The human digestive system. Nb! Carbohydrate digestion begins in the mouth Carbohydrates are digested in the mouth

AT oral cavity carbohydrates are digested by an enzyme in saliva α-amylase. The enzyme cleaves internal α(1→4)-glycosidic bonds. In this case, products of incomplete hydrolysis of starch (or glycogen) are formed - dextrins. Maltose is also formed in a small amount. The active center of α-amylase contains Ca 2+ ions. Na + ions activate the enzyme.

In the gastric juice, the digestion of carbohydrates is inhibited, since amylase is inactivated in an acidic environment.

The main site of carbohydrate digestion is the duodenum, where it is excreted as part of the pancreatic juice. α- amylase. This enzyme completes the breakdown of starch and glycogen, initiated by salivary amylase, to maltose. Hydrolysis of the α(1→6)-glycosidic bond is catalyzed by the intestinal enzymes amylo-1,6-glucosidase and oligo-1,6-glucosidase .

Digestion of maltose and disaccharides from food is carried out in the area of ​​the brush border of epithelial cells (enterocytes) of the small intestine. Disaccharidases are integral proteins of enterocyte microvilli. They form a polyenzymatic complex consisting of four enzymes, the active centers of which are directed into the intestinal lumen.

1M altaza(-glucosidase) hydrolyzes maltose for two molecules D-glucose.

2. Lactase(-galactosidase) hydrolyzes lactose on the D-galactose and D-glucose.

3. Isomaltase / Sugarase(double-acting enzyme) has two active centers located in different domains. Enzyme hydrolyzes sucrose before D-fructose and D-glucose, and with the help of another active site, the enzyme catalyzes the hydrolysis isomaltose up to two molecules D-glucose.

Milk intolerance in some people, manifested by abdominal pain, bloating (flatulence) and diarrhea, is due to a decrease in lactase activity. There are three types of lactase deficiency.

1. hereditary lactase deficiency. Impaired tolerance symptoms develop very quickly after birth . Feeding lactose-free food leads to the disappearance of symptoms.

2. Low primary lactase activity(gradual decrease in lactase activity in predisposed persons). In 15% of children in Europe and 80% of children in the countries of the East, Asia, Africa, Japan, the synthesis of this enzyme gradually stops as they grow older, and adults develop intolerance to milk, accompanied by the above symptoms. Dairy products are well tolerated by such people.

2. Low secondary lactase activity. Indigestibility of milk is often the result of intestinal diseases (tropical and non-tropical forms of sprue, kwashiorkor, colitis, gastroenteritis).

Symptoms similar to those described for lactase deficiency are characteristic of other disaccharidases deficiency. Treatment is aimed at eliminating the relevant disaccharides from the diet.

Nb! Glucose enters the cells of different organs by different mechanisms.

The main products of complete digestion of starch and disaccharides are glucose, fructose and galactose. Monosaccharides enter the blood from the intestine, overcoming two barriers: the brush border membrane facing the intestinal lumen and the basolateral membrane of the enterocyte.

Two mechanisms of glucose entry into cells are known: facilitated diffusion and secondary active transport associated with the transfer of Na + ions. Fig.5.1. The structure of the glucose transporter

Glucose transporters (GLUTs), which provide a mechanism for its facilitated diffusion through cell membranes, form a family of related homologous proteins, a characteristic structural feature of which is a long polypeptide chain that forms 12 transmembrane helical segments (Fig. 5.1). One of the domains located on the outer surface of the membrane contains an oligosaccharide. N- and C- terminal sections of the carrier are turned inside the cell. The 3rd, 5th, 7th, and 11th transmembrane segments of the transporter appear to form a channel through which glucose enters the cell. A change in the conformation of these segments ensures the process of moving glucose into the cell. The carriers of this family contain 492-524 amino acid residues and differ in their affinity for glucose. Each transporter appears to perform specific functions.

The carriers that provide secondary, sodium ion-dependent, active glucose transport from the intestine and renal tubules (SGLT) differ significantly in amino acid composition from the GLUT family of carriers, although they are also built from twelve transmembrane domains.

Below, in tab. 5.1. some properties of monosaccharide carriers are given.

The transition of glucose and other monosaccharides into the enterocyte is facilitated by GLUT 5, located in the apical membrane of the enterocyte (facilitated diffusion along the concentration gradient) and SGLT 1, which provides, together with sodium ions, the movement (symport) of glucose into the enterocyte. Sodium ions are then actively, with the participation of Na + -K + -ATPase, removed from the enterocyte, which maintains a constant gradient of their concentration. Glucose leaves the enterocyte through the basolateral membrane with the help of GLUT 2 along a concentration gradient.

Absorption of pentoses occurs by simple diffusion.

The vast majority of monosaccharides enter the portal circulatory system and the liver, a small part - in lymphatic system and pulmonary circulation. Excess glucose is stored in the liver in the form of glycogen.

NB! The exchange of glucose in the cell begins with its phosphorylation.

P
The entry of glucose into any cell begins with its phosphorylation. This reaction solves several problems, the main of which is the "capture" of glucose for intracellular use and its activation.

The phosphorylated form of glucose does not pass through the plasma membrane, becomes the “property” of the cell and is used in almost all pathways of glucose metabolism. The only exception is the recovery path (Fig.5.2.).

