The process of mechanical processing of food in the digestive canal and chemical breakdown by enzymes nutrients 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 a continuous supply of oxygen, the body needs a wide variety of chemical substances. The body receives them through 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.
| Table 12.2. Digestive juices and their characteristics | |||
| Digestive juice | Enzyme | Substrate | Cleavage product |
| Saliva | Amylase | Starch | Maltose |
| Gastric juice | Pepsin (ogen) | Squirrels | Polypeptides |
| Lipase | Emulsified fats | Fatty acids, glycerol | |
| Pancreatic juice | Trypsin (ogen) | Squirrels | Polypeptides and amino acids |
| Chymotrypsin (ogen) | Squirrels | Polypeptides and amino acids | |
| Lipase | Fats | Fatty acids, glycerol | |
| Amylase | Starch | Maltose | |
| Bile | - | Fats | Drops of fat |
| Intestinal juice | Enterokinase | Trypsinogen | Trypsin |
| Other enzymes | Affects all food components | ||
| Dipeptidases | Dipeptides | Amino acids | |
Proteins containing the necessary amino acids are mainly used as building materials. From these, the body synthesizes its own proteins, unique to it. With insufficient amounts of them in food, a person develops various pathological conditions. Proteins cannot be replaced by other nutrients, while fats and carbohydrates can replace each other within certain limits. Therefore, human food must contain a certain minimum amount of 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 their qualitative composition. Human food must necessarily include products of both plant and animal origin.
Many chemicals contained in food, in the form in which they enter the body, cannot be absorbed. Their careful mechanical and chemical processing is necessary. Mechanical processing involves chopping, mixing and mashing food into a paste. Chemical processing is carried out by enzymes 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 environment (salivary amylase). Maximum enzyme activity is observed at a temperature of 37 - 40 °C. At higher temperatures, most enzymes are destroyed; at low temperatures, their activity is suppressed. Digestive enzymes are strictly specific: each of them acts only on a specific substance 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) - occurs in the cavity of the gastrointestinal tract intestinal tract.
- membrane (parietal) - occurs at the border of the extra- and intracellular environment, 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 protozoan organisms.
STRUCTURE AND FUNCTIONS OF DIGESTIVE ORGANS
In the digestive system, a distinction is made between the digestive canal and the digestive glands communicating with it through the excretory ducts: salivary, gastric, intestinal, pancreas and liver, located outside the digestive canal and communicating with it through their ducts. All digestive glands are classified as exocrine glands (endocrine glands secrete their secretions into the blood). An adult produces up to 8 liters of digestive juice per day.
The human digestive canal is about 8-10 m long 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 digestive canal for most of its length consists of three layers:
- outdoor [show]
Outer layer- serous membrane - formed by connective tissue and mesentery, which separate the digestive canal from the internal organs.
- average [show]
Middle layer- muscular layer - in the upper section (oral cavity, pharynx, upper part of the esophagus) it is represented by striated tissue, and in the remaining sections - smooth muscle tissue. Smooth muscles are located in two layers: the outer - longitudinal, the inner - circular.
Thanks to the contraction of these muscles, food moves through the digestive canal and mixes substances with digestive juices.
The muscle layer contains nerve plexuses, consisting of clusters of nerve cells. They regulate the contraction of smooth muscles and the secretion of digestive glands.
- internal [show]
Inner layer consists of mucous and submucosal layers with abundant blood and lymph supply. The outer layer of the mucous membrane is represented by epithelium, the cells of which secrete mucus, which facilitates the passage of contents through the digestive canal.
In addition, endocrine cells that produce hormones that take part in the regulation of motor and secretory activity are diffusely located in the mucous layer of the digestive canal. digestive system, and also contains many lymph nodes that perform a protective function. They neutralize (partially) pathogenic microorganisms that enter the body with food.
The submucosal layer has numerous small glands that secrete digestive juices.
Digestion in the oral cavity. The oral cavity is limited above by the hard and soft palate, below by the mylohyoid muscle (oral diaphragm), 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 consist of a special substance called dentin, which is a modified bone tissue. They are covered with enamel on the outside. Inside the tooth there is a cavity filled with loose connective tissue containing nerves and blood vessels. Teeth are designed to grind food and play a role in the production of sounds.
The oral cavity is lined with mucous membrane. The ducts of three pairs of salivary glands open into it - the parotid, sublingual and submandibular. In the oral cavity there is a 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, at the root of the tongue - bitter, on the side surfaces - sour and salty. The tongue is used to mix food during chewing and push it through when swallowing. The tongue is the organ of human speech.
The area where the oral cavity enters the pharynx is called the pharynx. On its sides there are accumulations of lymphoid tissue - tonsils. The lymphocytes they contain play a protective role in the fight against microorganisms. The pharynx is a muscular tube in which the 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 mucous membrane 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 digestive 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 cardiac part, located to the left of the esophagus and elevated upward from the place of their connection, is designated as the fundus of the stomach, and the descending middle part is designated as the body. Smoothly tapering, the stomach passes into small intestine. This outlet of the stomach is called 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 stomach capacity of an adult is about 2 liters.
The size and shape of the stomach change depending on the amount of food taken and the degree of contraction of the muscles of its walls. At the junction of the esophagus 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 several types of secretory cells: main cells that produce the enzyme pepsin, parietal cells that produce hydrochloric acid, mucous cells that produce mucus, and endocrine cells that produce hormones.
Digestion in the intestines. The small intestine is the longest part of the digestive canal, 5-6 m long in an adult. It contains the duodenum, jejunum and ileum. The duodenum is shaped like a horseshoe and is the shortest section 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 the jejunum and ileum is not clearly defined. These sections of the intestine form numerous bends - intestinal loops and are suspended along the entire length by 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. An artery, vein, and lymphatic vessel pass through the villi.
The surface of each villi is covered with single-layer columnar epithelium. Each epithelial cell of the villi has outgrowths of the apical membrane - microvilli (3-4 thousand). Circular folds, villi, and microvilli increase the surface area of the intestinal mucosa (Fig. 2). These structures facilitate the final stages of digestion and the absorption of digestion products.
Between the villi, the mucous membrane of the small intestine is penetrated by a huge number of orifices of tubular glands that secrete intestinal juice and a number of hormones that provide various functions digestive system.
The pancreas is oblong in shape and is located on the back wall of the abdominal cavity under the stomach. The gland has three sections: head, body and tail. The head of the gland is surrounded by the duodenum, and its tail part is adjacent to the spleen. Its main duct passes through the thickness of the entire gland, opening into the duodenum. The pancreas contains two types of cells: some cells secrete digestive juice, others - special hormones that regulate carbohydrate metabolism. Therefore, it belongs to the glands of mixed secretion.
The liver is a large digestive gland; its weight in an adult reaches 1.8 kg. It is located in the upper 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 - the right (large) and the left. On the lower surface of the right lobe there are the so-called gates of the liver, through which the hepatic artery, portal vein and corresponding nerves enter it; The gallbladder is also located here. The functional unit of the liver is the lobule, consisting of a vein located in the center of the lobule and rows of liver cells radiating from it. The product of liver cells - bile - flows through special bile capillaries into the biliary system, including the bile ducts and gallbladder, and then into the duodenum. In the gallbladder, bile accumulates between meals and is 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. It neutralizes and then removes by the kidneys many toxic substances carried with the blood from the gastrointestinal tract. This function is so important that if the liver is completely disabled (for example, due to injury), the person immediately dies.
The last section of the digestive 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 divided 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 intestines 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 helps move denser food debris through the colon.
In the area where the small intestine transitions to the large intestine (the cecum), there is a special valve (valve) that ensures the movement of intestinal contents in one direction - from the small to the large. The cecum contains a vermiform appendix, the appendix, which plays a role in the body's immune defense. The rectum ends with a sphincter, a circular striated muscle that regulates bowel movements.
In the digestive system, sequential mechanical and chemical processing of food is carried out, specific to each of its sections.
Food enters the oral cavity in the form of solid pieces or liquids of varying consistency. Depending on this, it either immediately enters the pharynx, or is subjected to mechanical and initial chemical treatment. The first is carried out by the masticatory apparatus - the coordinated work of the masticatory 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 breakdown products - disaccharides - are formed. Salivary enzymes are active only in a neutral or slightly alkaline environment. The mucus secreted with saliva neutralizes acidic foods that enter the mouth. Saliva lysozyme has a detrimental effect on many microorganisms contained in food.
