3. Digestive system The dog's body is built from complex organic substances - proteins, carbohydrates, fats. The most important of these is protein. In addition to these organic substances, the body also contains inorganic substances - salts and a large amount of water (from 65 to

5. Blood and lymph circulatory system Cells of the body require constant delivery of nutrients and removal of unnecessary and harmful substances - the products of their vital activity. These functions in the body are performed by the blood and lymph circulatory system. System

6. Urinary organ system In the process of constantly occurring metabolism in the body, waste products of cell nutrition and mainly protein breakdown products that are harmful to the body are formed. In addition, substances that are not harmful accumulate in the body, but

7. System of reproductive organs Reproduction is one of the most important functions of the body and ensures procreation. To perform functions related to reproduction, dogs use the reproductive apparatus. The reproductive apparatus of a male dog. The male reproductive system consists of

8. System of internal secretion organs Internal secretion organs are glands that produce and release special substances - hormones - directly into the blood. A characteristic feature of hormones is their ability to exert

Respiratory diseases V. A. Lipin

Examination of the respiratory system To determine respiratory disease when examining a dog, the following methods are used: inspection, palpation, percussion and auscultation. Additional methods include X-ray examination. By inspection

Chapter IX The respiratory system, nose and sinuses The air we breathe Clean, fresh air nourishes the lungs and cleanses the soul - just as good nutrition provides vital energy to the body (it is no coincidence that the words “soul” and “breath” come from the same root in all languages) .

Topic 8. AGE FEATURES OF THE RESPIRATORY ORGANS 8.1. Structure of the respiratory organs and vocal apparatus. Nasal cavity. When you breathe with your mouth closed, air enters the nasal cavity, and when you breathe open, it enters the oral cavity. Bones and cartilages are involved in the formation of the nasal cavity, of which

8.1. Structure of the respiratory organs and vocal apparatus. Nasal cavity. When you breathe with your mouth closed, air enters the nasal cavity, and when you breathe open, it enters the oral cavity. The formation of the nasal cavity involves bones and cartilage, which also make up the nasal skeleton. Most of

Nasal cavity. The anterior portion of the nose in dogs is easily movable; its posterior border runs approximately at the level of the canine, and the free end protrudes somewhat forward, beyond the body of the incisor bones. The movable section has a cartilaginous skeleton, slightly expanding towards the free end (Fig. 336). The cartilaginous nasal septum thickens towards the oral edge and forms small paired (dorsal and ventral) lateral nasal cartilages (2, 3).
The dorsal lateral cartilage curves and hangs from the dorsal edge of the nasal septum. It is thin, long and the convex side is directed outward. Towards the oral (free) end it becomes shorter and forms the frame of the upper wing of the nose. The ventral lateral cartilage begins from the lower edge of the septum. It is smaller, but much thicker than the dorsal one and is also convex outward. It does not reach the very anterior end of the nasal septum, since there lies additional cartilage in the form of a triangular plate (4); it serves as the skeleton of the medial wing of the nose.
The nasal area (Fig. 362) is covered with normal hairy skin with its inherent sebaceous and sweat glands. Only in the anterior area - the nasal mirror - does it change greatly, as it loses hair and any glands; The epidermis here is of considerable thickness and is divided from the surface by many grooves into small fields of the speculum. The nasal speculum covers the top of the nose on all sides, without, however, descending onto the upper lip; on its front surface, along the midsagittal line, there is a groove, or filter, of different depths in different rocks. The nasal mirror in healthy animals is moistened and, due to the constant evaporation of fluid, is always somewhat cooled.

The dog is a typical representative of the wolf family (Canidae), a predatory animal; Under natural conditions, it is active at dusk. The body structure is adapted to an active lifestyle. The skeleton is characterized by great strength and relative lightness. When walking, the dog relies on its toes. The claws are blunt and strong, non-retractable.

The respiratory system of a dog has a structure typical of mammals. Air enters the nasal cavity through the nostrils, where it is heated and cleared of the bulk of dust. The anterior portion of the nose in dogs is easily movable. The cartilaginous nasal septum thickens towards the oral edge and forms small (dorsal and ventral) lateral cartilages.

