Plan
Introduction
1. The structure of the digestive system
Oral cavity
Small intestine
2. Functions of the gastrointestinal tract
Digestion in the oral cavity, chewing
Functions of saliva
Swallowing
Digestion in the stomach
Principles of regulation of digestive processes
Transition of chyme from the stomach to the intestines.
Digestion in the small intestine
Digestion in the colon
Bibliography
Introduction
During the life of the body, nutrients are continuously consumed, which perform plastic and energy functions.
The body has a constant need for nutrients, which include: amino acids, monosaccharides, glycine and fatty acids. The source of nutrients is various foods consisting of complex proteins, fats and carbohydrates, which during the digestion process are converted into simpler substances that can be absorbed. The process of breaking down complex food substances under the action of enzymes into simple chemical compounds that are absorbed, transported to cells and used by them is called digestion. A sequential chain of processes leading to the breakdown of nutrients into monomers that can be absorbed is called the digestive conveyor. The digestive conveyor is a complex chemical conveyor with a pronounced continuity of food processing processes in all departments. Digestion is the main component of a functional nutrition system.
1. The structure of the digestive system
The digestive system includes organs that perform mechanical and chemical processing of food, absorption of nutrients and water into the blood or lymph, formation and removal of undigested food debris. The digestive system consists of the alimentary canal and digestive glands, details of which are given in Figure 1.
Digestive system
Let us consider schematically the passage of food through the digestive tract. Food first enters the oral cavity, which is limited by the jaws: upper (fixed) and lower (movable).
Oral cavity
The jaws contain teeth - organs used for biting and grinding (chewing) food. An adult has 28-32 teeth.
An adult tooth consists of a soft part - pulp, penetrated by blood vessels and nerve endings. The pulp is surrounded by dentin, a bone-like substance. Dentin makes up the basis of the tooth - it consists of most of the crown (the part of the tooth protruding above the gum), the neck (the part of the tooth located at the border of the gum) and the root (the part of the tooth located deep in the jaw). The crown of the tooth is covered with tooth enamel, the hardest substance of the human body, which serves to protect the tooth from external influences (increased wear, pathogens, excessively cold or hot food, etc. factors).
Teeth according to their purpose are divided into: incisors, canines and molars. The first two types of teeth are used for biting food and have a sharp surface, and the last one is for chewing it and for this purpose it has a wide chewing surface. An adult has 4 canines and an incisor, and the remaining teeth are molars.
In the oral cavity, during the process of chewing food, it is not only crushed, but also mixed with saliva, turning into a food bolus. This mixing in the oral cavity is carried out using the tongue and cheek muscles.
The mucous membrane of the oral cavity contains sensitive nerve endings - receptors, with the help of which it perceives taste, temperature, texture and other qualities of food. Excitation from the receptors is transmitted to the centers of the medulla oblongata. As a result, according to the laws of the reflex, the salivary, gastric and pancreatic glands begin to work sequentially, then the above-described act of chewing and swallowing occurs. Swallowing is an act characterized by pushing food into the pharynx using the tongue and then, as a result of contraction of the muscles of the larynx, into the esophagus.
Pharynx
The pharynx is a funnel-shaped canal lined with mucous membrane. The upper wall of the pharynx is fused with the base of the skull; at the border between the VI and VII cervical vertebrae of the pharynx, narrowing, it passes into the esophagus. Food enters the esophagus from the mouth through the pharynx; in addition, air passes through it, coming from the nasal cavity and from the mouth to the larynx. (The crossover of the digestive and respiratory tracts occurs in the pharynx.)
Esophagus
The esophagus is a cylindrical muscular tube located between the pharynx and the stomach, 22-30 cm long. The esophagus is lined with a mucous membrane; its submucosa contains numerous own glands, the secretion of which moistens food as it passes through the esophagus into the stomach. The movement of the food bolus through the esophagus occurs due to wave-like contractions of its wall - contraction of individual sections alternates with their relaxation.
Stomach
From the esophagus, food enters the stomach. The stomach is a retort-like, extensible organ that is part of the digestive tract and is located between the esophagus and the duodenum. It connects to the esophagus through the cardiac opening, and to the duodenum through the pyloric opening. The inside of the stomach is covered with a mucous membrane, which contains glands that produce mucus, enzymes and hydrochloric acid. The stomach is a reservoir for absorbed food, which is mixed in it and partially digested under the influence of gastric juice. Produced by the gastric glands located in the gastric mucosa, gastric juice contains hydrochloric acid and the enzyme pepsin; These substances take part in the chemical processing of food entering the stomach during the process of digestion. Here, under the influence of gastric juice, proteins are broken down. This, along with the mixing effect exerted on food by the muscular layers of the stomach, turns it into a partially digested semi-liquid mass (chyme), which then enters the duodenum. The mixing of chyme with gastric juice and its subsequent expulsion into the small intestine is carried out by contracting the muscles of the stomach walls.
Small intestine
The small intestine occupies most of the abdominal cavity and is located there in the form of loops. Its length reaches 4.5 m. The small intestine, in turn, is divided into the duodenum, jejunum and ileum. It is here that most of the processes of digestion of food and absorption of its contents take place. The inner surface area of the small intestine is increased by the presence of a large number of finger-like projections called villi. Next to the stomach is the duodenum 12, which is isolated in the small intestine, because the cystic duct of the gallbladder and the pancreatic duct flow into it.
The duodenum is the first of three sections of the small intestine. It starts from the pylorus of the stomach and reaches the jejunum. The duodenum receives bile from the gallbladder (via the common bile duct) and pancreatic juice from the pancreas. In the walls of the duodenum there are a large number of glands that secrete an alkaline secretion rich in mucus, which protects the duodenum from the effects of acidic chyme entering it from the stomach.
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The jejunum is part of the small intestine. The jejunum makes up approximately two-fifths of the entire small intestine. It connects the duodenum and ileum.
The small intestine contains many glands that secrete intestinal juice. This is where the main digestion of food and absorption of nutrients into the lymph and blood occurs. The movement of chyme in the small intestine occurs due to longitudinal and transverse contractions of the muscles of its wall.