The mechanism for separating saliva is a reflex. When food comes into contact with the receptors of the oral cavity, they are excited, which is transmitted along 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 secretion not only when the oral cavity receptors are irritated by food, but also when they see, smell, or hear food associated with food intake. 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 quantity 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 towards the pharynx with the movement of the tongue and cheeks and causes irritation of the receptors of the root of the tongue, palate and the back wall of the pharynx. The resulting excitation is transmitted along afferent nerve fibers to the medulla oblongata - to the center of swallowing, and from there - to the muscles of the oral cavity, pharynx, larynx, and esophagus. Thanks to the contraction of these muscles, the food bolus is pushed into the pharynx, bypassing the respiratory tract (nasopharynx, larynx). Then, by contracting the muscles of the pharynx, the food bolus moves into the open opening of the esophagus, from where, through its peristaltic movements, it moves into the stomach.
Food entering the stomach cavity causes contractions of its muscles and increased secretion of gastric juice. Food is mixed with gastric juice and turns into a liquid pulp - chyme. An adult produces up to 3 liters of juice per day. 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 undergo further chemical changes in the intestines. It acts only in an acidic environment, which is provided by the presence of hydrochloric acid in the stomach, secreted by the parietal cells. Gastric lipase breaks down only the emulsified milk fat. Carbohydrates are not digested in the stomach cavity. 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 processing 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 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 gastric digestion is regulated by nervous and humoral mechanisms. The secretion of gastric juice begins even before eating (conditioned reflexes). Thus, preparing for food, talking about food, the sight and smell of it cause the secretion of not only saliva, but also gastric juice. This pre-released gastric juice is called appetizing or incendiary. It prepares the stomach for digestion of food and is an important condition for its normal functioning.
Eating is accompanied by mechanical irritation of the receptors in the oral cavity, pharynx, esophagus and stomach. This leads to increased gastric secretion (unconditioned reflexes). The centers of secretory reflexes are located in the medulla oblongata and diencephalon, in the hypothalamus. From them, impulses travel along the vagus nerves to the gastric glands.
In addition to reflex (nervous) mechanisms, humoral factors participate in the regulation of gastric juice 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 increased secretion of hydrochloric acid, the release of gastrin is inhibited and thus self-regulation of gastric secretion occurs.
Gastric secretion stimulants include histamine, which is produced in the gastric mucosa. Many food substances and their breakdown products, which enter the bloodstream when absorbed in the small intestine, have a sokogonny effect. Depending on the factors that stimulate the secretion of gastric juice, several phases are distinguished: cerebral (nervous), gastric (neuro-humoral) and intestinal (humoral).
The breakdown of nutrients is completed in the small intestine. It digests the main amount of carbohydrates, proteins and fats. Both extracellular and membrane digestion take place here, in which bile and enzymes produced by the intestinal glands and pancreas are involved.
Liver cells secrete bile continuously, but it is released into the duodenum only with the intake of food. Bile contains bile acids, bile pigments and many other substances. The pigment bilirubin determines the light yellow color of bile in humans. Bile acids promote 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. Under the influence of bile, fat droplets are converted into a finely dispersed emulsion, and then broken down by lipase into glycerol and fatty acids that can penetrate the intestinal mucosa. If bile is not released into the intestines (blockage of the bile duct), then fats are not absorbed by the body and are excreted in the feces.
Enzymes produced by the pancreas and secreted into the duodenum are capable of breaking 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 occurs in the cavity of the duodenum. Thus, 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 enzyme enterokinase, the second - trypsin. Trypsin and chymotrypsin break down proteins into polypeptides and peptides. Dipeptidases in intestinal juice break down dipeptides into amino acids. Lipase hydrolyzes bile-emulsified fats into glycerol and fatty acids. Under the action of amylase and glucosidase, most carbohydrates are broken down into 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. The specialized organs of absorption are the villi. By contracting, they promote contact of the surface of the mucosa with the chyme, as well as the outflow of blood and lymph saturated with nutrients. When relaxed, fluid flows from the intestinal cavity into their vessels again. 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 and water formed during the digestion of food are absorbed in the small intestine. Undigested food remains enter the large intestine, where the absorption of water, minerals and vitamins continues. Numerous bacteria contained in the large intestine are essential for the decomposition of undigested food residues. Some of them are capable of breaking down the cellulose of plant foods, while others are capable of destroying unabsorbed products of the digestion of proteins and carbohydrates. In the process of fermentation and rotting 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 feces, which 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. Food hygiene rules should be observed at all times.
- Try to stick to specific meal times. This promotes the formation of conditioned juice secretion reflexes and better digestion of food taken and significant preliminary juice secretion.
- Food should be tasty prepared and beautifully presented. The sight, smell of served food, and table setting stimulate the appetite and increase the secretion of digestive juices.
- You should eat food slowly, chewing well. Crushed food is digested faster.
- The food temperature should not be higher than 50-60 °C and lower than 8-10 °C. Hot and cold foods irritate the mucous membranes of the mouth and esophagus.
- Food should be prepared from benign products so as not to cause food poisoning.
- Try to regularly consume raw vegetables and fruits. They contain a lot of vitamins and fiber, which stimulates intestinal motility.
- Raw vegetables and fruits must be washed with boiled water before eating and protected from contamination by flies - carriers of pathogenic microbes.
- Strictly observe the rules of personal hygiene (wash hands before eating, after contact with animals, after visiting the toilet, etc.).
I. P. PAVLOV’S TEACHING 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 using an operation in dogs to expose the opening of the excretory duct of one of the salivary glands to the surface of the skin of the cheek. After the dog has recovered from surgery, saliva is collected, its composition is examined and its quantity is measured.
Thus, I.P. Pavlov established that saliva secretion occurs reflexively, as a result of food irritation of the nerve (sensory) receptors of the oral mucosa. Excitation is transmitted to the salivary center located in the medulla oblongata, from where it is sent along centrifugal nerves to the salivary glands, which intensively secrete saliva. This is an unconditional reflex separation of saliva.
I.P. Pavlov discovered that saliva can be secreted even when the dog only sees food or smells it. These reflexes discovered by I.P. Pavlov were called conditioned reflexes by him, since they are caused by conditions that precede the emergence of the unconditioned salivary reflex.
Study of digestion in the stomach, regulation of the secretion of gastric juice and its composition at various stages of the digestive process became possible thanks to research methods developed by I. P. Pavlov. He perfected the method of performing a gastric fistula in a dog. A stainless metal cannula (fistula) is inserted into the formed opening of the stomach, which is brought out and fixed on the surface of the abdominal wall. The contents of the stomach can be taken through a fistula tube for examination. However, it is not possible to obtain pure gastric juice using this method.
To study the role of the nervous system in regulating the activity of the stomach, I. P. Pavlov developed another special method, which made it possible to obtain pure gastric juice. I.P. Pavlov combined the application of a fistula to the stomach with 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 - by the type of food or by any irritant combined with food. I. P. Pavlov called the gastric juice secreted as a 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 within 4-8 hours. Consequently, the complex-reflex phase cannot explain all the patterns of gastric juice secretion. In order to clarify these questions, it was necessary to study the effect of food on the secretion of the gastric glands. This problem was brilliantly solved by I.P. Pavlov, who developed the small ventricle operation. During this operation, a flap is cut out from the fundus of the stomach, without completely separating it from the stomach and preserving all the blood vessels and nerves approaching it. The mucous membrane is cut and stitched so as to restore the integrity of the large stomach and form a small ventricle in the form of a pouch, the cavity of which is isolated from the large stomach, and the open end is brought out onto 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 neuro-humoral, phase of gastric secretion begins. Food entering the stomach mechanically irritates the nerve receptors of its mucous membrane. Their excitement causes increased reflex secretion of gastric juice. In addition, during digestion, chemical substances enter the bloodstream - products of food breakdown, physiologically active substances (histamine, the hormone gastrin, etc.), which are carried by the blood to the glands of the digestive system and enhance secretory activity.
