After evacuation from the stomach into the small intestine, food undergoes the most intensive digestion..

An extremely important role in this process is played by the pancreas, or rather, its secrets..

The main components of pancreatic juice are bicarbonate, which creates an alkaline environment and neutralizes the acidic gastric chyme in the duodenum to pH 6-8 (this pH range is necessary for pancreatic enzymes), and digestive enzymes that break down the main components of food.

The pancreas is an exocrine (secreting) and at the same time endocrine (increasing) organ involved in digestion, in the regulation of metabolism, as well as other organs and systems..

The pancreas, which weighs approximately 110 g, secretes from 1.5 to 2.5 liters of juice per day. Juice is isotonic to blood plasma (regardless of stimulation), contains a number of electrolytes and salts, as well as digestive enzymes. The main juice anions are C1- and HCO3-, cations are Na+ and K+. In addition, Ca2+, Mg2+ cations and HPO4- anions are present in the juice.. During stimulation, the concentration of cations remains unchanged, while anions change in opposite directions.. At maximum secretion, the concentration of HCO3 is 130-140 mmol / l, and pH is 8.2.

The exocrine function of the pancreas is essential for digestion.. Under the influence of mental, alimentary, humoral and other stimuli, the cells of the pancreatic acini synthesize and release into the duodenum more than 20 proenzymes and enzymes (mainly hydrolases), which are involved in the breakdown of various food components in the intestine.

Digestive enzymes make up about 90% of pancreatic juice proteins. This function of the pancreas is called ecbolic, in contrast to the second exocrine function - hydrokinetic, which consists in the secretion of water, bicarbonates (up to 150 mmol / l) and other electrolytes.. The hydrokinetic function of the pancreas ensures the neutralization of acidic gastric contents and creates an alkaline environment in the intestine, which is optimal for the action of pancreatic and intestinal enzymes..

Pancreatic enzymes are divided into amylolytic (hydrolysis of starch), proteolytic (hydrolysis of proteins), lipolytic (hydrolysis of fats) and nucleolytic (hydrolysis of nucleic acids).

Amylolytic enzymes - amylases.

The breakdown of starch begins with a-amylase, which consists of several isoenzymes and accounts for approximately 20% of the proteins in the pancreatic secretion.. The main amount of this enzyme is secreted by the pancreas in its active form..

A similar isoenzyme is synthesized by the salivary glands. a-Amylase breaks down polysaccharides (starch, glycogen) to dextrins, maltooligosaccharides, maltose and a small amount of glucose. These polymers are further converted into glucose by intestinal enzymes - maltase, ?-amylase, isomaltase.

Lipolytic enzymes - lipases.

Lipolysis is carried out by pancreatic enzymes, however, only lipase (hydrolyzes triglycerides) currently has diagnostic value. Phospholipase (hydrolysis of phospholipids, lecithin) and carboxylesterase (hydrolysis of fatty acid esters) have also been isolated from pancreatic juice..

The pancreas secretes the main amount of lipase (a little lipase is also found in saliva and intestinal juice), which breaks down triglycerides into monoglycerides and fatty acids, which pass through the enterocyte membrane.

Lipase hydrolyzes a water-insoluble substrate, which is possible only on the surface of small emulsified fat particles.. The same amount of enzyme exhibits different activity depending on the quality of the emulsion: the thinner it is, the higher the activity of the enzyme. Lipase is active in the small intestine in the presence of bile acids, which promote the emulsification of fats..

Proteolytic enzymes - proteases.

There are many of them in pancreatic juice (endopeptidases - trypsin, chymotrypsin, elastase, exopeptidases - carboxypeptidases A and B). They belong to the group of serine proteases and make up 44% of the total pancreatic juice protein.. There are multiple forms of trypsin and chymotrypsin, as well as gastric pepsins.. Acinar cells do not synthesize active proteolytic enzymes (this would threaten the self-digestion of the organ).

They are secreted as inactive proenzymes that are activated in the gut.. Trypsinogen is activated first. Under the action of the intestinal enzyme enterokinase, it is converted into trypsin, and then the active trypsin molecules provide the activation of other proteolytic enzymes, including trypsinogen (the activation process continues already autocatalytically).

In fact, two trypsinogens are secreted with pancreatic juice, which make up about 19% of all its proteins, two chymotrypsinogens and two proelastase. All of them are called endopeptidases, since during the hydrolysis of proteins they " Endopeptidases are specific.

For example, trypsin hydrolyzes only bonds to the right of lysine or arginine, chymotrypsin hydrolyzes mainly those next to phenylalanine, tyrosine and tryptophan.. Elastase is able to hydrolyze elastin, connective tissue protein, and other proteins.. Unlike endopeptidases, exopeptidases break the C-terminal, t. final, bond (carboxypeptidases) or first, N-terminal (aminopeptidases), thus “freeing”, thus, amino acids one after another.

Pancreatic juice contains a trypsin inhibitor, a non-enzymatic protein closely associated with proteolysis.. Its physiological significance is to prevent premature activation of trypsin in the pancreatic ducts.. Determination of its activity in the blood serum in dynamics is important, indicating the inflammatory-destructive processes of the organ during hyperenzymemia ("

Kallikrein is a proteolytic enzyme of the pancreas. Activated by trypsin, it is responsible for the formation in the blood of kallidin, a hypotensive polypeptide identical to bradykinin, one of the neurovasoactive peptides..

Nucleolytic enzymes - nucleases.

Belong to phosphodiesterases. In pancreatic juice, they are represented by ribonuclease, which hydrolyzes ribonucleic acid, and deoxyribonuclease, which breaks down deoxyribonucleic acid..

