Digestion in the mouth. The human digestive system How carbohydrates are fermented in the oral cavity

The oral cavity includes the vestibule and the mouth itself. The vestibule is formed by the lips, the outer side of the cheeks, teeth and gums. The lips are covered on the outside with a thin layer of epithelium, from the inside they are lined with a mucous membrane, which is a continuation of the inner side of the cheeks. Tightly cover the teeth, attached to the gums with the help of the upper and lower bridles.

The mouth is formed by:

buccal mucosa;
incisors, canines, large and small molars;
gums;
language;
soft and hard palate.

Rice. 1. The structure of the oral cavity.

More details about the structure of the oral cavity are presented in the table.

*Oral cavity*	*Structure*	*Functions*
	The outer side is covered with skin epithelium, the inner side is covered with a mucous membrane. The intermediate layer is made up of muscle fibers penetrated by blood vessels and nerves.	They open and close the oral fissure, participate in the formation of the food bolus
	Muscular (striated muscles) organ penetrated by nerve fibers and blood vessels. From above it is covered with a mucous membrane, on the surface of which there are sensitive papillae containing receptors. Retained in the mouth with a bridle	Evaluates the quality and physical parameters of food, forms and promotes the food bolus
	Hard - a bone covered with a mucous membrane, soft - a mucous fold lying behind the hard palate	Helps form a food bolus and move it down the throat
	They consist of dentin covered with enamel. Inside the dentin is a cavity filled with pulp - loose connective tissue. Channels leave the cavity through which blood vessels and nerve fibers enter the tooth.	Mechanical grinding of food. The incisors and fangs grab and hold food, the molars grind
	Processes of jaws covered with mucous membrane	Hold teeth and lips

Rice. 2. The internal structure of the tooth.

Functions

The main functions of the oral cavity in the process of digestion:

Digestion

Briefly describe how digestion occurs in the oral cavity, as follows:

the food piece enters the cavity through the incisors;
due to the chewing muscles that hold the jaw, the process of chewing begins;
molars grind food, which is abundantly moistened with saliva;
cheeks, tongue and hard palate roll up a food lump;
The soft palate and tongue push the prepared food down the throat.

Food entering the oral cavity irritates receptors for various purposes (temperature, tactile, olfactory), which respond with the production of saliva, gastric juice, bile.

What have we learned?

The oral cavity is of great importance in the process of digestion. Through the cheeks, teeth, tongue, incoming food is crushed and moves to the pharynx. Food moistened with saliva softens and sticks together into a single food lump. Enzymes in saliva begin digestion by breaking down starch and other sugars.

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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.

Motor function in the oral cavity begins with the act of chewing. Chewing is a physiological act that ensures the grinding of nutrients, wetting them with saliva and the formation of a food bolus. Chewing ensures the quality of mechanical processing of food in the oral cavity. It affects the process of digestion in other parts of the digestive tract, changing their secretory and motor functions.

One of the methods for studying the functional state of the chewing apparatus is masticography - recording the movements of the lower jaw during chewing. On the record, which is called a masticogram, a chewing period can be distinguished, consisting of 5 phases (Fig. 31).

* 1 phase - rest phase;

* Phase 2 - the introduction of food into the oral cavity (the first ascending knee of the record, which starts from the line of rest);

* Phase 3 - approximate chewing or initial chewing function, it corresponds to the process of approbation of the mechanical properties of food and its initial crushing;

* Phase 4 - the main or true phase of chewing, it is characterized by the correct alternation of chewing waves, the amplitude and duration of which is determined by the size of the food portion and its consistency;

* Phase 5 - the formation of a food bolus has the form of a wavy curve with a gradual decrease in the amplitude of the waves.

The nature of the masticogram depends mainly on the mechanical properties of the food and its volume. Changes in the masticogram also occur when the integrity of the dentition is violated, with diseases of the teeth and periodontium, with diseases of the oral mucosa, etc.

Chewing is a self-regulatory process based on the functional chewing system. A useful adaptive result of this functional system is a food bolus formed during chewing and prepared for swallowing. The functional chewing system is formed for each chewing period.

