Intestinal juice. Glands of the small intestine or where intestinal juice is produced. What does intestinal juice consist of?
Intestinal juice is a colorless liquid, slightly alkaline, containing about 3% dry matter.
Secretion of intestinal juice
Throughout the intestine, starting from the pyloric opening, there are many small glands of various types that secrete intestinal juice. Some of them are of an alveolar structure - Brunner's glands - located only in the duodenum, others - tubular Lieberkühn's glands - throughout the entire length of the intestine.
During fasting, little intestinal juice is released, but when eating, the secretion of juice increases. The secretion of juice especially increases with mechanical irritation of the intestinal walls with food. Intestinal juice secretion also increases under the influence of certain chemicals: food digestion products, extracts from certain organs.
Composition of intestinal juice
Intestinal juice contains enzymes that decompose all nutrients: into carbohydrates - amylase, invertase, lactase, maltase, phosphatase; for proteins - erepsin; for fats - lipase.
Erepsin
The protein enzyme erepsin turned out to be a complex of different peptidases. It quickly and completely decomposes protein products formed under the influence of pepsin and trypsin.
Lipase
Intestinal juice lipase breaks down fats according to the general type.
Carbohydrate enzymes
The amount of carbohydrate enzymes in intestinal juice depends on the type of food. This indicates that the composition of food affects the activity of cells that produce enzymes. So, for example, with a diet devoid of milk, lactase is absent in the intestinal juice, but it appears in it when feeding with milk. In suckling suckers, lactase is a constant component of the intestinal juice, which gradually disappears when the animal switches to another type of food. The same was noted for the enzyme invertase, which decomposes cane sugar. Intestinal amylase and maltase are always present in intestinal juice. Material from the site
Intestinal juice can be obtained from the Thiri-Vella fistula. To form it, a segment of the intestine is isolated, which maintains a vascular and nervous connection with the rest of the intestine through the mesentery. Both ends of this segment are sewn into the skin wound, and the integrity of the intestine is restored by applying sutures (Fig. 26). However, from the Thiri-Vell fistula it is possible to obtain only the juice of the Lieberkühn glands, since the Brunner's glands take up so little space (in a dog) that it is impossible to make a separate fistula to obtain pure juice of the Brunner's glands.
Instructions
The main component of gastric juice is hydrochloric acid. It also contains inorganic (chlorides, bicarbonates, sodium, potassium, phosphates, magnesium, sulfates) and organic substances (proteolytic enzymes). The regulation of the secretory function of the gastric glands is carried out by nervous and humoral mechanisms. The process of synthesis of gastric juice is conventionally divided into 3 phases: cephalic (complex reflex), gastric, intestinal.
During the complex-reflex phase, the gastric glands are excited by irritation of the olfactory, visual, and auditory receptors by the sight and smell of the dish, and by the perception of the situation associated with eating. Such effects are layered with irritation of the receptors of the oral cavity and esophagus during the process of chewing and swallowing food. As a result, the secretory activity of the gastric glands is triggered. The juice that is released under the influence of the sight and smell of food, during chewing and swallowing, is called “appetizing” or “igniting”; it has high acidity and great proteolytic activity. At the same time, the stomach becomes prepared for food intake.
The complex-reflex phase of secretion is superimposed on the second phase – gastric. The vagus nerve and intramural local reflexes take part in its regulation. During this phase, juice secretion is associated with a reflex response to the effects of mechanical and chemical stimuli on the gastric mucosa. Irritation of the receptors in the gastric mucosa promotes the release of gastrin, which is the most powerful cell stimulant. At the same time, the histamine content in the mucous membrane increases; this substance is a key stimulator of hydrochloric acid production.
The intestinal phase of gastric juice secretion occurs when food passes from the stomach to the intestines. The amount of secretion released during this period is no more than 10% of the total volume of gastric juice; it increases in the initial period and then begins to decrease. As the duodenum fills, secretory activity continues to decrease under the influence of peptides that are secreted by the endocrine gastrointestinal glands.
The most effective stimulator of gastric juice secretion is protein food. Long term leads to an increase in the amount of secretion in response to other food stimuli, as well as to an increase in acidity and increased digestive activity of gastric juice. Carbohydrate foods (for example, bread) are the weakest stimulants of secretion. Among non-nutritive factors that increase the secretory activity of the gastric glands, the most important role is played by stress, rage, and irritation. Melancholy, fear, and depressive states have a depressing effect.
