What enzymes function in the small intestine. What are pancreatic enzymes and how are they produced? Types of intestinal digestion


Pancreatic enzymes play a major role in the digestive system. They perform the function of breaking down fats, carbohydrates and protein. Enzymes stimulate work gastrointestinal tract, break down various elements and speed up the metabolic process.

The main producer of enzymes in the human body is the pancreas. In fact, it is a unique organ that produces special digestive juice. This juice is filled with enzymes, bicarbonates, water and electrolytes. Without these substances, the digestion process as a whole is impossible. They enter the small intestine as pancreatic juice and break down fats, proteins and complex carbohydrates. This whole complex process already occurs in the duodenum.

Pancreatic enzymes necessary for humans are divided into 3 groups. Lipase is included in the first group. It breaks down fats that cannot enter the blood into glycerol and fatty acid. The second group contains amylase. Amylase directly breaks down starch, which, under the action of the enzyme, becomes an oligosaccharide.

Other digestive enzymes convert oligosaccharides into glucose, which, when released into the blood, becomes a source of energy for humans. The third group contains proteases (trypsin, chymotrypsin, carboxypeptidase, elastase). Trypsin, in turn, breaks down the protein into peptides. Peptides are converted to amino acids by carboxyptidase. Elastase is responsible for the breakdown different types protein and elastin.

All these pancreatic enzymes in pancreatic juice are in a passive state so that they do not begin to break down the tissue of the pancreas itself. Their activation begins only under the influence of a sufficient amount of bile. IN small intestine Under the influence of bile, the enzyme enterokinase is released, which “awakens” inactive trypsinogen into active trypsin.

It is the main one, and “starts” the remaining inactive enzymes under gastric juice. Active trypsin activates the process of autocatalysis, after which it comes into action as the main one. Trypsin is synthesized as a proenzyme. It is in this form that it enters the small intestine. The production of enzymes in the pancreas begins immediately after food enters the small intestine and lasts about twelve hours.

Their premature activation leads to the fact that they begin to break down not only food, but also the organ itself (the pancreas), which consists mainly of proteins. This process is a symptom of such a common disease as pancreatitis. When the pancreas is destroyed little by little over a couple of years, it is called chronic pancreatitis. To diagnose this disease, it is enough to pay attention to its symptoms.

Symptoms of pancreatitis are as follows:

  • frequent vomiting that occurs after a heavy meal;
  • pain in the right and left hypochondrium, sometimes they manifest themselves in the entire upper abdomen;
  • dryness and bitterness in the mouth;
  • hiccups;
  • belching;
  • nausea.

If you have several symptoms, you should immediately see a doctor. If there is acute girdling pain and severe vomiting, these symptoms indicate acute pancreatitis. In this case you need to call emergency assistance. For such symptoms, treatment is carried out in a hospital under the supervision of doctors.

Video “Chronic pancreatitis. Everything about him"

Enzyme analysis

In order to establish the correct diagnosis and prescribe appropriate treatment, it is necessary to take an enzyme test, undergo an X-ray, ultrasound, tomography, MRI and submit feces for coprogram. Using coprogram analyses, you can determine the state of the microflora of the small intestine. To determine the exact amount of enzymes and their condition, donate blood for biochemical analysis. It helps determine the level of trypsin, amylase and lipase. A deficiency of these enzymes indicates the presence of a disease.

The amount of trypsin in the blood is a very important indicator of the activity of the pancreas as a whole. Therefore, when checking the analysis, special attention is given to general level trypsin in the human body. Its lack in the blood also indicates the presence of the disease. Analysis for the activity and level of amylase, trypsin and lipase is carried out only in laboratory conditions.

If pancreatitis is suspected and certain symptoms are present, a test is performed to determine the level of lipase in the blood. Its activity increases during exacerbation of the disease. In order to accurately determine the level of enzymes, a general analysis of urine and feces is prescribed. During testing, you must adhere to special rules. Don't forget that you need to take them on an empty stomach.

