Digestive system table. The structure and function of the digestive system

Useful components necessary to maintain vital functions. The well-being of the whole organism depends on how well it works. What are the organs of the digestive system and what are their functions? This is worth understanding in more detail.

Functions

In the human body, nature does not provide for anything superfluous. Each of its components is assigned a certain responsibility. Well-coordinated work ensures the well-being of the body and maintains health.

Functions of organs digestive system the following:

  1. Motor-mechanical. This includes chopping, moving and separating food.
  2. Secretory. There is the production of enzymes, saliva, digestive juices, bile, which take part in digestion.
  3. Suction. The absorption of proteins, carbohydrates and fats, minerals, water and vitamins by the body is ensured.

The motor-mechanical function is to contract muscles and chop food, as well as stir and move it. The secretory work consists in the production of digestive juices by the glandular cells. Due to the suction function, the supply of nutrients to the lymph and blood is ensured.

Structure

What is the structure of the human digestive system? Its structure is aimed at the processing and movement of useful components entering the body from the outside, as well as the removal of unnecessary substances into the environment. The walls of the organs of the digestive system consist of four layers. They are lined from the inside. It moisturizes the walls of the canal and facilitates easier passage of food. The submucosa is located under it. Due to its numerous folds, the surface alimentary canal getting bigger. The submucosa is permeated with nerve plexuses, lymphatic and blood vessels. The other two layers are the outer and inner muscular membranes.

The digestive system consists of the following organs:

  • oral cavity:
  • esophagus and pharynx;
  • stomach;
  • colon;
  • small intestine;
  • digestive glands.

To understand their work, you need to dwell on each in more detail.

Oral cavity

At the first stage, food enters the mouth, where it is carried out primary processing... The teeth perform the function of grinding, the tongue, thanks to the taste buds located on it, evaluates the quality of the incoming products. Then they begin to produce special enzymes for wetting and primary breakdown of food. After processing in oral cavity it enters further into the internal organs, the digestive system continues its work.

This section also includes the muscles that take part in the chewing process.

Esophagus and pharynx

Food enters the funnel-shaped cavity, which consists of muscle fibers... This is the structure of the pharynx. With the help of it, a person swallows food, after which it moves along the esophagus, and then enters the main organs of the human digestive system.

Stomach

In this organ, food mixing and splitting occurs. Stomach over appearance is a muscle sac. It is hollow inside, the volume is up to 2 liters.

Its inner surface contains many glands, due to which the production of juice and hydrochloric acid, which are necessary for the digestion process, occurs. They break down the components of food and contribute to their further promotion.

Small intestine

What organs does the digestive system consist of besides the mouth, pharynx, esophagus and stomach? Bypassing them, food enters - the initial Food is split under the influence of bile and special juices, and then goes to the next sections small intestine- skinny and iliac.

Here, the substances are finally broken down, and microelements, vitamins and other useful components are absorbed into the blood. Its length is approximately six meters. The small intestine is filled with the abdominal cavity. The absorption process takes place under the influence of special villi that cover the mucous membrane. Thanks to a special valve, a so-called flap is formed, which stops the reverse movement of feces.

Colon

The human digestive system is very important in the body. What organs it consists of, you need to know to understand its functions. Answering this question, it is worth pointing out one more, no less important section, in which the digestion process ends. This is the large intestine. It is in it that all undigested food residues fall. This is where water is absorbed and feces are formed, final cleavage proteins and microbiological synthesis of vitamins (in particular groups B and K).

The structure of the large intestine

The organ is approximately one and a half meters long. It includes the following departments:

  • cecum (appendix is ​​present);
  • the colon (it, in turn, includes the ascending, transverse, descending and sigmoid;
  • rectum (it consists of an ampulla and an anal canal).

The large intestine ends with an anus through which processed food is excreted from the body.

Digestive glands

What are the organs of the digestive system? A great deal of responsibility rests with the liver, pancreas, and gallbladder. Without them, the process of digestion, in principle, as well as without other organs, would be impossible.

The liver contributes to the production an important component- bile. Main - The organ is located under the diaphragm, with right side... The task of the liver is to retain harmful substances, which helps to avoid poisoning the body. Thus, it is a kind of filter, therefore it often suffers from a large accumulation of toxins.

The gallbladder is a reservoir for bile produced by the liver.

The pancreas secretes special enzymes that are capable of breaking down fats, proteins and carbohydrates. It is known that it is capable of forming up to 1.5 liters of juice per day. Also insulin (a hormone of a peptide nature). It affects metabolism in almost all tissues.

Among the digestive glands, it is necessary to note the salivary glands, which are located in the oral cavity, they secrete substances to soften food and its primary breakdown.

What are the risks of malfunctioning of the digestive system?

A clear, well-coordinated work of organs ensures the correct functioning of the whole organism. But disorders of the digestive process, unfortunately, are not uncommon. This threatens the appearance various diseases, among which the leading place is occupied by gastritis, esophagitis, ulcers, dysbiosis, intestinal obstruction, poisoning, etc. In the event of such ailments, it is necessary to take up treatment in a timely manner, otherwise, as a result of delays in admission nutrients the work of other organs can be disrupted into the blood. Not worth using folk methods without consulting a doctor. Funds alternative medicine are used only in combination with medications and under the supervision of a healthcare professional.

To understand the whole principle of functioning, you need to know what organs the digestive system consists of. This will help you to deeper understand the problem when it appears and find a way to solve it. The presented scheme is simple, only the main points are touched upon. In fact, the human digestive system is much more complex.

Indeed, in our life we ​​eat about 40 tons of different foods that directly affect almost all aspects of our life. It is no accident that in ancient times they said: "Man is what he eats."

Human digestive system carries out the digestion of food (through its physical and chemical processing), absorption of products, splitting through the mucous membrane into the lymph, as well as the removal of undigested residues.

The grinding process begins in the mouth. There it is softened with saliva, chewed with teeth and sent down the throat. Further, the formed food lump enters the stomach through the esophagus.

