The human and animal body is an open thermodynamic system that constantly exchanges matter and energy with the environment. The body requires replenishment of energy and building materials. It is necessary for work, temperature maintenance, tissue repair. Man and animals receive these materials from the environment in the form of animal or plant origin. In foods, in different proportions, nutrients are proteins, fats. Nutrients are large polymer molecules. Food also contains water, mineral salts, vitamins. And although these substances are not a source of energy, they are very important components for life. Nutrients from foods cannot be absorbed immediately; this requires the processing of nutrients in the gastrointestinal tract so that the digested products can be used.
The length of the digestive tract is approximately 9 m. The digestive system includes the oral cavity, pharynx, esophagus, stomach, small and large intestine, rectum and anal canal. There are additional organs of the gastrointestinal tract - these include the tongue, teeth, salivary glands, pancreas, liver and gallbladder.
The alimentary canal is composed of four layers or membranes.
- Mucous
- Submucosa
- Muscular
- Serous
Each shell performs its own function.
Mucous membrane surrounds the lumen of the alimentary canal and is the main suction surface and secretory surface. The mucous membrane is covered with a columnar epithelium, which is located on its own plate. There are numerous limf in the plate. Nodules and they perform a protective function. Outside, the layer of smooth muscles is the muscle plate of the mucous membrane. Due to the contraction of these muscles, the mucous membrane forms folds. The mucosa also contains goblet cells that produce mucus.
Submucosa represented by a layer of connective tissue with a large number of blood vessels. The submucosa contains glands and the submucous nerve plexus - Yeissner's plexus... The submucosal layer provides nutrition to the mucous membrane and autonomic innervation of the glands, smooth muscles of the muscle plate.
Muscular membrane... Consists of 2 layers of smooth muscle. Internal - circular and external - longitudinal. Muscles are arranged in bundles. The muscular membrane is designed to perform a motor function, for mechanical processing of food and for moving food along the alimentary canal. The muscular membrane contains the second plexus - Auerbach. The fibers of the sympathetic and parasympathetic nerves end on the plexus cells in the gastrointestinal tract. In the composition there are sensitive cells - Doggel's cells, there are motor cells - of the first type, there are inhibitory neurons. The set of elements of the gastrointestinal tract is an integral part of the autonomic nervous system.
Outer serous membrane- connective tissue and squamous epithelium.
In general, the gastrointestinal tract is intended for the course of digestion processes and the basis of digestion is the hydrolytic process of splitting large molecules into simpler compounds that can be obtained by blood and tissue fluid and delivered to the site. The functioning of the digestive system resembles that of a disassembly conveyor.
Digestion stages.
- Food absorption... It includes absorbing food into the mouth, chewing food into smaller pieces, moisturizing, forming a food lump, and swallowing
- Digestion of food... In the course of it, further processing and enzymatic breakdown of nutrients are carried out, while proteins are cleaved by proteases and amino dipeptides and amino acids. Carbohydrates are broken down by amylase to monosaccharides, and fats are broken down by lipases and esterases to monoglycerin and fatty acids.
- The formed simple connections undergo the following process - absorption of products... But not only the breakdown products of nutrients are absorbed, but water, electrolytes, vitamins are absorbed. During absorption, substances are transferred into the blood and lymph. There is a chemical process in the digestive tract, as in any production by-products and wastes arise, which can often be poisonous.
- Excretion- are removed from the body in the form of feces. For the implementation of digestion processes, the digestive system performs motor, secretory, absorption and excretory functions.
The digestive tract is involved in water-salt metabolism, a number of hormones are produced in it - endocrine function, has a protective immunological function.
Digestion types- are subdivided depending on the intake of hydrolytic enzymes and are divided into
- Own - enzymes of the macroorganism
- Symbiotic - due to enzymes that bacteria and protozoa that live in the gastrointestinal tract give us
- Autolytic digestion - due to enzymes that are contained in the food itself.
Depending on localization the process of hydrolysis of nutrients, digestion is divided into
1. Intracellular
2. Extracellular
Distant or cavity
Contact or parietal
Cavity digestion will occur in the lumen of the gastrointestinal tract, by enzymes, on the membrane of the microvilli of the intestinal epithelium cells. The microvilli are coated with a layer of polysaccharides and form a large catalytic surface for fast degradation and fast absorption.
The value of the work of I.P. Pavlova.
Attempts to study the processes of digestion begin already in the 18th century, for example Reamur tried to get gastric juice by placing a sponge tied on a string into the stomach and received digestive juice. There were attempts to implant glass or metal tubes into the ducts of the glands, but they quickly fell out and an infection was added. The first clinical observations in humans were carried out with a stomach wound. In 1842 the Moscow surgeon Basov put a fistula on the stomach and closed with a stopper outside the digestion process. This operation made it possible to obtain gastric juice, but the disadvantage was that it was mixed with food. Later, in Pavlov's laboratory, this operation was supplemented by an incision of the esophagus and neck. Such an experience is called the experience of sham feeding, and after feeding, the chewed food is digested.
English physiologist Heidenhain suggested isolating a small ventricle from a large one, this made it possible to obtain pure gastric juice unmixed with food, but the disadvantage of the operation - the incision - perpendicular to the greater curvature - it crossed the nerve - the vagus. Only humoral factors could act on the small ventricle.
Pavlov suggested doing parallel to the greater curvature, the vagus was not cut, it reflected the entire course of digestion in the stomach with the participation of both nervous and humoral factors. I.P. Pavlov set the task of studying the function of the digestive tract as close as possible to normal conditions, and Pavlov develops methods of physiological surgery by carrying out a variety of operations on animals, which later helped in the study of digestion. Basically, operations were aimed at imposing fistulas.
Fistula- artificial communication of the cavity of the organ or duct of the gland with the environment to obtain the contents and after the operation the animal was recovering. This was followed by recovery, long-term nutrition.
In physiology, poignant experiences- once under anesthesia and chronic experience- in conditions as close to normal as possible - with anesthesia, without pain factors - this gives a more complete picture of the function. Pavlov develops fistulas of the salivary glands, small ventricular surgery, esophagotomy, gallbladder and pancreatic duct.
First merit Pavlova in digestion consists in the development of chronic experiment experiments. Further, Ivan Petrovich Pavlov established the dependence of the quality and quantity of secrets on the type of food stimulus.
Thirdly- the adaptability of the glands to nutritional conditions. Pavlov showed the leading role of the nervous mechanism in the regulation of the digestive glands. Pavlov's works in the field of digestion were summarized in his book "On the work of the most important digestive glands" In 1904, Pavlov was awarded the Nobel Prize. In 1912, the University of England, Newton, Byron elected Pavlov as an honorary doctor of the University of Cambridge, and at the initiation ceremony there was such an episode when Cambridge students released a toy dog with numerous fistulas.
Physiology of salivation.
Saliva is formed by three pairs of salivary glands - the parotid, located between the jaw and the ear, the submandibular, located under the lower jaw, and the sublingual. Small salivary glands - work constantly, unlike large ones.
Parotid gland consists only of serous cells with a watery secretion. Submandibular and sublingual glands allocate a mixed secret, tk. include both serous and mucous cells. The secretory unit of the salivary gland - salivon, which includes the acinus, blindly ending expansion and formed by acinar cells, the acinus, then opens into the intercalary duct, which passes into the striated duct. Acinus cells secrete proteins and electrolytes. Water also comes here. Then, the correction of the electrolyte content in saliva is carried out by the intercalated and striated ducts. The secretory cells are still surrounded by myoepithelial cells, capable of contraction, and myoepithelial cells, by contracting, squeeze out the secret and promote its movement along the duct. The salivary glands receive an abundant blood supply, there are 20 times more beds in them than in other tissues. Therefore, these small organs have a rather powerful secretory function. From 0.5 - 1.2 liters are produced per day. saliva.
Saliva.
- Water - 98.5% - 99%
- Solid residue 1-1.5%.
- Electrolytes - К, НСО3, Na, Cl, I2
Saliva secreted in the ducts is hypotonic compared to plasma. In the acini, electrolytes are secreted by secretory cells and they are contained in the same amount as in plasma, but as saliva moves through the ducts, sodium and chlorine ions are absorbed, the number of potassium and bicarbonate ions becomes larger. Saliva is characterized by a predominance of potassium and bicarbonate. Organic composition of saliva represented by enzymes - alpha-amylase (ptyalin), lingual lipase - produced by the glands located at the root of the tongue.
The salivary glands contain calycrein, mucus, lactoferin - they bind iron and help to reduce bacteria, lysozyme glycoproteins, immunoglobulins - A, M, antigens A, B, AB, 0.
Saliva is excreted through the ducts - functions - wetting, the formation of a food lump, swallowing. In the oral cavity - the initial stage of the breakdown of carbohydrates and fats. Complete splitting cannot occur because short time the food is in the food cavity. The optimum action of saliva is a slightly alkaline medium. The pH of saliva = 8. Saliva restricts the growth of bacteria, promotes healing of injuries, hence the licking of wounds. We need saliva for normal speech function.
Enzyme salivary amylase carries out the splitting of starch to maltose and maltotriose. Salivary amylase is similar to pancreatic amylase, which also breaks down carbohydrates to maltose and maltotriose. Maltase and isomaltase, breaks down these substances to glucose.
Saliva lipase begins to break down fats and enzymes continue their action in the stomach until the pH value changes.
Regulation of salivation.
Regulation of salivary secretion is carried out by parasympathetic and sympathetic nerves, and the salivary glands are regulated only reflexively, since they are not characterized by a humoral regulation mechanism. Salivary excretion can be carried out using unconditioned reflexes that occur when the oral mucosa is irritated. In this case, there may be food and non-food irritants.
Mechanical irritation of the mucous membrane also affects salivation. Salivation can be caused by the smell, sight, memory of delicious food. Salivation is formed with nausea.
Inhibition of salivation is observed during sleep, with fatigue, with fear and with dehydration.
The salivary glands receive double innervation from the autonomic nervous system. They are innervated by the parasympathetic and sympathetic divisions. Parasympathetic innervation is carried out by 7 and 9 pairs of nerves. They contain 2 salivary nuclei - upper -7 and lower - 9. The seventh pair innervate the submandibular and sublingual glands. 9 pair - parotid gland. In the endings of the parasympathetic nerves, acetylcholine is released, and under the action of acetylcholine on the receptors of secretory cells through G-proteins, the secondary messenger inositol-3-phosphate is innervated, and it increases the calcium content inside. This leads to an increase in the secretion of saliva, poor in organic composition - water + electrolytes.
The sympathetic nerves reach the salivary glands through the superior cervical sympathetic ganglion. At the endings of postganglionic fibers, norepinephrine is released, i.e. secretory cells of the salivary glands have adrenergic receptors. Norepinephrine causes the activation of adenylate cyclase with the subsequent formation of cyclic AMP and cyclic AMP enhances the formation of protein kinase A, which is necessary for protein synthesis, and sympathetic effects on the salivary glands increase secretion.
Highly viscous saliva with a lot of organic matter. As an afferent link in the excitation of the salivary glands, it will involve the nerves that provide general sensitivity. The taste sensitivity of the anterior third of the tongue is the facial nerve, the posterior third is the glossopharyngeal. The posterior sections are still innervated from the vagus nerve. Pavlov showed that the secretion of saliva on the rejected substances, and the ingress of river sand, acids, other chemicals, there is a large release of saliva, namely liquid saliva. Salivation also depends on the fragmentation of food. For nutrients, less saliva is given, but with a higher content of the enzyme.
Physiology of the stomach.
The stomach is a part of the digestive tract, where food is retained from 3 to 10 hours for mechanical and chemical processing. A small amount of food is digested in the stomach, and the absorption area is also not large. This is a reservoir for storing food. In the stomach, we isolate the bottom, the body, the pyloric section. The contents of the stomach are confined from the esophagus by the cardiac sphincter. At the transition of the pyloric section to the duodenum. There is a functional sphincter.
Stomach function
- Depositing food
- Secretory
- Motor
- Suction
- Excretory function. Promotes the removal of urea, uric acid, creatine, creatinine.
- Endocrine function is the formation of hormones. The stomach has a protective function
On the basis of functional characteristics, the mucous membrane is divided into acid-producing, which is located in the proximal section on the central part of the body, antral mucosa is also isolated, which does not form hydrochloric acid.
Composition- mucous cells that form mucus.
- The lining cells that produce hydrochloric acid
- The main cells that produce enzymes
- Endocrine cells that produce the hormone G-cells - gastrin, D - cells - somatostatin.
Glycoprotein - forms a slimy gel, it envelops the wall of the stomach and prevents the effect of hydrochloric acid on the mucous membrane. This layer is very important otherwise the mucous membrane is disturbed. It is destroyed by nicotine, little mucus is produced during stressful situations, which can lead to gastritis and ulcers.
The glands of the stomach produce pepsinogens, which act on proteins, they are inactive and need hydrochloric acid. Hydrochloric acid is produced by the parietal cells, which also produce Castle factor- which is needed to assimilate the external factor B12. In the area of the antrum, there are no parietal cells, the juice is produced in a slightly alkaline reaction, but the mucous membrane of the antrum is rich in endocrine cells that produce hormones. 4G-1D - ratio.
To study the function of the stomach methods are being studied that impose fistulas - the secretion of a small ventricle (according to Pavlov) and in humans, gastric secretion is studied by probing and obtaining gastric juice on an empty stomach without giving food, and then after a test breakfast and the most common breakfasts is a glass of tea without sugar and a slice of bread. These simple foods are powerful stomach stimulants.
Composition and properties of gastric juice.
At rest in the stomach in a person (without food intake) there is 50 ml of basal secretion. It is a mixture of saliva, gastric juice, and occasionally a reflux from the duodenum. About 2 liters of gastric juice is formed per day. It is a transparent opalescent liquid with a density of 1.002-1.007. Has an acidic reaction, since there is hydrochloric acid (0.3-0.5%). pH 0.8-1.5. Hydrochloric acid can be free and bound to protein. Gastric juice also contains inorganic substances - chlorides, sulfates, phosphates and bicarbonates of sodium, potassium, calcium, magnesium. Organic matter is represented by enzymes. The main enzymes in gastric juice are pepsins (proteases that act on proteins) and lipases.
Pepsin A - pH 1.5-2.0
Gastrixin, pepsin C - pH-3.2-, 3.5
Pepsin B - gelatinase
Renin, pepsin D chymosin.
Lipase, acts on fats
All pepsins are excreted in an inactive form as pepsinogen. Now it is proposed to divide pepsins into groups 1 and 2.
Pepsins 1 are secreted only in the acid-forming part of the gastric mucosa - where there are parietal cells.
Antral part and pyloric part - pepsins are secreted there group 2... Pepsins carry out digestion to intermediate products.
Amylase, which is ingested with saliva, can break down carbohydrates in the stomach for some time until the pH changes into an acidic groan.
The main component of gastric juice is water - 99-99.5%.
An important component is hydrochloric acid. Its functions:
- It promotes the conversion of an inactive form of pepsinogen into an active form - pepsins.
- Hydrochloric acid creates the optimal pH value for proteolytic enzymes
- Causes denaturation and swelling of proteins.
- The acid has an antibacterial effect and bacteria that enter the stomach are killed
- Participates in the formation of hormones - gastrin and secretin.
- Locks milk
- Participates in the regulation of the transfer of food from the stomach to the 12-persistent intestine.
Hydrochloric acid formed in the parietal cells. These are fairly large pyramidal cells. Inside these cells there are a large number of mitochondria, they contain a system of intracellular tubules and a vesicular system in the form of vesicles is closely connected with them. These vesicles bind to the tubule when they are activated. A large number of microvilli form in the tubule, which increase the surface area.
The formation of hydrochloric acid occurs in the intratubular system of the parietal cells.
At the first stage there is a transfer of the chlorine anion into the lumen of the tubule. Chlorine ions are supplied through a special chlorine channel. A negative charge is created in the tubule, which attracts intracellular potassium there.
In the next step there is an exchange of potassium for a hydrogen proton, due to the active transport of hydrogen to potassium ATPase. Potassium is exchanged for a hydrogen proton. With this pump, potassium is driven into the intracellular wall. Carbonic acid is formed inside the cell. It is formed as a result of the interaction of carbon dioxide and water due to carbonic anhydrase. Carbonic acid dissociates into a hydrogen proton and an HCO3 anion. The hydrogen proton is exchanged for potassium, and the HCO3 anion is exchanged for the chlorine ion. Chlorine enters the lining cell, which then goes into the lumen of the tubule.
There is another mechanism in the parietal cells - sodium - potassium atphase, which removes sodium from the cell and returns sodium.
The formation of hydrochloric acid is an energy-consuming process. ATP is produced in the mitochondria. They can occupy up to 40% of the volume of the parietal cells. The concentration of hydrochloric acid in the tubules is very high. PH inside the tubule up to 0.8 - concentration of hydrochloric acid 150 ml mol per liter. The concentration is 4,000,000 higher than plasma. The formation of hydrochloric acid in the parietal cell is regulated by the effects on the parietal cell of acetylcholine, which is secreted at the endings of the vagus nerve.
The covering cells have cholinergic receptors and the formation of HCl is stimulated.
Gastrin receptors and the hormone gastrin also activates the formation of HCl, and this occurs through the activation of membrane proteins and the formation of phospholipase C and inositol-3-phosphate is formed and this stimulates an increase in calcium and the hormonal mechanism is triggered.
The third type of receptor is histamine receptorsH2 ... Histamine is produced in the stomachs by enterochromatin mast cells. Histamine acts on H2 receptors. Here the influence is realized through the adenylate cyclase mechanism. Adenylate cyclase is activated and cyclic AMP is formed
Inhibits - somatostatin, which is produced in D cells.
Hydrochloric acid- the main factor of damage to the mucous membrane in violation of the protection of the membrane. Treatment of gastritis - suppression of the action of hydrochloric acid. Histamine antagonists are very widely used - cimetidine, ranitidine, block H2 receptors and reduce the formation of hydrochloric acid.
Suppression of hydrogen-potassium atphase. A substance was obtained that is the pharmacological drug omeprazole. It suppresses the hydrogen-potassium phase. This is a very mild action that reduces the production of hydrochloric acid.
Mechanisms of regulation of gastric secretion.
The process of gastric digestion is conventionally divided into 3 phases overlapping each other
1. Difficult reflex - cerebral
2. Gastric
3. Intestinal
Sometimes the latter two are combined into a neurohumoral one.
Difficult reflex phase... It is caused by the excitation of the gastric glands by a complex of unconditioned and conditioned reflexes associated with food intake. Conditioned reflexes arise when the olfactory, visual, and auditory receptors are irritated, by sight, smell, or by the environment. These are conditional signals. They are superimposed on the effect of irritants on the oral cavity, pharyngeal receptors, esophagus. These are unconditional irritations. It was this phase that Pavlov studied in the experience of imaginary feeding. The latency period from the beginning of feeding is 5-10 minutes, that is, the gastric glands are turned on. After stopping feeding, secretion lasts 1.5-2 hours if food does not enter the stomach.
