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

Properties and composition of saliva

In the mouth, the taste properties of food are analyzed, protection digestive tract from low-quality nutrients and exogenous microorganisms (saliva contains lysozyme, which has a bactericidal effect, and endonuclease, which has an antiviral effect), grinding, wetting food with saliva, initial hydrolysis of carbohydrates, formation food bolus, irritation of receptors with subsequent stimulation of the activity of not only the glands of the oral cavity, but also the digestive glands of the stomach, pancreas, liver, duodenum.

Salivary glands. In humans, saliva is produced by 3 pairs of large salivary glands: parotid, sublingual, submandibular, as well as many small glands (labial, buccal, lingual, etc.) scattered in the oral mucosa. Every day, 0.5 - 2 liters of saliva is formed, the pH of which is 5.25 - 8.0. Saliva begins to be secreted in response to stimulation of receptors oral cavity food, which is an unconditioned stimulus, as well as the sight, smell of food and the environment (conditioned stimuli). Signals from the taste, thermo- and mechanoreceptors of the oral cavity are transmitted to the center of salivation of the medulla oblongata, where the signals are switched to secretory neurons, the totality of which is located in the nucleus of the facial and glossopharyngeal nerves. As a result, a complex reflex reaction of salivation occurs.

Saliva- a viscous, opalescent, slightly cloudy liquid containing 98.5 - 99.5% water and 0.5 - 1.5% solids: potassium, sodium, calcium, magnesium, iron, chlorine, phosphate, sulfate, bicarbonate ions. Of the organic substances in saliva, proteins are contained (albumins, globulins, bactericidal substances and enzymes: b-amylase and maltase, which begin the breakdown of carbohydrates).

Chewing consists in grinding food, wetting it with saliva and forming a food bolus ( chyme). Further using swallowing food enters the stomach. Chewing and swallowing requires the coordinated work of many muscles, the contractions of which regulate and coordinate the chewing and swallowing centers located in the central nervous system. During swallowing, the entrance to the nasal cavity closes, but the upper and lower esophageal sphincters open, and food enters the stomach. Dense food passes through the esophagus in 3-9 seconds, liquid food in 1-2 seconds.

5.5. The structure and functions of the stomach. Composition and properties of gastric juice. Phases of gastric secretion

Food is retained in the stomach for an average of 4-6 hours for chemical and mechanical processing. In the stomach, 4 parts are distinguished: the entrance, or cardial part, the upper one - the bottom (or arch), the middle largest part - the body of the stomach and the lower, horizontally located - the pyloric part, or the pylorus (the pylorus opening leads to the duodenum)

The wall of the stomach consists of three layers: outer - serous, middle - muscular and inner - mucous. Contractions of the stomach muscles cause both undulating (peristaltic) and pendulum movements, due to which food is mixed and moves from the entrance to the exit of the stomach. The lining of the stomach contains numerous glands that produce gastric juice. From the stomach, chyme enters the intestines. At the site of the transition of the stomach into the intestines, there is a pyloric sphincter, which, when reduced, completely separates the stomach cavity from the duodenum. The mucous membrane of the stomach forms longitudinal, oblique and transverse folds, which straighten out when the stomach is full. Outside of the digestion phase, the stomach is in a collapsed state. After 45 - 90 minutes of the rest period, periodic contractions of the stomach occur, lasting 20 - 50 minutes (hungry peristalsis). The capacity of the stomach of an adult is from 1.5 to 4 liters.

Functions of the stomach:

1) deposition of food;

2) secretory - secretion of gastric juice for food processing;

3) motor - for moving and mixing food;

4) absorption of certain substances into the blood (water, alcohol);

5) excretory - the release into the cavity of the stomach along with gastric juice of some metabolites;

6) endocrine - the formation of hormones that regulate the activity of the digestive glands (for example, gastrin);

7) protective - bactericidal (most microbes die in the acidic environment of the stomach).

Composition and properties of gastric juice. Gastric juice is produced by the gastric glands, which are located in the fundus (arch) and body of the stomach. They contain 3 types of cells:

1) the main ones, which produce a complex of proteolytic enzymes (pepsinogen);

2) lining, which produce hydrochloric acid;

3) additional, in which mucus (mucin), gastromucoprotein (Castle's internal factor) and bicarbonates are produced.

At rest (“on an empty stomach”), approximately 20–50 ml of gastric juice, pH 5.0, can be extracted from the human stomach. The total amount of gastric juice secreted in a person during normal diet, equal to 1.5 - 2.5 liters per day. active gastric pH

juice is 0.8 - 1.5, because it contains approximately 0.5% HCl.

