Digestive system. Nose and nasal cavity. The exocrine section is built from glandular end sections - acini and brood ducts.

10 - gum
11 - sublingual-maxillary fold
22 - language
30 - tooth enamel
31 - tooth crown

A tooth is made up of dentin, enamel and cementum.

Dentine- tissue that forms the basis of the tooth.
Dentin consists of a calcified matrix pierced by dentinal tubules containing outgrowths of odontoblast cells lining the tooth cavity. The intercellular substance contains organic (collagen fibers) and mineral components(hydroxyapatite crystals). Dentin has different zones, differing in microstructure and color.

Enamel- a substance that covers the dentin in the area of ​​the crown. Consists of crystals of mineral salts, oriented in a special way to form enamel prisms. Enamel does not contain cellular elements and is not a tissue. Enamel color is normal from white to cream with a yellowish tint (distinguish from plaque).

Cement- tissue covering the dentin in the root area. The structure of cement is close to bone tissue. It consists of cells of cementocytes and cementoblasts and a calcified matrix. The supply of cement occurs diffusely from the periodontium.

Inside the tooth is cavity, which is subdivided into coronal cavity and root canal, opening with the aforementioned apex of the tooth. dental cavity fills dental pulp, consisting of nerves and blood vessels immersed in a loose connective tissue and providing metabolism in the tooth. Distinguish coronal and root pulp.

Gum- the mucous membrane that covers the dental edges of the corresponding bones, tightly growing together with their periosteum.
The gum covers the tooth in the cervical area. It is abundantly supplied with blood (tendency to bleeding), but relatively weakly innervated. The grooved depression located between the tooth and the free edge of the gum is called the gingival sulcus.

Periodontium, alveolar wall and gums form supporting apparatus of the tooth - periodontium.

Periodontist- provides attachment of the tooth to the dental alveolus.
It consists of the periodontium, the wall of the dental alveoli and the gums. The periodontium performs the following functions: supporting and shock-absorbing, barrier, trophic and reflex.

CHANGING TEETH

Dog teeth, like most mammals, are diphyodont type, that is, during the life of the animal there is one change of teeth: the first generation - temporary, or baby teeth replaced by second generation teeth - permanent. In dogs, only P1 is not replaced, which erupt along with milk teeth and remain permanent.

Table Timing of teething in dogs
(according to J. Hosgood et al., 2000).

Change of teeth (plain radiograph)

TYPES OF TEETH

Dogs are heterodont animals, i.e. have teeth of various structures depending on the functions they perform. There are the following types of teeth: incisors, fangs and permanent teeth: pre-root (false, small root), or premolars and truly indigenous, or molars having no dairy predecessors.

Teeth arranged in sequence in a row form topand lower dental arches (arcades) . The upper arcade is represented by the 20th, and the lower one by 22 teeth (10 and 11 on each side, respectively).

Anatomy of the incisors of the superior arcade

incisors

Between the margin and the canine of the upper arch, as well as the canine and the first premolar of the lower, there are gaps - diastemas, which ensure the closing of the canines.

The molars of each arcade increase in size distally to the largest secant teeth, also called predatory. The molars have a different structure on the upper and lower arches, and therefore their structure will be considered separately.

Premolars - 4 on each side.
P I - has 1 (rarely 2) crown tubercle and 1 root.
P 2.3 - the crown has 3 teeth: large medial and 2 smaller distal; the tooth has 2 roots - medial and distal;
P 4 - the crown has 3 tubercles: large medial
both distal and lesser lingual; roots 3, they correspond to tubercles in location.

Molars - 2 on each side. Their longitudinal axes are parallel to each other and perpendicular to the median plane.

M 1 - the crown has 6 tubercles: 2 large buccal, middle - lingual and 3 small ones between them. The tooth has 3 roots: powerful lingual
and 2 smaller buccal - medial and distal.
M 2 - the crown has 4-5 tubercles: 2 buccal (medial and distal) and 2-3 lingual. Roots 3, their location is similar to that of M 1.

P 1-4 are similar in structure to those of the upper arcade, with the exception of somewhat longer and narrower roots.
The lower P 1 in the literature is sometimes referred to as a wolf's tooth.

molars- 3 on each side.

M 1 is the largest of the molars. The crown has 5 tubercles: medial, 2 distal and 2 middle between them: powerful buccal
and lesser lingual. Roots 2: medial and distal.

M 2 - the crown has 3-4 tubercles: 2 medial and 2 distal. The tooth has 2 roots, identical in size: medial and distal.

M 3 - the smallest of the molars, the crown usually has 1 or 2 tubercles. Root one, rarely two.

DENTAL FORMULA

Recording teeth in the form of a digital row, where each number indicates the number of teeth of a certain type on one side of each arcade in the direction from the median plane is called dental formula.

The dental formula looks like:
baby teeth D: ICP/ICP
molars: P: ICPM/ICPM.

Dog teeth formulas:
D: 3130/3130
R: 3142/3143.
Thus, 28 milk teeth (the first premolars, which are essentially permanent teeth, although they erupt with a milk change, should not be taken into account here) and 42 permanent teeth.

In medical dental practice, the dental formula is recorded according to the following scheme: D: PCI|ICP/PCI|ICP; R: MPCI|ICPM/ MPCI|ICPM reflects the number of teeth in the entire arcade, and not just on one side. In this case, the dog's dental formula will look like D: 313| 313/ 313|313; R: 2413|3142/3413|3143.

This form of recording the dental formula seems to be the most rational. Using this type of notation, you can briefly designate any tooth of the arcade. For example, a permanent lower left second premolar is designated as P|P2, a milky upper right toe as DI1|-, or abbreviated as OP]. The entry D|P1 is erroneous,
since there is no milk first premolar in dogs.

BITE
The closing of the dental arches is called occlusion, or bite.

When the dog's jaws close, the upper incisors go in front of the lower incisors in such a way that the lingual surfaces of the first freely contact the vestibular (pre-door) surface of the second, and the canines freely enter the corresponding diastema, forming the so-called lock. This is due to the fact that the upper dental arcade is somewhat wider than the lower one (anisognathic arcades). Contiguous teeth are called antagonists.

The bite may vary depending on the shape and size of the jaws and incisor bone, the direction of growth of the incisors and canines, which in turn is determined by the breed, the type of constitution of the animal, age and other factors.

Options for physiological bite are:

orthognathia or scissor bite as described above. It is characteristic for dogs with gentle, strong and strong rough types of constitution. It is normal for most breeds. With this bite, the erasure of the incisors occurs most slowly.

If the lower incisors are located behind the upper, but separated from them at some distance, such a bite is called undershot bite.
In this case, the medial surface upper canines and the distal surface of the lower canines are worn down due to friction.
Such a bite may be due to anomalies in bone development (elongated upper jaw and / or shortened lower jaw - microgenia) or tooth growth. It is more common in dogs of dolichocephalic breeds with a sharp muzzle. It occurs in puppies with a massive head in the cheekbones and a wide lower jaw in the branches. As a rule, with the end of the formation of the skeleton, the bite in such puppies is restored to a scissor or straight bite.
For adult dogs of most breeds, it is considered a vice, as it greatly complicates the intake of food and reduces the performance of the animal. In addition, when undershot, the fangs of the lower jaw do not form a lock, but injure the palate.

Progenia or snack The lower incisors are in front of the upper ones. Significant shortening of the bones facial department with a normal or elongated lower jaw, it causes the protrusion of not only the lower incisors, but also the canines - a bulldog bite. It is standard for breeds such as English and French Bulldog, pug, boxer and some others, provided that the incisors and fangs of the lower jaw do not protrude beyond the upper lip.

Level bite (pincer)- incisors touching edges.
Such a bite is typical for dogs of coarse and coarse loose types of constitution with a massive lower jaw. For some breeds, a level bite is allowed by the standard unconditionally or from a certain age. For example, the FCI-335 breed standard for the Central Asian Shepherd Dog (entered into force on March 22, 2000) states: “scissor bite, straight or tight bite (without a waste), regardless of age.” With a direct bite, the incisors wear down most quickly.

Gradual wear of enamel and dentin with age physiological process. With the correct bite, physiological loads in the dental organ, adequate compensatory changes occur, ensuring the full functioning of the worn teeth.

TERMS OF TEETH ERASING

The timing of the erasure of crowns in dogs, as in other animals, depends on many factors. These include, first of all, bite. As stated above, in a scissor bite, the grinding of incisors and canines is much slower than in a pincer bite and other types of bite.
It should not be forgotten that in addition to the types described, there is a great variety of pathological forms of bite, in which the grinding of individual teeth occurs inappropriately for age.

Also, the intensity of wear of the crowns is determined by the feeding conditions, such as: the consistency of the feed (dry or wet food); the depth of the dish from which the dog takes food, and the material from which it is made (whether the dog has the ability to physiologically capture the food and not injure the teeth). The habit of some dogs to gnaw and carry hard objects greatly affects the timing of grinding incisors and other teeth.

Of particular importance for erasing teeth are the individual characteristics of the microstructure and chemical composition enamel and dentin. Such deviations can be either congenital (hereditary factor, the use of teratogenic drugs in pregnant dogs, severe feeding disorders and diseases during pregnancy), or acquired (experience with plague and other infectious diseases during the period of changing teeth, taking tetracycline drugs in young animals, excess fluoride in the body (dental fluorosis), the use of aggressive chemicals (mineral acids) for the treatment of the oral cavity, etc.

Given the above factors, it becomes obvious that it is impossible to establish a strict relationship between the degree of abrasion of individual teeth and the age of the animal. The exception is animals under the age of 10-12 months, in which the sequence of eruption of permanent teeth is quite stable, and after its completion (6-7 months) up to 10-12 months, the crowns of permanent teeth are finally pushed into the oral cavity.
Above 1 year, the correlation of erasure with age is rather conditional.

Below are approximate dates dental changes in dogs.

The erasure of shamrocks begins at the age of about 2 years. First, they grind down on the lower incisors, by the age of 3 - on the upper hooks, by the 4th - on the middle ones, and by the age of 5-6, shamrocks, as a rule, are absent on all incisors, except for the upper edges.

From 5-6 to 10-12 years old, with varying intensity, the lower incisors advance (the first, usually, the lower hooks move forward), the canines and large tubercles of the molars are worn down.

In dogs older than 10-12 years, the crowns of the lower toes are usually almost completely worn off. The crowns of other teeth are slightly evenly ground off. If the animal does not suffer from periodontal disease (which is rare in domestic dogs), then natural tooth loss begins by the age of 14-17.

Note that with periodontitis and periodontal disease, complete loss of teeth can occur by the age of 8-10 years.

A more reliable criterion for determining the age of a dog is the relative size of the tooth cavity. With age, there is a gradual decrease in the cavity of the tooth up to its complete obliteration in older dogs. This parameter is practically not affected by external and internal factors and can be the basis for developing a methodology for determining age.
To determine the size of the cavity of the tooth, it is necessary to take an x-ray. Using this technique, it will be possible to determine the age from a radiograph or thin section, with only one tooth available.

MECHANICAL DIGESTION

Digestion in the oral cavity occurs mainly mechanically, when chewing large fragments of food are broken into pieces and mixed with saliva. Chewing is especially important in terms of the absorption of plant-derived ingredients, as nutrients are often trapped in cellulose-containing membranes that are not digestible. These membranes must be destroyed before the nutrients inside them can be used.

Mechanical digestion also allows you to increase the area exposed to the action of digestive enzymes.

BOTTOM OF THE MOUTH

STRUCTURE

The bottom of the oral cavity is covered with a mucous membrane located below the free surface of the tongue and on the sides of its body, it is a slit-like space under the sublingual mucous membrane. Sagittally, the floor of the mouth is divided by a fold of the frenulum of the tongue.

On the sides of the body of the tongue, the bottom mucosa with a powerful submucosal layer forms folds into which multiple short ducts open. sublingual salivary gland. Lateral to the frenulum of the tongue are small sublingual (hungry) warts. They are the openings of the excretory ducts mandibular
and long duct sublingual salivary glands.

SALIVARY GLANDS

1 - parotid gland
2 - mandibular gland
3 - sublingual gland
7 - zygomatic gland

Jaw (mandibular) salivary gland located behind the branch of the lower jaw, ventral to the parotid salivary gland, reaches the neck, where it lies between the maxillary veins.
It is large, oval, yellowish waxy in color and larger than the parotid gland. Its excretory ducts follow in the intermaxillary space over the intermaxillary muscle medially from the sublingual salivary gland to the hungry warts. The gland secretes serous-mucous secretions.

Parotid salivary gland lies ventral to the auricle, relatively small in size. The excretory duct runs across the chewing muscle and opens into the buccal vestibule with a low salivary papilla.

sublingual salivary gland lies under the mucous membrane on the sides of the body of the tongue. Subdivided into multi-channel, which with a large number of ducts opens on the lateral surface of the hyoid fold, and single-flow- one duct - in a hungry wart. Produces a mucous secretion.

ENZYMATIVE DIGESTION

Saliva is secreted into the oral cavity by four pairs of salivary glands.
There is usually a small amount of saliva in the mouth, but the amount can increase with the sight and smell of food. This effect, called "taste reaction", was first studied by Academician Pavlov I.P.

Salivation continues when food enters the mouth, and its effect is enhanced by the chewing process.
Saliva is 99% water, while the remaining 1% is mucus, inorganic salts and enzymes.
Mucus acts as an effective lubricant and promotes swallowing, especially dry food. Unlike humans, cats and dogs lack the starch-digesting enzyme amylase in their saliva, which prevents starch from being rapidly hydrolyzed in the mouth.
The absence of this enzyme is consistent with the observed behavior of dogs, which tend to swallow all but the hardest food without chewing, and the behavior of cats, which is characteristic of carnivores, which tend to consume food with a low starch content.

LANGUAGE

Language- a muscular, mobile organ lying at the bottom of the oral cavity.

The structure of the language

The papillae of the mucous membrane of the tongue perform the function of a taste analyzer, its surface provides thermoregulation of the dog's body, and also performs the function of touch.

Curving in a spoon-like manner, the tongue serves to receive water.

According to the external form, the tongue of dogs is long, wide and thin. The skeleton of the tongue makes up the inner surface of the lower jaw, as well as the hyoid bone.

The structure of the language

2 - tongue muscles
3 - the body of the tongue
4 - the root of the tongue

The language distinguishes: root, body and top.

Root The tongue is located between the molars and is covered with mucous membrane of the palatoglossal arch.
Body tongue lies between the branches of the lower jaw, it distinguishes the back and side surfaces. There are many papillae on the back. The dorsum of the tongue is concave and divided by a deep sagittal groove extending to the apex of the tongue. On the sides of the back, the lateral surfaces of the body of the tongue converge into its frenulum.

