Big encyclopedia of oil and gas. Secretory function of the stomach. The process of digestion in the stomach

Education, composition and properties gastric juice. Gastric juice is produced by the glands of the stomach, located in its mucous membrane. It is covered with a layer of cylindrical epithelium, the cells of which secrete mucus and a slightly alkaline fluid. Mucus is secreted in the form of a thick gel that covers the entire mucosa in an even layer.
On the surface of the mucous membrane, small depressions are visible - gastric pits. Their total number reaches 3 million. In each of them, gaps of 3-7 tubular gastric glands open. There are three types of gastric glands: own glands of the stomach, cardiac and pyloric.
Own glands of the stomach are located in the area of ​​​​the body and fundus of the stomach (fundic). The fundic glands consist of three main types of cells: the main cells - secreting pepsinogens, parietal (parietal, oxinth glandulocytes) - hydrochloric acid and additional - mucus. Ratio different types cells in the glands of the mucous membrane of different parts of the stomach is not the same. The cardiac glands, located in the cardia of the stomach, are tubular glands composed primarily of mucus-producing cells. In the pyloric section of the gland, there are practically no parietal cells. The pyloric glands secrete a small amount of secretion, unstimulated by food intake. Leading value in gastric digestion has gastric juice produced by the fundic glands.
During the day, the human stomach secretes 2-2.5 liters of gastric juice. It is a colorless transparent liquid containing hydrochloric acid (0.3-0.5%) and therefore acidic (pH 1.5-1.8). The pH value of the contents of the stomach is much higher, since the juice of the fundic glands is partially neutralized by the food taken.
The gastric juice contains many inorganic substances: water (995 g/l), chlorides (5-6 g/l), sulfates (10 mg/l), phosphates (10-60 mg/l), sodium bicarbonates (0-1.2 g/l), potassium, calcium, magnesium, ammonia (20-80 kg/l). The osmotic pressure of gastric juice is higher than that of blood plasma.
Parietal cells produce hydrochloric acid of the same concentration (160 mmol/l), but the acidity of the secreted juice varies due to changes in the number of functioning parietal glandulocytes and neutralization of hydrochloric acid by the alkaline components of gastric juice. The faster the secretion of hydrochloric acid, the less it is neutralized and the higher the acidity of gastric juice.
The synthesis of hydrochloric acid in parietal cells is associated with cellular respiration and is an aerobic process; hypoxia stops acid secretion. According to the "carbonic anhydrase" hypothesis, H+ ions for the synthesis of hydrochloric acid are obtained as a result of hydration of CO2 and dissociation of the resulting H2CO3. This process is catalyzed by the enzyme carbonic anhydrase. According to the “redox” hypothesis, H+ ions for the synthesis of hydrochloric acid are supplied by the mitochondrial respiratory chain, and the transport of H+ and C1 ions is carried out at the expense of the energy of redox chains. The "ATPase" hypothesis states that the energy of ATP is used to transport these ions, and H + can come from various sources, including those supplied by carbonic anhydrase from the phosphate buffer system.
Complex processes culminating in the synthesis and extrusion of hydrochloric acid from parietal cells include three stages: 1) phosphorylation-dephosphorylation reactions; 2) mitochondrial oxidative chain operating in pump mode; i.e., carrying protons from the matrix space outward;

1. H+, K+-ATPase of the secretory membrane, which carries out the "pumping" of these protons from the cell into the lumen of the glands due to the energy of ATP.

1. The ratio of pepsin and gastrixin in human gastric juice ranges from 1:2 to 1:5. These enzymes differ in their action on different types proteins.

Rice. 9.11. Curves of juice secretion of the Pavlovian ventricle for meat, bread and milk.