The role of HCl. It increases the release of pepsinogen by the chief cells, promotes the transfer of pepsinogen to pepsin, creates an optimal environment (pH) for the activity of proteases, which ensures increased protein breakdown, and contributes to the death of microbes.

Castle factor. Food contains vitamin B12, necessary for the formation of red blood cells, the so-called external factor Castle. But it can be absorbed into the blood only if there is an internal factor of Castle in the stomach. This is gastromucoprotein, which includes a peptide that is cleaved from pepsinogen when it is converted to pepsin, and a mucoid that is secreted by additional cells of the stomach. Thanks to this mucoid, the gastric mucosa is protected from the action of pepsin and self-digestion. When the secretory activity of the stomach decreases, the production of the Castle factor also decreases and, accordingly, the absorption of vitamin B12 decreases, resulting in anemia.

Phases of gastric secretion:

1. Complex reflex, or cerebral, lasting 1.5 - 2 hours, which secretion of gastric juice occurs under the influence of all factors that accompany food intake. Wherein conditioned reflexes, arising from the sight, smell of food, environment, are combined with unconditional, arising from chewing and swallowing. Juice, released under the influence of the type and smell of food, chewing and swallowing, is called "appetizing", or "fire". It prepares the stomach for food intake. The center of regulation of gastric secretion is a collection of neurons located in the cortex hemispheres, hypothalamus and medulla oblongata (neurons of the vagus nerve). Sympathetic neurons are located in thoracic region spinal cord. Through the neurons of the vagus nerve, gastric secretion is activated, and the sympathetic nerves have an inhibitory effect.

2. Gastric, or neurohumoral, phase, in which secretion stimuli arise in the stomach itself: secretion is enhanced by stretching the stomach (mechanical stimulation) and by the action of extractive substances of food and protein hydrolysis products on its mucosa (chemical stimulation). The main hormone in the activation of gastric secretion in the second phase is gastrin. The production of gastrin and histamine also occurs under the influence of local reflexes of the metasympathetic nervous system.

Humoral regulation joins 40-50 minutes after the onset of the cerebral phase. In addition to the activating effect of the hormones gastrin and histamine, the activation of gastric juice secretion occurs under the influence of chemical components - extractive substances of the food itself, primarily meat, fish, and vegetables. When cooking food, they turn into decoctions, broths, are quickly absorbed into the bloodstream and activate the activity of the digestive system. These substances primarily include free amino acids, vitamins, biostimulants, a set of mineral and organic salts. Fat initially inhibits secretion and slows down the evacuation of chyme from the stomach into the duodenum, but then it stimulates the activity of the digestive glands. Therefore, with increased gastric secretion, decoctions, broths, cabbage juice are not recommended. Most strongly gastric secretion increases under the influence of protein food and can last up to 2 hours, it changes least of all under the influence of bread (no more than 1 hour). With a long stay of a person on a carbohydrate diet, the acidity and digestive power of gastric juice decreases.

3. Intestinal phase. In the intestinal phase, inhibition of the secretion of gastric juice occurs. It develops when the chyme passes from the stomach to the duodenum. When an acidic food bolus enters the duodenum, hormones begin to be produced that quench gastric secretion - secretin, cholecystokinin and others. The amount of gastric juice is reduced by 90%.

Internal organs- organs located in cavities. They provide the exchange of substances between the body and the external environment and reproduction. The doctrine of the entrails is splanchnology.

The digestive system is a complex of organs that provide digestion. It consists of the alimentary canal and the digestive glands located in its walls or outside. The alimentary canal has a length of 8 - 10 m and parts:

1. oral cavity

3. esophagus

4. stomach

5. small intestine

6. large intestine

All sections of the alimentary canal are typically hollow organs. The structure of the wall of the digestive tube:

1. inner shell- mucosa with submucosa

2. middle shell– smooth muscle

3. outer shell - serous - adventitia

important organs digestive system are digestive glands that secrete digestive juices into different parts of the system. Juices contain digestive catalysts that accelerate the breakdown of proteins to amino acids, fats to glycerol and fatty acids, carbohydrates to monosaccharides (glucose, fructose, galactose). These substances are absorbed by the mucous membrane into the blood and lymph. Digestive juices contain digestive enzymes. Enzyme properties:

1. hydrolases (hydrolysis)

2. specificity

3. for operation they require temperature (36 - 37 degrees) and environment - alkaline, acidic, neutral)

Functions of the alimentary canal:

motor

secretory

endocrine (production of hormones)