When food enters the oral cavity, irritation of the mucosal receptors occurs in the same sequence: mechano-, thermo- and chemoreceptors. Excitation from these receptors through the sensory fibers of the lingual (a branch of the trigeminal nerve), glossopharyngeal, tympanic string (a branch of the facial nerve) and the upper laryngeal nerve (a branch of the vagus nerve) enters the sensory nuclei of these nerves of the medulla oblongata (the nucleus of the salitary tract and the nucleus of the trigeminal nerve). Further, the excitation along a specific path reaches the specific nuclei of the visual hillocks, where the excitation switches, after which it enters the cortical section of the oral analyzer. Here, based on the analysis and synthesis of incoming afferent excitations, a decision is made about the edibility of substances that have entered the oral cavity. Inedible food is rejected (spit out), which is one of the important protective functions of the oral cavity. Edible food remains in the mouth and chewing continues. In this case, excitation from the mechanoreceptors of the periodontium, the supporting apparatus of the tooth, joins the flow of afferent impulses.

Collaterals depart from the afferent pathways at the level of the brain stem to the nuclei of the reticular formation, which is part of the extrapyramidal system and provides an efferent function. From the motor nuclei of the reticular formation of the brain stem (which are the motor nuclei of the trigeminal, hypoglossal and facial nerves) in a downward direction as part of the efferent fibers of the trigeminal, hypoglossal and facial nerves, impulses go to the muscles that provide chewing: actually chewing, mimic and muscles of the tongue. Voluntary contraction of the masticatory muscles is provided by the participation of the cerebral cortex.

51. In the act of chewing and the formation of a food bolus, saliva takes an obligatory part. Saliva is a mixture of the secrets of three pairs of large salivary glands and many small glands located in the oral mucosa. Epithelial cells, food particles, mucus, salivary bodies (neutrophilic leukocytes, sometimes lymphocytes), and microorganisms are mixed with the secretion secreted from the excretory streams of the salivary glands. Such saliva, mixed with various inclusions, is called oral fluid. The composition of the oral fluid varies depending on the nature of the food, the state of the body, and also under the influence of environmental factors.

The secret of the salivary glands contains about 99% water and 1% dry residue, which includes anions of chlorides, phosphates, sulfates, bicarbonates, iodites, bromides, fluorides. Saliva contains sodium, potassium, magnesium, calcium cations, as well as trace elements (iron, copper, nickel, etc.). Organic matter is represented mainly by proteins. In saliva there are proteins of various origins, including the protein mucous substance - mucin. Saliva contains nitrogen-containing components: urea, ammonia, creatinine, etc.

Functions of saliva.

1. digestive function saliva is expressed in the fact that it wets the food lump and prepares it for digestion and swallowing, and saliva mucin glues a portion of food into an independent lump. More than 50 enzymes were found in saliva, which belong to hydrolases, oxidoreductases, transferases, lipases, isomerases. Small amounts of proteases, peptidases, acid and alkaline phosphatases were found in saliva. Saliva contains the enzyme kallikrein, which is involved in the formation of kinins, which dilate blood vessels.

Despite the fact that food is in the oral cavity for a short time - about 15 s, digestion in the oral cavity is of great importance for the implementation of further food splitting processes, since saliva, by dissolving food substances, contributes to the formation of taste sensations and affects appetite. In the oral cavity, under the influence of saliva enzymes, the chemical processing of food begins. The saliva enzyme amylase breaks down polysaccharides (starch, glycogen) to maltose, and the second enzyme, maltase, breaks down maltose to glucose.

2. Protective function, saliva is expressed as follows:

* saliva protects the oral mucosa from drying out, which is especially important for a person who uses speech as a means of communication;

* the protein substance of saliva mucin is able to neutralize acids and alkalis;

* saliva contains an enzyme-like protein substance lysozyme (muramidase), which has a bacteriostatic effect and takes part in the processes of regeneration of the epithelium of the oral mucosa;

* nuclease enzymes contained in saliva are involved in the degradation of nucleic acids of viruses and thus protect the body from viral infection;

* blood clotting factors were found in saliva, the activity of which determines local hemostasis, processes of inflammation and regeneration of the oral mucosa;

* a substance stabilizing fibrin was found in saliva (similar to factor XIII in blood plasma);

* Substances that prevent blood clotting (antithrombin plates and antithrombins) and substances with fibrinolytic activity (plasminogen, etc.) were found in saliva;

* saliva contains a large amount of immunoglobulins, which protects the body from pathogenic microflora.

