Digestion is a process of chemical and machining food, during which it is digested and absorbed by the cells of the body. Digestive pigments process incoming food and break it down into complex and simple food components. First, proteins, fats and carbohydrates are formed in the body, which in turn become amino acids, glycerol and fatty acids, monosaccharides.

The components are absorbed into the blood and tissues, promoting further synthesis of complex organic matter necessary for the proper functioning of the body. Digestive processes are important for the body for energy purposes. Through the digestion process, calories are extracted from food, which improves performance. internal organs, muscles, central nervous system. The digestive system is complex mechanism, which involves the human oral cavity, stomach and intestines. If the products are not digested correctly, and minerals will remain unchanged, it will not benefit the body. U healthy person All stages of the digestion process last for 24 – 36 hours. Let's study the physiology and features of the digestive process to understand how it works human body.

To understand what digestion is, it is necessary to consider the structure and functions of the digestive system.

It consists of organs and departments:

• oral cavity and salivary glands;
• pharynx;
• esophagus;
• stomach;
• small intestine;
• large intestine;
• liver;
• pancreas.

The listed organs are structurally interconnected and represent a kind of tube, 7–9 meters long. But the organs are laid out so compactly that with the help of loops and bends they are located from oral cavity to the anus.

Interesting! Disturbances in the digestive system lead to various diseases. To ensure proper digestion, avoid eating rational nutrition, fatty foods, strict diets. Also, the organs are adversely affected by poor ecology, regular stress, alcohol and smoking.

The main function of the digestive process is to digest food and gradually process it in the body to form nutrients absorbed into the lymph and blood.

But besides this, digestion performs a number of other important tasks:

• motor or motor is responsible for grinding food, mixing with the secretions of the digestive glands and further movement through the gastrointestinal tract;
• secretory ensures the breakdown of nutritional components into mucous membranes, electrolytes, monomers and final metabolic products;
• absorption promotes the movement of nutrients from the tract cavity into the blood and lymph;
• protective consists of creating barriers using the mucous membrane;
• excretory removes from the body toxic substances and foreign bodies;
• endocrine produces biologically active substances to regulate digestive functions;
• Vitamin-forming ensures the production of vitamins B and K.

TO digestive functions includes sensory, motor, secretory and absorption. Among non-digestive tasks, scientists distinguish protective, metabolic, excretory and endocrine.

Features of the digestion process in the oral cavity

Stages of digestion in humans in the oral cavity, where the grinding of food for further processing begins - important processes. Products interact with saliva, microorganisms and enzymes, after which the taste of food appears and starchy substances are broken down into sugars. The processing process involves teeth and tongue. During coordinated swallowing, the uvula and palate are involved. They prevent food from entering the epiglottis and nasal cavity. The body analyzes incoming food, softens and grinds it. After this, it enters the stomach through the esophagus.

Digestive processes in the stomach

The stomach is located in the human body in the left hypochondrium under the diaphragm and is protected by three membranes: external, muscular and internal. The main function of the stomach is to digest food due to abundant capillary shunting blood vessels and arteries. This is the most wide part digestive tract, which can increase in size for suction large quantity food. During the processing of food in the stomach, the walls and muscles contract, after which it mixes with gastric juice. The process of chemical and mechanical treatment in the stomach lasts for 3 to 5 hours. Food is affected by hydrochloric acid, which is contained in gastric juice and pepsin.

Following the logical flow of the digestion process, proteins are processed into amino acids and low molecular weight peptides. Carbohydrates in the stomach stop being digested, so amylase activity in the stomach is lost. acidic environment. In the stomach cavity, due to hydrochloric acid, proteins swell and also provide a bactericidal effect. The peculiarity of the gastric digestion process is that foods rich in carbohydrates are processed briefly and after 2 hours they move on to the next process. Proteins and fats remain in the compartment for up to 8 – 10 hours.

How does digestion occur in the small intestine?

Partially digested food, along with gastric juice, moves in small portions into the small intestine. This is where more important digestive cycles take place. Intestinal juice consists of alkaline environment due to the flow of bile, secretions intestinal walls and pancreatic juice. The digestion process in the intestines may slow down due to a lack of lactase, which hydrolyzes milk sugar. In the small intestine, more than 20 enzymes are consumed as a result of the digestion process. The work of the small intestine depends on the uninterrupted functioning of three sections that smoothly transform into each other: the duodenum, jejunum and ileum.

