The essence of digestion in the oral cavity. How food is broken down in the human oral cavity: saliva enzymes and stages of digestion

Man must eat food in order to sustain his life. Food products contain all the substances necessary for life: water, mineral salts and organic compounds. Proteins, fats and carbohydrates are synthesized by plants from inorganic substances using solar energy. Animals build their bodies from nutrients of plant or animal origin.

Nutrients that enter the body with food are a building material and at the same time a source of energy. During the breakdown and oxidation of proteins, fats and carbohydrates, a different, but constant amount of energy is released for each substance, characterizing their energy value.

Digestion

Once in the body, food products undergo mechanical changes - they are crushed, moistened, split into simpler compounds, dissolved in water and absorbed. The set of processes by which nutrients from the environment pass into the blood is called digestion.

play an important role in the process of digestion enzymes- biologically active protein substances that catalyze (accelerate) chemical reactions. In the processes of digestion, they catalyze the reactions of hydrolytic breakdown of nutrients, but they themselves do not change.

The main properties of enzymes:

• specificity of action - each enzyme breaks down nutrients only of a certain group (proteins, fats or carbohydrates) and does not break down others;
• act only in a certain chemical environment - some in alkaline, others in acid;
• enzymes are most active at body temperature, and at a temperature of 70-100ºС they are destroyed;
• a small amount of enzyme can break down a large amount of organic matter.

Digestive organs

The alimentary canal is a tube that runs through the entire body. The canal wall consists of three layers: outer, middle and inner.

outer layer(serous membrane) is formed by connective tissue that separates the digestive tube from surrounding tissues and organs.

middle layer(muscular membrane) in the upper sections of the digestive tube (oral cavity, pharynx, upper esophagus) is represented by striated, and in the lower - by smooth muscle tissue. Most often, the muscles are arranged in two layers - circular and longitudinal. Due to the contraction of the muscular membrane, food moves through the alimentary canal.

The inner layer(mucous membrane) is lined with epithelium. It contains numerous glands that secrete mucus and digestive juices. In addition to small glands, there are large glands (salivary, liver, pancreas) that lie outside the digestive canal and communicate with them with their ducts. In the digestive canal, the following sections are distinguished: the oral cavity, pharynx, esophagus, stomach, small intestine and large intestine.

Digestion in the mouth

Oral cavity- initial part of the digestive tract. From above, it is limited by the hard and soft palate, from below by the diaphragm of the mouth, and in front and from the sides by the teeth and gums.

The ducts of three pairs of salivary glands open into the oral cavity: parotid, sublingual and submandibular. In addition to these, there is a mass of small mucous salivary glands scattered throughout the oral cavity. The secret of the salivary glands - saliva - wets food and participates in its chemical change. Saliva contains only two enzymes - amylase (ptyalin) and maltase, which digest carbohydrates. But since food is not in the oral cavity for long, the breakdown of carbohydrates does not have time to end. Saliva also contains mucin (mucous substance) and lysozyme, which has bactericidal properties. The composition and amount of saliva may vary depending on the physical properties of the food. During the day, a person secretes from 600 to 150 ml of saliva.

In the oral cavity of an adult there are 32 teeth, 16 in each jaw. They capture food, bite off and chew.

Teeth consist of a special substance of dentin, which is a modification of bone tissue and has greater strength. Outside, the teeth are covered with enamel. Inside the tooth there is a cavity filled with loose connective tissue, which contains nerves and blood vessels.

Most of the oral cavity is occupied language, which is a muscular organ covered with a mucous membrane. It distinguishes the top, root, body and back, on which the taste buds are located. The tongue is the organ of taste and speech. With its help, food is mixed during chewing and pushed through when swallowing.

Food prepared in the oral cavity is swallowed. Swallowing is a complex movement that involves the muscles of the tongue and pharynx. During swallowing, the soft palate rises and blocks food from entering the nasal cavity. The epiglottis at this time closes the entrance to the larynx. The food bolus enters throat- the upper part of the alimentary canal. It is a tube, the inner surface of which is lined with a mucous membrane. Through the pharynx, food enters the esophagus.