Thanks to the acidic gastric juice, a very complex enzymatic process of food digestion begins in this muscle organ.

Enzymes are protein substances that accelerate chemical processes in cages.

The structure of the digestive system

The human digestive system consists of organs gastrointestinal tract and auxiliary organs (salivary glands, liver, pancreas, gall bladder, etc.).

Three divisions of the digestive system are conventionally distinguished.

  • The anterior section includes the organs of the oral cavity, pharynx and esophagus. Mainly mechanical processing of food is carried out here.
  • The middle section consists of the stomach, small and large intestine, liver and pancreas, in this section it is carried out mainly chemical treatment food, absorption of nutrients and the formation of feces.
  • The posterior section is represented by the caudal part of the rectum and ensures the excretion of feces from the body.

Digestive system organs

We will not consider all the organs of the digestive system, but we will give only the main ones.

Stomach

The stomach is a muscle sac, the volume of which in adults is 1.5-2 liters. Gastric juice contains corrosive hydrochloric acid, so every two weeks the inner lining of the stomach is replaced with a new one.

Food moves through the digestive tract by contracting the smooth muscles of the esophagus, stomach and intestines. This is called peristalsis.

Small intestine

The small intestine is a section of the human digestive tract located between the stomach and the large intestine. From the stomach, food enters the 6-meter small intestine (duodenum, jejunum and ileum). It continues the digestion of food, but already by the enzymes of the pancreas and liver.

Pancreas

The pancreas is the most important organ of the digestive system; largest gland. Its main function of external secretion is the secretion of pancreatic juice, which contains digestive enzymes necessary for the complete digestion of food.

Liver

The liver is the largest internal organ person. It cleans the blood of toxins, "monitors" the level of glucose in the blood and produces bile, which breaks down fats in the small intestine.

Gall bladder

The gallbladder is an organ that stores bile from the liver for release into the small intestine. Anatomically, it is part of the liver.

Colon

The large intestine is the lower, final part of the digestive tract, namely the lower part of the intestine, in which water is mainly absorbed and formed from food gruel (chyme) formed feces. The muscles of the colon work independently of the will of the person.

Soluble sugars and proteins are absorbed through the walls of the small intestine and enter the bloodstream, while undigested residues move further into the large intestine (blind, colon and rectum).

There, water is absorbed from the food masses, and they gradually become semi-solid and, ultimately, are excreted from the body through the rectum and anus.

Interesting facts about the digestive system

When chewing food, the jaw muscles develop an effort of up to 72 kg on the molars, and up to 20 kg on the incisors.

By the age of three, a child has 20 milk teeth. Beginning from six to seven years, milk teeth fall out, and permanent teeth grow in their place. There are 32 of these teeth in humans.

What are vitamins

Vitamins (from Latin vita- life) are substances, without which the full-fledged work of all human organs is impossible. They are found in various foods, but mainly in vegetables, fruits and herbs. Vitamins are designated by letters of the Latin alphabet: A, B, C, etc.

Together with food, we receive a supply of "fuel", which provides cells with energy (fats and carbohydrates), "building materials" necessary for the growth and repair of our body (proteins), as well as vitamins, water and minerals.

A lack of a particular substance can adversely affect human health.

The human digestive system is extremely important and complex mechanism... If you have any discomfort after eating, and this discomfort has been observed for a long time, be sure to consult a gastroenterologist.

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The state of our health depends not only on what kind of food we eat, but also on the work of those organs that digest this food and bring it to every cell of our body.

The digestive system begins with the oral cavity, followed by the pharynx, then the esophagus and, finally, the basis of the foundations of the digestive system - the gastrointestinal tract.

Oral cavity is the first section of the digestive system, therefore, the whole further process of digestion depends on how well and correctly all the processes for the initial processing of food proceed in it. It is in the oral cavity that the taste of food is determined, here it is chewed and moistened with saliva.

Pharynx follows the oral cavity and is a funnel-shaped canal lined with mucous membrane. Respiratory and digestive tract, the activity of which should be strictly regulated by the body (it is not for nothing that they say that when a person chokes, that the food has gone "in the wrong throat").

Esophagus is a cylindrical tube located between the pharynx and the stomach. Through it, food enters the stomach. The esophagus, like the pharynx, is lined with a mucous membrane, which contains special glands that produce a secret that moisturizes food as it passes through the esophagus into the stomach. The total length of the esophagus is about 25 cm. In a resting state, the esophagus is folded, but it has the ability to lengthen.

Stomach- one of the main components of the digestive tract. The size of the stomach depends on its fullness and ranges from about 1 to 1.5 liters. It performs a number of important functions, which include: directly digestive, protective, excretory. In addition, processes associated with the formation of hemoglobin take place in the stomach. It is lined with a mucous membrane, which contains a mass of digestive glands that secrete gastric juice. Here the food mass is saturated with gastric juice and crushed, or rather, the intensive process of its digestion begins.

Main components gastric juice are: enzymes, hydrochloric acid and mucus. In the stomach, solid food that has entered it can be up to 5 hours, liquid - up to 2 hours. The components of gastric juice carry out chemical processing of food entering the stomach, turning it into a partially digested semi-liquid mass, which then enters duodenum.

Duodenum represents the upper, or first, part of the small intestine. The length of this part of the small intestine is equal to the length of twelve fingers folded together (hence its name). It connects directly to the stomach. Here, in the duodenum, bile comes from the gallbladder and pancreatic juice. In the walls of the duodenum, there is also a fairly large number of glands, which produce an alkaline secretion rich in mucus, which protects the duodenum from the effects of acidic gastric juice entering it.