Gastric juice is secreted by the glands of the stomach. An average of 2 liters of gastric juice is secreted per day. It consists of organic and inorganic components.
Instructions
The inorganic components of gastric juice include hydrochloric acid. Its concentration determines the level of acidity of gastric juice. The content of hydrochloric acid is minimal on an empty stomach, and maximum when food enters the stomach.
Pepsin A affects the process of protein absorption. Under its influence, proteins are broken down into peptones. This enzyme is formed under the influence of hydrochloric acid.
Gastricsin is similar in function to pepsin A. Pepsin B dissolves gelatinase better than all other enzymes. The rennet enzyme rennin promotes the breakdown of milk casein in the presence of calcium ions.
Gastric juice also includes gastric mucus or mucin, secreted by accessory cells of the gastric glands. This is a collection of colloidal solutions of high-molecular biopolymers, the latter are found in all tissues and fluids of the body. It consists of low molecular weight organic and mineral substances, leukocytes, lymphocytes, and desquamated epithelium.
Gastric mucus includes soluble and insoluble fractions. Insoluble mucin lines the stomach from the inside, part of it passes into gastric juice. Soluble mucin arises from the secretions of secretory epithelial cells of the gastric glands.
Gastric acid is a colorless, transparent liquid with an acidic reaction. The pH of the juice ranges from 1.5 to 5. The composition of gastric juice includes 99.4% water and 0.6% solid substances. The dry residue of gelatinous juice is represented by inorganic (hydrochloric acid, chloride salts of potassium, sodium, calcium ammonium and magnesium. Phosphates and sulfates.) and organic substances (proteins, lactic acid, creatinine, urea, uric acid, ATP, amino acids.) Gastric juice includes the following enzymes: pepsin (pepsin A acts on proteins, breaking them down into protein and peptones. It is produced in the inactive form of pepsinogen, activated by hydrochloric acid and converted to pepsin. This enzyme acts only in an acidic environment; in an alkaline environment it is inactivated and loses the ability to break down proteins; cathepsin - breaks down proteins into peptides; chymosin or renin, produced in large quantities in young animals, especially in the abomasum of calves; gelatinase acts in a slightly acidic environment. Has a proteolytic property, causing liquefaction of gelatin; lipase acts on neutral fats , breaking them down to glycerol and fatty acids. The main glands of the stomach do not function constantly, but when eating food. Gastric juice is produced 5-7 minutes after the onset of the stimulus. First, appetizing juice is released when food has not entered the stomach (6-8 hours)
9. Phases of gastric secretion
Complex reflex – carried out through conditioned and unconditioned reflexes. With a conditioned reflex, the stimulus is perceived by the corresponding analyzer. Excitation from its receptors enters the corresponding center of the cortex - visual, olfactory, from them the excitations flow to the food center of the cortex, and from it to the center of juice secretion of the prolongated brain, from this center impulses flow to the glands of the stomach, the secretory nerves are the sympathetic nerves (inhibit the secretion of juice ) and parasympathetic (the vagus nerve increases secretion) With an unconditioned reflex, excitation occurs in the receptors of the mouth. When eating food, cavities and pharynxes, impulses from them are transmitted along sensory nerves to the center of juice secretion of the medulla, from it they rise to the food center of the cortex, return to the center of juice secretion and go along secretory nerves to the glands of the stomach. The secretory nerves are the same as the sympathetic and parasympathetic nerves. The complex reflex phase of gastric secretion lasts 1.5-2 hours.
The neurohumoral phase begins when food enters the stomach. The irritants are chemical. Substances that act through the blood or directly on the walls of the stomach (continued breakdown of feed, histamine, intestinal irritants) last 4-6 hours. Less juice is produced and it is not very active; the more active the juice is released in phase 1, the more active phase 2 is.