The phosphorylation reaction is catalyzed by two enzymes: hexokinase and glucokinase. Although glucokinase is one of the four hesokinase isoenzymes ( hexokinase 4), there are important differences between hexokinase and glucokinase: 1) hexokinase is able to phosphorylate not only glucose, but also other hexoses (fructose, galactose, mannose), while glucokinase activates only glucose; 2) hexokinase is present in all tissues, glucokinase - in hepatocytes; 3) hexokinase has a high affinity for glucose ( To M< 0,1 ммоль/л), напротив, глюкокиназа имеет высокую К M (около 10 ммоль/л), т.е. ее сродство к глюкозе мало и фосфорилирование глюкозы возможно только при массивном поступлении ее в клетки, что в физиологических условиях происходит на высоте пищеварения в печеночных клетках. Активирование глюкокиназы препятствует резкому увеличению поступления глюкозы в общий кровоток; в перерывах между приемами пищи для включения глюкозы в обменные процессы вполне достаточно гексокиназной активности. При диабете из-за низкой активности глюкокиназы (синтез и активность которой зависят от инсулина) этот механизм не срабатывает, поэтому глюкоза не задерживается в печени и вызывает гипергликемию.

Glucose-6-phosphate formed in the reaction is considered an allosteric inhibitor hexokinase (but not glucokinase).

Since the glucokinase reaction is insulin-dependent, instead of glucose, diabetic patients can be prescribed fructose (fructose is phosphorylated by hexokinase directly into fructose-6-phosphate).

Glucose-6-phosphate is used in the mechanisms of glycogen synthesis, in all oxidative pathways for the conversion of glucose, and in the synthesis of other monosaccharides required by the cell. The place that this reaction occupies in glucose metabolism allows it to be considered the key reaction of carbohydrate metabolism.

The hexokinase reaction is irreversible (G = -16.7 kJ / mol), therefore, to convert glucose-6-phosphate into free glucose in the cells of the liver and kidneys, the enzyme glucose-6-phosphate phosphatase is present, catalyzing the hydrolysis of glucose-6-phosphate. The cells of these organs can thus supply glucose to the blood and provide other cells with glucose.

To sustain life, first of all, people need food. Products contain a lot of essential substances: mineral salts, organic elements and water. Nutrient components are the building material for cells and a resource for constant human activity. During the decomposition and oxidation of compounds, a certain amount of energy is released, which characterizes their value.

The digestion process begins in the mouth. The product is processed by the digestive juice, which acts on it with the help of the contained enzymes, due to which, even when chewing, complex carbohydrates, proteins and fats are transformed into molecules that are absorbed. Digestion is a complex process that requires exposure to products of many components synthesized by the body. Proper chewing and digestion is the key to health.

Functions of saliva in the process of digestion

The digestive tract includes several main organs: the oral cavity, pharynx with esophagus, pancreas and stomach, liver and intestines. Saliva performs many functions:

What happens to food? The main task of the substrate in the mouth is to participate in digestion. Without it, certain types of foods would not be broken down by the body or would be dangerous. The liquid wets the food, the mucin glues it into a lump, preparing it for swallowing and movement through the digestive tract. It is produced depending on the quantity and quality of food: less for liquid food, more for dry food, and does not form when drinking water. Chewing and salivation can be attributed to the most important process of the body, at all stages of which there is a change in the consumed product and the delivery of nutrients.

Composition of human saliva

Saliva is colorless, tasteless and odorless (see also: what to do if you have ammonia breath?). It can be saturated, viscous or very rare, watery - it depends on the proteins that make up the composition. The glycoprotein mucin gives it the appearance of mucus and makes it easier to swallow. It loses its enzymatic qualities soon after it enters the stomach and mixes with its juice.

The oral fluid contains a large number of gases: carbon dioxide, nitrogen and oxygen, as well as sodium and potassium (0.01%). It contains substances that digest some carbohydrates. There are other components of organic and inorganic origin, as well as hormones, cholesterol, vitamins. It is 98.5% water. The activity of saliva can be explained by the huge number of elements contained in it. What functions does each of them perform?

organic matter

The most important component of the intraoral fluid are proteins - their content is 2-5 grams per liter. In particular, these are glycoproteins, mucin, A and B globulins, albumins. It contains carbohydrates, lipids, vitamins and hormones. Most of the protein is mucin (2-3 g / l), and due to the fact that it contains 60% carbohydrates, it makes saliva viscous.

About a hundred enzymes are present in the mixed liquid, including ptyalin, which is involved in the breakdown of glycogen and its conversion into glucose. In addition to the presented components, it contains: urease, hyaluronidase, glycolysis enzymes, neuraminidase and other substances. Under the action of the intraoral substance, food changes and transforms into the form necessary for assimilation. With pathology of the oral mucosa, diseases internal organs used frequently laboratory research enzymes to identify the type of disease and the causes of its formation.

What substances can be classified as inorganic?

The composition of the mixed oral fluid includes inorganic components. These include:

Mineral components create an optimal reaction of the environment to incoming food, maintain the level of acidity. A significant part of these elements is absorbed by the mucous membrane of the intestines, stomach and sent to the blood. The salivary glands are actively involved in maintaining the stability of the internal environment and the functioning of organs.

The process of salivation

The production of saliva occurs both in the microscopic glands of the oral cavity, and in the large: parolingual, submandibular and parotid pairs. The canals of the parotid glands are located near the second molar from above, the submandibular and sublingual canals are brought out under the tongue at one mouth. Dry foods produce more saliva than wet foods. The glands under the jaw and tongue synthesize 2 times more fluid than the parotid glands - they are responsible for the chemical processing of products.

An adult produces about 2 liters of saliva per day. The release of fluid throughout the day is uneven: during the use of products, active production begins up to 2.3 ml per minute, in a dream it decreases to 0.05 ml. In the oral cavity, the secret obtained from each gland is mixed. It washes and moisturizes the mucous membrane.

Salivation is controlled by autonomic nervous system. Increased fluid synthesis occurs under the influence of taste sensations, olfactory stimuli, and when irritated by food during chewing. Excretion is significantly slowed down by stress, fright and dehydration.

