Gastric juice. The main components that make up human gastric juice Intestinal juice is produced
intestinal juice- It is a colorless liquid, slightly alkaline, containing about 3% dry matter.
Secretion of intestinal juice
Throughout the intestines, starting from the pyloric opening, there are many small glands. different type secreting intestinal juice. Some of them of the alveolar structure - Brunner's glands - are located only in duodenum, others - tubular Lieberkunov - throughout the intestines.
During starvation, intestinal juice is secreted a little, while eating, the secretion of juice increases. Particularly increases the separation of juice with mechanical irritation of the intestinal walls with food. Intestinal juice secretion increases and under the influence of some chemical substances: food digestion products, extracts from some organs.
Composition of intestinal juice
In the intestinal juice there are enzymes that decompose all nutrients: into carbohydrates - amylase, invertase, lactase, maltase, phosphatase; on proteins - erepsin; for fats - lipase.
Erepsin
The protein enzyme erepsin turned out to be a complex of various peptidases. It quickly and completely decomposes protein products formed under the action of pepsin and trypsin.
Lipase
Intestinal juice lipase breaks down fats general type.
carbohydrate enzymes
The amount of carbohydrate enzymes in the intestinal juice depends on the type of food. This indicates that the composition of food affects the activity of cells that produce enzymes. So, for example, with food devoid of milk, there is no lactase in the intestinal juice, but it appears in it when fed with milk. In suckers, lactase is a constant component of the intestinal juice, gradually disappearing when the animal passes to another kind of food. The same was noted for the enzyme invertase, which decomposes cane sugar. Intestinal amylase and maltase are always present in the intestinal juice. material from the site
Intestinal juice can be obtained from a Tiri Vell fistula. For its formation, a segment of the intestine is isolated, which maintains a vascular and nervous connection with the rest of the intestine through the mesentery. Both ends of this segment are sutured into the skin wound, and the integrity of the intestine is restored by suturing (Fig. 26). However, only the juice of the Lieberkühn glands can be obtained from the Tiry-Vell fistula, since the Brunner glands take up so little space (in a dog) that it is impossible to make a separate fistula to obtain pure Brunner gland juice.
51. Properties and composition of intestinal juice. regulation of intestinal secretion.
intestinal juice- cloudy alkaline liquid, rich in enzymes and mucus impurities, epithelial cells, cholesterol crystals, microbes (small amount) and salts (0.2% sodium carbonate and 0.7% sodium chloride). The glandular apparatus of the small intestine is its entire mucous membrane. Up to 2.5 liters of intestinal juice is excreted per day in a person.
The content of enzymes is low. Intestinal enzymes that break down various substances are as follows: erepsin - polypeptides and peptones to amino acids, catapepsins - protein substances in a weakly acidic environment (in the distal part of the small intestine and large intestines, where a weakly acidic environment is created under the influence of bacteria), lipase - fats for glycerol and higher fatty acid, amylase - polysaccharides (except fiber) and dextrins to disaccharides, maltase - maltose per two molecules of glucose, invertase - cane sugar, nuclease - complex proteins (nucleins), lactase acting on milk sugar and splitting it into glucose and galactose, alkaline phosphatase, hydrolyzing orthophosphoric acid monoesters in an alkaline environment, acid phosphatase, which has the same effect, but exhibits its activity in an acidic environment, etc.
The secretion of intestinal juice includes two processes: the separation of the liquid and dense parts of the juice. The ratio between them varies depending on the strength and type of irritation of the mucous membrane of the small intestine.
The liquid part is a yellowish alkaline liquid. It is formed by a secret, solutions of inorganic and organic substances transported from the blood, and partially by the contents of the destroyed cells of the intestinal epithelium. The liquid part of the juice contains about 20 g/l of dry matter. Among the inorganic substances (about 10 g/l) are chlorides, bicarbonates and phosphates of sodium, potassium, and calcium. The pH of the juice is 7.2-7.5, with increased secretion it reaches 8.6. The organic substances of the liquid part of the juice are represented by mucus, proteins, amino acids, urea and other metabolic products.
The dense part of the juice is a yellowish-gray mass that looks like mucous lumps and includes undestroyed epithelial cells, their fragments and mucus - the secret of goblet cells has a higher enzymatic activity than the liquid part of the juice.
In the mucous membrane of the small intestine, there is a continuous change in the layer of cells of the surface epithelium. Complete renewal of these cells in humans takes 1-4-6 days. Such a high rate of formation and rejection of cells provides a sufficiently large number of them in the intestinal juice (in humans, about 250 g of epitheliocytes are rejected per day).
Mucus forms a protective layer that prevents excessive mechanical and chemical effects of chyme on the intestinal mucosa. In mucus, the activity of digestive enzymes is high.