Small intestine, in addition to the duodenum, it also combines the jejunum and the ileum. The small intestine as a whole has a length of about 5–6 m. Almost all the main processes of digestion (food digestion and absorption) take place in the small intestine. On inside the small intestine has finger-like outgrowths, due to which its surface is significantly increased. In humans, the digestion process ends in the small intestine, which is also lined with a mucous membrane, very rich in glands that secrete intestinal juice, which contains enough big number enzymes. Intestinal juice enzymes finish the process of breaking down proteins, fats and carbohydrates. The mass in the small intestine is mixed by peristalsis. Food gruel moves slowly through the small intestine, in small portions entering the large intestine.

Colon about twice as thick as thin. It consists of the cecum with the appendix - the appendix, the colon and rectum. Here, in the large intestine, the remains of undigested food accumulate, and the digestion processes are practically absent. There are two main processes in the colon: absorption of water and the formation of feces. The rectum serves as a place of accumulation of feces, which are removed from the body during the process of defecation.

Appendix, as we have already said, it is part of the large intestine and is a short and thin appendix of the cecum about 7-10 cm long. Its functions, as well as the causes of its inflammation, are still not clearly understood by doctors. According to modern data and the opinion of some scientists, the appendix, in the wall of which there are many lymphoid nodules, is one of the organs of the immune system.

But the digestive system, no matter how correctly its individual organs are arranged, could not work without certain substances - enzymes that are produced in the body by special glands. The triggering mechanisms for the digestive system are digestive enzymes, which are proteins that break down large food molecules into smaller ones. The activity of enzymes in our body under the conditions of the digestion process is aimed at substances such as proteins, fats and carbohydrates, and minerals, water and vitamins are absorbed practically unchanged.

For the breakdown of each group of substances, there are specific enzymes: for proteins - proteases, for fats - lipase, for carbohydrates - carbohydrase. The main glands that produce digestive enzymes are the glands of the mouth (salivary glands), the glands of the stomach and small intestine, the pancreas, and the liver. Main role the pancreas plays in this, which produces not only digestive enzymes, but also hormones, such as insulin and glucagon, which are involved in the regulation of protein, carbohydrate and lipid metabolism.

The human digestive system has a very well thought-out structure and is a whole set of digestive organs that provide the body with the energy it needs, without which intensive restoration of tissues and cells would not be possible.

The main function of the digestive system, as its name suggests, is digestion. The essence of this process is the mechanical and chemical processing of food. Certain digestive organs break down the nutrients coming from food into separate components, due to which, under the action of certain enzymes, they penetrate through the walls of the digestive system. The whole process of digestion consists of several successive stages, and absolutely all parts of the digestive tract are involved in it. Better understand the importance of the digestive system for human body, will allow a more detailed examination of its structure. Digestive tract consists of three main broad divisions. Top or front section includes organs such as the oral cavity, pharynx, and esophagus. Here food enters and undergoes initial mechanical processing, then goes to the middle section, consisting of the stomach, small and large intestines, pancreas, gallbladder and liver. A complex chemical processing of food is already taking place here, its splitting into individual components, as well as their absorption. In addition, the middle section is responsible for the formation of undigested fecal residues, which enter the back section, intended for their final excretion.

Upper section

Like all parts of the digestive system, the upper section consists of several organs:

  1. the oral cavity, which includes lips, tongue, hard and soft palate, teeth and salivary glands;
  2. pharynx;
  3. esophagus.

The structure of the upper part of the digestive tract begins with the oral cavity, the entrance to which is formed by the lips, consisting of muscle tissue with a very good blood supply. Due to the presence of many nerve endings in them, a person can easily determine the temperature of the absorbed food. The tongue is a movable muscular organ, consisting of sixteen muscles and covered with a mucous membrane.

It is due to its high mobility that the tongue is directly involved in the process of chewing food, moving it between the teeth, and then into the pharynx. There are also many taste buds on the tongue, thanks to which a person feels a particular taste. As for the walls of the oral cavity, it is formed from the hard and soft palate. In the anterior region there is a hard palate, consisting of the palatine bone and upper jaw. Soft sky, formed from muscle fibers, is located in the back of the mouth and forms an arch with the palatine tongue.

Also to upper section it is customary to include the muscles necessary for the chewing process: buccal, temporal and chewing. Since the digestive mechanism begins its work in the mouth, the salivary glands are directly involved in the digestion of food, producing saliva, which promotes the breakdown of food, which facilitates the process of swallowing. A person has three pairs salivary glands: submandibular, sublingual, ear. The oral cavity is connected to the esophagus with the help of a funnel-shaped pharynx, which has the following sections: nasopharynx, oropharynx and hypopharynx. The esophagus, which extends towards the stomach, is about twenty-five centimeters long. Pushing food through it is provided by reflex contractions called peristalsis.

The esophagus is almost entirely composed of smooth muscles, and its membrane has great amount mucous glands moisturizing the organ. In the structure of the esophagus, the upper sphincter, which connects it to the pharynx, and the lower sphincter, which separates the esophagus from the stomach, are also distinguished.

Middle department

The structure of the middle section of the human digestive system is formed by three main layers:

  1. peritoneum- an outer layer with a dense texture that produces a special lubricant to facilitate the sliding of internal organs;
  2. muscle layer- the muscles that form this layer have the ability to relax and contract, which is called peristalsis;
  3. submucosa composed of connective tissue and nerve fibers.

Chewed food through the pharynx and the esophageal sphincter enters the stomach - an organ that can contract and stretch when filled. In this organ, due to the gastric glands, a special juice is produced that breaks down food into individual enzymes. It is in the stomach that the thickest area of ​​the muscle layer is located, and at the very end of the organ is the so-called pylorus sphincter, which controls the flow of food into the following sections of the digestive tract. The small intestine has a length of about six meters, it is she who fills the abdominal cavity. This is where absorption occurs - the absorption of nutrients. The initial segment of the small intestine is called the duodenum, to which the ducts of the pancreas and liver fit. Other parts of the organ are called the small intestine and ileum. The absorbing surface of the small intestine is significantly increased due to the special villi that cover its mucous membrane.

