What are the functions of the digestive organs. Functions and features of the process of digestion in the human small intestine. Diagram of the structure of the human stomach

To ensure human life, energy is needed, which can be obtained by eating food. For their processing in the human body, there is a digestive system, which is complex mechanism, consisting of various interconnected organs. The main functions of the digestive system are: mechanical - grinding food, as well as its movement and excretion; suction - extraction nutrients, vitamins , water; secretory - the production of saliva, bile and enzymes, as well as excretory - excretion of undigested food residues from the body.

The digestive system includes the following bodies digestion: as the gastrointestinal tract and accessory organs - salivary glands, liver, pancreas, bile ducts and gallbladder. The process of digestion takes place in the following way - oral cavity, esophagus, stomach, small intestine, large intestine and rectum. If we consider the digestive system from a topographical point of view, then it includes several parts - the head, neck, abdominal and pelvic.

The process of digestion goes through 3 stages - mechanical processing, chemical and waste disposal. Stage 1 begins from the moment food enters the oral cavity, where it is crushed. In addition, at this stage, salivary glands play a role, which process food particles with their enzymes. Further, already crushed food products pass into the pharynx and esophagus, from where they enter the next stage of processing. This is where complex chemical processes, as a result of which nutrients are extracted and masses of waste are formed. At this stage of digestion, the stomach, liver, pancreas, small and large intestine work. The final stage is the process of excretion of waste through the rectum and anus.

The oral cavity is the opening through which food enters the human body and the process of digestion starts. The mouth has a tongue and teeth, and its surface is covered with a mucous membrane. The tongue not only helps us to distinguish tastes with the help of receptors, but also mixes food in the mouth. Human teeth are divided into 3 groups - incisors, canines and molars, each of which performs its important function for grinding food products. Further processing falls on the salivary glands, of which there are 3 pairs in the human body - parotid, submandibular and sublingual. Their saliva wets the food and starts the chemical processes of digestion.

When swallowing food, it passes into the pharynx, where it bypasses the airways with the help of the epiglottis. The size of the pharynx is about 12 centimeters, and visually it resembles a funnel. The connecting link between the pharynx and the stomach is the esophagus - a muscular tube, reaching a length of 30 centimeters, and covered with a mucous membrane. The movement of food into the stomach occurs due to muscle contractions. Food passing through the esophagus stretches it and gives a reflex to open the entrance to the stomach. The stomach is a hollow organ into which food enters. Here the process of its digestion takes place, in which gastric juice takes an active part. It visually looks like clear liquid without color. The cells of the stomach produce 3 substances that are necessary for normal functioning digestive system- mucus, pepsinogen and hydrochloric acid. When exposed to hydrochloric acid, pepsinogen is converted to pepsin. It is this substance that is able to break down proteins into polypeptides.

The digestive organs, namely the small intestine, is a food processor. It starts with duodenum followed by the jejunum and ileum. This section of digestion is the longest, the length of the small intestine can vary from 4 to 7 meters. At this stage, nutrients are absorbed and food is broken down with the help of bile, as well as gastric and pancreatic juices. It is important that pancreatic juice enters the duodenum intermittently, but only at those moments when a person eats food and a little after. The amount of bile directly depends on the food eaten. For example, a very large amount is allocated for meat processing and less for fat. The last part of the digestive tract is the large intestine. Here, water absorption and the formation of feces occur to a greater extent. High content various bacteria contributes to the assimilation of food, the production of substances and vitamins that are important for the body, the need for which decreases. The size of the colon reaches 2 meters, its surface is covered with mucous, which helps to maintain the integrity of its walls and easier passage of feces. The rectum completes the process of human digestion, being the last part of the large intestine. In the normal state, it should be empty, since the feces are collected higher - in the large intestine. When it is filled, there is an urge to defecate, during which the feces exit the human body through the rectum and anus.

In addition to all of the above organs that make up the inextricable chain of digestion, such auxiliary organs as the liver, pancreas and gallbladder play an equally significant role in this process.

Liver - incredible important organ human body, located on the right side abdominal cavity below the diaphragm. The functionality of the liver is very high. This organ secretes bile, which is necessary for the breakdown of fats, which, along with food, enter the human body. 2 hepatic ducts - the right and left secrete bile, and united into one, redirect it to the gallbladder.

A small sac, up to 14 centimeters long and 5 centimeters wide, in the lower part of the liver is called the gallbladder. It is an elongated tank with a narrow and wide end. The passage of food through the digestive system entails a contraction of the gallbladder, and as a result, the release of bile, which enters the duodenum through the sphincter of Oddi, mixes with food.

The pancreas is another important organ that takes part in the process of digestion. Its dimensions are quite large, and the functions are divided into functions of external and internal secretion. This body is one of the most significant sources enzymes for the digestion of proteins, fats and carbohydrates. In addition, the pancreatic juice secreted by the pancreas is involved in the process of neutralizing the acidic gastric chyme. There is also an islet apparatus that produces important hormones such as insulin and glucagon. They are responsible for the metabolism of carbohydrates - insulin lowers the level of glucose in the blood, and glucagon, on the contrary, increases it.

The digestive system is a complex of organs, the function of which is the mechanical and chemical processing of ingested nutrients, the absorption of processed and the release of the remaining undigested food components. It includes the oral cavity, pharynx, esophagus, stomach, small and large intestine, liver, gallbladder and pancreas (Fig. 2). The esophagus, stomach, and entire intestine form the gastrointestinal tract.

Rice. 2. General plan of the structure of the digestive system.

Oral cavity It is divided into two sections: the vestibule of the mouth and the oral cavity proper. mouth vestibule called the space located between the lips and cheeks on the outside and the teeth and gums on the inside. Through the mouth opening, the vestibule of the mouth opens outward.

Oral cavity extends from the teeth anteriorly and laterally to the posterior pharyngeal inlet. From above, the oral cavity is limited by the hard and soft palate, the bottom is formed by the diaphragm of the mouth and is occupied by the tongue. The ducts of three pairs of large salivary glands: parotid, submandibular and sublingual. In addition, there are numerous small glands in the oral mucosa, which, by the nature of the secret, can be serous, mucous, or mixed.

The sky consists of two parts (Fig. 3). The anterior two-thirds of it has a bone base ( palatine process upper jaw and the horizontal plate of the palatine bone), this is - solid sky; back third - soft sky (is a muscle formation). The free posterior edge of the soft palate hangs down freely, having a protrusion in the middle - uvula, and on the sides passes into two pairs of folds, forming two pairs of arches, between which are located palatine tonsils (tonsils). In the thickness of the soft palate there are muscles that determine its participation in swallowing and sound production.

Rice. 3. The structure of the oral cavity.

1 - upper lip, 2, 9 - gums, 3 - teeth, 4 - hard palate, 5 - soft palate, 6 - tongue, 7 - tonsil, 8 - tongue, 10 - frenulum of the lower lip, 11 - lower lip 12 - frenulum upper lip, 13 - pharynx.

The opening, bounded from the sides by the arches of the soft palate, from above by the tongue, and from below by the initial section of the tongue, is called pharynx. Thanks to him, the oral cavity communicates with the pharynx.

Language is a muscular organ. It has three parts - root, top and between them body. Numerous lymphoid accumulations are located at the root of the tongue - lingual tonsil. The upper surface of the tongue is called back of the tongue it contains numerous papillae, which contain receptors that determine the sensitivity of the tongue to touch, pain, temperature, perception and taste identification.

Teeth(Fig. 4) are ossified papillae of the mucous membrane, which serve for the mechanical processing of food. In humans, the change of teeth occurs 2 times, therefore, milk teeth and permanent teeth are distinguished.

Rice. 4. The structure of the tooth.

Number permanent teeth equals 32, 16 each in the top and bottom row. Each half of the dentition has 8 teeth. Human tooth development begins around the 7th week of embryonic life. The teeth are located in the cells of the alveolar processes of the upper and lower jaws.

The fabric that covers alveolar processes, is called gums. Each tooth consists of a crown, neck and root. Crown protrudes above the gum neck covered by the gum, and root sits in the dental alveolus and ends at the top, on which there is a small hole. Vessels and nerves enter the tooth through this opening. Inside the crown of the tooth there is a cavity that is filled with dental pulp ( pulp), rich in vessels and nerves. The solid substance of the tooth consists of dentin, enamel and cementum. The bulk of the tooth is dentin. Enamel covers the outside of the crown, and the root is covered with cement. A fully developed and preserved chewing apparatus of an adult contains 32 teeth, forming the upper and lower dentition. Each half of the dentition contains 8 teeth: 2 incisors, 1 canine, 2 small molars (premolars) and 3 large molars (molars). The third root is called the wisdom tooth and is the last to erupt.

