The small intestine which is the most. Small intestine

The human body has not yet been fully studied by scientists, and time after time new secrets of the body are revealed to us. is one of the most complex multi-component processes in which a significant number of organs are involved.

An important part of the digestive tract is the digestive tract, in which the process of breaking down consumed food into individual elements that are easily absorbed by the body occurs.

Anatomy of the small intestine

The digestion process is very complex

The small intestine is one of the main sections gastrointestinal tract, in which food is digested.

It is often referred to as the “small intestine.” But this definition is incorrect from an anatomical point of view and therefore is not used in scientific medicine.

The organ received its name due to the fact that research revealed a difference in the thickness of the walls of the large and small intestines. The walls of the small intestine are correspondingly thinner and, as a result, more capable of stretching.

The diameter of the internal lumen (cavity) is thin and healthy person almost the same. This value decreases in the small intestine after the death of the body.

The small intestine has the longest length among other organs human body. It reaches 6 m and occupies the lower third of the peritoneum, as well as partially the pelvic cavity. The diameter of the small intestine differs in different places and varies from 2.5 to 6 cm.

Due to the large length of the organ, the small intestine is located in abdominal cavity loops. To ensure that these loops do not twist among themselves, and the intestine itself is secured, the human digestive system provides for the presence of such an organ as the mesentery.

The mesentery is a double peritoneal layer, which is a thin film. It contains nerve plexuses, blood vessels and lymph glands.

The presence of the mesentery in the human body was known back in the time of the great scientist Leonardo da Vinci, but only relatively recently it became clear that this organ is complete and indivisible and performs certain functions in the body.

The structure of the small intestine includes 3 main sections:

• jejunum;
• ileum.

The small intestine begins with duodenum, next from the pylorus of the stomach under the liver. The edge of the organ is located at the level of the first or second vertebra lumbar region spinal column.

The location of the duodenum resembles the shape of a horseshoe and has several sections: upper, descending, horizontal and ascending parts. In the central part of the descending duodenum there are the major and minor (not all people have) papillae.

The jejunum is the proximal part of the small intestine, that is, occupying its central part. The department received its name due to the fact that when examining corpses, the intestines turned out to be empty.

The jejunum is located on the left side of the peritoneum and has fewer blood vessels compared to the ileum, which is located on the right side of the abdominal cavity.

The ileum ends at the beginning of the large intestine. The separation of these organs is carried out by the presence of the ileocecal valve, which is also known in anatomy as the Bauhinian valve.

Functions of the small intestine

Intestines - schematically

The functions of the small intestine are partly determined by the structure of the tissues of this organ. Its inner surface is covered with a mucous membrane, which has a characteristic relief.

It is formed from intestinal glands (crypts), circular folds and intestinal villi. The structure of the mucous membrane ensures the high absorption capacity of the small intestine.

In the submucosal tissue, located immediately behind the mucosa, there are nerve plexuses, lymphatic and blood vessels, and lobules of adipose tissue.

The muscular layer of the small intestine consists of two layers of muscle cells separated by loose connective tissue. Thanks to the work of the muscles, the contents of the stomach are pushed further through the intestines.

The outer lining of the small intestine is represented by serous tissue - the actual film of the peritoneum, represented by a dense connective tissue membrane.

The purpose of the small intestine is to provide the following functions:

• Chemical processing of food using digestive enzymes (catalyst proteins), which are secreted by the glands of the small intestine. These enzymes include trypsin, enterokinase, kinaseogen, nuclease for the breakdown of proteins, lipase for the processing of fats, sucrase, phosphatase, maltase, lactase, amylase for the decomposition of carbohydrates.
• Absorption of nutrients obtained as a result of food processing by the intestinal walls, from where they enter the circulatory system and further to the internal organs that need them.
• Mechanical pushing of a bolus of food and its remains through the intestines towards the anus.
• Endocrine function - the production of biologically active elements necessary for the normal functioning of the body (serotonin, histamine, gastrin, secretin, etc.).