mucosal lining of the stomach. The destruction of the mucous barrier and stimulation of the secretion of hydrochloric acid contributes to the activity of microorganisms Helicobacter pylori. In an acidic environment and under conditions of a disturbed mucosal barrier, digestion of the elements of the mucosa by pepsin (peptic factor of ulcer formation) is possible. This is also facilitated by a decrease in the secretion of bicarbonates and blood microcirculation in the gastric mucosa.
Regulation of gastric secretion. Outside of digestion, the glands of the stomach secrete a small amount of gastric juice. Eating dramatically increases its excretion. This occurs due to the stimulation of the gastric glands by nervous and humoral mechanisms that make up single system reflation. Stimulating and inhibitory regulatory factors ensure the dependence of gastric juice secretion on the type of food taken. This dependence was first discovered in the laboratory of IP Pavlov in experiments on dogs with an isolated Pavlovian ventricle, which were fed various foods. The volume and nature of secretion in time, the acidity and content of pepsins in the juice are determined by the type of food taken (Fig. 9.11).
Stimulation of hydrochloric acid secretion by parietal cells is carried out directly and indirectly through other mechanisms. The cholinergic fibers of the vagus nerves directly stimulate the secretion of hydrochloric acid by parietal cells, the mediator of which, acetylcholine (ACh), excites the M-cholinergic receptors of the basolateral membranes of glandulocytes. The effects of ACh and its analogues are blocked by atropine. Indirect stimulation of cells by the vagus nerves is also mediated by gastrin and histamine.
Gastrin is released from G-cells, most of which are located in the mucosa of the pyloric part of the stomach. After surgical removal of the pyloric part of the stomach
secretion is sharply reduced. The release of gastrin is enhanced by impulses of the vagus nerve, as well as local mechanical and chemical irritation of this part of the stomach. Chemical stimulators of G-cells are the products of protein digestion - peptides and some amino acids, extractives of meat and vegetables. If the pH in the antrum of the stomach decreases, which is due to an increase in the secretion of hydrochloric acid by the glands of the stomach, then the release of gastrin decreases, and at pH 1.0 it stops and the volume of secretion decreases sharply. Thus, gastrin is involved in the self-regulation of gastric secretion depending on the pH value of the contents of the antrum. Gastrin stimulates the parietal glandulocytes of the gastric glands to the greatest extent and increases the secretion of hydrochloric acid.
Histamine, which is formed in the ECL cells of the gastric mucosa, also belongs to the stimulants of the parietal cells of the gastric glands. The release of histamine is provided by gastrin. Histamine stimulates glandulocytes, affecting the Hg receptors of their membranes and causing the release of a large amount of juice of high acidity, but poor in pepsin.
The stimulating effects of gastrin and histamine depend on the preservation of the innervation of the gastric glands by the vagus nerves: after surgical and pharmacological vagotomy, the secretory effects of these humoral stimulants decrease.
Gastric secretion is also stimulated by the products of protein digestion absorbed into the blood.
Inhibition of hydrochloric acid secretion is caused by secretin, CCK, glucagon, GIP, VIP, neurotensin, UU polypeptide, somatostatin, thyroliberin, enterogastron, ADH, calcitonin, oxytocin, prostaglandin PGE2, bulbogastron, cologastron, serotonin (see Table 9.2 ). The release of some of them in the respective endocrine cells The intestinal mucosa is controlled by the properties of the chyme. In particular, the inhibition of gastric secretion by fatty foods is largely due to the effect of CCK on the gastric glands. An increase in the acidity of the contents of the duodenum inhibits the release of hydrochloric acid by the glands of the stomach. Inhibition of secretion is carried out reflexively, as well as due to the formation of duodenal hormones.
The mechanism of stimulation and inhibition of hydrochloric acid secretion by various neurotransmitters and hormones varies. Thus, ACh enhances acid secretion by parietal cells by activating membrane Na+, K+-ATPase, increasing the transport of Ca?+ ions and the effects of an increased intracellular cGMP content, releasing gastrin and potentiating its effect.
Gastrin enhances the secretion of hydrochloric acid through histamine, as well as by acting on membrane gastrin receptors and enhancing intracellular transport of Ca2+ ions. Histamine stimulates the secretion of parietal cells through their membrane H2 receptors and the adenylate cyclase (AC) - cAMP system.
The chief cells that stimulate pepsinogen secretion are the cholinergic fibers of the vagus nerves, gastrin, histamine, sympathetic fibers ending in p-adrenergic receptors, secretin, and CCK. Increased secretion of pepsinogens by the main cells of the gastric glands is carried out by several mechanisms. Among them, an increase in the transfer of Ca? + ions into the cell and stimulation of Na +, K + -ATPase; increased intracellular movement of zymogen granules, activation of membrane phosphorylase, which enhances their passage through the apical membranes, activation of the cGMP and cAMP systems.
These mechanisms are unequally activated or inhibited by various neurotransmitters and hormones, their direct and indirect effects on chief cells and pepsinogen secretion. It has been shown that histamine and gastrin affect it indirectly - they increase the secretion of hydrochloric acid, and a decrease in the pH of the contents of the stomach through a local cholinergic reflex enhances the secretion of chief cells. A direct stimulating effect of gastrin on them has also been described. In high doses, histamine inhibits their secretion. CCK, secretin, and p-agonists directly stimulate the secretion of chief cells, but inhibit the secretion of parietal cells, which indicates the existence of different receptors for regulatory peptides on them.
Stimulation of mucus secretion by mucosal cells is carried out by cholinergic fibers of the vagus nerves. Gastrin and histamine moderately stimulate mucocytes, apparently due to the removal of mucus from their membranes with a pronounced secretion of acidic gastric juice. A number of inhibitors of hydrochloric acid secretion - serotonin, somatostatin, adrenaline, dopamine, enkephalin, prostaglandin PGE2 - enhances mucus secretion. It is believed that PGE2 enhances mucus secretion by these substances.
When eating and digestion in the heavily secreting glands of the stomach, the blood flow increases, which is ensured by the action of cholinergic neural mechanisms, peptides of the digestive tract and local vasodilators. In the mucous membrane, the blood flow increases more intensively than in the submucosa and the muscular layer of the gastric wall.