The number of teeth is usually represented by a dental formula in which upper teeth are indicated in the numerator, and the lower ones - in the denominator. The teeth are marked starting from the middle, and since the right and left halves are symmetrical, only the left is taken into account. The first digit indicates the number of incisors, the second - canines, the third - small molars and the fourth - large molars.

Formula of permanent teeth:

Milk teeth formula:

In dental practice, the following digital formulas are used:

On right Left

The number 1 indicates the medial incisor, the number 8 - the third large molar. Based on this formula, individual teeth are designated as follows:

- right upper first molar;

- left upper canine;

- lower right first small molar;

In the oral cavity there are three pairs of large glands - parotid, sublingual and submandibular, which produce digestive enzymes and mucus secreted through the excretory ducts into the oral cavity.

Pharynx (Fig. 5) - part of the digestive tube and respiratory tract, which is a connecting link between the oral cavity and nose on the one hand, the esophagus and larynx on the other. It starts from the base of the skull and ends at the level of 6-7 cervical vertebrae. Inner space pharynx makes up the pharyngeal cavity. The pharynx is located behind the nasal and oral cavities and larynx. According to the organs located anterior to the pharynx, it can be divided into three parts: nasal, oral, laryngeal.

Rice. 5. The cavity of the pharynx.

bow(nasopharynx)- This is the upper section, which has nothing to do with digestion and is functionally part of the respiratory system. Through choan the pharynx communicates with the nasal cavity. On the lateral walls of the nasopharynx are openings of the auditory (Eustachian) tubes connecting this department with the middle ear cavity. At the entrance to the throat is ring of lymphoid formations: tonsil of the tongue, two palatine, two tubal and pharyngeal tonsils. The mucous membrane of the nasal part of the pharynx is covered with ciliated epithelium in accordance with the respiratory function of this part of the pharynx.

Mouth (oropharynx) represents middle department pharynx, which communicates in front through the pharynx with the oral cavity. The opening of the pharynx is located under the choanae. In this section, the respiratory and digestive tracts cross. Here, the mucous membrane acquires a smooth surface that facilitates the sliding of the food bolus during swallowing. This is also facilitated by the secret of the glands embedded in the mucous membrane and the muscles of the pharynx, located longitudinally (dilators - dilators) and circularly (narrowers - constrictors).

Laryngeal part (larynx) is the lower part of the pharynx, located behind the larynx and extending from the entrance to the larynx to the entrance to the esophagus. On the front wall there is a hole - the entrance to the larynx, limited by the epiglottis. The basis of the pharyngeal wall is a fibrous membrane, which is attached to the bones of the base of the skull at the top. From the inside, the pharynx is covered with a mucous membrane, outside of it there is a muscular membrane, and behind it is a thin fibrous one that connects the wall of the pharynx with the surrounding organs. At the level of the VI cervical vertebra, the pharynx passes into the esophagus.

Throat function consists in conducting air from the nasal cavity to the entrance to the larynx, and the food bolus from the oral cavity to the esophagus, as well as in isolating the airways during swallowing.

The act of swallowing . In the oral cavity, mechanical and initial chemical processing of food takes place. As a result, it is formed food bolus, which moves to the root of the tongue, causing irritation of its receptors. At the same time, the soft palate rises reflexively and blocks communication with the nasopharynx. By contraction of the muscles of the tongue, the food bolus is pressed against the back of the tongue hard palate and pushed through the pharynx. At the same time, the muscles located above the hyoid bone pull the larynx upward, and the root of the tongue descends downward (due to muscle contraction) and presses on the epiglottis, lowering it and thereby blocking the entrance to the larynx. Next, there is a consistent contraction of the constrictor muscles of the pharynx, as a result of which the food bolus is pushed towards the esophagus.

Lymphatic pharyngeal ring. Alien substances and microorganisms constantly penetrate into the human body, their sources are air and food. These substances must be detained or rendered harmless. This role is performed by six tonsils located in the oral cavity at the entrance to the pharynx (pharyngeal, lingual, paired tubal and palatine), forming lymphatic pharyngeal ring (Pirogov's ring). Acute infection palatine tonsils called angina pharyngeal tonsil- adenoids.

Esophagus is the initial section of the gastrointestinal tract. It is a narrow and long tube 23-25 ​​cm long, located between the pharynx and the stomach and helping to move food from the pharynx to the stomach. The esophagus begins at the level of the VIth cervical vertebra and ends at the level of the XIth thoracic. The esophagus, starting in the neck, passes into the chest cavity and, piercing the diaphragm, enters the abdominal cavity, so it distinguishes between the cervical, thoracic and abdominal parts.

Starting from the stomach, all sections of the digestive tract, together with its large glands (liver, pancreas), as well as the spleen and genitourinary system located in the abdominal cavity and in the pelvic cavity.

abdominal cavity called the space located in the trunk below the diaphragm and filled with abdominal organs. The diaphragm is the upper wall of the abdominal cavity and separates it from chest cavity. The anterior wall is formed by tendon extensions of the three broad abdominal muscles and the rectus abdominis muscles. The lateral walls of the abdomen include the muscular parts of the three broad abdominal muscles, and the lumbar part serves as the back wall. spinal column and quadratus lumborum. Below, the abdominal cavity passes into the pelvic cavity. The pelvic cavity is bounded behind by the anterior surface of the sacrum, and in front and from the sides by parts of the pelvic bones with the muscles lying on them. The abdominal cavity is divided into the peritoneal cavity and the retroperitoneal space. The walls of the abdominal cavity are lined with a serous membrane - the peritoneum.

Peritoneum is a closed serous sac, which only in women communicates with the external environment through holes fallopian tubes. The peritoneum consists of two sheets: parietal parietal and splanchnic or visceral. The parietal sheet lines the walls of the abdominal cavity, and the visceral sheet covers the insides, forming their serous cover over a greater or lesser extent. Between the leaves is peritoneal cavity which contains a small amount serous fluid, moisturizing the surface of the organs and facilitating their movement relative to each other. The peritoneum, passing from the walls of the abdominal cavity to the organs, from one organ to another, forms ligaments, mesentery, omentums. By using ligaments the abdominal organs are fixed to each other and to the wall of the abdomen. mesentery serve to fix the position of the abdominal organs, they pass through the vessels and nerves going to the organ. Oil seals are folds of the peritoneum, between the sheets of which contains a large amount of fatty tissue. The space between the fascia covering the muscles and the peritoneum on the posterior abdominal wall is called retroperitoneal. It contains the pancreas and kidneys.

Stomach (Fig. 6) is a bag-like expansion of the digestive tract, food accumulates in the stomach after passing it through the esophagus and the first stages of its digestion proceed when the solid components of the food turn into a liquid or mushy mixture. The stomach is divided into anterior and posterior walls. The concave edge of the stomach, facing up and to the right, is called lesser curvature, convex edge facing down and to the left - great curvature. The stomach is divided into the following parts:

- cardiac part(cardia) - the initial section, the place of entry of the esophagus into the stomach;

- bottom- the domed part of the stomach cavity, located at the very top to the left of the cardia;

- body- the largest department in which food is "storage" at the time of its digestion;

- pyloric part, located behind the body and ending pyloric sphincter which separates the stomach cavity from the duodenal cavity.

The wall of the stomach consists of three membranes: mucous, muscular and serous.

mucous membrane The stomach is lined with a single-layer cylindrical epithelium, forms many folds, which are smoothed out when the stomach is full. It has special gastric glands that produce gastric juice containing pepsin and hydrochloric acid.

Rice. 6. Stomach.

Muscular membrane well expressed and consists of three layers: longitudinal, oblique and circular. When leaving the stomach, the circular muscle layer forms a powerful pyloric sphincter, which blocks the communication between the stomach and duodenum.

Serous membrane is a visceral sheet of peritoneum and covers the stomach from all sides. When performing some exercises (for example, hanging, hanging hanging, handstand), the stomach can shift and change its shape compared to its original position during normal standing.