From the small intestine, food enters the large intestine, 1.5 m long, which begins with a sac-like protrusion - the cecum, from which a 15 cm appendix extends. It is believed to have some protective functions. The colon is the main part of the large intestine, which includes four sections: the ascending, transverse, descending and sigmoid colon.
The large intestine primarily absorbs water, electrolytes, and fiber and ends at the rectum, which collects undigested food. The rectum is the terminal part of the large intestine (approximately 12 cm long) that starts from the sigmoid colon and ends at the anus. During the act of defecation, feces pass through the rectum. Next, this undigested food is eliminated from the body through the anus (anus).
2. Functions of the gastrointestinal tract
Motor or motor function is carried out by the muscles of the digestive apparatus and includes the processes of chewing in the oral cavity, swallowing, moving food through the digestive tract and removing undigested residues from the body.
The secretory function is the production of digestive juices by glandular cells: saliva, gastric juice, pancreatic juice, intestinal juice, bile. These juices contain enzymes that break down proteins, fats and carbohydrates into simple chemical compounds. Mineral salts, vitamins, and water enter the blood unchanged.
The endocrine function is associated with the formation in the digestive tract of certain hormones that affect the digestive process. These hormones include: gastrin, secretin, cholecystokinin-pancreozymin, motilin and many other hormones that affect the motor and secretory functions of the gastrointestinal tract.
The excretory function of the digestive tract is expressed in the fact that the digestive glands secrete metabolic products into the cavity of the gastrointestinal tract, for example, ammonia, urea, salts of heavy metals, medicinal substances, which are then removed from the body.
Suction function. Absorption is the penetration of various substances through the wall of the gastrointestinal tract into the blood and lymph. The products that are absorbed are mainly the products of hydrolytic breakdown of food - monosaccharides, fatty acids and glycerol, amino acids, etc. Depending on the location of the digestion process, it is divided into intracellular and extracellular.
Intracellular digestion is the hydrolysis of nutrients that enter the cell as a result of phagocytosis (the protective function of the body, expressed in the capture and digestion of foreign particles by special cells - phagocytes) or pinocytosis (the absorption of water and substances dissolved in it by cells). In the human body, intracellular digestion takes place in leukocytes.
Extracellular digestion is divided into distant (cavity) and contact (parietal, membrane).
Distant (cavity) digestion is characterized by the fact that enzymes in the digestive secretions hydrolyze nutrients in the cavities of the gastrointestinal tract. It is called distant because the digestion process itself takes place at a considerable distance from the place of enzyme formation.
Contact (parietal, membrane) digestion is carried out by enzymes fixed on the cell membrane. The structures on which enzymes are fixed are represented in the small intestine by the glycocalyx - a network-like formation of membrane processes - microvilli. Initially, the hydrolysis of nutrients begins in the lumen of the small intestine under the influence of pancreatic enzymes. The resulting oligomers are then hydrolyzed by pancreatic enzymes. Directly at the membrane, the hydrolysis of the formed dimers is carried out by the intestinal enzymes fixed on it. These enzymes are synthesized in enterocytes and transferred to the membranes of their microvilli.
The presence of folds, villi, and microvilli in the mucous membrane of the small intestine increases the internal surface of the intestine by 300-500 times, which ensures hydrolysis and absorption on the huge surface of the small intestine.
Digestion in the oral cavity, chewing
Digestion in the oral cavity is the first link in a complex chain of processes of enzymatic breakdown of nutrients into monomers. The digestive functions of the oral cavity include testing food for edibility, mechanical processing of food and partial chemical processing.
Motor function in the oral cavity begins with the act of chewing. Chewing is a physiological act that ensures the grinding of food substances, wetting them with saliva and the formation of a food bolus. Chewing ensures the quality of mechanical processing of food in the oral cavity. It affects the digestion process in other parts of the digestive tract, changing their secretory and motor functions.
One of the methods for studying the functional state of the masticatory apparatus is masticationography - recording the movements of the lower jaw during chewing. On the recording, which is called a masticationogram, one can distinguish the chewing period, consisting of 5 phases:
1st phase - resting phase;
Phase 2 - introduction of food into the oral cavity;
Phase 3 - indicative chewing or initial chewing function, it corresponds to the process of testing the mechanical properties of food and its initial crushing;
Phase 4 is the main or true phase of chewing, it is characterized by the correct alternation of chewing waves, the amplitude and duration of which is determined by the size of the food portion and its consistency;
Phase 5 - the formation of a food bolus has the form of a wave-like curve with a gradual decrease in the amplitude of the waves.
Chewing is a self-regulatory process, which is based on the functional chewing system. A useful adaptive result of this functional system is a food bolus formed during chewing and prepared for swallowing. A functional chewing system is formed for each chewing period.
When food enters the oral cavity, irritation of the receptors of the mucous membrane occurs.
Excitation from these receptors through the sensory fibers of the lingual (branch of the trigeminal nerve), glossopharyngeal, tympanic chord (branch of the facial nerve) and the upper laryngeal nerve (branch of the vagus nerve) enters the sensory nuclei of these nerves of the medulla oblongata (nucleus of the salitary tract and nucleus of the trigeminal nerve). Next, the excitation along a specific path reaches the specific nuclei of the visual thalamus, where a switching of excitation occurs, after which it enters the cortical part of the oral analyzer. Here, based on the analysis and synthesis of incoming stimuli, a decision is made on the edibility of substances entering the oral cavity.
Inedible food is rejected (spitted out), which is one of the important protective functions of the oral cavity. Edible food remains in the mouth and chewing continues. In this case, the flow of information from the receptors is joined by excitation from the mechanoreceptors of the periodontium - the supporting apparatus of the tooth.
Voluntary contraction of the masticatory muscles is ensured by the participation of the cerebral cortex. Saliva necessarily takes part in the act of chewing and the formation of a bolus of food. Saliva is a mixture of secretions from three pairs of large salivary glands and many small glands located in the oral mucosa. The secretion released from the excretory ducts of the salivary glands is mixed with epithelial cells, food particles, mucus, salivary bodies (leukocytes, lymphocytes), and microorganisms. This saliva, mixed with various inclusions, is called oral fluid. The composition of oral fluid changes depending on the nature of food, the state of the body, as well as under the influence of environmental factors.