The area of ​​the nose is covered with normal hairy skin, but in the anterior section (nasal mirror) it is devoid of hair, so the epidermis here is of considerable thickness and is divided from the surface by many grooves into small fields of the mirror. In the nasal cavity there are the dorsal and ventral conchae, and in its posterior-superior section there are curls of the labyrinth of the ethmoid bone.

The lining of the nasal cavity contains a mass of cells associated with the recognition of odors. The nasal cavity is followed by the nasopharynx and larynx, which is a complex cartilaginous formation. The larynx is relatively wide and almost square in shape.

Elastic fibers of the vocal cords are stretched between the cartilages of the larynx, their vibrations create sounds. Dogs can make a wide variety of sounds: barking, howling, growling, squealing, snorting, whining. The tonality of sounds changes significantly. Different sound signals carry information about the dog’s intentions, its emotional state, that is, they have some functions of language. Dogs widely use sound signals in communication, understanding each other perfectly. If desired, an observant owner can also learn to understand his pet perfectly.

The lower part of the dog's larynx passes into the trachea, which splits into two bronchi that pass into the lungs. The trachea consists of 42 - 46 rounded rings. The lungs themselves are a paired hollow organ divided into lobes. Each lobe, in turn, is divided into smaller lobules consisting of vesicles (alveoli).

The left lung has three lobes - apical, cardiac and diaphragmatic. The right lung has four lobes - apical, accessory, cardiac and diaphragmatic. In the alveoli of the lungs, air oxygen passes into the blood, combines with the hemoglobin of red blood cells and is transported to organs and tissues; venous blood is freed from carbon dioxide, which is removed from the body with exhaled air.

The cardiac notch, which is located between the 3rd and 7th ribs, leaves the ventral part of the heart uncovered.

The entire inner surface of the lungs is lined with a layer of mucus-covered cells. The mucus deposits dust particles and gradually carries them out. However, the self-cleaning capabilities of the lungs are not limitless - in heavily dusty and smoky air, solid particles, settling, gradually clog individual alveoli and thereby weaken the respiratory function

4. Respiratory system

Respiration is the process by which the body absorbs oxygen and releases carbon dioxide. This vital process involves the exchange of gases between the body and the surrounding atmospheric air. When breathing, the body receives the oxygen it needs from the air and removes the carbon dioxide accumulated in the body. The exchange of gases in the body must occur continuously. Stopping breathing for even a few minutes results in the death of the animal. Breathing is externally manifested by a series of alternating expansions and contractions of the chest. The breathing process is composed of: air exchange between the lungs and atmospheric air, gas exchange between the lungs and blood - external, or pulmonary, respiration, and gas exchange between blood and tissues - internal, or tissue, respiration. Breathing is carried out by an organ system, or respiratory apparatus. It consists of the airways - the nasal cavity, larynx, trachea and lungs. The chest also participates in the act of breathing.

Nasal cavity. The nasal cavity is the first section of the airways. The bony basis of the nasal cavity is the facial bones, the ethmoid bone and the anterior edge of the sphenoid and frontal bones. Inside, the nasal cavity is divided into two halves by the nasal septum. Its anterior part is cartilaginous, and its posterior part is bone. The nasal cavity begins with two, somewhat split below, openings called nostrils. The walls of the nostrils are formed by lateral cartilages that extend from the front of the nasal septum. These cartilages prevent the walls of the nostrils from collapsing when inhaling. Between the nostrils there is an area of ​​skin with a rough, slightly bumpy surface (usually black), devoid of hair, called the nasal planum. The movable part of a dog's nose is called the lobe. In a healthy dog, the nasal mucosa is always somewhat moist and cool.

In each half of the nasal cavity there are thin, spirally curved bone plates - the nasal turbinates. They divide the nasal cavity into three passages - lower, middle and upper. The lower nasal passage is narrow at first, but becomes wider posteriorly and merges with the middle passage. The upper passage is narrow and shallow. The lower and middle nasal passages serve for the passage of air during quiet breathing. When you inhale deeply, does the air stream reach the upper nasal passage? where the olfactory organ is located (Fig. 48).

The initial part of the nasal cavity is covered with flat, stratified epithelium, which in the deeper parts turns into columnar, ciliated epithelium. The latter is characterized by the fact that at the free end of the cell there are bundles of thin mobile filaments called cilia or ciliated hairs, which is where the name epithelium comes from.