The main functions of the stomach are enzymatic breakdown (hydrolysis) of proteins and other nutrients in an acidic environment, further grinding and softening of food (mechanical processing), deposition (food is in the stomach from 3 to 10 hours), carrying food to the intestines, absorption of medicinal substances. , bactericidal action.

Small intestine (Fig. 2) is the section of the alimentary canal following the stomach. It occupies the entire middle and lower divisions the abdominal cavity, forming a large number of loops, and passes into the region of the right iliac fossa into the large intestine. In a living person, the length of the small intestine does not exceed 2.7 m, in corpses - 6.5-7 m. In the small intestine, mechanical (promotion) and further chemical processing of food takes place in an alkaline environment, as well as the absorption of nutrients. Therefore, the small intestine contains special devices for the secretion of digestive juices (glands located both in the intestinal wall and outside it) and for the absorption of digested substances ( intestinal villi and folds). The small intestine is divided into three sections: the duodenum, jejunum, and ileum.

Duodenum(Fig. 7) starts from the pylorus of the stomach, goes around the head of the pancreas in a horseshoe shape and at the level of the 2nd lumbar vertebra on the left passes into the jejunum. The excretory ducts of the liver and pancreas open into the lumen of the duodenum, the secret of which contains a number of important enzymes involved in intestinal digestion. Often these ducts open with one common opening. In the area where the ducts of the liver and pancreas enter the duodenum, there are 2 sphincters that regulate the flow of bile and pancreatic juice into the lumen of the duodenum. If there is no need for juices, then these sphincters are in a reduced state.

Jejunum is a continuation of the duodenum. Going down, it forms bends and loops, located mainly in the umbilical region and in the left side of the abdomen.

Ileum is a continuation of the jejunum and at the level of the right sacroiliac joint, it flows into the large intestine. This place is located ileocecal valve, which regulates the movement of food from the small intestine into the large intestine and prevents its reverse passage.

Rice. 7. Duodenum.

The wall of the small intestine consists of three membranes: mucous with a well-defined submucosal layer, muscular and serous.

mucous membrane characterized by the presence of a large number of circular folds, especially pronounced in the duodenum. Throughout the small intestine, the mucous membrane forms numerous protrusions - intestinal villi(Fig. 8), increasing the absorption surface of the mucous membrane by 25 times. Outside, the intestinal villus is covered with epithelium, in the center of it are blood and lymphatic capillaries. Proteins and carbohydrates enter the bloodstream venous vessels goes to the liver, and fats go to lymphatic vessels.

Rice. 8. Intestinal villus.

Muscular membrane consists of smooth muscle cells that form two layers: the inner circular and the outer longitudinal. Contractions of muscle fibers are peristaltic in nature, they consistently spread towards the lower end, while the circular fibers narrow the lumen, and the longitudinal ones, shortening, contribute to its expansion.

Serous membrane covers the small intestine from almost all sides.

Colon (Fig. 2, 9) begins in the right iliac fossa, where the ileum passes into it. The length of the large intestine is 1.5-2 m, it absorbs water and forms feces.

The wall of the large intestine is made up of three layers. mucous membrane forms sparse semilunar folds, there are no villi in the large intestine, but there are much more intestinal crypts than in the small intestine. Outside of the mucosa are located two muscle layers: inner circular and outer longitudinal. The longitudinal layer is not continuous; it forms three longitudinal bands. Protrusions form between the tapes - gaustra. Outside, the large intestine is covered peritoneum.

Rice. 9. Large intestine.

In the large intestine, the following are distinguished departments: caecum with appendix, colon (ascending, transverse, descending and sigmoid colon) and rectum.

Cecum is the initial section of the large intestine. It is located in the right iliac fossa. A vermiform appendix (appendix) departs from the posterior surface of the caecum, in the mucous membrane of which there are accumulations of lymphoid tissue. At the point where the large intestine enters the small intestine ileocecal valve, containing a layer of circular muscles.

Colon consists of four parts. Ascending colon is a continuation of the caecum. It rises up to the liver, forms a bend to the left and passes into transverse colon, which runs across the abdominal cavity and reaches the spleen with its left end, where it forms a left bend, passing into descending colon. The latter is located on the left on the posterior abdominal wall and stretches to the iliac crest, from where it continues into sigmoid colon, which is located in the left iliac fossa and at the level of the 3rd sacral vertebra passes into the rectum. The mesentery attaches the transverse colon to the posterior abdominal wall.

Rectum(Fig. 9) begins at the level of the 3rd sacral vertebra and is the final section of the large intestine. It ends with an anus. The rectum is located in the small pelvis. An expansion is formed in the middle part of the intestine - ampoule in which feces accumulate. Mucous the shell forms transverse and longitudinal folds. In the area of anus in the thickness of the mucous membrane there are a large number of veins that form hemorrhoidal plexus. The fibers of the muscular membrane of the rectal wall are arranged longitudinally and circularly. In the region of the anus, the fibers of the circular layer thicken and form internal anal sphincter, unmanaged arbitrarily. Slightly below it is external sphincter, controlled by the arbitrary efforts of man.

The digestive system includes two large glands - the liver and pancreas.

Liver is the largest gland in human body. Its weight reaches 1.5 kg, the substance of its soft consistency, red-brown color.

Liver functions diverse:

o how the digestive gland, the liver, produces bile, which enters the duodenum through the excretory duct and promotes the digestion of fats;

o barrier (protective) function - toxic products of protein metabolism are neutralized in the liver, which are brought there with venous blood through portal vein;

o has phagocytic properties, i.e. properties to absorb and neutralize toxic substances absorbed in the intestines. These properties are possessed by cells of the reticuloendothelial system, i.e. capillary endothelium and the so-called Kupffer cells;

o participates in all types of metabolism, in particular carbohydrate, being a “depot” of glycogen (carbohydrates absorbed by the intestinal mucosa are converted into glycogen in the liver;

o in the embryonic period, it performs the function of hematopoiesis, since during this period it produces red blood cells;

o performs hormonal functions.

Rice. 10. Lobes and gates of the liver.

Thus, the liver is both an organ of digestion, circulation and all types of metabolism, including hormonal, and also performs protective function.

The liver is located directly under the diaphragm, in the upper part of the abdominal cavity on the right (in the right hypochondrium). Two surfaces are distinguished on it: the upper one is the diaphragmatic and the lower one is the visceral and two edges: the anterior acute and the posterior blunt.

On the diaphragmatic surface of the liver adjacent to bottom surface diaphragm, distinguish two lobes (right and left), separated by a falciform ligament.

On the visceral surface, facing down and back, there are two longitudinal and one transverse grooves that divide the liver into four lobes: right, left, square and caudate (Fig. 10). The longitudinal grooves contain the gallbladder and the inferior vena cava.

In the transverse furrow are gate of the liver(Fig. 10) , those. a place through which vessels, nerves and other formations enter and leave the organ. The gates of the liver include the portal vein, hepatic artery and nerves. Out of the gate go the general hepatic duct and lymphatic vessels. The common hepatic duct drains bile from the liver.

Almost the entire liver, with the exception of the posterior part of the diaphragmatic surface, is covered by the peritoneum. Under the serous membrane there is a thin fibrous membrane, which in the region of the gate of the liver, together with the vessels, enters the substance of the liver and continues into the thin layers of connective tissue surrounding hepatic lobules, which are the structural and functional unit of the liver (Fig. 11). The lobule has a transverse size of 1-2 mm and consists, in turn, of hepatic beams, which are located radially from the axial part of the lobule to the periphery. The hepatic beams are built from two rows of hepatic cells, between which the bile capillary passes. The hepatic beams are a kind of tubular glands. Between the liver cells that make up the liver lobules are bile ducts. Leaving the lobule, they fall into interlobular ducts, which merge together to form right and left hepatic ducts. From the confluence of the right and left ducts, common hepatic duct, which exits the gates of the liver and carries bile out of it.

The liver (unlike other internal organs) receives rich in oxygen blood from the hepatic artery and blood enriched with nutrients from the portal vein (from the stomach, spleen, small and large intestine). Arterial and venous blood is mixed in special capillaries (sinusoids) located between the beams of the liver. In the sinusoids, blood is washed through special holes in the liver cells, cleaned, and then poured into the central vein located in the center of the lobule. The central veins, merging together, form 3-4 hepatic veins, which exit the liver (not the gate) and flow into the inferior vena cava.