Top of the tongue- its most mobile part, expanded and flattened, has a ventral surface free from the bridle. The dorsal surface of the apex is noticeably wider than its dorsum.
In the thickness of the top of the tongue lies a specific intralingual cartilage (a remnant of the intralingual bone), which supports the protruding tongue of the dog and helps with the intake of liquid food.

papillae of the tongue

The papillae of the tongue are divided into mechanical and taste.

Mechanical:

1. Filiform
Cover the entire dorsal surface of the tongue, long, thin
and soft.
2. Tapered
They are located in the region of the root of the tongue instead of filiform ones.

Flavoring(contain taste nerve receptors - taste buds):

1. Mushroom
Scattered over the entire surface of the back of the tongue among the filiform.
2. Roll-shaped (grooved).
They lie on the border of the body and the root of the tongue in 2-3 pairs. They are large, rounded, around each there is a groove. In the latter, the mucous glands open.
3. Foliate
They lie on the sides of the root of the tongue in front of the palate-lingual arches. Oval in shape from 0.5 - 1.5 cm long, divided into segments - "leaves". Contains mucosal glands.

GLANDS OF LANGUAGE

Glands of the tongue - are parietal, they are scattered over the entire surface and edges of the tongue, lie in the thickness of the mucous membrane, secrete a mucous secret.

MUSCLES OF THE LANGUAGE

The tongue is made up of striated muscle tissue. Its muscle fibers are oriented in three mutually perpendicular directions: longitudinal (front to back), transverse (right to left) and oblique (top to bottom) and form differentiated muscles, which are divided into muscles of the tongue and hyoid bone.

The basis of the language is lingual muscle. It is built from vertical, oblique and longitudinal muscle fibers, following from the hyoid bone to the top of the tongue.
Function: changes the shape (thickness, length, width) of the tongue in different directions.

Lingual lateral muscle. It starts from the lateral surface of the middle segment of the hyoid bone, follows the lateral surface of the tongue to its apex.
Function: with bilateral action, pulls the tongue back, with one-sided - turns it in the appropriate direction.

Sublingual - lingual muscle. It starts on the body and laryngeal horns of the hyoid bone, ends in the thickness of the tongue medially from the lateral lingual muscle, laterally from the geniolingual muscle.
Function: pulls the tongue back, flattens the root of the tongue when swallowing.

Genio-lingual muscle. It starts at the chin angle of the lower jaw and branches fan-shaped in the middle sagittal plane from the top to the middle of the body of the tongue.
Function: flattens the tongue, pushes it forward.

MUSCLES OF THE HYLOGULASS

The geniohyoid muscle is fusiform, follows from the chin fragility of the lower jaw to the hyoid bone.
Function: pulls the hyoid bone and with it the tongue forward. Provides maximum lengthening of the tongue when lapping or licking.

Transverse intermaxillary (hyoid) muscle. It extends from the chin angle of the lower jaw, along the dental edge along the line of its muscular attachment to the tendon suture of the submandibular space and ends on the body and large horns of the hyoid bone.
Function: raises the tongue when chewing. Presses the back to the hard palate.

The stylohyoid muscle - from the large and small horns of the hyoid bone.
Function: brings branches together when swallowing.

Horn-hyoid muscle - follows from the laryngeal horns of the hyoid bone to its small horns.
Function: pulls up named branches.

Hyoid retractor muscles - the sternohyoid and sternothyroid muscles retract the hyoid bone during swallowing.

2. Throat (Pharynx)

Throat - pharynx - a tubular movable organ in which the digestive tract crosses, going through the pharynx from the oral cavity to the pharynx and further into the esophagus and the respiratory one through the choanae into the pharynx and further into the larynx.

1 - esophagus
2 - throat
4 - trachea
5 - larynx
6 - epiglottis

STRUCTURE

The pharyngeal cavity is divided into two different parts: the upper - respiratory - nasopharynx and the lower - digestive - (laryngeal), which are limited from each other by the palatopharyngeal arch. The palatopharyngeal arches converge before the beginning of the esophagus, forming the esophageal-pharyngeal border.

The respiratory part of the pharynx, located under the base of the skull, serves as a continuation of the nasal cavity behind the choanae. It is lined with a single layer of cylindrical ciliated epithelium, while the digestive part is lined with squamous stratified epithelium. In the lateral parts of the nasopharynx, the pharyngeal openings of the auditory (Eustachian) tubes open, which communicate the nasopharynx with tympanic cavity middle ear (pharyngitis can provoke otitis).

The anterior part of the digestive part of the pharynx borders on the pharynx, from which it is separated by a palatine curtain and, thus, serves as a continuation of the oral cavity, therefore it is called the oral cavity. Behind it rests against the anterior surface of the epiglottis. Then, located on top of the larynx, the pharynx continues back to the entrance
into the esophagus. This part of the digestive section of the pharynx is called the larynx, since the entrance to the larynx opens into it from below. Thus, the pharynx has 7 holes.

On the dorsal wall of the pharynx in the region of the arch is the pharyngeal tonsil.

The pharynx is located between the middle segments of the hyoid bone, they cover the organ from the sides, and the upper (proximal) segments of the hyoid bone suspend it to the mastoid part of the petrous bone.
The contraction of the pharyngeal muscles underlies the complex swallowing act, which also involves: the soft palate, tongue, larynx, esophagus.

X-ray: X-ray control
endoscopy of the pharynx

At the same time, the pharyngeal lifters pull it up, and the constrictors sequentially narrow its cavity backwards, pushing the food lump into the esophagus. At the same time, the larynx also rises, the entrance to it tightly covers the epiglottis, due to pressure on it with the root of the tongue. At the same time, the muscles of the soft palate pull it up and caudally in such a way that the palatine curtain lies on the palatopharyngeal arches, separating the nasopharynx.
During breathing, a shortened palatine curtain hangs obliquely down, covering the pharynx, while the epiglottis, built of elastic cartilage, directed upwards and forwards, provides air access to the larynx.

Outside, the pharynx is covered with connective tissue adventitia.
It is attached to the base of the skull by means of the basilar pharyngeal fascia.

The basis of the pharynx consists of three pairs of constrictors (narrowers) and one dilator (dilator). These paired muscles form top wall organ is the middle sagittal tendon suture, extending from the palatopharyngeal arch to the esophagus.

1. Cranial (rostral) constrictor of the pharynx - consists of paired muscles: palatopharyngeal and pterygopharyngeal.

The palatopharyngeal muscle makes up the lateral walls of the cranial pharynx, as well as the palatopharyngeal arch, starts from the palatine and pterygoid bones and ends at the tendon pharyngeal suture.
Function: brings the mouth of the esophagus closer to the root of the tongue.

The pterygopharyngeal tendinous muscle begins on the pterygoid bone and ends in the caudal part of the pharynx. Merges with the pharyngeal muscle.
Function: pulls the wall of the pharynx forward.
The main function of the anterior pharyngeal constrictor is to block the entranceinto the nasopharynx and expansion of the mouth of the esophagus.

2. The middle constrictor of the pharynx (hyoid-pharyngeal muscle) is formed by: the cartilage-pharyngeal and oropharyngeal muscles (belong to the muscle group of the hyoid bone) - follows from the laryngeal horns of the hyoid bone to the tendon suture of the pharynx.
Function: pushes the food lump to the esophagus.

3. The caudal constrictor of the pharynx is formed by: the thyroid-pharyngeal muscle, which goes from the thyroid cartilage of the larynx to the tendon suture, and the annular-pharyngeal muscle, which goes from the annular cartilage to the pharyngeal suture.
Function: pushes the food lump to the esophagus.

Pharyngeal dilator - follows from the medial surface of the middle segment of the hyoid bone under the middle and caudal constrictors to the lateral surface of the pharynx.
Function: expands the posterior pharynx after swallowing, narrows the nasopharynx.

3. Esophagus (Oesophagus)

Esophagus- is the initial section of the foregut
and in structure is a typical tubular organ. It is a direct continuation of the laryngeal part of the pharynx.

The mucous membrane of the esophagus along its entire length is collected
into longitudinal folds that straighten out when the food coma passes. In the submucosal layer there are many mucous glands that improve the sliding of food. The muscular membrane of the esophagus is a complex multilevel striated layer.

STRUCTURE

The outer shell of the cervical and thoracic parts of the esophagus is the connective tissue adventitia, and abdominal part covered with visceral peritoneum. The points of attachment of the muscle layers are: laterally - the arytenoid cartilages of the larynx, ventrally - its annular cartilage, and dorsally - the tendon suture of the larynx.

Schematic representation of the esophagus

Along the way, the diameter of the esophagus is uneven: it has 2 extensions and 2 narrowings. In dogs of medium size, the diameter at the entrance is up to 4 cm, and at the exit up to 6 cm. There are cervical, thoracic and abdominal parts of the esophagus.

The total length of the esophagus is on average 60 cm, and the average diameter of the collapsed esophagus is about 2 cm. Topographically, the esophagus is divided into the cervical, thoracic, and abdominal parts. Neck part long and is about half the length of the esophagus. Directly behind the pharynx, it is located above the semi-rings of the trachea.
and under the prevertebral sheet of the own fascia of the neck (surface plate).

Then, at level 4-6 cervical vertebra the esophagus bends down to the left side of the trachea and follows into the entrance to the chest cavity. This feature of the topography makes it possible to avoid tension of the organ in the thoracic part during movements of the head and neck; at the same time, it should be taken into account during medical manipulations on the organ.

AT chest cavity in the mediastinum, the esophagus accompanies the trachea on the left, and then in the area of ​​​​its bifurcation (bifurcation) again lies on the trachea. Thoracic part the esophagus first passes over the base of the heart to the right of the aortic arch, then through the esophageal opening of the diaphragm, located at the level of the third intercostal space, somewhat to the left. Behind the diaphragm, in the abdominal cavity, the short abdominal part of the esophagus forms the entrance to the stomach or cardiac opening (cardia).

FUNCTIONS

There is no secretion of digestive enzymes in the esophagus, however, the epithelial cells of the esophageal mucosa secrete mucus, which serves to lubricate the food coma during peristalsis, automatic wave-like muscle contractions that are stimulated by the presence of food in the esophagus and ensure its movement through the digestive canal. The process of moving food from the mouth to the stomach takes only a few seconds.

4. Stomach (Ventriculus)

The dog's stomach is single-chamber, intestinal type. It is an extension of the digestive tube behind the diaphragm.

Appearance of an isolated stomach

1 - pyloric part of the stomach
2 - cardial part of the stomach
3 - fundal part of the stomach
4 - exit of the duodenum 12
5 - cardiac opening (esophageal inlet)

The external ventral flexure of the stomach is called great curvature, and the dorsal small bend between the entrance and exit from the stomach - lesser curvature. The anterior surface of the stomach between the lesser and greater curvature faces the diaphragm and is called the diaphragmatic, and the opposite posterior surface is called the visceral. It is turned to the intestinal loops.

On the side of the greater curvature, a greater omentum is attached to the stomach - mesentery of the stomach. It is very extensive, lining the entire intestine to the hypogastrium like an apron and forming an omental sac. On the left surface of the greater curvature, in the fold of the omental sac, the spleen adjoins the stomach.
It is connected to the greater curvature of the stomach. gastrosplenic ligament containing numerous blood vessels. This ligament is a continuation of the mesentery of the stomach - the greater omentum.

The entrance to the omental sac is located between the caudal vena cava and the portal vein of the liver, medially right kidney. Small omentum located on the lesser curvature, it is short and consists of gastrohepatic ligament. In the cranial direction, it merges with esophageal-hepatic ligament, and in the caudal - with hepatoduodenal ligament. The above ligaments, except for the gastro-splenic ligament, perform only a mechanical function.

Endoscopy: the appearance of the stomach is normal

Endoscopy: appearance of the stomach.
Ulcerative gastritis

(various projections)

TOPOGRAPHY OF THE STOMACH

The stomach is located in the left hypochondrium in the region of 9-12 intercostal space and xiphoid cartilage (epigastrium), when filled, it can go beyond the costal arch and descend to the ventral abdominal wall.

In large dogs, this anatomical feature underlies the pathogenesis of non-contagious diseases of the stomach - its acute expansion or inversion.

PARTS OF THE STOMACH

It is customary to distinguish three parts of a single-chamber stomach: cardiac, bottom (fundal), pyloric, which differ not only in structure, but also in the specialization of the glands. The cardial part of the stomach is thicker and less vascular compared to other parts of the stomach, this fact must be taken into account when performing surgical interventions.

The cardia is an extension behind the inlet
into the stomach and is 1/10 of the area of ​​its greater curvature. The mucosa of the cardial part of the intestinal type is of a pinkish hue, rich in parietal cardiac glands, which secrete a serous-mucous secret of an alkaline reaction.

The middle part of the stomach behind the pars cardia from the side of the greater curvature is called the fundus of the stomach. It is the main part of the stomach where food is deposited in layers. There is located bottom gland zone(it is functional or bottom). In dogs, it occupies the left half of the greater curvature of the stomach.

The zone of the fundic glands is distinguished by dark staining of the mucosa, and is also equipped with gastric pits - the mouths of the parietal glands. The right half of the stomach is occupied area of ​​the pyloric glands. The mucosa of the stomach in an unfilled state is collected in folds. Only in the region of lesser curvature are they oriented from the entrance to the stomach to the pylorus.

The pyloric part of the dog's stomach has a powerfully developed constrictor (constrictor), which circularly covers it 5–7 cm from the entrance to the duodenum and ensures the evacuation of food from the stomach to the intestines.

GASTRIC MEMBRANES

The mucous membrane is white, lined with stratified squamous epithelium, collected in numerous longitudinal folds. Mucous glands are located in a well-developed submucosal layer.

The muscular layer of the stomach is built of smooth muscle tissue and has three layers of fibers: longitudinal, circular and oblique.

Longitudinal fiber layer thin follows from the esophagus to the pylorus. Circular layer located mainly in the bottom
and pyloric parts of the stomach. It forms the pylorus constrictor.

oblique layer prevails in the left half of the stomach, in the region of the circular layer it doubles (into the inner and outer).

The serous membrane of the stomach from the lesser curvature passes into the lesser omentum, and from the greater curvature into the ligament of the spleen and the greater omentum.

EMBRYOLOGY

During embryonic development, the stomach, as part of the straight digestive tube, undergoes two 180-degree turns. One in the frontal plane counterclockwise, and the other in the segmental.

FUNCTIONS

The stomach performs several functions:

It serves to temporarily store food and controls the rate at which food enters the small intestine.

The stomach also secretes enzymes necessary for the digestion of macromolecules.