Determining excess or deficiency

A failure in the production and functioning of pancreatic enzymes is called insufficiency. During insufficiency, the pancreas cannot produce the essential hormone insulin. The manifestation of this pathology is diabetes, among the symptoms of which the main one is an excess of glucose in the blood.

There are a number of reasons that cause deficiency. Such as poor nutrition (excess of fatty, salty and fried foods in the diet), vitamin deficiency, low level protein in the blood, injury to pancreatic tissue, low level of hemoglobin in the blood. Today, there are four types of insufficiency: exocrine, exocrine, enzyme and endocrine insufficiency.

Enzyme deficiency occurs due to the production of a small amount of one of the enzymes. Pancreatic insufficiency manifests itself in two forms: organic and functional. The cause of functional failure may be poisoning, infectious diseases, use of strong medical supplies. Symptoms usually go away on their own after some time.

In case of organic failure, complex treatment is used. Because the symptoms will not disappear on their own. Complex treatment implies a strict diet and the prescription of enzymes that are taken with food. These drugs improve the digestion process, which is complicated by a lack of natural enzymes.

Recovery course

Recovery normal level special enzymes are used medications. The main purpose of the drugs is to supplement the missing amount of your own enzymes. Doses of drugs depend on the age and condition of the patient. They must be taken in full course, strictly adhering to the dosage, during meals.

Active ingredient enzyme preparations is pancreatin, which is produced from animal organs. Such drugs include Mezim, Creon, Pankreon, Enzistal, Festal, Pangrol, Panzinorm.

For normal recovery the patient is prescribed a strict diet. It should not be adhered to less than a month. The diet excludes the consumption of fried, fatty, salty and sour foods. Alcohol, carbonated water, coffee, cocoa, and strong black tea are excluded from drinks. Food should be boiled with a minimum content of fats and seasonings.

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In order to properly establish sleep patterns, nutrition and the general mood of the body, you should have enough information about the benefits of such actions. In this video clip you will learn how to protect the pancreas and yourself as well.

Enzymes of the small intestine, and there are more than 20 of them, take part in the digestion process. They process food into nutrients, which are then absorbed by the body and enter the bloodstream. The small intestine is a long tube (2-4 m), which is part digestive tract and connects the stomach and colon. The processes of food digestion most actively occur in it. This is where most of the vitamins, minerals, fats and some water are absorbed. Muscle contractions called peristalsis move food toward the large intestine.

Functionally and anatomically, it is divided into 3 sections:

  • duodenum;
  • jejunum;
  • ileum.

The duodenum is the first and shortest section, its length is approximately 25 cm. Food enters it from the stomach through the muscular sphincter. The ducts from the pancreas and gallbladder exit here. Iron absorption occurs in this part. Skinny and ileum form numerous loops. Sugars, amino acids and fatty acids are absorbed here. In the last section of the intestine, vitamin B12 and bile acids are absorbed.

Internal structure

Throughout its entire length, the wall of the organ has 3 shells:

  • external serous (peritoneum);
  • middle muscle, consisting of 2 layers;
  • internal mucosa with submucosal layer.

The inner layer and sublayer have folds. The mucous membrane is equipped with projections (villi) that have close contact with incoming food. Between them are long depressions or crypts that secrete intestinal juice. At their base there are special cells that produce the antibacterial enzyme lysozyme. Special goblet cells secrete mucus, which is involved in digestion and helps move the liquid contents of the stomach (chyme).

Types of substances and their effects

The duodenum produces an alkaline fluid that neutralizes the acid in the stomach, thereby helping to provide optimal value pH from 7 to 9. This is a necessary condition for the productive work of enzymes. All enzymes produced in the small intestine are formed in the epithelium of the mucous membrane or on the villi and are part of the intestinal juice. They are divided according to the type of substrate they affect. The following enzymes are distinguished:

  • protease and peptidase break down proteins into amino acids;
  • lipase converts fats into fatty acids;
  • Carbohydrases break down carbohydrates such as starch and sugar;
  • nuclease converts nucleic acids into nucleotides;
  • hydrolases break down large molecules into smaller ones in the intestinal lumen.