Passing through the nasal cavity, the air warms up (up to 30-32°) and is cleared of foreign mineral and organic particles suspended in it. This is facilitated by the large surface of the folded mucous membrane, covered with ciliated epithelium, the purpose of which is to trap small particles of air dust with the movement of its cilia, which are then released from the nose with mucus. Irritation of the eyelashes causes sneezing.

In the olfactory region of the mucous membrane there are cells of special sensitivity, the so-called olfactory cells. Irritation by particles of odorous substances causes the sensation of odor. This part of the nasal cavity serves as the organ of smell.

Larynx. The inhaled air, heading from the nasal cavity to the trachea, passes through the larynx. The larynx lies under the entrance to the esophagus, communicating with the nasal cavity through the nasopharynx. The larynx consists of five cartilages connected to each other by muscles and ligaments. One of these cartilages, enclosing the entrance to the trachea in a ring, is called annular or cricoid, the other is called thyroid, and the two located above are called arytenoid. The anterior cartilage that projects into the pharynx is called the epiglottis.

The laryngeal cavity is lined with mucous membrane covered with ciliated epithelium. Irritation of the mucous membrane of the larynx causes a cough. On the inside of the larynx, the mucous membrane forms folds based on the vocal cords and muscles. The vocal cords, with their free ends directed towards each other, limit the glottis. When the muscles contract, the vocal cords tighten and the glottis narrows. The strong exhalation movement of air causes the tense vocal cords to vibrate, resulting in the creation of sound (voice).

Trachea, or windpipe. The trachea is a tube consisting of annular cartilaginous plates (a type of corrugated gas mask tube). In dogs, the trachea has an almost cylindrical shape. The ends of the cartilaginous plates do not reach each other. They are connected by a flat transverse ligament, which protects them from damage when pressed, for example, by a collar. From the side of this ligament, the trachea is adjacent to the esophagus located above it. The mucous membrane lining the trachea is covered with ciliated epithelium, between the cells of which individual mucous glands are scattered. The cilia of the ciliated epithelium oscillate towards the larynx, due to which the secreted mucus, and with it small particles of dust, are easily removed from the trachea (Fig. 49).

When there is a significant accumulation, they are expelled by coughing impulses.

Lungs. A dog has two lungs - right and left. The lungs lie in the chest cavity, occupying it almost completely and are supported in their position by the bronchi, blood vessels and fold of the pleura. Each lung is divided into three lobes - apical, cardiac and diaphragmatic. The dog has an additional lobe in the right lung (Fig. 50 and 51).

The structure of the lungs is as follows. The trachea, entering the chest cavity, is divided into two large bronchi, which enter the lungs. In the lungs, the bronchi branch into smaller branches and approach the so-called respiratory lobules in the form of terminal bronchi. Entering the lobules of the lung, each bronchus is divided into branches, the walls of which protrude into a large number of small sacs called pulmonary alveoli. It is in these alveoli that gas exchange occurs between air and blood.

The pulmonary artery approaches the lungs from the heart. Entering the lungs, it branches parallel to the bronchi and gradually decreases in size. In the lobules of the lung, the pulmonary artery forms a dense network of tiny capillary vessels surrounding the surface of the alveoli. Rice. 51. Cast of two lobes of bronchi. Having passed the alveoli, the capillaries, merging into larger vessels, form the pulmonary veins, running from the lungs to the heart.

Thoracic cavity. The chest cavity has the shape of a cone. Its lateral walls are the skeleton of the chest with the intercostal muscles, the diaphragm is located at the back, and the cervical muscles, blood vessels and nerves are at the front.

The chest cavity is lined with a serous membrane called the parietal pleura. The lungs are also covered by a serous membrane called the pulmonary pleura. Between the parietal and pulmonary pleura there remains a narrow gap filled with a small amount of serous fluid. In this narrow gap there is negative pressure, as a result of which the lungs are always in a somewhat stretched state and are always pressed close to the chest wall and follow all its movements.

In addition to the lungs, the thoracic cavity contains the heart and the esophagus, blood vessels and nerves.