10. The role of hydrochloric acid in the digestion process
In the gastric cavity, hydrochloric acid: 1) stimulates the secretory activity of the gastric glands; 2) promotes the conversion of pepsinogen into pepsin by cleaving the inhibitory protein complex; 3) creates optimal acidity for the action of proteolytic enzymes of gastric juice; 4) causes denaturation and swelling of proteins (which promotes their breakdown by enzymes); 5) provides an antibacterial effect of the secretion; 6) participates in the mechanism of transition of food from the stomach to the duodenum, irritating the chemoreceptors of its mucous membrane; 7) participates in the regulation of secretion of the gastric and pancreatic glands, stimulating the formation of gastrointestinal hormones (gastrin, secretin); 8) stimulates the secretion of the enzyme enterokinase by enterocytes of the duodenal mucosa; 9) participates in the curdling of milk; 10) stimulates the motor activity of the stomach.
Lesson topic: “The effect of intestinal juice on food”
Grade:8
Purpose of the lesson: to develop knowledge about the internal structure of the thin and thick sectionsintestines, their functional activity; the role of the large intestine in digestion: the importance of digestion regulation
During the classes:
1. Organizational moment (1-2 min)
Welcoming children. Checking that all students are in the class. Getting ready to work.
2. Updating knowledge (5-7 min)
In the last lesson, we talked about digestion in the stomach, about complex reflex and neurohumoral juice secretion, about the composition of gastric juice. Now we will check what you have learned on this topic.
Solve the crossword puzzle “Digestion in the stomach”
Questions for the crossword:
1. Juice secretion caused by the act of eating
2. Separation of gastric juice due to mechanical irritation of the gastric mucosa.
3. Nerves through which excitation is transmitted from the central nervous system to the gastric glands during neurohumoral juice secretion.
4. An environment that activates the action of gastric juice enzymes.
5. An acid that is part of gastric juice.
6.An enzyme that easily breaks down the proteins of meat and eggs.
7. A special hormone produced in the gastric mucosa.
8.Volume expansion of the digestive tract.
9. Stomach juice, odorless and colorless.
10.An enzyme that causes milk to curdle in the stomach.
Additional questions:
Tell us about the structure of the stomach.
How is the secretion of gastric juice regulated?
Composition of gastric juice.
3. Studying new material (20 min)
So, in previous lessons you studied digestion in the mouth and stomach. Next, the food bolus enters the longest section - the intestine.
What goals do you think we can set for ourselves today?
(It is necessary to find out what processes occur in the intestines.)As you know, there are special digestive glands throughout the entire digestive canal. Knowing this, what else can we learn in class?
(- You can find out how the digestive glands affect digestion.)
Purpose of the lesson: to study the processes occurring in the intestines, the role of glands in digestion and to understand what absorption is and how it occurs.
Let's open our notebooks, write down the topic and the topic of our lesson, “the effect of digestive juice on food.”
Food gruel from the stomach enters in small portions into the longest part of the digestive tract - the intestine, consisting of the small and large intestines.
The part of the small intestine closest to the stomach isduodenum. Digestion of food occurs mainly due to pancreatic enzymes and intestinal juice with the participation of bile secreted by the liver.Pancreatic juice flows through a special duct into the duodenum. It is colorless, transparent, has a slightly alkaline reaction and contains all the enzymes that break down proteins, fats and carbohydrates. Trypsin in pancreatic juice breaks down proteins into amino acids, lipase breaks down fats into glycerol and fatty acids, and amylase breaks down carbohydrates into monosaccharides. Bile secreted by the liver plays an important role in this process. Bile does not break down fats, but creates an alkaline environment in the duodenum, emulsifies - loosens fat into small droplets, and this enhances the action of the lipase enzyme.
Pancreas is the second largest gland in the digestive tract. The gland is grayish-red in color and extends transversely from the duodenum to the spleen.
Consists of 2 types of cells: some cells secrete digestive juice,
others are hormones that regulate the metabolism of carbohydrates and fats. per day
a person is separated about 1.5-2 liters. pancreatic juice.
Nervous and humoral regulation of juice secretion.
Outputjuicepancreas begins under the influence of conditioned and unconditioned reflexes. In preparation for food and the beginning of food absorption via the vagus nerveNerve impulses are sent to the organs. But most of the juice is produced under the influence of special hormones after food from the stomach enters the duodenum.
Pancreatic juice has a slightly alkaline reaction.
It gets here through a special channelbile - juice produced by the liver.
Liver - called a “chemical laboratory”, “food warehouse”, “dispatcher of the body”. What is the basis of these expressions?