Active enzymes involved in the digestion of food

The digestive system converts the nutrients in food into molecules. They become fuel for tissues, cells and organs that continuously perform metabolic functions. The absorption of vitamins and microelements occurs at all levels.

Food is digested from the moment it enters the mouth. Here, mixing with the oral fluid, which includes enzymes, is carried out, the food is lubricated and sent to the stomach. Substances contained in saliva break down the product into simple elements and protect the human body from bacteria.

Why do saliva enzymes work in the mouth but stop functioning in the stomach? They act only in an alkaline environment, and then, in the gastrointestinal tract, it changes to acidic. Proteolytic elements work here, continuing the stage of assimilation of substances.

Amylase enzyme or ptyalin - breaks down starch and glycogen

Amylase is a digestive enzyme that breaks down starch into carbohydrate molecules, which are absorbed in the intestines. Under the action of the component, starch and glycogen are converted into maltose, and with the help of additional substances they are converted into glucose. To detect this effect, eat a cracker - when chewed, the product exhibits a sweet aftertaste. The substance works only in the esophagus and in the mouth, converting glycogen, but loses its properties in the acidic environment of the stomach.

Ptyalin is produced by the pancreas and salivary glands. The type of enzyme produced by the pancreas is called pancreatic amylase. The component completes the stage of digestion and absorption of carbohydrates.

Lingual lipase - for the breakdown of fats

The enzyme promotes the conversion of fats into simple compounds: glycerol and fatty acids. In the oral cavity, the process of digestion begins, and in the stomach, the substance stops working. A small amount of lipase is produced by gastric cells, the component specifically breaks down milk fat and is especially important for babies, because it makes the process of assimilation of products and the absorption of elements easier for their underdeveloped digestive system.

Varieties of protease - for protein cleavage

Protease is a general term for enzymes that break down proteins into amino acids. There are three main types produced in the body:

The cells of the stomach produce pepsicogen, an inactive component that turns into pepsin upon contact with an acidic environment. It breaks peptides - the chemical bonds of proteins. The pancreas is responsible for the production of trypsin and chymotrypsin, which enter the small intestine. When already processed by gastric juice and fragmentally digested food is sent from the stomach to the intestines, these substances contribute to the formation of simple amino acids that are absorbed into the blood.

Why is there a lack of enzymes in saliva?

Proper digestion is mainly dependent on enzymes. Their deficiency leads to incomplete digestion of food, diseases of the stomach and liver may occur. Symptoms of their lack are heartburn, flatulence, and frequent belching. After a while, headaches may appear, work will be disrupted endocrine system. A small amount of enzymes leads to obesity.

Usually the production mechanisms active substances laid genetically, therefore, the violation of the activity of the glands is innate. Experiments have shown that a person receives enzyme potential at birth, and if it is spent without replenishing, it will quickly run out.

The processes occurring in the body can be controlled. To simplify its work, it is necessary to consume fermented food: steamed, raw, high-calorie (bananas, avocados).

The reasons for the lack of enzymes include:

• their small supply from birth;
• eating foods grown in soil poor in enzymes;
• eating overcooked, fried food without raw vegetables and fruits;
• stress, pregnancy, diseases and pathologies of organs.

The work of enzymes does not stop in the body for a minute, supporting every process. They protect a person from diseases, increase endurance, destroy and remove fats. With their small amount, incomplete splitting of products occurs, and the immune system begins to fight with them, as with an alien body. This weakens the body and leads to exhaustion.

Everyone knows that for the most important process of digestion, which is one of the life support systems of the human body. Responsible for this process are protein molecules or RNA molecules, to put it simply, enzymes.

The main purpose of these molecules is to speed up chemical reactions in the human body, thereby ensuring digestion. If you do not go into biology, enzymes, simply put, process substances, dividing them into useful and needed by the body and those that need to be eliminated urgently.

Lipases are found in the mouth; stomach; and pancreas. Because lingual lipase has been inactivated by gastric acid, it is believed to have been mainly introduced for oral hygiene and for its antibacterial action in the mouth, however it can continue to work on food stored in the fundus of the stomach and this lipase can be digested. up to 30% fat. Gastric lipase is of little importance to humans.

The following table shows the enzymes for digesting fats. Bile salts are secreted by the liver and have a hydrophobic and hydrophilic side. They will attach to the fat globules, emulsify them and cause them to form micelles. The anatomy of a micelle is shown in the following illustration along with the biochemical structure of bile salt.

In general, the human digestive system begins at the mouth and ends at the anus. For some reason, it is generally accepted that all digestive processes occur only in the stomach and intestines. In fact, this is far from being the case. The most important process of digestion begins in the mouth and throat of a person and, oddly enough, there are also enzymes.

Micelles are small, and because they have a hydrophilic side on the outside, they effectively allow fats to act as water-soluble particles. This allows them to penetrate into an unidentified layer adjacent to the epithelium. small intestine, and be absorbed. In the absence of bile salts, very little fatty acids penetrate this layer, and most of the fat will pass through the intestinal obstruction and unabsorbed, causing steatorrhea.

Micelles allow fatty acids and cholesterol to cross the unstable layer and come into contact with the edge of the brush, where they easily cross the fat-soluble cell membrane. Several smaller free fatty acids overflow through the cell and exit at the basal-lateral border, passing into the capillaries. However, most fatty acids enter the smooth endoplasmic reticulum where serum is repackaged into cholemicrons. They are carried out of the cell by exocytosis.

Digestion in the throat and mouth

The fact that the process of food processing begins in the oral cavity and pharynx has long been proven experimentally. First of all, human saliva begins to act on food in the process of chewing.