During digestion, the duodenum receives bile formed in the liver. Due to the compounds of bile and pancreatic juice, proteins and polypeptides are broken down into simple particles: elastase, aminopeptidase, trypsin, carboxypeptidase and chymotrypsin. They are absorbed into the intestines.

Liver functions

It should be noted the invaluable role of the liver, which produces bile during the digestion process. The work of the small intestine would not be complete without bile, as it helps emulsify fats, activate lipases and absorb triglycerides into the stomach. Bile stimulates perilstatics, enhances the absorption of proteins and carbohydrates, increases hydrolysis and promotes the inactivation of pepsin. Bile plays important role in the absorption and dissolution of fats and fat-soluble vitamins. If there is not enough bile in the body or it is secreted into the intestines, then the digestive processes are disrupted, and fats are released into the intestines. initial form when stool is released.

Importance of the Gallbladder

IN gallbladder In a healthy person, reserves of bile are deposited, which the body uses when processing a large volume. The need for bile disappears after the duodenum is empty. But the liver's work does not stop when food is eliminated. It produces bile, storing it in the gallbladder so that it does not spoil and is stored until the need for it arises again.

If the gallbladder is removed from the body for some reason, its absence is easily tolerated. Bile is stored in the bile ducts and from there it is easily and continuously sent to the duodenum, regardless of the fact of food intake. Therefore, after surgery, you need to eat often and in small portions so that there is enough bile to process it. This is due to the fact that there is no more space to store leftovers, which means that the reserve stock is extremely small.

Features of the large intestine

The remains of undigested food enter the large intestine. They stay in it for 10 – 15 hours. During this period, water absorption and microbial metabolization of nutrients occur. Thanks to the microflora of the large intestine, dietary fiber, which is classified as indigestible biochemical components, is destroyed in this section.

Among them are:

• wax,
• resin,
• gum,
• fiber,
• lignin,
• hemicellulose.

Forms in the large intestine feces. They consist of residues that have not been digested during digestion, mucus, microbes and dead cells of the mucous membrane.

Hormones that affect digestion

In addition to the main sections of the gastrointestinal tract, the quality and speed of the digestion process are influenced by biologically active substances.

As we see, the process of digestion in the human body is complex system, without which human life is impossible. Proper absorption of food contributes to the quality of the body. Each organ that makes up the gastrointestinal tract plays an important role. To maintain health, it is necessary to adhere to the principles of rational nutrition and exclude bad habits. Then the mechanisms will work like clockwork.

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Nutrition is a complex process through which food is received, digested and absorbed. necessary for the body substances. Over the past ten years, a special science devoted to nutrition—nutritionology—has been actively developing. In this article we will look at the process of digestion in the human body, how long it lasts and how to manage without a gallbladder.

The structure of the digestive system

It is represented by a set of organs that ensure the absorption of nutrients by the body, which are a source of energy for it, necessary for cell renewal and growth.

The digestive system consists of: the mouth, pharynx, small intestine, colon and rectum.

Digestion in the human oral cavity

The process of digestion in the mouth involves grinding food. In this process, energetic processing of food with saliva occurs, interaction between microorganisms and enzymes. After treatment with saliva, some of the substances dissolve and their taste appears. The physiological process of digestion in the mouth consists of the breakdown of starch into sugars by the amylase enzyme contained in saliva.

Let's follow the action of amylase using an example: while chewing bread for a minute, you can feel a sweet taste. The breakdown of proteins and fats does not occur in the mouth. On average, the digestion process in the human body takes approximately 15-20 seconds.

Digestive department - stomach

The stomach is the most wide part digestive tract, which has the ability to increase in size and can accommodate huge amounts of food. As a result of the rhythmic contraction of the muscles of its walls, the process of digestion in the human body begins with thorough mixing of food with gastric juice, which has an acidic environment.

Once a lump of food enters the stomach, it remains there for 3-5 hours, during which time it is subjected to mechanical and chemical treatment. Digestion in the stomach begins with exposure of food to gastric juice and the hydrochloric acid that is present in it, as well as pepsin.

As a result of digestion in the human stomach, proteins are digested with the help of enzymes into low molecular weight peptides and amino acids. The digestion of carbohydrates, which begins in the mouth, stops in the stomach, which is explained by the loss of amylases’ activity in an acidic environment.

Digestion in the stomach cavity

The process of digestion in the human body occurs under the influence of gastric juice containing lipase, which is capable of breaking down fats. At the same time great value is given to hydrochloric acid of gastric juice. Under the influence of hydrochloric acid, the activity of enzymes increases, denaturation and swelling of proteins is caused, and a bactericidal effect is exerted.