The secretory nerves will be the wandering ones. It is through them that the effect on the parietal cells that produce hydrochloric acid occurs.
Nervus vagus stimulates gastrin cells in the antrum and Gastrin is formed, and D cells, where somatostatin are produced, are inhibited. It was found that the vagus nerve acts on gastrin cells through a neurotransmitter - bombesin. This excites gastrin cells. On D cells, which produce somatostatin, it suppresses. In the first phase of gastric secretion - 30% of gastric juice. It has a high acidity, digestive power. The purpose of the first phase is to prepare the stomach for eating. When food enters the stomach, the gastric phase of secretion begins. In this case, the food content mechanically stretches the walls of the stomach and the sensitive endings of the vagus nerves are excited, as well as the sensitive endings, which are formed by the cells of the submucosal plexus. Local reflex arcs appear in the stomach. Doggel's cell (sensitive) forms a receptor in the mucous membrane and when irritated, it is excited and transmits excitation to type 1 cells - secretory or motor. A local local reflex arises and the gland begins to work. Cells of the 1st type are also postganlionars for the vagus nerve. The vagus nerves keep the humoral mechanism under control. Simultaneously with the nervous mechanism, the humoral mechanism begins to work.
Humoral mechanism associated with the release of Gastrin by G cells. They produce two forms of gastrin - of 17 amino acid residues - "small" gastrin and there is a second form of 34 amino acid residues - large gastrin. Small gastrin is more potent than large gastrin, but there is more large gastrin in the blood. Gastrin, which is produced by subgastrin cells and acts on the parietal cells to stimulate the formation of HCl. It also acts on the lining cells.
Functions of gastrin - stimulates the secretion of hydrochloric acid, enhances the production of an enzyme, stimulates gastric motility, is necessary for the growth of the gastric mucosa. It also stimulates the secretion of pancreatic juice. The production of gastrin is stimulated not only by nerve factors, but also food products that are formed during the breakdown of food are also stimulants. These include protein breakdown products, alcohol, coffee - caffeine and non-caffeine. The production of hydrochloric acid depends on the ph and when the ph drops below 2x, the production of hydrochloric acid is suppressed. Those. this is due to the fact that a high concentration of hydrochloric acid inhibits the production of gastrin. At the same time, the high concentration of hydrochloric acid activates the production of somatostatin, and it inhibits the production of gastrin. Amino acids and peptides can act directly on the parietal cells and increase the secretion of hydrochloric acid. Proteins, with their buffering properties, bind a hydrogen proton and maintain an optimal level of acid formation
Supports gastric secretion intestinal phase... When chyme enters the duodenum 12, it affects gastric secretion. 20% of gastric juice is produced during this phase. It produces enterogastrin. Enterooxyntin - these hormones are produced under the influence of HCl, which comes from the stomach into the duodenum, under the influence of amino acids. If the acidity of the environment in the duodenum is high, then the production of stimulating hormones is suppressed, and enterogastron is produced. One of the varieties will be - GIP - gastrointestinal peptide. It inhibits the production of hydrochloric acid and gastrin. Inhibitory substances also include bulbogastron, serotonin, and neurotensin. On the part of the duodenum, reflex influences can also arise that excite the vagus nerve and include the local nerve plexuses. In general, the separation of gastric juice will depend on the amount of food quality. The amount of gastric juice depends on the residence time of the food. In parallel with the increase in the amount of juice, its acidity also increases.
The digesting power of the juice is greater in the first hours. To assess the digestive power of juice, it is proposed Ment's method... Fatty foods inhibit gastric secretion; therefore, it is not recommended to eat fatty foods at the beginning of a meal. Hence, children are never given fish oil prior to eating. Pre-intake of fats - reduces the absorption of alcohol in the stomach.
Meat - protein product, bread - vegetable and milk - mixed.
For meat- the maximum amount of juice is allocated with the maximum secretion for the second hour. The juice has the maximum acidity, the fermentation is not high. The rapid increase in secretion is due to strong reflex irritation - sight, smell. Then, after the maximum, secretion begins to decline, the decline in secretion is slow. The high content of hydrochloric acid ensures protein denaturation. The final breakdown takes place in the intestines.
Secretion on bread... The maximum is reached by the 1st hour. The rapid build-up is associated with a strong reflex stimulus. Having reached the maximum, the secretion drops rather quickly, because few humoral stimulants, but secretion lasts a long time (up to 10 hours). Enzymatic capacity - high - no acidity.
Milk - a slow rise in secretion... Weak irritation of receptors. They contain fats, inhibit secretion. The second phase after reaching the maximum is characterized by a steady decline. Here, fat breakdown products are formed, which stimulate secretion. The enzymatic activity is low. You must eat vegetables, juices and mineral water.
The secretory function of the pancreas.
The chyme that enters the duodenum 12 is exposed to the action of pancreatic juice, bile and intestinal juice.
Pancreas- the largest gland. It has a double function - intrasecretory - insulin and glucagon and an exocrine function, which ensures the production of pancreatic juice.
Pancreatic juice is formed in the gland, in the acinus. Which are lined with transition cells in 1 row. An active process of enzyme formation takes place in these cells. They have a well-expressed endoplasmic reticulum, the Golgi apparatus, and from the acini, the pancreatic ducts begin and form 2 ducts that open into the duodenum 12. The largest duct is Wirsunga channel... It opens with a common bile duct in the area of Vater's nipple. The sphincter of Oddi is located here. Second accessory duct - Santorinni opens proximal to the Versung duct. Study - the imposition of fistulas on 1 of the ducts. In humans, it is studied by probing.
In their own way composition of pancreatic juice- transparent colorless liquid of alkaline reaction. The amount is 1-1.5 liters per day, pH 7.8-8.4. The ionic composition of potassium and sodium is the same as in plasma, but there are more bicarbonate ions and less Cl. In the acinus, the content is the same, but as the juice moves along the ducts, it leads to the fact that the duct cells provide the capture of chlorine anions and the amount of bicarbonate anions increases. Pancreatic juice is rich in enzyme composition.
Proteolytic enzymes acting on proteins - endopeptidases and exopeptidases. The difference is that endopeptidases act on internal bonds, while exopeptidases cleave terminal amino acids.
Endopepidase- trypsin, chymotrypsin, elastase
Ectopeptidase- carboxypeptidases and aminopeptidases
Proteolytic enzymes are produced in an inactive form - enzymes. Activation occurs under the action of enterokinase. It activates trypsin. Trypsin is excreted in the form of trypsinogen. And the active form of trypsin activates the rest. Enterokinase is an enzyme of intestinal juice. With blockages of the duct of the gland and with abundant alcohol consumption, activation of pancreatic enzymes inside it may occur. The process of self-digestion of the pancreas begins - acute pancreatitis.
For carbohydrates aminolytic enzymes - alphaamylase act, breaks down polysaccharides, starch, glycogen, cannot break down cellulo, with the formation of maltoyz, maltotiose, and dextrin.
Fatty litholytic enzymes - lipase, phospholipase A2, cholesterol. Lipase acts on neutral fats and breaks them down to fatty acids and glycerol, cholesterol esterase acts on cholesterol, and phospholipase acts on phospholipids.
Enzymes on nucleic acids- ribonuclease, deoxyribonuclease.
Regulation of the pancreas and its secretion.
It is associated with nervous and humoral mechanisms of regulation and the pancreas is included in 3 phases
- Difficult reflex
- Gastric
- Intestinal
Secretory nerve - nervus vagus, which acts on the production of enzymes in the acini cell and on the duct cells. There is no influence of sympathetic nerves on the pancreas, but sympathetic nerves cause a decrease in blood flow, and a decrease in secretion occurs.
Is of great importance humoral regulation pancreas - the formation of 2 hormones of the mucous membrane. There are C cells in the mucous membrane that produce the hormone secretin and secretin absorbed into the blood, it acts on the cells of the pancreatic ducts. Stimulates these cells by the action of hydrochloric acid
2nd hormone is produced by I cells - cholecystokinin... Unlike secretin, it acts on acin cells, the amount of juice will be less, but the juice is rich in enzymes and the excitation of type I cells is under the influence of amino acids and, to a lesser extent, hydrochloric acid. Other hormones act on the pancreas - VIP - has an effect similar to secretin. Gastrin is similar to cholecystokinin. In the complex reflex phase, secretion is released 20% of its volume, 5-10% falls on the gastric, and the rest in the intestinal phase, etc. the pancreas is in the next stage of influencing food, the production of gastric juice interacts very closely with the stomach. If gastritis develops, then pancreatitis follows.
Physiology of the liver.
The liver is the largest organ. An adult's weight is 2.5% of the total body weight. In 1 minute, the liver receives 1350 ml of blood and this is 27% of the minute volume. The liver receives both arterial and venous blood.
1. Arterial blood flow - 400 ml per minute. Arterial blood flows through the hepatic artery.
2. Venous blood flow - 1500 ml per minute. Venous blood flows through the portal vein from the stomach, small intestine, pancreas, spleen, and partly the large intestine. It is through the portal vein that nutrients and vitamins come from the digestive tract. The liver captures these substances and then distributes them to other organs.
The important role of the liver belongs to carbon metabolism. It maintains blood sugar levels as a glycogen depot. Regulates the content of lipids in the blood and especially low density lipoproteins, which it secretes. An important role in the protein department. All plasma proteins are produced in the liver.
The liver performs a detoxifying function in relation to toxic substances and drugs.
Performs a secretory function - the formation of the liver by bile and the excretion of bile pigments, cholesterol, medicinal substances. Provides endocrine function.
The functional unit of the liver is hepatic lobule, which is built from the hepatic tracts formed by hepatocytes. In the center of the hepatic lobule is the central vein, into which blood flows from the sinusoids. Collects blood from portal vein capillaries and hepatic artery capillaries. Central veins merging with each other gradually form the venous system of blood outflow from the liver. And the blood from the liver flows through the hepatic vein, which flows into the inferior vena cava. In the hepatic tracts, upon contact of neighboring hepatocytes, bile ducts. They are separated from the intercellular fluid by tight contacts, This prevents the mixing of bile and extracellular fluid. The bile formed by hepatocytes enters the tubules, which gradually merge to form the system of intrahepatic bile ducts. Ultimately, it enters the gallbladder or through the common duct into the duodenum. The common bile duct connects to Persungov duct of the pancreas and together with it opens at the top Faterova pacifier. There is a sphincter at the exit site of the common bile duct Oddi, which regulate the flow of bile into the duodenum.
Sinusoids are formed by endothelial cells that lie on the basement membrane, around - the perisinusoidal space - space Disse... This space separates sinusoids and hepatocytes. The membranes of hepatocytes form numerous folds, villi, and they protrude into the re-sinusoidal space. These villi increase the area of contact with the supersonic fluid. Weak expression of the basement membrane, sinusoid endothelial cells contain large pores. The structure resembles a sieve. The pores allow substances from 100 to 500 nm in diameter to pass through.
The amount of proteins in the re-sinusoidal space will be greater than in plasma. There are macrocytes of the macrophage system. These cells, through endocytosis, ensure the removal of bacteria, damaged erythrocytes, and immune complexes. Some sinusoidal cells in the cytoplasm may contain droplets of fat - cells Ito... They contain vitamin A. These cells are associated with collagen fibers, their properties are similar to fibroblasts. They develop with cirrhosis of the liver.
Bile production by hepatocytes - the liver produces 600-120 ml of bile per day. Bile has 2 important functions -
1. It is essential for the digestion and absorption of fats. Due to the presence of bile acids, bile emulsifies fat and turns it into small drops. The process will promote a better action of lipases, for better breakdown into fats and bile acids. Bile is necessary for the transport and absorption of cleavage products
2. Excretory function. Bilirubin, cholestrenin are excreted with it. Bile secretion occurs in 2 stages. Primary bile is formed in hepatocytes, it contains bile salts, bile pigments, cholesterol, phospholipids and proteins, electrolytes, which are identical in content to plasma electrolytes, except bicarbonate anion, which is more in bile. This gives the alkaline reaction. This bile enters the bile ducts from the hepatocytes. At the next stage, bile moves along the interlobular, lobular duct, then to the hepatic and common bile duct. As bile progresses, duct epithelial cells secrete sodium and bicarbonate anions. This is essentially a secondary secretion. The volume of bile in the ducts can increase by 100%. Secretin increases the secretion of bicarbonate to neutralize hydrochloric acid from the stomach.
Outside of digestion, bile accumulates in the gallbladder, where it passes through the cystic duct.
Bile acid secretion.
Liver cells secrete 0.6 acids and their salts. Bile acids are formed in the liver from cholesterol, which either enters the body with food or can be synthesized by hepatocytes during salt metabolism. When kaarboxyl and hydroxyl groups are added to the steroid nucleus, primary bile acids
ü Hollevaya
ü Chenodeoxycholic
They combine with glycine, but to a lesser extent with taurine. This leads to the formation of glycocholic or taurocholic acids. When interacting with cations, sodium and potassium salts are formed. Primary bile acids enter the intestines and intestines, intestinal bacteria convert them into secondary bile acids
- Deoxycholic
- Lithohole
Bile salts have a greater ion-forming ability than the acids themselves. Bile salts are polar compounds that reduce their penetration through the cell membrane. Consequently, absorption will decrease. Combining with phospholipids and monoglycerides, bile acids promote fat emulsification, increase lipase activity and convert fat hydrolysis products into soluble compounds. Since bile salts contain hydrophilic and hydrophobic groups, they take part in the formation with cholesterols, phospholipids and monoglycerides to form cylindrical discs, which will be water-soluble micelles. It is in such complexes that these products pass through the brush border of enterocytes. Up to 95% of bile salts and acids are reabsorbed in the intestine. 5% will be excreted in the feces.
The absorbed bile acids and their salts combine with high-density lipoproteins in the blood. Through the portal vein, they again enter the liver, where 80% are again captured from the blood by hepatocytes. Thanks to this mechanism, a supply of bile acids and their salts is created in the body, which ranges from 2 to 4 g. There, the intestinal-hepatic circulation of bile acids takes place, which promotes the absorption of lipids in the intestine. For people who do not eat a lot, such a turnover occurs 3-5 times per day, and for people who consume abundant food, such a turnover can increase up to 14-16 times per day.
Inflammatory conditions of the mucous membrane of the small intestine reduce the absorption of bile salts, which impairs the absorption of fats.
Cholesterol - 1.6-8, mmol / l
Phospholipids - 0.3-11 mmol / L
Cholesterol is considered a by-product. Cholesterol is practically insoluble in pure water, but when combined with bile salts in micelles, it turns into a water-soluble compound. In some pathological conditions, cholesterol is deposited, calcium is deposited in it and this causes the formation of gallstones. Gallstone disease is a fairly common disease.
- The formation of bile salts is facilitated by excessive absorption of water in the gallbladder.
- Excessive absorption of bile acids from bile.
- Increased cholesterol in bile.
- Inflammatory processes in the mucous membrane of the gallbladder
Gallbladder capacity 30-60 ml. In 12 hours, up to 450 ml of bile can accumulate in the gallbladder, and this happens due to the concentration process, while water, sodium and chlorine ions, and other electrolytes are absorbed and usually bile is concentrated in the bladder 5 times, but the maximum concentration is 12-20 times. About half of the soluble compounds in gallbladder bile are bile salts, and a high concentration of bilirubin, cholesterol and leucithin is also achieved here, but the electrolyte composition is identical to plasma. Emptying of the gallbladder occurs during the digestion of food and especially fat.
The process of emptying the gallbladder is associated with the hormone cholecystokinin. It relaxes the sphincter Oddi and helps to relax the muscles of the bladder itself. Perestaltic contractions of the bladder further go to the cystic duct, the common bile duct, which leads to the excretion of bile from the bladder into the duodenum. The excretory function of the liver is associated with the excretion of bile pigments.
Bilirubin.
Monocyte - macrophage system in the spleen, bone marrow, liver. 8 g of hemoglobin breaks down per day. When hemoglobin breaks down, 2-valent iron is split off from it, which combines with protein and is stored in reserve. From 8 g Hemoglobin => biliverdin => bilirubin (300mg per day) The norm of bilirubin in the blood serum is 3-20 μmol / l. Above - jaundice, staining of the sclera and mucous membranes of the oral cavity.
Bilirubin binds to a transport protein blood albumin. it indirect bilirubin. Bilirubin from blood plasma is captured by hepatocytes and in hepatocytes bilirubin combines with glucuronic acid. Bilirubin glucuronil is formed. This form enters the bile ducts. And already in bile, this form gives direct bilirubin... It enters the intestine through the bile duct system. In the intestine, intestinal bacteria cleave glucuronic acid and convert bilirubin into urobilinogen. Part of it undergoes oxidation in the intestines and enters the feces and is already called stercobilin. The other part will be absorbed and enter the bloodstream. From the blood it is captured by hepatocytes and again enters the bile, but some of it will be filtered in the kidneys. Urobilinogen passes into the urine.
Suprahepatic (hemolytic) jaundice caused by the massive breakdown of red blood cells as a result of the Rh conflict, the entry into the blood of substances that cause destruction of the membranes of red blood cells and some other diseases. With this form of jaundice, the content of indirect bilirubin in the blood is increased, the content of stercobilin is increased in the urine, there is no bilirubin, and the content of stercobilin is increased in the feces.
Hepatic (parenchymal) jaundice caused by damage to liver cells during infections and intoxications. With this form of jaundice, the content of indirect and direct bilirubin in the blood is increased, the content of urobilin is increased in the urine, bilirubin is present, and the content of stercobilin is low in the feces.
Subhepatic (obstructive) jaundice caused by a violation of the outflow of bile, for example, when the bile duct is blocked by a stone. With this form of jaundice, the content of direct bilirubin (sometimes indirect) is increased in the blood, stercobilin is absent in urine, bilirubin is present, and stercobilin is low in feces.
Regulation of bile formation.
Regulation is based on feedback mechanisms based on the level of concentration of bile salts. The content in the blood determines the activity of hepatocytes in bile production. Outside the period of digestion, the concentration of bile acids decreases and this is a signal for an increase in the formation of hepatocytes. The discharge into the duct will decrease. After eating, there is an increase in the content of bile acids in the blood, which, on the one hand, inhibits the formation in hepatocytes, but at the same time increases the secretion of bile acids in the tubules.
Cholecystokinin is produced by the action of fatty and amino acids and causes contraction of the bladder and relaxation of the sphincter - i.e. stimulation of the emptying of the bladder. Secretin, which is released by the action of hydrochloric acid on C cells, enhances tubular secretion and increases the content of bicarbonate.
Gastrin affects hepatocytes by enhancing secretory processes. Indirectly, gastrin increases the content of hydrochloric acid, which will then increase the content of secretin.