In the mouth and pharynx there are many small salivary glands and three pairs of large ones - their ducts open directly into the oral cavity. All of them begin to actively produce salivary fluid as soon as food enters the mouth.

The cholemicrons do not enter the capillaries, but instead pass into the lymphatic system, where they are carried into the thoracic duct. The thoracic canal empties into the superior vena cava. Nucleic bases are taken up by active transport, pentoses are taken up by other sugars.

Factors that cause fat malabsorption can also affect the absorption of these vitamins. Vitamin B12 is absorbed into ilium and requires to be associated with internal factor, a protein secreted in the stomach, for absorption. Between 30 and 80% of calcium intake in the body is absorbed. The rate of absorption depends on the human body. Nearly all iron absorption occurs in the glandular form in the duodenum. The ferric form is converted into ferroalloys by ferritic reductase.

For the sake of interest, you can find the location of the salivary glands and use a mirror to follow the process of digestion in the mouth and throat. This is done as follows:

• First, let's find the parotid salivary glands. Press the cheeks just below and in front of the ears on both sides. As soon as you feel the active secretion of saliva, then you have discovered the glands. At this moment, the active formation of saliva in the oral cavity can also be observed in the mirror.
• The submandibular salivary glands can be found by pressing on two points at a distance of 2-3 centimeters from the edge of the jaw. If done correctly, you will instantly feel your mouth fill with saliva.
• Sublingual gland. It is located quite far away, and it is very difficult to feel it. However, if you sharply raise your tongue to the sky, you will surely see a small fountain - this is the sublingual gland in action.

In the basolateral part of the enterocyte, iron ions are transported into the interstellar fluid by a transporter called ferroportin. In plasma, the iron form reverts back to the ferric form and is bound to the iron transfer protein carrier. The small intestine is represented by 9 liters, 2 external and 7 internal, of fluid per day for reabsorption. In health, all but 200 cc are reabsorbed.

The junctions between epithelial cells in the colon are much denser than in small intestine, which eliminates the leakage of sodium into the lumen. Most of the fluid and electrolytes are absorbed in the ascending colon. Although proteins and sugars are generally all absorbed when the fluid reaches the colon, the colon is able to absorb these substrates. Some indigestible substances, such as beans, can be digested by colon bacteria, and these bacteria can even digest small amounts of cellulose.

In general, the beginning of the digestive process in the mouth and throat can be felt even before you start eating. Remember how a mouth quickly fills with saliva from a delicious smell, or a ripe lemon cut into a slice causes its active formation.

These processes indicate that the enzymes in the mouth and throat are already ready to start the digestive process and all that remains is to put a piece of food in your mouth and start chewing it actively. By the way, as soon as you start chewing, stomach enzymes also begin to act.

Have you ever wondered how food is digested inside our body after we consume it? The internal structure of our body is extremely efficient in performing numerous functions, among which digestion is the most important of all the processes that take place.

Our body metabolism is controlled by a group of digestive enzymes that are secreted by various organs. digestive system. These enzymes help in the proper digestion of food. Enzymatic breakdown begins in the mouth and spreads to the intestines where it is converted to simpler particles and then excreted by our body. These digestive enzymes act as catalysts for the breakdown of carbohydrates, fats, and proteins.

As soon as the jaws begin to move, gastric juice is actively formed. That is why many doctors advise chewing gum about half an hour before a meal to improve digestion.

By the way, even now, for the knowledge of the digestive system, the study of human saliva continues. The biomaterial is extracted using a special suction cup capsule, which is attached to the mucous membrane. Thus, the salivary fluid through the test tube goes out, where it is collected and sent for research.

Source of digestive enzymes. These enzymes are also present in saliva where they help the first stage of digestion. Enzymes are classified according to the nature of the substrates in which they work. Digestive enzymes are broadly classified into four groups.

• Proteolytic enzyme: break down proteins into amino acids.
• Lipolytic enzyme: break down fats into fatty acids and glycerol.
• Amylolytic enzyme: break down carbohydrate and starch into simple sugars.
• Nucleolytic enzyme: break down nucleic acids into nucleotides.

Functions of saliva

In general, saliva performs the most important protective functions in the body, namely:

• Saliva protects the mucous membrane of the mouth and throat from drying out.
• Nuclease enzymes, which are contained in the salivary fluid, fight viruses and pathogenic bacteria as much as possible, being part of our immunity.
• Saliva also contains enzymes necessary for blood clotting, which prevent inflammatory processes in the mouth and throat.

However, the primary function of the salivary fluid is - digestive. If not the participation of saliva in this critical process, a person simply could not digest certain types of foods. And some familiar dishes would be deadly for us.

The salivary gland secretes the enzyme lysozyme, which has an antibacterial effect. Enzymes secreted by the oral cavity mainly provide protection against bacteria. Betaine helps maintain fluid balance inside the mouth. Amylase - converts starch into soluble sugars. Betaine. Maintains the balance of cell fluid as osmolytes. Bromelain is an anti-inflammatory agent that softens meat.

Enzymes secreted by the stomach are known as gastric enzymes. The stomach secretes hydrochloric acid, which kills bacteria and germs and provides an acidic environment for the proper enzymatic activity of the protease enzymes. Gastric amylase - Degradation of starch Gelatinase - Degradation of gelatin and collagen. Rennin. Converting liquid milk into solid particles. Gastric lipase - Degradation of oily fat.

Composition and enzymes of saliva

In fact, saliva is the only biomaterial due to which enzymes are present in the human mouth and throat. What the salivary fluid consists of directly depends on the age and state of health of the patient. First of all, fluid secretion is studied, which usually ranges from 1 to 200 milliliters per hour. Maximum rate occurs during food processing.