The physiology of digestion in the stomach is that food enriched with carbohydrates, which remains in the stomach for about two hours, undergoes an evacuation process faster than food containing proteins or fats, which lingers in the stomach for 8-10 hours.

Food that is mixed with gastric juice and partially digested, being in a liquid or semi-liquid consistency, passes into the small intestine in small portions at simultaneous intervals. In which department does the digestion process still take place in the human body?

Digestive department - small intestine

Digestion in the small intestine, into which the bolus of food enters from the stomach, has the most important place, from the point of view of the biochemistry of the absorption of substances.

In this section, the intestinal juice consists of an alkaline environment due to the arrival of bile, pancreatic juice and secretions of the intestinal walls into the small intestine. The digestive process in the small intestine does not go quickly for everyone. This is facilitated by the presence insufficient quantity lactase enzyme, which hydrolyzes milk sugar associated with the indigestibility of whole milk. During the digestion process this department In humans, more than 20 enzymes are consumed, for example, peptidases, nucleases, amylase, lactase, sucrose, etc.

Activity this process in the small intestine depends on the three intersecting sections of which it consists - the duodenum, jejunum and ileum. Bile formed in the liver enters the duodenum. Here food is digested thanks to the pancreatic juice and bile that act on it. This colorless liquid contains enzymes that promote the breakdown of proteins and polypeptides: trypsin, chymotrypsin, elastase, carboxypeptidase and aminopeptidase.

Role of the liver

An important role in the process of digestion in the human body (we will briefly mention this) is played by the liver, in which bile is formed. The peculiarity of the digestive process in the small intestine is due to the assistance of bile in emulsifying fats, absorbing triglycerides, activating lipase, also helps stimulate peristalsis, inactivate pepsin in the duodenum, has a bactericidal and bacteriostatic effect, increases hydrolysis and absorption of proteins and carbohydrates.

Bile does not contain digestive enzymes, but is important in the dissolution and absorption of fats and fat-soluble vitamins. If bile is not produced enough or is secreted into the intestines, then the processes of digestion and absorption of fats are disrupted, as well as an increase in their excretion in their original form with feces.

What happens in the absence of a gallbladder?

The person is left without the so-called small sac, in which bile was previously deposited “in reserve.”

Bile is needed in the duodenum only if there is food in it. And this is not a constant process, only during the period after eating. After some time, the duodenum is emptied. Accordingly, the need for bile disappears.

However, the work of the liver does not stop there; it continues to produce bile. It is for this purpose that nature created the gallbladder, so that the bile secreted in the intervals between meals does not deteriorate and is stored until the need for it arises.

And here the question arises about the absence of this “bile storage”. As it turns out, a person can do without a gallbladder. If the operation is performed in time and other diseases associated with the digestive organs are not provoked, then the absence of a gallbladder in the body is easily tolerated. The timing of the digestion process in the human body is of interest to many.

After surgery, bile can only be stored in the bile ducts. After bile is produced by liver cells, it is released into the ducts, from where it is easily and continuously sent to the duodenum. Moreover, this does not depend on whether the food is taken or not. It follows that after the gallbladder has been removed, food must be taken frequently and in small portions for the first time. This is explained by the fact that there is not enough bile to process large portions of bile. After all, there is no longer a place for its accumulation, but it enters the intestine continuously, albeit in small quantities.

It often takes time for the body to learn to function without a gallbladder and to find the necessary place to store bile. This is how the digestion process works in the human body without a gallbladder.

Digestive department - large intestine

The remains of undigested food move into the large intestine and remain there for approximately 10 to 15 hours. Here the following digestive processes take place in the intestines: absorption of water and microbial metabolization of nutrients.

In the digestion that occurs in the large intestine, food plays a huge role, which includes indigestible biochemical components: fiber, hemicellulose, lignin, gums, resins, waxes.

The structure of food affects the rate of absorption in small intestine and time of movement through the gastrointestinal tract.

Part dietary fiber, which are not broken down by enzymes belonging to the gastrointestinal tract, are destroyed by microflora.

The large intestine is the place of formation of feces, which includes: undigested food debris, mucus, dead cells of the mucous membrane and microbes that continuously multiply in the intestines and which cause the processes of fermentation and gas formation. How long does the digestion process in the human body last? This is a common question.

Breakdown and absorption of substances

The absorption process occurs throughout the entire digestive tract, which is covered with hairs. On 1 square millimeter of mucous membrane there are about 30-40 villi.