Many enzymes enter the intestines from the pancreas and gallbladder. The pancreatic enzymes he takes are lipase, trypsin and amylase. Trypsin breaks down proteins into shorter polypeptides, lipase converts fats and oils into fatty acids and glycerol, and amylase converts amylose (starch) into maltose. The incoming bile emulsifies fats and allows intestinal lipase, which is less active than pancreatic lipase, to work more efficiently.

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Under the influence of these compounds, proteins, fats and carbohydrates break down into smaller molecules. But they are not completely split yet. They are then affected by intestinal enzymes. These include:

  • sucrase, which converts sucrose into glucose and fructose;
  • maltase, which breaks down maltose into glucose;
  • isomaltase, which acts on maltose and isomaltose;
  • lactase, which breaks down lactose;
  • intestinal lipase, which promotes the breakdown of fats;
  • peptidases that break down peptides into simple amino acids.

The resulting simple molecules are absorbed into the blood via villi in the jejunum and ileum.

The general laws of digestion, valid for many species of animals and humans, are the initial digestion of nutrients in an acidic environment in the stomach cavity and their subsequent hydrolysis in a neutral or slightly alkaline environment of the small intestine.

Alkalization of acidic gastric chyme in the duodenum with bile, pancreatic and intestinal juices, on the one hand, stops the action of gastric pepsin, and on the other, creates an optimal pH for pancreatic and intestinal enzymes.

Initial hydrolysis nutrients in the small intestine it is carried out by enzymes of pancreatic and intestinal juices with the help of cavity digestion, and its intermediate and final stages - with the help of parietal digestion.

Nutrients (mainly monomers) formed as a result of digestion in the small intestine are absorbed into the blood and lymph and are used to satisfy the energy and plastic needs of the body.

14.7.1. Secretory activity of the small intestine

The secretory function is carried out by all parts of the small intestines (duodenum, jejunum and ileum).

A. Characteristics of the secretory process. In the proximal part of the duodenum, in its submucosal layer, there are Brunner's glands, which in structure and function are in many ways similar to the pyloric glands of the stomach. The juice of Brunner's glands is a thick, colorless liquid of a slightly alkaline reaction (pH 7.0-8.0), which has slight proteolytic, amylolytic and lipolytic activity. Its main component is mucin, which performs a protective function, covering the mucous membrane of the duodenum with a thick layer. The secretion of Brunner's glands sharply increases under the influence of food intake.

Intestinal crypts, or Lieberkühn's glands, are located in the mucous membrane of the duodenum and the rest of the small intestine. They surround each villi. Not only crypts, but also cells of the entire mucous membrane of the small intestine have secretory activity. These cells have proliferative activity and replenish the rejected epithelial cells at the tips of the villi. Within 24-36 hours they move from the crypts of the mucous membrane to the apex of the villi, where they undergo desquamation (morphonecrotic type of secretion). Entering the cavity of the small intestine, epithelial cells disintegrate and release the enzymes they contain into the surrounding fluid, due to which they participate in cavity digestion. Complete renewal of surface epithelial cells in humans occurs on average within 3 days. Intestinal epithelial cells covering the villus have a striated border on the apical surface formed by microvilli with a glycocalyx, which increases their absorption capacity. On the membranes of microvilli and the glycocalyx there are intestinal enzymes transported from enterocytes, as well as adsorbed from the cavity of the small intestine, which take part in parietal digestion. Goblet cells produce a mucous secretion that has proteolytic activity.

Intestinal secretion includes two independent processes - separation of the liquid and dense parts. The dense part of the intestinal juice is insoluble in water; it is

consists mainly of desquamated epithelial cells. It is the dense part that contains the bulk of the enzymes. Contractions of the intestine promote the desquamation of cells close to the stage of rejection and the formation of lumps from them. Along with this, the small intestine is capable of intensively separating liquid juice.

B. Composition, volume and properties of intestinal juice. Intestinal juice is a product of the activity of the entire mucous membrane of the small intestine and is a cloudy, viscous liquid, including a dense part. A person secretes 2.5 liters of intestinal juice per day.