Steroid hormones- estrogens and some androgens inhibit the formation of bile. In the mucous membrane of the small intestine, motilin- it contributes to the contraction of the gallbladder and the excretion of bile.
Influence of the nervous system- through the vagus nerve - enhances bile formation and the vagus nerve contributes to the contraction of the gallbladder. Sympathetic influences are inhibitory and cause relaxation of the gallbladder.
Intestinal digestion.
In the small intestine - the final digestion and absorption of digestive products. The small intestine receives 9 liters daily. Liquids. We absorb 2 liters of water with food, and 7 liters comes due to the secretory function of the gastrointestinal tract, and from this, only 1-2 liters will enter the large intestine. The length of the small intestine to the ileocecal sphincter is 2.85 m.The corpse is 7 m.
The mucous membrane of the small intestine forms folds that increase the surface by 3 times. 20-40 villi per 1 sq. Mm. This increases the area of the mucous membrane by 8-10 times, and each villi is covered with epithelial cells, endothelial cells containing microvilli. These are cylindrical cells with microvilli on their surface. From 1.5 to 3000 per 1 cell.
The length of the villi is 0.5-1 mm. The presence of microvilli increases the area of the mucosa and it reaches 500 square meters. Each villi contains a blindly terminating capillary, a supplying arteriole approaches the villus, which breaks down into capillaries, passing at the apex into the venous capillaries and produce blood outflow through the venules. Venous and arterial blood flow in opposite directions. Rotary countercurrent system. In this case, a large amount of oxygen passes from arterial and venous blood, without reaching the apex of the villi. It is very easy to create conditions under which the tops of the villi will receive less oxygen. This can lead to the death of these areas.
Glandular apparatus - Bruner glands in the duodenum. Libertune's glands in the jejunum and ileum. There are goblet mucous cells that produce mucus. The glands of the duodenum 12 resemble the glands of the pyloric part of the stomach and they secrete mucous secretions for mechanical and chemical irritation.
Their regulation occurs under the influence vagus nerves and hormones, especially secretin. Mucous secretion protects the duodenum from the action of hydrochloric acid. The sympathetic system reduces mucus production. When we experience strep, we have an easy chance of getting a duodenal ulcer. By reducing the protective properties.
Small intestine secret formed by enterocytes, which begin their maturation in crypts. As the enterocyte matures, it begins to move to the apex of the villi. It is in the crypts that the cells actively transfer chlorine and bicarbonate anions. These anions create a negative charge that attracts sodium. Osmotic pressure is created, which attracts water. Some pathogenic microbes - dysentery bacillus, cholera vibrio enhance the transport of chlorine ions. This leads to a large excretion of fluid in the intestine up to 15 liters per day. Normally, 1.8-2 liters per day. Intestinal juice is a colorless liquid, cloudy due to the mucus of epithelial cells, has an alkaline reaction pH 7.5-8. Enzymes of intestinal juice accumulate inside enterocytes and are secreted with them when they are rejected.
Intestinal juice contains a complex of peptidases, which is called eryxin, providing the final cleavage of protein products to amino acids.
4 aminolytic enzymes - sucrase, maltase, isomaltase and lactase. These enzymes break down the carbohydrate into monosaccharides. There is intestinal lipase, phospholipase, alkaline phosphatase and enterokinase.
Intestinal juice enzymes.
1. Complex of peptidases (erypsin)
2.Amylothytic enzymes- sucrase, maltase, isomaltase, lactase
3. Intestinal lipase
4. Phospholipase
5. Alkaline phosphatase
6. Enterokinase
These enzymes accumulate inside the enterocytes and the latter, as they mature, rise to the top of the villi. At the apex of the villi, enterocytes are rejected. Within 2-5 days, the intestinal epithelium is completely replaced with new cells. Enzymes can enter the intestinal cavity - cavity digestion, the other part is fixed on the membranes of microvilli and provides membrane or parietal digestion.
Enterocytes are covered with a layer glycocalyx- carbon surface, porous. It is a catalyst that promotes the breakdown of nutrients.
The regulation of the acid department is under the influence of mechanical and chemical stimuli acting on the cells of the nerve plexus. Doggel's cells.
Humoral substances- (increase secretion) - secretin, cholecystokinin, VIP, motilin and enterocrinin.
Somatostatin inhibits secretion.
In the colon libertine glands, a large number of mucous cells. Mucus and bicarbonate anions predominate.
Parasympathetic influences- increase mucus secretion. With emotional arousal within 30 minutes, a large amount of secretion is formed in the colon, which causes the urge to empty. Under normal conditions - mucus provides protection, adhesion of feces and neutralizes acids with the help of bicarbonate anions.
Normal microflora is very important for the function of the colon. It is non-pathogenic bacteria that take part in the formation of the immunobiological activity of the body - lactobacilli. They help to increase immunity and prevent the development of pathogenic microflora, when antibiotics are taken, these bacteria die. The body's defenses are weakened.
Colon bacteria synthesize vitamin K and B vitamins.
Bacterial enzymes break down fiber through microbial fermentation. This process takes place with the formation of gas. Bacteria can cause protein to rot. In this case, in the large intestine are formed poisonous foods- indole, skatole, aromatic hydroxy acids, phenol, ammonia and hydrogen sulfide.
The detoxification of toxic products occurs in the liver, where they combine with glucuric acid. Water is absorbed and feces are formed.
The composition of feces includes mucus, remnants of dead epithelium, cholesterol, products of changes in bile pigments - stercobilin and dead bacteria, which account for 30-40%. Feces may contain undigested food debris.
The motor function of the digestive tract.
We need motor function at the first stage - absorption of food and chewing, swallowing, movement along the alimentary canal. Motility contributes to the mixing of food and glandular secretions, participates in the processes of absorption. The motor system carries out the excretion of the end products of digestion.
The study of the motor function of the gastrointestinal tract is carried out using different methods, but it is widespread balloon cinegraphy- introduction into the cavity of the alimentary canal of a cartridge connected to a recording device, while the pressure is measured, which reflects motor skills. Motor function can be observed with fluoroscopy, colonoscopy.
X-ray gastroscopy- a method for recording electrical potentials in the stomach. Under experimental conditions, registration is removed from isolated sections of the intestine, visual observation of motor function. In clinical practice - auscultation - auscultation in the abdominal cavity.
Chewing- when chewing, food is crushed, grinded. Although this process is voluntary, chewing is coordinated by the nerve centers of the brain stem, which provide movement of the lower jaw in relation to the upper. When the mouth opens, the proprioceptors of the muscles of the lower jaw are excited and reflexively cause contraction of the masticatory muscles, the medial pterygoid and temporal lobes, and helps to close the mouth.
When the mouth is closed, food irritates the receptors of the oral mucosa. Which, when irritated, send to twoabdominal muscle and lateral pterygoid that help open the mouth. When the jaw drops, the cycle repeats again. With a decrease in the tone of the masticatory muscles, the lower jaw may drop under the force of gravity.
The muscles of the tongue are involved in the act of chewing.... They place food between the upper and lower teeth.
The main functions of chewing are -
They destroy the cellulose shell of fruits and vegetables, promote mixing and wetting of food with saliva, improve contact with taste buds, and increase the area of contact with digestive enzymes.
Chewing releases odors that act on the olfactory receptors. It increases the pleasure of eating and stimulates gastric secretion. Chewing helps the food lump to form and be swallowed.
The chewing process changes swallowing... We swallow 600 times a day - 200 swallows with food and drink, 350 without food and another 50 at night.
It is a complex coordinated act ... Includes oral, pharyngeal and esophageal phases... Allocate arbitrary phase- before the food lump hits the root of the tongue. This is an arbitrary phase that we can terminate. When the food lump hits the root of the tongue, non-voluntary swallowing phase... The act of swallowing begins from the root of the tongue to the hard palate. The food lump moves to the root of the tongue. The palatine curtain rises, like a lump passes the palatine arches, the nasopharynx closes, the larynx rises - the epiglottis goes down, the glottis goes down, this prevents food from entering the respiratory tract.
The food lump goes down the throat. Due to the muscles of the pharynx, the food lump is moved. At the entrance to the esophagus is the upper esophageal sphincter. When the lump moves, the sphincter relaxes.
Sensitive fibers of the trigeminal, glossopharyngeal, facial and vagus nerves take part in the swallowing reflex. It is through these fibers that signals are transmitted to the medulla oblongata. Coordinated muscle contraction is provided by the same nerves + the hypoglossal nerve. It is the coordinated contraction of the muscles that directs the food bolus into the esophagus.
With a contraction of the pharynx, relaxation of the upper esophageal sphincter. When a food lump enters the esophagus, esophageal phase.
In the esophagus there is a circular and longitudinal muscle layer. Moving a lump using a peristaltic wave, in which the circular muscles are above the food lump, and are longitudinal in front. Circular muscles narrow the lumen, and longitudinal ones widen. The wave moves the food bolt at a speed of 2-6 cm per second.
Solid food passes the esophagus in 8-9 seconds.
Liquid causes relaxation of the esophagus muscles and the liquid flows in a continuous column for 1 - 2 s. When the bolus reaches the lower third of the esophagus, it relaxes the lower cardiac sphincter. The cardiac sphincter is toned at rest. Pressure - 10-15 mm Hg. Art.
Relaxation occurs reflexively with the participation vagus nerve and mediators that induce relaxation - vasointestinal peptide and nitric oxide.
When the sphincter relaxes, the food lump passes into the stomach. With the work of the cardiac sphincter, 3 unpleasant disorders occur - achalosia- occurs with spastic contraction of the sphincters and weak peristalsis of the esophagus, which leads to the expansion of the esophagus. Food stagnates, decomposes, and an unpleasant odor appears. This condition does not develop as often as sphincter insufficiency and reflux condition- Throwing gastric contents into the esophagus. This leads to irritation of the esophageal mucosa, heartburn appears.
Aerophagia- swallowing air. It is typical for infants. When sucking, air is swallowed. The child cannot be placed horizontally at once. In an adult, it is observed with a hasty meal.
Outside the period of digestion, smooth muscles are in a state of tetanic contraction. During the act of swallowing, the proximal stomach relaxes. Together with the opening of the cardiac sphincter, the cardiac department relaxes. Decreased tone-receptive relaxation. Reducing the tone of the stomach muscles allows you to accommodate large volumes of food with minimal cavity pressure. Receptive relaxation of stomach muscles regulated by the vagus nerve.
Participates in relaxation of the stomach muscles hoelcystokinin- promotes relaxation. The motor activity of the stomach in the proximal and distal calving on an empty stomach and after eating is expressed in different ways.
Capable of fasting the contractile activity of the proximal part is weak, rare and the electrical activity of smooth muscles is not great. Most of the muscles of the stomach do not contract on an empty stomach, but approximately every 90 minutes, strong contractile activity develops in the middle sections of the stomach, which lasts 3-5 minutes. This periodic motility is called migratory myoelectric complex - MMK, which develops in the middle parts of the stomach and then moves on to the intestines. It is believed that it helps cleanse the gastrointestinal tract from mucus, exfoliated cells, bacteria. Subjectively, you and I feel the emergence of these contractions in the form of suction, murmur in the stomach. These signals increase the feeling of hunger.
For the gastrointestinal tract on an empty stomach, periodic motor activity is characteristic and it is associated with the excitation of the center of hunger in the hypothalamus. The glucose level decreases, the calcium content rises, and choline-like substances appear. This all acts on the center of hunger. From it, signals go to the cerebral cortex and then makes us realize that we are hungry. Downward pathways - periodic motility of the gastrointestinal tract. This prolonged activity gives signals that it is time to eat. If we take food in this state, then this complex is replaced by more frequent contractions in the stomach, which arise in the body and do not spread to the pyloric region.
The main type of stomach contraction during digestion is peristaltic contractions - contraction of the circular and longitudinal muscles. In addition to peristaltic, there are tonic contractions.
The basic rhythm of perilstalsis is 3 contractions per minute. The speed is 0.5-4 cm per second. The contents of the stomach move towards the pyloric sphincter. A small part is pushed through the digestive sphincter, but when it reaches the pyloric region, a powerful contraction occurs here, which throws the rest of the contents back into the body. - retropulsation... It plays a very important role in the processes of mixing, crushing the food lump, to smaller particles.
Food particles of no more than 2 cubic mm can pass into the duodenum.
The study of myoelectric activity showed that slow electrical waves appear in the smooth muscles of the stomach, which reflect the depolarization and repolarization of the muscles. The waves themselves do not lead to contraction. Contractions occur when the slow wave reaches a critical level of depolarization. An action potential appears at the top of the wave.
The most sensitive section is the middle third of the stomach, where these waves reach a threshold value - the pacemakers of the stomach. He creates the basic rhythm for us - 3 waves per minute. No such changes occur in the proximal stomach. The molecular basis has not been sufficiently studied, but such changes are associated with an increase in permeability for sodium ions, as well as an increase in the concentration of calcium ions in smooth muscle cells.
Found in the walls of the stomach are non-muscle cells that are excited periodically - Kajala cells These cells are associated with smooth muscle cells. Evacuation of the stomach into the duodenum 12. Grinding is important. Evacuation is influenced by the volume of gastric contents, chemical composition, calorie content and consistency of food, and the degree of its acidity. Liquid food is absorbed faster than solid food.
When part of the gastric contents enters the duodenum 12 from the side of the latter, blocking reflex- the pyloric sphincter reflexively closes, further intake from the stomach is not possible, gastric motility is inhibited.
Motor skills are inhibited when digesting fatty foods. In the stomach, the functional prepyloric sphincter- on the border of the body and the digestive part. There is a union of the digestive and 12 colon.
It is inhibited due to the formation of enterogastrons.
The rapid transition of the contents of the stomach to the intestines is accompanied by discomfort, severe weakness, drowsiness, and dizziness. This occurs when the stomach is partially removed.
Motor activity of the small intestine.
The smooth muscle of the small intestine can also contract in a fasting state due to the appearance of the myoelectric complex. Every 90 minutes. After a meal, the migrating myoelectric complex is replaced by motility, which is characteristic of digestion.
In the small intestine, motor activity can be observed in the form of rhythmic segmentation. The contraction of the circular muscles leads to the segmentation of the intestine. The declining segments change. Segmentation is necessary for mixing food if longitudinal contractions are added to the contraction of the circular muscles (narrowing the lumen). From the circular muscles - the movement of the contents is mask-like - in different directions
Segmentation occurs approximately every 5 seconds. This is a local process. It captures segments at a distance of 1-4 cm. In the small intestine, peristaltic contractions are also observed, which cause the contents to move towards the ileocecal sphincter. The contraction of the intestine occurs in the form of peristaltic waves, which occur every 5 seconds - multiples of 5 - 5.10.15, 20 seconds.
Contractions in the proximal regions are more frequent, up to 9-12 per minute.
In distal calving 5 - 8. Regulation of small intestine motility is stimulated by the parasympathetic system and suppressed by the sympathetic system. Local plexuses, which can regulate motor skills in small areas of the small intestine.
Muscle relaxation - humoral substances are involved- VIP, nitric oxide. Serotonin, methionine, gastrin, oxytocin, bile - stimulate motor skills.
Reflex reactions occur when irritation with food digestion products and mechanical stimuli.
The passage of the contents of the small intestine into the large intestine is carried out through ileocecal sphincter. This sphincter is closed outside the digestive period. After a meal, it opens every 20 to 30 seconds. Up to 15 milliliters of contents from the small intestine enters the blind.
Increased pressure in the cecum reflexively closes the sphincter. Periodic evacuation of the contents of the small intestine into the large intestine is carried out. Stomach filling - causes the ileoceclal sphincter to open.
The large intestine differs in that the longitudinal muscle fibers do not go in a continuous layer, but in separate ribbons. The large intestine forms a saccular expansion - haustra... It is an expansion that forms when smooth muscles and mucous membranes expand.
In the colon, we observe the same processes, only more slowly. There is segmentation, pendulum-like contractions. Waves can propagate to the rectum and back. Content moves slowly in one direction and then in the other. During the day, forcing peristaltic waves are observed 1-3 times, which move the contents to the rectum.
Motorboat regulation is carried out parasympathetic (arousing) and sympathetic (inhibiting) influences. Blind, transverse, ascending - the vagus nerve. Descending, sigmoid and straight - the pelvic nerve. Sympathetic- superior and inferior mesenteric node and hypogastric plexus. From humoral stimulants- substance P, tachykinins. VIP, Nitric oxide - inhibit.
The act of defecation.
The rectum is normally empty. Filling of the rectum occurs during the passage and forcing of a wave of peristalsis. When stool enters the rectum, it causes distension by more than 25% and a pressure above 18 mm Hg. relaxation of the internal smooth muscle sphincter occurs.
Sensory receptors inform the central nervous system, causing the urge. It is also controlled by the external sphincter of the rectum - striated muscles, it is regulated arbitrarily, the innervation is the pudendal nerve. Reduction of the external sphincter - suppression of the reflex, feces leave proximally. If an act is possible, relaxation of both the internal and external sphincter occurs. The longitudinal muscles of the rectum contract, the diaphragm relaxes. The act is facilitated by the contraction of the pectoral muscles, the muscles of the abdominal wall and the levator of the anus.
Digestion is the initial stage of metabolism. A person receives energy and all the necessary substances for the renewal and growth of tissues with food, however, proteins, fats and carbohydrates contained in food are foreign substances for the body and cannot be absorbed by its cells. For assimilation, they must turn from complex, large-molecular and water-insoluble compounds into smaller molecules, soluble in water and devoid of specificity.
Digestion - it is the process of converting nutrients into a form available for assimilation by tissues, carried out in the digestive system .
The digestive system is the organ system in which food is digested, processed and undigested substances are absorbed. It includes the digestive tract and digestive glands
Digestive tract consists of the following sections: oral cavity, pharynx, esophagus, stomach, duodenum, small intestine, large intestine (Fig. 1).
Digestive glands are located along the digestive tract and produce digestive juices (salivary, gastric glands, pancreas, liver, intestinal glands).
In the digestive system, food undergoes physical and chemical transformations.
Physical changes in food - consist in its mechanical processing, grinding, stirring and dissolving.
Chemical changes - it is a series of successive stages of hydrolytic breakdown of proteins, fats, carbohydrates.
As a result of digestion, digestion products are formed, which are able to be absorbed by the mucous membrane of the digestive tract and enter the blood and lymph, i.e. into the body fluids, and then assimilated by the body cells.
The main functions of the digestive system:
- Secretory- ensures the production of digestive juices containing enzymes. The salivary glands produce saliva, the gastric glands produce gastric juice, the pancreas produces pancreas juice, the liver produces bile, and the intestinal glands produce intestinal juice. In total, about 8.5 liters are produced per day. juices. Enzymes of digestive juices are highly specific - each enzyme acts on a specific chemical compound.