In order for the process of absorption of substances that dissolve in fats, or rather fat-soluble vitamins, to occur, fats and bile must be present in the intestines.

Absorption of water-soluble products such as amino acids, monosaccharides, mineral ions occurs with the participation of blood capillaries.

In a healthy person, the entire digestion process takes from 24 to 36 hours.

This is how long the digestion process in the human body lasts.

Food enters the human body through the mouth. There it is crushed, then swallowed and broken down in the digestive tract. Finally, food is absorbed from the intestines and enters the blood and lymph, from where it is extracted by the cells of the human body.

Food satisfies the body’s energy needs; it supplies the basic substances necessary for metabolic processes. It contains ballast substances, carbohydrates, fats, etc.

There are seven stages of food processing. Let's take a closer look at all stages of the digestion process.

Getting food into the mouth

In the oral cavity, solid food is crushed and mixed with saliva. Per day in the parotid, submandibular, sublingual glands About 1.5 liters of saliva are produced. It contains mucus, so food moistened with it easily moves through the esophagus. Thanks to amylase, an enzyme that is part of saliva and breaks down starch, the digestion of carbohydrates begins in the oral cavity. The smell and taste of food causes a person to salivate profusely.

Swallowing

After the food is crushed and processed by saliva, a food bolus is formed, which is then swallowed. The person begins to swallow consciously, pressing the bolus of food onto the soft palate. Then the swallowing process occurs rather as a reflex.

Esophagus

From the pharynx, food moves into the stomach through the esophagus, which is about 25 cm long. In the lower part of the esophagus there is a special “mechanism” that prevents the contents of the stomach from flowing back into the esophagus.

Stomach

Before entering the stomach, food enters its elastic top part, from there she moves on. During this movement, the contents of the stomach are mixed with gastric juice. The main components of gastric juice necessary for digestion are enzymes that break down proteins, mucus and hydrochloric acid. Digestion of proteins begins in the stomach. The acidic environment of gastric juice promotes the death of bacteria. Food mixed with gastric juice enters the duodenum in small portions.

Pancreatic juice and bile

After food enters the duodenum, the production of pancreatic juice and bile begins. About 2 liters of gastric juice are produced per day. It contains digestive enzymes necessary for the breakdown of carbohydrates, proteins and lipids. However, bile is also needed for their absorption. Bile is constantly produced in the liver and stored in the gallbladder. When food is digested, it bile ducts enters the duodenum. By the action of bile, fats are converted into water-soluble compounds and then absorbed through the mucous membrane of the small intestine.

Small intestine

In the small intestine, the final breakdown of all nutrients and the absorption of digestion products into the blood and lymphatic vessels. In the intestine, carbohydrates are broken down into monosaccharides, proteins into amino acids, fats into glycerol and fatty acids. One part of the fatty acids enters the liver, the other goes into the lymph, and from there into the blood. Substances formed as a result of the breakdown process enter into the blood along with the blood. various organs, where they are used for tissue regeneration, strengthening the cell membrane, etc.

Colon and rectum

The final section of the digestive tract is the large intestine, of which the rectum is a part. It absorbs water and electrolytes, forms feces, which accumulate in the rectum and are then excreted from the body. The digestion process ends at this stage.

The body needs fluid

Every day, about 2.5 liters of liquid enters the human body with food. In addition, another 6 liters are secreted into the digestive tract: saliva, bile, gastric, pancreatic and intestinal juice.

Majority useful substances To maintain vital functions, the human body receives it through the gastrointestinal tract.

However regular products that a person eats: bread, meat, vegetables - the body cannot use directly for its needs. To do this, food and drinks must be divided into smaller components - individual molecules.

These molecules are carried by the blood into the body's cells to build new cells and produce energy.

How is food digested?

The process of digestion involves mixing food with gastric juices and moving it through the gastrointestinal tract. During this movement, it is disassembled into components that are used for the needs of the body.

Digestion begins in the mouth - by chewing and swallowing food. And it ends in the small intestine.

How does food move through the gastrointestinal tract?

Large hollow organs gastrointestinal tract– stomach and intestines – have a layer of muscles that sets their walls in motion. This movement allows food and liquid to move through digestive system and mix.

Contraction of the organs of the gastrointestinal tract is called peristalsis. It looks like a wave that moves along the entire digestive tract with the help of muscles.

The intestinal muscles create a constricted area that slowly moves forward, pushing food and liquid in front of it.

How does digestion happen?