The pancreas is the main digestive gland in our body. Digestive enzymes carbohydrate breakdown of the pancreas and starch molecules to simple sugars. They also highlight a group of enzymes that promote the degradation of nucleic acids. It functions as an endocrine and exocrine gland.

Phospholipase - Hydrolysis of phospholipids into fatty acids. Trypsin - converts proteins into basic amino acids. Stepsin. Decomposition of triglycerides into glycerol and fatty acids. Carboxypeptidase - degradation of proteins to amino acids. pancreatic amylase. degradation of carbohydrates to simple sugars.

Externally, saliva is a viscous, colorless, slightly cloudy liquid. Slight turbidity occurs due to the fact that the liquid contains various organic and inorganic substances.

Now about enzymes. In saliva, they are found in three main types:

• Those that are formed by parenchymal cells.
• The waste products of the microflora of the body, or, more simply, bacteria.
• Those that appear as a result of the destruction of white blood cells in the mouth.

Amylase is the most important enzyme in saliva. It is she who is involved in such a complex process as the breakdown of starch, which is found in almost all types of food from plant to animal. Amylase breaks down starch into saccharide and a small amount of glucose, which are well absorbed by the body.

Elastase - degrade protein elastin nucleases - the conversion of nucleic acids into nucleotides and nucleosides. At the end of this section, you will be able to. Explain the specialized functions of the organs involved in the processing of food in the body. Describe how organs work together to digest food and absorb nutrients. Explain the processes of digestion and absorption. . All living organisms need nutrients to survive. While plants can obtain nutrients from their roots and the energy molecules needed to cellular function During photosynthesis, animals obtain their nutrients through the consumption of other organisms.

Amylase is produced by glandular cells, the enzyme accumulates in them in an inactive form. The activation of this enzyme occurs when food containing protein is ingested. The ideal environment for amylase to work is a temperature not higher than 36.6 degrees and a normal acid-base environment in the body.

It is also impossible not to mention such an enzyme as maltase. This enzyme is actively engaged in the breakdown of maltose saccharide and converts it into safe glucose for the body.

At the cellular level, the biological molecules necessary for the functioning of animals are amino acids, lipid molecules, nucleotides, and simple sugars. However, the food consumed consists of proteins, fats and complex carbohydrates. Animals must convert these macromolecules into the simple molecules needed to maintain cellular function. The conversion of food consumed into required nutrients is a multi-step process involving digestion and absorption. During digestion, food particles are broken down into smaller components that are later absorbed by the body.

Active work of saliva enzymes does not begin in the oral cavity, but precisely at the moment when the lump of food begins to move into the pharynx, and then into the esophagus and stomach. Everyone knows that stomach acid is incredibly acidic. As soon as food enters the stomach, the reaction of hydrolysis of carbohydrates begins, which begin to be digested. Gradually, the lump of food is mixed, and saliva enzymes begin to work.

This happens both through physical means, such as chewing, and through chemical means. One of the challenges in human nutrition is maintaining a balance between food intake, storage, and energy expenditure. Taking in more food energy than is used in activity leads to the accumulation of excess in the form of body fat. The rise in obesity and resulting diseases such as type 2 diabetes are making understanding of the role of diet and nutrition in maintaining good health all the more important.

The process of digestion begins in the mouth with the consumption of food. Teeth play an important role in grinding or physically breaking down food into smaller particles. Enzymes present in saliva also begin to chemically break down food. The food is then swallowed and enters the esophagus, a long tube that connects the mouth to the stomach. Using peristalsis, or wave-like contractions of smooth muscles, the muscles of the esophagus push food toward the stomach. The contents of the stomach are extremely acidic, with a pH between 5 and this acidity kills microorganisms, breaks down food tissues and activates digestive enzymes.

By the way, a curious fact, with the action of enzymes, is that when you chew bread or potatoes, they acquire a slightly sweet taste. This is due to the fact that saccharides and monosaccharides begin to actively break down as a result of the appearance of a sweetish, and quite safe taste.

And thanks to the enzymes of saliva, one can also say that they significantly speed up the processing time of fruits. Saliva actually facilitates the task of the intestines. Together with it, carbohydrates come to the intestines already in a partially digested form.

Further breakdown of food occurs in the small intestine, where bile produced by the liver and enzymes produced by the small intestine and pancreas continue the digestion process. Smaller molecules are absorbed into the bloodstream through epithelial cells lining the walls of the small intestine. The waste moves to the large intestine, where water is absorbed and the dry material condenses into feces; it persists until it is excreted through the anus.

Figure 4 Shows the components of the human digestive system. Both physical and chemical digestion begin in the mouth or oral cavity, which is the point of entry of food into the digestive system. Food is broken down into smaller particles by chewing, the chewing action of the teeth. All mammals have teeth and can chew their food to begin the process of physically breaking it down into smaller particles.

Causes of a decrease in the number of enzymes in the mouth and throat

It happens that in the human body there is a deficiency of enzymes, and problems with digestion begin. Most often the reason for this chronic diseases digestive or endocrine systems. For example, diabetes, inflammatory processes of the body, and very rarely to a violation of the composition of saliva, even severe stress can lead.

Saliva also contains lysozyme, which has an antibacterial effect. It also contains an enzyme called salivary amylase, which starts the process of converting starches in food into a disaccharide called maltose. Another enzyme called lipase is produced by cells in the tongue to break down fats. The chewing and wetting actions provided by teeth and saliva prepare food into a mass called a swallowing bolus. The tongue aids in swallowing - moving the bolus from the mouth to the throat. The pharynx opens into two passages: the esophagus and trachea.

Even a slight decrease in salivary enzymes can lead to the following symptoms:

• Indigestion, sometimes even diarrhea. Only the enzymes of the salivary fluid are capable of digesting starch and saccharides - this happens in the mouth and pharynx.
• Pain in the abdomen.
• body intoxication.