Excretory (excretion of metabolic products, water, salts by the digestive glands)

suction

bactericidal (due to lysozyme, hydrochloric acid of gastric juice, intestinal lactic acid)

The oral cavity (cavitas oris, stoma) is the initial section of the digestive tract. Functions:

1. mechanical processing of food

2. the beginning of its chemical processing (splitting of carbohydrates)

3. formation of a food bolus

4. articulation of speech

With the help of teeth and gums, the oral cavity is divided into the vestibule and the oral cavity itself. The vestibule is delimited from the outside by the lips and cheeks, from the inside by the teeth and gums. The oral cavity is delimited from the outside by teeth and gums, from above - by a hard and soft palate, from below - by the bottom of the oral cavity with the tongue. Behind, through the pharynx, it communicates with the pharynx. The hard palate is formed by the palatine processes of the upper jaw and the horizontal plates of the palatine bones and passes into the soft palate, formed by the muscles and fibrous tissue. Its free back part is the palatine curtain, which has a protrusion - a tongue. With calm breathing through the nose, the curtain hangs obliquely down and separates the oral cavity from the pharynx. On the sides, it passes into palatine folds - arches: palatoglossal and palatine - pharyngeal. Between them are palatine tonsils - organs immune system that perform a protective function due to lymphocytes. Inflammation palatine tonsils- tonsillitis (tonsillitis). The mucous membrane of the oral cavity is covered with stratified squamous non-keratinized epithelium containing a large number of glands. Part of it around the neck of the teeth is the gum (gingiva). Inflammation of the gums - gingivitis, oral mucosa - stomatitis. Tongue (lingua, glossa) is a mobile muscular organ covered with a mucous membrane. Functions:

1. assessment of the taste of food

2. chewing

3. swallowing

4. sucking

5. speech production

The muscles of the tongue are:

skeletal (chin-hyoid, sublingual-lingual, awl-lingual)

own (upper longitudinal, lower longitudinal, transverse, vertical)

Parts of the language:

1. front - top (tip)

2. middle - body

3. posterior - root (connects to the lower jaw and hyoid bone)

4. back of the tongue (upper part)

5. tongue bottom ( Bottom part)

The mucous membrane of the back is rough, has papillae:

1. general sensitivity (filamentous, cone-shaped, mushroom-shaped)

2. receptors of the taste analyzer (gutter-shaped, leaf-shaped)

The lower surface of the tongue has no papillae. Between the lower surface and the bottom of the tongue there is a narrow strip of mucous membrane - the frenulum of the tongue. Inflammation of the tongue - glossitis.

1. biting off food

2. food grinding

3. the formation of articulate speech

The teeth are located in the dental alveoli of the lower and upper jaws. The tooth forms a continuous connection with the alveolus - hammering.

Tooth Parts:

1. crown (protrudes above the gum)

2. neck (covered by gums)

3. root (in cell)

At the top there is an opening leading to the root canal and the cavity of the crown. They are filled with dental pulp - loose connective tissue, blood vessels and nerves. The teeth are built of dentin, which is covered with enamel in the crown area, and cementum in the neck and root area. Dentin resembles bone tissue, but is stronger than it. Enamel is harder than dentin and is close in strength to quartz - this is the most durable tissue in the body (95% of mineral salts).

Teeth are composed of prismatic calcium hydroxyapatite crystals that are not joined together. Between the prisms is a soft absorber - a network of tiny pores filled with liquid. When loaded, the liquid is squeezed out of the pores and becomes more viscous - a magnetic field.

The fixing apparatus of the teeth is a thin plate between the tooth and the inner surface of the alveoli - the periodontium. It contains a large number of nerves and blood vessels, its inflammation is periodontitis (leads to loosening and loss of teeth). Types of teeth:

1. dairy (2 incisors, 1 canine, 2 large molars) - 20 pieces

2. permanent (2 incisors, 1 canine, 2 small molars - premolars, 2 large molars - molars, 1 wisdom tooth) - 32 teeth

The teeth are examined in half of the dentition - the alveolar process of the jaw. Milk teeth appear from 6 - 8 months to 2.5 years. From 6 to 14 years old, milk teeth are replaced by permanent ones. Wisdom teeth grow from 17 to 40 years old, may not appear. They are associated with a large number dental operations to remove and fix different kind jamming of teeth.

The salivary glands are located in the mucous membrane of the lips and cheeks. They are small and are divided into:

1. protein (serous) - a lot of protein, no mucilage

2. mucous membranes (no protein, a lot of mucin)

3. mixed

The parotid salivary gland is the largest steam gland (20 g). It is located in the retromaxillary fossa in front of the external ear. Its excretory (stenon) duct opens in front of the mouth at the level of the 2nd large molar. It secretes a serous (protein) secret. Pavlov and Glinsky obtained pure saliva by placing a fistula into a cheek incision in a dog from the parotid salivary gland (the main gland).