Esophagus- a tube about 25 cm long, which is a direct continuation of the pharynx. In the esophagus, no changes in food occur, since digestive juices are not secreted in it. It serves to carry food into the stomach. The promotion of the food bolus along the pharynx and esophagus occurs as a result of the contraction of the muscles of these departments.

Digestion in the stomach

Stomach- the most expanded section of the digestive tube with a capacity of up to three liters. The size and shape of the stomach changes depending on the amount of food taken and the degree of contraction of its walls. In places where the esophagus enters the stomach and the transition of the stomach into the small intestine, there are sphincters (compressors) that regulate the movement of food.

The mucous membrane of the stomach forms longitudinal folds and contains a large number of glands (up to 30 million). The glands consist of three types of cells: main (producing enzymes of gastric juice), parietal (secreting hydrochloric acid) and additional (secreting mucus).

By contracting the walls of the stomach, food is mixed with juice, which contributes to its better digestion. Several enzymes are involved in the digestion of food in the stomach. The main one is pepsin. It breaks down complex proteins into simpler ones, which are further processed in the intestines. Pepsin acts only in an acidic environment, which is created by hydrochloric acid in gastric juice. A large role is given to hydrochloric acid in the disinfection of the contents of the stomach. Other enzymes of gastric juice (chymosin and lipase) are able to digest milk proteins and fats. Chymosin curdles milk, so it stays longer in the stomach and is digested. Lipase, present in small amounts in the stomach, breaks down only emulsified milk fat. The action of this enzyme in the stomach of an adult is weakly expressed. There are no enzymes that act on carbohydrates in the composition of gastric juice. however, a significant portion of the starch in the food continues to be digested in the stomach by salivary amylase. The mucus secreted by the glands of the stomach plays an important role in protecting the mucous membrane from mechanical and chemical damage, from the digestive action of pepsin. The glands of the stomach secrete juice only during digestion. At the same time, the nature of juice secretion depends on the chemical composition of the food consumed. After 3-4 hours of processing in the stomach, food slurry in small portions enters the small intestine.

Small intestine

Small intestine is the longest part of the digestive tube, reaching 6-7 meters in an adult. It consists of the duodenum, jejunum and ileum.

In the initial section of the small intestine - the duodenum - the excretory ducts of two large digestive glands - the pancreas and the liver - open. Here the most intensive digestion of food slurry takes place, which is exposed to the action of three digestive juices: pancreatic, bile and intestinal.

Pancreas located behind the stomach. It distinguishes the top, body and tail. The top of the gland is surrounded by a horseshoe-shaped duodenum, and the tail is adjacent to the spleen.

The cells of the gland produce pancreatic juice (pancreatic). It contains enzymes that act on proteins, fats and carbohydrates. The enzyme trypsin breaks down proteins into amino acids, but is active only in the presence of an intestinal enzyme, enterokinase. Lipase breaks down fats into glycerol and fatty acids. Its activity increases sharply under the influence of bile produced in the liver and entering the duodenum. Under the influence of amylase and maltose of pancreatic juice, most carbohydrates in food are broken down to glucose. All pancreatic enzymes are active only in an alkaline environment.

In the small intestine, food slurry undergoes not only chemical, but also mechanical processing. Due to the pendulum movements of the intestine (alternate lengthening and shortening), it mixes with digestive juices and liquefies. Peristaltic bowel movements cause the contents to move towards the large intestine.

Liver- the largest digestive gland of our body (up to 1.5 kg). It lies under the diaphragm, occupying the right hypochondrium. The gallbladder is located on the lower surface of the liver. The liver is made up of glandular cells that form lobules. Between the lobules are layers of connective tissue, in which nerves, lymphatic and blood vessels and small bile ducts pass.

Bile, produced by the liver, plays an important role in the digestion process. It does not break down nutrients, but prepares fats for digestion and absorption. Under its action, fats break up into small drops suspended in a liquid, i.e. turn into an emulsion. In this form, they are easier to digest. In addition, bile actively affects the absorption processes in the small intestine, enhances intestinal motility and the separation of pancreatic juice. Despite the fact that bile is produced continuously in the liver, it enters the intestines only when eating. Between periods of digestion, bile is collected in the gallbladder. Venous blood flows from the entire alimentary canal, pancreas and spleen through the portal vein to the liver. Poisonous substances that enter the bloodstream from the gastrointestinal tract are neutralized here and then excreted in the urine. Thus, the liver performs its protective (barrier) function. The liver is involved in the synthesis of a number of important substances for the body, such as glycogen, vitamin A, affects the process of hematopoiesis, the metabolism of proteins, fats, carbohydrates.