Rice. 11. Hepatic lobule.

gallbladder (Fig. 10) has a pear-shaped shape, it distinguishes the bottom, body and neck, which continues into the cystic duct.

From the confluence of the cystic duct and the common hepatic duct, common bile duct which opens into the lumen of the duodenum.

Ways of excretion of bile . Since bile is produced in the liver around the clock, and enters the intestines as needed, there was a need for a reservoir for storing bile. This reservoir is the gallbladder. The bile produced in the liver flows out of it through the common hepatic duct (Fig. 10). If necessary, it enters immediately into the duodenum through the common bile duct. This duct is formed by the confluence of the common hepatic and cystic ducts. If this is not necessary, then the common bile duct and its sphincter are in a contracted state and do not let bile into the intestine, as a result of which bile can only be directed to the cystic duct and then to the gallbladder. When food enters the stomach and a corresponding reflex occurs, the muscular wall of the gallbladder contracts and at the same time the muscles of the common bile duct and sphincters relax, as a result of which bile enters the lumen of the duodenum 12.

Pancreas (Fig. 7, 12) is the second largest gland of the digestive tract. Its weight in an adult is 70-80g, length - 12-15cm. The gland lies retroperitoneally, behind the stomach on the posterior abdominal wall. It is divided into head, body and tail. The head is covered by the duodenum. Structurally, the pancreas is a complex alveolar glands. It has a lobed structure. Excretory duct The pancreas goes inside the gland along its length and receives numerous small ducts extending from the lobules. Having connected with the common bile duct, it opens with a common opening into the duodenum.

Rice. 12. Pancreas.

In iron, they distinguish two components: the main mass of the gland has an exocrine function, releasing its secret through the excretory duct into the duodenum; a smaller part of the gland in the form of pancreatic islets (islets of Langergaans) refers to endocrine formations (i.e., glands that do not have excretory ducts, the secrets of which are called hormones). The cells of these islets secrete into the blood pancreatic hormones - insulin and glucagon, which regulate blood sugar levels.

The human digestive system in the arsenal of knowledge of a personal trainer occupies one of the places of honor, solely for the reason that in sports in general and in fitness in particular, almost any result depends on the diet. Kit muscle mass, weight loss or weight retention largely depends on what kind of "fuel" you load into the digestive system. The better the fuel, the better the result, but the goal is now to figure out exactly how it works and works. this system and what are its functions.

The digestive system is designed to provide the body with nutrients and components and remove the residual products of digestion from it. The food entering the body is first crushed by the teeth in the oral cavity, then it enters the stomach through the esophagus, where it is digested, then, in the small intestine, under the influence of enzymes, the digestive products break down into separate components, and feces (residual products of digestion) are formed in the large intestine. , which is ultimately subject to evacuation from the body.

The structure of the digestive system

The human digestive system includes the organs of the gastrointestinal tract, as well as auxiliary organs, such as the salivary glands, pancreas, gallbladder, liver, and more. The digestive system is conventionally divided into three sections. The anterior section, which includes the organs of the oral cavity, pharynx and esophagus. This department carries out grinding of food, in other words, mechanical processing. The middle section includes the stomach, small and colon, pancreas and liver. Here chemical processing of food, absorption of nutrients and the formation of residual products of digestion take place. The posterior section includes the caudal part of the rectum and performs the removal of feces from the body.

The structure of the human digestive system: 1- Oral cavity; 2- Sky; 3- Tongue; 4- Language; 5- Teeth; 6- Salivary glands; 7- Sublingual gland; 8- Submandibular gland; 9- parotid gland; 10- Throat; 11- Esophagus; 12- Liver; 13- Gallbladder; 14- Common bile duct; 15- Stomach; 16- Pancreas; 17- Pancreatic duct; 18- Small intestine; 19- Duodenum; 20- Jejunum; 21- Ileum; 22- Appendix; 23- Large intestine; 24- Transverse colon; 25- Ascending colon; 26- Blind gut; 27- Descending colon; 28- Sigmoid colon; 29- Rectum; 30- Anus.

Gastrointestinal tract

The average length of the alimentary canal in an adult is approximately 9-10 meters. The following sections are distinguished in it: the oral cavity (teeth, tongue, salivary glands), pharynx, esophagus, stomach, small and large intestine.

• Oral cavity An opening through which food enters the body. On the outside, it is surrounded by lips, and inside it are teeth, tongue and salivary glands. It is inside the oral cavity that food is crushed with teeth, wetting with saliva from the glands and pushing the tongue into the throat.
• Pharynx- digestive tube that connects the mouth and esophagus. Its length is approximately 10-12 cm. Inside the pharynx, the respiratory and digestive tracts cross, therefore, so that food does not enter the lungs during swallowing, the epiglottis blocks the entrance to the larynx.
• Esophagus- an element of the digestive tract, a muscular tube through which food from the pharynx enters the stomach. Its length is approximately 25-30 cm. Its function is to actively push the crushed food to the stomach, without any additional mixing or pushing.
• Stomach- a muscular organ located in the left hypochondrium. It acts as a reservoir for swallowed food, produces biologically active components, digests and absorbs food. The volume of the stomach ranges from 500 ml to 1 liter, and in some cases up to 4 liters.
• Small intestine The part of the digestive tract located between the stomach and large intestine. Enzymes are produced here, which, in conjunction with the enzymes of the pancreas and gallbladder, break down the products of digestion into separate components.
• Colon- the closing element of the digestive tract, in which water is absorbed and stool is formed. The walls of the intestine are lined with a mucous membrane to facilitate the passage of the residual products of digestion to the exit from the body.

The structure of the stomach: 1- Esophagus; 2- Cardiac sphincter; 3- Fundus of the stomach; 4- The body of the stomach; 5- Large curvature; 6- Folds of the mucous membrane; 7- Sphincter of the gatekeeper; 8- Duodenum.

Subsidiary Bodies

The process of digestion of food occurs with the participation of a number of enzymes that are contained in the juice of some large glands. In the oral cavity there are ducts of the salivary glands, which secrete saliva and moisten both the oral cavity and food with it to facilitate its passage through the esophagus. Also in the oral cavity, with the participation of saliva enzymes, the digestion of carbohydrates begins. Pancreatic juice and bile are secreted into the duodenum. Pancreatic juice contains bicarbonates and a number of enzymes such as trypsin, chymotrypsin, lipase, pancreatic amylase and more. Before entering the intestine, bile accumulates in the gallbladder, and bile enzymes allow the separation of fats into small fractions, which accelerates their breakdown by the lipase enzyme.

• Salivary glands divided into small and large. Small ones are located in the oral mucosa and are classified by location (buccal, labial, lingual, molar and palatine) or by the nature of the excretion products (serous, mucous, mixed). The size of the glands varies from 1 to 5 mm. The most numerous among them are the labial and palatine glands. There are three pairs of major salivary glands: parotid, submandibular, and sublingual.
• Pancreas- an organ of the digestive system that secretes pancreatic juice, which contains digestive enzymes necessary for the digestion of proteins, fats and carbohydrates. The main pancreatic substance of the ductal cells contains bicarbonate anions that can neutralize the acidity of the residual products of digestion. The islet apparatus of the pancreas also produces the hormones insulin, glucagon, and somatostatin.
• gallbladder acts as a reservoir for bile produced by the liver. It is located on the lower surface of the liver and anatomically is part of it. The accumulated bile is released into the small intestine to ensure the normal course of digestion. Since in the process of digestion bile is not needed all the time, but only periodically, the gallbladder doses its intake with the help of bile ducts and valves.
• Liver- one of the few unpaired organs in the human body that performs many vital important functions. Including she is involved in the processes of digestion. Provides the body's needs for glucose, transforms various energy sources (free fatty acids, amino acids, glycerol, lactic acid) into glucose. The liver also plays an important role in neutralizing toxins that enter the body with food.

The structure of the liver: 1- Right lobe of the liver; 2- Hepatic vein; 3- Aperture; four- Left lobe liver; 5- Hepatic artery; 6- Portal vein; 7- Common bile duct; 8- Gallbladder. I- Path of blood to the heart; II- Path of blood from the heart; III- The path of blood from the intestines; IV- The path of bile to the intestines.

