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The oral cavity is the initial section of the digestive tract where:
1. Analysis of the taste properties of substances;
2. Separation of substances into food and rejected;
3. Protection of the digestive tract from the ingress of low-quality nutrients and exogenous microflora;
4. Grinding, wetting food with saliva, initial hydrolysis of carbohydrates and formation of a food bolus;
5. Irritation of mechano-, chemo-, and thermoreceptors, causing stimulation of the activity of not only their own, but also the digestive glands of the stomach, pancreas, liver, and duodenum.
The oral cavity plays the role of an external barrier to protect the body from pathogenic microflora due to the presence of the bactericidal substance lysozyme (muromidase) in saliva, the antiviral effect of salivary nuclease, the ability of salivary immunoglobulin A to bind exotoxins, as well as as a result of phagocytosis of leukocytes (4000 in 1 cm 3 of saliva) and suppression of pathogenic microflora by normal flora of the oral cavity.
Salivation
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Salivary glands hormone-like substances are produced that are involved in the regulation of phosphorus-calcium metabolism in bones and teeth, in the regeneration of the epithelium of the mucous membrane oral cavity, esophagus, stomach and in the regeneration of sympathetic fibers when they are damaged.
Food is in the oral cavity for 16-18 seconds and during this time saliva, secreted by the glands into the oral cavity, moistens dry substances, dissolves soluble ones and envelops solid ones, neutralizes irritating liquids or reduces their concentration, facilitates the removal of inedible (rejected) substances, washing them away. oral mucosa.
Mechanism of saliva formation
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Saliva is produced both in the acini and in the ducts of the salivary glands. The cytoplasm of glandular cells contains secretory granules, located mainly in the perinuclear and apical parts of the cells, near the Golgi apparatus. In mucous and serous cells, granules differ both in size and in chemical nature. During secretion, the size, number and location of granules changes, and the Golgi apparatus acquires a clearer outline. As secretory granules mature, they move from the Golgi apparatus to the top of the cell. Synthesis takes place in granules organic matter, which move with water through the cell along endoplasmic reticulum. During secretion, the amount of colloidal material in the form of secretory granules gradually decreases and is resumed during the resting period.
The first stage of saliva formation takes place in the acini of the glands - primary secret containing alpha amylase and mucin. The content of ions in the primary secretion differs slightly from their concentration in extracellular fluids. In the salivary ducts, the composition of the secretion changes significantly: sodium ions are actively reabsorbed, and potassium ions are actively secreted, but at a lower rate than sodium ions are absorbed. As a result, the concentration of sodium in saliva decreases, while the concentration of potassium ions increases. The significant predominance of reabsorption of sodium ions over the secretion of potassium ions increases electronegativity in the salivary ducts (up to 70 mV), which causes passive reabsorption of chlorine ions, a significant decrease in the concentration of which at the same time is associated with a decrease in the concentration of sodium ions. At the same time, the secretion of bicarbonate ions by the ductal epithelium into the lumen of the ducts increases.
Secretory function of the salivary glands
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Humans have three pairs of major salivary glands: parotid, sublingual, submandibular and, in addition, a large number of small glands scattered in the oral mucosa. The salivary glands consist of mucous and serous cells. The former secrete a mucoid secretion of thick consistency, the latter - liquid, serous or proteinaceous. The parotid salivary glands contain only serous cells. The same cells are found on the lateral surfaces of the tongue. The submandibular and sublingual glands are mixed glands, containing both serous and mucous cells. Similar glands are located in the mucous membrane of the lips, cheeks, and on the tip of the tongue. The sublingual and small glands of the mucous membrane secrete constantly, and the parotid and submandibular glands secrete when they are stimulated.
From 0.5 to 2.0 liters of saliva are produced daily. Its pH ranges from 5.25 to 8.0. An important factor influencing the composition of saliva is the rate of its secretion, which in humans in the “resting” state of the salivary glands is 0.24 ml/min. However, the secretion rate can fluctuate even at rest from 0.01 to 18.0 ml/min and increase when chewing food up to 200 ml/min.
The secretion of different salivary glands is not the same and varies depending on the nature of the stimulus. Human saliva is a viscous, opalescent, slightly turbid (due to the presence of cellular elements) liquid with a specific gravity of 1.001-1.017 and a viscosity of 1.10-1.33.