Phases of gastric secretion. nervous, humoral factors and paracrine mechanisms finely regulate the secretion of the glands of the stomach, provide the release of a certain amount of juice, acid and enzyme secretion, depending on the quantity and quality of the food taken, the efficiency of its digestion in the stomach and small intestine. The secretion that occurs in this case is usually divided into three phases.
The initial secretion of the stomach occurs reflexively in response to irritation of distant receptors, excited by the sight and smell of food, by the entire environment associated with its intake (conditioned reflex irritations). In addition, the secretion of the stomach is excited reflexively in response to irritation of the oral and pharyngeal receptors taken with food (unconditioned reflex irritations). These reflexes provide triggering effects on the gastric glands. Gastric secretion, due to these complex reflex influences, is commonly called the first, or brain, phase of secretion (see Fig. 9.8).
The mechanisms of the first phase of gastric secretion have been studied in experiments on esophagotomized dogs with gastric fistula. When feeding such a dog, food falls out of the esophagus and does not enter the stomach, but 5-10 minutes after the start of imaginary feeding, gastric juice begins to stand out. Similar data were obtained in the study of people suffering from narrowing of the esophagus and undergoing as a result of this operation the imposition of a gastric fistula. Chewing food caused people to secrete gastric juice.
Reflex influences on the gastric glands are transmitted through the vagus nerves. After their transection in an esophagotomized dog, neither imaginary feeding nor the sight and smell of food cause secretion. If you irritate the peripheral ends of the cut vagus nerves, then there is a release of gastric juice with high content it contains hydrochloric acid and pepsin.
The gastrin mechanism is also included in the stimulation of the gastric glands in the first phase. The proof of this is the increase in the content of gastrin in the blood of people during imaginary feeding. After removal of the pyloric part of the stomach, where gastrin is produced, secretion in the first phase decreases.
Secretion in the cerebral phase depends on the excitability of the food center and can easily be inhibited by stimulation of various external and internal receptors. So, poor table setting, untidiness of the place of eating reduce and inhibit gastric secretion. Optimal eating conditions have a positive effect on gastric secretion. Reception at the beginning of a meal of strong food irritants increases gastric secretion in the first phase.
The secretion of the first phase is superimposed on the secretion of the second phase, which is called gastric, as it is due to the influence of the food content during its stay in the stomach. The presence of this phase of secretion is proved by the fact that putting food into the stomach through a fistula, infusing solutions through it or a probe into the stomach, irritation of its mechanoreceptors cause the separation of gastric juice. The volume of secretion is 2-3 times less than with a natural meal. This highlights the importance of launchers. reflex influences carried out mainly in the first phase on the gastric glands. In the second phase, the glands of the stomach experience mainly corrective influences. These influences, by strengthening and weakening the activity of the glands, ensure that the secretion corresponds to the quantity and properties of the food gastric contents, that is, they correct the secretory activity of the stomach.
Juice secretion during mechanical stimulation of the stomach is excited reflexively from the mechanoreceptors of the mucous membrane and the muscular layer of the stomach wall. Secretion is sharply reduced after transection of the vagus nerves. In addition, mechanical irritation of the stomach, especially its pyloric part, leads to the release of gastrin from G-cells.
An increase in the acidity of the contents of the antrum of the stomach inhibits the release of gastrin and reduces gastric secretion. In the fundic part of the stomach, the acidity of its contents reflexively enhances secretion, especially the release of pepsinogen. Of certain importance in the implementation of the gastric phase of secretion is histamine, a significant amount of which is formed in the gastric mucosa.
meat broth, cabbage juice, the products of protein hydrolysis, when introduced into the small intestine, cause the release of gastric juice. Nerve influences from the intestinal receptors to the glands of the stomach ensure secretion in the third, intestinal, phase. Excitatory and inhibitory influences from the duodenum and jejunum on the glands of the stomach are carried out with the help of nervous and humoral mechanisms that correct secretion. Nervous influences are transmitted from the mechano- and chemoreceptors of the intestine. Stimulation of the gastric glands in the intestinal phase is primarily the result of insufficiently physically and chemically processed gastric contents entering the duodenum. The hydrolysis products of nutrients, especially proteins, absorbed into the blood, take part in the stimulation of gastric secretion. These substances can excite the gastric glands indirectly through gastrin and histamine, as well as directly acting on the gastric glands.
Inhibition of gastric secretion in its intestinal phase is caused by a number of substances in the composition of the intestinal contents, which are arranged in the following order in decreasing force of inhibitory action: fat hydrolysis products, polypeptides, amino acids, starch hydrolysis products, H + (pH below 3 has a strong inhibitory effect ).
The release of secretin and CCK in the duodenum under the influence of the stomach contents entering the intestine and the resulting hydrolysis products of nutrients inhibits the secretion of hydrochloric acid, but enhances the secretion of pepsinogen. Gastric secretion is also inhibited by other intestinal hormones from the group of gastronomes and glucagon, as well as serotonin.
Influence food regimens for gastric secretion. In experiments on animals, IP Pavlov and his co-workers, and then IP Razenkov and his co-workers, showed that the secretion of the gastric glands changes significantly depending on the nature of nutrition. With prolonged (30-40 days) consumption of food containing a large amount of carbohydrates (bread, vegetables), secretion decreases (mainly in the second and third phases). If the animal for a long time (30-60 days) takes food rich in proteins, such as meat, then secretion increases, especially in the second and third phases. At the same time, not only the volume and dynamics of gastric secretion change, but also the enzymatic properties of gastric juice. A. M. Ugolev experimentally found that prolonged intake of plant foods increases the activity of gastric juice in relation to proteins plant origin(“phytolytic activity”), and the predominance of animal proteins in the diet increases the ability of gastric juice to hydrolyze them (“zoolytic activity”). This is due to a change in the acidity of the juice and the ratio of the types and properties of pepsins in it.