Submandibular salivary gland (15 gr). Located in the submandibular fossa, steam room. The excretory ducts open under the tongue. Mixed.

Sublingual salivary gland (5 gr). It is located under the tongue and is separated from it by a mucous membrane. It has 10 - 12 excretory ducts that open under the tongue. Mixed. Each salivary gland receives innervation from the sympathetic and parasympathetic divisions of the ANS. Parasympathetic fibers are part of the facial and glossopharyngeal nerves, sympathetic fibers - from the plexuses around the external carotid artery. Subcortical centers of parasympathetic innervation are located in the medulla oblongata, sympathetic - in the lateral horns of 2 - 6 thoracic segments of the spinal cord. When the parasympathetic nerves are irritated, a large amount of liquid saliva is released, when the sympathetic nerves are irritated, a small amount of viscous saliva is released. Saliva is a mixture of secretions of the glands of the oral mucosa, this is the first digestive juice. It is a transparent liquid stretching into threads, pH - 7.2. The daily compartment in an adult is 2 liters. Composition: 99% water, 1% - inorganic (potassium, chlorine, sodium and calcium), organic (mucin - a mucous substance that sticks together a food bolus - bonus) and enzymes:

1. amylase (ptyalin) - breaks down starch to maltose

2. maltase - breaks down maltose to glucose

3. lysozyme - has a bactericidal property

Amylase and maltase work only in a slightly alkaline environment. Functions of saliva:

1. digestive (carbohydrates)

2. excretory (excretory)

3. protective (mucin)

4. bactericidal (lysozyme)

5. hemostatic (thromboplastic substances, especially in cats and dogs)

Eating causes a reflex separation of saliva. It is carried out the whole process of eating on the principle of conditioned and unconditioned reflexes. The unconditioned reflex separation of saliva occurs when food enters the mouth, when the receptors of the oral cavity are irritated. Conditioned reflex separation of saliva occurs in response to the sound accompaniment of food intake and the smell of food (the type and smell of cooked food is important for digestion).

Lecture 20 . THE SIGNIFICANCE OF DIGESTION FOR THE ORGANISM AND ITS TYPES.

DIGESTION IN THE MOUTH. SWALLOWING.

General physiology of the digestive apparatus. The concept of secretion.

Digestion is a set of physiological, physical and chemical processes that ensure the reception and processing of products coming from the external environment into substances that can be absorbed by the body.

Types of digestion. The study of digestive processes in small intestine made it possible to establish the important role that belongs to the contact of nutrients with the surface of the membranes of mucosal cells. In experiments in vitro it turned out that in the presence of a strip of living intestine, the rate of enzymatic hydrolysis of some nutrients, such as starch, increases, significantly exceeding the total activity of the solution containing enzymes and the strip of intestine, taken separately. In accordance with this, it was found that the rate of hydrolysis of starch and protein occurs much faster inside the intestine than in a test tube under the influence of enzymes contained in the juice secreted in the intestine.

Data have been obtained that peptidase activity is concentrated mainly on the free surface of intestinal epithelial cells. It was found that pancreatic juice lipase is adsorbed on the surface of the epithelium of the small intestines. Based on these facts, Ugolev came to the conclusion that the large porous surface of the small intestine contributes to the enhancement of enzymatic processes, adsorbing enzymes and being a kind of porous catalyst. The final breakdown of nutrients occurs on the same surface of the small intestine that has the function of absorption. The breakdown of nutrients on the surface of the intestine is called wall, contact, or membrane digestion , Unlike cavity digestion , carried out in the cavity of the digestive tract without direct contact with the mucous membrane, and intracellular digestion that takes place in the cell (for example, during phagocytosis). Thus, three types of digestion are distinguished: cavity, parietal and intracellular.

Physiology of the secretory process. Since a huge proportion of these processes are due to the chemical processing of food by specific digestive enzymes, which are produced by billions of special secretory cells of the gastrointestinal tract (GIT), we must first, at least briefly, dwell on general issues physiology of secretory cells.

The secretory (glandular) cell is the most important structural and functional element of the digestive system. secretion A complex intracellular process is called a complex intracellular process during which a cell receives from the blood (actively or passively) initial substances, from some of which it synthesizes a secretory product that performs a certain, strictly specialized function in the body, and releases it together with water and some electrolytes in the form of a secret into internal environment body or on external surfaces of the body. Most often, the secretion process requires the expenditure of energy. In contrast to this excretion - the process of removing from the cell substances-decay products that are not needed by the cell.