3. Trophic function of saliva. Saliva is a biological medium that is in contact with tooth enamel and is its main source of calcium, phosphorus, zinc and other trace elements.

4. excretory function saliva. As part of saliva, metabolic products can be released - urea, uric acid, some medicinal substances, as well as salts of lead, mercury, etc.

Salivation is carried out by a reflex mechanism. There are conditioned reflex and unconditioned reflex salivation.

Conditioned salivation is caused by the sight, smell of food, sound stimuli associated with cooking, as well as talking and remembering food. At the same time, visual, auditory, olfactory receptors are excited. Nerve impulses from them enter the cortical section of the corresponding analyzer, and then to the cortical representation of the center of salivation. From it, excitation goes to the bulbar department of the salivation center, the efferent commands of which go to the salivary glands.

Unconditional reflex salivation occurs when food enters the oral cavity. Food irritates the mucosal receptors. The afferent pathway of the secretory and motor components of the chewing act is common. Nerve impulses through afferent pathways enter the center of salivation, which is located in the reticular formation of the medulla oblongata and consists of the upper and lower salivary nuclei (Fig. 32).

The efferent path of salivation is represented by fibers of the parasympathetic and sympathetic divisions of the autonomic nervous system. Parasympathetic innervation of the salivary glands is carried out by vegetative fibers of the cells of the salivary nuclei, passing as part of the glossopharyngeal and facial nerves.

From the upper salivary nucleus, excitation is directed to the submandibular and sublingual glands. Preganglionic fibers go as part of the tympanic string to the submandibular and sublingual autonomic ganglia. Here, excitation switches to postganglionic fibers, which go as part of the lingual nerve to the submandibular and sublingual salivary glands.

From the lower salivary nucleus, excitation is transmitted along the preganglionic fibers as part of the small stony nerve to the ear ganglion, here the excitation switches to postganglionic fibers, which, as part of the ear-temporal nerve, approach the parotid salivary gland.

The sympathetic innervation of the salivary glands is carried out by sympathetic nerve fibers that start from the cells of the lateral horns of the spinal cord at the level of 2-6 thoracic segments. Switching of excitation from prena to the postganglionic fibers takes place in the superior cervical sympathetic ganglion, from which the postganglionic fibers reach the salivary glands along the course of the blood vessels.

Irritation of the parasympathetic fibers that innervate the salivary glands leads to the separation of a large amount of liquid saliva, which contains many salts and few organic substances. Irritation of sympathetic fibers causes the separation of a small amount of thick, viscous saliva, which contains few salts and many organic substances.

Of great importance in the regulation of salivation are humoral factors, which include hormones of the pituitary, adrenal, thyroid and pancreas, as well as metabolic products.

The separation of saliva occurs in strict accordance with the quality and quantity of nutrients taken. For example, when taking water, saliva almost does not separate. When harmful substances enter the oral cavity, a large amount of liquid saliva is separated, which washes the oral cavity from these harmful substances, etc. Such an adaptive nature of salivation is provided by the central mechanisms for regulating the activity of the salivary glands, and these mechanisms are triggered by information coming from the receptors of the oral cavity .

52. Swallowing. 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 arbitrary).

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 pharyngeal nerves enters the swallowing center located in the medulla oblongata, from which efferent 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. Esophageal motility is regulated mainly by efferent fibers of the vagus and sympathetic nerves and intramural nerve formations of the esophagus.

The swallowing center is located next to the respiratory center of the medulla oblongata and is in reciprocal relations with it (when swallowing, the breath is held).

For many people, food is one of the few pleasures in life. Food, indeed, should be a pleasure, but ... the physiological meaning of nutrition is much broader. Few people think about how amazingly the food from our plate is converted into energy and building material, so necessary for the constant renewal of the body.

Our food is represented by different products, which consist of proteins, carbohydrates, fats and water. Ultimately, everything that we eat and drink is broken down in our body into universal, smallest components under the action of digestive juices (up to 10 liters are excreted in a person per day).

The physiology of digestion is a very complex, energy-consuming, remarkably organized process, consisting of several stages of processing food passing through the digestive tract. It can be compared to a well-regulated assembly line, on the coordinated work of which our health depends. And the occurrence of "failures" leads to the formation of many forms of diseases.