The secretion of the salivary glands contains about 99% water and 1% dry residue, which includes anions of chlorides, phosphates, sulfates, bicarbonates, iodites, bromides, and fluorides. Saliva contains sodium, potassium, calcium, magnesium cations, as well as trace elements (iron, copper, nickel, etc.).
Organic substances are represented mainly by proteins. Saliva contains proteins of various origins, including the protein mucous substance mucin. Saliva contains nitrogen-containing components: urea, ammonia, etc.
Functions of saliva
The digestive function of saliva is expressed in the fact that it moistens the food bolus and prepares it for digestion and swallowing, and salivary mucin glues a portion of food into an independent bolus. Over 50 enzymes have been found in saliva.
Despite the fact that food is in the oral cavity for a short time - about 15 seconds, digestion in the oral cavity is of great importance for further processes of food breakdown, since saliva, dissolving nutrients, contributes to the formation of taste sensations and affects appetite.
In the oral cavity, under the influence of salivary enzymes, chemical processing of food begins. The salivary enzyme amylase breaks down polysaccharides (starch, glycogen) into maltose, and the second enzyme, maltase, breaks down maltose into glucose.
The protective function of saliva is expressed in the following:
saliva protects the oral mucosa from drying out, which is especially important for a person who uses speech as a means of communication;
the protein substance of saliva mucin is able to neutralize acids and alkalis;
saliva contains an enzyme-like protein substance lysozyme, which has a bacteriostatic effect and takes part in the regeneration processes of the epithelium of the oral mucosa;
nuclease enzymes contained in saliva are involved in the degradation of viral nucleic acids and thus protect the body from viral infection;
blood clotting enzymes were found in saliva, the activity of which determines the processes of inflammation and regeneration of the oral mucosa;
Substances that prevent blood clotting (antithrombinoplastins and antithrombins) were found in saliva;
Saliva contains a large amount of immunoglobulins, which protects the body from pathogens.
Trophic function of saliva. Saliva is a biological medium that comes into contact with tooth enamel and is its main source of calcium, phosphorus, zinc and other microelements, which is an important factor for the development and preservation of teeth. Excretory function of saliva. Saliva can contain metabolic products - urea, uric acid, some medicinal substances, as well as salts of lead, mercury, etc., which are removed from the body after spitting, due to which the body is freed from harmful waste products.
Salivation occurs through a reflex mechanism. There are conditioned reflex and unconditioned reflex salivation.
Conditioned salivation is triggered by the sight and smell of food, sound stimuli associated with cooking, as well as conversation and memories of food. In this case, visual, auditory, and olfactory receptors are stimulated. Nerve impulses from them enter the cortical section of the corresponding brain analyzer, and then to the cortical representation of the salivation center. From it, excitement goes to the department of the salivary center, the commands of which are sent to the salivary glands.
Unconditionally reflex salivation occurs when food enters the oral cavity. Food irritates the receptors of the mucous membrane. Nerve impulses are transmitted to the salivary center, which is located in the reticular formation of the medulla oblongata and consists of the superior and inferior salivary nuclei.
Exciting impulses for the process of salivation pass through the fibers of the parasympathetic and sympathetic sections of the autonomic nervous system.
Irritation of the parasympathetic fibers that excite the salivary glands leads to the release of a large amount of liquid saliva, which contains many salts and few organic substances.
Irritation of sympathetic fibers causes the release of a small amount of thick, viscous saliva, which contains few salts and many organic substances.
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Humoral factors, which include hormones of the pituitary gland, adrenal glands, thyroid and pancreas, as well as metabolic products, are of great importance in the regulation of salivation.
Saliva secretion occurs in strict accordance with the quality and quantity of nutrients taken. For example, when drinking water, almost no saliva is released. And vice versa: with dry food, saliva is released more abundantly, its consistency is more liquid. When harmful substances enter the oral cavity (for example: too bitter or sour food enters the mouth), a large amount of liquid saliva is released, which washes the oral cavity of these harmful substances, etc. This adaptive nature of salivation is ensured by the central mechanisms regulating the activity of the salivary glands , and these mechanisms are triggered by information coming from the receptors of the oral cavity.
The secretion of saliva is a continuous process. An adult produces about one liter of saliva per day.
Swallowing
After the food bolus has formed, swallowing occurs. This is a reflex process in which there are three phases:
oral (voluntary and involuntary);
pharyngeal (fast involuntary);
esophageal (slow involuntary).
The swallowing cycle lasts about 1 s. By coordinated contractions of the muscles of the tongue and cheeks, the food bolus moves to the root of the tongue, which leads to irritation of the receptors of the soft palate, the root of the tongue and the back wall of the pharynx. Excitation from these receptors through the glossopharyngeal nerves enters the swallowing center located in the medulla oblongata, from which impulses go to the muscles of the oral cavity, larynx, pharynx and esophagus as part of the trigeminal, hypoglossal, glossopharyngeal and vagus nerves. Contraction of the muscles that elevate the soft palate closes the entrance to the nasal cavity, and elevation of the larynx closes the entrance to the respiratory tract. During the act of swallowing, contractions of the esophagus occur, which have the nature of a wave that arises in the upper part and spreads towards the stomach. Motility of the esophagus is regulated mainly by the fibers of the vagus and sympathetic nerves and the nerve formations of the esophagus.
The swallowing center is located next to the breathing center of the medulla oblongata and interacts with it (breathing is delayed when swallowing). From the pharynx, the food bolus enters the esophagus, and then into the stomach.
Digestion in the stomach
The digestive functions of the stomach are:
deposition of chyme (preservation for processing of stomach contents);
mechanical and chemical processing of incoming food;
evacuation of chyme into the intestines.
The excretory function of the stomach is to secrete metabolic products, medicinal substances, and heavy metal salts.