Functions of the digestive system

All functions of the human digestive system are divided into 4 categories:

• Mechanical. Involves grinding and pushing food;
• Secretory. Production of enzymes, digestive juices, saliva and bile;
• Suction. Assimilation of proteins, fats, carbohydrates, vitamins, minerals and water;
• Highlighting. Excretion from the body of the remnants of digestion products.

In the oral cavity, with the help of teeth, tongue and salivary gland secretion product, during chewing, the primary processing of food occurs, which consists in grinding, mixing and moistening with saliva. Further, in the process of swallowing, food in the form of a lump descends through the esophagus into the stomach, where it is further chemically and mechanically processed. In the stomach, food accumulates, mixes with gastric juice, which contains acid, enzymes and proteins that break down. Further, food already in the form of chyme (liquid contents of the stomach) in small portions enters the small intestine, where it continues to be chemically processed with the help of bile and excretory products of the pancreas and intestinal glands. Here, in the small intestine, nutrients are absorbed into the blood. Those food components, which are not digested, move further into the large intestine, where they undergo decay under the influence of bacteria. The large intestine also absorbs water and then forms feces from the residual products of digestion that have not been digested or absorbed. The latter are excreted from the body through the anus during defecation.

The structure of the pancreas: 1- Accessory duct of the pancreas; 2- Main pancreatic duct; 3- Tail of the pancreas; 4- Body of the pancreas; 5- Neck of the pancreas; 6- Uncinate process; 7- Vater papilla; 8- Small papilla; 9- Common bile duct.

Conclusion

The human digestive system is of exceptional importance in fitness and bodybuilding, but naturally it is not limited to them. Any intake of nutrients into the body, such as proteins, fats, carbohydrates, vitamins, minerals and more, occurs precisely through the intake through the digestive system. Achieving any results in terms of gaining muscle mass or losing weight also depends on the digestive system. Its structure allows us to understand which way food goes, what functions the digestive organs perform, what is absorbed and what is excreted from the body, and so on. Not only your athletic performance depends on the health of the digestive system, but, by and large, all health in general.

The process of mechanical processing of food in the digestive canal and the chemical breakdown of nutrients by enzymes into simpler components that are absorbed by the body.

To ensure physical and mental work, growth and development, to cover the energy costs that occur during the implementation of physiological functions, in addition to the continuous supply of oxygen, the body needs a wide variety of chemical substances. Their body receives with food, which is based on products of plant, animal and mineral origin. Foods consumed by humans contain nutrients: proteins, fats and carbohydrates, rich in energy released when they are broken down in the body. The body's need for nutrients is determined by the intensity of the energy processes occurring in it.

As a building material, mainly proteins containing the necessary amino acids are used. From them, the body synthesizes its own proteins, peculiar only to it. With their insufficient amount in food, a person develops various pathological conditions. Proteins cannot be replaced by other nutrients, while fats and carbohydrates, within certain limits, can replace each other. Therefore, human food must contain certain minimal amount each nutrient. When compiling a diet (composition and quantity of products), it is necessary to take into account not only their energy value, but also qualitative composition. Human food must necessarily include products of both plant and animal origin.

Many chemicals in food cannot be absorbed as they are in the body. Their careful mechanical and chemical processing is necessary. Mechanical processing consists in grinding, mixing and rubbing food to the state of gruel. Chemical processing is carried out by enzymes that are secreted by the digestive glands. In this case, complex organic substances are broken down into simpler ones and absorbed by the body. The complex processes of mechanical grinding and chemical breakdown of food products occurring in the body are called digestion.

Digestive enzymes act only in a certain chemical environment: some in an acidic environment (pepsin), others in an alkaline environment (trypsin), and others in a neutral one (saliva amylase). The maximum activity of enzymes is observed at a temperature of 37 - 40 °C. At higher temperatures, most enzymes are destroyed, and at low temperatures, their activity is suppressed. Digestive enzymes are strictly specific: each of them acts only on a substance of a certain chemical composition. Three main groups of enzymes are involved in digestion (Table 12.2): proteolytic (proteases) that break down proteins, lipolytic (lipases) that break down fats, and glycolytic (carbohydrases) that break down carbohydrates.

There are three types of digestion:

• extracellular (cavitary) - takes place in the cavity of the gastrointestinal tract.
• membrane (parietal) - occurs at the border of the extra- and intracellular environment, is carried out by enzymes associated with the cell membrane;

  Extracellular and membrane digestion is characteristic of higher animals. Extracellular digestion begins the digestion of nutrients, membrane digestion provides intermediate and final stages of this process.

• intracellular - found in the simplest organisms.

STRUCTURE AND FUNCTIONS OF THE DIGESTIVE ORGANS

In the digestive system, the alimentary canal and the digestive glands that communicate with it through the excretory ducts are distinguished: salivary, gastric, intestinal, pancreatic and liver, located outside the alimentary canal and communicating with it with their ducts. All digestive glands belong to the glands of external secretion (endocrine glands secrete their secret into the blood). For a day, an adult produces up to 8 liters of digestive juice.

The alimentary canal in humans has a length of about 8-10 m and is divided into the following sections: oral cavity, pharynx, esophagus, stomach, small and large intestines, rectum, anus (Fig. 1.). Each department has its own characteristic structural features and is specialized in performing a certain phase of digestion.

The wall of the alimentary canal for most of its length consists of three layers:

• outdoor [show]

  outer layer - serosa- formed by connective tissue and mesentery, which separate the alimentary canal from the internal organs.

• middle [show]

  middle layer- muscle membrane - in upper section(oral cavity, pharynx, upper part of the esophagus) is represented by striated, and in other departments - by smooth muscle tissue. Smooth muscles are located in two layers: outer - longitudinal, inner - circular.

  Due to the contraction of these muscles, food is promoted through the alimentary canal and the substances are mixed with digestive juices.

  In the muscle layer are nerve plexuses composed of clusters of nerve cells. They regulate the contraction of smooth muscles and the secretion of the digestive glands.

• internal [show]

  The inner layer consists of mucous and submucosal layers with abundant blood and lymphatic supply. The outer layer of the mucous membrane is represented by the epithelium, the cells of which secrete mucus, which facilitates the movement of the contents through the digestive canal.

  In addition, in the mucous layer of the alimentary canal diffusely located endocrine cells, which produce hormones that are involved in the regulation of the motor and secretory activity of the digestive system, and it also has many lymph nodes that perform a protective function. They neutralize (partially) pathogens that enter the body with food.

  The submucosal layer has numerous small glands that secrete digestive juices.

Digestion in the mouth. The oral cavity is bounded from above by the hard and soft palate, from below by the maxillohyoid muscle (diaphragm of the mouth), and on the sides by the cheeks. The mouth opening is limited by the lips. An adult has 32 teeth in the oral cavity: 4 incisors, 2 canines, 4 small molars and 6 large molars on each jaw. Teeth are made up of a special substance called dentin, which is a modified bone tissue. Outside they are covered with enamel. Inside the tooth there is a cavity filled with loose connective tissue, which contains nerves and blood vessels. Teeth are designed to grind food, they play a role in the formation of sounds.

The oral cavity is lined with a mucous membrane. The ducts of three pairs of salivary glands open into it - parotid, sublingual and submandibular. In the oral cavity is the tongue, which is a muscular organ covered with a mucous membrane, on which there are small numerous papillae containing taste buds. At the tip of the tongue there are receptors that perceive sweet taste, on the root of the tongue - bitter, on the lateral surfaces - sour and salty. With the help of the tongue, food is mixed during chewing and pushed through when swallowing. Language is the organ of human speech.

The region of transition of the oral cavity into the pharynx is designated as a pharynx. On the sides of it are accumulations of lymphoid tissue - the tonsils. The lymphocytes contained in them play a protective role in the fight against microorganisms. The pharynx is a muscular tube in which nasal, oral and laryngeal parts are distinguished. The last two connect the oral cavity with the esophagus. The length of the esophagus is about 25 cm. Its mucosa forms longitudinal folds that facilitate the passage of fluid. No food changes occur in the esophagus.

Digestion in the stomach. The stomach is the most expanded section of the alimentary canal, having the shape of an inverted chemical vessel - a retort. It is located in the abdominal cavity. The initial part of the stomach, connected to the esophagus, is called the cardial, located to the left of the esophagus and raised upwards from the place of their connection, is designated as the fundus of the stomach, and the descending middle part is referred to as the body. Smoothly narrowing, the stomach passes into the small intestine. This outlet section of the stomach is called the pyloric. The lateral edges of the stomach are curved. The left convex edge is called the greater curvature, and the right concave edge is called the lesser curvature of the stomach. The capacity of the stomach in an adult is about 2 liters.