Painless methods for studying digestion have now been developed and are widely used in humans. Thus, the method of sounding - inserting a rubber tube-probe into the cavity of the stomach and duodenum - allows you to obtain gastric and intestinal juices; radiographic method - image of the digestive organs; endoscopy - the introduction of optical instruments - makes it possible to examine the cavity of the digestive canal; Using radio pills - miniature radio transmitters swallowed by the patient, changes in the chemical composition of food, temperature and pressure in various parts of the stomach and intestines are studied.
| Digestive tract | Structure | Functions | |
| Oral cavity | teeth | There are 32 teeth in total: four flat incisors, two canines, four small and six large molars on the upper and lower jaws. A tooth consists of a root, neck and crown. Dental tissue - dentin. The crown is covered with durable enamel. The tooth cavity is filled with pulp containing nerve endings and blood vessels | Biting and chewing food. Mechanical processing of food is necessary for its subsequent digestion. Grinded food is accessible to the action of digestive juices |
| language | A muscular organ covered with a mucous membrane. The back of the tongue is the root, the front is free - the body, ending with a rounded tip, the upper side of the tongue is the back | Organ of taste and speech. The body of the tongue forms a bolus of food, the root of the tongue participates in the swallowing movement, which is carried out reflexively. The mucous membrane is equipped with taste buds | |
| salivary glands | Three pairs of salivary glands formed by glandular epithelium. A pair of glands are parotid, a pair are sublingual, a pair are submandibular. Glandular ducts open into the oral cavity | They secrete saliva reflexively. Saliva moistens food as it is chewed, helping to form a bolus for swallowing food. Contains the digestive enzyme ptyalin, which breaks down starch into sugar | |
| Pharynx, esophagus | The upper part of the digestive canal, which is a tube 25 cm long. The upper third of the tube consists of striated muscle tissue, the lower part - of smooth muscle tissue. Lined with squamous epithelium | Swallowing food. During swallowing, the food bolus passes into the pharynx, while the soft palate rises and blocks the entrance to the nasopharynx, the epiglottis closes the path to the larynx. Swallowing is a reflex | |
| stomach | The expanded part of the digestive canal is pear-shaped; There are inlet and outlet openings. The walls consist of smooth muscle tissue, lined with glandular epithelium. The glands produce gastric juice (containing the enzyme pepsin), hydrochloric acid and mucus. Stomach volume up to 3 l | Digestion of food. The contracting walls of the stomach help mix food with gastric juice, which is secreted reflexively. In an acidic environment, the enzyme pepsin breaks down complex proteins into simpler ones. The salivary enzyme ptyalin breaks down starch until the bolus is saturated with gastric juice and the enzyme is neutralized | |
| Digestive glands | liver | The largest digestive gland weighing up to 1.5 kg. Consists of numerous glandular cells forming lobules. Between them there is connective tissue, bile ducts, blood and lymphatic vessels. The bile ducts empty into the gallbladder, where bile is collected (a bitter, slightly alkaline transparent liquid of a yellowish or greenish-brown color - the color is given by split hemoglobin). Bile contains neutralized toxic and harmful substances | It produces bile, which accumulates in the gallbladder and enters the intestines through the duct during digestion. Bile acids create an alkaline reaction and emulsify fats (turn them into an emulsion that is broken down by digestive juices), which helps activate pancreatic juice. The barrier role of the liver is to neutralize harmful and toxic substances. In the liver, glucose is converted into glycogen under the influence of the hormone insulin |
| pancreas | The gland is grape-shaped, 10-12 cm long. Consists of a head, body and tail. Pancreatic juice contains digestive enzymes. The activity of the gland is regulated by the autonomic nervous system (vagus nerve) and humorally ( hydrochloric acid gastric juice) | The production of pancreatic juice, which passes through the duct into the intestines during digestion. The juice reaction is alkaline. It contains enzymes: trypsin (breaks down proteins), lipase (breaks down fats), amylase (breaks down carbohydrates). In addition to its digestive function, iron produces the hormone insulin, which enters the blood | |
| Intestines | duodenum (the first part of the small intestine) | The initial section of the small intestine is up to 15 cm long. The ducts of the pancreas and gall bladder open into it. The walls of the intestine consist of smooth muscles and contract involuntarily. The glandular epithelium produces intestinal juice | Digestion of food. Food gruel comes in portions from the stomach and is exposed to three enzymes: trypsin, amylase and lipase, as well as intestinal juice and bile. The environment is alkaline. Proteins are broken down into amino acids, carbohydrates into glucose, fats into glycerol and fatty acids. |
| small intestine | The longest part of the digestive system is 5-6 m. The walls consist of smooth muscles capable of peristaltic movements. The mucous membrane forms villi, to which blood and lymphatic capillaries approach | Digesting food, liquefying food gruel with digestive juices, moving it through peristaltic movements. Absorption of amino acids and glucose into the blood through the villi. Glycerol and fatty acids are absorbed into epithelial cells, where the body’s own fats are synthesized from them, which enter the lymph, then into the blood. | |
| large intestine, rectum | It has a length of up to 1.5 m, a diameter 2-3 times larger than that of a thin one. Produces only mucus. Symbiotic bacteria that break down fiber live here. Rectum - the final section of the tract, ends with the anus | Digestion of protein residues and breakdown of fiber. The toxic substances formed in this process are absorbed into the blood and travel through the portal vein to the liver, where they are neutralized. Water absorption. Formation of feces. Reflexively bringing them out | |
General characteristics of the digestive system
The digestive system includes the oral cavity, pharynx, esophagus, stomach, small and large intestines, liver, and pancreas. The organs that make up the digestive system are located in the head, neck, chest, abdomen and pelvis.
The main function of the digestive system is to ingest food, process it mechanically and chemically, assimilate nutrients and excrete undigested residues.
The digestion process is the initial stage of metabolism. With food, a person receives energy and substances necessary for his life. However, proteins, fats and carbohydrates supplied with food cannot be digested without prior processing. It is necessary that large complex water-insoluble molecular compounds turn into smaller ones that are water-soluble and lack their specificity. This process occurs in the digestive tract and is called digestion, and the products formed during this process are called digestion products.
The structure of the digestive tract
Oral cavity
Oral cavity(cavitas oris) is the beginning of the digestive system. With the help of teeth, food is crushed, chewed, softened with the tongue, mixed with saliva, which enters the oral cavity from the salivary glands, and then enters the pharynx.
The oral cavity, through the alveolar processes of the jaws and teeth, is divided into two sections: the vestibule of the mouth and the oral cavity itself.
Vestibule of the mouth(vestibulum oris) is a slit-like space, limited externally by the lips and cheeks, and internally by the upper and lower dental arches and gums. The vestibule of the mouth is connected to the external environment by the oral fissure, and to the oral cavity itself by the gap formed by the upper and lower teeth and the space behind the large molar. The oral fissure is limited by the lips, which are skin-muscular folds. The basis of the lips is formed by fibers orbicularis muscle mouth The lips at the corners of the mouth are connected by labial commissures. The outer surface of the lips is covered with skin, and the inner surface is covered with mucous membrane and stratified squamous non-keratinizing epithelium. At the junction of the mucous membrane and the gums there are frenulums of the upper and lower lips.
The oral cavity itself(cavitas oris propria) extends from the teeth to the entrance to the pharynx. It is bounded above by the hard and soft palate, below by the muscles that form the diaphragm of the mouth, in front and on the sides by the cheeks, teeth, and behind through a wide opening by the pharynx.
Cheeks(buccae) are formed by the cheek muscles. They are covered on the outside with skin and on the inside with mucous membrane. Between the skin and the cheek muscles there is a thick layer of fatty tissue that forms cheek fat pad. It is especially well developed in infants, which facilitates the act of sucking. On the mucous membrane of the cheek, on the threshold of the mouth, the duct of the parotid salivary gland opens.
Gums(gingivae) are a continuation of the mucous membrane of the lips and cheeks; go to the alveolar processes of the jaws and tightly enveloping the necks of the teeth.