Mixed human saliva contains 99.4-99.5% water and 0.5-0.6% solid residue, which consists of inorganic and organic substances. Inorganic components are represented by ions of potassium, sodium, calcium, magnesium, iron, chlorine, fluorine, thiocyanate compounds, phosphate, chloride, sulfate, bicarbonate and make up approximately 1/3 of the dense residue.
Organic substances of the dense residue - proteins (albumin, globulins), free amino acids, nitrogen-containing compounds of non-protein nature (urea, ammonia, creatine), bactericidal substances - lysozyme (muramidase) and enzymes: alpha-amylase and maltase.
Alpha-amylase is a hydrolytic enzyme and cleaves 1,4-glucosidic bonds in starch and glycogen molecules to form dextrins, and then maltose and sucrose.
Maltose (glucosidase) breaks down maltose and sucrose into monosaccharides. Saliva also contains other enzymes in small quantities - proteases, peptidases, lipase, alkaline and acid phosphatase, RNase, etc. The viscosity and mucus-producing properties of saliva are due to the presence of mucopolysaccharides (mucin).
Regulation of salivation
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The secretion of saliva is a complex reflex act, which occurs due to irritation of the receptors of the oral cavity with food or other substances ( unconditionally reflexive irritants), as well as irritation of visual and olfactory receptors appearance and the smell of food, the type of environment in which eating occurs (conditioned reflex irritants).
The excitation that arises from irritation of the mechano-, chemo- and thermoreceptors of the oral cavity reaches the center of salivation in the medulla oblongata along afferent fibers V, VII, IX, X pairs of cranial brain nerves. Efferent influences to the salivary glands arrive via parasympathetic and sympathetic nerve fibers. Preganglionic parasympathetic fibers to the sublingual and submandibular salivary glands go as part of the chorda tympani (branch of the VII pair) to the sublingual and submandibular ganglia located in the body of the corresponding glands, postganglionic - from these ganglia to secretory cells and vessels of the glands. TO parotid glands preganglionic parasympathetic fibers come from the inferior salivary nucleus of the medulla oblongata as part of the IX pair of cranial nerves. From the ear ganglion, postganglionic fibers are directed to secretory cells and vessels.
Preganglionic sympathetic fibers innervating the salivary glands are axons of the neurons of the lateral horns of the II-VI thoracic segments spinal cord and end in the superior cervical ganglion. From here, postganglionic fibers are sent to the salivary glands. Irritation of the parasympathetic nerves is accompanied by copious secretion of liquid saliva containing small amounts of organic substances. When the sympathetic nerves are irritated, a small amount of saliva is released, which contains mucin, making it thick and viscous. In this regard, the parasympathetic nerves are called secretory, and sympathetic - trophic. During “food” secretion, the parasympathetic influences on the salivary glands are usually stronger than the sympathetic ones.
Regulation of the volume of water and the content of organic substances in saliva is carried outsalivary center. In response to irritation of the mechano-, chemo- and thermoreceptors of the oral cavity by various food or rejected substances, packets of impulses differing in frequency are formed in the afferent nerves of the salivary reflex arc.
The diversity of afferent impulses, in turn, is accompanied by the appearance of a mosaic of excitation in the salivary center, corresponding to the frequency of impulses, and different efferent impulses to the salivary glands. Reflex influences inhibit salivation until it stops. Inhibition can be caused by painful stimulation, negative emotions, etc.
The occurrence of salivation at the sight and (or) smell of food is associated with the participation in the process of the corresponding zones of the cerebral cortex, as well as the anterior and posterior groups of hypothalamic nuclei (see Chapter 15).
The reflex mechanism is the main, but not the only mechanism for inducing salivation. The secretion of saliva is influenced by hormones of the pituitary gland, pancreas and thyroid glands, sex hormones. Copious secretion of saliva is observed during asphyxia due to irritation of the salivary center by carbonic acid. Saliva secretion can be stimulated by vegetotropic pharmacological substances(pilocarpine, proserine, atropine).
Chewing
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Chewing- a complex physiological act consisting of grinding food substances, wetting them with saliva and forming a food bolus. Chewing ensures the quality of mechanical and chemical processing of food and determines the time it remains in the oral cavity, has a reflex effect on the secretory and motor activity digestive tract. Chewing involves the upper and lower jaws, chewing and facial muscles, tongue, soft palate and salivary glands.