Breathing mechanism. To inhale, the chest cavity must expand. The intercostal muscles contract and raise the ribs. In this case, the middle of the ribs rises upward and moves away somewhat from the midline, and the sternum, motionlessly connected to the ends of the ribs, follows the movement of the ribs. This increases the volume of the chest cavity. The expansion of the thoracic cavity is also facilitated by the movement of the diaphragm. In a calm state, the diaphragm forms a dome, the convex part of which is directed towards the chest cavity. When inhaling, this dome becomes flatter, the edges of the diaphragm adjacent to the chest wall move away from it, and the chest cavity increases. With each expansion of the chest, the lungs passively follow its walls and expand with the pressure of the air in the alveoli. The pressure of this air, due to the increase in the volume of the alveoli, becomes less than atmospheric pressure, as a result of which outside air rushes into the alveoli and inhalation occurs.

After inhalation comes exhalation. During exhalation, the muscles of the chest and diaphragm relax. The costal ligaments and cartilages, due to their elasticity, tend to return to their previous position. The abdominal organs (liver, stomach), pushed aside by the diaphragm during inhalation, return to their normal position. All this causes a decrease in the chest cavity, the walls of which begin to put pressure on the lungs, and they collapse. In addition, the lungs collapse due to their elasticity, and at the same time the air pressure in them becomes greater than atmospheric pressure, which creates conditions that promote the pushing of air from the lungs outward - exhalation occurs. With increased exhalation, the abdominal muscles are also actively involved. They push the abdominal organs toward the chest, which increases pressure on the diaphragm.

When exhaling, the lungs are not completely freed from the air they contain, which is called residual air.

There are three types of breathing: abdominal, thoracic and costo-abdominal. In a calm state, a dog's breathing type is abdominal. With deep breathing, it becomes costo-abdominal. Chest breathing occurs only with shortness of breath.

The respiratory rate, i.e. the number of inhalations and exhalations per minute, in a dog in a calm state ranges from 14 to 24. Depending on various conditions (pregnancy, age, internal and external temperature), the respiratory frequency may vary. Young dogs breathe more quickly. The dog's breathing rate increases greatly during heat and during muscular work.

Respiratory movements are regulated by the respiratory center located in the medulla oblongata. Excitation of the respiratory center occurs predominantly automatically. An excess of carbon dioxide appears in the blood washing it, which excites the cells of the respiratory center. This creates a unique system of self-regulation of breathing. On the one hand, the accumulation of carbon dioxide causes increased ventilation of the lungs and promotes the removal of carbon dioxide from the blood. On the other hand, when increased ventilation of the lungs leads to saturation of the blood with oxygen and a decrease in the carbon dioxide content in it, the excitability of the respiratory center decreases and breathing is delayed for some time. The sensitivity of the respiratory center is very great. Breathing changes sharply during muscular work, when the products of muscle metabolism (lactic acid) do not have time to oxidize and enter the blood in significant quantities, stimulating the respiratory center. Excitation of the respiratory center can also occur by reflex, that is, as a result of excitation of peripheral nerves going to the medulla oblongata. For example, painful sensations can cause a short cessation of breathing, followed by prolonged wheezing, sometimes accompanied by a groan or bark. A short cessation of breathing also occurs when the end is exposed to cold, for example, when immersed in cold water.

Exchange of gases in the lungs and tissues. The exchange of gases in the lungs and tissues occurs due to diffusion. The essence of this physical phenomenon is as follows: the air entering the alveoli of the lungs contains more oxygen and less carbon dioxide than the blood flowing to the lungs. Due to the difference in gas pressure, oxygen will pass through the walls of the alveoli and capillaries into the blood, and carbon dioxide will pass in the opposite direction. Therefore, the composition of exhaled and inhaled air will be different. Inhaled air contains 20.9% oxygen and 0.03% carbon dioxide, and exhaled air contains 16.4% oxygen and 3.8% carbon dioxide.

Oxygen entering the blood from the alveoli of the lungs is distributed throughout the body. The cells of the body are in dire need of oxygen and suffer from excess carbon dioxide. Oxygen in cells is consumed for oxidative processes, so there is less oxygen in cells than in blood. Carbon dioxide, on the contrary, is constantly formed and there is more of it in the cells than in the blood. Due to this difference between blood and tissues, gas exchange or so-called tissue respiration occurs.

The connection between the respiratory organs and the functions of other organs. The respiratory organs are closely related to the circulatory system. The heart lies next to the lungs and is partially covered by them. Constant ventilation of the lungs during breathing cools the heart muscle and protects it from overheating.