At the end of the ileum there is a special valve - a kind of valve that prevents the movement of feces in the opposite direction, that is, from the large to the small intestine. The large intestine, about one and a half meters long, is somewhat wider than the thin one, and its structure includes several main sections:

  1. blind the intestine with the appendix - the appendix;
  2. colonic intestine - ascending, transverse colon, descending;
  3. sigmoid intestine;
  4. straight intestine with ampoule (expanded part);
  5. anal canal and the anus, which form the posterior part of the digestive system.

All kinds of microorganisms multiply in the large intestine, which are indispensable in creating the so-called immunological barrier that protects the human body from pathogenic microbes and bacteria. Besides intestinal microflora provides the final decomposition of individual components of digestive secretions, participates in the synthesis of vitamins, etc.

The size of the intestine increases with the age of a person, in the same way its structure, shape and position change.

In addition, the organs of the digestive system include glands, which are peculiar links of the entire human body, since their function extends to several systems at once. We are talking about the liver and pancreas. The liver is the largest organ in the digestive system and has two lobes. This organ performs many functions, some of which are not related to digestion. So, the liver is a kind of blood filter, helps to eliminate toxins from the body, provides storage nutrients and a certain amount of vitamins, and also produces bile for the gallbladder.

The time of bile excretion depends mainly on the composition of the food taken. So, when eating foods rich in fats, bile is secreted very quickly. The gallbladder has tributaries that connect it to the liver and duodenum. Bile coming from the liver is stored in the gallbladder exactly until it becomes necessary to send it to the duodenum to participate in the digestive process. The pancreas synthesizes hormones and fats, and is also directly involved in the process of digesting food.

It is also the metabolic regulator of the entire human body.

In the pancreas, pancreatic juice is produced, which then penetrates into the duodenum and takes part in the breakdown of carbohydrates, fats and proteins. Activation of enzymes of pancreatic juice occurs only when it enters the intestine, otherwise severe inflammatory disease- pancreatitis.

Back section

The end, also known as the posterior part, which includes the human digestive system, consists of the caudal part of the rectum. In its anal part, it is customary to distinguish the columnar, intermediate and skin zones. Its terminal area is narrowed and forms the anal canal, ending in the anus, formed from two muscles: the internal and external sphincter. The function of the anal canal is to retain and remove feces and gases.

Purpose

The functions of the digestive system necessary to ensure the vital activity of each person are to ensure the following processes:

  • primary mechanical processing of food and swallowing;
  • active digestion;
  • absorption;
  • excretion.

Food enters the mouth first, where it is chewed and takes the form of a bolus - a soft ball, which is then swallowed and reaches the stomach through the esophagus. Lips and teeth are involved in chewing food, and the cheek and temporal muscles provide the movement of the chewing apparatus. The salivary glands produce saliva, which dissolves and binds food, thereby preparing it for swallowing. During the process of digestion, the fragments of food are crushed so that the particles can be absorbed by the cells. The first stage is mechanical, it begins in the oral cavity. The saliva produced by the salivary glands contains a special substance called amylase, due to which the breakdown of carbohydrates occurs, and saliva also helps in the formation of boluses. The breakdown of food fragments by digestive juices occurs directly in the stomach. This process is called chemical digestion, during which boluses are transformed into chymes. Due to the gastric enzyme pepsin, proteins are broken down. Also, hydrochloric acid is produced in the stomach, which destroys harmful particles that enter with food. At a certain level of acidity, the digested food enters the duodenum. Juices from the pancreas also get there, continuing to break down proteins, sugar and digest carbohydrates. The breakdown of fats occurs for bile coming from the liver. When food is already digested, nutrients must enter the bloodstream. This process is called absorption, which takes place both in the stomach itself and in the intestines. However, not all substances are able to be completely digested, so there is a need to remove waste from the body. the transformation of undigested food particles into feces and their removal is called excretion. A person feels the urge to defecate when the formed feces reach the rectum.

The lower part of the digestive tract is designed in such a way that a person can independently control bowel movements. Relaxation of the internal sphincter occurs during the pushing of feces through the anal canal using peristalsis, and the movement of the external sphincter remains voluntary.

As you can see, the structure of the digestive system is well thought out by nature. When all of its departments work harmoniously, the digestion process can take only a few hours or days, depending on what kind of food has entered the body in terms of quality and density. Since the digestion process is complex and requires a certain amount of energy, the digestive system needs rest. This explains why most people feel sleepy after a hearty meal.

The vital activity of the human body is impossible without a constant exchange of substances with the external environment. Food contains vital nutrients used by the body as a plastic material (for building cells and tissues of the body) and energy (as a source of energy necessary for the body's life). Water, mineral salts, vitamins are absorbed by the body in the form in which they are in food. High molecular weight compounds: proteins, fats, carbohydrates - cannot be absorbed in the digestive tract without prior splitting into simpler compounds.

The digestive system provides food intake, its mechanical and chemical processing, the advancement of the food mass through the alimentary canal, the absorption of nutrients and water into the bloodstream and lymphatic channels, and the removal of undigested food residues from the body in the form of feces.
Digestion is a set of processes that provide mechanical grinding of food and chemical breakdown of macromolecules of nutrients (polymers) into components suitable for absorption (monomers).

The digestive system includes the gastrointestinal tract, as well as organs that secrete digestive juices (salivary glands, liver, pancreas). The gastrointestinal tract begins with the mouth opening, includes the oral cavity, esophagus, stomach, small and large intestines, and ends with the anus.

The main role in the chemical processing of food belongs to enzymes (enzymes), which, despite the huge variety, have some general properties... Enzymes are characterized by:

High specificity - each of them catalyzes only one reaction or acts on only one type of bond. For example, proteases, or proteolytic enzymes, break down proteins to amino acids (stomach pepsin, trypsin, duodenal chymotrypsin, etc.); lipases, or lipolytic enzymes, break down fats to glycerol and fatty acids(lipases of the small intestine, etc.); amylases, or glycolytic enzymes, break down carbohydrates into monosaccharides (salivary maltase, amylase, maltase and pancreatic lactase).