Absorption of nutrients

In order for the amino acids, simple sugars, fatty acids and glycerol formed as a result of the breakdown to be used by the body, they must be absorbed. In the oral cavity and esophagus, these substances are practically not absorbed. Small amounts of water, glucose and salts are absorbed in the stomach; in the large intestine - water and some salts. The main processes of nutrient absorption occur in the small intestine, which is well adapted for this function. In the process of absorption, the mucous membrane of the small intestine plays an active role. It has a large number of villi and microvilli, which increase the absorptive surface of the intestine. In the walls of the villi there are smooth muscle fibers, and inside them there are blood and lymphatic vessels.

The villi are involved in the absorption of nutrients. By contracting, they contribute to the outflow of blood and lymph, saturated with nutrients. When the villi relax, fluid from the intestinal cavity again enters their vessels. The breakdown products of proteins and carbohydrates are absorbed directly into the blood, and the bulk of the digested fats into the lymph.

Colon

Colon has a length of up to 1.5 meters. Its diameter is 2–3 times larger than the thin one. It gets undigested food residues, mainly vegetable, the fiber of which is not destroyed by the enzymes of the digestive tract. There are a lot of different bacteria in the large intestine, some of which play an important role in the body. Cellulosobacteria break down fiber and thereby improve the absorption of plant foods. There are bacteria that synthesize vitamin K, which is necessary for the normal functioning of the blood coagulation system. Thanks to this, a person does not need to take vitamin K from the external environment. In addition to the bacterial breakdown of fiber in the large intestine, a large amount of water is absorbed, which came there along with liquid food and digestive juices, completes with the absorption of nutrients and stool is formed. The latter pass into the rectum, and from there they are brought out through the anus. The opening and closing of the anal sphincter occurs reflexively. This reflex is under the control of the cerebral cortex and can be arbitrarily delayed for some time.

The whole process of digestion with animal and mixed food in humans lasts about 1–2 days, of which more than half of the time is spent on the movement of food through the large intestine. Feces accumulate in the rectum, as a result of irritation of the sensory nerves of its mucous membrane, defecation occurs (emptying of the large intestine).

The process of digestion is a series of stages, each of which takes place in a certain section of the digestive tract under the influence of certain digestive juices secreted by the digestive glands and acting on certain nutrients.

Oral cavity- the beginning of the breakdown of carbohydrates under the action of saliva enzymes produced by the salivary glands.

Stomach- the breakdown of proteins and fats under the action of gastric juice, the continuation of the breakdown of carbohydrates inside the food bolus under the action of saliva.

Small intestine- completion of the breakdown of proteins, polypeptides, fats and carbohydrates under the action of enzymes of pancreatic and intestinal juices and bile. As a result of biochemical processes, complex organic substances are converted into low-molecular substances, which, being absorbed into the blood and lymph, become a source of energy and plastic materials for the body.

Digestion of food is a rather complex process, which boils down to the breakdown of large molecules of proteins, fats and carbons into monomers that are easily absorbed by the cells of the body. In different parts of the digestive tract, various compounds break down, which are then absorbed by the mucous membrane of the small intestine and are carried throughout the body. Digestion begins in the mouth.

Before considering how digestion occurs in, it is necessary to at least briefly familiarize yourself with its structure.

The structure of the oral cavity

In anatomy, it is customary to divide into two departments:

• The vestibule of the mouth (the space between the lips and teeth);
• The oral cavity itself (limited by the teeth, the bony palate and the diaphragm of the mouth);

Each element of the oral cavity has its own function and is responsible for a specific food processing process.

The teeth are responsible for the mechanical processing of solid foods. With the help of fangs and incisors, a person bites off food, then crushes it with small ones. The function of large molars is to grind food.

The tongue is a large muscular organ that attaches to the floor of the mouth. The tongue is involved not only in the processing of food, but also in the processes of speech. Moving, this muscular organ mixes the crushed food with saliva and forms a food bolus. In addition, it is in the tissues of the tongue that taste, temperature, pain and mechanical receptors are located.