Enzymes are proteins and their activity requires a certain temperature, pH of the environment, etc. There are three main groups of digestive enzymes: protease, cleaving proteins to amino acids; lipases that break down fats to glycerol and fatty acids; amylase that break down carbohydrates into monosaccharides. A complete set of enzymes is present in the cells of the digestive glands - constitutive enzymes, the ratio between which may vary depending on the nature of the food. When a specific substrate arrives, adapted (induced) enzymes with a narrow focus of action.
- Motor-recovery- this is a motor function carried out by the muscles of the digestive apparatus and providing a change in the aggregate state of food, its grinding, mixing with digestive juices and movement in the oral-anal direction (from top to bottom).
- Suction- this function carries out the transfer of the end products of digestion, water, salts and vitamins, through the mucous membrane of the digestive tract into the internal environment of the body.
- Excretory- This is an excretory function that ensures the excretion of metabolic products (metabolites), undigested food, etc. from the body.
- Endocrine- is that specific cells of the mucous membrane of the digestive tract and pancreas, secrete hormones that regulate digestion.
- Receptor (analytical) - due to the reflex connection (through reflex arcs) of the chemo- and mechanoreceptors of the internal surfaces of the digestive organs with the cardiovascular, excretory and other systems of the body.
- Protective - it is a barrier function that protects the body from harmful factors (bactericidal, bacteriostatic, detoxification effect).
It is characteristic of a person own type of digestion, divided into three types:
- intracellular digestion- phylogenetically the most ancient type, in which enzymes hydrolyze the smallest particles of nutrients that enter the cell by membrane transport mechanisms.
- extracellular, distant or abdominal- occurs in the cavities of the digestive tract under the action of hydrolytic enzymes, and the secretory cells of the digestive glands are at some distance. As a result of extracellular digestion, food substances break down to a size available for intracellular digestion.
- membrane, parietal or contact- occurs directly on the cell membranes of the intestinal mucosa.
The structure and function of the digestive system
Oral cavity
Oral cavity - it includes the tongue, teeth, salivary glands. Here food intake, analysis, grinding, saliva wetting, and chemical processing are carried out. Food is in the mouth for an average of 10-15 seconds.
Language- a muscular organ covered with a mucous membrane, consisting of many papillae of 4 types. Distinguish filiform and conical papillae of general sensitivity (touch, temperature, pain); and leafy and mushroom e that contain gustatory nerve endings ... The tip of the tongue perceives sweetness, the body of the tongue perceives sour and salty, the root perceives bitter.
Taste is perceived when the analyte is dissolved in saliva. In the morning, the tongue is not very sensitive to the perception of taste, the sensitivity to the evening increases (19-21 hours). Therefore, breakfast should include foods that increase the irritation of taste buds (salads, snacks, fruits, etc.). The optimum temperature for the perception of gustatory sensations is 35-40 0 C. The sensitivity of the receptors decreases in the process of eating, with a monotonous diet, taking cold food, and also with age. It has been found that sweet foods cause a feeling of pleasure, have a beneficial effect on mood, while sour foods can have the opposite effect.
Teeth. In the oral cavity of an adult, there are only 32 teeth - 8 incisors, 4 canines, 8 small and 12 large molars. The front teeth (incisors) bite off the food, the canines tear it apart, the molars are chewed with the help of the chewing muscles. Teeth begin to erupt in the seventh month of life, by one year usually 8 teeth appear (all incisors). With rickets, teething is delayed. In children, by the age of 7-9 years, milk teeth (there are 20 in total) change to permanent ones.
A tooth consists of a crown, neck and root. The dental cavity is filled pulp- connective tissue penetrated by nerves and blood vessels. The base of the tooth is dentine- bone. The crown of the tooth is covered enamel, and the roots of the teeth cement.
Chewing food thoroughly with your teeth increases its contact with saliva, releases flavoring and bactericidal substances and makes it easier to swallow the food lump.
Salivary glands- in the mucous membrane of the oral cavity there are a large number of small salivary glands (labial, buccal, lingual, palatine). In addition, the excretory ducts of three pairs of large salivary glands - parotid, sublingual and submandibular - open into the oral cavity.
Saliva about 98.5% water and 1.5% inorganic and organic matter. The reaction of saliva is slightly alkaline (pH about 7.5).
Inorganic substances - Na, K, Ca, Mg, chlorides, phosphates, nitrogenous salts, NH 3, etc. From saliva, calcium and phosphorus penetrate into the tooth enamel.
Organic matter saliva is mainly represented by mucin, enzymes and antibacterial substances.
Mucin - mucoprotein, which makes saliva viscous, sticks together the food lump, making it slippery and easy to swallow.
Enzymes saliva presented amylase that breaks down starch to maltose and maltase, splitting maltose to glucose. These enzymes are highly active, but due to the short-term presence of food in the oral cavity, the complete breakdown of these carbohydrates does not occur.
Antibacterial substances- enzyme-like substances lysozyme, inhibins and sialic acids, which have bactericidal properties and protect the body from germs from food and inhaled air.
Saliva moistens food, dissolves it, envelops solid components, facilitates swallowing, partially breaks down carbohydrates, neutralizes harmful substances, cleans teeth from food debris.
A person produces about 1.5 liters of saliva per day. The secretion of saliva occurs continuously, but more during the daytime. Salivation is increasing when feeling hungry, the sight and smell of food, while eating, especially dry food, when exposed to flavoring and extractive substances, when drinking cold drinks, when speaking, writing, talking about food, as well as thinking about it. Inhibits secretion saliva, unattractive food and environment, strenuous physical and mental work, negative emotions, etc.
Influence of food factors on the functions of the oral cavity.
Insufficient intake of proteins, phosphorus, calcium, vitamins C, D, group B and excess sugar lead to the development of dental caries. Certain food acids, such as tartaric acid and calcium salts and other cations, can form tartar. A sharp change in hot and cold food leads to the appearance of microcracks in the enamel of the teeth and the development of caries.
A nutritional deficiency of B vitamins, especially B2 (riboflavin), contributes to the appearance of cracks in the corners of the mouth, inflammation of the mucous membrane of the tongue. Insufficient intake of vitamin A (retinol) is characterized by keratinization of the mucous membranes of the oral cavity, the appearance of cracks and their infection. With a deficiency of vitamins C (ascorbic acid) and P (rutin) develops paradontosis, which leads to a weakening of the fixation of the teeth in the jaws.
Lack of teeth, caries, periodontal disease, disrupt the chewing process and reduce the digestion processes in the oral cavity.
The initial stage of metabolism is digestion. For the regeneration and growth of body tissues, the intake of appropriate substances with food is necessary. Foods contain proteins, fats and carbohydrates, as well as vitamins, minerals and water that the body needs. However, proteins, fats and carbohydrates contained in food cannot be absorbed by its cells in their original form. In the digestive tract, not only mechanical processing of food occurs, but also chemical breakdown under the influence of enzymes of the digestive glands, which are located along the gastrointestinal tract.
Digestion in the mouth... V the oral cavity is hydrolyzed by polysaccharides (starch, glycogen). Wasp-Amylase of saliva breaks down the glycosidic bonds of glycogen and amylase and amylopectin molecules, which are part of the starch structure, with the formation of dextrins. The action of wasp-amylase in the oral cavity is short-term, however, hydrolysis of carbohydrates under its influence continues in the stomach due to the saliva entering here. If the contents of the stomach are processed under the influence of hydrochloric acid, then osamylase is inactivated and ceases to act.
Digestion in the stomach... V in the stomach, food is digested under the influence of gastric juice. The latter is produced by morphologically heterogeneous cells that are part of the digestive glands.
The secretory cells of the fundus and the body of the stomach secrete acidic and alkaline secretions, and the cells of the antrum - only alkaline. In humans, the daily secretion of gastric juice is 2-3 liters. On an empty stomach, the reaction of gastric juice is neutral or slightly acidic, after a meal - strongly acidic (pH 0.8-1.5). The gastric juice contains such enzymes as pepsin, gastrixin and lipase, as well as a significant amount of mucus - mucin.
In the stomach, the initial hydrolysis of proteins occurs under the influence of proteolytic enzymes of gastric juice with the formation of polypeptides. Here, about 10% of peptide bonds are hydrolyzed. The above enzymes are active only at an appropriate level of HC1. The optimum pH for pepsin is 1.2-2.0; for gastrixin - 3.2-3.5. Hydrochloric acid causes swelling and denaturation of proteins, which facilitates their further breakdown by proteolytic enzymes. The action of the latter is realized mainly in the upper layers of the food mass, adjacent to the wall of the stomach. As these layers are digested, the food mass is displaced into the pyloric section, from where, after partial neutralization, it moves into the duodenum. In the regulation of gastric secretion, the main place is occupied by acetylcholine, gastrin, histamine. Each of them excites secretory cells.
There are three phases of secretion: cerebral, gastric and intestinal. The stimulus for the appearance of secretion of the gastric glands in brain phase are all the factors that accompany food intake. In this case, conditioned reflexes that appear in the sight and smell of food are combined with unconditioned reflexes that are formed during chewing and swallowing.
V gastric phase secretion stimuli arise in the stomach itself, when it is stretched, when the mucous membrane is exposed to the products of protein hydrolysis, some amino acids, as well as extractive substances of meat and vegetables.
The effect on the glands of the stomach occurs in the third, intestinal, secretion phase, when insufficiently processed gastric contents enter the intestine.
Duodenal secretin inhibits the secretion of HCl, but increases the secretion of pepsinogen. A sharp inhibition of gastric secretion occurs when fat enters the duodenum. ...
Digestion in the small intestine. In humans, the glands of the mucous membrane of the small intestine form intestinal juice, the total amount of which reaches 2.5 liters per day. Its pH is 7.2-7.5, but with increased secretion, it can increase to 8.6. Intestinal juice contains over 20 different digestive enzymes. A significant release of the liquid part of the juice is observed with mechanical irritation of the intestinal mucosa. Digestion products also stimulate the secretion of enzyme-rich juice. Intestinal secretion is also stimulated by the vasoactive intestinal peptide.
There are two types of food digestion in the small intestine: cavity and membrane (parietal). The first is carried out directly by intestinal juice, the second - by enzymes adsorbed from the cavity of the small intestine, as well as by intestinal enzymes synthesized in intestinal cells and built into the membrane. The initial stages of digestion occur exclusively in the cavity of the gastrointestinal tract. Small molecules (oligomers) formed as a result of cavity hydrolysis enter the area of the brush border, where they are further degraded. As a result of membrane hydrolysis, mainly monomers are formed, which are transported into the blood.
Thus, according to modern concepts, the assimilation of nutrients is carried out in three stages: cavity digestion - membrane digestion - absorption. The last stage includes processes that ensure the transfer of substances from the lumen of the small intestine into the blood and lymph. Absorption occurs mostly in the small intestine. The total suction surface area of the small intestine is approximately 200 m 2. Due to the numerous villi, the cell surface is increased more than 30 times. Through the epithelial surface of the intestine, substances enter in two directions: from the lumen of the intestine into the blood and simultaneously from the blood capillaries into the intestinal cavity.
Physiology of bile formation and bile secretion. The process of bile formation occurs continuously both by filtering a number of substances (water, glucose, electrolytes, etc.) from the blood into the bile capillaries, and with the active secretion of bile salts and sodium ions by hepatocytes. ...
The final formation of bile occurs as a result of the reabsorption of water and mineral salts in the bile capillaries, ducts and gallbladder.
A person produces 0.5-1.5 liters of bile during the day. The main components are bile acids, pigments and cholesterol. In addition, it contains fatty acids, mucin, ions (Na +, K + , Ca 2+, Cl -, NCO - 3) and others; The pH of hepatic bile is 7.3-8.0, gallbladder - 6.0 - 7.0.
Primary bile acids (cholic, chenodeoxycholic) are formed in hepatocytes from cholesterol, combine with glycine or taurine and are excreted in the form of sodium salt of glycocholic and potassium salts of taurocholic acids. In the intestine, under the influence of microflora, they are converted into secondary bile acids - deoxycholic and lithocholic. Up to 90% of bile acids are actively reabsorbed from the intestine into the blood and returned to the liver through the portal vessels. Bile pigments (bilirubin, biliverdin) are the breakdown products of hemoglobin, they give bile a characteristic color.
The process of bile formation and excretion is associated with food, secretin, cholecystokinin. Among the foods, egg yolks, milk, meat and fats are strong causative agents of bile secretion. Food intake and associated conditioned and unconditional reflex stimuli activate bile secretion. Initially, the primary reaction occurs: the gallbladder relaxes and then contracts. 7-10 minutes after a meal, a period of evacuation activity of the gallbladder begins, which is characterized by alternating contractions and relaxation and lasts 3-6 hours. After the end of this period, the contractile function of the gallbladder is inhibited and hepatic bile begins to accumulate in it again.
Pancreas physiology. Pancreatic juice is a colorless liquid. During the day, the human pancreas produces 1.5-2.0 liters of juice; its pH is 7.5-8.8. Under the influence of enzymes of pancreatic juice, the intestinal contents are broken down into final products suitable for assimilation by the body. -amylase, lipase, nuclease are secreted in the active state, and trypsinogen, chymotrypsinogen, pro-phospholipase A, proelastase and procarboxypeptidase A and B - in the form of enzymes. Trypsinogen is converted into trypsin in the duodenum. The latter activates pro-phospholipase A, proelastase and procarboxypeptidases A and B, which are converted, respectively, into phospholipase A, elastase and carboxypeptidases A and B.
The enzymatic composition of pancreatic juice depends on the type of food taken: when carbohydrates are taken, the secretion of amylase mainly increases; proteins - trypsin and chymotrypsin; fatty foods - lipase. The composition of pancreatic juice includes bicarbonates, chlorides Na +, K +, Ca 2+, Mg 2+, Zn 2+.
The secretion of the pancreas is regulated by the neuro-reflex and humoral pathways. Distinguish between spontaneous (basal) and stimulating secretion. The first is due to the ability of pancreatic cells to automatism, the second is due to the influence on the cells of neurohumoral factors that are included in the process of food intake.
The main stimulants of exocrine pancreatic cells are acetylcholine and gastrointestinal hormones - cholecystokinin and secretin. They increase the secretion of enzymes and bicarbonates by pancreatic juice. Pancreatic juice begins to be secreted 2-3 minutes after the start of eating as a result of reflex excitation of the gland from the receptors in the oral cavity. And then the effect of gastric contents on the duodenum releases the hormones cholecystokinin and secretin, which determine the mechanisms of secretion of the pancreas.
Digestion in the large intestine. There is practically no digestion in the large intestine. The low level of enzymatic activity is due to the fact that the chyme entering this section of the digestive tract is poor in undigested food substances. However, the large intestine, unlike other parts of the intestine, is rich in microorganisms. Under the influence of the bacterial flora, the remains of undigested food and components of digestive secretions are destroyed, resulting in the formation of organic acids, gases (CO 2, CH 4, H 2 S) and substances toxic to the body (phenol, skatole, indole, cresol). Some of these substances are rendered harmless in the oven, the other is excreted with feces. Of great importance are the enzymes of bacteria that break down cellulose, hemicellulose and pectins, which are not affected by digestive enzymes. These hydrolysis products are absorbed by the colon and used by the body. In the large intestine, microorganisms synthesize vitamin K and B vitamins. The presence of normal microflora in the intestine protects the human body and increases immunity. The remains of undigested food and bacteria, glued together by the mucus of the juice of the colon, form feces. With a certain degree of stretching of the rectum, there is an urge to defecate and there is a voluntary emptying of the intestine; the reflex involuntary center of defecation is located in the sacral spinal cord.
Suction. Digestive products pass through the mucous membrane of the gastrointestinal tract and are absorbed into the blood and lymph by means of transport and diffusion. Absorption occurs mainly in the small intestine. The mucous membrane of the oral cavity also has the ability to absorb, this property is used in the use of certain drugs (validol, nitroglycerin, etc.). Absorption practically does not occur in the stomach. It absorbs water, mineral salts, glucose, medicinal substances, etc. In the duodenum, water, minerals, hormones, and protein breakdown products are also absorbed. In the upper parts of the small intestine, carbohydrates are mainly absorbed in the form of glucose, galactose, fructose, and other monosaccharides. Protein amino acids are absorbed into the bloodstream using active transport. Hydrolysis products of basic dietary fats (triglycerides) are able to penetrate the intestinal cell (enterocyte) only after appropriate physicochemical transformations. Monoglycerides and fatty acids are absorbed in enterocytes only after interacting with bile acids by passive diffusion. Having formed complex compounds with bile acids, they are transported mainly to the lymph. Some of the fats can go directly into the bloodstream, bypassing the lymphatic vessels. Fat absorption is closely related to the absorption of fat-soluble vitamins (A, D, E, K). Water-soluble vitamins can be absorbed by diffusion (eg, ascorbic acid, riboflavin). Folic acid is absorbed in conjugated form; vitamin B 12 (cyanocobalamin) - in the ileum with the help of an intrinsic factor that is formed on the body and fundus of the stomach.
In the small and large intestines, water and mineral salts are absorbed, which come with food and are secreted by the digestive glands. The total amount of water absorbed in the human intestine during the day is about 8-10 liters, sodium chloride - 1 mol. Water transport is closely related to and determined by the transport of Na + ions.
PHYSIOLOGY OF DIGESTION
Digestion is a physiological process that converts feed nutrients from complex chemical compounds into simpler ones that are available for assimilation by the body. In the process of performing various work, the body constantly expends energy. Energy recovery. These resources are provided by the intake of nutrients into the body - proteins, carbohydrates and fats, as well as water, vitamins, mineral salts, etc. Most proteins, fats and carbohydrates are high molecular weight compounds that cannot be absorbed from the alimentary canal into the blood and linfa without preliminary preparation absorbed by the cells and tissues of the body. In the alimentary canal, they are exposed to physical, chemical, biological influences and are converted into low molecular weight, water-soluble, easily absorbable substances.
Eating is conditioned by a special feeling - the feeling of hunger. Hunger (food deprivation) as a physiological state (as opposed to hunger as a pathological process) is an expression of the body's need for nutrients. This condition occurs due to a decrease in the content of nutrients in the depot and circulating blood. In a state of hunger, a strong excitement of the digestive tract occurs, its secretory and motor functions are enhanced, the behavioral reaction of animals aimed at searching for food changes, food behavior in hungry animals is due to the excitation of neurons in various parts of the central nervous system. The totality of these neurons Pavlov called the food center. This center forms and regulates eating behavior aimed at finding food, determines the totality of all complex reflex reactions that ensure finding, obtaining, testing and seizing food.
The food center is a complex hypothalamic-limbic-reticulocortical complex, the leading section of which is represented by the lateral nuclei of the hypothalamus. When these nuclei are destroyed, food refusal occurs (aphagia), and their irritation increases food intake (hyperphagia).