The stomach muscles regulate motility to move food caudally (away from the mouth) and aid digestion by mixing and grinding food.

The dog's stomach is large, its maximum volume can approach the volume of the entire large and small intestine. This is due to the irregular nutrition of the dog and eating food "for the future".
It is known that a dog can also use the stomach as a temporary reservoir for storing food: for example, when feeding grown puppies, the bitch regurgitates the food obtained for them.

PHASES OF GASTROINTESTINAL SECRETION

The secretion of the stomach is regulated by complex processes of the nervous and hormonal interaction through which it is carried out at the right time and in the required volume. The secretion process is divided into three phases: cerebral, gastric and intestinal.

brain phase

The cerebral phase of secretion is initiated by food anticipation, the sight, smell, and taste of food, which stimulates pepsinogen secretion, although small amounts of gastrin and hydrochloric acid are also released.

Gastric phase

The gastric phase is initiated by mechanical stretching of the gastric mucosa, a decrease in acidity, and also by the products of protein digestion. In the gastric phase, the main secretion product is gastrin, which also stimulates secretion. of hydrochloric acid, pepsinogen and mucus. Gastrin secretion is drastically slowed down if pH falls below 3.0 and may also be controlled by peptic hormones such as secretin.
or enteroglucagon.

Intestinal phase

The intestinal phase is initiated both by mechanical stretching of the intestinal tract and by chemical stimulation with amino acids and peptides.

5. Small intestine (Intestinum tenue)

STRUCTURE

The small intestine is a narrowed section of the intestinal tube.

The small intestine is very long, making up the main part of the intestine, and ranges from 2.1 to 7.3 meters in dogs. Suspended on a long mesentery, the small intestine forms loops that fill most of the abdominal cavity.

The small intestine emerges from the end of the stomach and divides into three distinct sections: the duodenum, jejunum, and ileum. The duodenum accounts for 10% of the total length of the small intestine, while the remaining 90% of the length of the small intestine is made up of the jejunum and ileum.

BLOOD SUPPLY

The wall of the thin section is richly vascularized.

Arterial blood enters through the branches of the abdominal aorta - the cranial mesenteric artery, and to the duodenum also through hepatic artery.

Venous drainage occurs in the cranial mesenteric vein, which is one of the roots of the portal vein of the liver.

Lymph outflow from the intestinal wall occurs from the lymphatic sinuses of the villi and intraorgan vessels through the mesenteric (intestinal) lymph nodes into the intestinal trunk, which flows into the lumbar cistern, then into the thoracic lymphatic duct and the cranial vena cava.

INNERVATION

Nerve supply thin section is represented by branches vagus nerve and postganglionic fibers solar plexus from the semilunar ganglion, which form two plexuses in the intestinal wall: intermuscular (Auerbach) between the layers of the muscular membrane and submucosal (Meissner) in the submucosal layer.

Control of intestinal activity by the nervous system is carried out both through local reflexes and through vagal reflexes involving the submucosal nerve plexus and intermuscular nerve plexus. The function of the intestine is regulated by the parasympathetic nervous system, the center of which is its medulla oblongata, from where the vagus nerve (the 10th pair of cranial nerves, the respiratory-intestinal nerve) departs to the small intestine. Sympathetic vascular innervation regulates trophic processes in the small intestine.

TOPOGRAPHY

A thin section begins from the pylorus of the stomach at the level of the 12th rib, ventrally covered by sheets of the greater omentum, and dorso-laterally limited by a thick section. There are no clear boundaries between the sections of the small intestine, and the allocation of individual sections is mainly topographic in nature.

Only the duodenum stands out most clearly, which is distinguished by its large diameter and topographic proximity to the pancreas.

Barium contrast radiography of the small intestine

MEMBRANES OF THE INTESTINE

DEFINITION

The functional features of the small intestine leave an imprint on its anatomical structure. Allocate the mucous membrane and submucosal layer, muscle (external longitudinal and internal transverse muscles) and serous membranes of the intestine.

MUCOSA OF THE INTESTINE

The mucous membrane forms numerous devices that significantly increase the absorption surface.
These devices include circular folds, or Kerkring's folds, in the formation of which not only the mucous membrane is involved, but also the submucosal layer, and villi, which give the mucous membrane a velvety appearance. The folds cover 1/3 or 1/2 of the circumference of the intestine. The villi are covered with a special border epithelium, which performs parietal digestion and absorption. The villi, contracting and relaxing, make rhythmic movements with a frequency of 6 times per minute, due to which, during suction, they act as a kind of pumps.

In the center of the villus is the lymphatic sinus, which receives the products of the processing of fats. Each villus from the submucosal plexus includes 1-2 arterioles, which break up into capillaries. Arterioles anastomose with each other and during suction, all capillaries function, while during a pause - short anastomoses. Villi are thread-like outgrowths of the mucous membrane formed by loose connective tissue rich in smooth myocytes, reticulin fibers and immunocompetent cellular elements, and covered with epithelium.
The length of the villi is 0.95-1.0 mm, their length and density decreases in the caudal direction, that is, in the ileum, the size and number of villi is much less than in the duodenum and jejunum.

HISTOLOGY

The mucous membrane of the thin section and villi is covered with a single-layer columnar epithelium, in which there are three types of cells: columnar epitheliocytes with a striated border, goblet exocrinocytes (mucus secrete) and gastrointestinal endocrinocytes.

The mucous membrane of the thin section is replete with numerous parietal glands - the general intestinal, or Lieberkün glands (Lieberkün's crypts), which open into the lumen between the villi. The number of glands averages about 150 million (in the duodenum and jejunum, there are 10 thousand glands per square centimeter of surface, and in the ileum 8 thousand).

The crypts are lined with five types of cells: epithelial cells with a striated border, goblet glandulocytes, gastrointestinal endocrinocytes, small borderless cells of the bottom of the crypts (stem cells intestinal epithelium) and enterocytes with acidophilic granules (Paneth cells). The latter secrete an enzyme involved in the cleavage of peptides and lysozyme.

LYMPHOID FORMATIONS

For duodenum tubular-alveolar duodenal, or Bruner's glands, which open into crypts, are characteristic. These glands are, as it were, a continuation of the pyloric glands of the stomach and are located only on the first 1.5-2 cm of the duodenum.

The final segment of the small intestine (ileum) is rich in lymphoid elements, which occur in the mucous membrane at different depths on the side opposite to the attachment of the mesentery, and are represented by both single (solitary) follicles and their clusters in the form of Peyer's patches.
Plaques begin already in the final section of the duodenum.

The total number of plaques is from 11 to 25, they are round or oval in shape, from 7 to 85 mm long and 4 to 15 mm wide.
The lymphoid apparatus takes part in the processes of digestion.
As a result of the constant migration of lymphocytes into the intestinal lumen and their destruction, interleukins are released, which have a selective effect on the intestinal microflora, regulate its composition and distribution between the thin and thick sections. In young organisms, the lymphoid apparatus is well developed, and the plaques are large.
With age, there is a gradual reduction of lymphoid elements, which is expressed in a decrease in the number and size of lymphatic structures.

MUSCLE SHELL

The muscular coat is represented by two layers of smooth muscle tissue: longitudinal and circular, and the circular layer is better developed than the longitudinal one.

The muscular coat provides peristaltic movements, pendulum movements and rhythmic segmentation, due to which the contents of the intestine are moved and mixed.

SEROUS MEMBRANE

The serous membrane - the visceral peritoneum - forms the mesentery, on which the entire thin section is suspended. At the same time, the mesentery of the jejunum and ileum is better expressed, and therefore they are combined under the name of the mesenteric intestine.

FUNCTIONS OF THE SMALL INTESTINE

In the small intestine, digestion of food is completed under the action of enzymes produced by the wall (liver and pancreas) and parietal (Lieberkün and Brunner) glands, digested products are absorbed into the blood and lymph, and biological disinfection of the substances received.
The latter is due to the presence of numerous lymphoid elements enclosed in the wall of the intestinal tube.

The endocrine function of the thin section is also great, which consists in the production of certain biologically active substances by intestinal endocrinocytes (secretin, serotonin, motilin, gastrin, pancreozymin-cholecystokinin, etc.).

SECTIONS OF THE SMALL INTESTINE

It is customary to distinguish three sections of the thin section: the initial segment, or duodenum, the middle segment, or jejunum, and the final segment, or ileum.

DUODENUM

Structure
The duodenum is the initial section of the small intestine, which is connected with the pancreas and the common bile duct and has the form of a loop facing caudally and located under the lumbar spine.

The length of the intestine is on average 30 cm or 7.5% of the length of the thin section. This section of the thin section is characterized by the presence of duodenal (Bruner's) glands and a short mesentery, as a result of which the intestine does not form loops, but forms four pronounced convolutions.

Contrast barium radiography
duodenum:

Topography
The cranial part of the intestine forms S-shaped, or sigmoid gyrus, which is located in the region of the pylorus, receives the ducts of the liver and pancreas and rises dorsally along the visceral surface of the liver.

Under the right kidney, the intestine makes a turn caudally - this cranial gyrus of the duodenum, and goes to descending part, which is located in the right iliac. This part passes to the right of the root of the mesentery and under 5-6 lumbar vertebra moves to the left transverse part, dividing the mesentery into two roots in this place, and forms caudal gyrus of the duodenum.

Then the intestine is directed cranially to the left of the root of the mesentery as ascending part. Before reaching the liver, it forms duodenal-jejunal gyrus and passes into the jejunum. Thus, a narrow loop of the anterior mesenteric root is formed under the spine, containing the right lobe of the pancreas.

JEJUNUM

Structure
The jejunum is the longest part of the thin section, is about 3 meters, or 75% of the length of the thin section.
The gut got its name due to the fact that it has a half-asleep appearance, that is, it does not contain bulk contents. In diameter, it exceeds the ileum located behind it and is distinguished by a large number of vessels passing in a well-developed mesentery.
Due to its considerable length, developed folds, numerous villi and crypts, the jejunum has the largest absorption surface, which is 4-5 times larger than the surface of the intestinal canal itself.

Topography
The intestine forms 6-8 skeins, which are located in the region of the xiphoid cartilage, the umbilical region, the ventral part of both sighs and groins.

ILEUM

Structure
The ileum is the final part of the thin section, reaching a length of about 70 cm, or 17.5% of the length of the thin section. Outwardly, the intestine is no different from the lean one. This department is characterized by the presence of a large number of lymphoid elements in the wall. The end section of the intestine is distinguished by thicker walls and the highest concentration of Peyer's patches. This section runs straight under the 1-2 lumbar vertebra from left to right and flows into the caecum in the region of the right iliac, connecting with it with a ligament. At the confluence of the ileum into the blind, the narrowed and thickened part of the ileum forms ileocecal valve, or ileal papilla, which has the form of a relief annular damper.

Topography
This section of the small intestine got its name because of the topographic proximity to the iliac bones, to which it belongs.

WALL GLANDS. LIVER.

Liver- the largest gland of the body, is a dark red parenchymal organ, weighing 400-500 g, or 2.8-3.4% of body weight.

Five tubular systems are formed in the liver:
1) biliary tract;
2) arteries;
3) branches of the portal vein (portal system);
4) hepatic veins (caval system);
5) lymphatic vessels.

STRUCTURE OF THE LIVER OF A DOG

The shape of the liver is irregularly rounded with a thickened dorsal margin and sharp ventral and lateral margins. The pointed edges are dissected ventrally by deep furrows into lobes. The surface of the liver is smooth and shiny due to the peritoneum covering it, only the dorsal edge of the liver is not covered by the peritoneum, which in this place passes to the diaphragm, and thus forms extraperitoneal field liver.

Under the peritoneum is a fibrous membrane. It penetrates the organ, divides it into lobes and forms perivascular fibrous capsule(Glisson's capsule), which surrounds the bile ducts, branches of the hepatic artery and portal vein.

The anterior surface of the liver - the diaphragmatic surface enters the niche formed by the dome of the diaphragm, and the posterior surface - the visceral surface is in contact with the organs located in the territorial vicinity of the liver.

The dorsal edge has two notches: on the left - esophageal depression, and on the right - groove of the vena cava. On the ventral edge is round ligament notch. In the center visceral surface are surrounded by connective tissue gate of the liver- this is the place where the vessels, nerves penetrate, from where the common bile duct comes out and where the hepatic lymph nodes lie.

The falciform ligament, which is a duplication of the peritoneum, passing from the diaphragm to the liver, and is a continuation round ligament- the remainder of the umbilical vein, divides the liver into two lobes: right- big and left- smaller. Thus, the entire area of ​​the liver located to the right of the round ligament is the right lobe.

On the right side of the liver lies the gallbladder. The area of ​​the liver between the gallbladder and the round ligament is average share. The middle lobe of the liver gate is divided into two sections: the lower one is called square fraction, and the top caudate lobe. The latter consists of caudate process, which has renal depression, and mastoid process, which occupies the lesser curvature of the stomach. Finally, the left and right lobes are subdivided
into two parts each: lateral and medial.

Thus, the liver has six lobes: right lateral, right medial, left lateral, left medial, quadrate, and caudate.

The liver is a polymeric organ in which several structural and functional elements can be distinguished: hepatic lobule, sector (section of the liver supplied by a branch of the portal vein of the 2nd order), segment (section of the liver supplied by a branch of the portal vein of the 3rd order), hepatic acinus (neighboring areas two adjacent lobules) and the portal hepatic lobule (areas of three adjacent lobules).

The classical morphofunctional unit is the hexagonal hepatic lobule located around the central vein of the hepatic lobule.

The hepatic artery and portal vein, having entered the liver, are repeatedly divided into lobar, segmental, etc. branches up
before interlobular arteries and veins, which are located along the side surfaces of the lobules along with interlobular bile duct forming hepatic triads. Branches depart from these arteries and veins, which give rise to sinusoidal capillaries, and they flow into the central veins of the lobule.

The lobules consist of hepatocytes, which form trabeculae in the form of two cell strands. One of the most important anatomical features of the liver is that, unlike other organs, the liver receives blood from two sources: arterial - through the hepatic artery, and venous - through the portal vein.

BILIOLOGY AND BILE PRODUCTION

One of the most important functions of the liver is the process of bile formation, which led to the formation of the bile ducts. Between the hepatocytes that form the lobules, there are bile ducts that flow into the interlobular ducts, and they, in turn, form two hepatic duct coming out of each share: right and left. Merging, these ducts form the common hepatic duct.

The gallbladder is a reservoir for bile, in which bile thickens 3-5 times, since it is produced more than is required for the digestion process. The color of gallbladder bile in dogs is red-yellow.