In the glandular cells, substances of various chemical composition, which can be released into the cavity of the digestive system or remain on the surface of the cell membrane, taking part in all stages of the digestion process.

The following can be distinguished phases of the secretory cycle:

Entry of raw materials into the cell.

Synthesis of the primary product.

Transport and maturation of the secret.

Secret accumulation.

Extraction of a secret.

Restoration of structures and functions of the cell.

The duration of the secretory cycle in different cells is not the same and ranges from several hours to several days.

Electrophysiology of glandular tissue. Membrane potential of the secretory cells of various glands of the digestive tract varies within a fairly wide range - from 10 to 80 mv., however, in the vast majority at rest, the polarization is 30-35 mv.

Electrophysiological studies of glandular cells revealed a number of features that distinguish them from other excitable structures. These should include:

1. Long latency period

No self-regenerative process.

Low rise rate of potential fluctuations.

Graduation of electrical responses.

Lack of electrical excitability.

Different degrees of polarization of the basal and apical membranes.

Hyperpolarization of membranes during excitation.

Due to the increase in K-permeability, the excitation of the glands first causes hyperpolarization of the basement membrane, and then the apical one, but to a lesser extent. This creates an electrical field of the cell, which at rest is 20-30 V/cm, when excited up to 50-60 V/cm, which promotes the movement of secretory granules to the apical end. It participates in the formation of a channel for the ejection of macromolecules during their extrusion.

Methods for studying the functions of the gastrointestinal tract. There are chronic and acute methods for studying the functions of the gastrointestinal tract, which allow you to study the dynamics of the secretion of individual glands, as well as the composition of the secrets. To obtain a secret, various devices are used - suckers for the salivary glands, fistulas (in animals), probes (in humans) for gastric and pancreatic juice, as well as bile. At present, traditional methods for studying the functions of the gastrointestinal tract have been supplemented by such methods as radiography, ultrasound, radioisotope sounding, radio pills, etc. You will learn more about all this in practical classes.

Digestion in the mouth.

Food processing begins already in the oral cavity, where it is crushed, moistened with saliva and the food bolus is formed. Food stays in the human mouth for an average of 15-18 seconds. Being in the mouth, food irritates taste, tactile and temperature receptors, as a result of which the secretion of salivary, gastric and pancreas is reflexively stimulated and motor acts of chewing and swallowing are carried out.

The ducts of three pairs of large salivary glands flow into the oral cavity: parotid, submandibular and sublingual, as well as many small glands located on the surface of the tongue and in the mucous membrane of the palate and cheeks. Mucous and serous cells of the salivary glands secrete saliva containing a number of enzymes.

To study the function of the salivary glands, I.P. Pavlov proposed the operation of removing the opening of the excretory duct of the parotid or submandibular gland to the surface of the skin, to collect which a special funnel is glued. The saliva of a particular gland is collected from a person using a Leshle-Krasnogorsky sucker capsule.

The composition and properties of saliva. Saliva is a mixed secret of all the salivary glands of the oral cavity. The secret of various glands has a different composition and consistency. The submandibular and sublingual glands secrete more viscous and thicker saliva than the parotid glands. This difference depends on the amount of mucin, which gives the food a slimy appearance and slipperiness.

In addition to mucin, saliva contains a small amount of globulins, amino acids, creatine, uric acid, urea, inorganic salts and enzymes. All these substances form a dense saliva residue (0.5-1.5%). The reaction of saliva is neutral.

The composition of saliva depends on the consistency and type of food, as well as on its chemical composition. Dry and small food causes the release of more saliva than wet. With the introduction of nutrients in the saliva there is more dense residue than with the introduction of rejected substances. The amount of saliva in a person can reach 1000-1500 ml per day, fluctuating depending on the food.

Human saliva contains enzymes that cause the hydrolytic breakdown of carbohydrates to glucose. Salivary amylase converts starch to dextrins and then dextrins to maltose. Under the influence of maltase, the latter is broken down to glucose. Saliva enzymes act in a neutral environment. Therefore, when swallowing food, they work only until the food is saturated with acidic gastric juice.

Non-digestive functions of saliva. In addition to participating in the processing of food and the formation of the food bolus, saliva has important non-digestive functions. It wets the oral mucosa, which is absolutely necessary for the normal implementation of the speech function. In addition, food substances dissolve in saliva, which contributes to their penetration to the receptors of the taste analyzer. In some animals, salivation is involved in thermoregulation (dogs). Some substances (lead, mercury, etc.) are excreted with saliva.