The size and shape of the stomach varies depending on the amount food taken and the degree of contraction of the muscles of its walls. In places where the esophagus passes into the stomach and the stomach into the intestines, there are sphincters (compressors) that regulate the movement of food. The mucous membrane of the stomach forms longitudinal folds, significantly increasing its surface. The thickness of the mucous membrane contains a large number of tubular glands that produce gastric juice. The glands consist of secretory cells of several types: the main ones, which produce the enzyme pepsin, the parietal cells - hydrochloric acid, the mucous membranes - mucus, and the endocrine cells - hormones.

Digestion in the intestine. The small intestine is the longest part of the alimentary canal, 5-6 m long in an adult. It contains the duodenum, jejunum and ileum. The duodenum is horseshoe-shaped and is the shortest part of the small intestine (about 30 cm). The excretory ducts of the liver and pancreas open into the cavity of the duodenum.

The border between skinny and ileum outlined vaguely. These sections of the intestine form numerous bends - loops of the intestines and are suspended throughout the mesentery to the posterior abdominal wall. The mucous membrane of the small intestine forms circular folds, its surface is covered with villi, which are a specialized absorption apparatus. Inside the villi are an artery, vein, lymphatic vessel.

The surface of each villus is covered with a single layer of cylindrical epithelium. Each epithelial cell of the villus has outgrowths of the apical membrane - microvilli (3-4 thousand). Circular folds, villi and microvilli increase the surface of the intestinal mucosa (Fig. 2). These structures facilitate the final stages of digestion and the absorption of digested products.

Between the villi, the mucous membrane of the small intestine is permeated with a huge number of mouths of tubular glands that secrete intestinal juice and a number of hormones that provide various functions of the digestive system.

The pancreas is oblong in shape and is located on the back wall of the abdominal cavity under the stomach. Three sections are distinguished in the gland: head, body and tail. The head of the gland is surrounded by the duodenum, its caudal part is adjacent to the spleen. Through the thickness of the entire gland passes its main duct, which opens into the duodenum. The pancreas contains two types of cells: some cells secrete digestive juice, others secrete special hormones that regulate carbohydrate metabolism. Therefore, it belongs to the glands of mixed secretion.

The liver is a large digestive gland, its mass in an adult reaches 1.8 kg. It is located in the upper part of the abdominal cavity, on the right under the diaphragm. The anterior surface of the liver is convex, while the lower surface is concave. The liver consists of two lobes - right (large) and left. On the lower surface of the right lobe are the so-called gates of the liver, through which the hepatic artery, portal vein and the corresponding nerves enter it; here is the gallbladder. The functional unit of the liver is the lobule, which consists of a vein located in the center of the lobule and rows of liver cells radially diverging from it. The product of the liver cells - bile - through special bile capillaries enters the biliary system, including the bile ducts and gallbladder, and then into the duodenum. Bile is stored in the gallbladder between meals and released into the intestines during active digestion. In addition to the formation of bile, the liver takes an active part in the metabolism of proteins and carbohydrates, in the synthesis of a number of substances important for the body (glycogen, vitamin A), and influences the processes of hematopoiesis and blood clotting. The liver performs a protective function. Many toxic substances brought with blood from the gastrointestinal tract are neutralized in it, and then excreted by the kidneys. This function is so important that with a complete shutdown of the liver (for example, in case of injury), a person immediately dies.

The last section of the alimentary canal is the large intestine. Its length is about 1.5 m, and its diameter is 2-3 times the diameter of the small intestine. The large intestine is located on the anterior wall of the abdominal cavity and surrounds the small intestine in the form of a rim. It is subdivided into the cecum, sigmoid and rectum.

A characteristic feature of the structure of the large intestine is the presence of swellings formed by the mucous and muscular membranes. Unlike the small intestine, the mucous membrane of the large intestine does not contain circular folds and villi, there are few digestive glands in it and they consist mainly of mucous cells. The abundance of mucus promotes the movement of denser food residues through the large intestine.

In the area of ​​​​the transition of the small intestine to the thick (to the caecum), there is a special valve (flap) that ensures the movement of the intestinal contents in one direction - from the small to the large. In the caecum there is a vermiform process - the appendix, which plays a role in the immune defense of the body. The rectum ends with a sphincter - an annular striated muscle that regulates bowel movements.

In the digestive system, sequential mechanical and chemical processing of food is carried out, specific for each of its departments.

Food enters the oral cavity in the form of solid pieces or liquids of various consistencies. Depending on this, it either immediately enters the throat, or undergoes mechanical and initial chemical processing. The first is carried out by the chewing apparatus - coordinated work chewing muscles, teeth, lips, palate and tongue. As a result of chewing, food is crushed, ground and mixed with saliva. The enzyme amylase contained in saliva begins the hydrolytic breakdown of carbohydrates. If food lingers in the oral cavity for a long time, then cleavage products are formed - disaccharides. Saliva enzymes are active only in a neutral or slightly alkaline environment. Mucus excreted with saliva neutralizes acidic foods that have entered the mouth. Saliva lysozyme has a detrimental effect on many microorganisms contained in food.

The mechanism of separation of saliva is reflex. When food comes into contact with the receptors of the oral cavity, they are excited, which is transmitted through the sensory nerves to the medulla oblongata, where the center of salivation is located, and from it the signal goes to the salivary glands. These are unconditioned salivary reflexes. The salivary glands begin to secrete their secret not only when the receptors of the oral cavity are irritated by food products, but also at the sight, smell of food, and sounds associated with eating. These are conditioned salivary reflexes. Saliva glues food particles into a lump and makes it slippery, facilitating passage through the pharynx and esophagus, preventing damage to the mucous membrane of these organs by food particles. The composition and amount of saliva may vary depending on physical properties food. During the day, a person secretes up to two liters of saliva.

The formed food bolus moves to the pharynx by the movement of the tongue and cheeks and causes irritation of the receptors of the root of the tongue, palate and posterior pharyngeal wall. The resulting excitation along the afferent nerve fibers is transmitted to the medulla oblongata - to the center of swallowing, and from there - to the muscles of the oral cavity, pharynx, larynx, esophagus. Due to the contraction of these muscles, the food bolus is pushed into the pharynx, bypassing the respiratory tract (nasopharynx, larynx). Then, by contraction of the muscles of the pharynx, the food bolus moves into open hole esophagus, from where, by means of its peristaltic movements, it moves to the stomach.

The food entering the cavity of the stomach causes contractions of its muscles and an increase in the secretion of gastric juice. Food mixes with gastric juice and turns into a liquid slurry - chyme. Up to 3 liters of juice is secreted per day in an adult. Its main components involved in the breakdown of nutrients are enzymes - pepsin, lipase and hydrochloric acid. Pepsin breaks down complex proteins into simple ones, which are further processed. chemical changes in the intestine. It only works in acidic environment, which is provided by the presence in the stomach of hydrochloric acid secreted by parietal cells. Gastric lipase only breaks down emulsified milk fat. Carbohydrates in the stomach cavity are not digested. An important component of gastric juice is mucus (mucin). It protects the stomach wall from mechanical and chemical damage and the digestive action of pepsin.

After 3-4 hours of treatment in the stomach, chyme begins to enter the small intestine in small portions. The movement of food into the intestines is carried out by strong contractions of the pyloric part of the stomach. The rate of gastric emptying depends on the volume, composition and consistency of the food taken. Liquids pass into the intestines immediately after entering the stomach, and poorly chewed and fatty foods linger in the stomach for up to 4 hours or more.

The complex process of stomach digestion is regulated by nervous and humoral mechanisms. The secretion of gastric juice begins even before eating (conditioned reflexes). So, cooking, talking about food, the sight and smell of it cause the release of not only saliva, but also gastric juice. Such previously secreted gastric juice is called appetizing or ignition. It prepares the stomach for the digestion of food and is an important condition for its normal functioning.

Eating is accompanied by mechanical irritation of the receptors of the oral cavity, pharynx, esophagus and stomach. This leads to increased gastric secretion ( unconditioned reflexes). The centers of secretory reflexes are located in the oblong and diencephalon, in the hypothalamus. From them, impulses travel through the vagus nerves to the gastric glands.