The salivary glands are parotid, sublingual and enter the oral cavity with the help of a duct. Their main function is the production and excretion of saliva, which is of great importance for the digestive process. The functions of saliva are as follows:

• Digestive (saliva contains enzymes that break down carbons);
• Protective (saliva contains lysozyme, which has strong bactericidal properties. In addition, saliva contains immunoglobulins and blood clotting factors. Saliva protects the oral cavity from drying out);
• Excretory (substances such as urea, salts, alcohol, some medicinal substances are excreted with saliva);

Digestion in the oral cavity: mechanical phase

A wide variety of food can enter the oral cavity and, depending on its consistency, it either immediately passes into the esophagus during the act of swallowing (drinks, liquid food), or undergoes mechanical processing, which facilitates further digestion processes.

As already mentioned, with the help of teeth, food is crushed. The movements of the tongue are needed in order to mix the chewed foods with saliva. Under the influence of saliva, food softens and is enveloped in mucus. Mucin, which is contained in saliva, takes part in the formation of a food bolus, which subsequently passes into the esophagus.

Digestion in the oral cavity: enzymatic phase

It also includes some enzymes that are involved in the breakdown of polymers. In the oral cavity, the breakdown of carbons occurs, which continues already in the small intestine.

Saliva contains an enzyme complex called ptyalin. Under their influence, the breakdown of polysaccharides to disaccharides (mainly maltose) occurs. In the future, maltose, under the influence of another enzyme, is broken down to glucose monosaccharide.

The longer the food is in the oral cavity and lends itself to enzymatic action, the easier it is to be digested in all other parts of the herbal tract. This is why doctors always recommend chewing food as long as possible.

This completes digestion in the oral cavity. The food bolus passes further and, falling on the root of the tongue, starts the reflex process of swallowing, in which food passes into the esophagus and then enters the stomach.

To summarize, processes such as grinding food, analyzing its taste, wetting with saliva, mixing and primary decomposition of carbohydrates take place in the oral cavity.

Digestion in the oral cavity is the first link in a complex chain of processes of enzymatic breakdown of nutrients to monomers. Digestive functions of the oral cavity include approbation of food for edibility, mechanical processing of food and its partial chemical processing.

In the oral cavity, food is crushed and exposed to saliva, which is produced by three pairs of salivary glands. Human saliva contains a bicarbonate buffer and has a slightly alkaline reaction inherent in all herbivores, in contrast to predators, which have an acidic saliva reaction.

Grinding, wetting and partial digestion of food in the mouth is of great importance for further digestion. Almost all nutritionists recommend chewing your food thoroughly. Well-processed food in the mouth is more efficiently digested in the subsequent stages of digestion.

The saliva in the oral cavity is mixed. Its pH is 6.8-7.4. In an adult, 0.5-2 liters of saliva is formed per day. It consists of 99% water and 1% solids. The dry residue is represented by organic and inorganic substances. Among inorganic substances - anions of chlorides, bicarbonates, sulfates, phosphates; cations of sodium, potassium, calcium, magnesium, as well as trace elements: iron, copper, nickel, etc. The organic substances of saliva are represented mainly by proteins. The protein mucous substance mucin sticks together individual food particles and forms a food lump. The main enzymes of saliva are amylase and maltase, which act only in a slightly alkaline environment. Amylase breaks down polysaccharides (starch, glycogen) to maltose (disaccharide). Maltase acts on maltose and breaks it down to glucose. Small amounts of other enzymes were also found in saliva: hydrolases, oxidoreductases, transferases, proteases, peptidases, acid and alkaline phosphatases. Saliva contains the protein substance lysozyme (muramidase), which has a bactericidal effect.

Food stays in the mouth for only about 15 seconds, so there is no complete breakdown of starch. But digestion in the oral cavity is very important, as it is the trigger for the functioning of the gastrointestinal tract and the further breakdown of food. http://www.medicinform.net/human/fisiology1_4.htm

The phenomenon of starch breakdown in the initial section of the digestive system is interesting from the point of view of expediency. The breakdown of starch in the stomach gradually stops and resumes in the duodenum. Since most of the enzymatic breakdown of food occurs in the stomach and intestines, it is highly likely that the enzymatic breakdown of starch in the oral cavity is important in determining edible versus inedible.