The bubble lies on the square lobe of the liver high from its ventral edge and is visible from both the visceral and diaphragmatic surfaces. The bubble has bottom, body and neck. The wall of the bladder is formed by a mucous membrane, a layer of smooth muscle tissue and is covered on the outside by the peritoneum, and the part of the bladder adjacent to the liver is loose connective tissue. From the bladder originates the cystic duct, which contains spiral fold.

As a result of the confluence of the cystic duct and the common hepatic duct, the common bile duct is formed, which opens
into the S-shaped gyrus of the duodenum next to the pancreatic duct at the apex major duodenal papilla. At the point of entry into the intestine, the duct has bile duct sphincter(sphincter of Oddi).

Due to the presence of a sphincter, bile can flow directly into the intestines (if the sphincter is open) or into the gallbladder (if the sphincter is closed).

TOPOGRAPHY OF THE LIVER

The liver is located in front of the stomach and is in contact with diaphragm. Lies almost symmetrically in both hypochondria. Caudal edge liver corresponds to the costal arch, only in old animals the liver can protrude beyond costal arch.
With x-ray and ultrasound examination the distance between the caudal edge of the liver and the diaphragm should be five times the length of the second lumbar vertebra.

The liver is held in its position with the help of a ligamentous apparatus, which includes round ligament liver - connects the ventral edge of the liver with the umbilical ring, the ligament continues in falciform ligament attaching the liver to the diaphragm; the liver is also connected to the diaphragm with the help of the coronary ligament, the left triangular ligament; The liver is connected to the right kidney by the hepatorenal ligament, to the stomach by the hepatogastric ligament, and to the duodenum by the hepatoduodenal ligament.

The liver receives blood supply through the hepatic arteries, the portal vein, and venous outflow occurs through the hepatic veins into the caudal vena cava.

The innervation of the liver is provided by the vagus nerve through the extra- and intramural ganglia and the sympathetic hepatic plexus, represented by postganglionic fibers from the semilunar ganglion. The phrenic nerve takes part in the innervation of the peritoneum covering the liver, its ligaments and the gallbladder.

LIVER FUNCTIONS

The liver is a multifunctional organ that takes part in almost all types of metabolism, plays a barrier and disinfecting role, is a depot of glycogen and blood (up to 20% of blood is deposited in the liver), and performs a hematopoietic function in the embryonic period.

The digestive function of the liver is reduced to the process of bile formation, which contributes to the emulsification of fats and the dissolution of fatty acids and their salts. Dogs excrete 250-300 ml of bile per day.

Bile is a mixture of bicarbonate ions, cholesterol, organic metabolites and bile salts. The basis on which bile salts work is fat. Bile salts break down large fat particles into small droplets that interact with various lipases.

Bile also serves to excrete organic residues, such as cholesterol and bilirubin, from the breakdown of hemoglobin. Liver cells produce bilirubin from the blood and actively secrete it into bile. It is due to this pigment that bile acquires a yellow color.

3D structure of bile salts
with indication of polar and non-polar sides

WALL GLANDS. PANCREAS

The pancreas is a large loose parenchymal organ, consisting of separate lobules united by loose connective tissue. By weight of iron is 30-40 g, or 0.20-0.25% of body weight, the color is pale pink.

According to the structure of iron, it belongs to the complex tubular-alveolar glands of mixed secretion. The gland does not have clear contours, since it lacks a capsule, it is stretched along the initial section of the duodenum and the lesser curvature of the stomach, it is covered by the peritoneum ventro-caudally, the dorsal part is not covered by the peritoneum.

The pancreas consists of exocrine lobules and endocrine parts.

Anatomically, in the gland they secrete body, which is located in the S-shaped gyrus of the duodenum, left lobe or lobe of the stomach, which is adjacent to the lesser curvature of the stomach, lies in the duplication of the omentum and reaches the spleen and left kidney, and right lobe, or duodenal lobe, which lies in the duplication of the mesentery of the duodenum and reaches the right kidney.

In dogs, the right lobe is highly developed, so the gland has an elongated (ribbon-like) shape bent at an angle. The gland has the main (wirzung) pancreatic duct, which exits the body of the gland and opens next to the bile duct at the top of the duodenal papilla (sometimes the duct may be absent),
and 1-2 accessory (santorini) ducts, which open at a distance of 3-5 cm from the main one.

The blood supply to the gland is provided by the branches of the splenic, hepatic, left gastric and cranial mesenteric arteries, and the venous outflow occurs in the portal vein of the liver.

Innervation is carried out by branches of the vagus nerve and the sympathetic plexus of the pancreas (postganglionic fibers from the semilunar ganglion).

FUNCTIONS OF THE PANCREAS

The pancreas is responsible for both exocrine and endocrine functions, but only exocrine digestive functions are considered in the context of this section.
The exocrine pancreas is responsible for secreting digestive secretions and large volumes of sodium bicarbonate ions, which neutralize the acidity of the chyme that comes from the stomach.

secretion products:

Trypsin: Breaks down whole and partially digested proteins into peptides of varying sizes, but does not release individual amino acids.
- chymotrypsin: breaks down whole and partially digested proteins into peptides of various sizes, but does not cause the release of individual amino acids.
- carboxypeptidase: cleaves individual amino acids from the amino terminus of large peptides.
- aminopeptidases: cleaves individual amino acids from the carboxyl end of large peptides.
- pancreatic lipase: hydrolyzes neutral fat into monoglycerides and fatty acids.
- pancreatic amylase: hydrolyzes carbohydrates, turning them into smaller di- and trisaccharides.

6. Large intestine (Intestinum crassum)

The large intestine is the end section of the intestinal tube, is on average 45 cm long and is divided into the caecum, colon and rectum. It has a number of characteristic features, which include relative shortness, volume, low mobility (short mesentery), the presence of a blind outgrowth - the caecum on the border with a thin section.

1 - stomach
2, 3, 4, 5 - duodenum
6 - jejunum
7 - ileum
8 - caecum
9, 10, 11 - colon
12 - rectum

The blood supply to the thick section is provided by branches of the cranial and caudal mesenteric arteries, and the rectum is supplied by three rectal arteries: cranial(branch of the caudal mesenteric artery), middle and caudal(branches of the inner iliac artery).

Venous outflow from the blind, colonic and cranial portion of the rectum occurs in the portal vein of the liver. From the middle and caudal sections of the straight cat into the caudal vena cava, bypassing the liver.

The innervation of the thick section is provided by branches vagus(transverse position colon) and pelvic nerves(blind, most of the colon and rectum). The caudal part of the rectum is also innervated by the somatic nervous system via the pudendal and caudal rectal nerves of the sacral spinal plexus. Sympathetic innervation is carried out along the mesenteric and rectal plexuses, which are formed by postganglionic fibers of the semilunar and caudal mesenteric ganglia.

Muscle control from the nervous system is carried out both through local reflexes and through vagal reflexes with the involvement of the submucosal nerve plexus and the intermuscular nerve plexus, which is located between the circular and longitudinal muscle layers. Normal bowel function is regulated by the parasympathetic nervous system. Control is directed from the brain part of the vagus nerve to the anterior section and away from the nuclei sacral department spine
through the pelvic nerve to the peripheral large intestine.

The sympathetic nervous system (control is directed from the ganglia in the paravertebral sympathetic trunk) plays a less important role. The processes of local control and coordination of motility and secretion of the intestine and associated glands are of a complex nature, they involve nerves, paracrine and endocrine chemical substances. The nerve supply of the thin section is represented by branches of the vagus nerve and postganglionic fibers of the solar plexus from the semilunar ganglion, which form two plexuses in the intestinal wall: intermuscular (Auerbach) between the layers of the muscular membrane and submucosal (Meissner) in the submucosal layer.

Control of intestinal activity by the nervous system is carried out both through local reflexes and through vagal reflexes involving the submucosal nerve plexus and intermuscular nerve plexus.
Bowel function is regulated by the parasympathetic nervous system. The control is directed from the brain part of the vagus nerve to the small intestine. The sympathetic nervous system (control is directed from the ganglia in the paravertebral sympathetic trunk) plays a less important role.
The processes of local control and coordination of motility and secretion of the intestine and associated glands are of a more complex nature, involving nerves, paracrine and endocrine chemicals.

Loops of the large intestine are located in the abdominal and pelvic cavities.

MEMBRANES OF THE COLON

The structure of the large intestine consists of several layers: mucous membrane, submucosal layer, muscular layer (2 layers - the outer longitudinal layer and the inner circular layer) and serosa.

The epithelium of the caecum does not contain villi, but has numerous goblet cells on the surface that secrete mucus.

The mucous membrane does not have villi and circular folds, which is why it is smooth. Villi are present only in the embryonic state and disappear shortly after birth. This is sometimes observed in some dogs in the first days of life, and in most individuals by the end of the second week.

In the mucous membrane, the following types of cells are distinguished: intestinal epitheliocytes with a striated border, goblet enterocytes, borderless enterocytes - a source of restoration of the mucous membrane, and single intestinal endocrinocytes. Paneth cells present in the small intestine are absent in the large intestine.

The general intestinal (Lieberkuhn) glands are well developed, lie deep and close to each other, and there are up to 1000 glands per 1 cm2.

The mouths of the Lieberkün glands give the mucous membrane an uneven appearance. In the initial part of the thick section, there is an accumulation of lymphoid elements that form plaques and lymphatic fields. An extensive field is located in the caecum at the confluence of the ileum, and plaques are located on the body of the caecum and at its blind end.

The muscular membrane in the thick section is well developed, which gives the entire thick section thickening.

THICK REGION FUNCTIONS

Undigested food remnants enter the large intestine, which are exposed to the microflora that inhabits the large section. The digestive capacity of the large intestine of dogs is negligible.

Some excretions (urea, uric acid) and salts of heavy metals are excreted through the mucous membrane of the large intestine, water is intensively absorbed mainly in the initial part of the colon. The thick section is functionally an organ of absorption and excretion rather than digestion, which leaves an imprint on its structure.

SECTIONS OF THE LARGE INTESTINE

The large intestine is made up of three main parts: caecum, colon and rectum.

CECUM

Structure
The caecum is a blind outgrowth on the border of the thin and thick sections. The entrance ilio-blind opening is well marked and represents a locking mechanism.
The exit blind-colon opening is not clearly expressed and has no locking mechanism. The caecum in dogs is greatly reduced. It has the appearance of a convoluted appendage, making from 1 to 3 curls, its walls are enriched with lymphoid elements, but the intestine does not have a worm-like process characteristic of higher primates. Depending on the size and number of whorls, 5 types of canine caecum can be distinguished.

Topography
The intestine hangs on the mesentery on the right lumbar region under the 2-4 lumbar vertebra, in length is from 2 to 16 cm, or 11% of the length of the thick section.

The caecum forms a sac closed at one end, located below the junction of the large and small intestines. In cats, the caecum is a vestigial organ, while in dogs, the size of the caecum is significant.

COLON

Structure
The colon makes up the bulk of the large intestine.
It reaches about 30 cm in length, or 66.7% of the total length of the thick section. The intestine is very narrow (narrower than the duodenum), but thick-walled. The shape forms a rim located in the frontal plane, under the spine, which in appearance resembles a horseshoe.
The colon consists of three relatively straight sections: the ascending colon, the transverse colon
and the descending colon, which passes into the rectum.

Topography
The colon begins on the right in the lumbar region and goes in the dorsal part of the right iliac rectilinearly to the diaphragm as the ascending colon.
Behind the diaphragm (in the hypochondrium) it forms a transverse bend - the transverse colon and, passing to the left side, goes caudally in the dorsal part of the left iliac as the descending colon. Having reached the left groin, the sigmoid colon forms a sigmoid bend and passes into the rectum.

RECTUM

Structure
The rectum is the final segment of the large intestine. The length of the rectum is about 10 cm, or 22.2% of the length of the large intestine. The intestine is suspended on the mesentery, and in the pelvic cavity is surrounded by loose connective tissue (pararectal fiber).

In the pelvic cavity, the intestine forms a poorly developed ampulla.
The rectum has even, elastic and thick walls, with a uniformly developed muscular layer. The mucosa is collected in longitudinal folds, contains modified Lieberkün glands and numerous mucous glands that secrete a large amount of mucus.
There are many venous plexuses in the submucosal layer, due to which water and aqueous solutions from the rectum are well and quickly absorbed.

Topography
Lies under the sacrum and the first tail vertebrae, ends with the anus.

anus
The perineal part of the rectum is called the anal canal. The mucous membrane of the rectum 2-3 cm before the anus ends with an anorectal line, caudally from which the stratified squamous epithelium begins. In this area, two annular zones are formed. The inner zone is called the columnar zone of the anus, the longitudinal folds of which are called the anal columns. Deepenings are formed between them - anal sinuses, in which mucus secreted by the anal glands accumulates.

outdoor area called the intermediate zone, which is separated from the skin zone of the anus with the help of the anal skin line.
In the latter, the circummanal glands and paraanal sinuses open. The rectum and anus have their own muscular apparatus, which in the anus is represented by two sphincters: external and internal. The first is an accumulation around the anus of smooth muscle tissue, which is formed from the muscle layer of the rectum, and the second is striated muscles. Both sphincters function synchronously.

A number of muscles extend from the anus to the sides:

The rectal-caudal muscle is represented by a longitudinal layer of the muscles of the rectum, which passes from the walls of the rectum to the first tail vertebrae;
- anus lifter - originates from the ischial spine and goes to the side of the rectum into the muscles of the anus;
- suspensory ligament of the anus - originates from the 2nd tail vertebra and in the form of a loop covers the rectum from below; built from smooth muscle tissue; in males it becomes a penis retractor; and in females it ends in the labia.

The digestive system performs a wide variety of functions, the main ones being the digestion and absorption of nutrients. The digestive system has a significant functional reserve, so small deviations, as a rule, do not lead to disturbances in the process of digestion and absorption of nutrients. For example, the pancreas is responsible for the synthesis and secretion of digestive enzymes. The functional reserve of this organ is such that only the loss of 90% of the activity of the organ causes the appearance clinical signs diseases in an animal.
In addition to a significant functional reserve, the digestive system has a large substitution capacity. For example, fat is digested mainly in the small intestine. However, about 1/3 to 1/4 of the entire cycle of fat digestion can take place in the stomach.
The ability for partial interchangeability and a large functional reserve are extremely important, since the digestive organs are significantly affected by external factors.