Language(lingua) - a muscular organ that is involved in mixing food in the oral cavity, determining taste qualities in the act of swallowing and in articulation. The tongue is located on the bottom (lower wall) of the oral cavity. It is a flat, oval-elongated body. The tongue has an apex, body and root, as well as a superior surface (dorsum of the tongue), an inferior surface and an edge. The mucous membrane of the back of the tongue forms outgrowths called papillae different shapes and sizes. There are mushroom-shaped, leaf-shaped, filiform, cone-shaped and grooved papillae. They contain blood vessels and nerve endings for taste or general sensitivity. The mucous membrane of the root of the tongue does not have papillae. There are many lymphoid nodules that form the lingual tonsil. On the lower surface of the tongue, the mucous membrane, when moving to the bottom of the oral cavity, forms a fold along the midline - frenulum of the tongue.
The muscles of the tongue (m. linguae) are paired, divided into skeletal and intrinsic. Three muscles are classified as skeletal: genioglossus(m. genioglossus) - pushes the tongue forward or deflects it to the side; hypoglossal(m. hyoglossus) - pulls the tongue down and back and styloglossal(m. styloglossus) - pulls the tongue up and back. The intrinsic muscles of the tongue are represented by four muscles that extend into the thickness of the tongue and intersect in mutually perpendicular directions: the upper and lower longitudinal muscles, the transverse and vertical muscles. When contracted, they change the shape of the tongue.
Teeth(dentes) are located in the dental alveoli of the upper and lower jaws on the upper edge of the gums. Teeth serve as an organ for grasping, biting and grinding food, and are involved in sound production.
A person’s teeth change twice throughout their life: first, 20 milk teeth appear in the appropriate sequence, and then 32 permanent teeth. All teeth are identical in structure. Each tooth has a crown, neck and root. Crown - the most massive part of the tooth protrudes above the gum. It distinguishes between the lingual, vestibular (facial), contact surface and closure surface (chewing).
Using a special type of continuous connection - hammering - the teeth are immovably fixed in the dental alveoli of the jaws. Each tooth has from one to three roots. The root ends top, there is a small hole on it through which blood vessels and nerves enter and exit the tooth cavity. The root is held in the dental cell of the jaw by connective tissue - periodon-ta. Tooth neck It is a slight narrowing of the tooth between the crown and the root of the tooth; it is covered by the mucous membrane of the gums. Inside the tooth there is a small tooth cavity, which forms crown cavity and continues into the root of the tooth in the form root canal. The tooth cavity is filled with pulp, which consists of connective tissue, blood vessels and nerves. The substance of the tooth includes dentin, enamel and cement. Dentine located around the cavity of the tooth and the root canal, it forms the bulk of the tooth. The outside of the crown is covered enamel, and the root cement.
The teeth of an adult are located symmetrically on the upper and lower jaws, with 16 teeth on each. They can be written as a formula:
(2 incisors, 1 canine, 2 molars and 3 molars in each half).
Each tooth has its own shape and performs a corresponding function, for example, incisors are designed for cutting (separation) food, fangs - for tearing, molars - for crushing and grinding.
The milk formula of teeth is as follows:
The first milk teeth begin to appear in children at 5-7 months of life and end by the beginning of the third year; They function only up to 6-7 years. Then, before the corresponding permanent tooth erupts, the baby tooth falls out. Permanent teeth appear in children at the age of 6-7 years, and this process ends by 13-15 years.
Sky(palatum) is divided into hard and soft. Solid sky formed by the subpalatal processes of the upper jaw and horizontal plates of the bones of the palate, interconnected suture of the palate. It is covered with a mucous membrane with stratified squamous non-keratinizing epithelium and tightly fused with the periosteum.
Soft sky It is a muscular aponeurotic formation covered with a mucous membrane. The anterior section of the soft palate is located horizontally, and the posterior section hangs freely, forming velum palatine with uvula in the middle. They separate the nasopharynx from the oropharynx. Two folds (arches) extend from the lateral edges of the velum palatine: anterior palatoglossus arch and back - palatopharyngeal arch. The first descends to the lateral surface of the tongue, and the second to the lateral wall of the pharynx. Between the arches there is an almond fossa with palatine tonsil. The basis of the soft palate includes paired striated muscles (tensor velum palatine muscle, levator velum palatine muscle, palatoglossus and palatopharyngeal muscles) and the unpaired uvula muscle. By contracting, they strain the velum palate, expanding and lowering the soft palate.
The oral cavity is posterior through isthmus of pharynx communicates with the pharynx. The isthmus of the pharynx is limited above by the soft palate, below by the root of the tongue, and laterally by the palatoglossal arches.
Glands of the mouth
The glands of the mouth include the major and minor salivary glands, the ducts of which open into the oral cavity. Minor salivary glands are located in the thickness of the mucous membrane or in the submucosa lining the oral cavity. Depending on their location, labial, molar, palatal and lingual glands are distinguished. Based on the nature of the secretion they secrete, they are divided into serous, mucous and mixed.
Large salivary glands - These are paired glands located outside the oral cavity. These include the parotid, submandibular and sublingual glands. They, like the minor salivary glands, secrete serous, mucous and mixed secretions. The mixture of secretions from all the salivary glands of the oral cavity is called saliva.
Parotid gland - the largest, lies on the lateral surface of the face, anterior and inferior to the auricle. Its excretory duct, about 5-6 cm long, opens into the vestibule of the mouth on the mucous membrane of the cheek at the level of the upper second molar.
Submandibular gland located slightly inside and below the body of the lower jaw; The excretory duct opens on the sublingual papilla. The secretion of the gland is serous-mucous.
Sublingual gland located at the bottom of the oral cavity directly under the mucous membrane; The large excretory duct connects to the terminal part of the duct of the submandibular gland and opens on the sublingual papilla. The small sublingual ducts independently flow into the oral cavity on the surface of the mucous membrane along the sublingual fold.
Pharynx
Pharynx(pharinx) - an unpaired organ, located in the head and neck area, is part of the digestive and respiratory systems, is a funnel-shaped tube 12-15 cm long, suspended at the base of the skull. It is attached to the pharyngeal tubercle of the basilar part of the occipital bone, to the pyramids of the temporal bones and to the pterygoid process of the sphenoid bone; at the level of the VI-VII cervical vertebrae it passes into the esophagus.
The openings of the nasal cavity (choanae) and oral cavity (pharynx) open into the pharynx. Air from the nasal cavity through the choanae or from the oral cavity through the pharynx enters the pharynx, and then into the larynx. During the act of swallowing, food mass from the oral cavity passes into the pharynx, and then into the esophagus. As a result of this, the pharynx is the place where the respiratory and digestive tracts intersect. Between the posterior wall of the pharynx and the plate of the cervical fascia is located retropharyngeal space, filled with loose connective tissue in which the retropharyngeal lymph nodes lie.
The pharynx is divided into three parts: nasal, oral and laryngeal.
Bow makes up the upper part of the pharynx and relates only to the respiratory tract. On the side wall of the nasopharynx there is a pharyngeal opening of the auditory tube with a diameter of 3-4 mm, which connects the pharyngeal cavity with the middle ear cavity. In addition, there are accumulations of lymphoid tissue in the form of pharyngeal and tubal tonsils.
Oral part extends from the velum to the entrance to the larynx. In front it communicates with the isthmus of the pharynx, and behind it corresponds to the third cervical vertebra.
Laryngeal part is the lower part of the pharynx and is located from the level of the entrance to the larynx to the transition of the pharynx to the esophagus. On the front wall of this part there is an opening that leads into the larynx. It is bounded above by the epiglottis, on the sides by the aryepiglottic folds, and below by the arytenoid cartilages of the larynx. The wall of the pharynx is formed by the mucous membrane, which lies on a dense connective tissue plate that replaces the submucosa. Outside the submucosa are the muscular layer and the connective tissue membrane (adventitia). The mucous membrane inside the pharynx has no folds, at the level of the nasopharynx it is covered with ciliated (ciliated) epithelium, and below - with stratified squamous epithelium. The mucous membrane contains mucous glands that produce a secretion that moisturizes its walls and promotes the sliding of the bolus of food when swallowing. On the outside, the submucosa is covered with pharyngeal muscles formed by striated muscle tissue.
The pharyngeal and tubal tonsils, as well as the palate and lingual tonsil form a lymphoepithelial ring (Pirogov-Waldeyer ring). These tonsils perform an important protective function in neutralizing microbes that constantly enter the body from the external environment.
