Digestion in the stomach and small intestine. Digestion in the small intestine

Lesson type: learning new material

Lesson type: lesson with elements of practical work

Target:

Introduce students to the features of digestion in the stomach and intestines;

Reveal the relationship between tissues and organs of humans and animals.

Educational objectives:

To form a concept about the levels of organization of living bodies;

Study the stomach and intestines

Show the types of fabrics and their differences in structure.

Developmental tasks:

Continue to develop the ability to compare the objects being studied and note the main thing;

Ability to present material consistently.

Educational tasks:

Form a scientific worldview;

Continue to develop a work culture based on keeping notes in a notebook.

Methods and methodological techniques: verbal (lecture elements, conversation), visual (demonstration via multimedia, tables), practical (demonstration experience).

Equipment: visual aids: table “Internal digestive organs”; test tube, chicken protein, natural gastric juice.

Lesson structure: (45 min lesson)

D/Z check (10 min.)

P. Learning new material (20 min.)

III. Consolidating new material (17 min.)

IV. Lesson summary (1-2 min.)

V. Homework(1-2 min.)

I . Organizing time(1-2 min.)

The teacher checks the students' readiness for the lesson and organizes the beginning of the lesson. Marks absentees.

D/Z check (10 min.)

What's happened and what organs are involved in this process?

What is digestion

What are teeth and what parts do they consist of?

Salivary glands and tongue function

II . Learning new material (20 min.)

The teacher announces the topic of the lesson, its purpose,

A) Problematic issues.

Guys, how does digestion proceed in the stomach and intestines?

Guys, to answer this question, you will get acquainted with the structural features of the stomach and intestines and the functions of these organs.

Write down the first point of the lesson in your notebooks:

1. Stomach

Stomach. The stomach serves as a reservoir for storing and digesting food. Outwardly, it resembles a large pear, its capacity is up to 2-3 liters. The shape and size of the stomach depend on the amount of food eaten.

Mucous membrane The stomach forms many folds, which significantly increase its total surface. This structure promotes better contact of food with its walls.

On the screen through multimedia the teacher shows internal organs digestion. Video Stomach.

The gastric mucosa contains about 35 million glands, which secrete up to 2 liters of gastric juice per day.Gastric juice is a transparent liquid, 0.25% of its volume is hydrochloric acid. This concentration of acid kills pathogens that have entered the stomach, but is not dangerous for its own cells. The mucous membrane is protected from self-digestion by mucus, which abundantly covers the walls of the stomach.

Look at Fig. on page the structure of the stomach wall.

Under the influence of enzymes: pepsin, chymosin, lipase contained in gastric juice, protein digestion begins. This process occurs gradually as the digestive juice permeates the food bolus, penetrating into its depths.Food stays in the stomach for up to 4-6 hours and as it turns into a semi-liquid or liquid pulp and is digested, it passes into the intestines in portions.

Regulation of juice secretion by the gastric glands occurs through reflex and humoral pathways . It begins with conditional and unconditional juice secretion.

In order to see how gastric juice affects the digestion process, let’s do the following experiment.

Demonstration experience.

Write it down in your notebooks

Target: study the effect of gastric juice enzyme on proteins.

Equipment: test tube, half-cooked chicken protein, gastric juice.

Progress. Add a little natural gastric juice to a test tube with half-cooked chicken protein and place it in warm water

(38-39 C). After 20-30 minutes, the protein flakes will disappear.

Explain why this happened?

Conclusion: Under the influence of the gastric juice enzyme - pepsin - protein molecules in an acidic environment break down into various amino acids.

Write down the second point of the plan:

2. Small intestine.

Small intestine. From the stomach, food enters the small intestine. This is the longest - up to 4.5-5 m - part of the digestive tube. The area closest to the stomach small intestine calledduodenum. Examine the internal organs of digestion (the teacher shows the intestines on the screen via multimedia) Video Small intestine

In it, food is exposed to pancreatic juice, bile and intestinal juice. Their enzymes act on proteins, fats and carbohydrates. In the small intestine, up to 80% of proteins ingested with food and almost 100% of fats and carbohydrates are digested. Here proteins are broken down into amino acids, carbohydrates into glucose, fats into fatty acids and glycerol.

Important role plays in this process bile , which is formed in the liver. Although bile itself does not digest fats, it enhances the action of enzymes and also decomposes fats into small droplets.

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.

Liver - the largest gland in our body, its mass reaches 1500 g. The liver takes part not only in the digestion process, many toxic substances are retained and neutralized in it. The liver stores a supply of carbohydrates in the form of glycogen - animal starch.Video Liver

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.

Thanks to folds and villi, the surface area of ​​the intestinal mucosa sharply increases, so almost complete food processing occurs here.On the screen the teacher shows structure of the wall of the small intestine.

The digestion process in the small intestine consists of three stages: cavity digestion, parietal digestion and absorption.

How it happens cavity digestion, you know: this is the digestion of nutrients under the influence of digestive juices in the intestinal cavity.Parietal digestion goes on the very surface of the intestinal mucosa. Food particles penetrating into the spaces between the villi undergo digestion. Larger particles cannot get here. They remain in the intestinal cavity, where they are exposed to digestive juices and are broken down to smaller sizes. This digestive mechanism promotes the most complete digestion of food.