Digestive enzymes are active only at a certain pH value of the medium. For example, stomach pepsin acts only in an acidic environment.

They act in a narrow temperature range (from 36 ° C to 37 ° C), outside this temperature range their activity decreases, which is accompanied by a violation of digestion processes.

They are highly active, therefore they break down a huge amount of organic matter.

The main functions of the digestive system:

1. Secretory- production and secretion of digestive juices (gastric, intestinal), which contain enzymes and other biologically active substances.

2. Motor-recovery, or motor, - provides crushing and advancement of food masses.

3. Suction- transfer of all end products of digestion, water, salts and vitamins through the mucous membrane from the alimentary canal into the blood.

4. Excretory (excretory)- excretion of metabolic products from the body.

5. Endocrine- secretion of special hormones by the digestive system.

6. Protective:

  • a mechanical filter for large antigen molecules, which is provided by the glycocalyx on the apical membrane of enterocytes;
  • hydrolysis of antigens by digestive system enzymes;
  • the immune system of the gastrointestinal tract is represented by special cells (Peyer's patches) in the small intestine and lymphoid tissue of the appendix, which contain T- and B-lymphocytes.

Digestion in the oral cavity. Functions of the salivary glands

In the mouth, the analysis of the taste properties of food is carried out, the protection of the digestive tract from low-quality nutrients and exogenous microorganisms (saliva contains lysozyme, which has a bactericidal effect, and endonuclease, which has an antiviral effect), grinding, wetting food with saliva, initial hydrolysis of carbohydrates, the formation of a food lump, irritation of receptors with subsequent stimulation of the activity of not only the glands of the oral cavity, but also the digestive glands of the stomach, pancreas, liver, duodenum.
Salivary glands. In humans, saliva is produced by 3 pairs of large salivary glands: parotid, sublingual, submandibular, as well as many small glands (labial, buccal, lingual, etc.), scattered in the oral mucosa. Every day, 0.5 - 2 liters of saliva is formed, the pH of which is 5.25 - 7.4.

Important components of saliva are proteins that have bactericidal properties (lysozyme, which destroys the cell wall of bacteria, as well as immunoglobulins and lactoferrin, which binds iron ions and prevents their capture by bacteria), and enzymes: a-amylase and maltase, which begin the breakdown of carbohydrates.

Saliva begins to be secreted in response to irritation of the receptors of the oral cavity with food, which is an unconditioned irritant, as well as at the sight, smell of food and the environment (conditioned stimuli). Signals from the gustatory, thermo- and mechanoreceptors of the oral cavity are transmitted to the center of salivation of the medulla oblongata, where signals are switched to secretory neurons, the aggregate of which is located in the region of the nucleus of the facial and glossopharyngeal nerves. As a result, a complex reflex reaction of salivation occurs. The parasympathetic and sympathetic nerves are involved in the regulation of salivation. When the parasympathetic nerve is activated salivary gland a larger volume of liquid saliva is released, when the sympathetic is activated, the volume of saliva is less, but it contains more enzymes.

Chewing consists in crushing food, moistening it with saliva and forming a food lump. In the process of chewing, an assessment is carried out taste food. Further, with the help of swallowing, food enters the stomach. Chewing and swallowing requires the coordinated work of many muscles, the contractions of which regulate and coordinate the centers of chewing and swallowing located in the central nervous system. During swallowing, the entrance to the nasal cavity is closed, but the upper and lower esophageal sphincters open, and food enters the stomach. Dense food passes through the esophagus in 3 - 9 seconds, liquid food - in 1 - 2 seconds.

Digestion in the stomach

In the stomach, food is retained for an average of 4-6 hours for chemical and mechanical processing. In the stomach, 4 parts are distinguished: the entrance, or cardial part, the upper one is the bottom (or vault), the middle largest part is the body of the stomach and the lower one, the antral part, ending with the pyloric sphincter, or pylorus, (the pyloric opening leads to the duodenum).

The wall of the stomach consists of three layers: outer - serous, middle - muscular and inner - mucous. Contractions of the stomach muscles cause both wave-like (peristaltic) and pendulum-like movements, due to which food is mixed and moves from the entrance to the exit from the stomach. The gastric mucosa contains numerous glands that produce gastric juice. From the stomach, semi-digested food gruel (chyme) enters the intestines. At the site of the transition of the stomach into the intestine is the pyloric sphincter, which, when contracted, completely separates the stomach cavity from the duodenum. The mucous membrane of the stomach forms longitudinal, oblique and transverse folds, which are straightened when the stomach is full. Outside of the digestion phase, the stomach is in a collapsed state. After 45 - 90 minutes of the rest period, periodic contractions of the stomach occur, lasting 20 - 50 minutes (hungry peristalsis). The capacity of an adult's stomach is 1.5 to 4 liters.

Stomach functions:

  • food deposition;
  • secretory - secretion of gastric juice for food processing;
  • motor - for moving and mixing food;
  • absorption of certain substances into the blood (water, alcohol);
  • excretory - the release of some metabolites into the stomach cavity together with gastric juice;
  • endocrine - the formation of hormones that regulate the activity of the digestive glands (for example, gastrin);
  • protective - bactericidal (in the acidic environment of the stomach, most microbes die).

Composition and properties of gastric juice

Gastric juice is produced by the gastric glands, which are located in the region of the fundus (fornix) and the body of the stomach. They contain 3 types of cells:

  • the main ones, which produce a complex of proteolytic enzymes (pepsin A, gastrixin, pepsin B);
  • lining, which produce hydrochloric acid;
  • additional, in which mucus is produced (mucin, or mucoid). Thanks to this mucus, the stomach wall is protected from the action of pepsin.