Only a doctor can make an accurate diagnosis, as well as prescribe adequate treatment. You should not engage in self-diagnosis, use enzyme preparations in large quantities - this can only aggravate the situation.

It is better to contact a qualified specialist as soon as possible, as well as start treatment in a timely manner - this will help to avoid many complications in the future.

Digestion in the mouth and stomach is a complex process that involves many organs. As a result of such activity, tissues and cells are nourished, and energy is also provided.

Digestion is an interrelated process that provides mechanical grinding of the food bolus and further chemical breakdown. Food is necessary for a person to build tissues and cells in the body and as a source of energy.

assimilation mineral salts, water and vitamins occurs in its original form, but more complex macromolecular compounds in the form of proteins, fats and carbohydrates require splitting into simpler elements. To understand how such a process occurs, let's analyze digestion in the oral cavity and in the stomach.

Before you "plunge" into the process of knowing the digestive system, you need to learn about its functions:

• production and secretion of digestive juices containing biological substances and enzymes;
• transfers decay products, water, vitamins, minerals, etc. through the mucous membranes of the gastrointestinal tract directly into the blood;
• secretes hormones;
• provides grinding and promotion of food mass;
• excretes the resulting end products of metabolism from the body;
• provides a protective function.

Attention: to improve the digestive function, it is necessary to monitor the quality of the products used, the price for them, although sometimes higher, but the benefits are much greater. It is also worth paying attention to the balance of nutrition. If you have digestive problems, it is best to consult a doctor about this issue.

Importance of Enzymes in the Digestive System

The digestive glands of the oral cavity and gastrointestinal tract produce enzymes that play one of the main roles in digestion.

If we generalize their meaning, then we can highlight some properties:

1. Each of the enzymes is highly specific, catalyzing only one reaction and acting on one type of bond. For example, proteolytic enzymes or proteases are able to break down proteins into amino acids, lipases break down fats into fatty acids and glycerol, amylases break down carbohydrates into monosaccharides.
2. They are able to act only at certain temperatures in the range of 36-37C. Anything that is outside these boundaries leads to a decline in their activity and disruption of the digestion process.
3. High "performance" is achieved only at a certain pH value. For example, pepsin in the stomach is activated only in an acidic environment.
4. They can break down a large amount of organic substances, since they are highly active.

Enzymes of the mouth and stomach:

Attention: in the stomach, the activity of enzymes is increased due to the production of hydrochloric acid. This is an inorganic element that performs one of the important functions in digestion, contributing to the destruction of protein. It also disinfects pathogenic microorganisms that come with food and, as a result, prevents the possible decay of food masses in the stomach cavity.

The role of enzymes in the body is multifaceted and this is evidenced by the photo below.

Digestion in the mouth

With a decrease in the concentration of nutrients in the blood, a feeling of hunger begins. The physiological basis of this feeling is localized in the lateral nuclei of the hypothalamus. It is the stimulation of the hunger center that is the motive for the search for food.

So, the food is before our eyes, we tasted its taste and got saturated, but I wonder what was happening in the body at that moment?

Initial department digestive tract is the oral cavity. From below, it is limited by the diaphragm of the mouth, from above by the palate (hard and soft), and from the sides and in front by the gums and teeth. Also here, the ducts of the digestive glands open into the oral cavity, these are the sublingual, parotid, submandibular.

In addition, there are other mucous small salivary glands located throughout the oral cavity. After capturing a lump of food with teeth (and there are only 32 of them, 16 for the lower and 16 for the upper jaw), it is chewed and moistened with saliva, which contains the enzyme ptyalin.

It has the ability to dissolve some easily soluble substances, and soften and cover the food with mucus, which greatly facilitates the process of swallowing. Saliva also contains mucin with lysozyme, which have bactericidal effects.

With the help of the tongue, a muscular organ covered with a mucous membrane, taste is realized and food is pushed to the pharynx after chewing. Next, the prepared lump of food passes through the esophagus to the stomach.

Swallowing is a complex process that involves the muscles of the pharynx and tongue. During this movement, the soft palate rises, due to which the entrance to the nasal cavity and the path of food to this area is blocked. With the help of the epiglottis, the inlet to the larynx is closed.

Through the upper part of the digestive tract - the pharynx, the food bolus begins to move along the esophagus - a tube about 25 cm long, which is a continuation of the pharynx. The upper and lower esophageal sphincters open at this time, and the passage of food to the stomach itself takes about 3-9 seconds, liquid food moves in 1-2 seconds.

No changes occur in the esophagus, since digestive juices are not secreted there, the rest of the splitting stage will occur in the stomach. You can learn more about digestion in the oral cavity from the video in this article.

Digestion in the stomach

After the esophagus, the food bolus enters the stomach. This is the most expanded part of the gastrointestinal tract, having a capacity of up to 3 liters.

The shape and size of this organ can vary depending on the degree of muscle contraction and the amount of food consumed. The mucous membrane is formed by longitudinal folds containing a huge number of glands that produce gastric juice.

It is represented by three types of cells:

• main are those that produce enzymes gastric juice;
• lining- they are able to produce hydrochloric acid;
• additional- with their help, mucus (mucoid and mucin) begins to be produced, thanks to which the walls of the stomach are protected from the action of pepsin.

If there is a violation of the secretion of gastric juice in the body, there are special preparations to normalize this process, which are accompanied by instructions for use. However, self-medication is not recommended, because this can cause complications.

The moment of penetration of gastric juice into the food mass implies the beginning of the gastric phase of digestion, during which the breakdown of protein particles occurs predominantly. This happens as a result well-coordinated work enzymes and stomach acid. The semi-digested food is then sent from the stomach to the duodenum through the pyloric sphincter, which completely separates the stomach and intestines during contraction.