In the intestines, food continues to mix and move using peristaltic movements of the muscles in its walls. The mechanism of these movements is simple: the circular muscles of the intestine contract in one place and relax in another. In this case, food moves to an area with relaxed walls. Then the reduction occurs exactly in this

area, and in the neighboring one the intestinal muscles relax, and the intestinal contents move further, etc.

The small intestine is also capable of pendulum-like movements due to alternate lengthening and shortening of the intestine in a certain area. The contents of the intestine are mixed and moved in both directions.

Suction - this is the process of entry of various substances through the layer of villi cells into the blood and lymph. Suction has great value, this is how our body receives all the necessary substances. Moreover, water, mineral salts, amino acids and glucose enter the bloodstream already in the stomach. 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 lymphatic vessels is squeezed out and goes into the general blood and lymph flow. The villi contract 4 to 6 times per minute. Water, mineral salts dissolved in it, amino acids and carbohydrate breakdown products are absorbed into the blood. Glycerin and fatty acid In the epithelial cells of the villi, fats characteristic of the human body are combined and formed, then they enter the lymph, then into the blood.Video Suction

3. Large intestine .

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.

Colon - the final section of the digestive tube. Its length ranges from 1.5 to 2 m. One of its sections iscecum - has a narrow appendix - appendix (6-8 cm long), which is an organ immune system. Look at Fig. structure of the large intestine on page 158.

Undigested food remains accumulate in the colon. Here they can stay for 12-20 hours. During this time, under the influence of bacteria, fiber is broken down, and water is absorbed into the blood vessels located in the walls of the colon. 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.

In the large intestine, water is predominantly absorbed (up to 4 liters per day), as well as glucose and some medicines. 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 defecation center is located in sacral region spinal cord. The act of defecation is also subordinated to the cerebral cortex, which causes voluntary delay in defecation.

Conclusion:
1. The stomach is a hollow muscular organ located in the left hypochondrium and epigastrium.
2. Partially digested food is excreted from the stomach into the duodenum.
3. The initial section of the small intestine, 25-30 cm long, is the duodenum, into which the ducts of the liver and pancreas open. Three digestive juices act on the food gruel: liver bile, pancreatic juice, and intestinal gland juice.
4. Gastric juice is a liquid secreted by the gastric glands and epithelial cells of the gastric mucosa. It is a colorless transparent liquid containing hydrochloric acid (0.3-0.5%).

As gastric juice penetrates into the food mass, the gastric phase of digestion begins, during which protein breakdown mainly occurs.

III . Consolidating new material (17 min.)

Correct errors in the text;

The outline of which organ is shown in this figure?

Test: The breakdown of: a) water b) proteins c) starch d) fats begins in the stomach

2. The breakdown of nutrients occurs under the influence of: a) vitamins b) water c) enzymes

3. The ducts of the pancreas and liver open into: a) stomach b) esophagus c) duodenum d) small intestine

4. Bile is produced by: a) the pancreas b) the liver c) the glands of the stomach

5. Pancreatic enzymes break down: a) only fats b) only starch c) proteins, fats, starch d) only proteins

Give names to all organs digestive system

Choose the correct statements:

Digestion and absorption begins in the oral cavity. *

Bile is produced by the glands of the stomach.

Proteins are digested both in the stomach and in small intestine. *

Some intestinal bacteria synthesize vitamins. *

Peritonitis is inflammation of the appendix.

Bile activates some pancreatic enzymes.*

Trypsin - breaks down fats.

The stomach and intestines have an acidic environment.*

Enzymes are biological catalysts.*

Hydrochloric acid plays the role of a pepsin activator. *

6. Anagram.

Make words from letters. Find the extra word and explain why it is extra.

UELZHOKD – stomach

IVPESHDO – esophagus

JECHPEN – liver

KICHIKSHEN – intestines

KEBLI – squirrels

TOP - mouth

Superfluous word PROTEIN, since it is a nutrient, and the stomach, esophagus, liver, intestines, mouth are organs.

7. Questions:

1 . What is the stomach used for?

2. How is food digested in the stomach?

3. Where does food go after processing in the stomach?

4. What is the name of the part of the small intestine closest to the stomach?

5. What is the name of the largest gland in our body?

6. What functions does the liver perform besides digestion?

7. What are the stages of the digestion process?

8. How does food move in the intestines?

9. What is the name of the final section of the digestive tube?

10.What is an organ of the immune system?

Reflection:

I was interested to know that...

It was difficult for me to understand, but I still managed that...

It was not at all clear to me that......

I can apply this material in life in (situation)…

IV . Lesson summary (1-2 min.)

V . Homework (1-2 min.) Page. 156-158.

VI . Assessment of knowledge and marking with commentary (1-2 min.)

Digestive are food deposit, her mechanical And chemical treatment, gradual portioned evacuation stomach contents into the intestines. Food, being in the stomach for several hours, swells, liquefies, many of its components dissolve and undergo hydrolysis by enzymes of gastric juice. also has an antibacterial effect.