The small intestine is able to perform these functions in full only in the case of a normal condition, excluding various pathologies.

Digestion process in the small intestine

Digestive processes depend on proper nutrition

In the small intestine, the food bolus is digested and further decomposed into simpler components. Digestion in the small intestine is the main stage of the entire process of absorption and processing of food products entering the gastrointestinal tract.

At X-ray studies activity of the sections of the small intestine, the approximate timing of the passage of the contrast mass through all its organs was established.

It has been established that, on average, the absorbed contents enter the jejunum half an hour after ingestion, the ileum after an hour and a half, and the cecum (upper colon) after four hours. Eight hours later, the absorbed radiopaque mass completely fills the rectum.

Digestion with good nutrition occurs in approximately the same time frame.
When food enters the small intestine, gastric juice begins to secrete. Its production is stimulated by the following elements:

1. active hydrochloric acid that remained unneutralized and reached the beginning of the duodenum;
2. mechanical irritation of receptors located on the walls of the intestine by particles of food passing through them;
3. pancreatic juice coming from the duodenum;
4. conditioned reflexes triggered by the sight of food;
5. products of the breakdown of nutrients.

These products as well fatty acids, vitamins and minerals enter the circulatory system and are distributed throughout the human body. The intestinal epithelium is formed by cells that have selective permeability and allow only simple components to pass through.

After 7-8 hours from eating, the products broken down into individual nutrients enter the blood, and the non-decomposed food residue is pushed further into the large intestine with the aim of removing it from the body through the anus.

Causes and types of diseases of the small intestine

Due to many endo- and exogenous factors, the small intestine is susceptible to a number of diseases. The most common ones are:

• duodenal ulcer;
• duodenitis;
• celiac disease;
• enteritis;
• Meckel's diverticulum;
• intestinal obstruction.

These diseases appear due to exposure to various events:

1. congenital pathologies;
2. poor nutrition;
3. frequent stress;
4. environmental pollution;
5. food and chemical poisoning;
6. decreased immunity;
7. genetic inheritance, etc.

Diseases of the small intestine most often manifest themselves as general malaise, dyspeptic disorders, abdominal pain and other specific symptoms.

If you notice such symptoms, you should not delay visiting a doctor, who can accurately determine the causes and type of disease and prescribe an effective treatment program.

The small intestine is an organ of the gastrointestinal tract in which the main process of digestion of ingested food and its decomposition into simple nutrients takes place, which are subsequently delivered to everyone. internal organ through the circulatory system.

This organ, like the entire human body, requires careful treatment. The food you eat requires special attention, since the body is not able to assimilate well all foods, some of which pose a direct threat to the functioning of the small intestine and human health in general.

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  Human small intestine: anatomy, functions and process...

Isolate organs oral cavity, esophagus, gastrointestinal tract and auxiliary organs. All parts digestive system functionally interconnected - food processing begins in the oral cavity, and final processing of products is ensured in the stomach and intestines.

The human small intestine is part of the digestive tract. This department is responsible for the final processing of substrates and absorption (absorption).

IN small intestine Vitamin B12 is absorbed.

The human body is a narrow tube about six meters long.

This section of the digestive tract got its name due to its proportional features - the diameter and width of the small intestine are much smaller than those of the large intestine.

The small intestine is divided into the duodenum, jejunum and ileum. - This is the first segment of the small intestine, located between the stomach and jejunum.

The most active digestive processes take place here; it is here that pancreatic and gallbladder enzymes are secreted. The jejunum follows the duodenum, its length on average is one and a half meters. Anatomically, the jejunum and ileum are not separated.

Mucous membrane jejunum on the inner surface it is covered with microvilli that absorb nutrients, carbohydrates, amino acids, sugar, fatty acids, electrolytes and water. The surface of the jejunum increases due to special fields and folds.

Other water-soluble vitamins are also absorbed in the ileum. In addition, this part of the small intestine is also involved in the absorption of nutrients. The functions of the small intestine are somewhat different from the stomach. In the stomach, food is crushed, ground and initially decomposed.