Motor function of the stomach. The motor function of the stomach is carried out due to the contraction of smooth muscles located in the wall of the stomach. The motor function of the stomach ensures the deposition of ingested food in the stomach, its mixing with gastric juice, the movement of stomach contents to the outlet into the intestine and, finally, portioned evacuation of gastric contents into the duodenum.
There are two main types of movement in the stomach - peristaltic and tonic.
Peristaltic movements are carried out by contraction of the circular muscles of the stomach. These movements begin at the greater curvature in the area adjacent to the esophagus, where the cardiac pacemaker is located. The peristaltic wave traveling along the body of the stomach moves a small amount of chyme into the pyloric part, which is adjacent to the mucous membrane and is most exposed to the digestive action of gastric juice. Most of the peristaltic waves are damped in the pyloric region of the stomach. Some of them spread throughout the pyloric region with increasing amplitude (suggesting the presence of a second pacemaker localized in the pyloric region of the stomach), which leads to pronounced peristaltic contractions of this region, increased pressure and part of the stomach contents passes into the duodenum.
The second type of stomach contraction is tonic contraction. They arise due to changes in muscle tone, which leads to a decrease in the volume of the stomach and an increase in pressure in it. Tonic contractions help to mix the contents of the stomach and soak it with gastric juice, which greatly facilitates the enzymatic digestion of food gruel.
The intestinal phase of gastric secretion begins from the moment chyme enters the duodenum. Chyme irritates the receptors of the intestinal mucosa and reflexively changes the intensity of gastric secretion. In addition, local hormones (secretin, cholecystokinin-pancreozymin) influence gastric juice secretion during this phase, the production of which is stimulated by acidic gastric chyme entering the duodenum.
Principles of regulation of digestive processes
The activity of the digestive system is regulated by nervous and humoral mechanisms.
Juice secretion from the digestive glands is carried out conditionally-reflexively and unconditionally-reflexively. Such influences are especially pronounced in the upper part of the digestive tract. As you move away from it, the participation of reflexes in the regulation of digestive functions decreases and the importance of humoral mechanisms increases. In the small and large intestines, the role of local regulatory mechanisms is especially important - local mechanical and chemical irritation increases the activity of the intestine at the site of action of the stimulus. Consequently, there is an unequal distribution of nervous, humoral and local regulatory mechanisms in the digestive tract. Local mechanical and chemical stimuli influence through peripheral reflexes and through hormones of the digestive tract. Chemical stimulants of nerve endings in the gastrointestinal tract are: acids, alkalis, products of hydrolysis of nutrients. Entering the blood, these substances are carried by its current to the digestive glands and stimulate them.
The role of hormones produced in the endocrine cells of the mucous membrane of the stomach, duodenum, jejunum, and pancreas is especially important in the humoral regulation of the activity of the digestive organs.
The main hormones and the effects that their action leads to: Gastrin - increased secretion of the stomach and pancreas, hypertrophy of the gastric mucosa, increased motility of the stomach, small intestine and gall bladder.
Secretin - increases the secretion of bicarbonates by the pancreas, inhibits the secretion of hydrochloric acid in the stomach.
CCK-PZ (cholecystokinin-pancreozymin) - increased contraction of the gallbladder and bile secretion, secretion of enzymes by the pancreas, inhibition of the secretion of hydrochloric acid in the stomach, increased secretion of pepsin in it, increased motility of the small intestine.
MOTILIN - increased motility of the stomach and small intestine, increased secretion of pepsin by the stomach.
Villikinin - enhances the motility of the villi of the small intestine, etc.
From this we can conclude about the important role of gastrointestinal hormones. They influence the functions of the entire gastrointestinal tract, namely: motility, the secretion of water, electrolytes and enzymes, the absorption of water, electrolytes and nutrients, and the functional activity of endocrine cells of the gastrointestinal tract. In addition, they affect metabolism, the endocrine and cardiovascular systems, and the central nervous system. Some hormones are found in various brain structures.
Stimulate gastric secretion: the hormone gastrin is formed in the gastric mucosa; histamine - found in food substances and formed in the gastric mucosa; protein digestion products; extractives of meat and vegetables; secretin - is formed in the intestinal mucosa (inhibits the secretion of hydrochloric acid, but enhances the secretion of pepsinogens); cholecystokinin-pancreozymin enhances the secretion of pepsins (inhibits the secretion of hydrochloric acid) and other substances.
Inhibit gastric secretion: fat hydrolysis products and other substances.
Transition of chyme from the stomach to the intestines.
The rate of evacuation of stomach contents into the intestine is influenced by many factors:
Consistency of food - the contents of the stomach pass into the intestine when its consistency becomes liquid or semi-liquid. Liquids begin to pass into the intestine immediately after they enter the stomach.
Nature of food - carbohydrate foods are evacuated faster than protein foods, fatty foods linger in the stomach for 8-10 hours.
The degree of filling of the stomach and duodenum.
Motor function of the stomach and duodenum.
Hormones: secretin, cholecystokinin-pancreozymin - inhibit gastric motility and the rate of evacuation of its contents.
Enterogastric reflex - is expressed in inhibition of the motor activity of the stomach when chyme enters the duodenum.
Digestion in the small intestine
Contractions of the small intestine are carried out as a result of coordinated movements of the longitudinal (outer) and transverse (inner) layers of smooth muscle cells. According to their functional characteristics, abbreviations are divided into two groups:
1) local - provide rubbing and mixing of the contents of the small intestine;
There are several types of abbreviations:
pendulum-shaped,
rhythmic segmentation,
peristaltic,
tonic.
Pendulum-like contractions are caused by sequential contraction of the circular and longitudinal muscles of the intestine. Consecutive changes in the length and diameter of the intestine lead to the movement of food gruel in one direction or the other (like a pendulum). Pendulum-like contractions help mix chyme with digestive juices.
Rhythmic segmentation is ensured by contraction of the circular muscles, as a result of which the resulting transverse interceptions divide the intestine into small segments. Rhythmic segmentation helps to grind the chyme and mix it with digestive juices. Peristaltic contractions are caused by the simultaneous contraction of the longitudinal and annular layers of muscles. In this case, the circular muscles of the upper section of the intestine contract and the chyme is pushed into the simultaneously expanded lower section of the intestine due to the contraction of the longitudinal muscles. Thus, peristaltic contractions ensure the movement of chyme through the intestine.