Salivary enzymes act on food carbohydrates located in the central part of the food contents of the stomach, where gastric juice has not yet entered, stopping the action of these enzymes. Gastric juice enzymes act on the proteins of food contents in the area of ​​direct contact with the gastric mucosa and at a short distance from it, where the gastric juice has entered.

Secretory function of the stomach

Secretory function - a set of processes that ensure the formation and secretion of a specific secretion by a glandular cell. The total volume of gastrointestinal secretion is 6-8 l/day, most of it is reabsorbed.

Gastric juice is produced by the glands of the stomach located in its mucous membrane. It is covered with a layer of columnar epithelium, the cells of which secrete mucus and a slightly alkaline liquid. Mucus is secreted in the form of a thick gel, which covers the entire mucous membrane in an even layer.

On the surface of the mucous membrane, small depressions are visible - gastric pits, total which reaches 3 million. The lumens of 3-7 tubular gastric glands open into each of them. There are three types of gastric glands:

• own glands of the stomach - located in the area of ​​the body and fundus of the stomach (fundic). Fundic glands are composed of three main types of cells: main - secreting pepsinogens, lining (parietal) - hydrochloric acid and additional - mucoid secretion mucus (Fig. 1);
• cardiac glands - located in the cardiac part of the stomach; these are tubular glands consisting mainly of mucus-producing cells;
• pyloric glands - located in the pyloric region of the stomach. They have virtually no parietal cells and secrete a small amount of secretion that is not stimulated by food intake.

Rice. 1. Physiological anatomy of the stomach: A - sections; B - some types of secretory cells

Leading value in gastric digestion has juice produced by the fundic glands.

Gastric juice

Gastric juice - it is a transparent liquid consisting of 99.0-99.5% water, 0.4-0.5% of hydrochloric acid and 0.3-0.4% dense substances. It has an acidic reaction (pH 1.0-2.5). It contains enzymes, digesting proteins - pepsin, chymosin and fats - lipase. A person secretes 1.5-2.5 liters of gastric juice per day.

Hydrochloric acid causes denaturation and swelling of proteins and thereby promotes their subsequent breakdown by pepsins, activates pepsinogens, creates an acidic environment necessary for the breakdown of food proteins by pepsins; participates in the antibacterial effect of gastric juice and regulation of the activity of the digestive tract (depending on the pH of its contents, the nervous and humoral mechanisms of regulation of its activity are enhanced or inhibited).

Functions of hydrochloric acid:

• Denaturation of proteins
• Activation of the transition of pepsinogens to pepsins
• Creating an optimum pH for the manifestation of the enzymatic properties of pepsins
• Protective function
• Regulation of gastric and duodenal motility
• Stimulation of enterokinase secretion

The chief cells of the gastric glands synthesize several pepsinogens. When pepsinogens are activated by the cleavage of a polypeptide from them, several pepsins are formed. Pepsins are commonly called protease enzymes that hydrolyze proteins at a maximum speed at pH 1.5-2.0. Pepsins cleave a small number of peptide bonds—about 10%.

Pepsin secreted by the pyloric glands, unlike pepsin produced by the fundic glands, acts in a less acidic and even neutral environment. Chymosin acts on milk proteins. By causing curdling of milk, it leads to the precipitation of casein protein in the form of calcium salt. Chymosin acts in any environment - slightly acidic, neutral and alkaline.

Gastric lipase - an enzyme of very low digestive power, it acts mainly on emulsified fats, such as milk fats.

The glands located in the area of ​​the lesser curvature of the stomach produce a secretion with higher acidity and pepsin content than the glands of the greater curvature of the stomach.

An important component of gastric juice are mucoids. Slime - mucoid secretion - is represented mainly by two types of substances - glycoproteins and proteoglycans.

Function of gastric mucus ( colloidal solution glycoproteins and proteoglycans)

• Protects the gastric mucosa from the action of gastric secretions
• Adsorbs and inhibits enzymes
• Neutralizes hydrochloric acid
• Enhances the efficiency of proteolysis
• Hematopoietic function (Castle factor/gastromucoprotein)
• Regulation of gastric secretion

A layer of mucus 1-1.5 mm thick protects the gastric mucosa and is called the gastric mucus protective barrier. Mucoids include internal Castle factor, which binds vitamin B 12 and protects it from destruction by enzymes. Complex internal factor interact with vitamin B 12 in the presence of Ca 2+ ions by receptors epithelial cell e legal part of the ileum. In this case, vitamin B 12 enters the cell, and the intrinsic factor is released. The absence of an internal factor leads to the development of anemia.

The glands of the pyloric part secrete a small amount of slightly alkaline juice with a high content of mucus. An increase in secretion occurs with local mechanical and chemical irritation of the pyloric part of the stomach. The secretion of the pyloric glands has low enzymatic activity. These enzymes are not essential in gastric digestion. The alkaline pyloric secretion partially neutralizes the acidic contents of the stomach, evacuated into the duodenum.

Has great protective value gastric mucous barrier, the destruction of which may be one of the causes of damage to the gastric mucosa and even deeper structures of its wall.