The dense part of the juice has a much greater enzymatic activity than the liquid part. The main part of the enzymes is synthesized in the intestinal mucosa, but some of them are transported from the blood. There are more than 20 different enzymes in the intestinal juice that are involved in digestion.
regulation of intestinal secretion.
Eating, local mechanical and chemical irritation of the intestine enhance the secretion of its glands with the help of cholinergic and peptidergic mechanisms.
In the regulation of intestinal secretion, local mechanisms play a leading role. Mechanical irritation of the mucous membrane of the small intestine causes an increase in the release of the liquid part of the juice. Chemical stimulants of the secretion of the small intestine are the products of digestion of proteins, fats, pancreatic juice, hydrochloric and other acids. The local action of the products of digestion of nutrients causes the separation of intestinal juice rich in enzymes.
The act of eating does not significantly affect intestinal secretion, at the same time, there are data on the inhibitory effects on it of irritation of the antrum of the stomach, modulating effects of the central nervous system, on the stimulating effect on the secretion of cholinomimetic substances and the inhibitory effect of anticholinergic and sympathomimetic substances. Stimulate intestinal secretion of GIP, VIP, motilin, inhibits somatostatin. The hormones enterocrinin and duocrinin, produced in the mucous membrane of the small intestine, stimulate the secretion of intestinal crypts (Lieberkün's glands) and duodenal (Brunner's) glands, respectively. These hormones have not been isolated in purified form.
Instruction
The main component of gastric juice is hydrochloric acid. It also includes inorganic (chlorides, bicarbonates, sodium, potassium, phosphates, magnesium, sulfates) and organic substances (proteolytic enzymes). regulation secretory function gastric glands carry out nervous and humoral mechanisms. The process of synthesis of gastric juice is conditionally divided into 3 phases: cephalic (complex reflex), gastric, intestinal.
During the complex reflex phase, the gastric glands are excited by irritation of the olfactory, visual, auditory receptors by the sight and smell of the dish, the perception of the situation associated with eating. Irritation of receptors is superimposed on such influences. oral cavity, esophagus in the process of chewing and swallowing food. As a result, the secretory activity of the gastric glands is launched. The juice that is released under the influence of the type and smell of food, in the process of chewing and swallowing, is called "appetizing" or "fire", it has a high acidity and high proteolytic activity. In this case, the stomach becomes prepared for eating.
The 2nd gastric phase is superimposed on the complex reflex phase of secretion. are involved in its regulation. nervus vagus and intramural local reflexes. In this phase, juice secretion is associated with a reflex response to mechanical and chemical stimuli on the gastric mucosa. Irritation of the receptors of the gastric mucosa promotes the release of gastrin, which is the most powerful of cell stimulants. At the same time, the content of histamine in the mucous membrane increases, this substance is a key stimulator of the production of hydrochloric acid.
The intestinal phase of secretion of gastric juice occurs when food passes from the stomach to the intestines. The amount of secretion secreted during this period is no more than 10% of the total volume of gastric juice, it increases in the initial period, and then begins to decrease. As the duodenum fills up, secretory activity continues to decrease under the influence of peptides that are secreted by the endocrine gastrointestinal glands.
The most effective causative agent of the secretion of gastric juice is protein food. Prolonged leads to an increase in the amount of secretion in response to other food stimuli, as well as an increase in acidity and an increase in the digestive activity of gastric juice. Carbohydrate food (for example, bread) is the weakest causative agent of secretion. Among the non-food factors that increase the secretory activity of the gastric glands, stress, rage, and irritation play the greatest role. Anxiety, fear, depressive states have a depressing effect.
Gastric juice is secreted by the glands of the stomach. An average of 2 liters of gastric juice is secreted per day. It consists of organic and inorganic components.
Instruction
The inorganic constituents of gastric juice include hydrochloric acid. Its concentration determines the level of acidity of gastric juice. The minimum content of hydrochloric acid on an empty stomach, the maximum - when food enters the stomach.
Pepsin A affects the process of protein digestion. Under its influence, proteins are broken down into peptones. This enzyme is formed under the influence of hydrochloric acid.
Gastrixin is similar in function to pepsin A. Pepsin B dissolves gelatinase better than all other enzymes. Rennet promotes the breakdown of milk casein in the presence of calcium ions.
Also, the composition of gastric juice includes gastric mucus or mucin, secreted by additional cells of the gastric glands. This is a collection of colloidal solutions of high molecular weight biopolymers, the latter are found in all tissues and body fluids. It consists of low molecular weight organic and minerals, leukocytes, lymphocytes, desquamated epithelium.
Gastric mucus includes soluble and insoluble fractions. Insoluble mucin lines the stomach from the inside, part of it passes into gastric juice. Soluble mucin arises from the secretions of cells of the secretory epithelium of the glands of the stomach.