Regulation of chewing
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Chewing is regulated reflexively. Excitation from the receptors of the oral mucosa (mechano-, chemo- and thermoreceptors) is transmitted along the afferent fibers of the II, III branches of the trigeminal, glossopharyngeal, superior laryngeal nerve and the chorda tympani to the chewing center, which is located in the medulla oblongata. Excitement from center to masticatory muscles transmitted via efferent fibers of the trigeminal, facial and hypoglossal nerve. The ability to voluntarily regulate the chewing function suggests that there is cortical regulation of the chewing process. In this case, excitation from the sensitive nuclei of the brain stem along the afferent pathway through specific nuclei of the thalamus switches to cortical section taste analyzer (see Chapter 16), where, as a result of analyzing the received information and synthesizing the image of the stimulus, the question of the edibility or inedibility of the substance entering the oral cavity is decided, which affects the nature of the movements of the masticatory apparatus.
IN infancy The process of chewing corresponds to sucking, which is ensured by a reflex contraction of the muscles of the mouth and tongue, creating a vacuum in the oral cavity within the range of 100-150 mm of water column.
Swallowing
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Swallowing- a complex reflex act by which food is transferred from the mouth to the stomach. The act of swallowing is a chain of successive interconnected stages that can be divided into three phases:
(1) oral(arbitrary),
(2) pharyngeal(involuntary, fast)
(3) esophageal(involuntary, slow).
First phase of swallowing
The bolus of food (volume 5-15 cm 3) moves towards the root of the tongue, behind the anterior arches of the pharyngeal ring, with coordinated movements of the cheeks and tongue. From this moment on, the act of swallowing becomes involuntary (Fig. 9.1).
Fig.9.1. Swallowing process.
Irritation by the food bolus of the receptors of the mucous membrane of the soft palate and pharynx is transmitted along the glossopharyngeal nerves to the swallowing center in the medulla oblongata, efferent impulses from which go to the muscles of the oral cavity, pharynx, larynx and esophagus along the fibers of the hypoglossal, trigeminal, glossopharyngeal and vagus nerves, which ensures the occurrence of coordinated contraction of the muscles of the tongue and the muscles that lift the soft palate.
Thanks to this, the entrance to the nasal cavity from the pharynx is closed by the soft palate and the tongue moves the food bolus into the pharynx.
At the same time, the hyoid bone is displaced, the larynx is raised, and as a result, the entrance to the larynx is closed by the epiglottis. This prevents food from entering the respiratory tract.
Second phase of swallowing
At the same time, the upper esophageal sphincter opens - a thickening of the muscular lining of the esophagus, formed by fibers of a circular direction in the upper half of the cervical part of the esophagus, and the food bolus enters the esophagus. The upper esophageal sphincter contracts after the bolus passes into the esophagus, preventing the esophagopharyngeal reflex.
Third phase of swallowing
The third phase of swallowing is the passage of food through the esophagus and transfer it to the stomach. The esophagus is a powerful reflexogenic zone. The receptor apparatus is represented here mainly by mechanoreceptors. Due to irritation of the latter by the food bolus, a reflex contraction of the muscles of the esophagus occurs. In this case, the circular muscles are consistently contracted (with simultaneous relaxation of the underlying ones). Waves of contractions (called peristaltic) successively spread towards the stomach, moving the food bolus. The speed of propagation of the food wave is 2-5 cm/s. Contraction of the esophageal muscles is associated with the arrival of efferent impulses from the medulla oblongata along the fibers of the recurrent and vagus nerves.
Movement of food through the esophagus
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The movement of food through the esophagus is determined by a number of factors.
Firstly, pressure difference between the pharyngeal cavity and the beginning of the esophagus - from 45 mm Hg. in the pharyngeal cavity (at the beginning of swallowing) up to 30 mm Hg. (in the esophagus).
Secondly, the presence of peristaltic contractions of the esophageal muscles,
Third- muscle tone of the esophagus, which in the thoracic region is almost three times lower than in the cervical region, and,
Fourth- gravity of the food bolus. The speed at which food passes through the esophagus depends on the consistency of the food: dense food passes in 3-9 seconds, liquid food in 1-2 seconds.