Salivation regulation. The secretion of the salivary glands is excited reflexively. Food or rejected substances that enter the oral cavity and irritate receptors cause unconditioned salivary reflexes. Salivation after a short (1-3 sec) latent period continues for the entire time while the stimulus is acting and stops at the end of its action. In the medulla oblongata in the region of the nuclei of the facial and glossopharyngeal nerve lies the center of salivation. With electrical stimulation of this area, abundant secretion of saliva occurs.

The parasympathetic innervation of the parotid gland is carried out by the secretory fibers of the glossopharyngeal nerve, the submandibular and sublingual glands receive them as part of the chorda thympani, a branch of the facial nerve. The sympathetic innervation of the salivary glands is carried out by fibers from the upper cervical sympathetic ganglion.

Transection of these nerves leads to the cessation of salivation. Irritation of parasympathetic fibers causes the separation of copious amounts of liquid saliva, poor in organic matter. On the contrary, irritation of the sympathetic nerve causes separation of very little a large number saliva containing many organic substances and enzymes.

Along with unconditioned salivary reflexes, conditioned - natural and artificial reflexes - also play an important role. Painful irritations, negative emotions (fear) inhibit salivation.

swallowing.

With movements of the cheeks and tongue, chewed, moistened with saliva and become more slippery food turns into a lump, which moves to the back of the tongue. By contractions of the anterior part of the tongue, the food bolus is pressed against the hard palate, then by successive contractions of the middle part of the tongue, it is pressed backwards and rolls onto the root of the tongue behind the anterior arches. Elevation of the soft palate prevents food from entering the nasal cavity. The movements of the tongue help push food down the throat. At the same time, there is a contraction of the muscles that close the entrance to the larynx (raising the larynx and lowering the epiglottis). The return of food that has entered the pharynx back into the oral cavity is prevented by the root of the tongue that has risen upwards and the arches that are tightly adjacent to it.

Following the entry of food into the pharyngeal cavity, muscle contraction occurs, narrowing the lumen of the pharynx above the food bolus, as a result of which it moves into the esophagus.

A large number of muscles are involved in the act of swallowing, the contraction of which occurs as a result of irritation of the receptors of the root of the tongue. Swallowing in the absence of food or saliva in the oral cavity is impossible. This is a complex chain reflex act, regulated by special swallowing centers located at the bottom of the 4th ventricle and in the hypothalamus. The swallowing center is in a complex relationship with other centers of the medulla oblongata - the centers of respiration and cardiac activity. This explains the changes in the activity of the heart and respiratory apparatus during swallowing - during each sip, the breath is held and the heart rate increases.

Following the entry of the food bolus into the initial segment of the esophagus, its muscles contract and food is pushed into the stomach. The movements of the esophagus are in connection with the movements of the swallowing apparatus. The duration of the passage of solid food through the esophagus is 8-9 seconds. Liquid food passes faster - in 1-2 seconds.

Outside of swallowing movements, the entrance to the stomach is closed. When food passes through the esophagus and stretches it, a reflex opening of the entrance to the stomach occurs.

The esophagus is not only an esophageal organ. In its mucosa there are thermo-, mechano- and chemoreceptors, from which esophageal-gastric, esophageal-intestinal, etc. arise. reflexes. An example is the protective esophageal-gastric reflex - inhibition of gastric secretion when juice enters the esophagus.

Food is in the mouth for only 15 seconds and during this period the digestion process starts. Despite the fact that saliva does not contain such aggressive components as gastric juice, it breaks down polysaccharides. Digestion in the mouth is an important step in the process of food digestion. Let's consider its meaning in more detail.

Composition and functions of saliva

In the mouth, not only mechanical, but also chemical processing of food takes place. And all this thanks to such a biological fluid as saliva. It contains enzymes that begin to grind and digest food.

The mouth contains the submandibular, parotid, and sublingual salivary glands. These are the three largest glands. In addition to them, there are others, smaller ones. They are located on top of the tongue, palate and cheeks.

During the day, a person produces up to two liters of saliva with all glands, the largest number released during the consumption of food.

Saliva is 99% water and has a pH of 6.8-7.4, it contains:

• anions (chlorides, bicarbonates, sulfates and phosphates);
• cations (sodium, potassium and calcium);
• trace elements (iron, copper and nickel);
• proteins, in particular mucin, a substance that sticks food particles together;
• enzymes (amylase, maltase, transferase, protease and others).