Digestion begins in the oral cavity, when chewed food is abundantly moistened with saliva. Saliva contains enzymes that begin the breakdown of starch.

Swallowed food enters esophagus, which connects throat and stomach. At the junction of the esophagus and stomach there are circular muscles. This is the lower esophageal sphincter, which opens under the pressure of swallowed food and allows it to pass into the stomach.

The stomach has three main tasks:

1. Storage. To take in large amounts of food or liquid, the muscles in the upper part of the stomach relax. This allows the walls of the organ to stretch.

2. Mixing. Bottom part The stomach contracts to allow food and liquid to mix with gastric juices. This juice consists of hydrochloric acid and digestive enzymes that help in the breakdown of proteins. The walls of the stomach secrete a large amount of mucus, which protects them from the effects of hydrochloric acid.

3. Transportation. Mixed food passes from the stomach to the small intestine.

From the stomach, food enters upper section small intestine - duodenum. Here the food is exposed to juice pancreas and enzymes small intestine, which promotes the digestion of fats, proteins and carbohydrates.

Here food is processed by bile, which is produced by the liver. Between meals, bile is stored in gallbladder. When eating, it is pushed out into duodenum where it is mixed with food.

Bile acids dissolve fat in the intestinal contents in much the same way as detergents– fat from the frying pan: they break it into tiny droplets. Once the fat is crushed, it is easily broken down by enzymes into its components.

Substances that are obtained from food digested by enzymes are absorbed through the walls of the small intestine.

The mucous membrane of the small intestine is covered with tiny villi, which create a huge surface area that allows the absorption of large amounts of nutrients.

Through special cells, these substances from the intestines enter the blood and are carried throughout the body - for storage or use.

Undigested parts of food go to large intestine, in which water and some vitamins are absorbed. Digestive waste is then formed into feces and removed through rectum.

What disrupts the gastrointestinal tract?

The most important thing

The gastrointestinal tract allows the body to break down food into its simplest compounds, from which new tissue can be built and energy can be obtained.

Digestion occurs in all parts of the gastrointestinal tract - from the mouth to the rectum.

Nutritional physiology is a field of human physiology that studies the processes of converting nutrients into energy and structural elements of tissues human body. The body is enriched with energy and structural elements due to the food that a person receives during the day.

Food is the most important factor, aimed at maintaining and ensuring such basic processes as growth, development and the ability to be active. These processes can be maintained using only balanced nutrition.

Before we begin to consider issues related to the basics of rational nutrition various groups population, it is necessary to get acquainted with the processes of digestion in the body, where complex transformations of food occur, which are subsequently used for plastic and energy purposes of the body.

Digestion- a complex physiological and biochemical process during which ingested food in the digestive tract undergoes physical and chemical changes.

Digestion is the most important physiological process, resulting in complex nutrients food under the influence of mechanical and chemical processing is transformed into simple, soluble and, therefore, digestible substances. Their further path is to be used as a building and energy material in the human body.

Physical changes in food consist of its crushing, swelling, and dissolution. Chemical - in the consistent degradation of nutrients as a result of the action on them of the components of digestive juices secreted into the cavity of the digestive tract by its glands. The most important role in this belongs to hydrolytic enzymes.

Types of digestion

Depending on the origin of hydrolytic enzymes, digestion is divided into three types: intrinsic, symbiont and autolytic.

Own digestion carried out by enzymes synthesized by the body, its glands, enzymes of saliva, stomach and pancreatic juices, and the epithelium of the intestine.

Symbiont digestion- hydrolysis of nutrients due to enzymes synthesized by symbionts of the macroorganism - bacteria and protozoa of the digestive tract. Symbiont digestion occurs in humans in the large intestine. Fiber in food in humans, due to the lack of the corresponding enzyme in the secretions of the glands, is not hydrolyzed (this has a certain physiological meaning - the preservation of dietary fiber, which plays an important role in intestinal digestion), therefore its digestion by the enzymes of symbionts in the large intestine is an important process.

As a result of symbiont digestion, secondary food substances are formed, in contrast to the primary ones, which are formed as a result of one’s own digestion.

Autolytic digestion carried out due to enzymes that are introduced into the body as part of the food consumed. The role of this digestion is essential when one’s own digestion is underdeveloped. In newborns, their own digestion has not yet developed, so nutrients breast milk are digested by enzymes that enter the baby’s digestive tract as part of breast milk.

Depending on the location of the process of nutrient hydrolysis, digestion is divided into intra- and extracellular.