The swallowing center is connected through the reticular formation to other centers of the medulla oblongata and spinal cord, the excitation of which at the moment of swallowing causes inhibition of the activity of the respiratory center and a decrease in tone vagus nerve. This is accompanied by cessation of breathing and increased heart rate.
In the absence of swallowing contractions, the entrance from the esophagus to the stomach is closed - the muscles of the cardiac part of the stomach are in a state of tonic contraction. When the peristaltic wave and bolus of food reach the final part of the esophagus, the tone of the muscles of the cardiac part of the stomach decreases and the bolus of food enters the stomach. When the stomach is filled with food, the tone of the cardiac muscles increases and prevents the backflow of gastric contents from the stomach into the esophagus.
Internal organs are organs located in cavities. They provide metabolism between the body and external environment and reproduction. The study of the insides - splanchnology.
The digestive system is a complex of organs that provide digestion. It consists of the digestive canal and digestive glands located in its walls or outside. The digestive canal is 8–10 m long and has parts:
1. oral cavity
3. esophagus
4. stomach
5. small intestine
6. large intestine
All parts of the digestive canal are typically hollow organs. The structure of the wall of the digestive tube:
1. inner shell – mucous membrane with submucosa
2. tunica media – smooth muscle
3. outer shell– serous – adventitia
Important organs of the digestive system are the digestive glands, which secrete digestive juices in different departments systems. Juices contain digestive catalysts that accelerate the breakdown of proteins into amino acids, fats into glycerol and fatty acids, carbohydrates into 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 work they require temperature (36 - 37 degrees) and environment - alkaline, acidic, neutral)
Functions of the digestive canal:
· motor
secretory
endocrine (hormone production)
· excretory (excretion of metabolic products, water, salts by the digestive glands)
· suction
· bactericidal (due to lysozyme, of hydrochloric acid gastric juice, intestinal lactic acid)
The oral cavity (cavitas oris, stoma) is the initial section of the digestive tract. Functions:
1. mechanical food processing
2. the beginning of its chemical processing (breakdown 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 externally by the lips and cheeks, and internally by teeth and gums. The oral cavity is delimited from the outside by the teeth and gums, from above by the hard and soft palate, and from below by the bottom of the oral cavity with the tongue. Posteriorly, through the pharynx, it communicates with the pharynx. Solid sky formed by the palatine processes of the upper jaw and horizontal plates of the palatine bones and passes into the soft, formed by muscles and fibrous tissue. Its free rear part is the velum, which has a protrusion - the uvula. When breathing calmly through the nose, the curtain hangs obliquely down and separates the oral cavity from the pharynx. On the sides it passes into the palatal folds - arches: palatine - lingual and palatine - pharyngeal. Between them are located in the recesses the palatine tonsils - organs of the immune system that perform protective function due to lymphocytes. Inflammation of the tonsils - tonsillitis (tonsillitis). The oral mucosa is covered with stratified squamous non-keratinizing epithelium containing a large number of glands. The part of it around the neck of the teeth is the gum (gingiva). Inflammation of the gums - gingivitis, of the oral mucosa - stomatitis. The tongue (lingua, glossa) is a mobile muscular organ covered with a mucous membrane. Functions:
1. assessing the taste of food
2. chewing
3. swallowing
4. sucking
5. speech formation
The basis of the tongue is the muscles:
· skeletal (mentio-hyoid, sublingual-lingual, styloglossal)
· own (upper longitudinal, lower longitudinal, transverse, vertical)
Parts of the tongue:
1. anterior – apex (tip)
2. middle – body
3. back – root (connects to lower jaw and hyoid bone)
4. dorsum of tongue ( top part)
5. bottom of tongue ( Bottom part)
The mucous membrane of the dorsum is rough and has papillae:
1. general sensitivity (thread-like, cone-shaped, mushroom-shaped)
2. receptors of the taste analyzer (grooved, leaf-shaped)
The lower surface of the tongue does not have 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 food
2. grinding food
3. formation of articulate speech
The teeth are located in the dental alveoli of the lower and upper jaw. The tooth forms a continuous connection with the alveolus - impaction.