Methods for studying absorption in humans.

1. By the rate of occurrence of the pharmacological effect (nicotinic acid - redness of the skin of the face). 2. Radioisotope method(labeled substances pass from the intestines into the blood).

Study of the excretory function of the digestive tract.

Excretory function is studied by the amount of any substance in the contents of various departments gastrointestinal tract at certain intervals of time after the introduction of this substance into the blood.

Secretion is the process of synthesis by secretory cells of specific

substances, mainly enzymes, which, together with water and salts, are released into the lumen of the gastrointestinal tract and form digestive juices.

The production of secrets is carried out by secretory cells that combine in the gland.

The digestive tract contains the following types of glands :

1. Unicellular (goblet cells of the intestine). 2. Multicellular glands . They are subdivided on the:

a) simple - one duct (glands of the stomach, intestines); b) complex glands - several ducts, formed by a large number of heterogeneous cells (large salivary, pancreas, liver).

By the nature of functioning There are two types of glands:

1. Glands with continuous secretion . These include glands that produce mucus; liver. 2. Glands with intermittent secretion . These include some salivary, gastric, intestinal glands, and the pancreas.

In the study of the mechanisms of formation of secrets,

three mechanisms of secretion : 1. Holocrine - secretion is accompanied by cell destruction. 2. Apocrine - the secret accumulates in the apex, the cell loses the apex, which then collapses in the cavity of the organ. 3. Merocrine - the secret is released without morphological changes in the cell.

Types of digestion(from hydrolysis origin) :

1. Autolytic- due to enzymes found in foods of plant and animal origin. 2. Symbiotic - enzymes are produced by bacteria and protozoa of this macroorganism;

3. Own- due to enzymes synthesized by the digestive tract: a ) Intracellular - the most ancient type (not cells secrete enzymes, but the substance enters the cell and is broken down by enzymes there). b) Extracellular (distant, cavitary ) - enzymes are secreted into the lumen of the gastrointestinal tract, acting at a distance; in) Membrane (wall, contact) - in the mucous layer and the zone of the brush border of enterocytes adsorbed on enzymes (significantly higher rate of hydrolysis).

All secrets are

1. water 2. dry residue.

In the dry matter contains two groups of substances:

1. Substances that perform a specific function in this part of the digestive tract. 2. Enzymes . They are divided into: proteases, carbohydrases, lipases and nucleases.

Factors affecting enzyme activity:

1. Temperature, 2. pH of the medium, 3. The presence of activators for some of them (produced in an inactive form so that autolysis of the gland does not occur), 4. The presence of enzyme inhibitors

The activity of the glands and the composition of the juices depend on diet and dietary patterns. The total amount of digestive juices per day is 6-8 liters.

secretion in oral cavity

In the oral cavity, saliva is produced by 3 pairs of large and many small ones. salivary glands. The sublingual and small glands secrete a secret constantly. Parotid and submandibular - during stimulation.

1) The time spent by food in the oral cavity is on average 16-18 seconds. 2) The volume of daily secretion is 0.5-2 liters. Abdominal digestion 3) Secretion rate - from 0.25 ml / min. up to 200 ml / min. 4) pH - 5.25-8.0. The optimal environment for the action of enzymes is slightly alkaline. 5) The composition of saliva: BUT). Water - 99.5%. B). ions K, Na, Ca, Mg, Fe, Cl, F, PO 4 , SO 4 , CO 3 .B) . Squirrels (albumins, globulins, free amino acids), nitrogen-containing compounds of non-protein nature (ammonia, urea, creatinine). Their content increases with kidney failure. G). Specific Substances : -mucin (mucopolysaccharide), gives saliva viscosity, forms a food bolus. - lysozyme (muromidase) substance that provides bactericidal action (dogs lick the wound), - saliva nuclease - antiviral action, - immunoglobulin A - binds exotoxins. D) active white blood cells - phagocytosis (in cm 3 of saliva - 4000 pieces). E) normal microflora oral cavity, which depresses the pathological. AND). saliva enzymes . Refer to carbohydrase :1. Alpha amylase - breaks down starch into disaccharides.2. Alpha glucosidase - into sucrose and maltose - split to monosaccharides (active in a slightly alkaline environment).

Within the oral cavity, saliva enzymes have practically no effect (due to the short time spent food bolus in the oral cavity). The main effect is in the esophagus and stomach (until the acidic contents soak the food bolus).

Secretion in the stomach

The residence time of food in the stomach is 3-10 hours. On an empty stomach in the stomach is about 50 ml of contents (saliva, gastric secretion and contents of the duodenum 12) neutral pH (6.0). The volume of daily secretion is 1.5 - 2.0 l / day, pH - 0.8 - 1.5.

The glands of the stomach are made up of three types of cells.: chief cells - produce enzymes Parietal (cover)- HCl; Additional - slime.

The cellular composition of the glands changes in various parts of the stomach (in the antral - there are no main cells, in the pyloric - there are no parietal).

Digestion in the stomach is predominantly abdominal.