The liquid part of the intestinal juice, separated from the dense part by centrifugation, consists of water (98%) and dense substances (2%). The dense residue is represented by inorganic and organic substances. The main anions of the liquid part of the intestinal juice are SG and HCO3. A change in the concentration of one of them is accompanied by an opposite shift in the content of the other anion. The concentration of inorganic phosphate in the juice is significantly lower. Among the cations, Na + , K + and Ca 2+ predominate.

The liquid part of the intestinal juice is isoosmotic to the blood plasma. pH value in upper section of the small intestine is 7.2-7.5, and with an increase in the rate of secretion it can reach 8.6. The organic substances of the liquid part of the intestinal juice are represented by mucus, proteins, amino acids, urea and lactic acid. The enzyme content in it is low.

The dense part of the intestinal juice - a yellowish-gray mass that looks like mucous lumps, which includes decaying epithelial cells, their fragments, leukocytes and mucus produced by goblet cells. Mucus forms a protective layer that protects the intestinal mucosa from excessive mechanical and chemical irritation of the intestinal chyme. The intestinal mucus contains adsorbed enzymes. The dense part of the intestinal juice has significantly greater enzymatic activity than the liquid part. More than 90% of all secreted enterokinase and most of the other intestinal enzymes are contained in the dense part of the juice. The main part of the enzymes is synthesized in the mucous membrane of the small intestine, but some of them enter its cavity from the blood through recretion.

B. Enzymes of the small intestine and their role in digestion. In intestinal secretions and mucous membranes

The lining of the small intestine contains more than 20 enzymes involved in digestion. Most enzymes of intestinal juice carry out the final stages of digestion of nutrients, which began under the action of enzymes of other digestive juices (saliva, gastric and pancreatic juices). In turn, the participation of intestinal enzymes in cavity digestion prepares the initial substrates for parietal digestion.

The intestinal juice contains the same enzymes that are formed in the mucous membrane of the small intestine. However, the activity of enzymes involved in cavity and parietal digestion can vary significantly and depends on their solubility, ability to adsorb and strength of connection with the membranes of enterocyte microvilli. Many enzymes (leucine aminopeptidase, alkaline phosphatase, nuclease, nucleotidase, phospholipase, lipase], synthesized by the epithelial cells of the small intestine, they exhibit their hydrolytic effect first in the zone of the brush border of enterocytes (membrane digestion), and then, after their rejection and breakdown, the enzymes pass into the contents of the small intestine and participate in cavity digestion. Enterokinase, highly soluble in water, easily passes from desquamated epithelial cells into the liquid part of the intestinal juice, where it exhibits maximum proteolytic activity, ensuring the activation of trypsinogen and, ultimately, all proteases of the pancreatic juice. Leucine aminopeptidase is present in large quantities in the secretions of the small intestine, breaking down peptides of various sizes to form amino acids. Intestinal juice contains cathepsins, hydrolyzing proteins in a slightly acidic environment. Alkaline phosphatase hydrolyzes monoesters of orthophosphoric acid. Acid phosphatase has a similar effect in an acidic environment. The secretions of the small intestine contain nuclease, depolymerizing nucleic acids, and nucleotidase, dephosphorylating mononucleotides. Phospholipase breaks down the phospholipids of the intestinal juice itself. Cholesterol esterase breaks down cholesterol esters in the intestinal cavity and thereby prepares it for absorption. The secretion of the small intestine has weakly expressed lipolytic and amylolytic activity.

The main part of intestinal enzymes takes part in parietal digestion. Formed as a result of cavity

Digestion under the influence of os-amylase of pancreatic juice, the products of carbohydrate hydrolysis undergo further breakdown by intestinal oligosaccharidases and disaccharidases on the membranes of the brush border of enterocytes. Enzymes that carry out the final stage of carbohydrate hydrolysis are synthesized directly in intestinal cells, localized and firmly fixed on the membranes of enterocyte microvilli. The activity of membrane-bound enzymes is extremely high, so the limiting link in the absorption of carbohydrates is not their breakdown, but the absorption of monosaccharides.