Tooth parts:
1. crown (protrudes above the gum)
2. neck (covered with gum)
3. root (in cell)
At the apex there is a hole leading into the root canal and crown cavity. They are filled with dental pulp - loose connective tissue, blood vessels and nerves. Teeth are made of dentin, which is covered with enamel in the crown area, and with cement in the neck and root area. Dentin resembles bone tissue, but stronger than it. Enamel is harder than dentin and is close in strength to quartz - it is the strongest tissue in the body (95% mineral salts).
The teeth are composed of prismatic crystals of calcium hydroxyapatite that are not connected to each other. Between the prisms there is a soft absorber - a network of tiny pores filled with liquid. Under load, 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 - 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. milk (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 of age, baby teeth are replaced with permanent ones. Wisdom teeth grow from 17 to 40 years of age and may not appear. They involve a large number of dental operations to remove and correct various types jammed 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 mucus
2. mucous membranes (no protein, lots of mucin)
3. mixed
The parotid salivary gland is the largest paired gland (20 g). Located in the retromaxillary fossa in front of the external ear. Its excretory (stenon) duct opens into the vestibule of the mouth at the level of the 2nd molar. Produces serous (protein) secretion. Pavlov and Glinsky obtained pure saliva by placing a fistula in the incision of the dog’s cheek from the parotid salivary gland(main piece of iron).
Submandibular salivary gland (15 g). Located in the submandibular fossa, steam room. The excretory ducts open under the tongue. Mixed.
Sublingual salivary gland (5 g). Located under the tongue and separated from it by the mucous membrane. Has 10 – 12 excretory ducts, opening under the tongue. Mixed. Each salivary gland receives innervation from the sympathetic and parasympathetic divisions of the ANS. Parasympathetic fibers come from the facial and glossopharyngeal nerves, sympathetic fibers come from the plexuses around the external carotid artery. The subcortical centers of parasympathetic innervation are located in the medulla oblongata, and the sympathetic innervation is located in the lateral horns of the 2nd to 6th thoracic segments of the spinal cord. When the parasympathetic nerves are irritated, a large amount of liquid saliva is released, and when the sympathetic nerves are irritated, a small amount of viscous saliva is released. Saliva is a mixture of secretions from the glands of the oral mucosa; it is the first digestive juice. It is a transparent liquid, stretching in threads, pH – 7.2. The daily volume for an adult is 2 liters. Composition: 99% water, 1% - inorganic (potassium, chlorine, sodium and calcium), organic (mucin - a mucous substance that glues the food bolus - bonus) and enzymes:
1. amylase (ptialin) – breaks down starch to maltose
2. maltase - breaks down maltose into glucose
3. lysozyme – has bactericidal properties
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 abundant in cats and dogs)
Eating food causes a reflex secretion of saliva. It carries out the entire process of eating according to the principle of conditioned and unconditioned reflexes. Unconditioned reflex separation of saliva occurs when food enters the mouth, when the receptors of the oral cavity are irritated. The conditioned reflex secretion of saliva occurs in response to the sound of eating and the smell of food (the sight and smell of cooked food is important for digestion).
For many people, food is one of the few joys in life. Food should indeed be a pleasure, but... the physiological meaning of nutrition is much broader. Few people think about how amazingly food from our plate is converted into energy and building material, so necessary for the constant renewal of the body.
Our food is presented different products, which consist of proteins, carbohydrates, fats and water. Ultimately, everything we eat and drink is broken down in our body into universal, smallest components under the influence of digestive juices (a person secretes up to 10 liters of them 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 conveyor belt, on the well-coordinated operation of which our health depends. And the occurrence of “failures” leads to the formation of many forms of diseases.
Knowledge is great power, helping to prevent any violations. Knowledge of how our digestive system works should help us not only enjoy food, but also prevent many diseases.
I will act as a guide on a fascinating sightseeing tour, which I hope will be useful to you.
So, our various foods of plant and animal origin go through a long journey before (after 30 hours) the final products of its breakdown enter the blood and lymph and are integrated into the body. The process of food digestion is ensured by unique chemical reactions and consists of several stages. Let's look at them in more detail.
Digestion in the mouth
The first stage of digestion begins in the oral cavity, where food is crushed/chewed and processed by a secretion called saliva. (Up to 1.5 liters of saliva are produced daily.) In fact, the digestion process 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 pairs of salivary glands. It is 99% water and contains enzymes, the most important of which 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! Salivary enzymes do not act on either fats or proteins. For the process of breaking down carbohydrates it is necessary alkaline environment!
