It stimulates the secretory activity of the main cells to a lesser extent. In addition, acetylcholine, released from the endings of the vagus, causes the formation of histamine by the mast cells of the mucosa. Histamine acts on the H3 receptors of parietal cells, increasing their release of hydrochloric acid. Histamine plays a major role in enhancing the production of hydrochloric acid. To a certain extent, the intramural ganglia of the stomach, which also stimulate secretion, are also involved in the regulation of secretion.

The final intestinal phase begins with the passage of acidic chyme into the duodenum. The amount of juice released during it is small. The role of nervous mechanisms in the regulation of gastric secretion at this moment is insignificant. Initially, irritation of the mechano- and chemoreceptors of the intestine, the release of gastrin by its G-cells, stimulates the secretion of juice by the gastric glands. The products of protein hydrolysis especially enhance the release of gastrin. However, then the cells of the intestinal mucosa begin to produce the hormone secretin, which is a gastrin antagonist and inhibits gastric secretion. In addition, under the influence of fats, hormones such as gastric inhibitory peptide (GIP) and cholecystokinin-pancreozymin begin to be produced in the intestine. They also oppress her.

The composition of food affects gastric secretion. For the first time this phenomenon was studied in the laboratory of IP Pavlov. It has been established that proteins are the most powerful causative agents of secretion. They cause the secretion of highly acidic juice and great digestive power. They contain many extract substances (histamine, amino acids, etc.). The weakest causative agents of secretion are fats. They do not contain extractives and stimulate the production of GIP and cholecystokinin-pancreozymin in the duodenum. These effects of nutrients are used in diet therapy.

Violation of secretion is manifested by gastritis. Distinguish gastritis with increased, preserved and reduced secretion. They are caused by violations of neurohumoral mechanisms of regulation of secretion or damage to the glandular cells of the stomach. Excessive production of gastrin by G cells results in Zollinger-Ellison disease. It is manifested by hypersecretory activity of the parietal cells of the stomach, as well as the appearance of mucosal ulcers.

Motor and evacuation functions of the stomach

In the wall of the stomach there are smooth muscle fibers located in the longitudinal, circular and oblique directions. In the region of the pylorus, the circular muscles form the pyloric sphincter. During the period of food intake, the wall of the stomach relaxes and the pressure in it falls. This state is called receptive relaxation. It promotes the accumulation of food. The motor activity of the stomach is manifested by movements of three types:

1. Peristaltic contractions. They start in the upper parts of the stomach. There are cells pacemakers (pacemakers). From here, these circular contractions extend to the pyloric region. Peristalsis provides mixing and promotion of the chyme to the pyloric sphincter.

2. Tonic contractions. Rare single-phase contractions of the stomach. Contribute to the mixing of food masses.

3. Propulsive contractions. These are strong contractions of the antral and pyloric regions. They provide passage of chyme into the duodenum. The rate of transition of food masses into the intestine depends on their consistency and composition. Poorly ground food lingers longer in the stomach. Liquid moves faster. Fatty food slows down this process, and protein accelerates it.

The motor function of the stomach is regulated by myogenic mechanisms, extramural parasympathetic and sympathetic nerves, intramural plexuses, and humoral factors. Smooth muscle cells are pacemakers of the stomach are concentrated in the cardiac part. They are under the control of extramural nerves and intramural plexuses. The main role is played by the vagus. When the mechanoreceptors of the stomach are stimulated, impulses from them go to the centers of the vagus, and from them to the smooth muscles of the stomach, causing their contractions. In addition, impulses from mechanoreceptors go to the neurons of the intramural nerve plexuses, and from them to smooth muscle cells. Sympathetic nerves have a weak inhibitory effect on gastric motility. Gastrin and histamine speed up and increase the movement of the stomach. Inhibits their secretion and gastric inhibitory peptide.

The protective reflex of the digestive tract is vomiting. It consists in the removal of gastric contents. Vomiting is preceded by nausea. The vomiting center is located in the reticular formation of the medulla oblongata. Vomiting begins with a deep breath, after which the larynx closes. The stomach relaxes. Due to strong contractions of the diaphragm, the contents of the stomach are thrown out through the open esophageal sphincters.

Methods for studying the functions of the stomach

In the experiment, the main method for studying the functions of the stomach is chronic experience. For the first time, the operation of imposing a fistula of the stomach was performed in 1842 by the surgeon V. A. Basov. However, with the help of the Basov fistula, it was impossible to obtain pure gastric juice. Therefore, IP Pavlov and Shumova-Simonovskaya proposed a method of imaginary feeding. This is the operation of imposing a fistula of the stomach in combination with the transection of the esophagus - esophagotomy. This technique allowed not only to study pure gastric juice, but also to detect the complex reflex phase of gastric secretion. At the same time, Heidengays proposed the operation of an isolated stomach. It consists in cutting a triangular flap of the stomach wall from the greater curvature. Subsequently, the edges of the flap and the remaining parts of the stomach are sutured, and a small ventricle is formed. However, the Heidengais technique did not allow us to study the reflex mechanisms of secretion regulation, since the nerve fibers leading to the stomach were cut. Therefore, IP Pavlov proposed his own modification of this operation. It consists in the formation of an isolated stomach from a flap of greater curvature, when the serous layer is preserved. In this case, the nerve fibers going there are not cut.

In the clinic, gastric juice is taken with a thick gastric tube according to the Boas-Ewald method. Probing with a thin probe according to S. S. Zimnitsky is more often used. At the same time, portions of juice are collected every 15 minutes for an hour and its acidity is determined. Before probing, a trial breakfast is given. According to Boas-Ewald, this is 50 g of white bread and 400 ml of warm tea. In addition, meat broth according to Zimnitsky, cabbage juice, 10% alcohol solution, caffeine or histamine solution are used as a test breakfast. Subcutaneous administration of gastrin is also used as a secretion stimulator. Gastric motility in the experiment is studied using mechanoelectric sensors implanted in the wall of the stomach. The clinic uses fluoroscopy with barium sulfate. Now, for the diagnosis of disorders of secretion and motility, the method of fibrogastroscopy is widely used.