In a hungry animal, which has been transfused with blood from a well-fed animal, the reflexes for obtaining and eating food are inhibited. Various substances are known that cause a state of full and hungry blood. Depending on the type and chemical nature of these substances, several theories have been proposed to explain the feeling of hunger. According to the metabolic theory, the intermediate products of the Krebs cycle, formed during the breakdown of all nutrients, circulating in the blood, determine the degree of food excitability of animals. Found a biologically active substance isolated from the mucous membrane of the duodenum - areterin - which regulates appetite. Suppresses appetite with cystokinin - pancreozymin. In the regulation of specific appetite, an important role is played by the taste analyzer and its higher section in the cerebral cortex.
The main types of digestion. There are three main types of digestion: intracellular, extracellular and membrane. In poorly organized representatives of the animal world, for example, in protozoa, intracellular digestion is carried out. There are special areas on the cell membrane, from which pinocytic vesicles or so-called phagocytic vacuoles are formed. With the help of these formations, the unicellular organism captures food material and digests it with its enzymes.
In mammals, intracellular digestion is characteristic only of leukocytes - blood phagocytes. In higher animals, digestion occurs in an organ system called the digestive tract, which performs a complex function - extracellular digestion.
The digestion of nutrients by enzymes localized on the structures of the cell membrane, mucous membranes of the stomach and intestines, which are spatially intermediate between intracellular and extracellular digestion, is called membrane or parietal digestion.
The main functions of the digestive system are secretory, motor (motor), absorption and excretory (excretory).
Secretory function. The digestive glands produce and secrete juices into the alimentary canal: salivary glands - saliva, stomach glands - gastric juice and mucus, pancreas - pancreas juice, intestinal glands - intestinal juice and mucus, liver - bile.
Digestive juices, or, as they are also called, secrets, moisten the feed and, due to the presence of enzymes in them, promote the chemical conversion of proteins, fats and carbohydrates.
Motor function. The musculature of the digestive organs, due to its powerful contractile properties, facilitates the intake of food, its movement along the alimentary canal and mixing.
Suction function. It is performed by the mucous membrane of individual sections of the alimentary canal: it ensures the transfer of water and split food parts into the blood and lymph.
Excretory function. The mucous membrane of the gastrointestinal tract, liver, pancreas and salivary glands secrete their secretions into the cavity of the alimentary canal. Through the digestive canal, the internal environment of the body is connected with the environment.
The role of enzymes in digestion. Enzymes are biological catalysts, accelerators of the digestion of food substances. By their chemical nature, they belong to proteins, by their physical nature - to colloidal substances. Enzymes are produced by the cells of the digestive glands, mostly in the form of enzymes, precursors of enzymes that do not have activity. Proenzymes become active only when exposed to a number of physical and chemical activators that are different for each of them. For example, the proenzyme pepsinogen, produced by the glands of the stomach, is converted into the active form - pepsin - under the influence of hydrochloric (hydrochloric) acid of gastric juice.
Digestive enzymes are specific, that is, each of them has a catalytic effect only on certain substances. The activity of one or another enzyme is manifested in a certain reaction of the environment - acidic or neutral. IP Pavlov found that the enzyme pepsin loses its effect in an alkaline medium, and restores it in an acidic medium. Enzymes are also sensitive to changes in the temperature of the environment: with a slight increase in temperature, the effect of enzymes is suppressed, and when heated above 60 ° C, it is completely lost. They are less sensitive to low temperatures - their effect weakens somewhat, but it is reversible when the optimum temperature of the environment is restored. For the biological action of enzymes in an animal organism, the optimum temperature is 36-40 ° C. The enzyme activity also depends on the concentration of individual nutrients in the substrate. Enzymes are hydrolases - they break down the chemicals in the feed by attaching H- and OH-ions. Enzymes that break down carbohydrates are called amylolytic enzymes, or amylases; proteins (proteins) - proteolytic, or proteases; fats - lipolytic, or lipases.
Methods for studying the functions of the digestive system. The most perfect and objective method for studying the function of the digestive organs is the Pavlovian method. In pre-Pauline times, the physiology of digestion was studied in primitive ways. To get an idea of the changes in food in the digestive tract, it is necessary to take contents from its various parts. RA Reaumur (XUII-XUIII centuries), in order to obtain gastric juice, introduced hollow metal tubes with holes to the animal through the oral cavity, having previously filled them with nutritious material (in dogs, birds and sheep). Then, after 14-30 hours, the animals were killed and the metal tubes were removed to study their contents. L. Spalantsani filled the same tubes not with food material, but with sponges, from which he subsequently squeezed out the liquid mass. Often, to study changes in food, the contents of the digestive tract of killed animals were compared with the assigned food (V. Ellenberger and others). VA Basov and N. Blondlot performed the operation of gastric fistula imposition in dogs a little later, but they could not isolate a pure secretion of the gastric glands, since the contents of the stomach were mixed with saliva and taken water. A pure secret was obtained as a result of the classical fistula technique developed by I.P. Pavlov, which made it possible to establish the basic patterns in the activity of the digestive organs. Pavlov and his colleagues, using surgical techniques on previously prepared healthy animals (mainly dogs), developed methods for removing the duct of the digestive glands (salivary, pancreas, etc.), for obtaining an artificial opening (fistula) of the esophagus and intestines. After recovery, operated animals for a long time served as objects for studying the function of the digestive system. Pavlov called this method the method of chronic experiments. Currently, the fistula technique has been greatly improved and is widely used to study the digestive and metabolic processes in farm animals.
In addition, to study the functions of the mucous membrane of various departments, a histochemical technique is used, with the help of which it is possible to establish the presence of certain enzymes. To register various sides of the contractile and electrical activity of the walls of the digestive canal, radiotelemetric, radiological other methods are used.
DIGESTION IN THE ORAL CAVITY
Digestion in the oral cavity consists of three stages: intake of food, proper oral digestion and swallowing.
Food and liquid intake. Before taking any food, the animal evaluates it with the help of sight and smell. Then, with the help of receptors in the oral cavity, it selects a suitable feed, leaving inedible impurities.
With the free choice and assessment of the taste of feed, solutions of various food and rejected substances, ruminants have two successive phases of feeding behavior. The first is the phase of testing the quality of feed and drink, and the second is the phase of taking in feed and drinking and refusing them. Milk, glucose, solutions of hydrochloric and acetic acids in the testing phase and especially in the drinking phase increase the number of swallowing acts, the amplitude and frequency of contractions of the parts of the complex stomach. Solutions of sodium bicarbonate and salts of potassium chloride, calcium of high concentration inhibit the manifestation of the first and second phases (KP Mikhaltsov, 1973).
Animals grab food with their lips, tongue and teeth. The well-developed musculature of the lips and tongue allows a variety of movements in different directions.
A horse, a sheep, a goat, when eating grain, grab it with their lips, the grass is cut with incisors and, with the help of the tongue, is directed into the oral cavity. In cows and pigs, the lips are less mobile, they take food with their tongue. Cows cut off the grass when the jaws move laterally, when the incisors of the lower jaw touch the dental plate of the intermaxillary bone. Carnivores grab food with their teeth (sharp incisors and canines).
The intake of water and liquid feed is also different for different animals. Most herbivores drink water as if sucking it through a small gap in the middle of the lips. The tongue pushed back, the jaws open, facilitate the passage of water. Carnivores lap up water and liquid food with their tongues.
Chewing. The feed that has got into the oral cavity is, first of all, subjected to mechanical processing as a result of chewing movements. Chewing is carried out by lateral movements of the lower jaw on one or the other side. In horses, the mouth is usually closed when chewing. Horses immediately chew the food they have received thoroughly. Ruminants chew it slightly and swallow it. The pigs chew the feed thoroughly, crushing the dense parts. Carnivores knead, crush the food and quickly swallow it without chewing.
Salivation... Saliva is a product of secretion (secretion) of three pairs of salivary glands: sublingual, submandibular and parotid. In addition, the secretion of small glands located on the mucous membrane of the lateral walls of the tongue and cheeks enters the oral cavity.
Liquid saliva, without mucus, is secreted by serous glands, thick, containing a large amount of glucoprotein (mucin), - mixed glands. Serous glands include the parotid glands. Mixed glands - sublingual and submandibular, since their parenchyma contains both serous and mucous cells.
To study the activity of the salivary glands, as well as the composition and properties of secretions (saliva) secreted by them, I. P. Pavlov and D. D. Glinsky on dogs developed a technique for superimposing chronic fistulas of the ducts of the salivary glands (Fig. 24). The essence of this technique is as follows. A piece of the mucous membrane with the excretory duct is cut out, brought to the surface of the cheek and sewn to the skin. After a few days, the wound heals and saliva is not released into the oral cavity, but outside.
Saliva is collected by n ciliadriks suspended from a funnel attached to the cheek.
In farm animals, the excretion of the duct is carried out as follows. A T-shaped cannula is inserted through the skin incision into the prepared duct. In this case, the saliva enters the oral cavity outside the experiment. But this method is applicable only for large animals, for small animals, in most cases, the method of removing the duct is used together with the papilla, which is implanted into the skin flap,
The main regularities of the activity of the salivary glands and their importance in the process of digestion were studied by I. P. Pavlov.
Salivation in dogs occurs periodically only when food or any other irritants enter the oral cavity. The quantity and quality of saliva separated mainly depends on the type and nature of the feed taken and a number of other factors. Long-term consumption of starchy feed causes the appearance of amylolytic enzymes in saliva. The amount of saliva separated is influenced by the degree of moisture and the consistency of the food: soft bread in dogs produces less saliva than crackers; more saliva is secreted when eating meat powder than raw meat. This is due to the fact that more saliva is needed to wet dry feed, this is also true for cattle, sheep and goats and has been confirmed by numerous experiments.
Salivation in dogs also increases when so-called rejected substances (sand, bitterness, acids, alkalis and other non-food substances) enter the mouth. For example, if you moisten the oral mucosa with a solution of hydrochloric acid, the secretion of saliva increases (salivation).
The composition of the secreted saliva for food and rejected substances is not the same. Saliva, which is rich in organic matter, especially protein, is released on food substances, and on rejected - the so-called washout. The latter should be considered as a defensive reaction: through increased salivation, the animal is freed from foreign non-food substances.
The composition and properties of saliva. Saliva is a viscous liquid of slightly alkaline reaction with a density of 1.002-1.012 and contains 99-99.4% water and 0.6-1% dry matter.
The organic matter of saliva is represented mainly by proteins, especially mucin. Of the inorganic substances in saliva, there are chlorides, sulfates, carbonates of calcium, sodium, potassium, magnesium. Saliva also contains some metabolic products: carbonic acid salts, urea, etc. Together with saliva, medicinal substances and paints introduced into the body can also be released.
Saliva contains enzymes - amylase and α-glucosidase. Ptialin acts on polysaccharides (starch), breaking them down to dextrins and malyose. Α-glucosidase acts on malyose, converting this disaccharide into glucose. Saliva enzymes are active only at a temperature of 37-40 ° C and in a slightly alkaline environment.
Saliva, moistening food, facilitates the chewing process. In addition, it liquefies the food mass by extracting flavoring substances from it. By means of mucin, saliva sticks together and envelops food and thus makes it easier to swallow. Diastatic enzymes of the feed dissolve in saliva and break down starch.
Saliva regulates acid-base balance, neutralizes stomach acids with alkaline bases. It contains substances with bactericidal action (inhiban and lysozyme). Takes part in the thermoregulation of the body. Through salivation, the animal is freed from excess heat energy. Saliva contains kallikrein and parotin, which regulate the blood supply to the salivary glands and change the permeability of cell membranes.
Salivation in animals of various types. Saliva in a horse occurs periodically, only when feeding. More saliva is separated for dry food, much less - for green grass and moist food. Since the horse thoroughly chews the food alternately on one side and then on the other, the saliva is more separated by the glands of the side where the chewing takes place.
With each chewing movement, saliva is sprayed from the fistula of the parotid duct to a distance of 25-30 cm. Apparently, in a horse, mechanical stimulation with food serves as the leading factor causing secretion. Gustatory stimuli also affect the activity of the salivary glands: when solutions of sodium chloride, hydrochloric acid, soda, pepper are introduced into the oral cavity, salivation increases. The secretion also increases when crushed feed is given, the taste of which is more noticeable, and when yeast is added to the feed. The secretion of saliva in a horse is caused not only by fodder, but also by rejected substances, just like in a dog.
During the day, the horse separates up to 40 liters of saliva. In horse saliva, 989.2 parts of water account for 2.6 parts of organic matter and 8.2 parts of inorganic; ph saliva n 345.
There are few enzymes in the horse's saliva, but the breakdown of carbohydrates still occurs mainly due to the pma enzymes, which are active in the slightly alkaline reaction of saliva. The action of the enzymes of saliva and feed can continue even when the feed mass enters the initial and central parts of the stomach, where a slightly alkaline reaction is still maintained.
The salivation process in ruminants proceeds somewhat differently than in horses, since the food in the oral cavity is not thoroughly chewed. The role of saliva in this case is reduced to wetting the feed, which facilitates the swallowing process. Saliva has the main effect on digestion in the oral cavity during chewing. The parotid gland profusely secretes both during the intake of food and gum, and during periods of rest, and the submandibular gland separates saliva periodically.
The activity of the salivary glands is influenced by a number of factors on the part of the proventriculus, especially the scar. With an increase in pressure in the rumen, the secretion of the parotid gland increases. Chemical factors also affect the salivary glands. For example, the introduction of acetic and lactic acids into the rumen first inhibits and then enhances salivation.
In cattle per day, production is 90-190, in sheep - 6-10 liters of saliva. The amount and composition of saliva produced depends on the type of animal, feed and its consistency. In the saliva of ruminants, organic matter is 0.3, inorganic - 0.7%; saliva pH 8-9. High alkalinity of saliva, its concentration contribute to the normalization of biotic processes in the proventriculus. The abundant amount of saliva flowing into the rumen neutralizes the acids formed during the fermentation of cellulose.
Salivation in pigs occurs periodically when feeding. The degree of secretory activity of the salivary glands in them depends on the nature of the food. So, when eating liquid talkers, saliva is almost not produced. The nature and method of preparation of the feed affect not only the amount of saliva separated, but also its quality. The pig produces up to 15 liters of saliva per day, and about half of it is secreted by the parotid salivary gland. Saliva contains 0.42% of dry matter, of which 57.5 is organic, and 42.5% is inorganic; pH 8.1-8.47. Pig saliva has a pronounced amylolytic activity. It contains the enzymes ptyalin and malase. The enzymatic activity of saliva can persist in individual portions of the contents of the stomach for up to 5-6 hours.
Regulation of salivation. Salivation is carried out under the influence of unconditioned and conditioned reflexes. This is a complex reflex reaction. Initially, as a result of the capture of food and its entry into the oral cavity, the receptor apparatus of the mucous membrane of the lips and tongue is excited. The food irritates the nerve endings of the fibers of the trigeminal and glossopharyngeal nerves, as well as the branches (superior laryngeal) of the vagus nerve. Through these centripetal paths, impulses from the oral cavity reach the medulla oblongata, where the center of salivation is located, then enter the thalamus, hypothalamus and cerebral cortex. From the salivary center, excitement is transmitted to the glands along the sympathetic and a pair of sympathetic nerves, the latter passing through the glossopharyngeal and facial nerves. The parotid gland is innervated by the glossopharyngeal branch and the ear-temporal branch of the trigeminal nerves. The submandibular and sublingual glands are equipped with a branch of the facial nerve called the tympanic string. Irritation of the drum string causes active secretion of liquid saliva. When the sympathetic nerve is irritated, a small amount of thick, mucus (sympathetic) saliva is secreted.
Nervous regulation has little effect on the function of the parotid gland of ruminants, since the continuity of its secretion is due to the constant influence of the chemo- and mechanoreceptors of the proventriculus. Their sublingual and submandibular glands secrete periodically.
D 
The activity of the salivary center of the medulla oblongata is regulated by the hypothalamus and cerebral cortex. The participation of the cerebral cortex in the regulator of salivation in dogs was established by I.P. Pavlov. A conditioned signal, for example a bell, was accompanied by the delivery of food.
After several such combinations, the dog salivated on just one call. Pavlov called this salivation conditioned reflex. Conditioned reflexes are also developed in horses, pigs, and ruminants. However, in the latter, a conditioned natural stimulus reduces the secretion of the parotid glands. This is due to the fact that they are constantly aroused and constantly secreting.
The center of salivation is affected by many different stimuli - reflex and humoral. Irritation of receptors in the stomach and intestines can excite or inhibit salivation.
Saliva production is a secretory process carried out by cells of the salivary glands. The process of secretion includes the synthesis of the cell of the same parts of the secretion, the formation of granules of the secretion, the removal of the secretion from the cell and the restoration of its original structure. It is covered with a membrane that forms microvilli, inside it contains a nucleus, mitochondria, Golgi complex, endoplasmic reticulum, the surface of the tubules of which is dotted with ribosomes. Water, mineral compounds, amino acids, sugars and other substances selectively enter the cell through the membrane.
The secretion is formed in the tubules of the endoplasmic reticulum. Through their wall, the secret passes into the vacuole of the Golgi complex, where its final formation takes place (Fig. 25). During rest, the glands are more granular due to the presence of many granules of secretion, during and after salivation, the number of granules decreases.
Swallowing. This is a complex reflex act. Chewed and moistened food is fed by the movement of the cheeks and tongue in the form of a coma on the back of the tongue. Then the tongue presses it against the soft palate and pushes first to the root of the tongue, then to the pharynx. The food, irritating the mucous membrane of the pharynx, causes a reflex contraction of the muscles that lift the soft palate, and the root of the tongue presses the epiglottis to the larynx, therefore, when swallowing, the lump does not enter the upper respiratory tract. By contractions of the muscles of the pharynx, the food lump is pushed further to the funnel of the esophagus. Swallowing can be carried out only with direct irritation of the afferent nerve endings of the pharyngeal mucosa with food or saliva. With a dry mouth, swallowing is difficult or absent.
The swallowing reflex is carried out as follows. Through the sensitive branches of the trigeminal and glossopharyngeal nerves, excitation is transmitted to the medulla oblongata, where the swallowing center is located. From it, excitation goes backwards along the efferent (motor) fibers of the trigeminal, glossopharyngeal and vagus nerves, which causes muscle contraction. With loss of sensitivity of the pharyngeal mucosa (transection of the afferent nerves or lubrication of the mucous membrane with cocaine), swallowing does not occur.
The movement of the food coma from the pharynx through the esophagus occurs due to its peristaltic movements, which are caused by the vagus nerve innervating the esophagus.
Peristalsis of the esophagus is a wave-like contraction, in which there is an alternation of contractions and relaxation of individual areas. Liquid food passes through the esophagus quickly, in a continuous stream, dense food - in separate portions. The movement of the esophagus causes a reflex opening of the entrance to the stomach.
DIGESTION IN THE STOMACH
In the stomach, food is subjected to mechanical processing and the chemical effects of gastric juice. Mechanical processing - stirring, and then moving it into the intestine - is carried out by contractions of the stomach muscles. Chemical transformations of food in the stomach occur under the influence of gastric juice.