Under unfavorable conditions, the barrier is destroyed within a few minutes, epithelial cell death, swelling and hemorrhages occur in the own layer of the mucous membrane. Factors unfavorable for maintaining the barrier: non-steroidal anti-inflammatory drugs (for example, aspirin, indomethacin); ethanol, bile salts, Helicobacterpylori- a gram-ripening bacterium that survives in the acidic environment of the stomach, infects the surface epithelium of the stomach and destroys the barrier, which contributes to the development of gastritis and ulcerative defect of the stomach wall. This microorganism is isolated from 70% of patients peptic ulcer stomach and 90% of patients with duodenal ulcer or antral gastritis.

Factors that protect the stomach from self-digestion are:

• the presence of mucus-mucin;
• synthesis of enzymes in inactive form;
• production of special substances that neutralize pepsin;
• slightly alkaline environment in the stomach (pepsin is active in an acidic environment);
• rapid replacement of old mucosal cells with new ones - 3-5 days;
• The environment in an empty stomach is neutral.

Phases of gastric secretion

Gastric secretion has three phases:

• cerebral (complex-reflex) phase begins before food enters the stomach, at the time of eating. The sight, smell, and taste of food increase the secretion of gastric juice.

The nerve impulses that cause the brain phase originate from the hunger centers in the amygdala, as well as the food center in the amygdala. From taste (unconditioned reflex separation of juice), visual, auditory, olfactory (conditioned reflex separation of juice) receptors, nerve impulses enter the brain and are processed. Efferent nerve impulses are transmitted through the motor nuclei of the vagus nerve and then through its fibers to the stomach. The secretion of gastric juice during this phase accounts for up to 20% of the secretion associated with food intake. This phase lasts 1.5-2 hours and is called the starting phase.

Secretion into the brain phase depends on the excitability of the food center and can be easily inhibited by stimulation of various external and internal receptors. Thus, poor table setting and untidiness of the eating area reduce and inhibit gastric secretion. Optimal conditions meals have a positive effect on gastric secretion. Taking strong food irritants at the beginning of a meal increases gastric secretion in the first phase.

The juice that forms in the stomach before food arrives was named I.P. Pavlov's "appetizing" The significance of the appetizing juice is that it prepares the stomach in advance for food intake, and when it enters the stomach, the breakdown of nutrients immediately begins;

• gastric (neurohumoral) phase - begins from the moment food enters the stomach due to irritation of mechanoreceptors. Incoming food causes a set of reflexes aimed at producing the hormone gastrin, which is absorbed into the blood and enhances gastric secretion during the several hours that food remains in the stomach. The release of gastrin is promoted by protein hydrolysis products and extractive substances contained in meat and vegetable broths. The amount of juice secreted in the gastric phase is 70% of the total secretion of gastric juice (1500 ml);
• intestinal (humoral) phase - is associated with the entry of food into the duodenum, which causes a slight increase in the secretion of gastric juice (10%) due to the release of enterogastrin from the intestinal mucosa under the influence of stretching and the action of chemical stimuli. Strengthening this phase is also facilitated by nutrients, absorbed into the blood from the small intestine.

Regulation of gastric secretion

Outside of digestion, the stomach glands secrete a small amount. Eating food sharply increases its secretion due to stimulation of the gastric glands by the nervous and humoral mechanisms that make up unified system regulation. Stimulating and inhibitory regulatory factors ensure the dependence of gastric juice secretion on the type of food taken. This dependence was first discovered in the laboratory of I.P. Pavlova in experiments on dogs with an isolated ventricle, which were fed various foods.

Triggers gastric secretion acetylcholine secreted by the fibers of the vagus nerves. Transection of the vagus nerves (vagotomy) leads to a decrease in gastric secretion (this operation is sometimes performed in order to normalize secretion when it increases). Sympathetic nerves have an inhibitory effect on the gastric glands, reducing the volume of secretion (Fig. 2).

A powerful stimulator of the gastric glands is gastrin. It is released from G cells, which are found in the pyloric mucosa of the stomach. After surgical removal In the pyloric part, gastric secretion sharply decreases. The release of gastrin is enhanced by impulses from the vagus nerve, as well as local mechanical and chemical irritation of this part of the stomach. Chemical stimulants (7-cells are the products of protein digestion - peptides and some amino acids, extractive substances of meat and vegetables. If the pH in the pyloric part of the stomach decreases, which is due to an increase in the secretion of hydrochloric acid by the gastric glands, then the release of gastrin decreases, and at a pH of 1.0 the volume of secretion sharply decreases and stops. Thus, gastrin takes part in the self-regulation of gastric secretion, depending on the pH value of the contents of the pyloric region. Gastrin most stimulates the parietal cells of the fundic glands and increases the secretion of hydrochloric acid.