Intracellular digestion consists in the fact that substances transported into the cell by phagocytosis are hydrolyzed by cellular enzymes.

Extracellular digestion is divided into cavitary, which is carried out in the cavities of the digestive tract by enzymes of saliva, gastric juice and pancreatic juice, and parietal. Parietal digestion occurs in the small intestine with the participation of a large number of intestinal and pancreatic enzymes on a colossal surface formed by folds, villi and microvilli of the mucous membrane.

Rice. Stages of Digestion

Currently, the digestion process is considered as a three-stage process: cavity digestion - parietal digestion - absorption. Cavitary digestion consists of the initial hydrolysis of polymers to the stage of oligomers, parietal digestion provides further enzymatic depolymerization of oligomers mainly to the stage of monomers, which are then absorbed.

The correct sequential operation of the elements of the digestive conveyor in time and space is ensured by regular processes at various levels.

Enzymatic activity is characteristic of each section of the digestive tract and is maximum at a certain pH value. For example, in the stomach, the digestive process takes place in an acidic environment. The acidic contents passing into the duodenum are neutralized, and intestinal digestion occurs in a neutral and slightly alkaline environment created by secretions released into the intestine - bile, pancreatic and intestinal juices, which inactivate stomach enzymes. Intestinal digestion occurs in a neutral and slightly alkaline environment, first according to the type of cavity and then parietal digestion, ending with the absorption of hydrolysis products - nutrients.

The degradation of nutrients according to the type of cavity and parietal digestion is carried out by hydrolytic enzymes, each of which has specificity expressed to one degree or another. The set of enzymes in the secretions of the digestive glands has a specific and individual characteristics, adapted to the digestion of the food that is characteristic of a given type of animal, and those nutrients that predominate in the diet.

Digestion process

The digestion process is carried out in the gastrointestinal tract, the length of which is 5-6 m. The digestive tract is a tube, expanded in some places. The structure of the gastrointestinal tract is the same throughout its entire length; it has three layers:

• outer - serous, dense membrane, which mainly has a protective function;
• average - muscle tissue participates in contraction and relaxation of the organ wall;
• internal - a membrane covered with mucous epithelium that allows simple nutrients to be absorbed through its thickness; the mucous membrane often has glandular cells that produce digestive juices or enzymes.

Enzymes are substances of protein nature. In the gastrointestinal tract they have their own specificity: proteins are broken down only under the influence of proteases, fats - lipases, carbohydrates - carbohydrates. Each enzyme is active only at a certain pH environment.

Functions of the gastrointestinal tract:

• Motor, or motor - due to the middle (muscular) lining of the digestive tract, muscle contraction and relaxation carries out food capture, chewing, swallowing, mixing and moving food along the digestive canal.
• Secretory - due to digestive juices, which are produced by glandular cells located in the mucous (inner) lining of the canal. These secretions contain enzymes (reaction accelerators) that perform chemical processing of food (hydrolysis of nutrients).
• The excretory (excretory) function carries out the release of metabolic products into the gastrointestinal tract by the digestive glands.
• Absorption function is the process of assimilation of nutrients through the wall of the gastrointestinal tract into the blood and lymph.

The gastrointestinal tract begins in the oral cavity, then food enters the pharynx and esophagus, which only transport function, the food bolus descends into the stomach, then into the small intestine, consisting of the duodenum, jejunum and ileum, where the final hydrolysis (splitting) of nutrients occurs and they are absorbed through the intestinal wall into the blood or lymph. The small intestine passes into the large intestine, where there is practically no digestion process, but the functions of the large intestine are also very important for the body.

Digestion in the mouth

Further digestion in other parts of the gastrointestinal tract depends on the process of digestion of food in the oral cavity.

The initial mechanical and chemical processing of food occurs in the oral cavity. It involves grinding food, moistening it with saliva, analyzing taste properties, initial breakdown of food carbohydrates and formation of the food bolus. The stay of the food bolus in the oral cavity is 15-18 s. Food in the oral cavity excites taste, tactile, and temperature receptors in the oral mucosa. This reflexively causes the activation of secretion not only salivary glands, but also the glands located in the stomach, intestines, as well as the secretion of pancreatic juice and bile.