Tonic contractions have a low speed and may not even spread at all, but only narrow the intestinal lumen over a small area.
The small intestine and, first of all, its initial section, the duodenum, are the main digestive section of the entire gastrointestinal tract. It is in the small intestine that nutrients are converted into compounds that can be absorbed from the intestine into the blood and lymph. Digestion in the small intestine occurs in its cavity - cavitary digestion, and then continues in the zone of the intestinal epithelium with the help of enzymes fixed on its microvilli and folds - parietal digestion. Folds, villi and microvilli of the small intestine increase the internal surface of the intestine by 300-500 times.
The pancreas plays a particularly important role in the hydrolysis of nutrients in the duodenum. Pancreatic juice is rich in enzymes that break down proteins, fats and carbohydrates.
Amylase in pancreatic juice converts carbohydrates into monosaccharides. Pancreatic lipase is very active due to the emulsifying effect of bile on fats. Ribonuclease in pancreatic juice breaks down ribonucleic acid into nucleotides.
Intestinal juice is secreted by the glands of the entire mucous membrane of the small intestine. More than 20 different enzymes have been found in intestinal juice, the main ones being: enterokinase, peptidases, alkaline phosphatase, nuclease, lipase, phospholipase, amylase, lactase, sucrase. Under natural conditions, these enzymes carry out parietal digestion.
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The motor activity of the small intestine is regulated by nervous and humoral mechanisms. The act of eating briefly inhibits and then enhances the motility of the small intestine. The motor activity of the small intestine largely depends on the physical and chemical properties of chyme: roughage and fats increase its activity.
Humoral substances have an effect directly on the muscle cells of the intestine, and through receptors on the neurons of the nervous system. Strengthen the motility of the small intestine: histamine, gastrin, motilin, alkalis, acids, salts, etc.
The initial secretion of the pancreas is caused by conditioned reflex signals (the sight, smell of food, etc.). Inhibition of pancreatic secretion is observed during sleep, during pain reactions, and during intense physical and mental work.
The leading role in the humoral regulation of pancreatic secretion belongs to hormones. The hormone secretin causes the secretion of large amounts of pancreatic juice, rich in bicarbonates but poor in enzymes. The hormone cholecystokinin-pancreozymin also enhances the secretion of the pancreas, and the secreted juice is rich in enzymes. Strengthens the secretion of the pancreas: gastrin, serotonin, insulin. Inhibit the secretion of pancreatic juice: glucagon, calcitonin, GIP, PP.
The secretion of intestinal glands increases during food intake, with local mechanical and chemical irritation of the intestine and under the influence of certain intestinal hormones.
Chemical stimulants of secretion of the small intestine are products of the digestion of proteins, fats, etc.
Digestion in the colon
The motor activity of the colon ensures the accumulation of intestinal contents, the absorption of a number of substances from it, mainly water, the formation of feces and their removal from the intestine. The following types of contractions of the colon are distinguished:
tonic,
pendulum-shaped,
rhythmic segmentation,
peristaltic contractions,
antiperistaltic contractions (promote the absorption of water and the formation of feces),
The regulation of motor activity of the colon is carried out by the autonomic nervous system, and sympathetic nerve fibers inhibit motor activity, while parasympathetic nerve fibers enhance it. The motility of the colon is inhibited by: serotonin, adrenaline, glucagon, as well as irritation of the mechanoreceptors of the rectum. Local mechanical and chemical irritations are of great importance in stimulating colon motility.
The secretory activity of the colon is weakly expressed. The glands of the colon mucosa secrete a small amount of juice, rich in mucous substances, but poor in enzymes. The following enzymes are found in small quantities in the juice of the colon:
cathepsin,
peptidases,
amylase and nucleases.
The microflora of the colon is of great importance in the life of the body and the functions of the digestive tract. Normal microflora of the gastrointestinal tract is a necessary condition for the life of the body. The stomach contains little microflora, much more in the small intestine and especially much in the large intestine.
The importance of intestinal microflora lies in the fact that it participates in the final decomposition of undigested food residues. Microflora is involved in the decomposition of enzymes and other biologically active substances. Normal microflora suppresses pathogenic microorganisms and prevents infection of the body. Bacterial enzymes break down fiber fibers that are undigested in the small intestine. Intestinal flora synthesizes vitamin K and B vitamins, as well as other substances needed by the body. With the participation of intestinal microflora, the body exchanges proteins, bile and fatty acids and cholesterol.
Juice secretion in the large intestine is determined by local mechanisms; with its mechanical irritation, secretion increases 8-10 times. Absorption is understood as a set of processes that ensure the transfer of various substances into the blood and lymph from the digestive tract.
A distinction is made between the transport of macro- and micromolecules. Transport of macromolecules and their aggregates is carried out using phagocytosis and pinocytosis. A certain amount of substances can be transported through intercellular spaces. Due to these mechanisms, a small amount of proteins (antibodies, enzymes, etc.) and some bacteria penetrate from the intestinal cavity into the internal environment.
Mainly micromolecules are transported from the gastrointestinal tract: nutrient monomers and ions. This transport is divided into:
active transport;
passive transport;
facilitated diffusion.
Active transport of substances is the transfer of substances across membranes with the expenditure of energy and with the participation of special transport systems: mobile carriers and transport membrane channels.
Passive transport occurs without energy consumption and includes: diffusion and filtration. The driving force for the diffusion of solute particles is the presence of a change in their concentration.
Filtration refers to the process of transferring a solution through a porous membrane under the influence of hydrostatic pressure.
Facilitated diffusion, like simple diffusion, occurs without the expenditure of energy to change the concentration of a dissolved substance. However, facilitated diffusion is a faster process and is carried out with the participation of a carrier.
Absorption of vital substances in various parts of the digestive tract.