The composition of saliva also includes: lysozyme, which has bactericidal properties and serves as a local protective factor for the oral mucosa; and mucin, a mucus-like substance that forms a smooth, chewable bolus of food that is easy to swallow and transport through the esophagus into the stomach.
Why is it important to chew your food well? Firstly, in order to grind it well and moisten it with saliva, and start the digestion process. Secondly, in oriental medicine teeth are connected to energy channels (meridians) passing through them. Chewing activates the movement of energy through the channels. The destruction of certain teeth indicates problems in the corresponding organs and systems of the body.
We don't think about the saliva in our mouth and don't notice its absence. We often walk around for a long time with a feeling of dry mouth. And saliva contains a lot chemical substances, necessary for good digestion and preservation of the oral mucosa. Its release depends on pleasant, familiar smells and tastes. Saliva provides the taste of food. Molecules broken down in saliva reach 10,000 taste buds on the tongue, which can detect and distinguish sweet, sour, bitter, spicy and even in new food. salty tastes. This allows you to perceive food as a pleasure, an enjoyment of tastes. Without moisture we cannot taste. If the tongue is dry, then we don’t feel like we’re eating. Without saliva we cannot swallow.
Therefore, it is so important for healthy digestion to eat food in a calm environment, not “on the run,” in beautiful dishes, tasty prepared. It is important, without rushing and without being distracted by reading, talking or watching TV, to chew your food slowly, enjoying the variety taste sensations. It is important to eat at the same time, as this promotes secretory regulation. It is important to drink enough plain water at least 30 minutes before meals and an hour after meals. Water is necessary for the formation of saliva and other digestive juices, and the activation of enzymes.
It is difficult to maintain an alkaline balance in the oral cavity if a person constantly eats something, especially sweets, which always leads to acidification of the environment. After eating, it is recommended to rinse your mouth and/or chew something that tastes bitter, such as cardamom seeds or parsley.
And I also want to add about hygiene, cleaning teeth and gums. It was, and still is, a tradition among many peoples to brush their teeth with twigs and roots, which often have a bitter, astringent taste. And tooth powders also taste bitter. Bitter and astringent tastes are cleansing, have a bactericidal effect, and increase the secretion of saliva. While sweet taste, on the contrary, promotes the growth of bacteria and stagnation. But manufacturers of modern toothpastes (especially sweet children's ones) simply add antimicrobials and preservatives, and we turn a blind eye to it. In our area, the pine taste is bitter, tart/astringent. If children are not accustomed to sweet tastes, they will normally accept 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 in the mouth for long, and after it has been crushed by the teeth and processed by saliva, it passes through the esophagus into the stomach. Here it can stay for up to 6-8 hours (especially meat), digesting under the influence of gastric juices. The normal volume of the stomach is about 300 ml (about the size of a fist), however, after a large meal or frequent overeating, especially at night, its size can increase many times.
What does gastric juice consist 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-breaking) enzymes. Acid corrodes tissue. The mucous membrane of the stomach constantly produces a layer of mucus that protects against the action of acid and mechanical damage from coarse food components (when food is not sufficiently chewed and processed with saliva, when snacking on dry food on the go, simply swallowing). The formation of mucus and lubrication also depends on whether we drink enough plain water. During the day, about 2-2.5 liters of gastric juice are secreted, depending on the quantity and quality of food. During meals, gastric juice is released in maximum quantities and differs in acidity and enzyme composition.
Hydrochloric acid in pure form- this is a powerful aggressive factor, but without it the digestion process in the stomach will not occur. The acid promotes the transition of the inactive form of the gastric juice enzyme (pepsinogen) to the active form (pepsin), and also denatures (destroys) proteins, which facilitates their enzymatic processing.
So, proteolytic (protein-breaking) enzymes act mainly in the stomach. This is a group of enzymes that are active in different 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 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 final product of protein breakdown is an amino acid - a molecule capable of absorption into the blood. This process occurs in small intestine, and in the stomach it is carried out preparatory stage breaking down the protein into pieces.