The process of formation of gastric mucosa by the glands and its separation into the cavity constitute the secretory function of the stomach. In the unicameral stomach and the abomasum of the ruminant, according to their location, they are divided into cardiac, fundic and pyloric.
Most of the glands are located in the fundus and lesser curvature of the stomach. The fundus glands occupy 2/3 of the surface of the gastric mucosa and consist of main, parietal and accessory cells. The main cells produce enzymes, the lining cells produce hydrochloric acid, and the additional cells produce mucus. The secrets of the main and parietal cells are mixed. The cardiac glands consist of accessory cells, the pyloric gland - of the main and accessory cells.
Methods for studying gastric secretion. The experimental study of gastric secretion was first begun by the Russian surgeon V. A. Basov and the Italian scientist Blondlot (1842), who created an artificial stomach fistula in dogs. However, the bass fistula method did not make it possible to obtain pure gastric juice, since it was mixed with saliva and food masses.
The method of obtaining pure gastric juice was developed by I.P. Pavlov and his colleagues. The dogs had a gastric fistula and the esophagus was cut. The ends of the cut esophagus were taken out and sutured to the skin. The swallowed food did not enter the stomach, but dumped out. During the act of eating, the dog exuded pure gastric juice, despite the fact that the food did not enter the stomach. Pavlov called this method the "imaginary feeding" experience. This method makes it possible to obtain pure gastric juice and proves the presence of reflex influences from the oral cavity. However, it cannot be used to establish the effect of feed directly on the stomach glands. The latter was studied by the isolated ventricle method. One of the options for the operation of an isolated ventricle was proposed by R. Heidenhain (1878). But this isolated ventricle had no nerve connection with the large stomach, its connection was carried out only through the blood vessels. This experience did not reflect reflex influences on the secretory activity of the stomach.
The human and animal body is an open thermodynamic system that constantly exchanges matter and energy with the environment. The body requires replenishment of energy and building materials. It is necessary for work, temperature maintenance, tissue repair. Man and animals receive these materials from the environment in the form of animal or plant origin. In foods, in different proportions, nutrients are proteins, fats. Nutrients are large polymer molecules. Food also contains water, mineral salts, vitamins. And although these substances are not a source of energy, they are very important components for life. Nutrients from foods cannot be absorbed immediately; this requires the processing of nutrients in the gastrointestinal tract so that the digested products can be used.
The length of the digestive tract is approximately 9 m. The digestive system includes the oral cavity, pharynx, esophagus, stomach, small and large intestine, rectum and anal canal. There are additional organs of the gastrointestinal tract - these include the tongue, teeth, salivary glands, pancreas, liver and gallbladder.
The alimentary canal is composed of four layers or membranes.
- Mucous
- Submucosa
- Muscular
- Serous
Each shell performs its own function.
Mucous membrane surrounds the lumen of the alimentary canal and is the main suction surface and secretory surface. The mucous membrane is covered with a columnar epithelium, which is located on its own plate. There are numerous limf in the plate. Nodules and they perform a protective function. Outside, the layer of smooth muscles is the muscle plate of the mucous membrane. Due to the contraction of these muscles, the mucous membrane forms folds. The mucosa also contains goblet cells that produce mucus.
Submucosa represented by a layer of connective tissue with a large number of blood vessels. The submucosa contains glands and the submucous nerve plexus - Yeissner's plexus... The submucosal layer provides nutrition to the mucous membrane and autonomic innervation of the glands, smooth muscles of the muscle plate.
Muscular membrane... Consists of 2 layers of smooth muscle. Internal - circular and external - longitudinal. Muscles are arranged in bundles. The muscular membrane is designed to perform a motor function, for mechanical processing of food and for moving food along the alimentary canal. The muscular membrane contains the second plexus - Auerbach. The fibers of the sympathetic and parasympathetic nerves end on the plexus cells in the gastrointestinal tract. In the composition there are sensitive cells - Doggel's cells, there are motor cells - of the first type, there are inhibitory neurons. The set of elements of the gastrointestinal tract is an integral part of the autonomic nervous system.
Outer serous membrane- connective tissue and squamous epithelium.
In general, the gastrointestinal tract is intended for the course of digestion processes and the basis of digestion is the hydrolytic process of splitting large molecules into simpler compounds that can be obtained by blood and tissue fluid and delivered to the site. The functioning of the digestive system resembles that of a disassembly conveyor.
Digestion stages.
- Food absorption... It includes absorbing food into the mouth, chewing food into smaller pieces, moisturizing, forming a food lump, and swallowing
- Digestion of food... In the course of it, further processing and enzymatic breakdown of nutrients are carried out, while proteins are cleaved by proteases and amino dipeptides and amino acids. Carbohydrates are broken down by amylase to monosaccharides, and fats are broken down by lipases and esterases to monoglycerin and fatty acids.
- The formed simple connections undergo the following process - absorption of products... But not only the breakdown products of nutrients are absorbed, but water, electrolytes, vitamins are absorbed. During absorption, substances are transferred into the blood and lymph. There is a chemical process in the digestive tract, as in any production by-products and wastes arise, which can often be poisonous.
- Excretion- are removed from the body in the form of feces. For the implementation of digestion processes, the digestive system performs motor, secretory, absorption and excretory functions.
The digestive tract is involved in water-salt metabolism, a number of hormones are produced in it - endocrine function, has a protective immunological function.
Digestion types- are subdivided depending on the intake of hydrolytic enzymes and are divided into
- Own - enzymes of the macroorganism
- Symbiotic - due to enzymes that bacteria and protozoa that live in the gastrointestinal tract give us
- Autolytic digestion - due to enzymes that are contained in the food itself.
Depending on localization the process of hydrolysis of nutrients, digestion is divided into
1. Intracellular
2. Extracellular
Distant or cavity
Contact or parietal
Cavity digestion will occur in the lumen of the gastrointestinal tract, by enzymes, on the membrane of the microvilli of the intestinal epithelium cells. The microvilli are coated with a layer of polysaccharides and form a large catalytic surface for fast degradation and fast absorption.
The value of the work of I.P. Pavlova.
Attempts to study the processes of digestion begin already in the 18th century, for example Reamur tried to get gastric juice by placing a sponge tied on a string into the stomach and received digestive juice. There were attempts to implant glass or metal tubes into the ducts of the glands, but they quickly fell out and an infection was added. The first clinical observations in humans were carried out with a stomach wound. In 1842 the Moscow surgeon Basov put a fistula on the stomach and closed with a stopper outside the digestion process. This operation made it possible to obtain gastric juice, but the disadvantage was that it was mixed with food. Later, in Pavlov's laboratory, this operation was supplemented by an incision of the esophagus and neck. Such an experience is called the experience of sham feeding, and after feeding, the chewed food is digested.
English physiologist Heidenhain suggested isolating a small ventricle from a large one, this made it possible to obtain pure gastric juice unmixed with food, but the disadvantage of the operation - the incision - perpendicular to the greater curvature - it crossed the nerve - the vagus. Only humoral factors could act on the small ventricle.
Pavlov suggested doing parallel to the greater curvature, the vagus was not cut, it reflected the entire course of digestion in the stomach with the participation of both nervous and humoral factors. I.P. Pavlov set the task of studying the function of the digestive tract as close as possible to normal conditions, and Pavlov develops methods of physiological surgery by carrying out a variety of operations on animals, which later helped in the study of digestion. Basically, operations were aimed at imposing fistulas.
Fistula- artificial communication of the cavity of the organ or duct of the gland with the environment to obtain the contents and after the operation the animal was recovering. This was followed by recovery, long-term nutrition.
In physiology, poignant experiences- once under anesthesia and chronic experience- in conditions as close to normal as possible - with anesthesia, without pain factors - this gives a more complete picture of the function. Pavlov develops fistulas of the salivary glands, small ventricular surgery, esophagotomy, gallbladder and pancreatic duct.
First merit Pavlova in digestion consists in the development of chronic experiment experiments. Further, Ivan Petrovich Pavlov established the dependence of the quality and quantity of secrets on the type of food stimulus.
Thirdly- the adaptability of the glands to nutritional conditions. Pavlov showed the leading role of the nervous mechanism in the regulation of the digestive glands. Pavlov's works in the field of digestion were summarized in his book "On the work of the most important digestive glands" In 1904, Pavlov was awarded the Nobel Prize. In 1912, the University of England, Newton, Byron elected Pavlov as an honorary doctor of the University of Cambridge, and at the initiation ceremony there was such an episode when Cambridge students released a toy dog with numerous fistulas.
Physiology of salivation.
Saliva is formed by three pairs of salivary glands - the parotid, located between the jaw and the ear, the submandibular, located under the lower jaw, and the sublingual. Small salivary glands - work constantly, unlike large ones.
Parotid gland consists only of serous cells with a watery secretion. Submandibular and sublingual glands allocate a mixed secret, tk. include both serous and mucous cells. The secretory unit of the salivary gland - salivon, which includes the acinus, blindly ending expansion and formed by acinar cells, the acinus, then opens into the intercalary duct, which passes into the striated duct. Acinus cells secrete proteins and electrolytes. Water also comes here. Then, the correction of the electrolyte content in saliva is carried out by the intercalated and striated ducts. The secretory cells are still surrounded by myoepithelial cells, capable of contraction, and myoepithelial cells, by contracting, squeeze out the secret and promote its movement along the duct. The salivary glands receive an abundant blood supply, there are 20 times more beds in them than in other tissues. Therefore, these small organs have a rather powerful secretory function. From 0.5 - 1.2 liters are produced per day. saliva.
Saliva.
- Water - 98.5% - 99%
- Solid residue 1-1.5%.
- Electrolytes - К, НСО3, Na, Cl, I2
Saliva secreted in the ducts is hypotonic compared to plasma. In the acini, electrolytes are secreted by secretory cells and they are contained in the same amount as in plasma, but as saliva moves through the ducts, sodium and chlorine ions are absorbed, the number of potassium and bicarbonate ions becomes larger. Saliva is characterized by a predominance of potassium and bicarbonate. Organic composition of saliva represented by enzymes - alpha-amylase (ptyalin), lingual lipase - produced by the glands located at the root of the tongue.
The salivary glands contain calycrein, mucus, lactoferin - they bind iron and help to reduce bacteria, lysozyme glycoproteins, immunoglobulins - A, M, antigens A, B, AB, 0.
Saliva is excreted through the ducts - functions - wetting, the formation of a food lump, swallowing. In the oral cavity - the initial stage of the breakdown of carbohydrates and fats. Complete splitting cannot occur because short time the food is in the food cavity. The optimum action of saliva is a slightly alkaline medium. The pH of saliva = 8. Saliva restricts the growth of bacteria, promotes healing of injuries, hence the licking of wounds. We need saliva for normal speech function.
Enzyme salivary amylase carries out the splitting of starch to maltose and maltotriose. Salivary amylase is similar to pancreatic amylase, which also breaks down carbohydrates to maltose and maltotriose. Maltase and isomaltase, breaks down these substances to glucose.
Saliva lipase begins to break down fats and enzymes continue their action in the stomach until the pH value changes.
Regulation of salivation.
Regulation of salivary secretion is carried out by parasympathetic and sympathetic nerves, and the salivary glands are regulated only reflexively, since they are not characterized by a humoral regulation mechanism. Salivary excretion can be carried out using unconditioned reflexes that occur when the oral mucosa is irritated. In this case, there may be food and non-food irritants.
Mechanical irritation of the mucous membrane also affects salivation. Salivation can be caused by the smell, sight, memory of delicious food. Salivation is formed with nausea.
Inhibition of salivation is observed during sleep, with fatigue, with fear and with dehydration.
The salivary glands receive double innervation from the autonomic nervous system. They are innervated by the parasympathetic and sympathetic divisions. Parasympathetic innervation is carried out by 7 and 9 pairs of nerves. They contain 2 salivary nuclei - upper -7 and lower - 9. The seventh pair innervate the submandibular and sublingual glands. 9 pair - parotid gland. In the endings of the parasympathetic nerves, acetylcholine is released, and under the action of acetylcholine on the receptors of secretory cells through G-proteins, the secondary messenger inositol-3-phosphate is innervated, and it increases the calcium content inside. This leads to an increase in the secretion of saliva, poor in organic composition - water + electrolytes.
The sympathetic nerves reach the salivary glands through the superior cervical sympathetic ganglion. At the endings of postganglionic fibers, norepinephrine is released, i.e. secretory cells of the salivary glands have adrenergic receptors. Norepinephrine causes the activation of adenylate cyclase with the subsequent formation of cyclic AMP and cyclic AMP enhances the formation of protein kinase A, which is necessary for protein synthesis, and sympathetic effects on the salivary glands increase secretion.
Highly viscous saliva with a lot of organic matter. As an afferent link in the excitation of the salivary glands, it will involve the nerves that provide general sensitivity. The taste sensitivity of the anterior third of the tongue is the facial nerve, the posterior third is the glossopharyngeal. The posterior sections are still innervated from the vagus nerve. Pavlov showed that the secretion of saliva on the rejected substances, and the ingress of river sand, acids, other chemicals, there is a large release of saliva, namely liquid saliva. Salivation also depends on the fragmentation of food. For nutrients, less saliva is given, but with a higher content of the enzyme.
Physiology of the stomach.
The stomach is a part of the digestive tract, where food is retained from 3 to 10 hours for mechanical and chemical processing. A small amount of food is digested in the stomach, and the absorption area is also not large. This is a reservoir for storing food. In the stomach, we isolate the bottom, the body, the pyloric section. The contents of the stomach are confined from the esophagus by the cardiac sphincter. At the transition of the pyloric section to the duodenum. There is a functional sphincter.
Stomach function
- Depositing food
- Secretory
- Motor
- Suction
- Excretory function. Promotes the removal of urea, uric acid, creatine, creatinine.
- Endocrine function is the formation of hormones. The stomach has a protective function
On the basis of functional characteristics, the mucous membrane is divided into acid-producing, which is located in the proximal section on the central part of the body, antral mucosa is also isolated, which does not form hydrochloric acid.
Composition- mucous cells that form mucus.
- The lining cells that produce hydrochloric acid
- The main cells that produce enzymes
- Endocrine cells that produce the hormone G-cells - gastrin, D - cells - somatostatin.
Glycoprotein - forms a slimy gel, it envelops the wall of the stomach and prevents the effect of hydrochloric acid on the mucous membrane. This layer is very important otherwise the mucous membrane is disturbed. It is destroyed by nicotine, little mucus is produced during stressful situations, which can lead to gastritis and ulcers.
The glands of the stomach produce pepsinogens, which act on proteins, they are inactive and need hydrochloric acid. Hydrochloric acid is produced by the parietal cells, which also produce Castle factor- which is needed to assimilate the external factor B12. In the area of the antrum, there are no parietal cells, the juice is produced in a slightly alkaline reaction, but the mucous membrane of the antrum is rich in endocrine cells that produce hormones. 4G-1D - ratio.
To study the function of the stomach methods are being studied that impose fistulas - the secretion of a small ventricle (according to Pavlov) and in humans, gastric secretion is studied by probing and obtaining gastric juice on an empty stomach without giving food, and then after a test breakfast and the most common breakfasts is a glass of tea without sugar and a slice of bread. These simple foods are powerful stomach stimulants.
Composition and properties of gastric juice.
At rest in the stomach in a person (without food intake) there is 50 ml of basal secretion. It is a mixture of saliva, gastric juice, and occasionally a reflux from the duodenum. About 2 liters of gastric juice is formed per day. It is a transparent opalescent liquid with a density of 1.002-1.007. Has an acidic reaction, since there is hydrochloric acid (0.3-0.5%). pH 0.8-1.5. Hydrochloric acid can be free and bound to protein. Gastric juice also contains inorganic substances - chlorides, sulfates, phosphates and bicarbonates of sodium, potassium, calcium, magnesium. Organic matter is represented by enzymes. The main enzymes in gastric juice are pepsins (proteases that act on proteins) and lipases.
Pepsin A - pH 1.5-2.0
Gastrixin, pepsin C - pH-3.2-, 3.5
Pepsin B - gelatinase
Renin, pepsin D chymosin.
Lipase, acts on fats
All pepsins are excreted in an inactive form as pepsinogen. Now it is proposed to divide pepsins into groups 1 and 2.
Pepsins 1 are secreted only in the acid-forming part of the gastric mucosa - where there are parietal cells.
Antral part and pyloric part - pepsins are secreted there group 2... Pepsins carry out digestion to intermediate products.
Amylase, which is ingested with saliva, can break down carbohydrates in the stomach for some time until the pH changes into an acidic groan.
The main component of gastric juice is water - 99-99.5%.
An important component is hydrochloric acid. Its functions:
- It promotes the conversion of an inactive form of pepsinogen into an active form - pepsins.
- Hydrochloric acid creates the optimal pH value for proteolytic enzymes
- Causes denaturation and swelling of proteins.
- The acid has an antibacterial effect and bacteria that enter the stomach are killed
- Participates in the formation of hormones - gastrin and secretin.
- Locks milk
- Participates in the regulation of the transfer of food from the stomach to the 12-persistent intestine.
Hydrochloric acid formed in the parietal cells. These are fairly large pyramidal cells. Inside these cells there are a large number of mitochondria, they contain a system of intracellular tubules and a vesicular system in the form of vesicles is closely connected with them. These vesicles bind to the tubule when they are activated. A large number of microvilli form in the tubule, which increase the surface area.
The formation of hydrochloric acid occurs in the intratubular system of the parietal cells.
At the first stage there is a transfer of the chlorine anion into the lumen of the tubule. Chlorine ions are supplied through a special chlorine channel. A negative charge is created in the tubule, which attracts intracellular potassium there.
In the next step there is an exchange of potassium for a hydrogen proton, due to the active transport of hydrogen to potassium ATPase. Potassium is exchanged for a hydrogen proton. With this pump, potassium is driven into the intracellular wall. Carbonic acid is formed inside the cell. It is formed as a result of the interaction of carbon dioxide and water due to carbonic anhydrase. Carbonic acid dissociates into a hydrogen proton and an HCO3 anion. The hydrogen proton is exchanged for potassium, and the HCO3 anion is exchanged for the chlorine ion. Chlorine enters the lining cell, which then goes into the lumen of the tubule.
There is another mechanism in the parietal cells - sodium - potassium atphase, which removes sodium from the cell and returns sodium.
The formation of hydrochloric acid is an energy-consuming process. ATP is produced in the mitochondria. They can occupy up to 40% of the volume of the parietal cells. The concentration of hydrochloric acid in the tubules is very high. PH inside the tubule up to 0.8 - concentration of hydrochloric acid 150 ml mol per liter. The concentration is 4,000,000 higher than plasma. The formation of hydrochloric acid in the parietal cell is regulated by the effects on the parietal cell of acetylcholine, which is secreted at the endings of the vagus nerve.