Pure gastric juice is a colorless liquid, sometimes slightly opalescent, with lumps of mucus. It contains hydrochloric acid, enzymes, minerals, the hormone gastrin, mucus, traces organic compounds. Gastric juice is acidic.
Hydrochloric acid - the main component of gastric juice
The most important component of gastric juice, which is produced by the parietal cells of the fundic glands of the stomach, is hydrochloric acid.
It maintains a certain level of acidity in the stomach, prevents the penetration of pathogens into the body and prepares food for efficient hydrolysis. Hydrochloric acid has a constant and unchanged concentration - 160 mmol / l.
Digestion begins in the mouth. Saliva enzymes - maltase and amylase - are involved in the breakdown of polysaccharides. The food bolus enters the stomach, where approximately 30-40% of carbohydrates are digested with the help of gastric juice, as a result of exposure to hydrochloric acid, the alkaline environment changes to acidic, maltase and amylase are inactivated.
Bicarbonates
Bicarbonates in gastric juice serve to neutralize hydrochloric acid at the surface of the gastric mucosa and duodenum and protect the mucosa from acid.
The concentration of bicarbonates in gastric juice is 45 mmol/l.
Slime
Mucus contains bicarbonates and protects the mucous membrane from hydrochloric acid and pepsin. Produced in the stomach by additional surface cells.
Pepsin
The main enzyme contained in the gastric juice, with the help of which the breakdown of proteins occurs. Medicine is familiar with several isoforms of pepsin, each of which is involved in the breakdown separate species proteins.
Lipase
An enzyme found in gastric juice a small amount. It performs the function of the initial hydrolysis of fats, splitting them into fatty acids and glycerol. Lipase is a surface-active catalyst, like the rest of the enzymes of gastric juice.
Castle's intrinsic factor
The enzyme, which is part of the gastric juice, converts the inactive form of vitamin B12, which enters the stomach with food, into the active form. It is produced by the parietal cells of the glands of the stomach.
The mucous surface of the stomach has many folds, elongated longitudinally, and elevations (gastric fields), on which a large number of pits. In these recesses, gastric juice is secreted. It is produced by the glands of the mucous surface of the organ, looks like a colorless clear liquid and has a sour taste.
Cells of the glands of the stomach are divided into three groups: main, additional and parietal. Each of them produces different components that are included in the gastric juice. The composition of the main cells is enzymes that help to decompose food substances into simpler, more easily digestible ones. Pepsin, for example, breaks down proteins, and lipase breaks down fats.
Parietal cells are produced without which the necessary acidic environment cannot form in the stomach cavity. Its concentration does not exceed 0.5%. A huge role in digestion also belongs to hydrochloric acid. It is she who helps to soften many substances of the lump of food, makes the enzymes of gastric juice active, and destroys microorganisms. Hydrochloric acid is involved in the formation of digestive hormones. It also stimulates the production of enzymes. Such a concept as "acidity" determines the amount of juice. She is not always the same. Acidity depends on how quickly the juice is released and whether it is neutralized by mucus, which has an alkaline reaction, its level changes with diseases of the digestive system.
Viscosity, which has gastric juice, gives it the mucus produced by additional cells. It makes the hydrochloric acid neutral, thereby reducing the juice. Also, this mucus promotes complete digestion. nutrients, protects the mucous membrane from irritation and damage.
In addition to the components listed above, gastric juice contains many inorganic and organic substances, including the Castle factor - a special substance, without which absorption into the body is impossible. small intestine vitamin B 12, necessary for the full maturation of red blood cells in the bone marrow.
Gastric juice secreted in different time secretion, has an unequal power of digestion. This was established by IP Pavlov. He stated that secretion does not continue continuously: when the process of digestion does not occur, no juice is secreted into the stomach cavity. It is produced only in connection with the reception of food. The secretion of gastric juice can provoke not only food that has entered the stomach or tongue. Even the smell of her, talking about her is the reason for his formation.
Gastric juice can have a different composition and quantity in diseases of the liver, blood, stomach, gallbladder, intestines, etc. Its study is the most important diagnostic method used in modern medicine. It is carried out using a gastric tube, which is inserted directly into the stomach, sometimes on an empty stomach, sometimes after taking a preparatory breakfast, consisting of special irritants. The extracted content is then analyzed. Modern probes have sensors that respond to temperature, pressure and acidity in the organ.
The quality and quantity of it can also change under the influence of experiences, on nervous ground. Therefore, it is sometimes necessary to repeated analyzes gastric juice to clarify the diagnosis.
It is known that in medical practice it is used as medicinal product with diseases of the stomach, which are accompanied by insufficient secretion of juice or a small amount of hydrochloric acid in it. Use it only as directed by a doctor. The gastric juice prescribed for this purpose can be both natural and artificial.