In addition to reflex (nervous) mechanisms, humoral factors are involved in the regulation of gastric secretion. The gastric mucosa produces the hormone gastrin, which stimulates the secretion of hydrochloric acid and, to a small extent, the release of pepsin. Gastrin is released in response to food entering the stomach. With an increase in the secretion of hydrochloric acid, the release of gastrin is inhibited and thus self-regulation of gastric secretion is carried out.

Stimulants of gastric secretion include histamine, which is formed in the gastric mucosa. Many nutrients and their cleavage products, which enter the bloodstream when they are absorbed in the small intestine, have a juice effect. Depending on the factors that stimulate the secretion of gastric juice, several phases are distinguished: cerebral (nervous), gastric (nerve-humoral) and intestinal (humoral).

The breakdown of nutrients is completed in the small intestine. It digests most of the carbohydrates, proteins and fats. Both extracellular and membrane digestion is carried out here, in which bile and enzymes formed by the intestinal glands and pancreas participate.

Liver cells secrete bile continuously, but it is released into the duodenum only with food intake. Bile contains bile acids, bile pigments, and many other substances. The pigment bilirubin determines the light yellow color of bile in humans. Bile acids contribute to the processes of digestion and absorption of fats. Bile, due to its inherent alkaline reaction, neutralizes the acidic contents entering the duodenum from the stomach and thereby stops the action of pepsin, and also creates favorable conditions for the action of intestinal and pancreatic enzymes. Fat droplets under the influence of bile are converted into a finely dispersed emulsion, and then split by lipase to glycerol and fatty acids that can penetrate the intestinal mucosa. If bile is not secreted into the intestines (blockage of the bile duct), then fats are not absorbed by the body and are excreted with feces.

Enzymes produced by the pancreas and secreted into the duodenum are able to break down proteins, fats and carbohydrates. During the day, a person produces up to 2 liters of pancreatic juice. The main enzymes contained in it are trypsin, chymotrypsin, lipase, amylase and glucosidase. Most enzymes are produced by the pancreas in an inactive state. Their activation is carried out in the cavity of the duodenum. So, trypsin and chymotrypsin in the composition of pancreatic juice are in the form of inactive trypsinogen and chymotrypsinogen and pass into the active form in the small intestine: the first under the action of the enterokinase enzyme, the second - trypsin. Trypsin and chymotrypsin break down proteins into polypeptides and peptides. Dipeptidases intestinal juice break down dipeptides into amino acids. Lipase hydrolyses bile emulsified fats into glycerol and fatty acids. Under the action of amylase and glucosidase, most carbohydrates are broken down to glucose. Effective absorption of nutrients in the small intestine is facilitated by its large surface, the presence of multiple folds, villi and microvilli of the mucous membrane. Villi are specialized organs of absorption. By contracting, they contribute to the contact of the mucosal surface with chyme, as well as the outflow of blood and lymph, saturated with nutrients. When relaxing from the intestinal cavity, fluid again enters their vessels. During the day, up to 10 liters of liquid are absorbed in the small intestine, of which 7-8 liters are digestive juices.

Most of the substances formed during the digestion of food and water are absorbed in the small intestine. Undigested food remains in the large intestine, which continues the absorption of water, minerals and vitamins. essential for decomposition undigested residues foods have numerous bacteria contained in the large intestine. Some of them are able to break down the cellulose of plant foods, others - to destroy the unabsorbed products of the digestion of proteins and carbohydrates. In the process of fermentation and decay of food residues, toxic substances are formed. When they enter the bloodstream, they are neutralized in the liver. Intensive absorption of water in the large intestine contributes to the reduction and compaction of chyme - the formation of feces that are removed from the body during the act of defecation.

Food hygiene

Human nutrition should be organized taking into account the laws of the digestive system. You should always follow the rules of food hygiene.

1. Try to keep certain time food intake. This contributes to the formation of conditioned juice reflexes and better digestion of ingested food and significant preliminary juice secretion.
2. Food should be deliciously prepared and beautifully presented. The sight, the smell of the food served, the table setting excite the appetite, increase the secretion of digestive juices.
3. Food should be taken slowly, chewing well. Chopped food is digested faster.
4. Food temperature should not be higher than 50-60 °C and lower than 8-10 °C. hot and cold food irritate the mucous membranes of the mouth and esophagus.
5. Food should be prepared from good quality products so as not to cause food poisoning.
6. Try to use regularly raw vegetables and fruits. They contain many vitamins and fiber, which stimulates the motor work of the intestines.
7. Raw vegetables and fruits should be washed before eating. boiled water and protect against contamination by flies that carry disease-causing microbes.
8. Strictly follow the rules of personal hygiene (wash hands before eating, after contact with animals, after visiting the toilet, etc.).

THE TEACHING OF I. P. PAVLOV ABOUT DIGESTION

Study of the activity of the salivary glands. Saliva is secreted into the oral cavity through the ducts of three pairs of large salivary glands and from many small glands located on the surface of the tongue and in the mucous membrane of the palate and cheeks. To study the function of the salivary glands, Ivan Petrovich Pavlov proposed to use in dogs the operation of bringing a hole to the surface of the skin of the cheek. excretory duct one of the salivary glands. After the dog has recovered from the operation, saliva is collected, its composition is examined and its amount is measured.

So I. P. Pavlov found that salivation occurs reflexively, as a result of irritation of the nerve (sensory) receptors of the oral mucosa by food. Excitation is transmitted to the center of salivation, located in medulla oblongata, from where it is sent along the centrifugal nerves to the salivary glands, which intensively secrete saliva. This is an unconditioned reflex separation of saliva.

IP Pavlov discovered that saliva can also be released when the dog only sees food or smells it. These reflexes discovered by IP Pavlov were called conditioned reflexes, since they are caused by conditions that precede the emergence of an unconditioned salivary reflex.

The study of digestion in the stomach, regulation of secretion of gastric juice and its composition in various stages digestion processes became possible thanks to the research methods developed by I. P. Pavlov. He improved the method of applying a gastric fistula in a dog. A cannula (fistula) made of stainless metal is inserted into the formed opening of the stomach, which is brought out and fixed on the surface of the abdominal wall. Through the fistula tube, you can take the contents of the stomach for examination. However, pure gastric juice cannot be obtained by this method.

To study the role of the nervous system in the regulation of the activity of the stomach, I.P. Pavlov developed another special method, which made it possible to obtain pure gastric juice. IP Pavlov combined the imposition of a fistula on the stomach with the transection of the esophagus. When eating, swallowed food falls out through the opening of the esophagus without entering the stomach. With such imaginary feeding, as a result of food irritation of the nerve receptors of the oral mucosa, gastric juice is reflexively released in the stomach.

The secretion of gastric juice can also be caused by a conditioned reflex - the type of food or any stimulus that is combined with food. I. P. Pavlov called gastric juice secreted by conditioned reflex before eating "appetizing" juice. This first complex-reflex phase of gastric secretion lasts about 2 hours, and food is digested in the stomach for 4-8 hours. Therefore, the complex-reflex phase cannot explain all the regularities in the separation of gastric juice. In order to clarify these questions, it was necessary to study the effect of food on the secretion of the gastric glands. IP Pavlov brilliantly solved this problem by developing the operation of the small ventricle. During this operation, a flap is cut out from the fundus of the stomach, without completely separating it from the stomach and preserving all blood vessels and nerves suitable for it. The mucous membrane is cut and sutured so as to restore the integrity of the large stomach and form a small ventricle in the form of a sac, the cavity of which is isolated from the large stomach, and the open end is brought to the abdominal wall. In this way, two stomachs are created: a large one, in which food is digested in the usual way, and a small, isolated ventricle, into which food does not enter.

With the entry of food into the stomach, the second - gastric, or neurohumoral, phase of gastric secretion begins. Food entering the stomach mechanically irritates the nerve receptors of its mucous membrane. Their excitation causes an increased reflex secretion of gastric juice. In addition, during digestion, chemicals enter the bloodstream - food breakdown products, physiologically active substances (histamine, the hormone gastrin, etc.), which are brought by the blood to the glands of the digestive system and enhance secretory activity.