Knowledge is a great power that helps to prevent any violations. Knowing how our digestive system works should help us not only enjoy food, but also prevent many diseases.

I will guide you on an exciting sightseeing tour that I hope will be of use to you.

So, our diverse food of plant and animal origin goes a long way before (after 30 hours) the end products of its breakdown enter the blood and lymph, and are integrated into the body. The process of digestion of food is provided by unique chemical reactions and consists of several stages. Let's consider them in more detail.

Digestion in the mouth

The first stage of digestion begins in the mouth, where food is crushed/chewed and processed with a secretion called saliva. (Up to 1.5 liters of saliva is produced daily.) In fact, the process of digestion begins even before food touches our lips, since the very thought of food already fills our mouth with saliva.

Saliva is a secret secreted by three paired salivary glands. It is 99% water and contains enzymes, of which the most significant is alpha-amylase, which is involved in the hydrolysis / breakdown of carbohydrates. That is, of all food components (proteins, fats and carbohydrates), only carbohydrates begin to hydrolyze in the oral cavity! Saliva enzymes do not act on fats or proteins. For the process of splitting carbohydrates, an alkaline environment is necessary!

The composition of saliva also includes: lysozyme, which has bactericidal properties and serves as a local factor in protecting the mucous membranes of the oral cavity; and mucin, a mucus-like substance that forms a smooth, chewable food bolus that is easy to swallow and transport through the esophagus to the stomach.

Why is it important to chew food well? Firstly, in order to crush it well and moisten it with saliva, and start the digestion process. Secondly, in oriental medicine, teeth are associated with energy channels (meridians) passing through them. Chewing activates the movement of energy through the channels. The destruction of certain teeth indicates problems in the relevant organs and systems of the body.

We do not think about the saliva in the mouth and do not notice its absence. Often we walk for a long time with a feeling of dry mouth. And saliva contains many chemicals necessary for good digestion and preservation of the oral mucosa. Its secretion depends on pleasant, familiar smells and tastes. Saliva provides a sense of taste of food. Molecules split in saliva reach 10,000 taste buds on the tongue, capable of detecting and highlighting sweet, sour, bitter, spicy and salty tastes even in new foods. This allows you to perceive food as a pleasure, enjoyment of tastes. Without moisture, we have no taste. If the tongue is dry, then we do not feel that we are eating. Without saliva, we cannot swallow.

Therefore, it is so important for healthy digestion to eat in a relaxed atmosphere, not on the run, in beautiful dishes, deliciously cooked. It is important, without rushing and not being distracted by reading, talking and watching TV, to slowly chew food, enjoying a variety of taste sensations. It is important to eat at the same time, as this contributes to secretory regulation. It is important to drink enough plain water, at least 30 minutes before meals and one hour after meals. Water is necessary for the formation of saliva and other digestive juices, the activation of enzymes.

It is difficult to maintain an alkaline balance in the oral cavity if a person constantly eats something, especially sweet, which always leads to acidification of the environment. After eating, it is recommended to rinse the mouth and / or chew on something bitter in taste, such as cardamom seeds or parsley.

And I also want to add about hygiene, cleaning teeth and gums. In many nations, it was, and still is, a tradition to brush your teeth with twigs and roots, which often have a bitter, bitter-astringent taste. And tooth powders also taste bitter. Bitter and astringent tastes are cleansing, bactericidal, and increase salivation. While the sweet taste, on the contrary, promotes the growth of bacteria and congestion. But manufacturers of modern toothpastes (especially sweet ones for children) simply add antimicrobial agents and preservatives, and we turn a blind eye to this. In our area, coniferous taste is bitter, tart / astringent. If children are not accustomed to the sweet taste, they normally perceive unsweetened toothpaste.

Let's get back to digestion. As soon as food enters the mouth, preparation for digestion begins in the stomach: hydrochloric acid is released and gastric juice enzymes are activated.

Digestion in the stomach

Food does not stay long in the mouth, and after it has been crushed by teeth and processed by saliva, it enters through the esophagus into the stomach. Here it can stay up to 6-8 hours (especially meat), being digested under the influence of gastric juices. The volume of the stomach is normally about 300 ml (with a “fist”), however, after a hearty meal or frequent overeating, especially at night, its size can increase many times over.