Breathing movements of the chest promote blood circulation.

The respiratory organs are closely related to digestion. When breathing, the diaphragm puts pressure on the abdominal organs and especially on the liver, which promotes better secretion of bile. The diaphragm helps the act of defecation. Breathing is also closely related to muscles. Even slight muscle tension causes increased breathing.

The respiratory organs serve as an important factor in thermoregulation.

The dog's respiratory organs are represented by the upper respiratory tract and lungs. The upper respiratory tract includes the nostrils, nasal passages and cavities, nasopharynx, larynx, trachea and major bronchi. The inhaled air, passing through them, is subjected to thermoregulation and purification from mechanical particles (dust). The mucous membrane lining the upper respiratory tract has bactericidal properties. Therefore, microbes die in the upper respiratory tract, and sterile air enters the lungs.

For dogs, the function of chemical analysis of inhaled air is of particular importance. The receptor apparatus of the olfactory organs is located in the nasal passages. Before taking a deep breath, the dog takes frequent shallow breaths, during which the air is in continuous contact with the receptor apparatus, and the animal receives rich information about the external environment. This behavior is especially noticeable in dogs in unfamiliar surroundings. Obviously, a dog trusts his sense of smell more than a human. During a walk, the dog walks around “its” territory, evaluates it with the help of its olfactory organs, not forgetting to leave scent marks.

The mechanism of inhalation and exhalation occurs due to the contraction of the respiratory muscles - the diaphragm and the muscles of the chest. When inhaling, the external intercostal muscles and the diaphragm contract.

The volume of the chest increases, due to the vacuum in the pleural cavity, the lungs stretch, and air passively fills them. When the respiratory muscles relax, the chest decreases in volume and air is squeezed out of them. Exhalation occurs.

The frequency of respiratory movements is regulated by the central nervous system, the functional activity of which depends on the concentration of carbon dioxide, oxygen and blood pH. At rest, medium and large dogs make 10-30 movements, small animals breathe more often.

Gas exchange itself occurs in the lungs as a result of the difference in the partial pressure of oxygen and carbon dioxide. The partial pressure of oxygen is higher in the alveolar air, so it passes into the blood. In the case of carbon dioxide, the picture is the opposite: in venous blood the partial pressure of CO 2 is higher than in the alveolar air, and carbon dioxide actively passes from the blood into the alveoli of the lung tissue.

Oxygen transport in the blood occurs with the help of hemoglobin in red blood cells, and carbon dioxide transport occurs with the help of carbonates and bicarbonates in the blood plasma.

NON-RESPIRATORY FUNCTIONS OF THE RESPIRATORY ORGANS

Along with the inhaled air, foreign or even harmful substances and particles can enter the respiratory system in the form of aerosols or gases. However, after contact with the mucous membrane of the upper respiratory tract, most of them are removed from the body. The depth of penetration of foreign air components depends on the size of these particles. Large particles (dust), the size of which exceeds 5 microns, are deposited on the mucous membrane due to inertial forces in places where the bronchi bend. Heavy particles cannot go around the bend of the bronchi and, due to inertia, hit the wall of the bronchus. Using the same scheme, the air is also freed from particles ranging in size from 0.5 to 5.0 microns. However, this process already occurs in the bronchioles of the lungs. Particles smaller than 0.5 microns penetrate the alveoli of the lungs and penetrate the mucous membrane of the respiratory epithelium.

The nature of breathing has a great influence on the retention of foreign particles in the upper respiratory tract of a dog: when it is slow and deep, microparticles penetrate into the lungs; when it is frequent and superficial, it helps to cleanse the air in the upper respiratory tract.

Thus, particles adsorbed on the mucous membrane of the upper respiratory tract are expelled towards the nasopharynx or nasal passages due to the oscillatory movements of the ciliated epithelium. Then they are either swallowed or thrown out into the external environment due to a sharp exhalation (sneezing). In the pulmonary alveoli, foreign particles undergo phagocytosis by macrophages. Bacterial cells are exposed to bactericidal substances in the mucus of the pulmonary epithelium (complement system, opsonins, lysozyme). As a result, all corpuscular particles are destroyed or transported by macrophages outside the respiratory organs.