In addition to proteolytic enzymes, gastric secretions contain an enzyme - lipase, which takes part in the breakdown of fats. Lipase works only with emulsified fats found in dairy products and is active in childhood. (You shouldn’t look for proper/emulsified fats in milk; they are also found in ghee, which no longer contains protein).
Carbohydrates in the stomach are not digested or processed because... the corresponding enzymes are active in an alkaline environment!
What else is interesting to know? Only in the stomach, thanks to the secretion component (Castle factor), does the transition of the inactive form of vitamin B12 supplied with food into the digestible form occur. The secretion of this factor may decrease or stop due to inflammatory damage to the stomach. Now we understand that it is not food enriched 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 left in the stomach for a long time, begin to ferment, which leads to acidification); from insufficient water consumption; from taking medications that both reduce acidity and dry out the gastric mucosa. This vicious circle can be broken correctly balanced food, drinking water and eating habits.
The production of gastric juice is regulated complex mechanisms, which I will not dwell on. I just want to remind you that one of them ( unconditioned reflex) we can observe when juices begin to flow just from the thought of a familiar delicious food, from smells, from the onset of the usual meal time. When something enters the oral cavity, the release of hydrochloric acid immediately begins with maximum acidity. Therefore, if after this food does not enter the stomach, the acid corrodes the mucous membrane, which leads to its irritation, erosive changes, even 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 other drink and run away in a hurry? We don’t think about our actions until “thunder strikes”, until it really hurts, because the acid is real...
The secretion of gastric juices is affected by the composition of food:
- fatty foods inhibit gastric secretion, as a result, food is retained in the stomach;
- the more protein, the more acid: consuming difficult-to-digest proteins (meat and meat products) increases the secretion of hydrochloric acid;
- carbohydrates in the stomach do not undergo hydrolysis; an alkaline environment is needed to break them down; carbohydrates that remain in the stomach for a long time increase acidity due to the fermentation process (therefore, it is important not to eat protein foods with carbohydrates).
The result of our incorrect attitude to nutrition is disturbances in the acid-base balance in the digestive tract and the appearance of diseases of the stomach and oral cavity. And here again it is important to understand that maintaining health and healthy digestion What will help is not drugs that reduce acidity or alkalize the body, but a conscious attitude towards what we are doing.
In the next article we will look at what happens to food in the small and large intestines.
Physiology of digestion.
Topic 6.5
Lecture No. 17 “Physiology of digestion. Metabolism and energy."
Plan:
1. Physiology of digestion.
Digestion in the mouth
Digestion in the stomach
Digestion in the small intestine
Digestion in the large intestine
2. General concept about metabolism and energy.
3. Metabolism of proteins, fats and carbohydrates.
4. Water-salt metabolism. The importance of vitamins.
Food in the form in which it enters the body cannot be absorbed into the blood and lymph and be used to perform various functions, so it is subjected to mechanical and chemical processing.
Mechanical and chemical treatment food and its conversion into substances digestible by the body is called digestion.
Let's look at digestion in each section of the gastrointestinal tract.
Digestion in the oral cavity.
Food is retained in the oral cavity for no more than 15-20 seconds, but despite this, mechanical and chemical processing occurs.
Mechanical restoration carried out by chewing.
Thorough grinding of food plays a role important role:
1) facilitates subsequent digestion and absorption.
2) stimulates salivation
3) affects the secretory and motor activity of the gastrointestinal tract.
4) ensures the formation of a digestive bolus suitable for swallowing and digestion.
Chemical treatment food is carried out with the help of salivary enzymes - amylase and maltase, which act on carbohydrates, subjecting them to partial digestion.
0.5-2.0 liters of saliva are released per day; it consists of 95.5% water and 0.5% dry matter, and has an alkaline reaction (pH = 5.8 - 7.4).
Dry residue consists of organic and inorganic substances. Inorganic substances in saliva contain potassium, chlorine, sodium, calcium, etc.
Of the organic substances in saliva there are:
1) enzymes: amylase and maltase, which begin to act on carbohydrates in the oral cavity;
2) mucin - a protein mucous substance that gives saliva viscosity, glues the food bolus and makes it slippery, facilitating the swallowing and passage of the bolus through the esophagus;
3) lysozyme - a bactericidal substance that acts on microbes.
Digestion in the stomach.