Muscles of the pharynx divided into elevators and compressors. The first group of muscles includes the stylopharyngeal and tubopharyngeal. In the second there are three compressors (constrictors): upper, middle and lower. When a bolus of food passes through the pharynx, the longitudinal muscles lift it, and the pharyngeal constrictors, sequentially contracting from top to bottom, push the food towards the esophagus. At the level of the VI-VII cervical vertebrae, the pharynx passes into the esophagus and then food from the pharynx enters the stomach.
Esophagus
Esophagus(esophagus) is a cylindrical tube 25-30 cm long that connects the pharynx to the stomach. It starts at level VI cervical vertebra, passes through the chest cavity, the diaphragm and flows into the stomach to the left of the X-XI thoracic vertebrae. There are three parts of the esophagus: cervical, thoracic and abdominal.
Neck part located between the trachea and the spine at the level of the VI cervical and up to the II thoracic vertebrae. The recurrent laryngeal nerve and the common carotid artery pass along the sides of the cervical part of the esophagus.
Thoracic part The esophagus is located first in the upper and then in the posterior mediastinum. At this level, the esophagus is surrounded by the trachea, pericardium, thoracic aorta, left main bronchus, and right and left vagus nerves.
Abdominal part The esophagus, 1-3 cm long, connects to the cardiac part of the stomach. It has anatomical narrowings in three places: the first - at the level of the VI-VII cervical vertebrae; second - IV-V thoracic vertebrae; the third is where the esophagus passes through the diaphragm. In addition, two physiological narrowings are distinguished: aortic - at the intersection of the esophagus with the aorta and caudal - at the junction with the stomach.
The wall of the esophagus consists of the mucous membrane, submucosa, muscular and adventitial membranes. The mucous membrane is lined with stratified squamous epithelium. The submucosa is well developed, which allows the mucous membrane to gather into longitudinal folds. In the mucous membrane and submucosa there are glands that open through their ducts into the lumen of the esophagus. The muscular layer is formed by outer longitudinal and inner circular layers. The adventitia covers only the cervical and thoracic parts of the esophagus, and the abdominal part is covered with the visceral layer of the peritoneum. The adventitium allows the esophagus to change the size of its transverse diameter as it passes through the bolus.
Stomach
Stomach(ventriculus, gaster) is an expanded part of the digestive tract, which serves as a container for food and is located between the esophagus and the duodenum.
In the stomach, there are anterior and posterior walls, lesser and greater curvature, cardiac part, fundus (vault), body and pyloric (pyloric) part (Fig. 76).
The size of the stomach varies greatly depending on the body type and the degree of filling of the organ. With average filling, the stomach has a length of 24-26 cm, and on an empty stomach - 18-20 cm. The capacity of the stomach of an adult is on average 3 liters (1.5-4.0 liters).
The gastric wall consists of the mucous membrane, submucosa, muscular and serous membranes.
Mucous membrane The stomach is covered with a single-layer cylindrical epithelium, forms many folds having different directions: along the lesser curvature - longitudinal, in the area of the fundus and body of the stomach - transverse, oblique and longitudinal. At the junction of the stomach and the duodenum there is a ring-shaped fold - the pylorus (pylorus) valve, which, when the pyloric sphincter contracts, delimits the cavity of the stomach and duodenum. On the mucous membrane there are small elevations, which are called gastric fields. On the surface of these fields there are depressions (gastric dimples), which represent the mouths of the gastric glands. The latter secrete gastric juice for chemical processing of food.
Submucosa of the stomach well developed, contains dense vascular and nerve plexuses.
Muscular lining of the stomach has an inner oblique layer of muscle fibers, the middle - circular layer - is represented by circular fibers, the outer - longitudinal smooth fibers. In the area of the pyloric part of the stomach, the circular layer is more developed than the longitudinal one, and forms around the outlet pyloric sphincter.
The stomach is located in the upper part of the abdominal cavity, under the diaphragm and liver. Three quarters of it are located in the left hypochondrium, one fourth - in the epigastric region. The entrance cardiac opening is located at the level of the bodies of the X-XI thoracic vertebrae, and the exit opening of the pylorus is at the right edge of the XII thoracic and I lumbar vertebrae.
The longitudinal spine of the stomach runs obliquely from top to bottom, from left to right and from back to front. The anterior surface of the stomach in the cardiac part of the fundus and body is in contact with the diaphragm, and in the area of the lesser curvature - with the left lobe of the visceral surface of the liver. A small part of the body of the stomach is adjacent directly to the anterior abdominal wall.
The posterior surface of the stomach along the greater curvature is in contact with the transverse colon, and in the fundus with the spleen.
Behind the stomach there is a slit-like space - greasy bag, which separates it from the organs lying on the posterior abdominal wall: the left kidney, adrenal gland and pancreas. The relatively stable position of the stomach is ensured by its connection with surrounding organs using the hepatogastric, gastrocolic and gastrosplenic ligaments.
Small intestine
Small intestine(intestinum tenue) - the longest part of the digestive tract. Here, further digestion of food occurs, the breakdown of all nutrients under the influence of intestinal juice, pancreatic juice, liver bile and absorption of products into the blood and lymphatic vessels (capillaries).
The length of the small intestine in humans ranges from 2.2 to 4.5 m. In men it is slightly longer than in women. The small intestine has the shape of a tube, which is about 47 mm across and about 27 mm at the end. The upper border of the small intestine is the pylorus of the stomach, and the lower border is the ileocecal valve at the entrance to the cecum.
The small intestine has three sections: duodenum, jejunum and ileum. Unlike the duodenum, the jejunum and ileum have a mesentery and are considered the mesenteric part of the small intestine.
Duodenum(duodenum) has a total length of 17-21 cm and is the initial section of the small intestine. It has four parts: upper, descending, horizontal and ascending.
The duodenum is located retroperitoneally and does not have its own mesentery. The peritoneum is adjacent to the intestine in front, covering on all sides only its initial section - the ampulla. The duodenum is fixed by the hepatoduodenal, duodenohepatic and suspensory ligaments. The mucous membrane of this intestine forms circular folds characteristic of the entire small intestine. In addition, on its inner wall there is a longitudinal fold, in the lower part of which there is major duodenal papilla, where the common bile duct and pancreatic duct open through a common opening. 2-3 cm above the papilla is sometimes located the minor duodenal papilla, on which the mouth of the accessory pancreatic duct opens.
In the submucosa there are many duodenal glands, the ducts of which open into the intestinal lumen. The muscular coat consists of an inner circular and outer longitudinal layer of smooth muscle fibers. The outside of the duodenum is covered with adventitia.
The part of the small intestine that has the mesentery lies below the transverse colon, and its mesentery forms 14-16 loops, covered in front by the greater omentum. About 2/5 of the mesenteric part of the small intestine belongs to the jejunum and 3/5 to the ileum. There is no clearly defined boundary between these parts of the small intestine.
Jejunum(jejunum) lies immediately after the duodenum, its loops are located in the left upper part of the abdominal cavity. The diameter of the jejunum is 3.5-4.5 cm.
Ileum(ileum) is a continuation of the jejunum. It occupies the lower right part of the abdominal cavity and connects with the cecum in the region of the right iliac fossa. The length of the ileum is about 2.7 cm.
The jejunum and ileum are covered by peritoneum, which forms outer serosa its walls, which are located on a thin subserous base. In this case, the peritoneum forms the mesentery, between the layers of which there are blood and lymphatic vessels and nerves.
Under subserous base lies the muscular layer, which consists of an outer longitudinal layer, well developed, and an inner circular layer.
Behind the muscular layer is submucosa, which includes loose connective tissue with many blood, lymphatic vessels and nerves.
Mucous membrane The jejunum and ileum form circular folds about 8 mm high, which cover ½ - 2/3 of the circumference of the intestine. The height of the folds in the direction from the jejunum to the ileum decreases. The folds are covered with intestinal villi 0.2 - 1.2 mm high, which significantly increases the absorption area of the mucous membrane of the small intestine, which is covered with single-layer prismatic epithelium and has a well-developed network of blood and lymphatic vessels. In the mucous membrane of the jejunum, in addition, there are single lymphoid nodules, and in the mucous membrane of the ileum there are many of them and they are combined into group lymphoid nodes (Peyer's patches).