Digestion - a set of physical, chemical and physiological processes that ensure the processing and transformation of food into simple chemical compounds capable of being absorbed by the cells of the body. These processes occur in a certain sequence in all parts of the digestive tract (oral cavity, pharynx, esophagus, stomach, small and large intestines with the participation of the liver and gallbladder, pancreas), which is ensured by regulatory mechanisms of various levels.
The feed consists of organic components, many of which are large insoluble molecules. In order for large molecules to pass through the intestinal mucosa and enter the common system blood circulation for delivery to organs, they need to be split into simpler compounds. The process of splitting is called "digestion", and the passage through the intestinal mucosa is called "absorption".
The combination of these two processes is central to the process of nutrition: a diet with an ideal set of nutrients and high palatability is of no value to the body if its constituent components that enter the body cannot be broken down and assimilated. The concept of digestion covers a complex of mechanical, chemical and microbiological processes that are involved in the sequential breakdown of nutrients. Under the action of the chewing muscles, the absorbed feed particles are mechanically crushed. Digestive juices rich in enzymes are secreted into the digestible mass in the stomach and small intestine and aid in the chemical breakdown of food. Bacteria living in the final part of the digestive tract also produce enzymes that help chemically break down food.

The main functions of the organs of the digestive system are:
=> secretory - the formation and secretion of digestive juices by glandular cells (saliva, gastric, pancreatic, intestinal juices, bile) containing enzymes and other substances that provide the breakdown of nutrients;
=> motor-evacuation, or motor - is carried out by the muscles of the digestive tract, providing a change in the aggregate state of food (grinding, mixing) and its promotion;
=> suction - provides transport of end products of digestion, water, salts and vitamins through the mucous membrane from the cavity of the digestive tract into the internal environment of the body (intercellular fluid, blood, lymph);
=> excretory - excretion with digestive secrets of natural metabolites, salts of heavy metals, drugs or their metabolites;
=> endocrine - excretion endocrine cells mucous membrane of the gastrointestinal tract and pancreas hormones that stimulate or inhibit the functions of the digestive organs, as well as affecting a number of other body systems;
=> protective (bactericidal, bacteriostatic, detoxification) - carried out thanks to the barrier systems of the gastrointestinal tract and reflex mechanisms;
=> receptor (analyzer) - associated with irritation of chemo- and mechanoreceptors, which evaluate the composition and nature of food products and chyme.
=> hematopoietic - associated with the formation of hemamine (a product of the glandular cells of the gastric mucosa), which stimulates the absorption of cyanocobalamin, which is necessary for the maturation of red blood cells. In addition, the mucous membrane of the stomach of the small intestine and liver deposits ferritin, which is involved in the synthesis of hemoglobin.

It is necessary to pay attention to the fact that the functions of the digestive system in different species of mammals have their own characteristics. Their difference lies in different sensitivity, activation and features of the course of digestive processes. Some features of the digestive processes also depend on the sex and age of the animal.

The structure of the digestive system.
The digestive system consists of the digestive tract and digestive glands - salivary, liver with gallbladder, pancreas. The digestive tract, in turn, is anatomically divided into the oral cavity, pharynx, esophagus, stomach, intestines, and anus.
The oral cavity is used to receive, grind, moisten food and form food bolus. The oral cavity is formed by the lips, cheeks, palate, tongue and bottom of the mouth, and behind it passes into the pharynx with a pharynx.
The tongue serves as an organ of taste, takes part in chewing, contributes to the formation of a food lump, pushes it to the throat. On the surface of the tongue there are many papillae, which can be divided into several types:
Filiform papillae are narrow, conical in shape, look like threads. These papillae are arranged in parallel rows, and at the root of the tongue resemble the pattern of the terminal groove. The filiform papillae have nerve endings that respond to touch. In dogs, these papillae are well developed and allow even hard matter to be licked off.
Fungiform papillae are located closer to the tip of the tongue. Most mushroom papillae contain taste buds.
Grooved papillae in the amount of 7-12 are located along the terminal groove and contain taste buds with taste receptors - chemoreceptors.

Digestion in the oral cavity is carried out mainly mechanically: during chewing, large fragments are crushed and food is mixed with saliva.
Saliva is 99% water, and 1% proteins, chlorides, phosphates, bicarbonates, thiocyanates and the bactericidal substance lysozyme, which is associated with the fact that dogs lick their wounds.
Saliva is always present in the mouth, but salivation is increased by the sight and smell of food. Salivation continues even after food enters the oral cavity. This effect is enhanced by chewing.
The intensity of secretion and the nature of saliva vary depending on the food. More saliva is secreted for dry food, and less for watery food. Thick, viscous saliva with a high content of mucin is released on food substances. Saliva secreted by rejected substances (pepper, acid, soda, etc.), liquid.
Saliva promotes the formation of the digestive bolus and impregnates it, which reduces friction when swallowing. Creates conditions for mineral metabolism in tooth enamel, helps prevent caries.
The secretion of the salivary glands in dogs is alkaline, rich in bicarbonates, but does not contain enzymes.
Saliva in the oral cavity of dogs is secreted by four paired salivary glands: parotid - near each ear; submandibular - on both sides of the lower jaw; sublingual (under the tongue) and zygomatic glands located on the upper jaw below the eyes and salivary ducts.
Since dog saliva does not contain the enzyme a-amylase that hydrolyzes starch, this explains the tendency to swallow all food at once, except for very hard ones, and is consistent with the nature of the cat - a strict predator that prefers food with a low starch content.
The teeth are located in the dental holes - the alveoli of the jaws. Their number and type is characteristic of a given species and is expressed by the dental formula. Distinguish: incisors, canines, molars. Each tooth has a crown, root and neck. Dogs have 42 permanent teeth; dental formula: I 3/3, C 1/1, R 4/4, M 2/3.
Teeth grind food, thereby increasing the surface on which saliva acts. Dogs have the same number of incisors (12) and canines (4), but a different number of molars, which provides the dog with the ability to grind coarser food.

The pharynx is a complex structure that connects the oral cavity with the esophagus and takes part in the promotion of the food bolus from the oral cavity to the esophagus.

Esophagus - tubular organ which connects the mouth to the stomach. A bolus of food moistened with mucus, as a result of wave-like contractions and relaxations, moves along the esophagus to the stomach. Thus, food passes from the mouth to the stomach in just a few seconds.
At the junction of the esophagus with the stomach is a muscular ring called the cardiac sphincter. Normally, the cardiac sphincter opens under the action of peristaltic contractions of the esophagus, which allows food to enter the stomach, and the pressure in the full stomach stimulates the contraction of the sphincter, and thereby prevents food from returning to the esophagus.

The stomach is a crescent-shaped reservoir with a convex greater and concave lesser curvature that is located caudal to the liver and deep below the costal arch. The stomach can be anatomically divided into 5 zones:
the cardiac site is the entry point of the esophagus;
the bottom of the stomach - forms a blind pocket and is a reservoir for food;
the body of the stomach is the largest area of ​​the stomach, which is the most functionally active area;
diverticulum cave - acts as a stomach mill, grinds food into chyme;
pyloric sphincter - the gate between the stomach and duodenum.

Each zone of the stomach contains different types of glandular cells. In the cardiac zone are epithelial cells that secrete mucus. In the areas of the bottom and body - parietal cells that secrete hydrochloric acid, as well as chief cells that secrete pepsinogen for protein breakdown.
The property of the stomach to stretch strongly allows for discrete, rather than continuous (not large portions) feed intake. It has great importance for dogs that eat large portions.

Functions of the stomach:
1) a short-term reservoir of food,
2) digestion of food,
3) liquefaction and mixing of food,
4) control the release of contents into the duodenum.

1) Food tank.
When food is ingested, the relaxation of the stomach allows it to fill without increasing intragastric pressure. Normal stomach capacity varies from 2-2.5 liters in dogs (medium size). Relaxation of the stomach is controlled by the nerves with each swallowing act. This action is enhanced by a local reflex, due to which the stretching of the stomach causes its further relaxation.

2) Digestion of food.
The initial stage of the digestion process is the addition of hydrochloric acid and pepsin to the food, and after thorough mixing, the chyme is slowly released into the duodenum.
Distension of the stomach and the presence of split protein stimulate the production of gastric juices (mucus, hydrochloric acid, digestive enzymes - pepsin, lipase, chymosin, etc.).
Pepsin breaks down proteins to albumose and peptones, while lipase breaks down neutral fats into fatty acids and glycerol. Young animals have more lipase, as it digests milk fat.
Different feed proteins are digested differently by pepsin. For example, meat proteins are digested faster than egg whites. The optimal concentration of hydrochloric acid for protein digestion is 0.1 - 0.2%.
Another enzyme of gastric juice is chymosin. It converts milk caseinogen into casein. Under the action of this enzyme, milk curdles in the stomach and undergoes digestion by the enzymes of gastric juice. Puppies have relatively more chymosin and less pepsin and hydrochloric acid, in adult animals the opposite is true. Gastric secretion depends on the conditions of feeding and maintenance. In interdigestive periods, secretion is absent and occurs when eating, which is typical for omnivores that eat food in large portions at significant intervals. In captive and domestic conditions, when animals are fed once or twice a day, secretion appears during the intake of food and is completely absent in the periods between feeding. Stress also stimulates secretion in the stomach.
Reflex secretion of gastric juice lasts up to two hours after eating. The gastric mucosal barrier is a protective mechanism that protects the stomach from irritation from ingested food, hydrochloric acid, and increased pepsin activity. The barrier consists of a layer of mucus covering the gastric mucosa and the gastric mucosa itself.
Mucus coats the gastric mucosa and protects it from acid and mechanical damage, and also acts as a lubricant. Mucus contains substances that have an inhibitory effect against hydrochloric acid.

3, 4) Mixing and liquefaction of food, as well as transporting chyme to the duodenum provides gastric motility. Gastric motility is controlled by both the nervous and endocrine systems.
In the proximal part of the stomach, a slight frequency of contractions creates pressure, which helps to move food forward and ensures the timely delivery of the stomach.
After eating, strong contractions of the distal part of the stomach lead to a change in the consistency of food, diluting it. As soon as the food is liquefied, the proximal gastric constrictors evacuate the stomach contents.
Small amounts of water, glucose, amino acids and minerals are absorbed in the stomach. Miscellaneous food passes through the stomach at different speeds. Coarse stays longer in the stomach, liquid leaves the stomach after a few minutes, warm - faster than cold. Food passes from the stomach to the intestines in portions.

The intestines can be anatomically divided into the small and large intestines. The main function of the small intestine is to break down and absorb food, while the large intestine absorbs water, electrolytes and some vitamins.
The small intestine begins at the pylorus (pylorus) and ends at the iliococolic foramen. Anatomically, it is divided into three parts: the duodenum, jejunum, and ileum. The main function of the small intestine is to complete the breakdown of nutrients and ensure their further absorption into the general circulation. In addition to this, the small intestine also performs a barrier function, protected from the penetration of damaging factors.
The mucous membrane of the small intestine is covered with finger-shaped protruding crypts, the main function of which is to increase the absorption surface of the intestine. On the area of ​​1 mm2 of the mucous membrane, there are up to 20-40 crypts, which are covered with a single-layer epithelium. Between the villi is a large number of tubuloalveolar glands that secrete mucus and protect the duodenal mucosa from the effects of gastric acid. Epithelial cells secrete a wide range of enzymes - various disaccharidases, peptidases and others. The motility of the small intestine consists of two types: peristaltic waves and segmental contractions. Peristaltic waves slowly move the chyme in the distal direction. In contrast, segmental contractions result in agitation of the chyme, which allows the chyme particles to have greater contact with digestive enzymes and the mucosal surface. A large volume of water is released into the duodenum, due to which the contents of the intestine remain isotonic, and this contributes to the process of digestion.
Digestion and absorption in the small intestine.
Enzymatic digestion of food is completed in the small intestine. All proteins, fats and carbohydrates of the feed are broken down into peptides and amino acids, glycerol and fatty acids, monosaccharides, which are absorbed along with water, vitamins and inorganic ions. For the implementation of these complex processes, a large number of enzymes, electrolytes, bile acids and other biologically active substances are needed, which are secreted by the duodenum, pancreas and liver.
Intestinal juice contains about 22 enzymes that are involved in digestion. Thanks to these enzymes, the final stages of hydrolysis of proteins, fats, carbohydrates pass. Intestinal juice contains enzymes that complete the breakdown of complex organic substances into simpler ones, the so-called membrane digestion. Compound intestinal juice varies depending on the nature of the food.

The pancreas is functionally divided into an endocrine part, which is responsible for the synthesis and secretion of various hormones, primarily insulin and glucagon, and an exocrine part, which is responsible for the synthesis and secretion of digestive enzymes.

The exocrine part is formed by cells and a system of ducts that ensure the secretion of pancreatic juice into the small intestine. The duct system in humans and in 80% of cats is connected to the common pancreatic duct, which opens with the common bile duct at the main duodenal papilla. Dogs and 20% of cats also have a second accessory pancreatic duct that opens with a small duodenal papilla.
During the day, the dog's pancreas secretes 600-800 ml of juice, which contains many enzymes, mucous substances, electrolytes (sodium, potassium, calcium, chlorine, phosphorus, zinc, copper and manganese).
Pancreatic juice is rich in enzymes. Trypsin breaks down proteins and peptides into amino acids. To digest carbohydrates, pancreatic juice contains amylase, which digests starch and glycogen to glucose. pancreatic lipase
breaks down fats into glycerol and fatty acids.
The composition of pancreatic juice enzymes varies depending on the nature of the diet. When animals eat cereals, more pancreatic juice is secreted, less milk. The duration of secretion when eating cereals is longer, meat - less. The largest number trypsin is contained in the juice allocated to milk, amylases - to cereals. The activity of the pancreas is strongly influenced by the mode of feeding. An abrupt transition to a different diet can cause an upset in the activity of the pancreas.
The synthesis and excretion of enzymes into the ductal system is relatively constant and increases in response to food intake. The pancreas secretes a large amount of bicarbonates into the lumen of the 12th colon, which maintain the optimal pH value (8.0) and create optimal conditions for the processes of enzymatic activity of the pancreas and intestines.
The secretion of digestive enzymes is regulated by the nervous and hormonal systems. The activity of pancreatic amylase in a dog is approximately 3 times higher than in a cat. High content starch leads to a 6-fold increase in amylase activity in the chyme of the small intestine of the dog in comparison with a 2-fold increase in the cat, which determines the differences in the absorption of feed carbohydrates between the dog and the cat.