Rice. 2. Regulation of gastric secretion. K - bark; P - subcortex; PM - medulla; Cm - spinal cord; F - stomach; Gl - sympathetic ganglion; Zc - visual center; Pc - food center; Yaz - language; n. lingualis - lingual nerve; n. Glossopharyngeus - glossopharyngeal nerve; n. vagus - nervus vagus; n. Sympathicus - sympathetic nerve

TO stimulants gastric glands histamine, formed in the gastric mucosa. The release of histamine is mediated by gastrin. Histamine affects the lining cells of the gastric glands, causing the secretion of large amounts of juice that is high in acidity but low in pepsin.

Gastric secretion is stimulated by the hormone enterogastrin, which is secreted by the duodenum under the influence of protein digestion products absorbed into the blood.

Table. Regulation of gastric secretion

Activators	Inhibitors
Nervus vagus	Sympathetic nerve
Acetylcholine HCI/E	Adrenaline HCI
Gastrin HCI/E	Secretin HCI
Histamine HCI/E	Prostaglandins (PGE 2) HCI
Protein hydrolysis products	Glucagon HCI
Cholesntokinin E	Cholecystokinin HCI
Secretin E	ZhIP, VIP HCI
β-adrenergic agonists E	Serotonin HCI
Glucocorticoids	Enterogastron HCI/E
	Bulbagastron HCI/E
	Antrum pH below 2.5 HCI
Rage, anger	Fear, longing

Note: E - effect on the enzyme; HCI - effect on hydrochloric acid.

Inhibition of gastric secretion causes excess hydrochloric acid, deli, formed in the pyloric part of the stomach, and enterogastron, formed in the duodenum. The passage of food into the intestines inhibits gastric secretion, which causes secretion of the duodenum by the mucous membrane secretin And cholecystokinin. These hormones stimulate the pancreas and liver and inhibit the activity of the gastric glands. Research by I.P. Pavlov has proven that fat has an inhibitory effect on gastric secretion.

Motor function of the stomach

During and in the first minutes after eating, the stomach relaxes - food receptive relaxation of the stomach occurs, which promotes the deposition of food in the stomach and its secretion. After some time, depending on the type of food, contractions increase, with the least contraction force observed in the cardial part of the stomach and the greatest in the pyloric part. Contractions of the stomach begin at the greater curvature in close proximity to the esophagus, where the cardiac pacemaker is located. The second pacemaker is localized in the pyloric part of the stomach.

In a stomach filled with food, three main types of movements occur: peristaltic waves, systolic contractions of the pyloric region and tonic contractions, which reduce the size of the cavity of the fundus and body of the stomach. The frequency of peristaltic contractions is about three per minute; they spread from the cardial part of the stomach to the pyloric part at a speed of about 1 cm/s, faster
along the greater than the lesser curvature and last about 1.5 s. In the pyloric part, the speed of propagation of the peristaltic wave increases to 3-4 cm/s.

Rice. Types motor activity stomach

The residence time of mixed food in the stomach of an adult is 6-10 hours. Food rich in carbohydrates is retained in the stomach less than food rich in proteins. Fatty food evacuated from the stomach at the lowest speed. Liquids begin to pass into the intestine immediately after they enter the stomach.

The evacuation of food from the stomach is caused not only by the opening of the sphincter, but also by contractions of the muscles of the entire stomach, especially its pyloric part (Fig. 3). They create a high pressure gradient between the stomach and duodenum. The pressure in the duodenum and its motor activity are of significant importance in changing the rate of evacuation. The combination of these factors ensures one or another rate of evacuation of food from the stomach with the participation of neurohumoral mechanisms. The latter change the evacuation speed depending on the consistency, chemical composition, pH, volume of stomach and intestinal contents. As a result, portioned loading of food contents of the main “chemical reactor” - WPC is ensured.

Rice. 3. Consecutive phases of gastric emptying: A, B - the pyloric sphincter is closed; B - the pyloric sphincter is open

The leading role in regulating the rate of evacuation of stomach contents is played by reflex influences from the stomach and duodenum. Effects on gastric mechanoreceptors accelerate, and effects on duodenal receptors slow down evacuation. Inhibition of the evacuation of stomach contents is also caused by chemical agents located in the duodenum: acidic (pH below 5.5) and hypertonic solutions, 10% ethanol solution, glucose and fat hydrolysis products. The rate of evacuation also depends on the efficiency of hydrolysis of nutrients in the stomach (protein) and small intestine.

Vomit - complex reflex motor act, starting with contraction of the small intestine, as a result of which its contents are pushed out into the stomach by antiperistaltic waves. After 10-20 seconds, the stomach contracts, the entrance to the stomach opens, and the muscles contract strongly abdominal cavity and the diaphragm, as a result of which the contents of the stomach at the moment of exhalation are expelled through the esophagus into the oral cavity, from where the vomit is removed. Vomiting has a protective significance and occurs reflexively as a result of irritation of the receptors of the root of the tongue, pharynx, mucous membrane of the stomach, intestines, peritoneum, vestibular apparatus(under the influence of pitching at seasickness). Vomiting may be caused by olfactory and gustatory stimuli, evoking feelings disgust (conditioned reflex vomiting). Some substances (for example, the alkaloid apomorphine) that act through the blood on nerve center vomiting, located in the medulla oblongata.