Composition of gastric juice

1. Water - 99 - 99,5%. 2. Specific Substances : Main inorganic component - HCl(m.b. in a free state and associated with proteins). The role of HCl in digestion : 1. Stimulates the secretion of the glands of the stomach.2. Activates the conversion of pepsinogen to pepsin.3. Creates optimal pH for enzymes. 4. Causes denaturation and swelling of proteins (easier to be broken down by enzymes). 5. Provides antibacterial action of gastric juice, and consequently, the preservative effect of food (there are no processes of decay and fermentation). 6. Stimulates gastric motility.7. Participates in the curdling of milk.8. Stimulates the production of gastrin and secretin ( intestinal hormones ). 9. Stimulates the secretion of enterokinase by the duodenal wall.

3. Organic specific substances: 1. Mucin - Protects the stomach from self-digestion. Mucin forms ( comes in 2 forms ):

a ) tightly bound with a cell, protects the mucosa from self-digestion;

b) loosely bound , covers the food bolus.2. Gastromucoprotein (Castle intrinsic factor) - necessary for the absorption of vitamin B12.

3. Urea, uric acid, lactic acid .4.Antienzymes.

Enzymes of gastric juice:

1) Basically - proteases , provide the initial hydrolysis of proteins (to peptides and a small amount amino acids). Common name - pepsins.

Are produced in inactive form(as pepsinogens). Activation occurs in the lumen of the stomach with the help of HCl, which cleaves off the inhibitory protein complex. Subsequent activation in progress autocatalytically (pepsin ). Therefore, patients with anacid gastritis are forced to take an HCl solution before meals to start digestion. Pepsins split bonds formed by phenylalanine, tyrosine, tryptophan and a number of other amino acids.

Pepsins:

1. Pepsin A - (optimum pH - 1.5-2.0) splits large proteins into peptides. It is not produced in the antrum of the stomach. 2. Pepsin B (gelatinase)- breaks down protein connective tissue- gelatin (active at pH less than 5.0). 3. Pepsin C (gastrixin) - an enzyme that breaks down animal fats, especially hemoglobin (optimum pH - 3.0-3.5). four. Pepsin D (re nn in ) - Curdles milk casein. Basically - in cattle, especially in calves - it is used in the manufacture of cheese (therefore, cheese is 99% absorbed by the body) In humans - chymosin (together with hydrochloric acid (curdles milk)). In children - fetal pepsin (optimum pH -3.5), curdles casein 1.5 times more actively than in adults. Curdled milk proteins are more easily digested.

2)Lipase. The gastric juice contains lipase, the activity of which is low, it acts only for emulsified fats(e.g. milk, fish oil). Break down fats into glycerol and fatty acids at pH 6-8(in a neutral environment). In children, gastric lipase breaks down up to 60% of milk fats.

3)Carbohydrates break down in the stomach by salivary enzymes(before their inactivation in an acidic medium). Gastric juice does not contain its own carbohydrases.

secretory function The gastrointestinal tract is carried out digestive glands. Distinguish glands tubular type (glands of the stomach and intestines) and acinar glands. The latter consist of groups of cells united around the duct into which the secret is secreted ( salivary glands, liver, pancreas). The cells of the digestive glands, according to the nature of the secret produced by them, are divided into protein-, mucoid- and mineral secreting. As part of the secret of the glands, enzymes, hydrochloric acid, bicarbonate, bile salts, and also mucoid substances enter the cavity of the gastrointestinal tract.

secretory cycle. Periodically repeating in a certain sequence processes that ensure the entry of water, inorganic and organic compounds from the bloodstream into the cell, the synthesis of a secretory product from them and its removal from the cell, constitute secretory cycle. The secretory cycle of protein-synthesizing cells has been studied the most. It has several phases. After the initial substances enter the cell, the primary secretory product is secreted on the ribosomes of the rough endoplasmic reticulum, the maturation of which occurs in the Golgi complex. The secret accumulates in condensing vacuoles, which then turn into zymogen granules. After the accumulation of granules, the phase of their exit from the cell (degranulation) begins. The removal of the zymogen from the cell occurs through exocytosis.

Depending on the timing of the phases of the secretory cycle, secretion can be continuous or intermittent. The first type of secretion is inherent in the surface epithelium of the esophagus and stomach, the secretory cells of the liver. The pancreas and major salivary glands are formed by cells with an intermittent type of secretion.

The secretion of the digestive glands is characterized adaptation to the diet. It manifests itself in a change in the intensity of secretion production by each cell, in the number of cells simultaneously functioning in the composition of a given gland, as well as in a change in the ratio between various hydrolytic enzymes.

Salivary glands. Saliva- mixed secret of three pairs of large salivary glands: parotid, submandibular, sublingual, as well as numerous small glands scattered throughout the oral mucosa. Small and sublingual glands constantly produce a secret that moisturizes the oral cavity; the parotid and submandibular glands secrete saliva only when they are stimulated. It contains the hydrolytic enzyme α-amylase, mucopolysaccharides, glycoproteins, proteins, ions. In smaller quantities, saliva contains lysozyme, cathepsins, kallikrein.

The reaction of saliva ranges from slightly acidic to slightly alkaline (pH 5.8-7.8). Saliva has a lower osmotic pressure than blood plasma. The secretion of the salivary glands is stimulated by food intake and the complex of conditioned and unconditioned reflex stimuli associated with it. Afferent paths of reflexes pass through the sensory fibers of the trigeminal, facial, glossopharyngeal and vagus nerves, efferent - through the cholinergic and adrenergic fibers of the autonomic nerves going to the salivary glands.