The liver is a gland responsible for a number of important body functions. One of them is the synthesis and secretion of bile, which, when it enters the intestine, promotes splitting, saponification, emulsification and absorption of fats, enhances intestinal motility and activates some digestive enzymes.
Bile consists of water (95-97%), mineral salts, mucus, phosphatidylcholine, cholesterol, bile acids and bile pigments. Bile is constantly produced in the liver, as it is not only digestive juice, but also a secret with which unnecessary substances are removed from the body. Outside the period of digestion, bile enters the gallbladder, which is its reservoir. It enters the intestines both from the bladder and from the liver only during digestion. After an intensive digestion process, the bladder may be empty. Bile provides hydrolysis of proteins and carbohydrates, increases the absorption of all fat-soluble substances, incl. vitamins D, E, K, enhances the action of lipase of pancreatic and intestinal juices, promoting the digestion of fats. Due to its bacteriostatic properties, bile has a positive effect on the bacterial flora of the small intestine. The average intensity of bile secretion in dogs is 25 ml/kg. Half of this amount passes through the gallbladder, whose capacity is approximately 5 times less than the total amount of bile.
When feeding dogs with meat, bile begins to enter the intestine after 5-8 minutes, cereals - after 8-12 minutes, milk - after 3-5 minutes.
Hydrochloric acid is a bile secretion stimulant.

Thus, the beginning of the small intestine (12-toed intestine), in combination with the pancreas and liver, is the "center" in digestion and regulation of the function of the digestive canal.
The absorption of nutrients takes place in the small intestine in two ways - abdominal (due to diffusion), and parietal (due to osmosis). Malabsorption of nutrients in the small intestine is called malabsorption.

Large Intestine - Digested food passes from the small intestine to the large intestine through the ileocecal valve. In dogs, the large intestine is relatively short because its main function is to absorb salts and water. Anatomically, the large intestine is divided into the caecum, colon, rectum, and anus.
The caecum is rudimentary and does not perform any clear function. The colon in dogs is relatively short (0.2-0.6 m) in comparison with herbivores, which reflects the difference in its functions in different species. Anatomically, the colon can be divided into ascending, transverse, and descending colons.
Normally, the colon takes the form of a large question mark, although in some cases there may be significant differences in location.
The rectum begins at the level of the superior pelvic inlet and passes through the pelvic canal to the anus, which passes into the skin of the perineum. The surface of the mucous membrane is smooth, without villi. In the mucosa are intestinal crypts that secrete mucus. Their function is to protect the mucous membrane of the large intestine from mechanical and chemical damage. Mucus provides lubrication to facilitate the passage of stool.

There is no breakdown or absorption of nutrients in the large intestine. As a result of bacterial fermentation, volatile fatty acids are produced. They are actively absorbed along with salt. When this process is disturbed, acids remain in the lumen of the large intestine and create a powerful osmotic force, drawing water into the lumen and thus causing diarrhea.
The main functions of the large intestine are: the absorption of water and electrolytes, the accumulation of feces.
Most of the water and electrolytes are absorbed in the ascending and transverse colon, while feces accumulate in the descending colon and rectum. This process is based on the active transport of Na + ions from the intestine. Through this transport route, the intestine returns approximately 90% of the water contained in the chyme. A drop in pressure in the intestinal tract leads directly to diarrhea. Water absorption by the large intestine plays an important role in maintaining homeostasis. This manifests itself in most in diseases of the small intestine, when the large intestine compensates for insufficient absorption in the small intestine. This "reserve capacity" helps dogs and cats control water loss from the gastrointestinal tract. For example, a dog weighing 20-25 kg absorbs 3-3.5 liters of water per day, of which 90% of the volume is absorbed in the small intestine, and approximately 10% in the large intestine.
Peristalsis of the large intestine is a complex but highly organized process that ensures the normal performance of its functions. Remains of food in humans usually reach the large intestine in about 5 hours, and the time of passage through the large intestine can be from 1 to 3 days.
There are two types of colonic motility: segmented contractions and peristaltic contractions. Segmented contractions - for sufficient mixing of the contents of the lumen with little progress through the large intestine. These primary contractions promote the absorption of water and electrolytes. Peristaltic movements move the contents of the lumen along the colon towards the rectum. In dogs and cats, retroperistalsis is also observed, which prevents the contents from entering the rectum too quickly. The main stimuli for colonic motility are increased intraluminal pressure or intestinal distention. Stretch stimulates both segmented and peristaltic contractions. This explains the positive role of dietary bulk factors such as fiber in the treatment of diarrhea and constipation. In diarrhea, fibers promote segmented contractions, thus improving absorption, and in constipation, they improve peristalsis, which ensures regular emptying of the large intestine.

bacterial fermentation.
The microflora of the gastrointestinal tract consists of hundreds of different types of bacteria. The main types of bacteria present in the body of a healthy dog ​​are streptococci, lactic acid bacteria and clostridia. In the intestines of dogs and cats, most gastrointestinal bacteria reside in the large intestine. Approximately 99% of the intestines of a normal healthy animal are anaerobes, the composition of which varies with the diet. For example, representatives of lactic acid bacteria are much more numerous in young animals that are fed dairy products. There are more representatives of Clostridium in the large intestine of dogs whose diet is dominated by meat.
Colon bacteria produce a significant amount of ammonia. If the animal is healthy, ammonia is converted to urea in the liver and excreted through the kidneys. At serious illness liver or porto-systemic anastomosis, ammonia has a powerful toxic effect on the central nervous system, known as hepatoencephaly.
The time of passage of food through the digestive tract in dogs mainly depends on the diet and is 12-15 hours. Plant foods cause stronger intestinal motility, so it passes faster than meat, after 4-6 hours. Digestibility of nutrients of different feeds is not the same. Meat in dogs after 2 hours is digested by half, after 6 hours - by 87.5%, and after 12 hours almost completely - by 96.5%; rice - after 1 hour - by 8%, after 3 hours - by 50%, after 8 hours - by 98%. With excessive feeding, the amount of feces increases, as part of the food is not digested. Under a normal feeding schedule, carnivores empty their rectum 2-3 times a day.

Addition:

Ministry of Agriculture and Food of the Republic of Belarus

educational institution

Vitebsk Order "Badge of Honor" State Academy of Veterinary Medicine

COURSE WORK

Physiology of Digestion in Dogs

Vitebsk 2011

INTRODUCTION

ORAL CAVITY

1 The structure of the oral cavity

2 Digestion in the mouth

3 Salivation, regulation of salivation

pharynx, esophagus, their participation in digestion

STOMACH

1 The structure of the stomach

2 Digestion in the stomach

DIGESTION IN THE INTESTINE

1 The pancreas and its role in digestion

2 Digestion in the small intestine

4.3 Structure and functions of the liver

4.4 Bile and its role in digestion

4.5 Digestion in the large intestine

5. FEATURES OF BLOOD SUPPLY AND INNERVATION OF THE GASTROINTESTINAL TRACT

SUCTION

LITERATURE

INTRODUCTION

In the total volume of pathology of non-contagious etiology, diseases of the digestive system occupy one of the leading places. In the light of the wide development of service, agricultural, decorative dog breeding and the increased interest in dogs among the population, knowledge normal functioning digestive system of dogs in general and individual bodies is a necessary set of knowledge in the training of veterinary specialists.

Knowledge of the anatomy and physiology of the digestive system in dogs is an essential element in understanding the mechanisms of development pathological processes in the digestive system, interpreting the observed changes and drawing up a treatment regimen for a particular pathology of the gastrointestinal tract of animals.

In addition, at present, modern research methods are being widely introduced into practical veterinary medicine to make the correct diagnosis in dogs, and their use is possible only with knowledge of the physiological and anatomical characteristics of the body, which is what this educational and methodological manual is aimed at.

Dogs belong to the order of carnivores - Comivora. From the very name of the detachment, it becomes clear that its representatives feed mainly on meat, that is, they are carnivores. Based on the nutritional characteristics of dogs, their digestive system has certain anatomical and physiological adaptations that allow them to easily absorb food of animal origin and use vegetable food worse.

The digestive system in dogs is made up of:

the oral cavity with the organs in it,

small and large intestines,

liver and pancreas.

Thus, if the digestive system is considered schematically, then it is a tube that begins with the oral cavity and ends with the anus.

The digestive tract performs the following functions:

Secretory - consisting in the production of digestive juices containing enzymes.

The motor-evacuation (motor) function performs the reception of food, its chewing, ingestion, mixing, promotion of the contents along the length of the digestive tract and the ejection of undigested food residues from the body.

Absorption - ensuring the supply of nutrients after their appropriate processing into the blood and lymph.

Excretory (excretory) function ensures the excretion of products from the body various kinds metabolism.

Incretory - associated with the production of enteric hormones and hormone-like substances by the digestive glands, affecting not only the functions of the digestive tract, but also other body systems.

Protective - acting as a barrier against the penetration of harmful agents into the body.

The receptor (analyzer) function is manifested in the assessment of the quality of the feed entering the body.

1. MOUTH

1 The structure of the oral cavity

The oral cavity serves to capture, crush and wet food. From the sides, the oral cavity is bounded by the cheeks, from the front, by the lips framing the entrance to the oral cavity. In dogs, the lips are inactive and almost do not participate in the capture of food. Dogs grasp solid food with their teeth, and liquid food with their tongue. The oral cavity is separated from the nasal cavity solid sky, and from the pharynx - the soft palate. Thanks to the soft palate (palatine curtain), the dog breathes freely while holding food in the mouth. The bottom of the oral cavity is filled with the tongue.

The tongue is a muscular organ consisting of striated muscles with fibers running in different directions. Due to the contraction of individual muscle groups, the tongue can produce all kinds of movements, which allows it to capture liquid food, water, put it under the teeth and push food into the throat. On the lateral surface of the tongue and on its back there are taste buds - filiform, mushroom and leaf-shaped. In dogs, in addition, the tongue is an organ of thermoregulation.

The dog uses its teeth for grasping, biting and tearing food, as well as for protection and defense. upper jaw dogs contains 20 teeth, lower - 22. Dogs have 6 incisors on each jaw, 4 canines and 12 molars on the upper and 14 on the lower jaw.

The change of milk teeth to permanent teeth in dogs occurs at the age of 3 to 6 months. Each tooth consists of a very dense substance - dentin, which serves as the basis of the tooth. Outside, dentin is covered with enamel. Inside the tooth there is a cavity containing dental pulp - pulp. The pulp contains blood vessels and nerves (Fig. 1).

Three pairs of salivary glands open into the oral cavity: submandibular and sublingual - in the sublingual groove, parotid - at the level of the 3rd-5th upper molars. As a rule, saliva is secreted simultaneously by all salivary glands and is a mixture of secretions from these glands. In addition, there are a large number of small salivary glands scattered in the oral mucosa, the secret of which keeps it moist.

The composition of saliva

Saliva is the secret of three pairs of salivary glands. It is a watery-viscous, cloudy, slightly apolescent in the light secret of a weakly alkaline or alkaline reaction (pH 7.2 - 8.5). Saliva contains 98 - 99.5% water and 0.6-1% solids. Dog saliva does not contain enzymes. Salivation occurs only when food enters the oral cavity or in the presence of strong odors. Salivation is regulated mainly by the autonomic nervous system, although there is also humoral regulation (estrogens, androgens). About 90% of saliva is produced by the parotid and submandibular glands. The secret of the parotid glands is predominantly serous and contains a small amount of organic substances, and the secret of the submandibular glands is mixed, including serous and mucous secretions.

The meaning of saliva

Moistens the food and makes it easier to chew;

By dissolving food particles, saliva is involved in determining its taste;

The mucous part of saliva (mucin) sticks together small particles of food, forms a food lump, mucus it and facilitates swallowing;

Due to its alkalinity, it neutralizes excess acids formed in the stomach;

In dogs, saliva is involved in thermoregulation. So, at a high temperature, part of the thermal energy is removed with saliva released from the mouth;

The protective role of saliva is due to the presence in it of lysozyme, ingiban, immunoglobulin A, which have antimicrobial and antiviral properties;

Saliva contains thromboplastic substances, so it has a hemostatic effect to some extent;

Regulates the species composition of the microflora in the stomach.

The entire oral cavity and its organs are covered with a mucous membrane lined with squamous stratified epithelium that can withstand the touch and friction of solid food.

2 Digestion in the mouth

Digestion in the mouth consists of four stages: feeding, moisturizing, chewing and swallowing.

Before starting to receive food, the animal must feel the necessary need for its intake.

The feeling of hunger is associated with an increase in the excitability of the food center located in different parts of the central nervous system, among which the hypothalamic center plays an important role. The functional state of the food center is determined by the chemical composition of the blood, the presence of glucose, amino acids, fatty acids and other metabolites, as well as pancreatic hormones. Along with humoral factors, the excitability of the food center is also affected by reflex reactions emanating from irritation of various receptors in the digestive tract.

Dogs look for food and determine its nutritional suitability with the participation of the organs of sight, smell, touch, taste.

Chewing is carried out by various movements of the lower jaw, due to which the food is crushed, crushed, and frayed. As a result of this, its surface increases, it is well moistened with saliva and becomes available for swallowing.

Chewing is a reflex act, but arbitrary. Excitation arising from irritation of the receptors of the oral cavity with food along the afferent nerves (lingual branch of the trigeminal nerve, glossopharyngeal nerve, upper laryngeal branch of the vagus nerve) is transmitted to the chewing center of the medulla oblongata. From it, excitation along the efferent fibers of the trigeminal, facial and hypoglossal nerves goes to chewing muscles and due to their contraction, the act of chewing occurs. With the grinding of coarse food particles, irritation of the receptors of the oral cavity decreases, as a result of which the frequency of chewing movements and their strength become weaker and they are now directed mainly to the formation of a food coma and preparing it for swallowing. The higher chewing centers are located in the hypothalamus and in the motor cortex.

The amount of saliva secreted is affected by the degree of moisture and the consistency of the feed. The drier the food, the more saliva is released. Salivation increases when the so-called rejected substances (sand, bitterness, acids, medicinal substances, etc.) enter the mouth. At the same time, saliva is rich mainly inorganic substances and is called laundering. In the absence of stimuli that cause salivation, the salivary glands are at rest.

Absorption of nutrients in the oral cavity does not occur, since food practically does not linger in it.