Signals to the center of vomiting from the receptors of these areas arrive through the afferent fibers of the vagus, glossopharyngeal and some other nerves. Efferent influences that cause vomiting travel along the fibers of the vagus and splanchnic nerves to the esophagus, stomach, intestines, as well as along motor fibers to the muscles abdominal wall and diaphragm. Vomiting is accompanied by changes in breathing, coughing, sweating, salivation and other reactions.

One of the most important processes occurring in the body is digestion in the stomach. The correct functioning of the intestines and pelvic organs depends on how well the food digestion scheme is established. The digestion process goes through several stages, each of which is impossible without the previous one.

What is the stomach?

The organ is a hollow reservoir, the size of which is no larger than a fist (in a situation where it is not filled with products). The walls of the stomach are elastic, so when products pass into its cavity, it stretches and acquires larger size, starting the digestive system. The anatomy of the stomach includes three sections:

• cardiac - located closest to the esophagus;
• the basis of the stomach - where hydrochloric and other enzymes are formed;
• gatekeeper - whose main task is the chemical processing of food.

Particular attention must be paid to the wall of the stomach. It consists of 4 layers: mucous, submucosal, muscular and serous. Despite the fact that the structure of the organ wall is similar to the structure of the esophagus, its mucous membrane is more functional due to the presence of pits, folds and fields with veins on the surface. The morphology of the stomach includes 3 additional layers:

• Epithelial part. Responsible for the production of mucus.
• Slime layer. Protects the mucous membrane.
• Muscle plate. Responsible for organ contraction.

In the submucosal layer there is a sphincter - a round muscle that separates the gastric cavity from the duodenum.

Characteristics of organ function

The process of digesting food is carried out by activating the functions of the gastrointestinal tract.

Digestion is regulated by the body fulfilling its purposes. Mechanical processing of food in the stomach occurs in several stages due to its passage through different departments gastric cavity. The digestion process is accompanied by the activation of such stomach functions as:

• Secretory. It involves the production of gastric juice, which contains many minerals and acids that can speed up the process of breaking down food. The composition of the substance depends on what food enters the stomach. An adult excretes up to 2 liters of fluid during the day; in children the norm is lower.
• Cumulative and motor. The residence time of products in the stomach is 3 hours. After this, the products are mixed with the produced substance and accumulated to a certain amount. Then comes the evacuation of food into the large intestine. This function is provided by the muscle layer.
• Suction. The developed microvascular circuit of the stomach carries nutrients to other internal organs.
• Excretory. When this function is activated, decomposition products formed in the human stomach after digestion are removed.
• Antianemic. In the parietal cells, internal production occurs, which is responsible for the body’s absorption of vitamin B12, necessary for the creation of blood.
• Protective barrier. Enzymes and acids found in the organ prevent the effects of toxins on the body.
• Endocrine. Special cells produce hormonal compounds necessary for the proper functioning of the gastric glands, gallbladder and circulatory system.

Basic secretions of the stomach

The juice produced to digest food is not harmful to the human body.

The organ produces secretions - special substances necessary for the movement of food from the gastric cavity to the intestine. Under the influence of the secretion the product passes structural changes and nutrients are absorbed. The juice produced by the stomach is an aggressive environment, but it does not harm the body. The processes occurring in the stomach cavity kill bacteria and pathogenic microorganisms. Regulators of secretion production are humoral system and CNS. Gastric juice is produced by glands that are located in the mucous membrane of the organ. The substance is presented in the form of a translucent liquid. One of the components of gastric juice is hydrochloric acid, which makes the environment acidic. The passage of food through all stages of food breakdown is also carried out due to the presence of the following components in the gastric secretion:

• ammonia;
• sodium bicarbonate;
• magnesium;
• potassium;
• water;
• phosphates;
• chlorides;
• sulfates.

Phases of food digestion by the stomach (briefly)

The smell of food provokes the production of special substances for digesting food.

Physiology suggests the fact that the processing of food in the stomach begins even before it enters the organ. The secretion of gastric juice begins before the time of a regular meal, as well as when smelling food while setting the table. Secretory regulation of digestion is carried out in three stages, all of them are necessary and dependent on what kind of food was consumed and in what quantity. The phases of gastric secretion are closely related to each other, and if the logical sequence is disrupted, the system will fail, and this fact slows down the evacuation of processed products.

Table of stages of secretory activity

Phases of gastric juice secretion	Process Features
Complex reflex (cerebral)	The body's reaction to conditioned reflex and unconditioned reflex factors: the sight and smell of food, the process of preparing dishes, irritation of recipes in the mouth
Gastric phase	When the first dose of food enters the gastric cavity, nerve impulses enter the medulla oblongata
	The release of secretin and histamine begins
Intestinal phase of secretion	After the transition of food into chyme (undigested food) is completed, the substance enters the duodenum
	Processes occur that accelerate or slow down the movement of residues

If there is a violation of food evacuation, chyme enters back into the stomach cavity and increases the acidity of the secretion produced by the organ.

Despite the fact that the breakdown of food begins in the mouth under the influence of saliva, it undergoes further processing in the stomach. Digestion in the stomach and intestines are the final stages of the process of digesting food. Let's look at how products are broken down and learn about the role of gastric juice in the whole process.