Reception of taste sensations takes place in the oral cavity. Glucose, like many carbohydrates, has a sweet taste. Proteins and fats in their pure form have no taste for humans (for example, egg white or refined vegetable oil). As a rule, sweet food is edible for humans, while bitter and sour food is inedible. At present, for one reason or another, a person ignores many natural physiological mechanisms, including, probably, the mechanism for determining “edible-inedible”. Based on this mechanism, many currently used food products should be recognized as inedible for humans. Although there is another point of view. For example, in China they say that all four tastes must be present in human food - bitter, sweet, sour and salty. 3

After the food bolus has formed, swallowing occurs. This is a reflex process in which three phases are distinguished:

Oral (voluntary and involuntary);

Pharyngeal (fast involuntary);

Esophageal (slow involuntary).

The swallowing cycle lasts about 1 s. With coordinated contractions of the muscles of the tongue and cheeks, the food bolus moves to the root of the tongue, which leads to irritation of the receptors of the soft palate, the root of the tongue and the posterior pharyngeal wall. Excitation from these receptors through the glossopharyngeal nerves enters the swallowing center located in the medulla oblongata, from which impulses go to the muscles of the oral cavity, larynx, pharynx and esophagus as part of the trigeminal, hypoglossal, glossopharyngeal and vagus nerves. The contraction of the muscles that lift the soft palate closes the entrance to the nasal cavity, and the elevation of the larynx closes the entrance to the respiratory tract. During the act of swallowing, contractions of the esophagus occur, which have the character of a wave that occurs in the upper part and spreads towards the stomach. The motility of the esophagus is mainly regulated by the fibers of the vagus and sympathetic nerves and the nerve formations of the esophagus.

The swallowing center is located next to the respiratory center of the medulla oblongata and interacts with it (when swallowing, the breath is held). From the pharynx, the food bolus enters the esophagus, and then into the stomach. four

Lesson topic: Digestion in the mouth. swallowing.

Lesson motto:"Who chews well, he lives long."

Tasks:

• Educational:
  • to form in students new anatomical and physiological concepts about nutrients, digestion, the structure and functions of the digestive organs, enzymes, digestive glands, absorption, and hygienic conditions for normal digestion.
  • develop the ability to experiment, work with a book, substantiate the rules of digestive hygiene.
• Educational:
  • for physical and hygienic education, explain the hygienic conditions of normal nutrition, prove the harm of smoking and drinking alcohol, the dependence of human health and performance on the prevention and treatment of gastrointestinal diseases.
• Educational:
  • using active, problem-search methods of teaching, questions for reflection and independent work with a textbook, to develop creative thinking, speech, and cognitive abilities of students.

Equipment: tab. "Scheme of the structure of the digestive organs", "Unconditioned salivary reflex", tab. "Conditioned reflex salivation".

Laboratory equipment for demonstration of experience: 2 pieces of starched gauze, matches, cotton wool, a Petri dish (or a regular saucer) with iodine and a glass of clean water.

The main content of the lesson:

1. Digestion in the oral cavity:
- the role of teeth in the mechanical processing of food;
- salivary glands and their functions (general characteristics)
2. Hygienic rules for the care of teeth and oral cavity.
3. Chemical processing of food in the oral cavity. Enzymes of saliva and the specifics of their action (laboratory work).
4. Reflex regulation of salivation (scheme of unconditioned salivary reflex; examples of conditioned reflex salivation).
5. Swallowing.

The main stages of the lesson:

1. Mobilizing and activating the beginning of the lesson. Creating a problematic situation by posing the question “What is health? Why do people say hello?
2. Frontal search conversation to resolve a problematic issue.
3. Knowledge update. Checking knowledge on the previous topic.
4. Explanation of the main material. Teacher's story, frontal filling of the table. Notes in a notebook.
5. Partial reinforcement.
6. Laboratory work. Heuristic (partial search method). Explanation of the purpose of the saliva experiment (expected result not reported).
7. A brief briefing on how the experiment is performed and what to do at the same time.
8. Organization of independent work, study of the results of experience, design of notebooks (short report and conclusion).
9. Generalization and consolidation.
10. Operational diagnostics of the quality of training using “are the statements true”.
11. Concluding the lesson with an appeal to the motto: "He who chews well, he lives long."