Lung macrophages are adapted to the conditions of the alveoli, that is, they are active in an oxygen-rich environment. Therefore, hypoxia suppresses phagocytosis in the lungs. Stressing an animal is also accompanied by a decrease in the protective properties of the respiratory organs, since corticosteroids suppress the activity of macrophages. A viral infection leads to a similar result. Alveolar macrophages constitute the dog's front line of defense. In the case when a large number of corpuscular particles are inhaled, other phagocytes come to the aid of macrophages - primarily blood neutrophils.

However, with excessive activity of phagocytes, the reactive oxygen radicals and proteolytic enzymes they release can damage the epithelium itself, lining the pulmonary alveoli. To restrain the excessive activity of phagocytes, protease inhibitors (α-antitrypsin) and antioxidants (glutathione peroxidase) enter the mucus of the pulmonary epithelium. These substances protect the lungs from the damaging effects of the respiratory system's own protective system.

The penetration of harmful gases in the respiratory air into the dog’s body depends on their concentration and solubility. Gases with high solubility (for example SO 2) in small concentrations are retained in the nasal cavities due to adsorption on the mucous membrane, but in large concentrations they penetrate into the lungs.

Gases with low solubility reach the pulmonary alveoli in an unchanged state. However, toxic gases stimulate protective mechanisms such as bronchospasm, hypersecretion of mucus, coughing and sneezing, which block their diffusion or provide mechanical removal from the respiratory system.

Having a huge area of ​​capillaries (a reactive surface with fixed enzymes), a high oxygen supply and a developed cellular antitoxic system, the lungs are an ideal place for thoroughly purifying the blood from biologically active and, therefore, potentially dangerous metabolites. Thus, the endothelial cells of the pulmonary capillaries absorb the entire volume of serotonin produced in the dog’s body. A number of prostaglandins, bradykinin and angiotensin are also metabolized here. Neutrophils found in the lungs ensure the destruction of leukotrienes.

Macrophages of the respiratory organs are related to the regulation of fat metabolism. The fact is that blood with a high level of lipids enters the lungs. High lysing activity of macrophages in relation to lipoproteins entering the body with lymph from the gastrointestinal tract was noted. As a result of the absorption of lipoproteins by macrophages, the latter increase in size (mast cells), and the blood is cleared of excess fatty substances. With active blood flow and hyperventilation of the lungs (physical activity), excess fat is oxidized and removed from the body in the form of thermal energy with exhaled air.

Dogs breathe differently in high temperatures - shortness of breath is a normal physiological phenomenon. The respiratory rate under these conditions can exceed 100 per minute. The physiological meaning of shortness of breath is hyperventilation of the upper respiratory tract and lungs in order to increase evaporation from the mucous membrane. The evaporation of moisture is accompanied by cooling of the surface of the upper respiratory tract and lungs and the blood flowing to them. Consequently, in dogs, the respiratory organs also perform the function of thermoregulation in conditions of elevated temperatures.

Thus, the physiological role of the dog’s respiratory organs is not limited to gas exchange. The dog's respiratory system is involved in immune reactions, metabolism, and thermoregulation of the body.

FEATURES OF THE DIGESTIVE SYSTEM

The digestive system is one of the most flexible physiological systems, which ensures relatively rapid adaptation of animals to a wide variety of sources of proteins, fats and carbohydrates. The dog is an omnivore, although its ancestors were mainly predators. The dog's digestive system has been studied in great detail. She has a rather short gastrointestinal tract, well adapted to use mixed diets, including both animal and plant foods.

The dog grabs food using its incisors. Mechanical processing of food in oral cavity quite superficial: the animal cuts the meat into large pieces, crushes them with its molars and swallows, i.e., the food is not thoroughly crushed in the dog’s mouth.

If the dog is very hungry, then it can swallow very large pieces, practically without chewing them. True, often after such a meal the dog regurgitates the contents of the stomach and chews the food again.

It is believed that the dog grasps food using the incisors, the premolars and molars (especially the 4th upper and 5th lower) provide crushing. Fangs are a killing weapon for hunters and a fighting weapon in fights for other dogs.

The age of dogs is determined by their teeth. The first baby teeth appear in puppies at the age of two weeks. A full set of baby teeth is formed (depending on the breed) at the age of 1-2 months. For example, in German Shepherd puppies, at the age of 5-6 weeks, all baby teeth are counted. And in Miniature Schnauzer puppies, a full set of teeth is formed later - at 7-9 weeks of age.