The stomach is a muscular organ of the digestive system. Its volume without contents is only 50 ml, but when eating food, the organ can stretch up to 4 liters.

The functions are as follows:

1. Food storage. The stomach is a storage place for the food a person eats.
2. Excretory. Food processing involving gastric juice. The food lump is mainly affected by hydrochloric acid and enzymes.
3. Motor. Mixing the food bolus with hydrochloric acid and moving it into the intestines, where digestion ends.
4. Absorption of nutrients. Only part of the beneficial substances is absorbed by the gastric mucosa, the rest of the substances enter the blood from the intestines.
5. Excretory. Together with gastric juice, metabolites such as urea and creatine, as well as substances from the outside (salts) penetrate into the organ heavy metals and medicines).
6. Incretory. Participates in the formation of hormones that regulate the functioning of the digestive glands.
7. Protective. Protects the intestines from the penetration of spoiled food into it. Gastric juice has a bactericidal effect.

Let's look at the secretory function in more detail, because it is important for the digestive process. Secretory function the organ performs with the participation of three glands, which are located in the mucous membrane and consist of cells. The glands produce hydrochloric acid, pepsinogens and mucus.

The cellular composition of the glands depends on which part of the stomach they are located in.

The role of gastric juice

The stomach always contains about 50 ml of liquid contents. This is saliva and gastric juice. When eating food, the stomach fills with juice. From 1.5 to 2.5 liters of this biological fluid are produced per day.

It appears to be a colorless liquid, sometimes containing mucus flakes. The acidity of the juice reaches 0.8-1.5 due to the content of hydrochloric acid.

Juice composition:

• hydrochloric acid is the main inorganic component;
• acidic compounds – acids (lactic and ureic), amino acids;
• phosphates, sulfates, chlorides and other substances;
• enzymes;
• slime.

The juice is 99% water and only 1% organic and inorganic substances. Hydrochloric acid makes up up to 0.5% of the total content. Its tasks are the following:

1. Stimulation of secretory activity (regulation of the secretion of gastric and pancreatic glands, activation of the secretion of hormones and enzymes, as well as gastric motility).
2. Activation of protein breakdown.
3. Increasing the acidity of gastric juice, thereby creating a favorable environment for the action of enzymes.
4. Antibacterial effect. Thanks to acidity, it kills all microbes and prevents bacteria from multiplying in the stomach.
5. Helps the passage of food from the stomach to the intestines, where it undergoes further processing.

Enzymes, like hydrochloric acid, are important for digesting food. The main enzyme is pepsin. Using hydrochloric acid, it breaks down proteins into pepsins, and then into albumoses.

Mucus is produced by the mucous membrane of the organ. It protects it from the aggressive effects of hydrochloric acid and prevents damage, either mechanical or chemical.

How does gastric digestion occur?

Digestion in oral cavity and in the stomach can be attributed to the initial stages of digestion of food and its breakdown into proteins, fats and carbohydrates. Cavity digestion mainly occurs in the stomach. The main task is the hydrolysis of proteins and fats before the food reaches the intestines.

Food comes out of the mouth already in a processed form, it is covered with saliva. It can take from 3 to 10 hours to digest food, depending on its composition. On average, under the influence of gastric juice, food is broken down in two hours.

TO chemical exposure include the processing of a food coma with gastric juice, and mechanical - mixing and crushing food with the help of smooth muscles that are located on the walls of the stomach.

Under the influence of gastric juice, food is not immediately broken down into useful material, first the surface of the food ball is exposed to the juice. Saliva enzymes act inside the coma until it is completely saturated with gastric juice.

It is worth noting that some products are subjected only to mechanical processing, because when they enter the gastrointestinal tract they are immediately absorbed into the mucous membrane. Among such products are alcohol, water, salts and glucose.

How are proteins and carbohydrates broken down?

Gastric juice is released reflexively when eating food. Glands are involved in the process of its production. Hydrochloric acid is involved in the breakdown of almost all substances that make up food, because it has high acidity. It makes proteins loose and accessible to destruction by enzymes. Juice enzymes are involved in the further breakdown of proteins into molecules. Protein substances are not absorbed in the stomach; they penetrate through the intestinal mucosa.

Carbohydrates begin to be broken down in the mouth, so they are digested in a short time, approximately 40 minutes. They are destroyed under the influence of salivary enzymes (amylase and maltase) and hydrochloric acid. The final breakdown of carbohydrates, like proteins, occurs in the intestines.

Fats are the worst to break down. They are not completely digested in the stomach, but are chemically processed using the enzyme lipase.

The role of the pancreas and liver

Gastric digestion is not the final stage. Then the food moves into the intestines, where it is acted upon by bile. The role of the liver, like the pancreas, in digestion is enormous. The liver secretes bile, which performs functions similar to gastric juice, only it acts on food in the intestines. Bile enters there 10 minutes after eating. At the end of the meal, it accumulates in the gallbladder.

Functions of bile:

• neutralizes the acidity of the food coma when it enters the intestines;
• increases intestinal motility;
• breaks down fats;
• activates lipase.