The duration of food in the stomach cavity depends on its composition. Solid protein food stimulates the secretion of gastric juice more actively and stays in this organ longer, while liquid food leaves much faster.

On average, food can linger in the stomach for 4-6 hours. At the end of the digestion phase, it is in a collapsed state, and every 45-90 minutes periodic contractions of the stomach begin, the so-called hungry peristalsis.

As we understood, digestion is a complex multi-stage process regulated by the central nervous system departments. Each stage smoothly follows each other and many organs are involved in each of them. All this is regulated by the nervous and humoral regulation system.

However, any violation can cause a failure in automatic actions digestive system, which will entail certain symptoms and signs. In this case, you should immediately seek medical helpwhere the doctor can examine and prescribe the necessary diagnosis.

Digestion in the oral cavity is the first link in a complex chain of processes of enzymatic breakdown of nutrients to monomers. Digestive functions of the oral cavity include approbation of food for edibility, mechanical processing of food and its partial chemical processing.

Motor function in the oral cavity begins with the act of chewing. Chewing is a physiological act that ensures the grinding of nutrients, wetting them with saliva and the formation of a food bolus. Chewing ensures the quality of mechanical processing of food in the oral cavity. It affects the process of digestion in other parts of the digestive tract, changing their secretory and motor functions.

One of the methods for studying the functional state of the chewing apparatus is masticography - recording the movements of the lower jaw during chewing. On the record, which is called a masticogram, a chewing period can be distinguished, consisting of 5 phases (Fig. 31).

* 1 phase - rest phase;

* Phase 2 - the introduction of food into the oral cavity (the first ascending knee of the record, which starts from the line of rest);

* Phase 3 - approximate chewing or initial chewing function, it corresponds to the process of approbation of the mechanical properties of food and its initial crushing;

* Phase 4 - the main or true phase of chewing, it is characterized by the correct alternation of chewing waves, the amplitude and duration of which is determined by the size of the food portion and its consistency;

* Phase 5 - the formation of a food bolus has the form of a wavy curve with a gradual decrease in the amplitude of the waves.

The nature of the masticogram depends mainly on the mechanical properties of the food and its volume. Changes in the masticogram also occur when the integrity of the dentition is violated, with diseases of the teeth and periodontium, with diseases of the oral mucosa, etc.

Chewing is a self-regulatory process based on the functional chewing system. A useful adaptive result of this functional system is a food bolus formed during chewing and prepared for swallowing. The functional chewing system is formed for each chewing period.

When food enters the oral cavity, irritation of the mucosal receptors occurs in the same sequence: mechano-, thermo- and chemoreceptors. Excitation from these receptors through the sensory fibers of the lingual (a branch of the trigeminal nerve), glossopharyngeal, tympanic string (a branch of the facial nerve) and the upper laryngeal nerve (a branch of the vagus nerve) enters the sensory nuclei of these nerves medulla oblongata(the nucleus of the salitary tract and the nucleus of the trigeminal nerve). Further, the excitation along a specific path reaches the specific nuclei of the visual hillocks, where the excitation switches, after which it enters the cortical section of the oral analyzer. Here, based on the analysis and synthesis of incoming afferent excitations, a decision is made about the edibility of substances that have entered the oral cavity. Inedible food is rejected (spit out), which is one of the important protective functions of the oral cavity. Edible food remains in the mouth and chewing continues. In this case, excitation from the mechanoreceptors of the periodontium, the supporting apparatus of the tooth, joins the flow of afferent impulses.

Collaterals depart from the afferent pathways at the level of the brain stem to the nuclei of the reticular formation, which is part of the extrapyramidal system and provides an efferent function. From the motor nuclei of the reticular formation of the brainstem (which are the motor nuclei of the trigeminal, hypoglossal and facial nerves) in a downward direction, as part of the efferent fibers of the trigeminal, hypoglossal and facial nerves, impulses arrive at the muscles that provide chewing: the actual chewing, facial and tongue muscles. Voluntary contraction of the masticatory muscles is provided by the participation of the cerebral cortex.

51. In the act of chewing and the formation of a food bolus, saliva takes an obligatory part. Saliva is a mixture of the secrets of three pairs of large salivary glands and many small glands located in the oral mucosa. Epithelial cells, food particles, mucus, salivary bodies (neutrophilic leukocytes, sometimes lymphocytes), and microorganisms are mixed with the secretion secreted from the excretory streams of the salivary glands. Such saliva, mixed with various inclusions, is called oral fluid. The composition of the oral fluid varies depending on the nature of the food, the state of the body, and also under the influence of environmental factors.

The secret of the salivary glands contains about 99% water and 1% dry residue, which includes anions of chlorides, phosphates, sulfates, bicarbonates, iodites, bromides, fluorides. Saliva contains sodium, potassium, magnesium, calcium cations, as well as trace elements (iron, copper, nickel, etc.). Organic matter is represented mainly by proteins. In saliva there are proteins of various origins, including the protein mucous substance - mucin. Saliva contains nitrogen-containing components: urea, ammonia, creatinine, etc.

Functions of saliva.

1. digestive function saliva is expressed in the fact that it wets the food lump and prepares it for digestion and swallowing, and saliva mucin glues a portion of food into an independent lump. More than 50 enzymes were found in saliva, which belong to hydrolases, oxidoreductases, transferases, lipases, isomerases. Small amounts of proteases, peptidases, acid and alkaline phosphatases were found in saliva. Saliva contains the enzyme kallikrein, which is involved in the formation of kinins, which dilate blood vessels.