Liver - the largest human gland, red-brown in color. its weight reaches 1.5 kg. It is located in the abdominal cavity under the diaphragm on the right, only a small part of it extends to the left of the midline. The name “liver” comes from the Russian words “oven”, “bake”. The liver has the highest temperature of all the organs in our body.
Liver functions.
It takes part not only in the digestion process.
It also performs one of the vital functions - neutralizing toxic substances entering the blood from the digestive organs. Many bacteria harmful to the body die in the liver.
If there is a lot of glucose in the blood, then some of it is retained. If she is poor, then on the contrary, she becomes rich. The liver stores carbohydrates in the form ofglycogen – animal starch.
The liver serves as a storehouse of vitamins and is enriched with them especially in summer and autumn.
One of the most important functions of the liver is the synthesis of plasma proteins - albumin and fibrinogen, as well as prothrombin.
The liver produces bile, which travels through the bile duct into the duodenum. Excess bile is collected in the gallbladder and can be used when increased digestion occurs in the duodenum.
The formation of bile in liver cells occurs continuously, but its release into the duodenum occurs only 5-10 minutes after eating and lasts 6-8 hours. The daily secretion of bile is about 1 liter. Bile does not contain enzymes.
What then is the meaning of bile?
Bile meaning:
Thanks to its action, the digestion of fats is facilitated;
It increases enzyme activity;
Increases the solubility of fatty acids;
Increases bowel movement;
Delays putrefactive processes in the intestines.
Intestinal juice.
Enzymes take part in the breakdown of proteins, carbohydrates, and fats
intestinal juice, which is produced by the glands of the mucous membrane of the small intestine, is secreted up to 2 liters per day. intestinal juice.
This is where digestion products are absorbed.
The small intestine is the central section of the digestive tract, where digestion processes end and digestion products are intensively absorbed into the blood.
This is facilitated by adaptations of the small intestine, which, on the one hand, should slow down the movement of food masses through this section (for better digestion), and on the other, increase the surface of the mucous membrane of the small intestine.
The average length of the human intestine is 5-6 meters. The intestine of an adult is 4 times longer than the body, and that of a child is 6 times longer. The longer the intestines, the longer food stays in it (therefore, it is better digested and absorbed). In addition, the peristaltic movements of the small intestine contribute to optimal mixing of the contents of the intestine with digestive juices and an increase in the time spent in it. Up to 80% of the proteins supplied with food and almost 100% of fats and carbohydrates are digested in the small intestine.
The wall of the small intestine is formed by:
Mucosa, submucosal tissue, muscular and serous membranes. The mucous membrane of the small intestine forms folds covered with villi.
On the mucous membrane of the small intestine, 1 square cm contains up to 2500 villi.
The length of the villi is up to 1 mm.
Digestion in the small intestine occurs in three stages:
1) cavity digestion;
What definition do you think fits this concept?
2) parietal or membrane digestion.
This phenomenon was discovered by the Russian scientist A.M. Ugolev. What is important is that parietal digestion occurs on the same surface of the small intestine, which has the function of absorption. Parietal digestion occurs on the very surface of the intestinal mucosa. Particles that penetrate into the spaces between the villi are digested. Larger particles remain in the intestinal cavity, where they are exposed to digestive juices. This digestive mechanism promotes the most complete digestion of food.
3) Absorption is the process of various substances entering the blood and lymph through the layer of villous cells. Absorption is of great importance; this is how our body receives all the necessary substances. The absorption process occurs in the villi.
Their wall consists of single-layer epithelium. Each villus contains blood and lymphatic vessels. Smooth muscle cells are laid along the villus, which contract during digestion, and the contents of their blood and lymph vessels are squeezed out and go into the general blood and lymph flow. The villi contract 4 to 6 times per minute.
Each villi, in turn, is covered with finger-like projections - microvilli.
So, if you hold a piece of sugar under your tongue for a long time, it will dissolve and begin to be absorbed. However, food remains in the mouth for a short time and does not have time to be absorbed. Alcohol and partly glucose are well absorbed in the stomach, and water and some salts are absorbed in the colon.
Proteins are absorbed in the form of water-soluble amino acids. Carbohydrates are absorbed into the blood in the form of glucose. This process occurs most intensively in the upper intestine. In the large intestine, carbohydrates are absorbed slowly.