Glands of the stomach. Gastric juice produced by cells of the gastric glands and surface epithelium. Glands located in the fundus and body of the stomach contain three types of cells: 1) lining, producing HCl; 2) main, producing proteolytic enzymes; 3) additional mucus secreting cells, mucopolysaccharides, gastromucoprotein and bicarbonate.

proteolytic enzymes. Synthesized in the chief cells of the gastric glands pepsinogen. The synthesized proenzyme accumulates in the form of granules and is released into the lumen of the gastric gland by exocytosis. In the stomach cavity, the inhibitory protein complex is cleaved off from pepsinogen and converted into pepsin. Activation of pepsinogen is triggered by HC1, and then pepsin itself activates its proenzyme. There is another proteolytic enzyme in gastric juice - gastrixin. AT breast period found in children chymosin- An enzyme that curdles milk.

Gastric mucus. It consists of glycoproteins, is released from the vesicles through the membrane and forms a layer of mucus, closely adjacent to the cell surface. Mucous cells also produce bicarbonate. The mucosal-bicarbonate barrier plays important role in preventing the damaging effects on the gastric mucosa of HC1 and pepsin.

Regulation of gastric secretion. Acetylcholine, gastrin and histamine occupy a central place in regulation. Each of them excites secretory cells. With the joint action of these substances, a potentiation effect is observed. Acetylcholine has a stimulating effect on the secretory cells of the stomach. It causes the release of gastrin from the G-cells of the antrum. Gastrin acts on secretory cells by the endocrine route. Histamine exerts its effect on the secretory cells of the stomach in a paracrine way, through the mediation of H 2 -histamine receptors.

In the regulation of gastric secretion, depending on the site of action of the stimulus, they secrete three phase- brain, stomach and intestines. Stimuli for the occurrence of secretion of the gastric glands in cerebral phase are all the factors that accompany the meal. AT gastric phase secretion stimuli originate in the stomach itself. Secretion is enhanced by stretching the stomach and the action on its mucous membrane of the products of protein hydrolysis, some amino acids, as well as extra active substances meat and vegetables. Activation of the gastric glands by stretching the stomach is carried out with the participation of both local and vagal reflexes. Involved in the regulation of gastric secretion somatostatin. The cells that produce this peptide form outgrowths that come close to the chief and parietal cells.

Influences on the glands of the stomach, coming from the intestines, determine their functioning in the third, intestinal, secretion phase. The latter first increases and then decreases. Stimulation of the gastric glands is the result of the entry into the intestine of the contents of the stomach, insufficiently processed mechanically and chemically. Gastric secretion in the intestinal phase can also be affected by secretion from the duodenal mucosa. secretin. It inhibits the secretion of HC1, but enhances the secretion of pepsinogen. A sharp inhibition of gastric secretion occurs when it enters the duodenum fat.

Of the gastrointestinal peptides that affect the secretory process in the stomach, one should also note the gastrin-releasing peptide, which enhances the secretion of HC1. Inhibition of the activity of parietal cells is caused by glucagon, vasoactive intestinal peptide, neurotensin and serotonin. The inhibitory effect on the main and parietal cells is characterized by the action of group E prostaglandins. Among the factors affecting gastric secretion, emotional arousal and stress are essential. It is known that some types of emotional excitation (fear, melancholy) cause inhibition, while others (irritation, rage) increase the secretory function of the stomach.

Pancreas. Acinar cells of the pancreas produce hydrolytic enzymes that break down all components nutrients. The enzymatic composition of pancreatic juice depends on the type of food consumed: when carbohydrates are taken, the secretion of amylase increases, proteins - trypsin and chymotrypsin increase, when fatty foods are taken, secretion of juice with increased lipolytic activity is noted. Pancreatic duct cells are a source of bicarbonate, chlorides, ions, pH pancreatic juice averages 7.5-8.8.

Distinguish between spontaneous (basal) and stimulated secretion of the pancreas Basal secretion due to the automatism inherent in the cells of the pancreas. stimulated secretion is the result of exposure to cells of regulatory factors of a neurohumoral nature, which are activated by food intake. Basal secretion of electrolytes is small or absent; The pancreas is very sensitive to the action of secretin, a stimulator of electrolyte secretion.

Major stimulants exocrine cells of the pancreas are acetylcholine and gastrointestinal hormones cholecystokinin and secretin. Acetylcholine enhances the secretion of the pancreas, increasing the output of bicarbonate and enzymes. Cholecystokinin is a strong stimulant of pancreatic enzyme secretion and slightly enhances bicarbonate secretion. Secretin stimulates the secretion of bicarbonate, slightly affecting the release of enzymes. Cholecystokinin and secretin mutually potentiate each other's action: cholecystokinin enhances secretin-induced bicarbonate secretion, and secretin enhances the production of enzymes stimulated by cholecystokinin.

Food intake is a natural stimulant for pancreatic secretion. The initial, cerebral, phase of pancreatic secretion is elicited by the sight, smell of food, chewing, and swallowing. The efferent pathways of these reflexes are part of the vagus nerves.

The entry of the contents of the stomach into the duodenum determines the impact on its mucous membrane of HC1 and the products of digestion of fat and protein, which causes the release of secretin and cholecystokinin; these hormones determine the mechanisms of pancreatic secretion in the intestinal phase.