At rest ("fasting"), about 20 - 50 ml of gastric juice, pH 5.0, can be extracted from the human stomach. The total amount of gastric juice secreted by a person with a normal diet is 1.5 - 2.5 liters per day. The pH of active gastric juice is 0.8 - 1.5, since it contains about 0.5% HCl.

Role of HCl... Increases the release of pepsinogens by the main cells, promotes the transfer of pepsinogens to pepsins, creates an optimal environment (pH) for the activity of proteases (pepsins), causes swelling and denaturation of food proteins, which provides increased protein breakdown, and also promotes the death of microbes.

Castle factor... Food contains vitamin B12, which is necessary for the formation of red blood cells, the so-called external factor Castle. But it can be absorbed into the blood only if it is present in the stomach internal factor Castle. This is a gastromucoprotein, which includes a peptide that is cleaved from pepsinogen when it is converted into pepsin, and a mucoid secreted by additional stomach cells. When the secretory activity of the stomach decreases, the production of the Castle factor also decreases and, accordingly, the absorption of vitamin B12 decreases, as a result of which gastritis with decreased secretion of gastric juice, as a rule, are accompanied by anemia.

Phases of gastric secretion:

1. Complex reflex, or cerebral, lasting 1.5 - 2 hours, in which the secretion of gastric juice occurs under the influence of all factors accompanying food intake. Wherein conditioned reflexes, arising in appearance, smell of food, environment, are combined with unconditioned, arising from chewing and swallowing. Juice released under the influence of the sight and smell of food, chewing and swallowing is called "appetizing" or "hot". It prepares the stomach for eating.

2. Gastric, or neurohumoral, the phase in which the stimuli of secretion arise in the stomach itself: the secretion increases when the stomach is stretched (mechanical stimulation) and when the extractive substances of food and products of protein hydrolysis act on its mucosa (chemical stimulation). The main hormone in the activation of gastric secretion in the second phase is gastrin. The production of gastrin and histamine also occurs under the influence of local reflexes of the metasympathetic nervous system.

Humoral regulation is added 40-50 minutes after the onset of the cerebral phase. In addition to the activating effect of the hormones gastrin and histamine, the activation of the secretion of gastric juice occurs under the influence of chemical components - extractive substances of the food itself, primarily meat, fish, vegetables. When cooking products, they turn into decoctions, broths, are quickly absorbed into the bloodstream and activate the activity of the digestive system. These substances primarily include free amino acids, vitamins, biostimulants, a set of mineral and organic salts. Fat initially inhibits secretion and slows down the evacuation of chyme from the stomach into the duodenum, but then it stimulates the activity of the digestive glands. Therefore, with increased gastric secretion, decoctions, broths, cabbage juice are not recommended.

Gastric secretion increases most strongly under the influence of protein foods and can last up to 6-8 hours, it changes least of all under the influence of bread (no more than 1 hour). With a long stay of a person on a carbohydrate diet, the acidity and the digestive power of gastric juice decrease.

3. Intestinal phase... In the intestinal phase, the secretion of gastric juice is inhibited. It develops when the chyme passes from the stomach to the duodenum. When an acidic food lump enters the duodenum, hormones that suppress gastric secretion begin to be produced - secretin, cholecystokinin and others. The amount of gastric juice is reduced by 90%.

Digestion in the small intestine

The small intestine is the longest part of the digestive tract, 2.5 to 5 meters long. The small intestine is divided into three sections: the duodenum, the jejunum, and the ileum. In the small intestine, nutrient breakdown products are absorbed. The mucous membrane of the small intestine forms circular folds, the surface of which is covered with numerous outgrowths - intestinal villi 0.2-1.2 mm long, which increase the absorbing surface of the intestine. An arteriole and a lymphatic capillary (lactiferous sinus) enter into each villi, and venules exit. In the villus, the arterioles are divided into capillaries, which merge to form venules. Arterioles, capillaries and venules in the villus are located around the lactiferous sinus. Intestinal glands are located in the thickness of the mucous membrane and produce intestinal juice. The mucous membrane of the small intestine contains numerous single and group lymph nodules that perform a protective function.

The intestinal phase is the most active phase in the digestion of nutrients. In the small intestine, the acidic contents of the stomach are mixed with the alkaline secretions of the pancreas, intestinal glands and liver and the breakdown of nutrients to the final products absorbed into the blood occurs, as well as the movement of the food mass towards the large intestine and the release of metabolites.

The entire length of the digestive tube is covered with a mucous membrane containing glandular cells that secrete various components of the digestive juice. Digestive juices are composed of water, inorganic and organic substances. Organic matter- these are mainly proteins (enzymes) - hydrolases that promote the splitting of large molecules into small ones: glycolytic enzymes break down carbohydrates to monosaccharides, proteolytic - oligopeptides to amino acids, lipolytic - fats to glycerol and fatty acids. The activity of these enzymes is highly dependent on the temperature and pH of the medium, as well as on the presence or absence of their inhibitors (so that, for example, they do not digest the stomach wall). The secretory activity of the digestive glands, the composition and properties of the secreted secretion depend on the diet and diet.

In the small intestine, cavity digestion occurs, as well as digestion in the area of ​​the brush border of enterocytes (mucosal cells) of the intestine - parietal digestion (A.M. Ugolev, 1964). Parietal, or contact, digestion occurs only in the small intestines when the chyme comes into contact with their wall. Enterocytes are equipped with mucus-covered villi, the space between which is filled with a thick substance (glycocalyx), which contains threads of glycoproteins. Together with mucus, they are able to adsorb digestive enzymes of the juice of the pancreas and intestinal glands, while their concentration reaches high values, and the decomposition of complex organic molecules to simple ones it goes more efficiently.