The amount and enzymatic activity of pancreatic juice depend on the amount and composition of the food taken.. Outside of digestion, on an empty stomach, pancreatic juice is secreted in small amounts.

The secretion of pancreatic juice is caused by voluminous and stimulating gastric acid production.. Solid, thick and fatty foods linger in the stomach for a long time (evacuated more slowly), so the secretion of the pancreas is longer than after taking a liquid meal.

The main secretion, however, begins in the intestinal phase, i.e.. after food and its digestion products enter the duodenum.

The secretion of pancreatic juice increases 2-3 minutes after a meal and lasts 6-14 hours (with a maximum secretion of juice at the 90th minute), depending on its composition.. Mixed food elicits a greater secretory response than single foods.

Neutral fats and their digestion products stimulate the enzyme-producing cells of the pancreas the most.. Proteins are also a fairly strong stimulant for the secretion of enzymes, to a lesser extent bicarbonates and the liquid part of pancreatic juice..

The intake of amino acids into the intestine causes a significant increase in the blood level of the hormone - cholecystokinin (former names - pancreozymin, cholecystokinin-pancreozymin), a local stimulator of the enzyme-synthesizing activity of pancreatic acinar cells. Phenylalanine, choline, methionine and other essential amino acids are especially strongly affected..

The predominance of carbohydrates in the diet " Low-concentration solutions of glucose and sucrose introduced into the duodenum cause short-term and slight stimulation of a-amylase secretion, and concentrated solutions cause a sharp inhibition of exocrine secretion..

Hydrochloric acid is a strong natural stimulant of the external secretion of the pancreas.. All drinks and foods that stimulate the appetite, along with the secretion of the stomach, increase the secretion of the pancreas.. So, some fruit and organic acids (malic, citric, tartaric, lactic), as well as alcohol, have a pronounced juice effect..

The dependence of the enzymatic composition of pancreatic juice on food quality is well known.. The granules located in the acinar cells contain all the enzymes present in the secret in a constant ratio, so that it is also constant in the pancreatic juice..

However, an increase in the proportion of any component of the diet (for example, proteins) in food gradually increases the synthesis of the corresponding hydrolyzing enzymes.. This adaptation to the diet has provided an opportunity to discuss the possibility of a dietary cure for some pancreatic dysfunctions..

Pancreatic secretion is regulated by nervous and humoral mechanisms..

In stimulating pancreatic secretion, direct nerve influences are less important than humoral ones.. The leading role in the humoral regulation of pancreatic secretion belongs to gastrointestinal hormones.. They are among the peptides and are synthesized by special cells of the stomach and duodenum under the influence of appropriate chemical, mechanical, nervous or other stimulating factors..

Pancreatic secretion is increased by secretin, cholecystokinin, as well as gastrin, serotonin, insulin, bombesin, substance II and bile salts.. Inhibit secretion of pancreatic juice glucagon, calcitonin, parenteral nutrition (PN), somatostatin. It can excite and inhibit pancreatic secretion. The effects of hormones are partly mediated through their influence on gastric secretion: with increasing its more acidic contents enter the duodenum and through its hormones increase pancreatic secretion.

Pathophysiology.

With structural and functional disorders of the pancreas, the synthesis of enzymes may be disrupted, and therefore there are digestive defects in the small intestine.. Fat digestion is especially affected, since pancreatic juice contains the most active lipase enzyme..

In pathology, up to 60-80% of the fat that is excreted with feces may not be absorbed.. To a lesser extent, the digestion of proteins is disturbed, up to 30-40% of their amount may not be absorbed.. The appearance of a large number of muscle fibers in the feces (creatorrhoea) after eating meat food indicates insufficient digestion of proteins.. Carbohydrate digestion is also impaired. Development of malnutrition.

Violations of the external secretion of the pancreas can be due to a number of reasons..

The main ones are the following:.

1) development of inflammatory processes in the pancreas (acute and chronic pancreatitis);

2) obstruction of the pancreatic duct with calculi (cholelithiasis, calculosis of the ducts), intestinal parasites, protein-mucous \;

3) inflammatory processes in the duodenum (duodenitis, peptic ulcer), accompanied by a decrease in the formation of secretin; as a result, the secretion of pancreatic juice decreases;

4) compression of the pancreatic duct (tumors, duodenitis, vaterite);

5) the development of severe disorders of the body's metabolic processes (obesity, protein-energy deficiency, hormonal disorders, etc.. ) with the formation of dystrophic lesions of the pancreas (lipomatosis, protein degeneration, hemochromatosis);

6) allergic restructuring of the body;

7) neurogenic inhibition of pancreatic functions (vagal dystrophy, prolonged atropinization);

8) tumor destruction.

In cases of development of obstructive processes that impede or even stop the outflow of pancreatic secretions into the duodenum, hypertension occurs in the pancreatic duct system, causing not only severe pain, but also internal ruptures, destruction of the organ parenchyma.

Enterokinase of lysed pancreatic cells in this case can catalyze the activation of pancreatic juice enzymes directly in the ductal system (especially trypsinogen).

Moreover, trypsin itself is able to activate trypsinogen, as if starting a " As a result of the described phenomena, pancreatic enzymes can carry out self-digestion of pancreatic tissue with the development of necrosis.

With the destruction of the pancreas, active pancreatic enzymes, products of tissue destruction, impaired metabolism can be absorbed into the blood, into the surrounding tissues. Necrosis develops in tissues as a result of the action of enzymes on them.; especially characteristic is the appearance of necrosis of fatty tissue (omentum), arising under the influence of pancreatic juice lipase. The syndrome of intoxication of the body is formed.

Baranovsky medbe. en.