In the small intestine, the hydrolysis of peptides under the action of aminopeptidase and dipeptidase continues and ends on the membranes of the brush border of enterocytes, resulting in the formation of amino acids that enter the blood of the portal vein.

Parietal hydrolysis of lipids is carried out by intestinal monoglyceride lipase.

The enzyme spectrum of the mucous membrane of the small intestine and intestinal juice changes under the influence of diet to a lesser extent than that of the stomach and pancreas. In particular, the formation of lipase in the intestinal mucosa does not change with either increased or decreased fat content in food.

First section of the small intestine called the duodenum, which is about 25 cm long. The ducts of the pancreas and gall bladder open into it. The duodenum passes into the ileum, the length of which during life is approximately 3 m (after death it relaxes and its length increases). The submucosa and mucosa have a folded structure.

In addition, the mucous membrane has numerous finger-like projections called villi. The walls of the villi are abundantly supplied with blood and lymphatic capillaries, and also contain smooth muscle fibers. The villi constantly contract and relax, thus ensuring close contact with the food in the small intestine. The free surfaces of the epithelial cells of the villi are covered with the finest microvilli. Microvilli greatly increases the surface area of ​​the small intestine.

Between the villi there are long tubular depressions called Lieberkühn crypts. It is here that new epithelial cells are formed, which will mix the constantly exfoliating cells of the villi ( average duration The lifespan of such cells is about five days). In addition, crypt cells secrete intestinal juice - a slightly alkaline liquid containing water and mucus and helping to increase the volume of the contents of the digestive tract. Paneth cells, located at the base of the crypts, secrete lysozyme, an antibacterial enzyme, which was already mentioned when talking about saliva.

Throughout the small intestine there are special epithelial cells called goblet cells; these cells secrete mucus, the functions of which have already been discussed in the corresponding article (see description of the mucous membrane). The duodenum also secretes an alkaline fluid that neutralizes gastric acid and maintains a pH value of 7-8, which is optimal for the functioning of small intestinal enzymes.

Digestion using enzymes in the small intestine

The figure shows the common pathways for the digestion of carbohydrates, proteins and lipids. All small intestinal digestive enzymes, in addition to pancreatic enzymes, are associated with the plasma membrane of epithelial microvilli or located inside the epithelial cells themselves. It is in these places that the final hydrolysis of disaccharides, dipeptides and some tripeptides occurs (Fig. 8.23). The end products of such hydrolysis are monosaccharides and amino acids, respectively. The list of enzymes involved in digestion is given in the table.

In addition to its own enzymes in the small intestine alkaline pancreatic juice comes from the pancreas and bile from the liver. Bile is produced in hepatocytes and stored in gallbladder. It contains a mixture of salts (bile salts), which, once in the small intestine, act as natural detergents, reducing the surface tension of fat globules. In this case, smaller droplets are formed, which increases their total surface area. (This process is called emulsification.) These small droplets are more effectively exposed to lipases (enzymes that break down lipids). More detailed information regarding the structure and function of the liver is given in the corresponding article.

Pancreas is a large gland located behind the stomach. It contains groups of cells that secrete a number of digestive enzymes that enter the duodenum through the pancreatic duct. These include the following enzymes:


1) amylase- converts amylose into maltose;
2) lipase- breaks down lipids (fats and oils) into fatty acids and glycerol;
3) trypsinogen- under the influence of enterokinase, it is converted into trypsin, which breaks down proteins into shorter polypeptides, and also converts excess trypsinogen into trypsin;
4) chymotrypsinogen- turning into chymotrypsin, it breaks down proteins into amino acids;
5) carboxypeptidase- converts peptides into amino acids.

Chinese sages said that if a person has a healthy intestine, he can overcome any disease. Delving into the work of this organ, you never cease to be amazed at how complex it is, how many degrees of protection are built into it. And how easy it is, knowing the basic principles of its work, to help the intestines maintain our health. I hope that this article, written based on the latest medical research Russian and foreign scientists will help you understand how the small intestine works and what functions it performs.