The amount of digestive juices produced by all digestive glands is 6 - 8 liters per day. Most of they are absorbed back in the intestines. Absorption is a physiological process of transfer of substances from the lumen of the alimentary canal into the blood and lymph. Total amount the liquid absorbed daily in the digestive system is 8 - 9 liters (approximately 1.5 liters from food, the rest is the liquid secreted by the glands of the digestive system). A little water, glucose and some medications... Water, alcohol, some salts and monosaccharides are absorbed in the stomach. The main section of the gastrointestinal tract where salts, vitamins and nutrients are absorbed is the small intestine. The high absorption rate is ensured by the presence of folds along its entire length, as a result of which the absorption surface is increased by three times, as well as by the presence of villi on the epithelial cells, due to which the absorption surface is increased by 600 times. Inside each villi there is a dense network of capillaries, and their walls have large pores (45 - 65 nm), through which even rather large molecules can penetrate.

Contractions of the wall of the small intestine ensure the advancement of the chyme in the distal direction, mixing it with digestive juices. These contractions occur as a result of a coordinated contraction of smooth muscle cells of the outer longitudinal and inner circular layers. Types of small intestine motility: rhythmic segmentation, pendulum movements, peristaltic and tonic contractions. The regulation of contractions is carried out mainly by local reflex mechanisms with the participation of the nerve plexuses of the intestinal wall, but under the control of the central nervous system (for example, with strong negative emotions, a sharp activation of intestinal motility can occur, which will lead to the development of "nervous diarrhea"). When parasympathetic fibers are excited vagus nerve intestinal motility increases, when sympathetic nerves are excited, it is inhibited.

The role of the liver and pancreas in digestion

The liver is involved in digestion by secreting bile. Bile is produced by liver cells constantly, and enters the duodenum through the common bile duct only if there is food in it. When digestion stops, bile accumulates in the gallbladder, where, as a result of the absorption of water, the concentration of bile increases 7 to 8 times. Bile secreted into the duodenum does not contain enzymes, but only participates in the emulsification of fats (for a more successful action of lipases). It produces 0.5 - 1 liter per day. Bile contains bile acids, bile pigments, cholesterol, many enzymes. Bile pigments (bilirubin, biliverdin), which are the breakdown products of hemoglobin, give bile a golden yellow color. Bile is secreted into the duodenum 3 - 12 minutes after the start of a meal.

Bile functions:

  • neutralizes acidic chyme coming from the stomach;
  • activates pancreatic juice lipase;
  • emulsifies fats, which makes them easier to digest;
  • stimulates intestinal motility.

Yolks, milk, meat, bread increase the secretion of bile. Cholecystokinin stimulates contractions gallbladder and the secretion of bile into the duodenum.

In the liver, glycogen is constantly synthesized and consumed - a polysaccharide, which is a glucose polymer. Adrenaline and glucagon increase the breakdown of glycogen and the flow of glucose from the liver into the blood. In addition, the liver neutralizes harmful substances that have entered the body from the outside or formed during the digestion of food, thanks to the activity of powerful enzyme systems for hydroxylation and neutralization of foreign and toxic substances.

The pancreas belongs to the glands of mixed secretion, consists of the endocrine and exocrine sections. The endocrine division (cells of the islets of Langerhans) releases hormones directly into the blood. In the exocrine section (80% of the total volume of the pancreas), pancreas juice is produced, which contains digestive enzymes, water, bicarbonates, electrolytes, and through special excretory ducts it enters the duodenum synchronously with the secretion of bile, since they have a common sphincter with the gallbladder duct ...

1.5 - 2.0 liters of pancreatic juice are produced per day, pH 7.5 - 8.8 (due to HCO3-), to neutralize the acidic contents of the stomach and create an alkaline pH, at which pancreatic enzymes work better, hydrolyzing all types of nutrients. substances (proteins, fats, carbohydrates, nucleic acids). Proteases (trypsinogen, chymotrypsinogen, etc.) are produced in an inactive form. To prevent self-digestion, the same cells that secrete trypsinogen simultaneously produce a trypsin inhibitor, therefore, in the pancreas itself, trypsin and other protein cleavage enzymes are inactive. Trypsinogen activation occurs only in the duodenal cavity, and active trypsin, in addition to protein hydrolysis, causes the activation of other pancreatic juice enzymes. The pancreatic juice also contains enzymes that break down carbohydrates (α-amylase) and fats (lipases).

Digestion in the large intestine


Intestines

The large intestine consists of the cecum, colon, and rectum. A vermiform appendix (appendix) departs from the lower wall of the cecum, in the walls of which there are many lymphoid cells, due to which it plays an important role in immune reactions. In the large intestine, the final absorption of essential nutrients occurs, the release of metabolites and salts of heavy metals, the accumulation of dehydrated intestinal contents and their removal from the body. An adult produces and excretes 150-250 g of feces per day. It is in the large intestine that the main volume of water is absorbed (5 - 7 liters per day).

The contractions of the large intestine occur mainly in the form of slow pendulum and peristaltic movements, which ensures maximum absorption of water and other components into the blood. The motility (peristalsis) of the large intestine increases during eating, the passage of food through the esophagus, stomach, duodenum. Inhibitory influences are carried out from the rectum, the irritation of the receptors of which reduces the motor activity of the large intestine. Eating food rich dietary fiber(cellulose, pectin, lignin) increases the amount of feces and accelerates its movement through the intestines.

Colon microflora. The last sections of the colon contain many microorganisms, primarily the bacilli of the genus Bifidus and Bacteroides. They are involved in the destruction of enzymes coming from the chyme from the small intestine, the synthesis of vitamins, the metabolism of proteins, phospholipids, fatty acids, cholesterol. Protective function bacteria is that the intestinal microflora in the host's body acts as a constant stimulus for the development of natural immunity. In addition, normal intestinal bacteria act as antagonists in relation to pathogenic microbes and inhibit their reproduction. The activity of the intestinal microflora can be disrupted after long-term intake antibiotics, as a result of which bacteria die, but yeast and fungi begin to develop. Intestinal microbes synthesize vitamins K, B12, E, B6, as well as other biologically active substances, support fermentation processes and reduce putrefaction processes.