It is enzymes such as amylase and maltase that are involved in the breakdown of food in the mouth. Amylase breaks down polysaccharides, and maltase breaks down maltose, converting it to glucose.

The antibacterial effect is exerted by a protein substance in the composition of saliva - lysozyme.

Digestion in the oral cavity is the first step on the way to the digestion of food, even the complete breakdown of carbohydrates in the mouth does not occur. But despite this, without it, the gastrointestinal tract would not function normally and food would not be broken down.

Saliva is an essential part of digestion in the mouth. It performs the following functions:

1. Digestive. Participates in the breakdown of food.
2. Excretory. In addition to the above components, saliva may contain salt, lead, urea, medications and other substances that entered the body.
3. Protective. Due to the content of lysozyme, it produces a bactericidal effect. Also high content immunoglobulins provide protection against pathogens, which can affect the state of the microflora. Saliva protects the oral mucosa from drying out.
4. Trophic. Due to the content of trace elements in the composition, it contributes to the formation of tooth enamel.

Consider how digestion occurs in the oral cavity, and what is the role of saliva in this process.

How does digestion work?

As mentioned above, digestion in the oral cavity is initial stage gastrointestinal digestion. After all, the oral cavity is the initial section of the esophagus, food enters it, is transformed for further digestion and splitting into useful substances.

After eating food, the receptors that are on the mucous membrane of the oral cavity and tongue are irritated. Thanks to them, a person recognizes the taste. Bitter, salty, sweet or bitter food leads to irritation of the receptors and the production of a large amount of saliva.

The volume of saliva that is produced when eating food depends on the degree of its dryness and chemical composition. The coarser the food, the more saliva is produced by the salivary glands.

It is worth noting that, in addition to saliva, organs of the oral cavity also take part in cavity digestion:

• Language. This is a mobile muscular organ that helps move food in the mouth and promote it for chewing and further digestion in the gastrointestinal tract;
• Teeth. They help to carry out main task oral cavity - mechanical grinding of food. An adult's mouth has 32 teeth.

When food enters the mouth cavity digestion begins. Food is wetted by saliva and begins to decompose it into certain substances. In addition to chemical processing, food is simultaneously subjected to mechanical processing, in which the tongue and teeth are involved.

Saliva enzymes come into play. Amylase breaks down complex carbohydrates and thereby helps to easily digest heavy food in the gastrointestinal tract. Since the food is in the mouth for a small amount of time, only carbohydrates have time to break down. After the passage of the food coma into the stomach, salivary enzymes still continue to act. Even in the gastrointestinal tract, abdominal digestion continues until the gastric juice comes into action.

Food in the mouth is no more than 30 seconds and during this time it is subjected to chemical and mechanical processing in sufficient volume. Crushed and moistened with saliva, it is formed in one lump. The food is ready to be swallowed and further digested.

final stage of digestion

It is swallowing and the movement of food through the esophagus that final stage digestion in the mouth. Consider this process in detail.

Swallowing refers to a complex reflex process in which food from the oral cavity enters the stomach.

The process of swallowing consists of three stages: oral, pharyngeal and esophageal.

At the first stage, the act of swallowing is involuntary. After processing, the food lump is in volume from 5 to 15 cm3. Thanks to chewing movements, in which the tongue and teeth are involved, the lump moves to the root of the tongue, after which swallowing becomes involuntary and is based only on physiological reflexes.

In case of involuntary swallowing, at the first stage, the food does not enter the Airways, because the entrance to the nasal cavity is blocked by a soft palate, while the tongue moves the food lump into the throat.

In the pharyngeal stage, food is on its way to the stomach. The sphincter of the esophagus opens, and it enters directly into the esophagus.

The esophageal stage is final. It is characterized by food entering the stomach for digestion. Food, passing through the esophagus, causes irritation of the mechanoreceptors, and this, in turn, affects the contraction of the muscles of the esophagus. The food lump moves towards the stomach. Food enters the stomach when the muscle tone of the organ decreases. After the act of eating food is over and the person feels full, the muscle tone of the stomach increases, which prevents the contents from entering back into the esophagus.

In a second, the food lump moves 3 cm down the esophagus. In addition to reflexes, the following influences the passage of a food coma through the esophagus:

• pressure difference between different departments gastrointestinal tract;
• contraction of the muscle tissue of the esophagus;
• low muscle tone;
• weight and density of the food coma. Coarse food passes more slowly than liquid.

The spinal cord sends impulses that cause the act of swallowing. When food passes from the mouth into the esophagus, the breathing process slows down, which causes heart contractions to increase, and breathing stops.