Normally, by the age of 6 months, all baby teeth are replaced with permanent ones. Starting from 12-18 months of age, noticeable tooth wear begins, and this phenomenon occurs at the same speed in most dogs, i.e. it is a general biological phenomenon. There is a prejudice that the degree of tooth wear determines the nature of nutrition. In particular, bones speed up this process. Our personal experience with dogs suggests the opposite: bones strengthen the jaws and improve blood supply to the gums.

The basis for determining the age of a dog is the rate of abrasion, primarily of the upper edge of the incisors. So, by the 2nd year of life, the teeth at the hooks wear out; to the 3rd - this process captures the middle incisors; by the 4th - the teeth disappear on the edges; by the 5th year of life, the teeth are visible only on the upper edges; by the age of 10, the incisors have a reverse oval edge; by 12, some incisors begin to fall out; By 14, canines, premolars and molars begin to fall out. The above diagram is quite approximate, and individual individuals do not fit into it. Thus, the 15-year-old Mittelynna-utser known to us can be given no more than 2 years of age based on the pattern of tooth abrasion.

In addition to mechanical processing, food in the oral cavity is exposed to saliva. Three large paired salivary glands open into the oral cavity - the parotid, submandibular and sublingual. In addition, on the dog's tongue, cheeks and lips there are multiple small salivary glands that secrete mucus.

Dogs salivate when they see, smell, or eat food. Salivation is especially strong in dogs when they chew something, such as a bone. The total amount of saliva per day reaches 1 liter in a medium-sized dog. However, the level of salivation is highly dependent on the moisture content of the feed. Dry food like “Chapi” produces more saliva than liquid soup.

Under the influence of saliva, the dry food is moistened and the food bolus becomes slimy. Moistening of the feed is provided mainly by the saliva of the parotid glands - it is quite liquid. The saliva of the submandibular and sublingual glands is mixed, that is, it wets and licks food. Small mucous glands secrete saliva containing a mucus-like substance - mucin.

After this treatment, the food lump is easily swallowed by the animal. Saliva contains glycolytic enzymes, i.e. enzymes that act on the carbohydrate part of the feed. Therefore, carbohydrate food is partially broken down in the dog’s mouth. But taking into account the short duration of the food’s stay in the dog’s mouth, a deep transformation of carbohydrates in the dog’s mouth is unlikely.

Dog saliva is highly bactericidal due to the presence of lysozyme, a substance that can destroy the bacterial cell wall. Consequently, in the oral cavity the food is partially disinfected under the action of saliva. The same reason underlies the high effectiveness of dog licking wounds. By licking a wound on the body, the dog cleans it of dirt, performs bactericidal treatment of the wound and, in addition, due to salivary kinins, increases the rate of blood clotting in damaged vessels.

The stomach of dogs is simple, single-chamber, only partial digestion of food occurs in it, and only proteins and emulsified fats undergo deep transformation.

Digestion in the dog's stomach occurs under the influence of gastric juice, which includes hydrochloric acid, enzymes, minerals and mucus. The secretion of gastric juice is carried out according to certain laws, which at one time were studied in detail by our outstanding compatriot, Nobel Prize laureate in physiology I. P. Pavlov.

In accordance with modern concepts, the secretion of gastric juice occurs in three phases.

First phase- nervous. The sight and smell of food leads to the release of so-called inflammatory gastric juice. Nervous excitement associated with the anticipation of food leads to the fact that nerve impulses from the central nervous system excite the intramural nervous system of the stomach, which, in turn, stimulates the secretion of gastrin and hydrochloric acid by the cells of the gastric wall. Gastrin stimulates the nerve endings of the intramural nervous system of the stomach, which leads to the release of acetylcholine. Acetylcholine paired with gastrin excites the lining cells of the digestive glands of the stomach, which causes even greater secretion of HCL.

Second phase- neuro-humoral - is ensured by ongoing nervous stimulation, irritation of the receptor apparatus of the stomach and absorption of extractive substances of feed into the blood. A complex of enzymes as part of gastric juice is secreted into the lumen of the stomach.