The covering cells have cholinergic receptors and the formation of HCl is stimulated.
Gastrin receptors and the hormone gastrin also activates the formation of HCl, and this occurs through the activation of membrane proteins and the formation of phospholipase C and inositol-3-phosphate is formed and this stimulates an increase in calcium and the hormonal mechanism is triggered.
The third type of receptor is histamine receptorsH2 ... Histamine is produced in the stomachs by enterochromatin mast cells. Histamine acts on H2 receptors. Here the influence is realized through the adenylate cyclase mechanism. Adenylate cyclase is activated and cyclic AMP is formed
Inhibits - somatostatin, which is produced in D cells.
Hydrochloric acid- the main factor of damage to the mucous membrane in violation of the protection of the membrane. Treatment of gastritis - suppression of the action of hydrochloric acid. Histamine antagonists are very widely used - cimetidine, ranitidine, block H2 receptors and reduce the formation of hydrochloric acid.
Suppression of hydrogen-potassium atphase. A substance was obtained that is the pharmacological drug omeprazole. It suppresses the hydrogen-potassium phase. This is a very mild action that reduces the production of hydrochloric acid.
Mechanisms of regulation of gastric secretion.
The process of gastric digestion is conventionally divided into 3 phases overlapping each other
1. Difficult reflex - cerebral
2. Gastric
3. Intestinal
Sometimes the latter two are combined into a neurohumoral one.
Difficult reflex phase... It is caused by the excitation of the gastric glands by a complex of unconditioned and conditioned reflexes associated with food intake. Conditioned reflexes arise when the olfactory, visual, and auditory receptors are irritated, by sight, smell, or by the environment. These are conditional signals. They are superimposed on the effect of irritants on the oral cavity, pharyngeal receptors, esophagus. These are unconditional irritations. It was this phase that Pavlov studied in the experience of imaginary feeding. The latency period from the beginning of feeding is 5-10 minutes, that is, the gastric glands are turned on. After stopping feeding, secretion lasts 1.5-2 hours if food does not enter the stomach.
The secretory nerves will be the wandering ones. It is through them that the effect on the parietal cells that produce hydrochloric acid occurs.
Nervus vagus stimulates gastrin cells in the antrum and Gastrin is formed, and D cells, where somatostatin are produced, are inhibited. It was found that the vagus nerve acts on gastrin cells through a neurotransmitter - bombesin. This excites gastrin cells. On D cells, which produce somatostatin, it suppresses. In the first phase of gastric secretion - 30% of gastric juice. It has a high acidity, digestive power. The purpose of the first phase is to prepare the stomach for eating. When food enters the stomach, the gastric phase of secretion begins. In this case, the food content mechanically stretches the walls of the stomach and the sensitive endings of the vagus nerves are excited, as well as the sensitive endings, which are formed by the cells of the submucosal plexus. Local reflex arcs appear in the stomach. Doggel's cell (sensitive) forms a receptor in the mucous membrane and when irritated, it is excited and transmits excitation to type 1 cells - secretory or motor. A local local reflex arises and the gland begins to work. Cells of the 1st type are also postganlionars for the vagus nerve. The vagus nerves keep the humoral mechanism under control. Simultaneously with the nervous mechanism, the humoral mechanism begins to work.
Humoral mechanism associated with the release of Gastrin by G cells. They produce two forms of gastrin - of 17 amino acid residues - "small" gastrin and there is a second form of 34 amino acid residues - large gastrin. Small gastrin is more potent than large gastrin, but there is more large gastrin in the blood. Gastrin, which is produced by subgastrin cells and acts on the parietal cells to stimulate the formation of HCl. It also acts on the lining cells.
Functions of gastrin - stimulates the secretion of hydrochloric acid, enhances the production of an enzyme, stimulates gastric motility, is necessary for the growth of the gastric mucosa. It also stimulates the secretion of pancreatic juice. The production of gastrin is stimulated not only by nerve factors, but also food products that are formed during the breakdown of food are also stimulants. These include protein breakdown products, alcohol, coffee - caffeine and non-caffeine. The production of hydrochloric acid depends on the ph and when the ph drops below 2x, the production of hydrochloric acid is suppressed. Those. this is due to the fact that a high concentration of hydrochloric acid inhibits the production of gastrin. At the same time, the high concentration of hydrochloric acid activates the production of somatostatin, and it inhibits the production of gastrin. Amino acids and peptides can act directly on the parietal cells and increase the secretion of hydrochloric acid. Proteins, with their buffering properties, bind a hydrogen proton and maintain an optimal level of acid formation
Supports gastric secretion intestinal phase... When chyme enters the duodenum 12, it affects gastric secretion. 20% of gastric juice is produced during this phase. It produces enterogastrin. Enterooxyntin - these hormones are produced under the influence of HCl, which comes from the stomach into the duodenum, under the influence of amino acids. If the acidity of the environment in the duodenum is high, then the production of stimulating hormones is suppressed, and enterogastron is produced. One of the varieties will be - GIP - gastrointestinal peptide. It inhibits the production of hydrochloric acid and gastrin. Inhibitory substances also include bulbogastron, serotonin, and neurotensin. On the part of the duodenum, reflex influences can also arise that excite the vagus nerve and include the local nerve plexuses. In general, the separation of gastric juice will depend on the amount of food quality. The amount of gastric juice depends on the residence time of the food. In parallel with the increase in the amount of juice, its acidity also increases.
The digesting power of the juice is greater in the first hours. To assess the digestive power of juice, it is proposed Ment's method... Fatty foods inhibit gastric secretion; therefore, it is not recommended to eat fatty foods at the beginning of a meal. Hence, children are never given fish oil prior to eating. Pre-intake of fats - reduces the absorption of alcohol in the stomach.
Meat - protein product, bread - vegetable and milk - mixed.
For meat- the maximum amount of juice is allocated with the maximum secretion for the second hour. The juice has the maximum acidity, the fermentation is not high. The rapid increase in secretion is due to strong reflex irritation - sight, smell. Then, after the maximum, secretion begins to decline, the decline in secretion is slow. The high content of hydrochloric acid ensures protein denaturation. The final breakdown takes place in the intestines.
Secretion on bread... The maximum is reached by the 1st hour. The rapid build-up is associated with a strong reflex stimulus. Having reached the maximum, the secretion drops rather quickly, because few humoral stimulants, but secretion lasts a long time (up to 10 hours). Enzymatic capacity - high - no acidity.
Milk - a slow rise in secretion... Weak irritation of receptors. They contain fats, inhibit secretion. The second phase after reaching the maximum is characterized by a steady decline. Here, fat breakdown products are formed, which stimulate secretion. The enzymatic activity is low. You must eat vegetables, juices and mineral water.
The secretory function of the pancreas.
The chyme that enters the duodenum 12 is exposed to the action of pancreatic juice, bile and intestinal juice.
Pancreas- the largest gland. It has a double function - intrasecretory - insulin and glucagon and an exocrine function, which ensures the production of pancreatic juice.
Pancreatic juice is formed in the gland, in the acinus. Which are lined with transition cells in 1 row. An active process of enzyme formation takes place in these cells. They have a well-expressed endoplasmic reticulum, the Golgi apparatus, and from the acini, the pancreatic ducts begin and form 2 ducts that open into the duodenum 12. The largest duct is Wirsunga channel... It opens with a common bile duct in the area of Vater's nipple. The sphincter of Oddi is located here. Second accessory duct - Santorinni opens proximal to the Versung duct. Study - the imposition of fistulas on 1 of the ducts. In humans, it is studied by probing.
In their own way composition of pancreatic juice- transparent colorless liquid of alkaline reaction. The amount is 1-1.5 liters per day, pH 7.8-8.4. The ionic composition of potassium and sodium is the same as in plasma, but there are more bicarbonate ions and less Cl. In the acinus, the content is the same, but as the juice moves along the ducts, it leads to the fact that the duct cells provide the capture of chlorine anions and the amount of bicarbonate anions increases. Pancreatic juice is rich in enzyme composition.
Proteolytic enzymes acting on proteins - endopeptidases and exopeptidases. The difference is that endopeptidases act on internal bonds, while exopeptidases cleave terminal amino acids.
Endopepidase- trypsin, chymotrypsin, elastase
Ectopeptidase- carboxypeptidases and aminopeptidases
Proteolytic enzymes are produced in an inactive form - enzymes. Activation occurs under the action of enterokinase. It activates trypsin. Trypsin is excreted in the form of trypsinogen. And the active form of trypsin activates the rest. Enterokinase is an enzyme of intestinal juice. With blockages of the duct of the gland and with abundant alcohol consumption, activation of pancreatic enzymes inside it may occur. The process of self-digestion of the pancreas begins - acute pancreatitis.
For carbohydrates aminolytic enzymes - alphaamylase act, breaks down polysaccharides, starch, glycogen, cannot break down cellulo, with the formation of maltoyz, maltotiose, and dextrin.
Fatty litholytic enzymes - lipase, phospholipase A2, cholesterol. Lipase acts on neutral fats and breaks them down to fatty acids and glycerol, cholesterol esterase acts on cholesterol, and phospholipase acts on phospholipids.
Enzymes on nucleic acids- ribonuclease, deoxyribonuclease.
Regulation of the pancreas and its secretion.
It is associated with nervous and humoral mechanisms of regulation and the pancreas is included in 3 phases
- Difficult reflex
- Gastric
- Intestinal
Secretory nerve - nervus vagus, which acts on the production of enzymes in the acini cell and on the duct cells. There is no influence of sympathetic nerves on the pancreas, but sympathetic nerves cause a decrease in blood flow, and a decrease in secretion occurs.
Is of great importance humoral regulation pancreas - the formation of 2 hormones of the mucous membrane. There are C cells in the mucous membrane that produce the hormone secretin and secretin absorbed into the blood, it acts on the cells of the pancreatic ducts. Stimulates these cells by the action of hydrochloric acid
2nd hormone is produced by I cells - cholecystokinin... Unlike secretin, it acts on acin cells, the amount of juice will be less, but the juice is rich in enzymes and the excitation of type I cells is under the influence of amino acids and, to a lesser extent, hydrochloric acid. Other hormones act on the pancreas - VIP - has an effect similar to secretin. Gastrin is similar to cholecystokinin. In the complex reflex phase, secretion is released 20% of its volume, 5-10% falls on the gastric, and the rest in the intestinal phase, etc. the pancreas is in the next stage of influencing food, the production of gastric juice interacts very closely with the stomach. If gastritis develops, then pancreatitis follows.
Physiology of the liver.
The liver is the largest organ. An adult's weight is 2.5% of the total body weight. In 1 minute, the liver receives 1350 ml of blood and this is 27% of the minute volume. The liver receives both arterial and venous blood.
1. Arterial blood flow - 400 ml per minute. Arterial blood flows through the hepatic artery.
2. Venous blood flow - 1500 ml per minute. Venous blood flows through the portal vein from the stomach, small intestine, pancreas, spleen, and partly the large intestine. It is through the portal vein that nutrients and vitamins come from the digestive tract. The liver captures these substances and then distributes them to other organs.
The important role of the liver belongs to carbon metabolism. It maintains blood sugar levels as a glycogen depot. Regulates the content of lipids in the blood and especially low density lipoproteins, which it secretes. An important role in the protein department. All plasma proteins are produced in the liver.
The liver performs a detoxifying function in relation to toxic substances and drugs.
Performs a secretory function - the formation of the liver by bile and the excretion of bile pigments, cholesterol, medicinal substances. Provides endocrine function.
The functional unit of the liver is hepatic lobule, which is built from the hepatic tracts formed by hepatocytes. In the center of the hepatic lobule is the central vein, into which blood flows from the sinusoids. Collects blood from portal vein capillaries and hepatic artery capillaries. Central veins merging with each other gradually form the venous system of blood outflow from the liver. And the blood from the liver flows through the hepatic vein, which flows into the inferior vena cava. In the hepatic tracts, upon contact of neighboring hepatocytes, bile ducts. They are separated from the intercellular fluid by tight contacts, This prevents the mixing of bile and extracellular fluid. The bile formed by hepatocytes enters the tubules, which gradually merge to form the system of intrahepatic bile ducts. Ultimately, it enters the gallbladder or through the common duct into the duodenum. The common bile duct connects to Persungov duct of the pancreas and together with it opens at the top Faterova pacifier. There is a sphincter at the exit site of the common bile duct Oddi, which regulate the flow of bile into the duodenum.
Sinusoids are formed by endothelial cells that lie on the basement membrane, around - the perisinusoidal space - space Disse... This space separates sinusoids and hepatocytes. The membranes of hepatocytes form numerous folds, villi, and they protrude into the re-sinusoidal space. These villi increase the area of contact with the supersonic fluid. Weak expression of the basement membrane, sinusoid endothelial cells contain large pores. The structure resembles a sieve. The pores allow substances from 100 to 500 nm in diameter to pass through.
The amount of proteins in the re-sinusoidal space will be greater than in plasma. There are macrocytes of the macrophage system. These cells, through endocytosis, ensure the removal of bacteria, damaged erythrocytes, and immune complexes. Some sinusoidal cells in the cytoplasm may contain droplets of fat - cells Ito... They contain vitamin A. These cells are associated with collagen fibers, their properties are similar to fibroblasts. They develop with cirrhosis of the liver.
Bile production by hepatocytes - the liver produces 600-120 ml of bile per day. Bile has 2 important functions -
1. It is essential for the digestion and absorption of fats. Due to the presence of bile acids, bile emulsifies fat and turns it into small drops. The process will promote a better action of lipases, for better breakdown into fats and bile acids. Bile is necessary for the transport and absorption of cleavage products
2. Excretory function. Bilirubin, cholestrenin are excreted with it. Bile secretion occurs in 2 stages. Primary bile is formed in hepatocytes, it contains bile salts, bile pigments, cholesterol, phospholipids and proteins, electrolytes, which are identical in content to plasma electrolytes, except bicarbonate anion, which is more in bile. This gives the alkaline reaction. This bile enters the bile ducts from the hepatocytes. At the next stage, bile moves along the interlobular, lobular duct, then to the hepatic and common bile duct. As bile progresses, duct epithelial cells secrete sodium and bicarbonate anions. This is essentially a secondary secretion. The volume of bile in the ducts can increase by 100%. Secretin increases the secretion of bicarbonate to neutralize hydrochloric acid from the stomach.
Outside of digestion, bile accumulates in the gallbladder, where it passes through the cystic duct.
Bile acid secretion.
Liver cells secrete 0.6 acids and their salts. Bile acids are formed in the liver from cholesterol, which either enters the body with food or can be synthesized by hepatocytes during salt metabolism. When kaarboxyl and hydroxyl groups are added to the steroid nucleus, primary bile acids
ü Hollevaya
ü Chenodeoxycholic
They combine with glycine, but to a lesser extent with taurine. This leads to the formation of glycocholic or taurocholic acids. When interacting with cations, sodium and potassium salts are formed. Primary bile acids enter the intestines and intestines, intestinal bacteria convert them into secondary bile acids
- Deoxycholic
- Lithohole
Bile salts have a greater ion-forming ability than the acids themselves. Bile salts are polar compounds that reduce their penetration through the cell membrane. Consequently, absorption will decrease. Combining with phospholipids and monoglycerides, bile acids promote fat emulsification, increase lipase activity and convert fat hydrolysis products into soluble compounds. Since bile salts contain hydrophilic and hydrophobic groups, they take part in the formation with cholesterols, phospholipids and monoglycerides to form cylindrical discs, which will be water-soluble micelles. It is in such complexes that these products pass through the brush border of enterocytes. Up to 95% of bile salts and acids are reabsorbed in the intestine. 5% will be excreted in the feces.
The absorbed bile acids and their salts combine with high-density lipoproteins in the blood. Through the portal vein, they again enter the liver, where 80% are again captured from the blood by hepatocytes. Thanks to this mechanism, a supply of bile acids and their salts is created in the body, which ranges from 2 to 4 g. There, the intestinal-hepatic circulation of bile acids takes place, which promotes the absorption of lipids in the intestine. For people who do not eat a lot, such a turnover occurs 3-5 times per day, and for people who consume abundant food, such a turnover can increase up to 14-16 times per day.
Inflammatory conditions of the mucous membrane of the small intestine reduce the absorption of bile salts, which impairs the absorption of fats.
Cholesterol - 1.6-8, mmol / l
Phospholipids - 0.3-11 mmol / L
Cholesterol is considered a by-product. Cholesterol is practically insoluble in pure water, but when combined with bile salts in micelles, it turns into a water-soluble compound. In some pathological conditions, cholesterol is deposited, calcium is deposited in it and this causes the formation of gallstones. Gallstone disease is a fairly common disease.
- The formation of bile salts is facilitated by excessive absorption of water in the gallbladder.
- Excessive absorption of bile acids from bile.
- Increased cholesterol in bile.
- Inflammatory processes in the mucous membrane of the gallbladder
Gallbladder capacity 30-60 ml. In 12 hours, up to 450 ml of bile can accumulate in the gallbladder, and this happens due to the concentration process, while water, sodium and chlorine ions, and other electrolytes are absorbed and usually bile is concentrated in the bladder 5 times, but the maximum concentration is 12-20 times. About half of the soluble compounds in gallbladder bile are bile salts, and a high concentration of bilirubin, cholesterol and leucithin is also achieved here, but the electrolyte composition is identical to plasma. Emptying of the gallbladder occurs during the digestion of food and especially fat.
The process of emptying the gallbladder is associated with the hormone cholecystokinin. It relaxes the sphincter Oddi and helps to relax the muscles of the bladder itself. Perestaltic contractions of the bladder further go to the cystic duct, the common bile duct, which leads to the excretion of bile from the bladder into the duodenum. The excretory function of the liver is associated with the excretion of bile pigments.
Bilirubin.
Monocyte - macrophage system in the spleen, bone marrow, liver. 8 g of hemoglobin breaks down per day. When hemoglobin breaks down, 2-valent iron is split off from it, which combines with protein and is stored in reserve. From 8 g Hemoglobin => biliverdin => bilirubin (300mg per day) The norm of bilirubin in the blood serum is 3-20 μmol / l. Above - jaundice, staining of the sclera and mucous membranes of the oral cavity.
Bilirubin binds to a transport protein blood albumin. it indirect bilirubin. Bilirubin from blood plasma is captured by hepatocytes and in hepatocytes bilirubin combines with glucuronic acid. Bilirubin glucuronil is formed. This form enters the bile ducts. And already in bile, this form gives direct bilirubin... It enters the intestine through the bile duct system. In the intestine, intestinal bacteria cleave glucuronic acid and convert bilirubin into urobilinogen. Part of it undergoes oxidation in the intestines and enters the feces and is already called stercobilin. The other part will be absorbed and enter the bloodstream. From the blood it is captured by hepatocytes and again enters the bile, but some of it will be filtered in the kidneys. Urobilinogen passes into the urine.