What is gastric juice made of? First of all, from hydrochloric acid, which begins to be produced as soon as something is in the oral cavity (this is important to keep in mind), and creates an acidic environment necessary for the activation of gastric proteolytic (protein-splitting) enzymes. The acid corrodes tissue. The mucous membrane of the stomach constantly produces a layer of mucus that protects against the action of acid and from mechanical damage by coarse food components (when the food is not chewed enough and treated with saliva, when they snack on dry food on the go, simply by swallowing). The formation of mucus, lubrication also depends on whether we drink plain water in sufficient quantities. During the day, about 2-2.5 liters of gastric juice is secreted, depending on the quantity and quality of food. During a meal, gastric juice is secreted in the maximum amount and differs in acidity and the composition of enzymes.

Hydrochloric acid in its pure form is a powerful aggressive factor, but without it, the process of digestion in the stomach will not occur. The acid promotes the transition of the inactive form of the enzyme of gastric juice (pepsinogen) into the active form (pepsin), and also denatures (destroys) proteins, which facilitates their enzymatic processing.

So, proteolytic (protein-splitting) enzymes mainly act in the stomach. This is a group of enzymes that are active in various ph-environments of the stomach (at the beginning of the digestion stage, the environment is very acidic, at the exit from the stomach it is the least acidic). As a result of hydrolysis, a complex protein molecule is divided into simpler components - polypeptides (molecules consisting of several amino acid chains) and oligopeptides (a chain of several amino acids). Let me remind you that the end product of protein breakdown is an amino acid - a molecule capable of being absorbed into the blood. This process takes place in the small intestine, and in the stomach, the preparatory stage of protein breakdown takes place.

In addition to proteolytic enzymes, there is an enzyme in the gastric secretion - lipase, which takes part in the breakdown of fats. Lipase only works with emulsified fats found in dairy products and is active during childhood. (Don't look for the correct/emulsified fats in milk, they are also found in ghee, which no longer contains protein).

Carbohydrates in the stomach are not digested and processed, because. the corresponding enzymes are active in an alkaline environment!

What else is interesting to know? Only in the stomach, due to the secret component (Castle factor), does the transition of the inactive form of vitamin B12 that comes with food into the digestible form take place. The secretion of this factor may decrease or stop with inflammatory lesions of the stomach. Now we understand that it is not food fortified with vitamin B12 (meat, milk, eggs) that is important, but the condition of the stomach. It depends on: sufficient mucus production (this process is affected by increased acidity due to excessive consumption of protein products, and even in combination with carbohydrates, which, when in the stomach for a long time, begin to ferment, which leads to acidification); from insufficient water consumption; from taking medications, both reducing acidity and drying up the mucous membranes of the stomach. This vicious circle can be broken with the right balance of food, water, and food intake.

The production of gastric juice is regulated by complex mechanisms, which I will not dwell on. I just want to remind you that we can observe one of them (an unconditioned reflex) when juices begin to stand out only from the thought of familiar tasty food, from smells, from the onset of the usual meal time. When something enters the oral cavity, the release of hydrochloric acid with maximum acidity immediately begins. Therefore, if after that food does not enter the stomach, the acid corrodes the mucous membrane, which leads to its irritation, to erosive changes, up to ulcerative processes. Don't similar processes occur when people chew gum or smoke on an empty stomach, when they take a sip of coffee or another drink and, in a hurry, run away? We don’t think about our actions until the “thunder breaks”, until it really hurts, because the acid is real ...

The composition of food affects the secretion of gastric juices:

fatty foods inhibit gastric secretion, as a result, food is retained in the stomach;
the more protein, the more acid: the use of proteins that are difficult to digest (meat and meat products) increases the secretion of hydrochloric acid;
carbohydrates in the stomach do not undergo hydrolysis, an alkaline environment is needed for their splitting; carbohydrates that stay in the stomach for a long time increase acidity due to the fermentation process (which is why it is important not to eat protein foods along with carbohydrates).

The result of our wrong attitude to nutrition is acid-base imbalance in the digestive tract and the appearance of diseases of the stomach and oral cavity. And here again it is important to understand that not means that reduce acidity or alkalize the body will help maintain health and healthy digestion, but a conscious attitude to what we are doing.

In the next article, we will look at what happens to food in the small and large intestines.