In the small intestine, substrates are degraded to components and are absorbed for transport to all parts of the body.

Anatomy of the small intestine

The small intestine is in contact with the pancreas.

As we noted above, in the digestive tract the small intestine follows immediately after the stomach. The duodenum is the initial section of the small intestine, following the pyloric section of the stomach.

The duodenum begins with the bulb, goes around the head and ends in the abdominal cavity with the ligament of Treitz.

The peritoneal cavity is a thin connective tissue surface covering some of the abdominal organs.

The rest of the small intestine is literally suspended in by the mesentery, which is attached to the posterior abdominal wall. This structure allows parts of the small intestine to be freely moved during surgery.

The jejunum occupies left side abdominal cavity, while the ileum is located in the upper right side of the abdominal cavity. The inner surface of the small intestine contains mucous folds called circular rings. Such anatomical structures are more numerous in the initial part of the small intestine and contract closer to the distal ileum.

The assimilation of food substrates is carried out with the help of primary cells of the epithelial layer. Cubic cells located throughout the entire area of ​​the mucous membrane secrete mucus, which protects the intestinal walls from an aggressive environment.

Enteric endocrine cells secrete hormones into the blood vessels. These hormones are essential for digestion. Flat cells of the epithelial layer secrete lysozyme, an enzyme that destroys. The walls of the small intestine are tightly connected to capillary networks circulatory and lymphatic systems.

The walls of the small intestine consist of four layers: mucosa, submucosa, muscularis and adventitia.

Functional significance

The small intestine consists of several sections.

The human small intestine is functionally connected with everything; the digestion of 90% of food substrates ends here, the remaining 10% is absorbed in the large intestine.

The main function of the small intestine is to absorb nutrients and minerals from food. The digestion process consists of two main parts.

The first part involves the mechanical processing of food by chewing, grinding, beating and mixing - all this occurs in the mouth and stomach. The second part of food digestion involves the chemical processing of substrates, which uses enzymes, bile acids and other substances.

All this is necessary in order to decompose whole products into individual components and absorb them. Chemical digestion occurs in the small intestine - this is where the most active enzymes and excipients are found.

Ensuring digestion

In the small intestine, proteins are broken down and fats are digested.

After rough processing of products in the stomach, it is necessary to decompose the substrates into separate components accessible for absorption.

1. Protein decomposition. Proteins, peptides and amino acids are affected by special enzymes, including trypsin, chymotrypsin and intestinal wall enzymes. These substances break down proteins into small peptides. The process of protein digestion begins in the stomach and ends in the small intestine.
2. Digestion of fats. Special enzymes (lipases) secreted by the pancreas serve this purpose. Enzymes break down triglycerides into free fatty acids and monoglycerides. An auxiliary function is provided by bile juices secreted by the liver and gall bladder. Bile juices emulsify fats - they separate them into small drops available for action.
3. Digestion of carbohydrates. Carbohydrates are divided into simple sugars, disaccharides and polysaccharides. The body needs the main monosaccharide – glucose. Act on polysaccharides and disaccharides pancreatic enzymes, promoting the decomposition of substances into monosaccharides. Some carbohydrates are not completely absorbed in the small intestine and end up in the small intestine, where they become food for intestinal bacteria.

Absorption of food in the small intestine

Decomposed into small components, nutrients are absorbed by the mucous membrane of the small intestine and move into the blood and lymph of the body.

Absorption is ensured by special transport systems of digestive cells - each type of substrate is provided with a separate method of absorption.

The small intestine has a significant internal surface area, which is essential for absorption. The circular circles of the intestine contain a large number of villi that actively absorb food substrates. Types of transport in the small intestine:

• Fats undergo passive or simple diffusion.
• Fatty acids are absorbed by diffusion.
• Amino acids enter the intestinal wall using active transport.
• Glucose enters through secondary active transport.
• Fructose is absorbed by facilitated diffusion.