Despite the fact that food is in the oral cavity for a short time - about 15 s, digestion in the oral cavity is of great importance for the implementation of further food splitting processes, since saliva, by dissolving food substances, contributes to the formation of taste sensations and affects appetite. In the oral cavity, under the influence of saliva enzymes, the chemical processing of food begins. The saliva enzyme amylase breaks down polysaccharides (starch, glycogen) to maltose, and the second enzyme, maltase, breaks down maltose to glucose.

2. Protective function, saliva is expressed as follows:

* saliva protects the oral mucosa from drying out, which is especially important for a person who uses speech as a means of communication;

* the protein substance of saliva mucin is able to neutralize acids and alkalis;

* saliva contains an enzyme-like protein substance lysozyme (muramidase), which has a bacteriostatic effect and takes part in the processes of regeneration of the epithelium of the oral mucosa;

* nuclease enzymes contained in saliva are involved in the degradation of nucleic acids of viruses and thus protect the body from viral infection;

* blood clotting factors were found in saliva, the activity of which determines local hemostasis, processes of inflammation and regeneration of the oral mucosa;

* a substance stabilizing fibrin was found in saliva (similar to factor XIII in blood plasma);

* Substances that prevent blood clotting (antithrombin plates and antithrombins) and substances with fibrinolytic activity (plasminogen, etc.) were found in saliva;

* saliva contains a large amount of immunoglobulins, which protects the body from pathogenic microflora.

3. Trophic function of saliva. Saliva is a biological medium that is in contact with tooth enamel and is its main source of calcium, phosphorus, zinc and other trace elements.

4. excretory function saliva. As part of saliva, metabolic products can be released - urea, uric acid, some medicinal substances, as well as salts of lead, mercury, etc.

Salivation is carried out by a reflex mechanism. There are conditioned reflex and unconditioned reflex salivation.

Conditioned salivation is caused by the sight, smell of food, sound stimuli associated with cooking, as well as talking and remembering food. At the same time, visual, auditory, olfactory receptors are excited. Nerve impulses from them enter the cortical section of the corresponding analyzer, and then to the cortical representation of the center of salivation. From it, excitation goes to the bulbar department of the salivation center, the efferent commands of which go to the salivary glands.

Unconditional reflex salivation occurs when food enters the oral cavity. Food irritates the mucosal receptors. The afferent pathway of the secretory and motor components of the chewing act is common. Nerve impulses through afferent pathways enter the center of salivation, which is located in the reticular formation of the medulla oblongata and consists of the upper and lower salivary nuclei (Fig. 32).

The efferent path of salivation is represented by fibers of the parasympathetic and sympathetic divisions of the autonomic nervous system. Parasympathetic innervation of the salivary glands is carried out by vegetative fibers of the cells of the salivary nuclei, passing as part of the glossopharyngeal and facial nerves.

From the upper salivary nucleus, excitation is directed to the submandibular and sublingual glands. Preganglionic fibers go as part of the tympanic string to the submandibular and sublingual autonomic ganglia. Here, excitation switches to postganglionic fibers, which go as part of the lingual nerve to the submandibular and sublingual salivary glands.

From the lower salivary nucleus, excitation is transmitted along the preganglionic fibers as part of the small stony nerve to the ear ganglion, here the excitation switches to postganglionic fibers, which, as part of the ear-temporal nerve, approach the parotid salivary gland.

The sympathetic innervation of the salivary glands is carried out by sympathetic nerve fibers that start from the cells of the lateral horns. spinal cord at the level of 2-6 thoracic segments. Switching of excitation from prena to the postganglionic fibers takes place in the superior cervical sympathetic ganglion, from which the postganglionic fibers reach the salivary glands along the course of the blood vessels.

Irritation of the parasympathetic fibers that innervate the salivary glands leads to the separation of a large amount of liquid saliva, which contains many salts and few organic substances. Irritation of sympathetic fibers causes the separation of a small amount of thick, viscous saliva, which contains few salts and many organic substances.

Of great importance in the regulation of salivation are humoral factors, which include hormones of the pituitary, adrenal, thyroid and pancreas, as well as metabolic products.

The separation of saliva occurs in strict accordance with the quality and quantity of nutrients taken. For example, when taking water, saliva almost does not separate. When harmful substances enter the oral cavity, a large amount of liquid saliva is separated, which washes the oral cavity from these harmful substances, etc. Such an adaptive nature of salivation is provided by the central mechanisms for regulating the activity of the salivary glands, and these mechanisms are triggered by information coming from the receptors of the oral cavity .

52. Swallowing. After the food bolus has formed, swallowing occurs. This is a reflex process in which three phases are distinguished:

* oral (voluntary and involuntary);

* pharyngeal (fast involuntary);

* esophageal (slow arbitrary).

The swallowing cycle lasts about 1 s. With coordinated contractions of the muscles of the tongue and cheeks, the food bolus moves to the root of the tongue, which leads to irritation of the receptors of the soft palate, the root of the tongue and the posterior pharyngeal wall. Excitation from these receptors through the pharyngeal nerves enters the swallowing center located in the medulla oblongata, from which efferent impulses go to the muscles of the oral cavity, larynx, pharynx and esophagus as part of the trigeminal, hypoglossal, glossopharyngeal and vagus nerves. Contraction of the muscles that lift the soft palate closes the entrance to the nasal cavity, and raising the larynx closes the entrance to the nasal cavity. Airways. During the act of swallowing, contractions of the esophagus occur, which have the character of a wave that occurs in the upper part and spreads towards the stomach. Esophageal motility is regulated mainly by efferent fibers of the vagus and sympathetic nerves and intramural nerve formations of the esophagus.

The swallowing center is located next to the respiratory center of the medulla oblongata and is in reciprocal relations with it (when swallowing, the breath is held).