Fatty acids and glycerol penetrate into the cells of the villi of the small intestine, where they form fats characteristic of the human body. They are absorbed into the lymph, so the lymph flowing from the intestines has a milky color.
Absorption of water begins in the stomach and continues most intensively in the intestines. Water is also absorbed into the blood. Mineral salts are absorbed into the blood in dissolved form.
From the small intestines, the unabsorbed part of the food passes into the initial part of the large intestine -cecum. The mucous membrane of the colon does not have villi; its cells secrete mucus. The large intestine contains a rich bacterial flora that causes the fermentation of carbohydrates and the putrefaction of proteins. As a result of microbial fermentation, plant fiber is broken down, which is not affected by the enzymes of digestive juices, so it is not absorbed in the small intestines and enters the large intestine unchanged. Under the influence of bacteria that cause putrefaction, unabsorbed amino acids and other products of protein digestion are destroyed. In this case, gases and toxic substances are formed, which, when absorbed into the blood, can cause poisoning of the body. These substances are neutralized in the liver.
The large intestine predominantly absorbs water (up to 4 liters per day), as well as glucose and some medications. From the food gruel, less than 130-150 g of feces remain, which includes mucus, remnants of dead epithelium of the mucous membrane, cholesterol, products of changes in bile pigments that give the feces a characteristic color, undigested food debris, and a large number of bacteria.
The movement of food debris in the large intestine occurs due to contraction of its walls. Feces accumulate inrectum. Defecation (bowel emptying) is a reflex process that occurs in response to stool irritation of the receptors of the rectal mucosa when a certain pressure is reached on its walls. The center of defecation is located in the sacrum
section of the spinal cord. The act of defecation is also subordinated to the cerebral cortex, which causes voluntary delay in defecation.
3. Consolidation of the material covered.
Now to check how you have mastered the material you have studied. Determine what substances are formed as a result of the digestion of proteins, fats, and carbohydrates. Fill the table:
Table: Organic Nutrients
Organic mattersquirrels
fats
carbohydrates
Substances formed during digestion
Answer the following questions:
1) What is the role of the liver and pancreas in digestion?
2) What are the stages of digestion in the small intestine?
3) Explain the mechanism of peristaltic movements of the walls of the small intestine?
4) What is the significance of the appendix?
5) Where is the center of defecation?
5.Homework.
Paragraph 46, pp. 171-174
Answer the questions
Table “Establish compliance” in writing.
Bile, its composition and significance.
Bile is the secretion and excretion of liver cells.
There are:
1. Cystic bile– has a high density due to the absorption of water (pH 6.5-5.5, density – 1.025-1.048).
2. Liver bile– located in the hepatic ducts (pH 7.5-8.8, density - 1.010-1.015).
In herbivores it is dark green.
Carnivores have a red-yellow color.
Bile is produced per day in dogs - 0.2-0.3 liters, pigs - 2.5-4 liters, cattle - 7-9 liters, horses - 5-6 liters.
Composition of bile:
1. Bile pigments (0.2%):
a.) bilirubin (formed during the breakdown of red blood cells);
b.) biliverdin (with the breakdown of bilirubin and there is very little of it).
2. Bile acids (1%):
a.) glycocholic (80%);
b.) taurocholic – about 20% and less representative of deoxycholic.
3. Mucin (0.3%).
4. Mineral salts (0.84%).
5. Cholesterol (0.08%), as well as neutral fats, urea, uric acid, amino acids, a small amount of enzymes (phosphatases, amylase).
Bile meaning:
1. Emulsifies fats, i.e. transforms them into a finely dispersed state, which contributes to their better digestion under the influence of lipases.
2. Provides absorption of fatty acids. Bile acids combine with fatty acids to form a water-soluble complex that is available for absorption, after which it disintegrates. Bile acids enter the liver and return to the composition of bile, and fatty acids combine with already absorbed glycerol, forming triglycerides. One molecule of glycerol combines with three molecules of fatty acids
3. Promotes the absorption of fat-soluble vitamins.
4. Enhances the activity of amylo-, proteo- and lipolytic enzymes of pancreatic and intestinal juices.
5. Stimulates the motility of the stomach and intestines and promotes the passage of contents into the intestines.
6. Participates in the neutralization of hydrochloric acid entering the intestines with the contents of the stomach, thereby stopping the action of pepsin and creating conditions for the action of trypsin.