For digestion, the chemical and mechanical processing of food in the mouth is of great importance. After all, it is in the mouth that after eating food, a powerful reflex reaction is triggered, which occurs due to irritation of the receptors of the oral mucosa. Nerve impulses sent by the neutral nervous system, activate the activity of all organs of the gastrointestinal tract, in particular, affect the stomach, pancreas, intestines, liver, as well as the smooth muscles of the digestive tract.

Digestion is a complex process. It starts in the mouth and ends in the intestines. At every stage, the food is exposed chemical attack due to the content of enzymes in biological fluids.

The digestive system consists of a digestive tube and a number of large glands. The digestive tube, the length of which in an adult can reach 7-8 m, forms extensions (oral cavity, stomach) and many bends and loops.

Begins digestive system oral cavity, in which food is crushed and moistened with saliva.

The entrance to the oral cavity is limited by the lips, they are covered with very thin skin rich in blood vessels and nerve endings. Lips are involved in the capture of food, determining its quality.

Having bitten off a piece of food, we chew it with the help of teeth located in the recesses of the upper and lower jaws. Lower jaw moves due to contractions of chewing muscles. This is very strong muscles, they can develop a force of up to 400 kg.

Teeth. Human teeth grow in two shifts; first dairy, then permanent. The replacement of milk teeth with permanent ones begins at the age of 6-7, and by the age of 15 it basically ends. Wisdom teeth (the third large molar) are the last to grow. Sometimes they erupt by the age of 25-30, or they may not appear at all.

In total, a person has 32 teeth: on each jaw there are 4 incisors, 2 canines, 4 small molars and 6 large molars.

The tooth is a complex organ, it distinguishes between the root hidden in the bone cell of the jaw and the visible part - the crown and neck.

The tooth is built of a dense bone-like substance - dentin, covered with cementum in the root area, and very dense enamel in the crown area, which protects the tooth from abrasion and bacteria penetration.

Salivary glands. The oral mucosa contains small salivary glands. The ducts of three pairs of large salivary glands also open here: parotid, sublingual, submandibular. The weight of these glands secrete saliva - more than 1 liter per day.

Saliva wets food, washes away harmful or foreign substances from the mucous membrane. Saliva contains up to 99.4% water and has a slightly acidic or slightly alkaline reaction. It contains enzymes, substances that give it stickiness and kill bacteria. Under the action of enzymes, the starch contained in food begins to break down into simpler molecules - to glucose.

Once in the mouth, food irritates numerous receptors (temperature, taste, tactile), and we feel its taste, temperature, movement. Irritation of the receptors also causes reflexes of chewing and salivation. These reflexes are unconditioned.

At the same time, during a person's life, conditioned salivary reflexes are also developed in response to the smell of food, its appearance, and other stimuli.

Language. Important role tongue plays in the mouth. When chewing, it directs food to the teeth, mixes it and moves it into the pharynx for swallowing. In addition, the tongue, like the lips, is involved in determining the quality of food.

Throat and esophagus. Chewed, moistened with saliva, a slippery lump of food enters the pharynx, and then into the esophagus. Food is pushed through the esophagus by peristalsis - wave-like contractions of its walls. In this case, the muscles located in the wall of the esophagus are compressed, pushing the lump of food into the stomach. This process takes 6-8 s.

In the pharynx, the paths of air and food entering the body intersect. It would seem that there is a danger that lumps of food can get into the respiratory organs - into the larynx, nasopharynx. However, this does not happen, because during swallowing, the cartilage - the epiglottis closes the entrance to the larynx, and the uvula of the soft palate rises and separates the nasopharynx from the oropharynx. These processes occur reflexively. And yet you should not talk and laugh while chewing and swallowing food.

• Until recently, it was believed that the use chewing gum leads to depletion of the salivary glands. However, it turned out that with prolonged chewing of gum, the salivary glands begin to produce saliva with a reduced content of enzymes, so depletion does not occur.

Test your knowledge

1. How is the digestive system organized?
2. Describe the structure of a tooth.
3. At what age do milk teeth change into permanent teeth?
4. What is the importance of tooth enamel?
5. What is dentine?
6. How many molars does a person have?
7. What happens to food in the mouth?
8. What is saliva? What function does it perform?
9. What role does language play?
10. What is the mechanism of movement of the food bolus through the esophagus?

Think

1. Why is it not recommended to talk while eating?
2. Why is it important to chew food thoroughly?

In the oral cavity, food undergoes mechanical and chemical processing. Teeth grind food, and saliva is digestive juice: under the action of its enzymes, starch begins to break down.