The basis of the villi is the connective tissue of the lamina propria of the mucous membrane with a small amount of smooth muscle cells. In the central part there is a lymphatic capillary, around which, closer to the epithelium, blood vessels pass.
Colon
Colon(intestinum crassum) is a continuation of the small intestine and the final section of the digestive tract. Digestion of food is completed in it, feces are formed and removed through the anus.
The large intestine is located in the abdominal cavity and in the pelvic cavity; its length ranges from 1 to 1.7 m; diameter - up to 4-8 cm. The large intestine includes the cecum with the vermiform appendix; ascending, transverse descending and sigmoid colons; rectum.
Cecum(caecum) has a length of about 6 cm and a diameter of 7.0-7.5 cm. It represents the initial expanded part of the colon below the entry point of the ileum into the colon. The peritoneum covers the cecum on all sides, but does not have a mesentery. The position of the cecum is very variable; it can often be located at the entrance to the pelvis. A vermiform appendix (appendix) extends from the posterior surface of the cecum. The latter is an outgrowth of the cecum 2-20 cm long (on average 8 cm) and 0.5-1.0 cm in diameter. Most often, the vermiform appendix is located in the right iliac fossa and can have a descending, lateral or ascending direction. When the ileum passes into the cecum, it forms ileocecal opening, resembling a horizontal slit, bounded above and below by two folds that form ileocecal valve, The latter prevents the return of contents from the cecum to the ileum. Somewhat below the ileocecal valve on the inner surface there is an opening of the vermiform appendix.
Ascending colon(colon ascendens) continues the cecum upward, located in the right lateral region of the abdominal cavity. Having reached the visceral surface of the right lobe of the liver, the intestine turns sharply to the left and forms the right convexity of the colon, and then passes into the transverse colon.
Transverse colon(colon transversum) originates from the right flexure of the colon, goes across to the left flexure of the colon. The liver is adjacent to the transverse colon, to its right bend, and the stomach and spleen to the left bend, the loops of the small intestine to the bottom, the anterior abdominal wall to the front, the duodenum and pancreas to the back. The intestine is covered on all sides by peritoneum and has a mesentery, with which it is attached to the posterior wall of the abdominal cavity.
Descending colon(colon descendens) has a length of 10-30 cm, starts from the left flexure of the colon and goes down to the left iliac fossa, where it passes into the sigmoid colon. Located in the left part of the abdominal cavity, the intestine is adjacent to the quadratus lumborum muscle, the left kidney, and the iliacus muscle; to the right of the intestine are the loops of the jejunum, to the left is the left abdominal wall; the anterior surface of the descending colon is in contact with the anterior abdominal wall. The peritoneum covers the descending colon from the sides and in front.
Sigmoid colon(colon sigmoideum) is located in the left iliac fossa, starts at the top from the level of the iliac crest and ends at the level of the sacroiliac joint, where it passes into the rectum. Along the way, the sigmoid colon forms two loops, the shape and size of which can have individual variability. The length of this intestine in an adult varies from 15 to 67 cm. The peritoneum covers it on all sides and, forming the mesentery, is attached to the posterior wall of the abdominal cavity.
The wall of the colon consists of the mucous membrane, submucosa, muscular and serous membranes.
The mucous membrane is covered with columnar epithelium, which contains mucous (goblet) cells. The mucous membrane does not form villi; it contains only semilunar folds of the colon, which are located in three rows and correspond to the boundaries of numerous pouch-like protrusions of the wall - haustra of the colon. Located outside the mucous membrane muscle membrane, which consists of an inner circular and outer longitudinal layer. The latter forms three longitudinal bundles (ribbons) of the colon. Each of these bands is about 1 cm wide and is called mesenteric, free, and omental, respectively. In the wall of the appendix and rectum they merge into a single muscle layer. The serous membrane completely covers the appendix, cecum, transverse colon and sigmoid colon, as well as the initial part of the rectum; the remaining parts of the colon are partially covered by the peritoneum.
In the area of the free and omental bands, on the outer surface of the colon, the serous membrane forms omental processes from adipose tissue.
Rectum(rectum) - the final part of the large intestine; feces accumulate in it and then are removed from it. The average length of the rectum is about 15 cm, the diameter ranges from 2.5 to 7.5 cm; it is located in the pelvic cavity. Behind it are the sacrum and coccyx, in front are the prostate gland, bladder, seminal vesicles and ampoules of the vas deferens in men, the uterus and vagina in women. Along the way, the rectum forms two bends in the sagittal plane: the sacral, which corresponds to the curvature of the sacrum, and perineal, convexly directed forward. At the level of the sacrum, the rectum forms an extension - ampoule. The narrow part of the intestine passing through the perineum is called the anal canal, which opens into an external opening - the anus.
The rectal mucosa contains intestinal glands (mucosal and goblet) and single lymphoid nodules; forms longitudinal and transverse folds.
The submucosa contains vascular and nerve plexuses, lymphoid follicles. In the ampulla of the rectum there are 2-3 transverse folds, and in the anal canal there are 6-10 permanent longitudinal folds (columns). Between them there are depressions - the anal anal sinuses, bounded below by the anal (anal) valves. The latter form the rectal-anal line.
The muscular layer of the rectum has a circular and longitudinal layer. The inner circular layer of the anal canal forms the internal (involuntary) anal sphincter, 2-3 cm high. The external (voluntary) anal sphincter is formed from a layer of circular striated muscle fibers, which then become part of the muscles of the pelvic diaphragm. The muscle fibers of the longitudinal layer in the wall of the rectum form a continuous layer into which the fibers of the levator ani muscle are woven below.
The serous membrane covers all sides top part rectum, the middle one on three sides, and the lower one lies in the peritoneal position.
Glands of the digestive tract
Nutrition is a complexly coordinated process aimed at replenishing the energy of a living organism through processing, digestion, breakdown, and absorption of nutrients. All these and some other functions are performed by the gastrointestinal tract, which consists of many important elements combined into a single system. Each of its mechanisms is capable of performing a variety of actions, but when one element suffers, the operation of the entire structure is disrupted.
This is due to the fact that food entering our body undergoes multi-stage processing; these are not only the familiar processes of digestion in the stomach and absorption in the intestines. Digestion also includes the absorption of those same substances by the body. Thus, the diagram of the human digestive system takes on a broader picture. Pictures with captions will help you visualize the topic of the article. 
The digestive system usually consists of the gastrointestinal tract and additional organs called glands. The organs of the digestive tract include:
The visual arrangement of the organs of the gastrointestinal tract is shown in the figure below. Having familiarized yourself with the basics, it is worth considering the structure of the organs of the human digestive system in more detail. 
The initial section of the gastrointestinal tract is oral cavity. Here, under the influence of teeth, mechanical processing of incoming food is performed. Human teeth have various shapes, which means their functions are also different: incisors cut, canines tear, premolars and molars grind.
In addition to mechanical treatment, chemical treatment also begins in the oral cavity. This happens under the influence of saliva, or rather, its enzymes that break down some carbohydrates. Of course, complete breakdown of carbohydrates cannot occur here due to the short stay of the food bolus in the mouth. But enzymes saturate the lump, and the astringent components of saliva hold it together, ensuring its easy movement to the pharynx.
Pharynx- this tube, consisting of several cartilages, performs the function of carrying the bolus of food to the esophagus. In addition to carrying food, the pharynx is also a respiratory organ; 3 sections are located here: the oropharynx, nasopharynx and laryngopharynx - the last two belong to the upper respiratory tract.
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From the pharynx, food enters esophagus- a long muscular tube that also performs the function of carrying food to the stomach. A feature of the structure of the esophagus is 3 physiological narrowings. The esophagus is characterized by peristaltic movements.
At its lower end, the esophagus opens into the stomach cavity. The stomach has a rather complex structure, since its mucous membrane is rich in a large number of tissue glands, various cells that produce gastric juice. Food stays in the stomach for 3 to 10 hours, depending on the nature of the food taken. The stomach digests it, impregnates it with enzymes, turns into chyme, then the “food gruel” enters the duodenum in portions.