DURING THE CLASSES

1. Updating knowledge

A. What is health? Why are they saying hello? (Conversation with students)
B. What is the importance of digestion?
Student's answer: "For chemical and mechanical processing of food"

Today the purpose of our lesson:

1) reveal the importance of mechanical and chemical processing of food in the oral cavity;
2) get acquainted with enzymes that break down salivary substances into simpler ones in the oral cavity.

You have to find out how and what happens to food in the oral cavity, to investigate the effect of enzymes on starch.

2. Survey

1. Work at the blackboard.

Bring in line.

Writing on the blackboard: meat, fish, milk, bread, vermicelli, fats, carbohydrates, vegetables, fruits.

2. Collect the digestive tract on a magnetic board (fig. in the textbook).

3. Write the sequence of the digestive tract.

Student record.

Mouth--> pharynx--> esophagus--> stomach--> small intestine--> large intestine--> rectum--> anus.

Parallel work with the class

Repetition of basic biological concepts (along the chain) term - definition.

Products, nutrition, digestion, enzymes, organ, tissue, organism, cell, esophagus, nutrients, anatomy, biology, hygiene, physiology.

The guys have finished their work at the blackboard - they voice their answers.
Summarizes the repetition of homework and the transition to a new topic.
Issues for discussion.
What path must the product take in order to be absorbed by the body and reach each cell?
What nutrients are included in food?
Proteins, fats, carbohydrates (student answer).
Where does the breakdown of these substances take place? (students answer).
What substances are these substances broken down into?
Proteins are amino acids
Fats - glycerin
Carbohydrates are starch.

Teacher: Today it is necessary to consider the breakdown of carbohydrates.

3. New theme

Writing in the notebook of the topic of the lesson.

Explanation of the material.

Issues for discussion.

• Why does the sight of a cut lemon cause salivation?
• Why is it not recommended to talk while eating?

(Answers vary).

The teacher works at the blackboard, the students write in notebooks.
What happens in the oral cavity?

Filling in the table:

4. Fixing

1. What happens in the oral cavity?

• Approbation of food (38 - 52 C).
• Mechanical processing of food.
• Wetting with saliva.
• Disinfection.
• Chemical processing of food.
• Formation of a food bolus.
• Ingestion.

2. Laboratory work.

"The action of saliva on starch" using a tubeless test with saliva.
Before the lesson, students are given two pieces of starched gauze, matches, cotton wool, a glass of clean water on their desks.
Students briefly talk about digestive enzymes, the breakdown of starch in the mouth, and swallowing.
As a result of this conversation, students should repeat the general properties of enzymes:
1) Enzymes are catalysts and therefore can speed up certain processes.
2) Enzymes act only on certain substrates.
3) Enzymes are able to act only under certain temperature conditions and in a certain environment: acidic, alkaline, neutral.

4) Enzymes - proteins, when boiled, they are destroyed and lose their enzymatic properties.

Properties of digestive enzymes:

1) Salivary enzymes act on salivary carbohydrates, they convert starch into glucose. Starch is insoluble, it cannot be absorbed into the blood, but glucose is absorbed.

2) Saliva enzymes act on starch. They break down these substances into products that can be absorbed into the blood and lymph.

Exercise. Prove that saliva enzymes are capable of decomposing starch.

The results of the experiment in a notebook.

Conclusion(make notes).

3. Are the statements true:

1) In the oral cavity, only mechanical processing of food occurs. (-)
2) Saliva is released into the oral cavity only during meals. (-)
3) Saliva enzymes break down starch into glucose. (+)
4) Saliva is produced by three pairs of salivary glands. (+)
5) Enzymes slow down the digestion process. (-)
6) The breakdown of carbohydrates begins in the oral cavity. (+)
7) The epiglottis prevents food from entering the respiratory tract. (+)
8) The salivary glands produce enzymes that break down carbohydrates. (+)
9) Lysozyme corrodes enamel. (-)
10) Each jaw has 4 incisors. (+)

5. Summary of the lesson

6. Homework