The intestine is the longest organ digestive system and consists of two departments. The small intestine, or small intestine, forms a large number of loops and passes into the large intestine. The human small intestine is approximately 2.6 meters long and is a long, tapering tube. Its diameter decreases from 3-4 cm at the beginning to 2-2.5 cm at the end.

At the junction of the small and large intestines there is an ileocecal valve with a muscular sphincter. It closes the exit from the small intestine and prevents the contents of the large intestine from entering the small intestine. From 4-5 kg ​​of food gruel passing through the small intestine, 200 grams of feces are formed.

The anatomy of the small intestine has a number of features in accordance with its functions. So inner surface consists of many semicircular folds
forms. Thanks to this, its suction surface increases 3 times.

In the upper part of the small intestine, the folds are higher and located closely to each other; as they move away from the stomach, their height decreases. They can completely
absent in the area of ​​transition to the large intestine.

Sections of the small intestine

The small intestine has 3 sections:

  • jejunum
  • ileum.

The initial section of the small intestine is the duodenum.
It distinguishes between the upper, descending, horizontal and ascending parts. The small intestine and ileum do not have a clear boundary between themselves.

The beginning and end of the small intestine are attached to back wall abdominal cavity. On
throughout the rest of its length it is fixed by the mesentery. The mesentery of the small intestine is the part of the peritoneum that contains blood and lymphatic vessels and nerves and allows intestinal motility.


Blood supply

The abdominal part of the aorta is divided into 3 branches, two mesenteric arteries and the celiac trunk, through which blood is supplied to the gastrointestinal tract and abdominal organs. ends mesenteric arteries As they move away from the mesenteric edge, the intestines narrow. Therefore, the blood supply to the free edge of the small intestine is much worse than the mesenteric one.

The venous capillaries of the intestinal villi unite into venules, then into small veins and into the superior and inferior mesenteric veins, which enter the portal vein. Deoxygenated blood first enters through the portal vein into the liver and only then into the inferior vena cava.

Lymphatic vessels

The lymphatic vessels of the small intestine begin in the villi of the mucous membrane; upon leaving the wall of the small intestine they enter the mesentery. In the mesenteric area, they form transport vessels that are capable of contracting and pumping lymph. The vessels contain a white liquid similar to milk. That's why they are called milky. At the root of the mesentery are the central The lymph nodes.

Part lymphatic vessels may flow into the thoracic stream, bypassing the lymph nodes. This explains the possibility of rapid spread of toxins and microbes through the lymphatic route.

Mucous membrane

The mucous membrane of the small intestine is lined with single-layer prismatic epithelium.

Epithelial renewal occurs in different parts of the small intestine within 3-6 days.

The cavity of the small intestine is lined with villi and microvilli. Microvilli form a so-called brush border, which provides protective function small intestine. Like a sieve, it sifts out high-molecular toxic substances and does not allow them to penetrate the blood supply and lymphatic system.

Nutrients are absorbed through the epithelium of the small intestine. Through blood capillaries, located in the centers of the villi, absorption of water, carbohydrates and amino acids occurs. Fats are absorbed by lymphatic capillaries.

The formation of mucus lining the intestinal cavity also occurs in the small intestine. It has been proven that mucus performs a protective function and helps regulate intestinal microflora.

Functions

The small intestine performs the most important functions for the body, such as

  • digestion
  • immune function
  • endocrine function
  • barrier function.

Digestion

It is in the small intestine that the processes of food digestion occur most intensively. In humans, the digestion process practically ends in the small intestine. In response to mechanical and chemical irritations, the intestinal glands secrete up to 2.5 liters of intestinal juice per day. Intestinal juice is secreted only in those parts of the intestine in which the food lump is located. It contains 22 digestive enzymes. The environment in the small intestine is close to neutral.

Fright, angry emotions, fear and strong pain may inhibit the functioning of the digestive glands.

Rare diseases - eosinophilic enteritis, common variable hypogammaglobulinemia, lymphangiectasia, tuberculosis, amyloidosis, malrotation, endocrine enteropathy, carcinoid, mesenteric ischemia, lymphoma.

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