Currently developed painless methods digestion studies that are widely applied to humans. So, the probing method - the introduction of a rubber tube-probe into the cavity of the stomach and duodenum - allows you to get gastric and intestinal juices; X-ray method - image of the digestive organs; endoscopy - introduction optical devices- makes it possible to examine the cavity of the digestive canal; with the help of radio pills - miniature radio transmitters swallowed by the patient, changes in the chemical composition of food, temperature and pressure in various departments stomach and intestines.

The main functions of the digestive system are:

secretory - consists in the synthesis and secretion of digestive juices (saliva, gastric, pancreatic, intestinal juices, bile) by glandular cells;

motor or motor: chewing, swallowing, advancing and mixing with digestive juices, and excretion of residues - is carried out by smooth muscles, and only the oral cavity, the initial section of the esophagus and the external sphincter of the rectum have striated muscles;

suction- penetration through the mucous membrane into the blood or lymph of the breakdown products of proteins, fats and carbohydrates, water, salts and vitamins.

The processes of secretion, motility and absorption are interconnected and are subject to complex neuro-humoral mechanisms of regulation. In addition to digestive functions, the digestive system has: endocrine function associated with the secretion of hormones and biologically active substances into the blood; excretory, associated with the removal of toxins and food debris into the external environment; protective function.

Protective systems of the digestive tract

The theory of adequate nutrition considers the intake of food into the body not only as a way to restore plastic and energy costs, but also as an allergic and toxic aggression. Nutrition is associated with the danger of penetration into the body of exogenous food antigens (food proteins and peptides), autoantigens of desquamated intestinal cells. With food through the digestive tract, a lot of bacteria, viruses and various toxic substances enter the body. It is safe to say that at present, environmentally friendly food and natural water Hardly ever. In the second half of the 20th century, there was widespread pollution of the environment by industrial, in some regions, radioactive waste. In plant growing and animal husbandry, chemical and biological technologies are widely used without appropriate strict sanitary and epidemic control of the products produced.

Currently, food additives (preservatives, dyes, flavoring agents) are widely used in the manufacture of food products. These are, as a rule, chemicals, the use of which in food production must be scientifically substantiated, and their content in the product must not exceed the permissible limits. Many of these substances can cause not only allergic reactions, but also have a carcinogenic effect. Plant foods can contain excessive amounts of nitrates and pesticides (chemicals used to protect plants from pests), many of which are poisonous to humans. Products of animal origin may contain drugs used to treat animals, growth stimulants used in their cultivation. The presence of these drugs in food can change the sensitivity to antibiotics and cause endocrine disorders. The above negative aspects of nutrition in a healthy body are neutralized due to the complex system of protection of the digestive tract. There are non-specific and specific (immune) defense mechanisms.

Types of non-specific protection:

Mechanical or passive protection is associated with the limited permeability of the mucous membrane of the digestive tract for macromolecular substances (with the exception of newborns).

The mucous membrane is lined with a layer of mucus, which protects it not only from mechanical, but also chemical influences. The outer layer of mucus adsorbs viruses, toxic substances, salts of heavy metals (mercury, lead) and, being rejected into the cavity of the stomach and intestines, promotes their excretion from the body.

Saliva, gastric juice, bile have antibacterial activity. Hydrochloric acid creates an acidic environment in the stomach, has a bacteriostatic effect, preventing the development of putrefactive processes.

The nonspecific protective barrier is associated with the preliminary enzymatic hydrolysis of antigenic molecules, which lose their antigenic properties.

Specific protection in the digestive tract is carried out by immunocompetent lymphoid tissue. In the mucous membrane of the mouth and tonsils there are a large number of cellular elements: macrophages, neutrophils, lymphocytes that carry out phagocytosis of bacteria and antigenic proteins. In the mucous membrane of the small intestine there is a powerful leukocyte layer that separates the enteric and internal environments of the body. It consists of a large number of plasma cells, macrophages, eosinophils, lymphocytes. The intestinal immune system is part of the body's immune system. The lymphatic tissue of the small intestine (25% of the entire mucosa) consists of Peyer's patches, individual lymphatic nodules localized in the region of the lamina propria of the villi and T- and B-lymphocytes scattered in the epithelium (see Fig. 3). Designations in the figure, description in the text. There are also intraepithelial lymphocytes.

Fig. 3 Cross section of the intestinal villus.

In the epithelium above the plaques, special M-cells are localized, which transport antigens to the lymph nodes. Thus, lymphocytes carry out both cellular and humoral immunity.. They produce immunoglobulins adsorbed on the surface of the epithelium in the area of ​​the glycocalyx and create an additional protective layer. In addition to these tissues, the defense system includes the mesenteric lymph nodes and the reticuloendothelial system of the liver. The detoxification and barrier functions of the liver are essential in neutralizing the products of protein decay (indole, skatole, phenol) formed in the intestine, as well as toxic substances and drugs that come with food, and are considered in detail by biological chemistry.

General principles of regulation of digestive functions

Central nervous regulation is carried out by the digestive centers of the brain and spinal cord with the help of conditioned and unconditioned reflexes. The type and smell of food, the time and environment of its intake, a reminder of food excite the digestive glands (salivary, gastric, pancreas) in a conditioned reflex way.

Eating, irritating the receptors of the mouth and stomach, causes unconditioned reflexes. Afferent pathways of unconditioned reflexes are represented by sensitive fibers of the cranial nerves: lingual, glossopharyngeal, upper laryngeal, vagus. Efferent pathways common to conditioned and unconditioned reflexes are formed by parasympathetic and sympathetic fibers.

As the distance from the proximal part increases, the participation of central reflexes in the regulation of functions decreases. The main importance in the small and large intestines is acquired by local nervous and humoral regulation. local nervous regulation is based on "short" reflex arcs. In the wall of the stomach and intestines there is a developed network of nerve cells that form two main plexuses: intermuscular (Auerbach) and submucosal (Meissner). Among nerve cells there are sensory neurons, intercalary and effector. The latter innervate smooth muscles, secretory epithelium and endocrine cells.

Figure 4. Metasympathetic system of the small intestine

A is local reflex arc regulation of motility, B - local reflex arc regulation of the secretion of exocrine and endocrine cells: 1. vagus nerve; 2. mucous membrane; 3. exocrine cell; 4. Meisner's plexus; 5.circular muscle; 6. Auerbach's plexus; 7. longitudinal muscle; 8.endocrine cell

Along with acetylcholine and norepinephrine, more than ten neuropeptides take part in the transmission of regulatory effects on target cells: cholecystokinin, somatostatin, neurotensin, substance P, enkephalin, etc. There are neurons whose mediators are serotonin and purine bases. The set of nerve cells lying inside the organ and forming local reflex arcs was called the metasympathetic nervous system (A.D. Nozdrachev). This system interacts with the central nervous system, but is more independent of it than the autonomic nervous system, because it has its own sensory link (receptive field). Various receptors respond to the initial composition of food and the changes that occur during hydrolysis. The metasympathetic nervous system (Fig. 4) programs and coordinates motor activity, regulates secretion and carries out the relationship between these processes, regulates the secretion of endocrine cells, local blood flow.

Digestion of food is a gradual and continuous process, therefore Humoral mechanisms are of great importance in the regulation of secretion, motility and absorption. In the epithelial layer of the mucous membrane of the stomach and small intestine, the pancreas there are diffusely scattered endocrine cells (the mass of these cells is greater than the mass of all endocrine glands), which secrete hormones and peptides. Some hormones are secreted into the blood and through it have a distant effect on target cells (gastrin  parietal cell), others have a local or paracrine effect, being released into the intercellular fluid, others (neuropeptides) are released in nerve endings along with mediators. The secretion of hormones can be activated by the CNS (eg, the vagus nerve), but many endocrine cells have receptors in the enteric environment that are directly affected by food hydrolysis products. Since all textbooks give a detailed description of gastrointestinal hormones and their influences, let us only note that hormones have both synergism of varying severity and antagonism. They can activate or inhibit secretion, motility, absorption.

Thus, in the digestive tract there is gradient distribution of regulatory mechanisms. AT primary departments dominated by central reflex mechanisms. In the middle sections (stomach, duodenum, jejunum, pancreas) - central reflexes have a starting value, and hormonal regulation complements it and becomes dominant. In the small and especially in the large intestine, the role of local (nervous and humoral) regulatory mechanisms is important. However, all mechanisms can regulate the activity of the same organ (stomach, pancreas).