Regulation of the activity of the digestive system

Regulation of the activity of the gastrointestinal tract is carried out with the help of central and local nervous, as well as hormonal influences. Central nervous influences are most characteristic of the salivary glands, to a lesser extent for the stomach, and local nervous mechanisms play an essential role in the small and large intestines.

The central level of regulation is carried out in the structures of the medulla oblongata and the brainstem, the totality of which forms the food center. The food center coordinates the activities of the digestive system, i.e. regulates the contraction of the walls of the gastrointestinal tract and the secretion of digestive juices, and also regulates eating behavior v general outline... Purposeful eating behavior is formed with the participation of the hypothalamus, limbic system and cerebral cortex.

Reflex mechanisms play an important role in the regulation of the digestive process. They were studied in detail by academician I.P. Pavlov, having developed methods of chronic experiment, which make it possible to obtain the pure juice necessary for analysis at any moment of the digestion process. He showed that the secretion of digestive juices is largely associated with the process of eating. Basal secretion of digestive juices is very insignificant. For example, on an empty stomach, about 20 ml of gastric juice is secreted, and in the process of digestion - 1200 - 1500 ml.

Reflex regulation of digestion is carried out using conditioned and unconditioned digestive reflexes.

Conditioned food reflexes are developed in the process of individual life and appear in the sight, smell of food, time, sounds and environment. Unconditioned food reflexes originate from the receptors of the oral cavity, pharynx, esophagus and the stomach itself when food is ingested and play a major role in the second phase of gastric secretion.

The conditioned reflex mechanism is the only one in the regulation of salivation and is important for the initial secretion of the stomach and gastric gland, triggering their activity ("fiery" juice). This mechanism is observed during phase I of gastric secretion. The intensity of secretion during phase I depends on appetite.

Nervous regulation of gastric secretion is carried out by vegetative nervous system through the parasympathetic (vagus nerve) and sympathetic nerves. Through the neurons of the vagus nerve, gastric secretion is activated, and the sympathetic nerves have an inhibitory effect.

The local mechanism of regulation of digestion is carried out with the help of peripheral ganglia located in the walls of the gastrointestinal tract. The local mechanism is important in the regulation of intestinal secretion. It activates the secretion of digestive juices only in response to the entry of chyme into the small intestine.

A huge role in the regulation of secretory processes in the digestive system is played by hormones, which are produced by cells located in various parts of the digestive system itself and act through the blood or through the extracellular fluid on neighboring cells. Gastrin, secretin, cholecystokinin (pancreozymin), motilin, etc. act through the blood. Somatostatin, VIP (vasoactive intestinal polypeptide), substance P, endorphins, etc. act on neighboring cells.

The main place of secretion of hormones in the digestive system is the initial section of the small intestine. There are about 30 of them in total. The release of these hormones occurs when the cells are exposed to diffuse endocrine system chemical components from the food mass in the lumen of the digestive tube, as well as under the action of acetylcholine, which is a mediator of the vagus nerve, and some regulatory peptides.

The main hormones of the digestive system:

1. Gastrin is formed in the accessory cells of the pyloric part of the stomach and activates the main cells of the stomach, producing pepsinogen, and the lining cells, producing hydrochloric acid, thereby increasing the secretion of pepsinogen and activating its transformation into an active form - pepsin. In addition, gastrin promotes the formation of histamine, which in turn also stimulates the production of hydrochloric acid.

2. Secretin formed in the wall of the duodenum under the action of hydrochloric acid coming from the stomach with chyme. Secretin inhibits the secretion of gastric juice, but activates the production of pancreatic juice (but not enzymes, but only water and bicarbonates) and enhances the effect of cholecystokinin on the pancreas.

3. Cholecystokinin, or pancreozymin, is released under the influence of food digestion products entering the duodenum. It increases the secretion of pancreatic enzymes and causes the gallbladder to contract. Both secretin and cholecystokinin are capable of inhibiting gastric secretion and motility.

4. Endorphins... They inhibit the secretion of pancreatic enzymes, but increase the secretion of gastrin.

5. Motilin enhances the motor activity of the gastrointestinal tract.

Certain hormones can be released very quickly, helping you feel full at the table.

Appetite. Hunger. Saturation


Hunger- This is a subjective sensation of nutritional need, which organizes human behavior in the search for and consumption of food. The feeling of hunger manifests itself in the form of burning and pain in the epigastric region, nausea, weakness, dizziness, hungry peristalsis of the stomach and intestines. Emotional hunger is associated with the activation of the limbic structures and the cerebral cortex.

The central regulation of the feeling of hunger is carried out due to the activity of the food center, which consists of two main parts: the center of hunger and the center of satiety, located in the lateral (lateral) and central nuclei of the hypothalamus, respectively.

The activation of the hunger center occurs due to the flow of impulses from chemoreceptors that respond to a decrease in blood glucose, amino acids, fatty acids, triglycerides, glycolysis products, or from mechanoreceptors of the stomach, which are excited during its hungry peristalsis. A decrease in blood temperature can also make you feel hungry.

The saturation center can be activated even before the hydrolysis products of nutrients enter the bloodstream from the gastrointestinal tract, on the basis of which sensory saturation (primary) and metabolic (secondary) saturation are distinguished. Sensory saturation occurs as a result of irritation of the receptors of the mouth and stomach by incoming food, as well as as a result of conditioned reflex reactions in response to the sight and smell of food. Exchange saturation occurs much later (1.5 - 2 hours after eating), when the breakdown products of nutrients enter the bloodstream.

Appetite- This is the feeling of a need for food, which is formed as a result of the excitation of neurons in the cerebral hemispheres and the limbic system. Appetite promotes the organization of the digestive system, improves digestion and absorption of nutrients. Appetite disorders manifest as decreased appetite (anorexia) or increased appetite (bulimia). Prolonged deliberate restriction of food intake can lead not only to metabolic disorders, but also to pathological changes appetite, up to a complete refusal to eat.

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