7. Stimulates the secretion of pancreatic and intestinal juices.
8. Has a bactericidal effect on putrefactive microflora of the gastrointestinal tract and inhibits the development of many pathogenic microorganisms.
9. Many drugs and hormone breakdown products are excreted with bile.
Bile is secreted continuously, and eating food increases its secretion. Nervus vagus causes increased contraction of the bladder wall and opening of the sphincter. Sympathetic nerves act on the contrary, causing the closure of the sphincter. Stimulates the secretion of bile by fatty foods, the hormone cholecystokinin, which acts similarly to the vagus nerve, gastrin, secretin.
Methods for obtaining intestinal juice:
1. The Thiri method is based on the formation of an isolated piece of intestine, one end of which is sutured tightly, and the second is brought to the surface of the skin and sewn to its edges.
2. Thiri-Vell method – modification of the 1st method. In this case, both ends of the segment are brought to the surface. The disadvantage of this method is that the holes quickly contract, so a glass tube is inserted into them, but this area did not take part in digestion and it atrophied.
3. Method of external enteroanastomosis (according to Sineshchekov) - this method allows you to obtain objective data.
There are 2 types of glands in the small intestine:
1. Brunner's (they are only in the 12th section of the gut).
2. Lieberkühn's (found in the mucous membrane of the entire small intestine).
These glands produce intestinal juice is a colorless, cloudy liquid with a specific odor (pH 8.2-8.7), containing 97.6% water and 2.4% dry substances, which are represented by carbon dioxide salts, NaCl, cholesterol crystals and enzymes.
Intestinal juice consists of 2 parts:
1. Dense – consists of desquamated epithelial cells.
2. Liquid part.
The bulk of enzymes (more than 20 of them) are located in the dense part and most of all in the upper parts of the small intestine, as well as in the upper layers of the mucous membrane.
Enzymes of intestinal juice act on intermediate products of nutrient hydrolysis and complete their hydrolysis.
Among the enzymes are:
Peptidases (break down proteins), of which enteropeptidase converts trypsinogen into the active form trypsin.
Lipase – acts on fats.
Amylase, maltase, sucrase - act on carbohydrates.
Nucleases, phospholipase.
Alkaline phosphatase (in alkaline gray hydrolyzes phosphoric acid esters, participates in the processes of absorption and transport of substances).
Acid phosphatase – young animals have a lot of it.
Intestinal juice is formed by a morphonecrotic type of secretion associated with rejection of the intestinal epithelium.
Intestinal juice is secreted continuously into the intestinal cavity, mixed with food and forms chyme - a homogeneous liquid mass (cattle - up to 150 liters, pigs - up to 50 liters, sheep - up to 20 liters). 14-15 liters of chyme are formed per 1 kg of dry food.
The secretion of intestinal juice also occurs in 2 phases:
1. Complex reflex.
2. Neurochemical.
Increase secretion - nervus vagus, mechanical irritation, acetylcholine, mucosal hormone enterocrinin, duocrenin. Inhibit secretion - with sympathetic nerves, adrenaline, norepinephrine.
4. Intestinal digestion occurs in 3 stages:
1. Cavity.
2. Parietal digestion.
3. Suction.
Cavity digestion - (that is, in the cavity of the digestive canal, enzymatic processing occurs first of what is eaten (in the oral cavity), then of the food coma, gruel (in the stomach), and finally of chyme (in the intestines). Cavity hydrolysis is carried out due to the enzymes of pancreatic, intestinal juices and bile, which enters the intestinal cavity. In this case, mainly large-molecular compounds are hydrolyzed and oligomers (peptides, disaccharides, diglyceride) are formed.
Parietal (membrane digestion) - discovered academician A.M. Ugolev (1958). This type of digestion actively occurs in the small intestine. There are villi and microvilli that form a brush border, which is covered with mucus to form a mucopolysaccharide network - or glycocalyx.
The resulting monomers are transferred into the cell due to enzymes adsorbed on the surface of the villi that are structurally associated with cell membranes.
During parietal digestion, the final stage of hydrolysis of nutrients (monomers) that have already been subjected to cavity digestion is carried out.
Parietal (membrane) digestion is a highly economical mechanism that occurs under sterile conditions, since the distance between the villi is less than the size of the microorganism.
This is the initial stage of nutrient absorption.