The duodenum belongs to the small intestine, but it is worth paying special attention to, since this is where some of the most important elements of the digestive process come - intestinal and pancreatic juices and bile. Bile is a liquid rich in special enzymes produced by the liver. There are cystic and hepatic biles; they differ slightly in composition, but perform the same functions. Pancreatic juice, together with bile and intestinal juice, constitute the most important enzymatic factor in digestion, which involves the almost complete breakdown of substances. The duodenal mucosa has special villi that are capable of capturing large lipid molecules that, due to their size, are not able to be absorbed by blood vessels. 
Next, the chyme passes into the jejunum, then into the ileum. Following the small intestine comes the large intestine, it begins with the cecum with a vermiform appendix, best known as the “appendix”. The appendix does not have any special properties during digestion since it is a vestigial organ, that is, an organ that has lost its functions. The large intestine is represented by the cecum, colon and rectum. Performs functions such as absorption of water, secretion of specific substances, formation of feces and, finally, excretory function. A feature of the large intestine is the presence of microflora that determines the normal functioning of the entire human body as a whole.
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Digestive glands are organs capable of producing enzymes that enter the gastrointestinal tract and digest nutrients.
Large salivary glands. These are paired glands, distinguished:
- Parotid salivary glands (located in front and below the auricle)
- Submandibular and sublingual (located under the diaphragm of the oral cavity)
They produce saliva - a mixture of secretions from all salivary glands. This is a viscous transparent liquid consisting of water (98.5%) and dry residue (1.5%). The dry residue includes mucin, lysozyme, enzymes that break down carbohydrates, salts, etc. Saliva enters the oral cavity through the excretory ducts of the glands during meals or during visual, olfactory and auditory stimulation. 
Liver. This unpaired parenchymal organ, located in the right hypochondrium, is the largest gland in the human body; its weight in an adult can be approximately 1.5-2 kg. The shape of the liver resembles an irregular wedge; with the help of ligaments it is divided into 2 lobes. The liver produces golden-colored bile. It consists of water (97.5%) and dry residue (2.5%). The dry residue is represented by bile acids (cholic acid), pigments (bilirubin, biliverdin) and cholesterol, as well as enzymes, vitamins, and inorganic salts. In addition to digestive activity, bile also performs an excretory function, that is, it is capable of removing metabolic products from the body, for example, the above-mentioned bilirubin (a breakdown product of hemoglobin).
Hepatocytes are specific cells of the liver lobules; they are the tissue of the organ. They serve as filters for toxins that enter the blood, therefore, the liver has the ability to protect the body from poisons that poison it.
The gallbladder is located under the liver and adjacent to it. It is a kind of reservoir for hepatic bile, which enters it through the excretory ducts. Here, bile accumulates and enters the intestines through the bile ducts. This bile is now called bladder bile and is dark olive in color.
The human digestive system occupies one of the honorable places in the arsenal of knowledge of a personal trainer, solely for the reason that in sports in general and in fitness in particular, almost any result depends on diet. Gaining muscle mass, losing weight, or keeping it off largely depends on what kind of “fuel” you put into your digestive system. The better the fuel, the better the result will be, but the goal now is to understand exactly how this system works and works and what its functions are. The digestive system is designed to provide the body with nutrients and components and remove residual digestive products from it. Food entering the body is first crushed by the teeth in the oral cavity, then through the esophagus it enters the stomach, where it is digested, then in the small intestine, under the influence of enzymes, the digestive products break down into individual components, and in the large intestine, feces (residual digestive products) are formed. , which is ultimately subject to evacuation from the body. The human digestive system includes the organs of the gastrointestinal tract, as well as auxiliary organs, such as the salivary glands, pancreas, gall bladder, 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 food grinding, in other words, mechanical processing. The middle section includes the stomach, small and large intestines, pancreas and liver. Here the chemical processing of food, the absorption of nutritional components and the formation of residual digestive products occur. The posterior section includes the caudal part of the rectum and removes feces from the body. Structure of the human digestive system: 1- Oral cavity; 2- Palate; 3- Tongue; 4- Language; 5- Teeth; 6- Salivary glands; 7- Sublingual gland; 8- Submandibular gland; 9- Parotid gland; 10- Pharynx; 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- Caecum; 27- Descending colon; 28- Sigmoid colon; 29- Rectum; 30- Anal opening. The average length of the digestive canal in an adult is approximately 9-10 meters. It contains the following sections: oral cavity (teeth, tongue, salivary glands), pharynx, esophagus, stomach, small and large intestine. Structure of the stomach: 1- Esophagus; 2- Cardiac sphincter; 3- Fundus of the stomach; 4- Body of the stomach; 5- Greater curvature; 6- Folds of the mucous membrane; 7- Pyloric sphincter; 8- Duodenum. The process of digesting 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 salivary 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. Bile accumulates in the gallbladder before entering the intestines, and bile enzymes allow fats to be separated into small fractions, which accelerates their breakdown by the enzyme lipase. Structure of the liver: 1- Right lobe of the liver; 2- Hepatic vein; 3- Aperture; 4- Left lobe of the 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- Path of blood from the intestines; IV- The path of bile to the intestines. All functions of the human digestive system are divided into 4 categories: In the oral cavity, with the help of teeth, tongue and the secretion product of the salivary glands, during chewing, primary processing of food occurs, which consists of grinding it, mixing it and moistening it with saliva. Further, during 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 and mixes with gastric juice, which contains acid, enzymes and breakdown proteins. Next, food in the form of chyme (liquid contents of the stomach) enters in small portions into the small intestine, where its chemical processing continues with the help of bile and secretion products of the pancreas and intestinal glands. Here, in the small intestine, nutrients are absorbed into the blood. Those food components that are not absorbed move further into the large intestine, where they undergo breakdown under the influence of bacteria. In the colon, water is also absorbed, and then feces are formed from residual digestive products that have not been digested or absorbed. The latter are removed from the body through the anus during defecation. 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- Papilla of Vater; 8- Lesser papilla; 9- Common bile duct. The human digestive system is of exceptional importance in fitness and bodybuilding, but of course 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 digestive system. Achieving any muscle gain or weight loss results also depends on your 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, but, by and large, your overall health depends on the health of your digestive system. Brief summary of the topic Digestion is served by three groups of glands: 1) unicellular intraepithelial glands (goblet exocrinocytes, apical granular Paneth cells; 2) intramural simple tubular glands of the gastric mucosa and more complex branched glands of the submucosa of the esophagus and duodenum; 3) large extraorgan salivary glands, pancreas and liver. Complex salivary glands
. The excretory ducts of three pairs of complex salivary glands open into the oral cavity. All salivary glands develop from the stratified squamous epithelium lining the oral cavity of the embryo. They consist of secretory terminal sections and pathways that remove secretions. Secretory sections, based on the structure and nature of the secreted secretion, are of three types: proteinaceous, mucous, proteinaceous and mucous. The excretory ducts of the salivary glands are divided into intercalary ducts, striated, intralobular, interlobular excretory ducts and the common excretory duct. According to the mechanism for separating secretions from cells, all salivary glands are merocrine. Parotid glands