The bolus of food enters the stomach from the esophagus, where it remains there for 4-6 hours.
During the first 30-40 minutes after food enters the stomach, the salivary enzymes amylase and maltase act on it, continuing to break down carbohydrates. As soon as the food bolus is saturated with acidic gastric juice, chemical treatment begins, under the influence of:
1) proteolytic enzymes (pepsinogen, gastrixin, chymosin), which break down proteins into simpler ones;
2) lipolytic enzymes - gastric lipases, which break down fats into simpler ones.
In addition to chemical processing, mechanical processing of food occurs in the stomach, which is carried out by the muscular layer.
Due to the contraction of the muscular membrane, the food bolus is saturated with gastric juice.
All period gastric secretion normally lasts 6 – 10 hours and is divided for 3 phases:
1 phase– complex reflex (brain) lasts 30-40 minutes, and is carried out on a mixture of conditioned and unconditioned reflexes.
The secretion of gastric juice is caused by the sight, smell of food, sound stimuli associated with cooking, i.e. olfactory, visual and auditory receptors are irritated. Impulses from these receptors enter the brain - the food center (the medulla oblongata) and along the nerves to the glands of the stomach.
2 phase– gastric (chemical) lasts 6-8 hours, that is, while the food is in the stomach.
3 phase- intestinal lasts from 1 to 3 hours.
Digestion in the small intestine.
The food mass in the form of gruel from the stomach enters in separate portions into the small intestine and is subjected to further mechanical and chemical processing.
Mechanical restoration consists in the pendulum-like movement of food gruel and mixing it with digestive juices.
Chemical treatment- this is the effect of pancreatic, intestinal juice and bile enzymes on food gruel.
Under the influence of pancreatic juice enzymes (trypsin and chymotrypsin), intestinal juice enzymes (cathepsin and aminopeptidase), polypeptides are broken down into amino acids.
Under the influence of the enzymes amylase and maltase, intestinal and pancreatic juices break down complex carbohydrates (disaccharides) into simpler ones - glucose.
The breakdown of fats occurs under the influence of enzymes - lipase and phospholipase of intestinal and pancreatic juices to glycerol and fatty acids.
The most intensive chemical processing occurs in the duodenum, where food is affected by pancreatic juice and bile. In the remaining parts of the small intestine, the process of splitting nutrients ends under the influence of intestinal juice and the absorption process begins.
In the small intestine, depending on the localization of the digestive process, there are:
cavity digestion - in the lumen of the small intestine;
parietal digestion.
Cavity digestion carried out due to digestive juices and enzymes that enter the cavity of the small intestine (pancreatic juice, bile, intestinal juice) and here act on nutrients. Large-molecular substances are broken down according to the type of cavity digestion.
Parietal digestion is provided by microvilli of the intestinal epithelium and is the final stage digestion of food, after which absorption begins.
Suction- This is the passage of nutrients from the digestive canal into the blood and lymph.
Absorption occurs through villi on the mucous membrane of the small intestine.
Water, mineral salts, amino acids, and monosaccharides are absorbed into the blood.
Glycerin is well absorbed into the lymph, and fatty acid, are insoluble in water, and in this form cannot be absorbed, so they are first combined with alkalis and converted into soaps, which dissolve well and are absorbed into the lymph.
Digestion in the large intestine.
The main function of the large intestine is:
1) water absorption
2) formation of feces
Nutrient absorption is negligible.
The secretion of the colon mucosa has an alkaline reaction.
The secretion contains a significant amount of rejected epithelial cells, lymphocytes, mucus, and contains a small amount of enzymes (lipase, amylose, etc.) because little undigested food mass enters this department.
Microflora plays a significant role in the digestion process - coli and lactic acid fermentation bacteria.
Bacteria perform both beneficial and negative functions for the body.
Positive role bacteria:
1. Lactic acid fermentation bacteria produce lactic acid, which has antiseptic properties.
2. Synthesize B vitamins and vitamin K.
3. Inactivate (suppress) the action of enzymes.
4. Suppress the proliferation of pathogenic microbes.
Negative role of bacteria:
1. They form endotoxins.
2. Cause fermentation and putrefactive processes with the formation of toxic substances.
3. When bacteria change in quantitative and species ratio, a disease may occur - dysbacteriosis.