Bile secretion and bile secretion. bile secretion This is the process by which bile is produced by the liver. Bile formation occurs continuously both by filtering a number of substances (water, glucose, electrolytes, etc.) from the blood into the bile capillaries, and by active secretion of bile salts and Na + ions by hepatocytes. The final formation of the composition of bile occurs as a result of the reabsorption of water and mineral salts in the bile capillaries, ducts and gallbladder.

The main components of bile are bile acids, pigments and cholesterol. In addition, it contains fatty acid, mucin, various ions and other substances; The pH of hepatic bile is 7.3-8.0, cystic - 6.0-7.0. primary bile acids(cholic and chenodeoxycholic), formed in hepatocytes from cholesterol, combine with glycine or taurine and are excreted as sodium salt glycocholic and potassium salts of taurocholic acids. In the intestine, under the influence of bacterial flora, they turn into secondary bile acids- deoxycholic and lithocholic. Up to 90% of bile acids are actively reabsorbed from the intestine into the blood and returned to the liver through the portal vessels. Thus carried out hepato-intestinal circulation of bile acids.

Bile pigments (bilirubin and biliverdin) are breakdown products of hemoglobin. They give bile its characteristic color. In humans, bilirubin predominates, which determines the golden yellow color of bile.

The process of bile formation is enhanced as a result of eating. The most powerful stimulant of choleresis is secretin, under the influence of which the volume of secretion and the release of bicarbonate in the composition of bile increase. Bile acids have a significant effect on the process of bile formation: they increase the volume of bile and the content of organic components in it.

bile secretion- The flow of bile into the duodenum is a periodic process associated with food intake. The movement of bile is due to the pressure gradient in the bile excretory system and in the duodenal cavity. The main stimulant contractile activity gallbladder is cholecystokinin. Strong causative agents of bile secretion are egg yolks, milk, meat and fats. Eating and associated conditioned and unconditional reflex stimuli cause activation of bile secretion.

Secretion of the intestinal glands.brunner glands, located in the mucous membrane of the duodenum, and Lieberkuhn's glands small intestine produce intestinal juice, the total amount of which per day reaches 2.5 liters in a person. Its pH is 7.2-7.5. significant portion juice consists of mucus and sloughed epithelial cells. Intestinal juice contains over 20 different digestive enzymes. Selection liquid part juice containing various minerals and a significant amount of mucoprotein, sharply increases with mechanical irritation of the intestinal mucosa. Intestinal secretion is stimulated by vasoactive intestinal peptide. Somatostatin has an inhibitory effect on it.

The kidneys are an organ that belongs to the excretory system of the body. However, excretion is not the only function of this organ. The kidneys filter the blood, return the necessary substances to the body, regulate blood pressure, and produce biologically active substances. The production of these substances is possible due to the secretory function of the kidneys. The kidney is a homeostatic organ, it provides constancy internal environment organism, the stability of the metabolism of various organic substances.

What does the secretory function of the kidneys mean?

Secretory function - this means that the kidneys produce the secretion of certain substances. The term "secretion" has several meanings:

• Transfer by nephron cells of substances from the blood into the lumen of the tubule for the excretion of this substance, that is, its excretion,
• Synthesis in the cells of the tubules of substances that need to be returned to the body,
• Synthesis of biologically active substances by kidney cells and their delivery into the blood.

What happens in the kidneys?

Blood purification

About 100 liters of blood passes through the kidneys every day. They filter it, separating harmful toxic substances and moving them into the urine. The filtration process takes place in the nephrons, cells located inside the kidneys. In each nephron, a tiny glomerular vessel connects to a tubule that collects urine. The process takes place in the nephron chemical exchange, as a result of which unnecessary and harmful substances are removed from the body. First, primary urine is formed. This is a mixture of decay products, which still contains needed by the body substances.

tubular secretion

The filtration process occurs due to blood pressure, and further processes already require additional energy for active transport of blood into the tubules. It happens in them following processes. From primary urine, the kidney extracts electrolytes (sodium, potassium, phosphate) and sends them back to circulatory system. Kidneys are removed only required amount electrolytes, maintaining and regulating their correct balance.

It is very important for our body acid-base balance. The kidneys help in its regulation. Depending on which side this balance shifts, the kidneys secrete acids or bases. The shift should be very small, otherwise the coagulation of certain proteins in the body may occur.

The speed with which the blood enters the tubules “for processing” depends on how they cope with their function. If the transfer rate of substances is insufficient, then the functional abilities of the nephron (and the entire kidney) will be low, which means that there may be problems with blood purification and urine excretion.

To determine this secretory function of the kidneys, a method is used to detect the maximum tubular secretion of substances such as paraaminohyppuric acid, hippuran and diodrast. With a decrease in these we are talking about dysfunction of the proximal nephron.

In another section of the nephron, distal, the secretion of potassium, ammonia and hydrogen ions is carried out. These substances are also necessary to maintain the acid-base and water-salt balance.

In addition, the kidneys separate from the primary urine and return some vitamins, sucrose to the body.

Secretion of biologically active substances

The kidneys are involved in the production of hormones:

• erythroepin,
• Calcitriol
• Renin.

Each of these hormones is responsible for the operation of some system in the body.