. On the outside, the glands are covered with a dense, unformed connective tissue capsule. The gland has a pronounced lobular structure. In structure it is a complex alveolar branched gland, proteinaceous in nature of the secretion. The lobules of the parotid gland contain terminal protein sections, intercalary ducts, striated ducts (salivary tubes) and intralobular ducts. It is believed that in the striated sections the secretion is diluted with water and inorganic substances. It is believed that salivary gland hormones are secreted in these sections, such as saliparotin (regulates the balance of phosphorus and calcium in the bone), nerve growth factor, insulin-like factor, and epithelial growth factor. The intralobular excretory ducts are covered with a bilayer epithelium, the interlobular excretory ducts are located in the interlobular connective tissue. As the excretory ducts strengthen, the bilayer epithelium gradually becomes multilayered. The common excretory duct is covered with stratified squamous non-keratinizing epithelium. Its mouth is located on the surface of the mucous membrane of the cheek at the level of the 2nd upper molar. Submandibular glands. In the submandibular glands, along with purely proteinaceous glands, mucous-proteinaceous terminal sections are formed. In some parts of the gland, mucus of the intercalary ducts occurs, from the cells of which the mucous cells of the terminal sections are formed. This is a complex alveolar, in places tubular-alveolar, branched protein-mucosal gland. The surface of the iron is covered with a connective tissue capsule. The lobular structure in it is less pronounced than in the parotid gland. The submandibular gland is dominated by the terminal sections, which are structured in the same way as the corresponding terminal sections of the parotid gland. Mixed end sections are larger. They consist of two types of cells - mucous and protein (protein crescents of Gianutzi). The intercalary ducts of the submandibular gland are less branched and shorter compared to the parotid gland. The striated ducts in the submandibular gland are very well developed. They are long and highly branched. The epithelium of the excretory ducts is lined with the same epithelium as in the parotid gland. The main excretory duct of this gland opens next to the duct of the paired sublingual gland on the anterior edge of the frenulum of the tongue. Sublingual gland- This is a mixed, mucous-protein gland with a predominance of mucous secretion. It contains the following terminal secretory sections: mucous, protein and mixed with a predominance of mucous. Protein terminal sections are few in number. The mucous terminal sections consist of characteristic mucous cells. Myoepithelial elements form the outer layer in all terminal sections, as well as in the intercalary and striated ducts, which are extremely poorly developed in the sublingual gland. Connective tissue intralobular and interlobular septa are better expressed than in the two types of previous glands. Pancreas. The pancreas is divided into a head, body and tail. The gland is covered with a thin transparent connective tissue capsule, from which numerous interlobular septa, consisting of loose connective tissue, extend deep into the parenchyma. They contain interlobular excretory ducts, nerves, blood and lymphatic vessels. Thus, the pancreas has a lobular structure. Pancreas consists of an exocrine section (97% of its mass) and an endocrine section formed by the islets of Langerhans. The exocrine part of the gland produces a complex digestive secretion - pancreatic juice, which flows through the excretory ducts into the duodenum. Trypsin, chemotrypsin, carboxylase act on proteins, the lipolytic enzyme lipase breaks down fats, and the amylolytic enzyme amylase breaks down carbohydrates. The secretion of pancreatic juice is a complex neurohumoral act in which an important role is played by a special hormone - secretin, produced by the mucous membrane of the duodenum and delivered to the gland through the bloodstream. General principle of organization exocrine department pancreas is similar to the salivary glands. Its terminal sections have the form of vesicles, from which intercalary excretory ducts originate, passing into intralobular, and those in turn into interlobular and common excretory duct, which opens together with the hepatic duct on the ventral wall of the duodenum. The sphincter of Oddi is formed for the common hepatopancreatic duct. A special feature is the absence of a striated section and the single-layer epithelial lining throughout. The structural and functional unit of the exocrine part of the pancreas is the acinus, which includes the terminal and intercalary sections. Between the terminal and intercalary sections there are different types relationships, in connection with which the concepts of simple and complex acinus are distinguished. Endocrine part The organ produces the hormone insulin, under the influence of which in the liver and muscle tissue, glucose coming from the blood is converted into the polysaccharide glycogen. The effect of insulin is to lower blood sugar levels. In addition to insulin, the pancreas produces the hormone glucagon. It ensures the conversion of liver glycogen into simple sugars and thereby increases the amount of glucose in the blood. Thus, these hormones have important in the regulation of carbohydrate metabolism in the body. Morphologically, the endocrine part of the pancreas is a collection of special cell groups occurring in the form of islets (islets of Langerhans) in the parenchyma of the gland. Their shape is most often round; islands of irregular angular shapes are less common. There are much more insulocytes in the tail part of the gland than in the head. The stroma of the islets is composed of a delicate reticular network. The islets are usually separated from the surrounding glandular parenchyma by a thin connective tissue membrane. In the human pancreas, using special staining methods, several main types of islet cells were discovered - cells A, B, PP, D, Dg. The bulk - 70% of pancreatic islets - are B cells (produce insulin). They have a cubic or prismatic shape. Their nuclei are large and accept dyes well. The cytoplasm of insulocytes contains granules that are highly soluble in alcohols and insoluble in water. A distinctive feature of B cells is their close contact with the walls of sinusoidal capillaries. These cells form compact strands and are often located along the periphery of the islet. About 20% of all islet cells in humans are acidophilic endocrinocytes A (produce glucagon). These are large, round or angular cells. The cytoplasm contains relatively large granules that are highly soluble in water, but insoluble in alcohols. The cell nuclei are large and pale in color because they contain a small amount of chromatin. The remaining endocrinocytes account for no more than 5%. PP cells secrete pancreatic peptide, D cells secrete somatostatin, D cells secrete VIP hormone. Age-related changes in the human pancreas are clearly detected in the process of development, growth and aging of the body. Thus, the relatively large content of young connective tissue in newborns quickly decreases in the first months and years of life. It's connected with active development in children early age exocrine glandular tissue. The amount of islet tissue also increases after the birth of a child. In an adult, the ratio between glandular parenchyma and connective tissue remains relatively constant. With the onset of old age, exocrine tissue undergoes involution and partially atrophies. The amount of connective tissue in the organ increases significantly, and it takes on the appearance of adipose tissue. Liver- the largest digestive gland in humans. Its weight is 1500-2000 g. The liver is a vital organ that performs the following functions
:1) metabolic
- synthesis of blood proteins (albumin, globulin), blood clotting factors (fibrinogen, prothrombin), cholesterol cholesterol; 2) protective
- chemical protection from harmful substances (detoxification) is carried out using a smooth endoplasmic reticulum; cellular type of protection is performed by hepatic macrophages - Kupffer cells; 3) depositing
- formation and accumulation of glycogen (mainly at night), deposition of a number of vitamins (A, D, C, K, PP); 4) excretory - the formation of bile and its excretion into the duodenum; 5) hematopoietic - occurs during the period of intrauterine development; at the 5-6th week, foci of erythropoiesis, granulocytopoiesis, and megakaryocytopoiesis appear extravascularly. The liver is covered with a dense connective tissue capsule and has a lobular organization. In the human liver there is little connective tissue, so the lobulation is not as noticeable as in the pig liver. In this animal, the lobule is surrounded on all sides by connective tissue and is clearly individualized. In humans, areas of connective tissue are visible only in the tetrad area. The organization of the liver can be distinguished three structural and functional units
: 1) hepatic lobule
- a hexagonal prism through the center of which passes the central vein, collecting blood from the sinusoidal capillaries. Next to the lobule there is a tetrad (portal tract), which consists of an interlobular artery (a branch of the hepatic artery of the systemic circulation), an interlobular vein (a branch of the portal vein), an interlobular bile duct (into which bile flows from the bile capillaries of the lobule) and an interlobular lymphatic vessel. Due to the insignificant amount of connective tissue in the human liver, complex lobules are formed, in which hepatocytes in the composition of hepatic trabeculae, without interruption, pass from one lobule to another; 2) portal lobule and 3) hepatic acinus
. In all three structural and functional units of the liver, there are hepatic beams formed from hepatocytes and sinusoidal capillaries located between the beams. Both lie parallel to each other and radially relative to the central vein. In the wall of the sinusoidal capillary, numerous Kupffer cells (macrophages) are found between the endothelial cells. The space of Disse is located between the hepatic beams and the wall of the sinusoidal capillaries: it contains lipocytes (Ito cells), fibroblasts, processes of Kupffer cells, pericytes, pit cells, mastocytes. The vascular bed of the liver is represented by a blood flow system - the portal vein and hepatic arteries, lobar vessels, segmental, interlobular, intralobular, sinusoidal capillaries. The blood outflow system includes the central veins, sublobular, (collecting) veins, segmental lobar veins enter the vena cava. Chronocard 1. Organizational part with motivation for the topic - 5 min. 2. Programmed control - 10 min. 3. Survey-conversation - 35 min. 4. Explanation of drugs - 10 min. 5. Break - 15 min. 6. Monitoring students’ independent work. Assistance in working with medications - 65 min. 7. Summing up. Checking albums - 10 min. Laboratory time: 3 hours. Related information.The structure of the digestive system
Gastrointestinal tract
Auxiliary organs
Functions of the digestive system
Conclusion