Suprahepatic (hemolytic) jaundice caused by the massive breakdown of red blood cells as a result of the Rh conflict, the entry into the blood of substances that cause destruction of the membranes of red blood cells and some other diseases. With this form of jaundice, the content of indirect bilirubin in the blood is increased, the content of stercobilin is increased in the urine, there is no bilirubin, and the content of stercobilin is increased in the feces.
Hepatic (parenchymal) jaundice caused by damage to liver cells during infections and intoxications. With this form of jaundice, the content of indirect and direct bilirubin in the blood is increased, the content of urobilin is increased in the urine, bilirubin is present, and the content of stercobilin is low in the feces.
Subhepatic (obstructive) jaundice caused by a violation of the outflow of bile, for example, when the bile duct is blocked by a stone. With this form of jaundice, the content of direct bilirubin (sometimes indirect) is increased in the blood, stercobilin is absent in urine, bilirubin is present, and stercobilin is low in feces.
Regulation of bile formation.
Regulation is based on feedback mechanisms based on the level of concentration of bile salts. The content in the blood determines the activity of hepatocytes in bile production. Outside the period of digestion, the concentration of bile acids decreases and this is a signal for an increase in the formation of hepatocytes. The discharge into the duct will decrease. After eating, there is an increase in the content of bile acids in the blood, which, on the one hand, inhibits the formation in hepatocytes, but at the same time increases the secretion of bile acids in the tubules.
Cholecystokinin is produced by the action of fatty and amino acids and causes contraction of the bladder and relaxation of the sphincter - i.e. stimulation of the emptying of the bladder. Secretin, which is released by the action of hydrochloric acid on C cells, enhances tubular secretion and increases the content of bicarbonate.
Gastrin affects hepatocytes by enhancing secretory processes. Indirectly, gastrin increases the content of hydrochloric acid, which will then increase the content of secretin.
Steroid hormones- estrogens and some androgens inhibit the formation of bile. In the mucous membrane of the small intestine, motilin- it contributes to the contraction of the gallbladder and the excretion of bile.
Influence of the nervous system- through the vagus nerve - enhances bile formation and the vagus nerve contributes to the contraction of the gallbladder. Sympathetic influences are inhibitory and cause relaxation of the gallbladder.
Intestinal digestion.
In the small intestine - the final digestion and absorption of digestive products. The small intestine receives 9 liters daily. Liquids. We absorb 2 liters of water with food, and 7 liters comes due to the secretory function of the gastrointestinal tract, and from this, only 1-2 liters will enter the large intestine. The length of the small intestine to the ileocecal sphincter is 2.85 m.The corpse is 7 m.
The mucous membrane of the small intestine forms folds that increase the surface by 3 times. 20-40 villi per 1 sq. Mm. This increases the area of the mucous membrane by 8-10 times, and each villi is covered with epithelial cells, endothelial cells containing microvilli. These are cylindrical cells with microvilli on their surface. From 1.5 to 3000 per 1 cell.
The length of the villi is 0.5-1 mm. The presence of microvilli increases the area of the mucosa and it reaches 500 square meters. Each villi contains a blindly terminating capillary, a supplying arteriole approaches the villus, which breaks down into capillaries, passing at the apex into the venous capillaries and produce blood outflow through the venules. Venous and arterial blood flow in opposite directions. Rotary countercurrent system. In this case, a large amount of oxygen passes from arterial and venous blood, without reaching the apex of the villi. It is very easy to create conditions under which the tops of the villi will receive less oxygen. This can lead to the death of these areas.
Glandular apparatus - Bruner glands in the duodenum. Libertune's glands in the jejunum and ileum. There are goblet mucous cells that produce mucus. The glands of the duodenum 12 resemble the glands of the pyloric part of the stomach and they secrete mucous secretions for mechanical and chemical irritation.
Their regulation occurs under the influence vagus nerves and hormones, especially secretin. Mucous secretion protects the duodenum from the action of hydrochloric acid. The sympathetic system reduces mucus production. When we experience strep, we have an easy chance of getting a duodenal ulcer. By reducing the protective properties.
Small intestine secret formed by enterocytes, which begin their maturation in crypts. As the enterocyte matures, it begins to move to the apex of the villi. It is in the crypts that the cells actively transfer chlorine and bicarbonate anions. These anions create a negative charge that attracts sodium. Osmotic pressure is created, which attracts water. Some pathogenic microbes - dysentery bacillus, cholera vibrio enhance the transport of chlorine ions. This leads to a large excretion of fluid in the intestine up to 15 liters per day. Normally, 1.8-2 liters per day. Intestinal juice is a colorless liquid, cloudy due to the mucus of epithelial cells, has an alkaline reaction pH 7.5-8. Enzymes of intestinal juice accumulate inside enterocytes and are secreted with them when they are rejected.
Intestinal juice contains a complex of peptidases, which is called eryxin, providing the final cleavage of protein products to amino acids.
4 aminolytic enzymes - sucrase, maltase, isomaltase and lactase. These enzymes break down the carbohydrate into monosaccharides. There is intestinal lipase, phospholipase, alkaline phosphatase and enterokinase.
Intestinal juice enzymes.
1. Complex of peptidases (erypsin)
2.Amylothytic enzymes- sucrase, maltase, isomaltase, lactase
3. Intestinal lipase
4. Phospholipase
5. Alkaline phosphatase
6. Enterokinase
These enzymes accumulate inside the enterocytes and the latter, as they mature, rise to the top of the villi. At the apex of the villi, enterocytes are rejected. Within 2-5 days, the intestinal epithelium is completely replaced with new cells. Enzymes can enter the intestinal cavity - cavity digestion, the other part is fixed on the membranes of microvilli and provides membrane or parietal digestion.
Enterocytes are covered with a layer glycocalyx- carbon surface, porous. It is a catalyst that promotes the breakdown of nutrients.
The regulation of the acid department is under the influence of mechanical and chemical stimuli acting on the cells of the nerve plexus. Doggel's cells.
Humoral substances- (increase secretion) - secretin, cholecystokinin, VIP, motilin and enterocrinin.
Somatostatin inhibits secretion.
In the colon libertine glands, a large number of mucous cells. Mucus and bicarbonate anions predominate.
Parasympathetic influences- increase mucus secretion. With emotional arousal within 30 minutes, a large amount of secretion is formed in the colon, which causes the urge to empty. Under normal conditions - mucus provides protection, adhesion of feces and neutralizes acids with the help of bicarbonate anions.
Normal microflora is very important for the function of the colon. It is non-pathogenic bacteria that take part in the formation of the immunobiological activity of the body - lactobacilli. They help to increase immunity and prevent the development of pathogenic microflora, when antibiotics are taken, these bacteria die. The body's defenses are weakened.
Colon bacteria synthesize vitamin K and B vitamins.
Bacterial enzymes break down fiber through microbial fermentation. This process takes place with the formation of gas. Bacteria can cause protein to rot. In this case, in the large intestine are formed poisonous foods- indole, skatole, aromatic hydroxy acids, phenol, ammonia and hydrogen sulfide.
The detoxification of toxic products occurs in the liver, where they combine with glucuric acid. Water is absorbed and feces are formed.
The composition of feces includes mucus, remnants of dead epithelium, cholesterol, products of changes in bile pigments - stercobilin and dead bacteria, which account for 30-40%. Feces may contain undigested food debris.
The motor function of the digestive tract.
We need motor function at the first stage - absorption of food and chewing, swallowing, movement along the alimentary canal. Motility contributes to the mixing of food and glandular secretions, participates in the processes of absorption. The motor system carries out the excretion of the end products of digestion.
The study of the motor function of the gastrointestinal tract is carried out using different methods, but it is widespread balloon cinegraphy- introduction into the cavity of the alimentary canal of a cartridge connected to a recording device, while the pressure is measured, which reflects motor skills. Motor function can be observed with fluoroscopy, colonoscopy.
X-ray gastroscopy- a method for recording electrical potentials in the stomach. Under experimental conditions, registration is removed from isolated sections of the intestine, visual observation of motor function. In clinical practice - auscultation - auscultation in the abdominal cavity.
Chewing- when chewing, food is crushed, grinded. Although this process is voluntary, chewing is coordinated by the nerve centers of the brain stem, which provide movement of the lower jaw in relation to the upper. When the mouth opens, the proprioceptors of the muscles of the lower jaw are excited and reflexively cause contraction of the masticatory muscles, the medial pterygoid and temporal lobes, and helps to close the mouth.
When the mouth is closed, food irritates the receptors of the oral mucosa. Which, when irritated, send to twoabdominal muscle and lateral pterygoid that help open the mouth. When the jaw drops, the cycle repeats again. With a decrease in the tone of the masticatory muscles, the lower jaw may drop under the force of gravity.
The muscles of the tongue are involved in the act of chewing.... They place food between the upper and lower teeth.
The main functions of chewing are -
They destroy the cellulose shell of fruits and vegetables, promote mixing and wetting of food with saliva, improve contact with taste buds, and increase the area of contact with digestive enzymes.
Chewing releases odors that act on the olfactory receptors. It increases the pleasure of eating and stimulates gastric secretion. Chewing helps the food lump to form and be swallowed.
The chewing process changes swallowing... We swallow 600 times a day - 200 swallows with food and drink, 350 without food and another 50 at night.
It is a complex coordinated act ... Includes oral, pharyngeal and esophageal phases... Allocate arbitrary phase- before the food lump hits the root of the tongue. This is an arbitrary phase that we can terminate. When the food lump hits the root of the tongue, non-voluntary swallowing phase... The act of swallowing begins from the root of the tongue to the hard palate. The food lump moves to the root of the tongue. The palatine curtain rises, like a lump passes the palatine arches, the nasopharynx closes, the larynx rises - the epiglottis goes down, the glottis goes down, this prevents food from entering the respiratory tract.
The food lump goes down the throat. Due to the muscles of the pharynx, the food lump is moved. At the entrance to the esophagus is the upper esophageal sphincter. When the lump moves, the sphincter relaxes.
Sensitive fibers of the trigeminal, glossopharyngeal, facial and vagus nerves take part in the swallowing reflex. It is through these fibers that signals are transmitted to the medulla oblongata. Coordinated muscle contraction is provided by the same nerves + the hypoglossal nerve. It is the coordinated contraction of the muscles that directs the food bolus into the esophagus.
With a contraction of the pharynx, relaxation of the upper esophageal sphincter. When a food lump enters the esophagus, esophageal phase.
In the esophagus there is a circular and longitudinal muscle layer. Moving a lump using a peristaltic wave, in which the circular muscles are above the food lump, and are longitudinal in front. Circular muscles narrow the lumen, and longitudinal ones widen. The wave moves the food bolt at a speed of 2-6 cm per second.
Solid food passes the esophagus in 8-9 seconds.
Liquid causes relaxation of the esophagus muscles and the liquid flows in a continuous column for 1 - 2 s. When the bolus reaches the lower third of the esophagus, it relaxes the lower cardiac sphincter. The cardiac sphincter is toned at rest. Pressure - 10-15 mm Hg. Art.
Relaxation occurs reflexively with the participation vagus nerve and mediators that induce relaxation - vasointestinal peptide and nitric oxide.
When the sphincter relaxes, the food lump passes into the stomach. With the work of the cardiac sphincter, 3 unpleasant disorders occur - achalosia- occurs with spastic contraction of the sphincters and weak peristalsis of the esophagus, which leads to the expansion of the esophagus. Food stagnates, decomposes, and an unpleasant odor appears. This condition does not develop as often as sphincter insufficiency and reflux condition- Throwing gastric contents into the esophagus. This leads to irritation of the esophageal mucosa, heartburn appears.
Aerophagia- swallowing air. It is typical for infants. When sucking, air is swallowed. The child cannot be placed horizontally at once. In an adult, it is observed with a hasty meal.
Outside the period of digestion, smooth muscles are in a state of tetanic contraction. During the act of swallowing, the proximal stomach relaxes. Together with the opening of the cardiac sphincter, the cardiac department relaxes. Decreased tone-receptive relaxation. Reducing the tone of the stomach muscles allows you to accommodate large volumes of food with minimal cavity pressure. Receptive relaxation of stomach muscles regulated by the vagus nerve.
Participates in relaxation of the stomach muscles hoelcystokinin- promotes relaxation. The motor activity of the stomach in the proximal and distal calving on an empty stomach and after eating is expressed in different ways.
Capable of fasting the contractile activity of the proximal part is weak, rare and the electrical activity of smooth muscles is not great. Most of the muscles of the stomach do not contract on an empty stomach, but approximately every 90 minutes, strong contractile activity develops in the middle sections of the stomach, which lasts 3-5 minutes. This periodic motility is called migratory myoelectric complex - MMK, which develops in the middle parts of the stomach and then moves on to the intestines. It is believed that it helps cleanse the gastrointestinal tract from mucus, exfoliated cells, bacteria. Subjectively, you and I feel the emergence of these contractions in the form of suction, murmur in the stomach. These signals increase the feeling of hunger.
For the gastrointestinal tract on an empty stomach, periodic motor activity is characteristic and it is associated with the excitation of the center of hunger in the hypothalamus. The glucose level decreases, the calcium content rises, and choline-like substances appear. This all acts on the center of hunger. From it, signals go to the cerebral cortex and then makes us realize that we are hungry. Downward pathways - periodic motility of the gastrointestinal tract. This prolonged activity gives signals that it is time to eat. If we take food in this state, then this complex is replaced by more frequent contractions in the stomach, which arise in the body and do not spread to the pyloric region.
The main type of stomach contraction during digestion is peristaltic contractions - contraction of the circular and longitudinal muscles. In addition to peristaltic, there are tonic contractions.
The basic rhythm of perilstalsis is 3 contractions per minute. The speed is 0.5-4 cm per second. The contents of the stomach move towards the pyloric sphincter. A small part is pushed through the digestive sphincter, but when it reaches the pyloric region, a powerful contraction occurs here, which throws the rest of the contents back into the body. - retropulsation... It plays a very important role in the processes of mixing, crushing the food lump, to smaller particles.
Food particles of no more than 2 cubic mm can pass into the duodenum.
The study of myoelectric activity showed that slow electrical waves appear in the smooth muscles of the stomach, which reflect the depolarization and repolarization of the muscles. The waves themselves do not lead to contraction. Contractions occur when the slow wave reaches a critical level of depolarization. An action potential appears at the top of the wave.
The most sensitive section is the middle third of the stomach, where these waves reach a threshold value - the pacemakers of the stomach. He creates the basic rhythm for us - 3 waves per minute. No such changes occur in the proximal stomach. The molecular basis has not been sufficiently studied, but such changes are associated with an increase in permeability for sodium ions, as well as an increase in the concentration of calcium ions in smooth muscle cells.
Found in the walls of the stomach are non-muscle cells that are excited periodically - Kajala cells These cells are associated with smooth muscle cells. Evacuation of the stomach into the duodenum 12. Grinding is important. Evacuation is influenced by the volume of gastric contents, chemical composition, calorie content and consistency of food, and the degree of its acidity. Liquid food is absorbed faster than solid food.
When part of the gastric contents enters the duodenum 12 from the side of the latter, blocking reflex- the pyloric sphincter reflexively closes, further intake from the stomach is not possible, gastric motility is inhibited.
Motor skills are inhibited when digesting fatty foods. In the stomach, the functional prepyloric sphincter- on the border of the body and the digestive part. There is a union of the digestive and 12 colon.
It is inhibited due to the formation of enterogastrons.
The rapid transition of the contents of the stomach to the intestines is accompanied by discomfort, severe weakness, drowsiness, and dizziness. This occurs when the stomach is partially removed.
Motor activity of the small intestine.
The smooth muscle of the small intestine can also contract in a fasting state due to the appearance of the myoelectric complex. Every 90 minutes. After a meal, the migrating myoelectric complex is replaced by motility, which is characteristic of digestion.
In the small intestine, motor activity can be observed in the form of rhythmic segmentation. The contraction of the circular muscles leads to the segmentation of the intestine. The declining segments change. Segmentation is necessary for mixing food if longitudinal contractions are added to the contraction of the circular muscles (narrowing the lumen). From the circular muscles - the movement of the contents is mask-like - in different directions
Segmentation occurs approximately every 5 seconds. This is a local process. It captures segments at a distance of 1-4 cm. In the small intestine, peristaltic contractions are also observed, which cause the contents to move towards the ileocecal sphincter. The contraction of the intestine occurs in the form of peristaltic waves, which occur every 5 seconds - multiples of 5 - 5.10.15, 20 seconds.
Contractions in the proximal regions are more frequent, up to 9-12 per minute.
In distal calving 5 - 8. Regulation of small intestine motility is stimulated by the parasympathetic system and suppressed by the sympathetic system. Local plexuses, which can regulate motor skills in small areas of the small intestine.
Muscle relaxation - humoral substances are involved- VIP, nitric oxide. Serotonin, methionine, gastrin, oxytocin, bile - stimulate motor skills.
Reflex reactions occur when irritation with food digestion products and mechanical stimuli.
The passage of the contents of the small intestine into the large intestine is carried out through ileocecal sphincter. This sphincter is closed outside the digestive period. After a meal, it opens every 20 to 30 seconds. Up to 15 milliliters of contents from the small intestine enters the blind.
Increased pressure in the cecum reflexively closes the sphincter. Periodic evacuation of the contents of the small intestine into the large intestine is carried out. Stomach filling - causes the ileoceclal sphincter to open.
The large intestine differs in that the longitudinal muscle fibers do not go in a continuous layer, but in separate ribbons. The large intestine forms a saccular expansion - haustra... It is an expansion that forms when smooth muscles and mucous membranes expand.
In the colon, we observe the same processes, only more slowly. There is segmentation, pendulum-like contractions. Waves can propagate to the rectum and back. Content moves slowly in one direction and then in the other. During the day, forcing peristaltic waves are observed 1-3 times, which move the contents to the rectum.
Motorboat regulation is carried out parasympathetic (arousing) and sympathetic (inhibiting) influences. Blind, transverse, ascending - the vagus nerve. Descending, sigmoid and straight - the pelvic nerve. Sympathetic- superior and inferior mesenteric node and hypogastric plexus. From humoral stimulants- substance P, tachykinins. VIP, Nitric oxide - inhibit.
The act of defecation.
The rectum is normally empty. Filling of the rectum occurs during the passage and forcing of a wave of peristalsis. When stool enters the rectum, it causes distension by more than 25% and a pressure above 18 mm Hg. relaxation of the internal smooth muscle sphincter occurs.
Sensory receptors inform the central nervous system, causing the urge. It is also controlled by the external sphincter of the rectum - striated muscles, it is regulated arbitrarily, the innervation is the pudendal nerve. Reduction of the external sphincter - suppression of the reflex, feces leave proximally. If an act is possible, relaxation of both the internal and external sphincter occurs. The longitudinal muscles of the rectum contract, the diaphragm relaxes. The act is facilitated by the contraction of the pectoral muscles, the muscles of the abdominal wall and the levator of the anus.
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