1.3 Salivation, regulation of salivation

Salivation is a complex reflex act, carried out as a result of irritation of the mechano-, chemo- and thermoreceptors of the oral cavity with feed or other irritating substances. Excitation along the fibers of the afferent nerves is transmitted to the medulla oblongata to the center of salivation and further to the thalamus, hypothalamus and cerebral cortex. From the center of salivation, excitation along the fibers of the efferent sympathetic and parasympathetic nerves passes to salivary glands and they start to salivate. Efferent parasympathetic fibers are part of the facial and glossopharyngeal nerves. Postganglionic sympathetic fibers originate from the superior cervical ganglion. This mechanism of salivation is called unconditionally reflex. Parasympathetic influences cause a copious secretion of liquid, watery saliva with a small content of organic substances in it. Sympathetic nerves, on the contrary, reduce the amount of saliva secreted, but it contains more organic substances. The regulation of the amount of excretion of water and organic substances is carried out by the nerve center due to miscellaneous information coming to him through the afferent nerves. Saliva is also released at the sight, smell of food, a certain time of feeding animals and other manipulations associated with the upcoming intake of food. This is a conditioned reflex mechanism of salivation with the manifestation of the so-called natural, food salivary reflexes. In these cases, salivation occurs with the participation of the overlying parts of the CNS-hypothalamus and the cerebral cortex. But saliva can also be allocated to artificial (indifferent) stimuli. When a conditional signal (light, calls, etc.) is accompanied by giving food after 15-30 seconds. After several such combinations for one conditioned, extraneous stimulus, conditioned reflex salivation occurs, and such reflexes are called artificial conditioned reflexes, which can be used in animal husbandry as signals to start eating. Salivation is influenced by kallikrenin, pituitary, thyroid, pancreatic and sex hormones.

2. pharynx, esophagus, their participation in digestion

The pharynx is a joint pathway for food and air. Air enters the larynx through the pharynx from the nasal cavity into the larynx and back when breathing. Through it, food and drink enter the esophagus from the oral cavity. The pharynx is a funnel-shaped organ covered with a mucous membrane, in which the mucous pharyngeal glands and lymphatic follicles are laid, with its enlarged part facing the oral and nasal cavities, and the narrowed end towards the esophagus. The pharynx communicates with the oral cavity through the pharynx, and with the nasal cavity through the choanae. In the upper part of the pharynx, the opening of the Eustachian tubes (auditory) opens, with the help of which the pharynx communicates with the tympanic cavity of the middle ear.

Swallowing is a complex reflex act that ensures the evacuation of food from the oral cavity into the esophagus. Formed and mucilaginous with saliva, the food lump is directed by the movement of the cheeks and tongue to its root behind the anterior arches of the pharyngeal ring. Excitation arising from irritation of the receptors of the mucous membrane of the root of the tongue and soft palate is transmitted through the fibers of the glossopharyngeal nerve to the medulla oblongata to the center of swallowing. From it, impulses along the fibers of the efferent nerves (hyoid, trigeminal, vagus nerve) are transmitted to the muscles of the oral cavity, pharynx, larynx and esophagus. There is a contraction of the muscles that lift the soft palate and larynx. The entrance to the respiratory tract is blocked, the upper esophageal sphincter opens and the food lump enters the esophagus.

In the act of swallowing, an arbitrary phase is distinguished, when the food lump is located in the oral cavity up to the root of the tongue and the animal can still throw it away, and then the involuntary phase begins, when swallowing movements are carried out. The swallowing center is connected with other centers of the medulla oblongata, therefore, at the time of swallowing, the respiratory center is inhibited, resulting in breath holding and increased heart rate. The higher swallowing centers are located in the hypothalamic part of the diencephalon and in the cerebral cortex. Swallowing in the absence of food or saliva in the oral cavity is practically difficult or impossible.

The esophagus is a simple hollow organ representing a muscular tube, the walls of which consist of striated muscle tissue. The mucous membrane of the esophagus is lined with epithelium and is collected in longitudinal, easily straightened folds. The presence of folds provides expansion of the esophagus. In dogs, the esophagus contains a large number of glands throughout. The esophagus transports food from the pharynx to the stomach, despite eating, it always remains empty.

The movement of food through the esophagus is carried out reflexively due to peristaltic contractions of the muscles of the esophagus. The beginning of this reflex is the act of swallowing. The movement of food through the esophagus is also facilitated by the severity of the food itself, the pressure difference between the pharyngeal cavity and the beginning of the esophagus of 45-30 mm Hg. Art. and the fact that the muscle tone of the esophagus in the cervical region at this time is 3 times higher than in the thoracic region. The average duration of the passage of solid food through the esophagus is 10-12 seconds, but this depends on the size of the dog and the consistency of the food. Outside of swallowing movements, the cardiac sphincter of the stomach is closed, and when food passes through the esophagus, it opens reflexively. The contraction of the muscles of the esophagus occurs under the influence of the vagus nerve.

3. STOMACH

1 The structure of the stomach

The stomach is the first section of the digestive tube where food is digested. The stomach is an enlarged and sac-like part of the digestive tube. The stomach lies in the anterior part of the abdominal cavity, directly behind the diaphragm, for the most part in the left hypochondrium in the region of the 9th-12th intercostal space. Normal stomach capacity is 0.6 liters in small dogs and 2.0-3.5 liters in medium dogs.

The stomach serves as a reservoir in which food is retained and chemically processed into acidic environment. The wall of the stomach consists of an outer serous layer, a muscular layer, and an inner mucous layer. In the muscular membrane of the stomach, consisting of smooth muscle tissue, there are three layers of muscle fibers: longitudinal, oblique and circular.

Sections of the stomach

The mucous membrane of the stomach in dogs throughout its length contains glands and is covered with a single-layer cylindrical epithelium. The mucous membrane of the stomach is constantly exposed to acid and pepsin, in this regard, it needs reliable protection from damaging factors. In the protective barrier of the stomach, mucosal cells are the first line of defense against damaging factors. They play a special role in this superficial cells secreting mucus and bicarbonates. This barrier consists of mucus that maintains a neutral pH at the cell surface. This protective mucus layer is unmixed and consists of bicarbonates, phospholipids, and water. It has been established that factors that stimulate the synthesis of hydrochloric acid and pepsin simultaneously stimulate the secretion of mucus and bicarbonates. An important role in maintaining the resistance of the gastric mucosa to damaging factors is played by the ability of cells to repair. The mucous membrane of the stomach is able to recover very quickly after damage, within 15-30 minutes. This process usually occurs not due to cell division, but as a result of their movement from the crypts of the glands along the basement membrane and thus closing the defect.

In the gastric mucosa, there are three types of secreting cells - main, parietal and additional. The chief cells produce enzymes, the parietal cells produce hydrochloric acid and mucous secretions, and the accessory cells produce mucus.

2 Digestion in the stomach

The chewed food enters the stomach through the esophagus. Food particles are mechanically processed, turning into a homogeneous liquid mass - chyme, which improves absorption processes in the small intestine.

Pure gastric juice is a colorless, transparent liquid of acid reaction (pH 0.8-1.2) with a small amount of mucus and cells of the rejected epithelium. The acid reaction of juice is due to the presence of hydrochloric acid and other acid-reactive compounds in it. The composition of the inorganic part of the juice includes minerals present in saliva. The organic part of the juice is represented by proteins, amino acids, enzymes, urea, uric acid.

In gastric juice, seven types of inactive precursors (proenzymes) are isolated, which are located in the cells of the gastric glands in the form of granules of pepsinogens, united under the general name pepsins. In the cavity of the stomach, pepsinogen is activated by hydrochloric acid by splitting off an inhibitory protein complex from it. Pepsin acts on the peptide bonds of the protein molecule, and it breaks down into peptones, proteases and peptides.

There are the following main pepsins:

Pepsin A - a group of enzymes that hydrolyze proteins at pH 1.5-2.0;

Pepsin C (gastric cathepsin) realizes its action at pH 3.2-3.5;

Pepsin B (gelatinase) liquefies gelatin, acts on connective tissue proteins at pH less than 5.6;

Pepsin D (rennin, chymosin) acts in the presence of calcium ions on milk caseinogen and converts it into casein with the formation of curd and milk whey.

Other enzymes in the stomach include:

ü gastric lipase that breaks down emulsified fats (milk fat) into glycerol and fatty acids at pH 5.9-7.9. The enzyme is more produced in young animals during their milk feeding;

ü urease breaks down urea at pH=8.0 to ammonia, which neutralizes hydrochloric acid;

ü lysozyme (muramidase) has antibacterial properties.

The importance of hydrochloric acid in digestion

Being in a free and bound state, it plays an important role in digestion:

1.Activates pepsinogen to pepsin and creates an acidic environment for its action;

2.Converts the hormone prosecretin into the active form of secretin, which affects the secretion of pancreatic juice;

.Activates the hormone progastrin to gastrin, which is involved in the regulation of gastric juice secretion;

.Decalcifies bones;

.Denatures proteins, causing them to swell, which facilitates their hydrolysis;

.Acts bactericidal on putrefactive microflora;

.Participates in the mechanism of the transition of contents from the stomach to the intestines;

.Promotes curdling of milk in the stomach;

.Activates gastric motility.

Juice secretion occurs under the influence of various external and internal stimulants. Conventionally, three overlapping phases of juice extraction are distinguished.

The first phase is complex reflex. It is initially associated with conditioned reflex reactions to irritation of visual, auditory, olfactory receptors, which are subsequently joined by unconditioned reflex irritations of oral cavity receptors associated with food intake and chewing.

When food is taken, excitation from the receptor of the oral cavity along the afferent fibers enters the medulla oblongata to the food center and from it along the efferent fibers of the vagus nerve to the glands of the stomach and the secretion of juice begins. The reflex phase was proven in the laboratory of I.P. Pavlova in experience with imaginary feeding dogs. When feeding such an experimental dog, the food falls out through the cut esophagus, and after 5-7 minutes from the start of feeding, juice is released. Transection of the vagus nerves does not cause the secretion of juice during imaginary feeding, while irritation of the peripheral end of the vagus nerve stimulates the secretion of juice.

Juice that stands out in appearance, smell and other irritants associated with the start of food intake, I.P. Pavlov named fuse or appetizing which prepares the stomach for food intake and digestion.

Conditioned reflex reactions to the sight and smell of food are carried out with the participation of the sensory zones of the corresponding analyzers and the food center of the cerebral cortex.

The gastric (nerve-humoral) phase is gradually superimposed on the complex reflex phase. By the still ongoing secretion of juice from the first phase, the secretion is already beginning to be influenced by the mechanical and chemical factors of the feed, as well as the hormones gastrin, enterogastrin, and histamine. The role of food digestion products and other chemicals in the secretion of juice is proved by the experiment with the introduction of food through the fistula directly into the stomach, imperceptible to the animal, bypassing the complex reflex phase. In these cases, juice secretion begins only after 20-30 minutes or more - when the first products of feed hydrolysis appear. A good example of this is the experiments of I.P. Razenkov with a blood transfusion from a well-fed, fed dog - a hungry one, in which juice secretion immediately begins after that. But all these chemicals act with the participation of the nervous system and, mainly, the vagus nerves, since the introduction of atropine against the background of high gastric secretion sharply reduces it.

The third - the intestinal phase occurs when the contents of the stomach pass into the intestines. Gastric secretion at the beginning of this phase still increases due to chemicals absorbed in the intestine, and then it gradually fades due to the formation of secretin in the intestine, which is a gastrin antagonist.

In the laboratory of I.P. Pavlov in experiments on dogs with small isolated ventricles when feeding animals with different foods (meat, bread, milk), a clear functional adaptability of the gastric glands to the type of food fed was revealed, expressed in different amounts, the nature of juice secretion and the chemical composition of the juice. Yes, through regulatory mechanisms the secretory activity of the digestive glands adapts to the feed being fed. Each type of food corresponds to its characteristic secretory function of the digestive glands. This fact is essential for the organization of rational feeding of healthy and sick animals.

The motor function of the stomach is stimulated by mechanical and chemical irritations of the receptor apparatus of its mucous membrane. The greatest importance in the regulation of motility is performed by the vagus nerves (strengthen) and sympathetic - they inhibit the contractile function of the stomach. Humoral motility activators are acetylcholine, gastrin, histamine, potassium ions. The inhibitory effect is exerted by adrenaline, norepinephrine, gastron, enterogastron and calcium ions.

The evacuation of the contents from the stomach to the intestine is carried out in small portions through the pyloric sphincter. The speed of feed transition depends on the degree of its processing in the stomach, consistency, chemical composition, reaction, osmotic pressure, etc. Carbohydrate feeds are evacuated faster. Fatty foods are delayed for a longer time, which, according to some authors, is associated with the formation of enterogastron in the intestine. Shredded, mushy, warm, isotonic contents pass into the intestines faster. When the duodenum is full, the passage of the next portion from the stomach is delayed until the contents move down the intestine. The carbohydrate components of food enter the duodenum first, followed by proteins and then fats.

The transition of contents from the stomach to the intestines is carried out due to the coordinated function of the motility of the stomach and intestines, contractions and relaxations of the pyloric sphincter, which is carried out under the influence of the central nervous system, local intramural reflexes, hydrochloric acid and enteric hormones.

dog digestion gastric intestinal

4. DIGESTION IN THE INTESTINE

The small intestine is the main site of digestion and absorption of nutrients. The small intestine is made up of the duodenum, jejunum, and ileum. The duodenum is located in the right hypochondrium, starting from the stomach, forms an S-shaped bend and then goes under the spine. Reaching the pelvis renal area it turns from right to left, passing into the jejunum. The jejunum is located mainly in the central part of the abdominal cavity and forms many intestinal loops. The jejunum without clear boundaries passes into the ileum. The ileum goes to the right iliac region and here it passes into a small caecum and its continuation - the colon. The terminal section of the ileum has a highly developed muscular layer and a narrow lumen, which helps to push the food slurry into the large intestine and prevents its reverse flow. In addition, at the very beginning of the duodenum, two large digestive glands open their gaps - the liver and pancreas.

The contents coming in small portions from the stomach to the intestines undergo further hydrolysis processes in it under the action of the secrets of the pancreas, intestines and bile. The highest value in intestinal digestion has pancreatic juice.

1 The pancreas and its role in digestion

The pancreas is a gland with a dual external and intrasecretory function. In dogs, the gland is long, narrow, red in color, with the right branch reaching the kidneys. The pancreatic duct opens along with the bile duct. Based on the functional features, the pancreas is represented by two different departments in morphological and functional respects: exocrine and endocrine.

Pancreatic juice - colorless clear liquid alkaline reaction (pH 7.5-8.5). The inorganic part of the juice is represented by sodium, calcium, potassium, carbonates, chlorides, etc. Organic substances include enzymes for the hydrolysis of proteins, fats and carbohydrates, and various other substances. Proteins are cleaved by proteolytic enzymes - endopeptidases and exopeptidases. Endopeptidases (trypsin, chemotrypsin and elastase) act on the peptide bonds of proteins, forming peptides and amino acids. Exopeptidases (carboxypeptidase A and B, aminopeptidase) cleave end bonds in proteins and peptides with the release of amino acids. These proteolytic enzymes are secreted by the cells of the pancreas in the form of proenzymes. They are activated in the duodenum. Trypsinogen is converted to the active form trypsin under the influence of intestinal juice enteropeptidase. Trypsin, in turn, activates chemotrypsinogen into chemotrypsin, procarboxypeptidase A and B into carboxypeptidase A and B, and proelastase into elastase.