0.5-1 liters of bile are produced per day. If there are problems with its production, then it is necessary to consume yolks, milk, bread and meat. Such products will increase the production of bile.

What is the composition of this biological fluid? It consists of acids, pigments (bilirubin and biliverdin) and cholesterol.

In addition to producing bile, the liver synthesizes glycogen (a polysaccharide) and neutralizes harmful substances that enter the body with food. The organ protects against alcohol intoxication and food poisoning.

The role of the pancreas in digestion is great. This organ produces pancreatic juice. Up to 2 liters of this liquid are synthesized per day. Pancreatic juice has a pH=7.5-8.8. It neutralizes the acidity of the contents in the stomach and creates alkaline environment to improve performance digestive enzymes.

Pancreatic juice consists of digestive enzymes (trypsin, chymotrypsin, carboxypolypeptidase, aminopeptidase, lipase, amylase, maltase), water, bicarbonates and electrolytes.

The organ itself belongs to the glands of mixed secretion. It consists of two departments. Juice is produced in the exocrine. This section occupies up to 80% of the organ’s volume. After production, pancreatic juice flows through the ducts into the duodenum. This happens simultaneously with the production of bile.

Gastric digestion is a rather complex process that involves enzymes, acids and other substances. If the functioning of any organ of the gastrointestinal tract is disrupted, the production of biological fluids and the digestion process itself. In this case, drug treatment will help.

With a lack of enzymes, the process of digesting food becomes difficult. If such a problem occurs, it is necessary to take enzyme preparations. It is better not to self-medicate, but to consult a doctor, who will prescribe treatment. Sometimes it is necessary to take medications to improve gastric or intestinal motility.

Stomach in humans it is located under the diaphragm on the left side of the abdominal cavity. It is a hollow, sac-like muscular organ that can stretch when food enters it. The walls of the empty stomach form folds, and it is the size of two fists. A fully distended adult stomach can contain 2-4 liters. food.

What functions does the stomach perform?

In it, food accumulates, mixes and is subjected to further chemical treatment. Mixing food is facilitated by the contraction of the muscle layer, which, in addition to the longitudinal and circular muscles, has oblique muscles. Chemical changes occur in food under the influence of gastric juice. The length of time food stays in the stomach depends on its composition: the more fat it contains, the longer it stays in the stomach.

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Gastric juice- a colorless, odorless liquid. It is produced by numerous glands in the gastric mucosa. 1 mm2 of mucous membrane contains approximately 100 such glands. Some of them produce enzymes, others produce hydrochloric acid, and others secrete mucus. A person usually produces 2-2.5 liters of gastric juice per day.

The main enzyme in gastric juice is pepsin. It breaks down protein molecules into simpler molecules consisting of several amino acids. Pepsin acts only at a temperature of 35-37 ° C and in the presence of hydrochloric acid. Hydrochloric acid destroys pathogenic microorganisms, performing protective function. The mucus that covers the gastric mucosa prevents the action of hydrochloric acid and pepsin on its wall, protecting it from self-etching and mechanical damage.

In the stomach, swallowed food lumps turn into a semi-liquid mass - chyme. From time to time it is pushed out of the stomach into the intestines through an opening surrounded by a sphincter that prevents the chyme from returning to the stomach. Digestion in the small intestine. The section of the small intestine that extends from the stomach is called the duodenum, its length is about 25 cm. The ducts of the pancreas and gall bladder open into it. The following sections of the small intestine are the hollow intestine (1.5-2.5 m) and ileum (about 3 m). Due to the length of the small intestine, food digestion occurs over a considerable period of time. By contracting, the smooth muscles of the intestines carry out peristaltic and pendulum-like movements, moving and mixing the chemical mousse.

Chyme and bile

While driving chyme turns into compounds that are absorbed by the body. This occurs under the influence of pancreatic enzymes and gall bladder secretions, as well as enzymes secreted by the glands of the small intestine. It finally breaks down about 80% of carbohydrates and almost 100% of proteins and fats supplied with food. Proteins are broken down by two main enzymes: trypsin and chemotrypsin, carbohydrates - under the action of amylases, fats are broken down by lipases. These enzymes do not work in acidic environments. Therefore, to neutralize hydrochloric acid, which enters the small intestine as part of the chyme, its glands and pancreas secrete alkaline substances.

IN bile, which enters the intestines from the gallbladder, there are no enzymes. Bile substances “break” water-insoluble fat droplets into smaller droplets. The fats in these droplets become accessible to lipases and are broken down more efficiently.

Where does digestion take place in the small intestine? In this process, a distinction is made between cavity and parietal digestion. The task of cavity digestion is to break down large organic molecules with the help of enzymes from the glands of the intestines and pancreas, as well as bile. The final splitting occurs during parietal digestion.

You can see many folds on the inner surface of the intestine with the naked eye. Looking at them under a microscope, you will see numerous villi covered with epithelial cells that produce enzymes, mucus, etc. If you look closely at such a cell, you will see many microvilli on its membrane. Villi and mucus, enriched with enzymes, are the medium where parietal digestion occurs.