Third phase gastric juice secretion is purely humoral. It develops as a result of the absorption of hydrolysis products of proteins and fats into the blood.

While gastrin is being secreted, the pH value of the gastric chyme is constantly decreasing. When the pH reaches 2.0, inhibition of gastrin secretion begins. At pH 1.0, gastrin secretion stops. At such a low pH value, the pyloric sphincter opens and gastric chyme is evacuated in small portions into the intestine.

A dog's gastric juice contains many proteolytic enzymes: several forms of pepsin, cathepsin, gelatinase, chymosin elastase (the latter is found in large quantities in the gastric juice of suckling puppies). All these enzymes break the internal bonds of long protein chains of food. The final fragmentation of protein molecules occurs in the small intestine.

The role of the stomach in fat digestion is limited to emulsified fats. Fat emulsion is a mixture of tiny fat particles and water molecules. The prevalence of fat emulsions in dog foods is very limited. An example of emulsification of fats is only whole milk. Therefore, gastric lipase is most active in puppies during the suckling period. In adult dogs, there is virtually no digestion of fats in the stomach. Moreover, fatty foods also inhibit gastric digestion of proteins.

IN thin department intestines All feed nutrients - proteins, fats, carbohydrates - undergo deep breakdown. Pancreatic enzymes, intestinal juice and bile are involved in this process.

Here, in the small intestine, absorption of hydrolysis products occurs. Proteins are broken down and absorbed in the form of amino acids, carbohydrates - in the form of monosaccharides (glucose), fats - in the form of fatty acids, mono-glycerides and glycerol.

In a dog large intestineka relatively short. Nevertheless, it has its own irreplaceable functions. In particular, the absorption of water and mineral salts dissolved in it occurs in the large intestine. In the large intestine, although limited, under conditions of poor nutrition, the vital synthesis of B vitamins and essential amino acids occurs.

It should be said that biologically active substances synthesized in the colon by symbiotic microbes can no longer be absorbed practically in this part of the intestine. Consequently, this synthesis makes biological sense only in cases of autocaprophagy, i.e., eating one’s own excrement during forced starvation of dogs.

The large intestine in its wall has a huge number of lymphoid formations, which are related to the body's immune defense, for example, the formation of |3-lymphocytes.

Bowel motor function very pronounced in dogs. It is represented by three types of contractions - worm-shaped, pendulum-shaped, segmenting peristalsis and antiperistalsis. Worm-like peristalsis ensures the movement of food gruel through the digestive tube. Pendulum-shaped and segmenting - mixing chyme with digestive juices. Antiperistalsis for a dog is an absolutely normal phenomenon:

when the stomach is full, the dog is freed from excess food;

when consuming cartilage and bones, secondary, more thorough processing is often required, which is what the dog does after belching.

The following behavior can be observed in many lactating bitches with a highly developed maternal instinct: the dog clearly eats more than it can, and then regurgitates food for the puppies.

A medium-sized lactating female ate almost a bucket of food waste in the backyard of one cafeteria. Then she moved with great difficulty towards her kennel (while her stomach was literally dragging along the ground). Finally reaching the kennel, she vomited the contents of her stomach onto the puppies. Thus, using her own stomach for transportation, she created a large supply of food for the puppies. Moreover, the regurgitated food mass also seemed more preferable for adult members of the dog pack compared to unprocessed food.

The gastronomic preferences of dogs often shock their owners. Even among city dogs provided with adequate nutrition, the phenomenon of caprophagia, i.e., eating the feces of other animal species (horses, cattle and humans), is common.

When slaughtering sheep and cattle, several dogs (domestic and stray) were given the right to choose. After slaughter and opening of the abdominal cavity, all dogs gave preference to the gastrointestinal tract, i.e., gastric and intestinal chyme turned out to be more attractive compared to meat. This phenomenon is quite normal and understandable. Chyme contains semi-digested nutrients and, in addition, is rich in vitamins of microbiological origin and minerals of endogenous origin.

Eating chyme and caprophagia is a way to satisfy the dog’s needs for biologically active substances and easily digestible nutrients. This type of dog behavior should not be considered abnormal. Objections on the part of people in this matter are purely aesthetic.

The frequency of defecation and the amount of feces produced in dogs varies depending on the breed (live weight), the amount of daily ration and the frequency of feeding.