Absorption occurs throughout the digestive tract, but its intensity varies in different sections. In the oral cavity, absorption is practically absent due to the short-term presence of substances in it and the absence of monomeric (simple) hydrolysis products. However, the oral mucosa is permeable to sodium, potassium, some amino acids, alcohol, and some drugs.
In the stomach, the intensity of absorption is also low. Here water and mineral salts dissolved in it are absorbed; in addition, weak solutions of alcohol, glucose and small amounts of amino acids are absorbed in the stomach.
In the duodenum, the intensity of absorption is greater than in the stomach, but even here it is relatively small. The main absorption process occurs in the small intestine. The motility of the small intestine is of great importance in the absorption process, since it not only promotes the hydrolysis of substances (by changing the parietal layer of chyme), but also the absorption of its products. During absorption in the small intestine, contractions of the villi are of particular importance. Stimulators of villi contraction are products of hydrolysis of nutrients (peptides, amino acids, glucose, food extractives), as well as some components of the secretions of the digestive glands, for example, bile acids. Humoral factors also enhance the movements of the villi, for example, the hormone villikinin, which is formed in the mucous membrane of the duodenum and in the jejunum.
Absorption in the colon is negligible under normal conditions. Here, mainly the absorption of water and the formation of feces occurs. In small quantities, glucose, amino acids, and other easily absorbed substances can be absorbed in the colon. On this basis, nutritional enemas are used, i.e., the introduction of easily digestible nutrients into the rectum.
Proteins, after hydrolysis to amino acids, are absorbed in the intestine. Absorption of different amino acids in different parts of the small intestine occurs at different rates. The absorption of amino acids from the intestinal cavity is carried out actively with the participation of the transporter and with the expenditure of energy. Then the amino acids are transported into the intercellular fluid through the mechanism of facilitated diffusion. Amino acids absorbed into the blood travel through the portal vein system to the liver, where they undergo various transformations. A significant portion of amino acids is used for protein synthesis. Amino acids carried by the bloodstream throughout the body serve as the starting material for the construction of various tissue proteins, hormones, enzymes, hemoglobin and other protein substances. Some amino acids are used as a source of energy.
The intensity of amino acid absorption depends on age (it is more intense at a young age), on the level of protein metabolism in the body, on the content of free amino acids in the blood, on nervous and humoral influences.
Carbohydrates are absorbed mainly in the small intestine in the form of monosaccharides. Hexoses (glucose, galactose, etc.) are absorbed at the highest speed; pentoses are absorbed more slowly. The absorption of glucose and galactose is the result of their active transport through the membranes of the intestinal walls. The transport of glucose and other monosaccharides is activated by the transport of sodium ions across membranes.
Absorption of different monosaccharides in different parts of the small intestine occurs at different rates and depends on the hydrolysis of sugars, the concentration of the resulting monomers, and on the characteristics of the transport systems of intestinal epithelial cells.
Various factors, especially the endocrine glands, are involved in the regulation of carbohydrate absorption in the small intestine. Glucose absorption is enhanced by hormones of the adrenal glands, pituitary gland, thyroid and pancreas. Monosaccharides absorbed in the intestines enter the liver. Here, a significant part of them is retained and converted into glycogen. Some of the glucose enters the general bloodstream and is distributed throughout the body and used as a source of energy. Some of the glucose is converted into triglycerides and deposited in fat depots (fat storage organs - liver, subcutaneous fat layer, etc.). Under the action of pancreatic lipase in the cavity of the small intestine, diglycerides are formed from complex fats, and then monoglycerides and fatty acids. Intestinal lipase completes the hydrolysis of lipids. Monoglycerides and fatty acids with the participation of bile salts pass into intestinal epithelial cells through membranes using active transport. Complex fats are broken down in intestinal epithelial cells. Triglycerides, cholesterol, phospholipids and globulins form chylomicrons - tiny fat particles enclosed in a lipoprotein shell. Chylomicrons leave the epithelial cells through the membranes, pass into the connective tissue spaces of the villi, from there they pass through the contractions of the villi into its central lymphatic vessel, thus, the main amount of fat is absorbed into the lymph. Under normal conditions, a small amount of fat enters the blood.
Parasympathetic influences increase, and sympathetic influences slow down the absorption of fats. The absorption of fats is enhanced by the hormones of the adrenal cortex, thyroid gland and pituitary gland, as well as the hormones of the duodenum - secretin and cholecystokinin - pancreozymin.
Fats absorbed into the lymph and blood enter the general bloodstream. The main amount of lipids is deposited in fat depots, from which fats are used for energy purposes.
The gastrointestinal tract takes an active part in the water-salt metabolism of the body. Water enters the gastrointestinal tract as part of food and liquids, and the secretions of the digestive glands. The main amount of water is absorbed into the blood, a small amount into the lymph. Absorption of water begins in the stomach, but it occurs most intensively in the small intestine. Actively absorbed solutes by epithelial cells “draw” water with them. The decisive role in the transfer of water belongs to sodium and chlorine ions. Therefore, all factors affecting the transport of these ions also affect the absorption of water. Water absorption is associated with the transport of sugars and amino acids. Excluding bile from digestion slows down the absorption of water from the small intestine. Inhibition of the central nervous system (for example, during sleep) slows down water absorption.
Sodium is intensively absorbed in the small intestine. Sodium ions are transferred from the cavity of the small intestine into the blood through intestinal epithelial cells and through intercellular channels. The entry of sodium ions into the epithelial cell occurs passively (without energy consumption) due to the difference in concentrations. From epithelial cells through membranes, sodium ions are actively transported into the intercellular fluid, blood and lymph.
In the small intestine, the transfer of sodium and chlorine ions occurs simultaneously and according to the same principles; in the large intestine, absorbed sodium ions are exchanged for potassium ions. With a decrease in sodium content in the body, its absorption in the intestine increases sharply. The absorption of sodium ions is enhanced by the hormones of the pituitary gland and adrenal glands, and inhibited by gastrin, secretin and cholecystokinin-pancreozymin.
Absorption of potassium ions occurs mainly in the small intestine. Absorption of chlorine ions occurs in the stomach, and is most active in the ileum.