To better understand the processes, it is necessary to clarify the terminology. Diffusion is the process of absorption along a concentration gradient of substances; it does not require energy. All other types of transport require cellular energy. We found out that the human small intestine is the main department of food digestion in the.

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The contents of the stomach enter the intestines, namely the duodenum. It is a section of the small intestine (small intestine), which also includes the jejunum (2-2.5 m long) and the ileum (2.5-3.2 m).

The duodenum is the thickest with a length of 25-30 cm. On its inner surface there are many villi, and in the submucosal layer there are small glands, the secretion of which breaks down proteins and carbohydrates.

In the cavity of the duodenum there is the main pancreatic duct and the common bile duct; here pancreatic juice, bile, and intestinal juice act on food. This is where carbohydrates, fats and proteins are digested so that they can be absorbed by the body.

Pancreatic juice

Pancreatic juice is also called pancreatic juice from the Latin "pancreas" - pancreas. It is the second largest gland in humans, with a length of 15–22 cm and a weight of 60–100 g. It consists of two glands - the exocrine gland, which synthesizes 500 - 700 ml of pancreatic juice, and the endocrine gland, which produces hormones.

Pancreatic juice is a clear, colorless liquid with an alkaline reaction with a pH of 7.8 - 8.4. It begins to be produced 2-3 minutes after food consumption, and this process continues for 6-14 hours. The longest juice secretion is caused by eating fatty foods.

Pancreatic juice enzymes

The protein-digesting enzyme trypsin is synthesized by gland cells in an inactive form (trypsinogen), the intestinal juice enzyme enterokinase makes it active, as a result of which trypsin breaks down proteins into amino acids.

The enzyme lipase converts fats into glycerol and fatty acids, its activity enhances bile.

Pancreatic juice also contains the enzyme amylase, which breaks down starch into disaccharides, and maltase, which converts disaccharides into monosaccharides.

The enzyme composition of pancreatic juice is determined by the nature. A diet rich in fat has been found to increase lipase activity in pancreatic juice. Systematic consumption of carbohydrate foods increases the activity of amylase, and protein foods - the protease enzyme.

Thus, pancreatic juice neutralizes acidic contents in the duodenum and breaks down fats, carbohydrates, proteins, nucleic acids through cavity digestion.

Bile in digestion

A major role is played by the liver, the largest gland in the body. It synthesizes and secretes bile, which accumulates in gallbladder. Its volume is approximately 40 ml, but the bile here is concentrated - dark with a greenish tint due to the large amount of bile acids and pigments. It is 3-5 times more concentrated than liver bile, since mineral salts, water and a number of other substances are constantly absorbed from it.

Bile begins to flow into the duodenum 5-10 minutes after eating and ends when the last portion leaves the stomach. Bile stops the action of gastric juice and its enzymes.

Functions of bile:

• activates the enzyme lipase, which breaks down fats;
• mixes with fats, forming an emulsion and thus improving their breakdown, since the surface of contact of fat particles with enzymes increases many times;
• takes part in the absorption of fatty acids;
• increases the production of pancreatic juice;
• activates intestinal peristalsis (motility).

Disturbances in the synthesis of bile or in its flow into the intestines cause problems with the digestion and absorption of fats.

Bile contains fatty acids, fats, bile pigment bilirubin, cholesterol, lecithin, mucin (mucus), soaps and inorganic salts.

The bile reaction is slightly alkaline. The volume of bile secreted per day in an adult is 500 - 1000 ml, a rather impressive amount.

Intestinal juice

The inner lining of the small intestine contains special glands that produce and secrete intestinal juice. It complements the process with its action.

Intestinal juice is a colorless liquid, cloudy from mucus and epithelial cells. It has an alkaline reaction and contains a complex of digestive enzymes - over 20 (aminopeptidases, dipeptidases, etc.).

Types of digestion in the small intestine

There are 2 types of digestion in the intestines: cavity and parietal. Cavity digestion is carried out by enzymes in the organ cavity, parietal digestion is carried out by enzymes that are localized on the mucous membrane of the inner surface of the small intestine, and here the concentration of enzymes is much higher. This view digestion in the small intestine also called contact or membrane.