Mechanical processing of food in the oral cavity is carried out using chewing. The act of chewing involves the upper and lower jaws with teeth, masticatory muscles, oral mucosa, soft palate. While chewing lower jaw moves in horizontal and vertical planes, the lower teeth are in contact with the upper ones. In this case, the front teeth bite off food, and the molars crush and grind it. Contraction of the muscles of the tongue and cheeks ensures the supply of food between the teeth. Contraction of the lip muscles prevents food from falling out of the mouth. The act of chewing is carried out reflexively. Food irritates the receptors of the oral cavity, the nerve impulses from which are carried along afferent nerve fibers trigeminal nerve enter the chewing center, located in the medulla oblongata, and excite it. Next, along the efferent nerve fibers of the trigeminal nerve, nerve impulses travel to the masticatory muscles.

During the chewing process, an assessment occurs taste qualities food and determining its edibility. The more complete and intensive the chewing process is, the more active the secretory processes occur both in the oral cavity and in the underlying parts of the digestive tract.

The secretion of the salivary glands (saliva) is formed by three pairs of large salivary glands (submandibular, sublingual and parotid) and small glands located in the mucous membrane of the cheeks and tongue. 0.5-2 liters of saliva are produced per day.

The functions of saliva are as follows.

Wetting food, dissolution of solids, impregnation with mucus and formation of food bolus. Saliva facilitates the swallowing process and contributes to the formation of taste sensations.

Enzymatic breakdown of carbohydrates due to the presence of a-amylase and maltase. The enzyme a-amylase breaks down polysaccharides (starch, glycogen) into oligosaccharides and disaccharides (maltose). The action of amylase inside the bolus of food continues when it enters the stomach as long as it maintains a slightly alkaline or neutral environment.

Protective function associated with the presence of antibacterial components in saliva (lysozyme, immunoglobulins of various classes, lactoferrin). Lysozyme, or muramidase, is an enzyme that breaks down the cell wall of bacteria. Lactoferrin binds iron ions necessary for the life of bacteria, and thus stops their growth. Mucin also performs a protective function, as it protects the oral mucosa from damaging effects. food products(hot or sour drinks, spicy seasonings).

Participation in the mineralization of tooth enamel - calcium enters tooth enamel from saliva. It contains proteins that bind and transport Ca 2+ ions. Saliva protects teeth from the development of caries.

The properties of saliva depend on the diet and type of food. When eating solid and dry food, more viscous saliva is released. When inedible, bitter or sour substances enter the oral cavity, a large amount of liquid saliva is released. The enzyme composition of saliva can also change depending on the amount of carbohydrates contained in food.

Regulation of salivation. Swallowing. Regulation of salivation is carried out by autonomic nerves innervating the salivary glands: parasympathetic and sympathetic. When excited parasympathetic nerve salivary gland a large amount of liquid saliva is formed with low content organic substances (enzymes and mucus). When excited sympathetic nerve a small amount of viscous saliva is formed, containing a lot of mucin and enzymes. Activation of salivation when eating food first occurs according to the conditioned reflex mechanism when seeing food, preparing to eat it, inhaling food aromas. At the same time, from visual, olfactory, auditory receptors, nerve impulses along afferent nerve pathways enter the salivary nuclei medulla oblongata (salivation center), which send efferent nerve impulses along parasympathetic nerve fibers to the salivary glands. The entry of food into the oral cavity excites the receptors of the mucous membrane and this ensures the activation of the salivation process according to the mechanism of the unconditioned reflex. Inhibition of the activity of the salivary center and a decrease in the secretion of the salivary glands occurs during sleep, with fatigue, emotional arousal, as well as with fever and dehydration.

Digestion in the oral cavity ends with the act of swallowing and the entry of food into the stomach.

Swallowing is a reflex process and consists of three phases: 1st phase - oral - is arbitrary and consists in the entry of a food bolus formed during the chewing process onto the root of the tongue. Next, the muscles of the tongue contract and the bolus of food is pushed into the throat; 2nd phase - pharyngeal - is involuntary, occurs quickly (within approximately 1 s) and is under the control of the swallowing center of the medulla oblongata. At the beginning of this phase, contraction of the muscles of the pharynx and soft palate lifts the velum and closes the entrance to the nasal cavity. The larynx moves upward and forward, which is accompanied by lowering of the epiglottis and closing of the entrance to the larynx. At the same time, the muscles of the pharynx contract and the upper esophageal sphincter relaxes. As a result, food enters the esophagus; 3rd phase - esophageal - slow and involuntary, occurs due to peristaltic contractions of the esophageal muscles (contraction of the circular muscles of the esophageal wall above the food bolus and longitudinal muscles located below the food bolus) and is under control vagus nerve. The speed of food movement through the esophagus is 2 - 5 cm/s. After the lower esophageal sphincter relaxes, food enters the stomach.