Of the divalent cations absorbed in the intestine, the most important are calcium, magnesium, zinc, copper and iron ions. Calcium is absorbed along the entire length of the gastrointestinal tract, but its most intense absorption occurs in the duodenum and the initial part of the small intestine. In the same section of the intestine, magnesium, zinc and iron ions are absorbed. Copper absorption occurs primarily in the stomach. Bile has a stimulating effect on calcium absorption.
Water-soluble vitamins can be absorbed by diffusion (vitamin C, riboflavin). Vitamin B2 is absorbed in the ileum. The absorption of fat-soluble vitamins (A, D, E, K) is closely related to the absorption of fats.
Bibliography
Great Medical Encyclopedia Vasilenko V. Kh., Galperin E. I. et al., Moscow, “Soviet Encyclopedia”, 1974.
Disease of the digestive system Daikhovsky Ya. I., Moscow, Medgiz, 1961.
Diseases of the liver and biliary tract Tareev E. M., Moscow, Medgiz, 1961.
Treatment of diseases of the digestive system Gazhev B. N., Vinogradova T. A., St. Petersburg, “MiM-Express”, 1996.
Directory for paramedic Bazhanov N.N., Volkov B.P. et al., Moscow, “Medicine”, 1993.
Light-optical micrograph of the area of transition of the esophagus to the stomach Artery Muscular plate of the mucosa Submucosa of the esophagus Vein Adipocytes Submucosa of the stomach Muscular membrane Cardiac glands of the esophagus Lamina propria of the esophagus mucosa Zone of transition of the esophagus to the stomach Single-layer prismatic. epithelium of the stomach Gastric pits Cardiac glands of the stomach Multilayer neocorns. esophageal epithelium
Features of the relief of the mucous membrane of the small intestine. Arrows indicate the displacement of cells of the epithelial layer Villi Epithelium lamina propria Muscular lamina Exfoliation of epithelial cells from the upper edge of the villus into the intestinal lumen Crypts (glands of Lieberkühn)
Electron micrograph of the epithelial lining of the small intestine. Goblet cell surrounded by columnar epithelial cells with a striated border Granular endoplasmic reticulum Microvilli Goblet cell Golgi complex Columnar epithelial cell with a border Granules of mucous secretion Columnar epithelial cell with a striated border
Semi-schematic reproduction of the relief of the mucous membrane of the large intestine Lymphatic nodule with a germinative center Muscular lamina of the mucous membrane Goblet cells Proper lamina of the mucous membrane Crypts (glands of Lieberkühn Mucous membrane Epithelium with a striated border Blood vessels Submucosa
Scheme of topographic zones and features of the micromorphology of the rectum External hemorrhoidal plexus Circular layer of the muscular layer Pectinate line External anal sphincter Anal gland Zone of epithelial change Internal hemorrhoidal plexus Longitudinal layer of the muscular layer Internal anal sphincter Pelvic floor muscle Pillars of Morgagni Anal canal Skin of the anus Submucosa Fibroelastic septum
Liver functions: 1. detoxification 2. protective 3. takes part in: a) protein metabolism - synthesis of blood proteins b) carbohydrate metabolism - glycogen synthesis c) fat metabolism - production of bile d) vitamin metabolism - accumulation of vitamins A, D, E, To d) metabolism of cholesterol, iron 4. hematopoietic organ (in the embryonic period!) 5. endocrine - the hormone somatomedin
Structure The structural and functional unit of the liver, according to classical concepts, is the hepatic lobule. The liver lobules are shaped like hexagonal prisms. In the center of the lobules is the hepatic vein, along the periphery there are triads (interlobular arteries, veins, bile ducts), which are located in poorly developed connective tissue. The liver lobules are built from hepatic beams, which run in a radial direction - from the periphery to the center of the lobule. The hepatic beams consist of two rows of hepatocytes. Sinusoidal hemocapillaries pass between the beams, and bile capillaries pass inside the beams.
Features of the blood supply to the liver. 1) receives blood from two vessels: a) the hepatic artery - blood rich in oxygen, b) the portal vein - blood rich in substances that are absorbed in the intestines; 2) perilobular veins form sphincters; 3) intralobular capillaries are sinusoidal type, lined with endothelium between which there are stellate macrophages (Kupffer cells), the blood is mixed and flows slowly; 4) central vein - muscleless type; 5) the blood that leaves the liver differs in chemical composition from the blood that comes to the gate of the liver.
Biliary tract. Bile is formed in the biliary poles of hepatocytes, then enters the bile capillaries (go inside the hepatic beams), then into the cholangioles, interlobular bile ducts, right and left hepatic ducts, common hepatic duct, cystic duct, common bile duct.
Pancreas. Functions: 1. Exocrine - pancreatic juice is produced (enzymes trypsin, lipase, amylase, etc.) - which cause the breakdown of proteins, fats and carbohydrates. 2.Endocrine - produces hormones that regulate carbohydrate, protein and fat metabolism.
The structure of the exocrine part is a complex, alveolar, branched, merocrine gland with a protein secretion. The structural and functional unit of the exocrine part of the pancreas is the pancreatic acinus, consisting of the terminal secretory section and the intercalary duct. The secretory department consists of 8-12 large pancreatocytes (acinocytes) having a conical shape. Their basal pole contains a highly developed granular endoplasmic reticulum and is stained basophilically - this is a homogeneous zone. The apical pole contains zymogen granules (enzymes in inactive form), which are oxyphilic stained - this is the zymogenic zone. In the center of the acinus there are centroacinous cells, the cells of the intercalary region. Excretory ducts: intercalary interacinous intralobular interlobular common excretory duct.
Endocrine part The structural part is represented by the pancreatic islets of Langerhans, which have a round or oval shape. On the outside, the islets are covered with a connective tissue capsule containing sinusoidal capillaries. The islands are located between the acini, most in the caudal part of the gland.