Contact digestion (enzymes lactase, maltase, sucrase) breaks down disaccharides into monosaccharides and small peptides into amino acids. Nutrients crushed in the intestine as a result of the action of bile and pancreatic juice penetrate into the dense border formed by the villi of intestinal cells, where large molecules, and especially bacteria, are not able to enter.

Enzymes are released into the same area by intestinal cells, and nutrients are separated into their elementary components - amino acids, fatty acids, monosaccharides, which are then absorbed. Both processes - splitting and absorption into the blood - are carried out within a limited space and quite often represent one interconnected process.

Absorption in the small intestine

The intestines are able to absorb 2 - 3 liters of liquid in 1 hour, which contains nutrients dissolved in it. This is possible due to the large total absorption surface of the intestine, a significant number of folds and protrusions of the mucous membrane - villi, including due to the special structure of the epithelial cells lining the intestine.

The surface of these cells is covered with the finest thread-like processes (microvilli). One cell contains from 1600 to 3000 microvilli, inside of which there are microtubules. Villi and especially microvilli expand the absorption surface of the intestinal mucosa to an enormous size - 500 m2.

As a result of the process absorption in the small intestine the resulting food substances penetrate into the blood, but not into the general bloodstream, otherwise the person would die after the first meal. All the blood that is sent from the stomach and intestines accumulates in the portal vein and moves to the liver, since when food is broken down, not only useful compounds are formed, but also by-products - toxins that are released by the intestinal microflora, drugs and poisons contained in food products. level of modern ecology. In addition, the immediate entry of nutritional components into the general bloodstream would exceed all permissible limits.

It is not for nothing that the liver is otherwise called the biochemical laboratory of the body, since harmful compounds are disinfected here, in addition, fat, protein and carbohydrate metabolism is regulated.

The intensity of liver work is determined by the energy consumed: with a weight of 1.5 kg, it consumes 1/7 of the body’s energy. Within one minute, virtually 1.5 liters of blood passes through the liver, and the vessels of the organ contain up to 20% of the total blood volume.

At the end of the process digestion in the small intestine undigested food remains from the ileum enter through the valve (sphincter), where this process continues.

The role of the small intestine is very important and can be said to be the final stage in the hydrolysis of food to the final substances that our body needs.

General information about the human small intestine

The main stages of digestion are contained in the small intestine, which is the longest organ, with an absorption surface area of ​​almost 200 square meters. It is in this part of the gastrointestinal tract that most useful substances, as well as poisons, toxins, drugs, and xenobiotics that enter the body orally. In addition to digestion, absorption and transportation of all these substances, the small intestine performs the functions of hormone secretion, as well as immune defense.

The small intestine includes 3 sections:

• duodenum;
• jejunum;
• ileum.

However, there is no clearly defined boundary between the last two sections.

All sections of the small intestine are layered and have 4 membranes:

• mucous;
• submucosa;
• muscular;
• serous.

How does digestion occur in the small intestine?

Food from the stomach enters the duodenum, where it is exposed to bile, as well as pancreatic enzymes and intestinal juices. Digestion in the human small intestine works to a greater extent on the absorption of useful substances, and therefore it is here that the final breakdown of the food eaten occurs with the help of intestinal juice, which contains three groups of enzymes. At the same time, there are two types of digestion in the small intestine: cavity and parietal. Unlike strip digestion, parietal digestion in the small intestine carries about 80% of the final stages of hydrolysis and, at the same time, absorption of substances consumed in food.

Enzymes produced by the glands of the small intestine can only break down short chains of peptides and sugars, which get there as a result of preliminary “work” with food from other organs. After the complete breakdown of food into vitamins, amino acids, fatty acids, minerals and others, the important process of their absorption into the blood occurs. In this way, the cells of the entire human body are saturated.