Digestion in the stomach

The stomach is a muscular organ where food is deposited, mixed with gastric juice and moved to the outlet of the stomach. The mucous membrane of the stomach has four types of glands that secrete gastric juice, hydrochloric acid, enzymes and mucus.

Rice. 3. Digestive tract

Hydrochloric acid imparts acidity to the gastric juice, which activates the enzyme pepsinogen, converting it into pepsin, participating in protein hydrolysis. The optimal acidity of gastric juice is 1.5-2.5. In the stomach, protein is broken down into intermediate products (albumoses and peptones). Fats are broken down by lipase only when they are in an emulsified state (milk, mayonnaise). Carbohydrates are practically not digested there, since carbohydrate enzymes are neutralized by the acidic contents of the stomach.

During the day, from 1.5 to 2.5 liters of gastric juice are released. Food in the stomach is digested from 4 to 8 hours, depending on the composition of the food.

The mechanism of gastric juice secretion is a complex process, it is divided into three phases:

• cerebral phase, acting through the brain, involves both unconditioned and conditioned reflex(sight, smell, taste, food entering the oral cavity);
• gastric phase - when food enters the stomach;
• intestinal phase, when some types of food ( meat broth, cabbage juice etc.), entering the small intestine, cause the release of gastric juice.

Digestion in the duodenum

From the stomach, small portions of food gruel enter the initial section of the small intestine - the duodenum, where the food gruel is subjected to active influence pancreatic juice and bile acids.

Pancreatic juice, which has an alkaline reaction (pH 7.8-8.4), enters the duodenum from the pancreas. The juice contains the enzymes trypsin and chymotrypsin, which break down proteins into polypeptides; amylase and maltase break down starch and maltose into glucose. Lipase only affects emulsified fats. The emulsification process occurs in the duodenum in the presence of bile acids.

Bile acids are a component of bile. Bile is produced by the cells of the largest organ - the liver, whose mass is from 1.5 to 2.0 kg. Liver cells constantly produce bile, which accumulates in the gallbladder. As soon as the food gruel reaches the duodenum, bile from the gallbladder enters the intestines through the ducts. Bile acids emulsify fats, activate fat enzymes, enhance motor and secretory function small intestine.

Digestion in the small intestine (jejunum, ileum)

The small intestine is the longest section of the digestive tract, its length is 4.5-5 m, diameter is from 3 to 5 cm.

Intestinal juice is a secretion of the small intestine, the reaction is alkaline. Intestinal juice contains a large number of enzymes involved in digestion: peitidase, nuclease, enterokinase, lipase, lactase, sucrase, etc. The small intestine, due to the different structure of the muscle layer, has an active motor function(peristalsis). This allows food gruel to move into the true intestinal lumen. This is facilitated by chemical composition food - the presence of fiber and dietary fiber.

According to theory intestinal digestion The process of assimilation of nutrients is divided into cavity and parietal (membrane) digestion.

Cavity digestion is present in all cavities of the gastrointestinal tract due to digestive secretions - gastric juice, pancreatic and intestinal juice.

Parietal digestion is present only in a certain segment of the small intestine, where the mucous membrane has protrusions or villi and microvilli that increase inner surface guts 300-500 times.

Enzymes involved in the hydrolysis of nutrients are located on the surface of microvilli, which significantly increases the efficiency of the absorption of nutrients in this area.

The small intestine is the organ where most of the water-soluble nutrients pass through the intestinal wall and are absorbed into the blood; fats initially enter the lymph and then into the blood. All nutrients enter the liver through the portal vein, where, having been cleared of toxic substances digestion, used to nourish organs and tissues.

Digestion in the large intestine

The movement of intestinal contents in the large intestine takes up to 30-40 hours. Digestion in the large intestine is practically absent. Here glucose, vitamins, and minerals are absorbed that remain undigested due to the large number of microorganisms in the intestines.

In the initial segment of the large intestine, almost complete absorption of the liquid received there occurs (1.5-2 l).

The microflora of the large intestine is of great importance for human health. More than 90% are bifidobacteria, about 10% are lactic acid and E. coli, enterococci, etc. The composition of the microflora and its functions depend on the nature of the diet, the time of movement through the intestines and the use of various medications.

Basic functions normal microflora intestines:

• protective function - creation of immunity;
• participation in the digestive process - final digestion of food; synthesis of vitamins and enzymes;
• maintaining a constant biochemical environment of the gastrointestinal tract.

One of important functions The large intestine is the formation and removal of feces from the body.