Erythroepin

This hormone is able to stimulate the production of red blood cells in the body. This may be necessary for blood loss or increased physical exertion. In these cases, the body's need for oxygen increases, which is satisfied by increasing the production of red blood cells. Since it is the kidneys that are responsible for the number of these blood cells, anemia can develop if they are damaged.

Calcitriol

This hormone is the end product of the formation of the active form of vitamin D. This process begins in the skin under the influence of sunlight, continues in the liver, from where it enters the kidneys for final processing. Thanks to calcitriol, calcium is absorbed from the intestines and enters the bones, ensuring their strength.

Renin

Renin is produced by periglomerular cells when blood pressure needs to be raised. The fact is that renin stimulates the production of angiotensin II enzyme, which constricts blood vessels and causes the secretion of aldosterone. Aldosterone retains salt and water, which, like vasoconstriction, leads to an increase in blood pressure. If the pressure is normal, then renin is not produced.

Thus, the kidneys are a very complex body system that is involved in the regulation of many processes, and all their functions are closely related to each other.

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Secretory function is provided by the sebaceous and sweat glands. With sebum, some medicinal substances(iodine, bromine), products of intermediate metabolism (metabolism), microbial toxins and endogenous poisons. The function of the sebaceous and sweat glands is regulated by the autonomic nervous system.

Secretory function is provided by the sebaceous and sweat glands. With sebum, some medicinal substances (iodine, bromine), products of intermediate metabolism, microbial toxins and endogenous poisons can be released.

Changes in the secretory function of the gastrointestinal tract with inhibition of activity digestive enzymes.  

Restoration of the secretory function of the ciliary body occurs within a few days or even a few weeks. Goniosinechia, segmental and diffuse atrophy of the iris, displacement and deformation of the pupil remain forever. These consequences influence the further course of the glaucoma process. Goniosinechia and damage to the trabecular apparatus and helmet canal during an attack lead to the development of chronic angle-closure glaucoma. Diffuse atrophy of the root of the iris reduces the resistance of its tissue. As a result, the bombardment of the iris increases, which facilitates the onset of a new attack of glaucoma. Atrophy of the processes of the ciliary body leads to a persistent decrease in its secretory function. This compensates to some extent for the deterioration of the outflow from the eye and reduces the possibility of developing new attacks and their intensity. A pronounced displacement of the pupil in some cases gives the same effect as iridectomy.

The conjunctiva has a secretory function due to the activity of goblet cells of the cylindrical epithelium, a number of depressions in its tarsal part, which look like cylindrical tubes lined with an epithelium with a narrow lumen, and the presence of additional complex tubular glands resembling lacrimal glands. They are located in the transitional fold (Krause's glands) and on the border of the tarsal and orbital parts of the conjunctiva (Waldeyer's glands); there are more of them towards the outer corner, in the area excretory ducts lacrimal gland.

Nerve centers, which regulate the secretory function of the chromaffin tissue of the adrenal glands, are located in the hypothalamus.

Already in early stages disease, the secretory function of the gastrointestinal tract is disturbed with inhibition of the activity of digestive enzymes. The change in metabolism is a reflection of the high metabolic activity of the young connective tissue in the lungs. Although the main pathological processes in silicosis develop in the respiratory organs and the circulatory organs functionally related to them, the disease is general character. This is indicated, in particular, by changes in the central and autonomic nervous system: shifts in the state of the analyzers, the reflex sphere, and the neurological status.

However, by the nature of the processes of motility and secretory function, the stomach of a teenager differs significantly from the stomach of an adult. Along with the frequency and severity of the phenomena of achilia and depression of motility among adolescents, there are individuals with hypersecretion and hyperkinesia.

The reverse development of the attack is associated with paresis of the secretory function of the ciliary body. The pressure in the posterior part of the eye decreases, and the iris, due to the elasticity of its tissue, gradually moves away from the angle of the anterior chamber. Injection eyeball, corneal edema and pupil dilation persist for some time after intraocular pressure. After each attack, goniosinechia remain, sometimes posterior synechia along the edge of the pupil and focal (in the form of a sector) atrophy of the iris caused by strangulation of its vessels.

Observations have shown that Yangan-Tau baths inhibit the secretory function of the stomach and enhance its evacuation activity. The results of the study give grounds to send patients with chronic gastritis and peptic ulcer stomach and duodenum, with increased secretion and acidity of gastric juice, that is, with increased excitability of the receptor apparatus of the stomach. A particularly good therapeutic effect was noted in the treatment of this group of patients with dry air and steam baths Yangan-Tau in combination with regular ingestion of water from the Kurgazak spring.

The phase of reverse development of an attack begins with paresis of the secretory function of the ciliary body. The suppression of secretion is caused high level ophthalmotonus, inflammatory and degenerative changes in the ciliary body. We also attach a certain importance to reactive phenomena. Reactive hypertension of the eye is replaced by hypotension caused by paralysis of aqueous humor secretion.

In adolescents with retardation of physical and especially sexual development, the secretory function of the stomach is reduced. In healthy adolescents, the limits of fluctuation in the amount of gastric secretion and its acidity are very wide and often exceed the average values ​​for adults. Often there are adolescents with the phenomena of heterochilia.

The next group of experiments was devoted to elucidating the effect of flavonoids on the secretory function of the stomach and liver.