The epithelial cells of the small intestine also form a so-called mesh, through which only completely broken down substances will be passed, and unchanged molecules of starch or protein, for example, will not be able to penetrate and are transported for further “processing”.

DIGESTION IN THE SMALL INTESTINE

There are 2 types of food digestion: CAVITY AND MEMBRANE. The first is carried out by intestinal juice, the second - by enzymes. Initial stages Digestion occurs in the cavity of the gastrointestinal tract. As a result of membrane hydrolysis, monomers are formed that are transported into the blood.

The absorption of nutrients is carried out in 3 stages: cavity digestion - membrane digestion - absorption. The last stage includes processes that ensure the transfer of substances from the small intestine to the blood and lymph. Absorption occurs in the small intestine.

MOTOR FUNCTION OF THE SMALL INTESTINE

The motility of the small intestine ensures the mixing of its contents with digestive secretions, the movement of contents through the intestine, and an increase in intraintestinal pressure, which facilitates the filtration of solutions from the intestinal cavity into the blood and lymph. Therefore, small intestinal motility promotes hydrolysis and absorption of nutrients.

REGULATION OF SMALL INTESTINE MOTORICS.

Motor function is changed by stimulation of the spinal and medulla oblongata, hypothalamus, limbic system, cerebral cortex. Irritation of the nuclei of the anterior and middle parts of the hypothalamus primarily excites, and the rear - inhibits the motility of the stomach, small and large intestine.

HUMORAL REGULATION. Serotonin, histamine, gastrin, motilin, vasopressin, oxytocin increase, and secretin inhibit the motility of the small intestine.

ABSORPTION OF WATER AND MINERAL SALTS. Water enters the digestive tract as part of food and liquids drunk, and the secretions of the digestive glands. Some water is absorbed from the digestive tract into the blood, and a small amount into the lymph. Absorption of water begins in the stomach, but it occurs most intensively in the small and especially large intestine. Absorbs sodium, potassium and chlorine.

ABSORPTION OF PROTEIN HYDROLYSIS PRODUCTS. Proteins are absorbed mainly in the intestine after they are hydrolyzed to amino acids. Absorption of different amino acids occurs at different rates in different parts of the small intestine.

Sodium transport stimulates the absorption of amino acids.

The absorption of fructose (and some other monosaccharides) does not depend on sodium transport and occurs actively. The absorption of carbohydrates by the small intestine is enhanced by certain amino acids.

Glucose absorption is enhanced by hormones of the adrenal glands, pituitary gland, thyroid gland, as well as serotonin and acetylcholine. Somatostatin inhibits glucose absorption, and to a lesser extent, histamine.

ABSORPTION OF LIPID HYDROLYSIS PRODUCTS. The main amount of fat is absorbed into the lymph, so 3-4 hours after eating lymphatic vessels filled with a lot of lymph.

The rate of hydrolysis and lipid absorption are regulated by the central nervous system. Parasympathetic nerves speed up and sympathetic nerves slow down lipid absorption. Their absorption is stimulated by hormones from the adrenal cortex, thyroid gland and pituitary gland, as well as hormones produced in the duodenum.

MOTOR FUNCTION OF THE COLON

The entire process of digestion in an adult lasts 1-3 days, of which the longest time is spent with food residues remaining in the large intestine. Its motor skills provide a RESERVOIR FUNCTION - accumulation of contents, absorption of a number of substances from it, mainly water, its promotion, formation feces and their removal.

The contents of the cecum undergo small and long-term movements in one direction or the other due to slow contractions of the intestine. The colon is characterized by several types of contractions: small and large pendular, peristaltic and antiperistaltic, propulsive.

Irritation of the mechanoreceptors of the rectum inhibits the motility of the overlying parts of the small intestine. Serotonin, adrenaline, and glucagon also inhibit it.

The large intestine is rich in microorganisms. The remains of undigested food are being destroyed. Organic acids and toxic substances are formed. One part is neutralized in the liver, the other is excreted. Cellulose breakdown. Synthesizes vitamins K and group B. Availability normal microflora protects the body and improves immunity.