P/n Insulocytes Secreted hormones Effect 1. B-cells (70-75%) insulin Reduced blood glucose levels 2. A-cells (20-25%) glucagon Increased blood glucose levels 3. D-cells (5-10 %) somatostatin Inhibits the secretion of insulin and glucagon, as well as pancreatic juice 4.F-cells Pancreatic polypeptide Stimulates the secretion of gastric and pancreatic juice
Lesson on the topic: The importance of digestion. Digestive system: digestive tract, digestive glands.
The purpose of the lesson: Give an idea of the importance of nutrition and digestion. Ensure the acquisition of knowledge about the structure and functions of the digestive tract and digestive glands.
Tasks:
Educational:
Development of knowledge about the structure and functions of the digestive system;
Development of skills to analyze, establish relationships between structure and function; improve the ability to highlight the main thing;
Provide hygiene education to students.
Educational:
Teach how to apply the acquired knowledge about the digestion process in everyday life;
-development of logical thinking;
- continue to develop the skills to compare objects, work with drawings and diagrams;
Teach to analyze and systematize information, process it creatively.
Educational:
-development of interest in knowledge, motivation and culture of mental work;
-development of a culture of communication and reflexive personality traits,
-creating conditions for emotionally pleasant intellectual activity of students, with high cognitive activity of students
-show the significance of biological knowledge;
- carry out hygienic education of students.
Lesson type: learning new material, repeating and consolidating what has been learned.
Forms of organization of educational activities : oquestioning at the board, frontal questioning, conversation, working with computer presentation slides, watching a video, differentiated homework.
Lesson plan:
Organizational moment.2 min.
Homework survey. 12 min.
Problematic task. 3 min.
Learning new material. 18 min.
Fixing the material. 3 min.
Summarizing. Homework. 2 minutes.
Lesson summary.
I. Hello guys! Let's smile, clap our hands, and have a positive attitude towards the lesson.
II. In the last lesson, we began to study a large section. Today we will continue to study it.
Homework survey.
Several students work with cards. (Annex 1).
Those interested answer the following questions at the board:
What importance do nutrients have for the body?
What substances should be in our food?
What organic compounds does the body receive from food?
What are the functions of proteins and what organic compounds do they break down into?
What are the functions of fats and what organic compounds do they break down into?
What are the functions of carbohydrates and what organic compounds do they break down into?
What is the role of water in the body?
III. We looked at the importance of nutrients to find out what the topic is today
Let's look at the historical background...
… Even in ancient India they used the “rice test”. At trial, to decide the question of guilt or innocence, the defendant was offered to eat dry rice. If he eats it, then he is not guilty, if not, then he is guilty.
What do you think this test was based on? Knowledge about which organ systems helped to find out the truth?
Students: Oh, the digestive organs.
That's right, today in class we will learn about sin the area of digestion. digestive system: digestive tract, digestive glands." We will return to the rice problem a little later.
Students write down the topic of the lesson.
Who can tell what the purpose of our lesson is?
Students' guess.
Summarizing the answers and formulating the goal.
The purpose of our lesson: to learn about the meaning of digestion, the structure and functions of the digestive tract and digestive glands.
Did everyone have breakfast today? Why do we eat? what digestive organs do you know?
Students' answers.
We will now look at how food is converted into energy and building materials.
IV. Digestion- a process that ensures the breakdown of complex organic substances and their entry into the blood and lymph.
The role of the digestive organs is to make nutrients available to the cells of our body.
Students draw diagrams in their notebooks.
Functions of the digestive system
Mechanical Chemical Intake, grinding of food Suction Splitting of food
under the influence of enzymes
Composition of the digestive system
Alimentary canal Digestive glands
Oral cavity Salivary glands
Pharynx Liver
Esophagus Pancreas
Stomach Intestinal glands
Small intestine
Colon
Composition of the walls of the digestive canal
External Medium Internal
(connective tissue) (muscle tissue) (epithelial tissue)
Digestive canal. Watch the video.
The oral cavity is closed on the outside by the muscles of the cheeks and lips. Inside there are jaws, gums, teeth, pharynx, palate, and tongue. The space between the cheeks, lips and oral cavity is called the vestibule. At the bottom there is a tongue - it mixes food and pushes it into the throat. The ducts of the salivary glands open into the oral cavity. (Slide No. 7).
The pharynx is formed by striated muscle tissue and is located in front of the cervical vertebrae. It is divided into 2 sections, one connects to the larynx, the other to the esophagus. (Slide No. 9).
The esophagus is a hollow muscular organ 25 cm long. The mucous membrane is formed by multilayered epithelium. (Slide number 10).
The stomach is a hollow muscular organ located in the upper part of the abdominal cavity, just below the diaphragm. At the junction with the esophagus and duodenum there are circular muscles (sphincters). The place of transition to the duodenum is the pylorus (Slide No. 11).
The small intestine is about 5 m long. It is divided into: duodenum (25-30 cm), jejunum, ileum. The walls consist of 2 muscle layers - longitudinal and transverse, their rhythmic contraction is called intestinal peristalsis. Here the process of digestion of food is completed. Numerous villi absorb nutrients. (Slide No. 12).
The large intestine is 1.3 m long. Water is absorbed and fiber is broken down in it.
Consists of:
1. The cecum, an appendix extends from it.
2. Colon (ascending, transverse, descending, sigmoid).
Liver(1.5 kg., bile, ducts empty into the duodenum, barrier role, glucose storage, activates digestive enzymes). Slide number 19.
Pancreasgland (pancreatic juice, ducts empty into the duodenum, insulin) Slide number 16
Intestinalglands (enzymes that can break down food substances and secrete mucus). Slide number 18.
Glands of the mucosastomach (transparent viscous odorless secretion, pepsin proteins, NSIbactericidal effect). Slide number 16.
V. Today in class we learned about the structure of the digestive tract and the digestive glands.
Oral survey of students.
Name the organs of the digestive tract?
Name the digestive glands?
Briefly describe the properties of enzymes?
What main groups of enzymes do you know?
VI. Lesson summary: So, our lesson is coming to an end. What did you know before the lesson? What did you learn in today's lesson?
Students' answers.
Homework §41 §43 §44. Fill out the table p. 196 – 197.
You worked hard today, let's clap your hands for it. Goodbye!
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