Lipolytic enzymes are secreted in an inactive (prophospholipase A) and active (lipase, lecithinase) state. Pancreatic lipase hydrolyzes neutral fats to monoglycerides and fatty acids. Phospholipase A breaks down phospholipids into fatty acids. The action of lipase is enhanced in the presence of bile and calcium ions.

Amylolytic enzyme (pancreatic alpha-amylase) breaks down starch and glycogen into di- and monosaccharides. Disaccharides are further broken down by maltase and lactase into monosaccharides.

Nucleotic enzymes: ribonuclease, carries out glycolysis of ribonucleic acid, and deoxynuclease hydrolyzes deoxynucleic acid.

In order to protect the pancreas from self-digestion, the same secretory cells also produce a trypsin inhibitor.

Pancreatic juice in dogs is secreted periodically - when taking food. In the mechanism of juice secretion, a mild, short, complex reflex phase is distinguished, associated with the preparation of feed for feeding and its intake, as a result of which the continuous secretion of juice increases. The gastric phase occurs when food enters the stomach and the effect on the secretory cells of the products of digestion of food, hydrochloric acid, gastrin. After the passage of contents from the stomach into the intestines, the intestinal phase occurs. This phase is supported by the reflex effects of chyme on the duodenal mucosa and hormones - secretin, pancreozymin, insulin, prostaglandins.

The secretion of juice is inhibited by glucagon, calcitonin, somatostatin, adrenaline. There is no consensus on the influence of nerves on the secretion of juice. There is evidence that secretin acts on pancreatic cells with the participation of the sympathetic nervous system, tk. blocking it with dihydroergotamine inhibits juice secretion. Therefore, the intestinal phase of pancreatic juice secretion can be considered as a neurochemical phase. The nature of juice secretion and its enzymatic activity also depend on the type of feed fed.

The exocrine section is built from glandular end sections - acini and brood ducts.

The endocrine portion of the pancreas is made up of small clusters of cells known as the islets of Langerhans (Figure 6). They are separated from the acini of the endocrine part of the gland by layers of connective tissue. These islets are surrounded and permeated by a rich capillary network that carries blood from the islets to the acinar cells.

4.2 Digestion in the small intestine

There are more than 20 digestive enzymes in intestinal juice. They act on products already exposed to the action of stomach and pancreatic enzymes. The juice contains peptidases - aminopolypeptidases, dipeptidases, etc., united under the general name - erypsins. The cleavage of nucleotides and nucleic acids is carried out by the enzymes nucleotidase and nuclease.

Lipolytic enzymes of intestinal juice are lipase, phospholipase.

Amylase, lactase, sucrose, gamma-amylase are amylolytic enzymes.

Important enzymes of intestinal juice are alkaline and acid phosphatase, enterpeptidase.

Intestinal enzymes complete the hydrolysis of nutrient intermediates. The dense part of the juice has a much greater enzymatic activity. Using the method of layer-by-layer study of the distribution of enzymes in the mucous membrane, it was determined that the main content of intestinal enzymes is concentrated in upper layers mucous membrane of the duodenum, and the distance from it, the number of enzymes decreases.

Secretion of intestinal juice occurs continuously. Reflex influences from the receptors of the oral cavity are weakly expressed and only in the cranial sections of the small intestine. Secretion increases when the mucous membrane is exposed to mechanical and chemical stimuli by chyme, which occurs with the participation of intramural nerve formations and the central nervous system. Vagus nerves, acetylcholine, enterocrinin, duocrinin stimulate the secretion of juice. Sympathetic nerves and adrenaline - inhibit juice secretion.

In the small intestine, along with cavity digestion, carried out by juices and enzymes of the pancreas, bile and intestinal juice, membrane or parietal hydrolysis of nutrients occurs. During abdominal digestion, the initial stage of hydrolysis occurs and large molecular compounds (polymers) are cleaved, and during membrane digestion, the hydrolysis of nutrients is completed with the formation of smaller particles available for absorption. Cavitary hydrolysis is 20-50%, and membrane - 50-80%. Membrane digestion is facilitated by the structure of the intestinal mucosa, which, in addition to villi, has great amount and microvilli forming a kind of brush border.

Each villus has a central lymphatic capillary that runs through its middle and connects to lymphatic vessels in the submucosal layer of the intestine. In addition, in each villus there is a plexus of blood capillaries, through which the outflowing blood eventually enters the portal vein (Fig. 7). In addition to the villi, there are crypts in the mucous membrane of the small intestine; invaginations containing relatively undifferentiated cells. Although the villi contain both goblet cells and immune cells, the main cells of the villi are enterocytes. At the apical portion of its membrane, each enterocyte is covered with microvilli, which enhance digestion and increase the absorptive surface of the small intestine. Enterocytes live only 3-7 days, then they are renewed. Enterocytes are closely connected to each other, so that almost all absorption takes place in the microvilli, and not through the extracellular space.

The mucus secreted by goblet cells creates a mucopolysaccharide network on the surface of the brush border - glycocalyx, which prevents the penetration of large molecules of nutrients and microbes into the lumen between the villi, so membrane hydrolysis occurs under sterile conditions. Enzymes that carry out membrane hydrolysis or are adsorbed from chyme are pancreatic juice enzymes ( a -amylase, lipase, trypsin), or are synthesized in intestinal epitheliocytes and are fixed on the membranes of the villi, being in a structurally bound state with them. Thus, parietal digestion is final stage hydrolysis of nutrients and initial stage their absorption through the membranes of epithelial cells.

In the intestine, the biological neutralization of the contents takes place. This is achieved by the fact that in the mucous membrane of the small intestine there is a large amount of reticular tissue, which forms single lymphatic nodules and their accumulations - lymphatic plaques.

Chyme moves from the duodenum along the small intestine for complete digestion and absorption by the villi and microvilli. The muscular wall of the small intestine consists of an inner circular and outer longitudinal layers and performs two types of contractions: segmentation and peristalsis. Segmentation causes agitation of the chyme, moving the contents of the intestine in a pendulum-like manner, due to periodic contractions of segments of the small intestine. Peristalsis is the movement of digested material towards the large intestine. These muscle contractions are controlled by the intestinal nervous system, modulated by the parasympathetic nervous system and hormones.

There are four main types of contractions in the intestines:

.Rhythmic segmentation occurs as a result of rhythmic alternation (8-10 times per minute) of areas of contraction of the circular muscles with the formation of segments - with areas of relaxation between them.

2.Peristaltic contractions are characterized by the formation of a constriction located above a separate portion of the chyme, and its undulating distribution in the aboral direction with simultaneous mixing and promotion of the chyme.

.Pendulum movements are carried out by contraction of the annular and longitudinal layers of muscles, which provide oscillation of the intestinal wall section forward and backward, which, together with rhythmic segmentation, creates good conditions for mixing the chyme.

.Tonic contractions are characterized by a prolonged tone of the smooth muscles of the intestine, against which other types of intestinal contractions occur.

Tonic contractions often occur in pathology. The smooth muscles of the intestine are also capable of spontaneous (automatic) contractions caused by the intramural nervous system. Intestinal motility is stimulated by mechanical and chemical stimulation of the intestinal mucosa by chyme. Nervous regulation of motility is carried out by the intramural nervous system and the central nervous system.

The vagus and splanchnic nerves, depending on their initial functional state, can excite or inhibit motor activity intestines, because they carry different fibers. Parasympathetic nerves, as a rule, excite, and sympathetic - inhibit bowel contractions. The influence of various emotions, verbal stimuli testify to the role of the higher parts of the central nervous system (the hypothalamus and the cerebral cortex) in the regulation of the motility of the digestive tract. A variety of chemicals have a certain effect. Acetylcholine, histamine, serotonin, gastrin, enterogastrin, oxytocin, etc. stimulate, and adrenaline, gastron, enterogastron - inhibit intestinal motility.

3 The structure and functions of the liver

The liver is the largest digestive gland. It lies in the abdominal cavity, directly adjacent to the diaphragm, reaching, on the right and left, the last ribs. The dog's liver is divided into 6-7 lobes. On the curved visceral surface of the liver in the center of the organ are the gates of the liver, through which the portal vein enters it. On the same side of the liver, between its lobes, lies the gallbladder. The liver consists of hepatic lobules located on the branches of the hepatic veins (Fig. 8). Hepatic lobules consist of hepatic beams formed by hepatic cells - hepatocytes, located in one row. Hepatocytes are separated from the bile capillaries by a basement membrane, and from the sinusoids by a sinusoidal membrane. Adjacent hepatic beams are separated from each other by sinusoids, which are lined with endothelial cells. The processes of endothelial cells form pores that serve for direct contact of the plasma and hepatocyte with the sinusoidal membrane. The endothelium of the sinusoids does not have a basement membrane, it is surrounded by a perivascular space filled with blood plasma, which contributes to the transfer of protein-bound substances to hepatocytes, as well as from the hepatocyte to the sinusoids. Thus, functionally, the sinusoidal membrane is involved in the process of two-way transfer of substances. The main function of the membrane facing the bile capillaries is the secretion of bile. On the same part of the hepatocyte membrane, specific enzymes are located: alkaline phosphatase, γ- glutamyl transpeptidase. From the capillaries, bile enters the terminal bile ducts, which gradually merge into larger ducts, then into the introlobular ducts lined with cuboidal epithelium. From them, bile enters the gallbladder and duodenum.

In addition to parenchymal cells (hepatocytes - 60%), the liver contains Kupffer cells - 25%, endothelial cells - 10%, fat storage cells - 3% and Pit cells - 2%. The main function of Kupffer cells is phagocytosis of microbes, tumor cells, aging erythrocytes, production of cytotoxic factors, interleukins, interferon. Fat-depositing cells are responsible for storing vitamin A, the synthesis of extracellular matrix proteins, and the regulation of blood flow in the sinusoids. The task of Pit cells is to activate natural killer cells.

Main functions of the liver

bile-forming and excretory,

barrier and protective

neutralizing and biotransformational,

metabolic,

homeostatic,

depositing,

regulatory.

4 Bile and its role in digestion

Bile is the secretion and excretion of hepatocytes. Dogs are red and yellow. There are hepatic bile, located in the bile ducts with a density of 1.010-1.015 and pH 7.5-8.0, and cystic bile, which, due to the absorption of part of the water in the gallbladder, acquires a darker color, its density reaches 1.026-1.048 and pH-6, 5-5.5. The composition of gallbladder bile includes 80-86% water, cholesterol, neutral fats, urea, uric acid, amino acids, vitamins A, B, C, a small amount of enzymes - amylase, phosphatase, protease, etc. The mineral part is represented by the same elements as and other digestive juices. Bile pigments (bilirubin and biliverdin) are products of hemoglobin transformations during the breakdown of red blood cells. They give the bile the appropriate color. The bile of carnivores contains more bilirubin.

The true secret of hepatocytes are bile acids - glycocholic and taurocholic. In the distal small intestine, under the influence of microflora, about 20% of primary cholic acids are converted into secondary ones - deoxycholic and lithocholic. Here, 85-90% of bile acids are reabsorbed and returned to the liver as bile, and the rest of their deficiency is replenished by hepatocytes.

The value of bile:

1.The value of bile for the hydrolysis of fats in the gastrointestinal tract lies, first of all, in the fact that it turns them into a finely dispersed emulsified state, thus creating favorable conditions for the action of lipases.

2.Bile acids, when combined with fatty acids, form a water-soluble complex available for absorption, after which it breaks down. Bile acids enter the liver and again go into bile, and fatty acids combine with already absorbed glycerol, forming triglycerides. One molecule of glycerol combines with three molecules of fatty acids. Thus, bile ensures the absorption of fatty acids.

.Bile enters the intestine to promote absorption fat soluble vitamins- retinol, carotene, tocopherol, phylloquinone, as well as unsaturated fatty acids.

.Bile substances enhance the activity of amylo-, proteo- and lipolytic enzymes of pancreatic and intestinal juices.

.Bile stimulates the motility of the stomach and intestines and promotes the passage of contents into the intestines.

.Due to the content of alkaline salts, bile is involved in the neutralization of hydrochloric acid, which enters the intestine with the contents from the stomach, thereby stopping the action of pepsin and creating conditions for the action of trypsin.

.Bile proteins form a precipitate that binds pepsin, and this contributes to the protection of the duodenal mucosa from the destructive action of gastric proteases.

8.Bile components stimulate the secretion of pancreatic and intestinal juices.

.Bile has a bactericidal effect on the putrefactive microflora of the gastrointestinal tract and inhibits the development of many pathogens.

10.Many are excreted in the bile medicinal substances and hormonal breakdown products.

Bile is secreted continuously and enters the bile ducts and gallbladder.

The secretion of bile reflexively increases with the intake of food, due to irritation of the receptors of the oral cavity, stomach and duodenum. The secretion of bile is regulated by the vagus nerves, which cause the sphincter of the gallbladder to relax and contract its wall, which ensures the flow of bile into the duodenum. Irritation of the sympathetic nerves causes the opposite effect - relaxation of the bladder wall and contraction of the sphincter, which contributes to the accumulation of bile in the bladder. Stimulate the secretion of bile hormones cholecystokinin, gastrin, secretin and fatty foods.

5 Digestion in the large intestine

The large intestine consists of the caecum, colon, and rectum. The large intestine begins at the ileocecal valve and ends anus- anus.

The caecum, representing the first section of the large intestine, is located in the border of the ileum and colon and has the form of a short curved protrusion. It is located in the right half of the abdominal cavity in the region of the 2nd-4th lumbar vertebrae. The colon is a simple smooth narrow loop that passes into the rectum. The rectum is a short terminal section of the large intestine, which is a continuation of the descending knee of the colon, ending under the first tail vertebra with the anus. In dogs, in the region of the anus, the ducts of two anal glands open, releasing a thick mass of secretion with a specific odor.

The main differences in the structure of the large and small intestines are that the mucous membrane of the large intestines has only simple intestinal glands that secrete mucus that promotes the intestinal contents.

Food processing in the large intestine

Chyme of the small intestine every 30-60 with small portions through the ileocecal sphincter enters the thick section. When filling the cecum, the sphincter closes tightly. There are no villi in the mucous membrane of the large intestine. There are a large number of goblet cells that produce mucus. Juice is released continuously under the influence of mechanical and chemical irritations of the mucous membrane. The juice of the large intestine contains a small amount of peptidases, amylase, lipase, nuclease. Enteropeptidase and sucrose are absent. Hydrolysis of nutrients is carried out both due to its own enzymes and enzymes brought here with the contents of the small intestine. Particularly important in the digestive processes of the large intestine is the microflora, which finds here favorable conditions for its abundant reproduction.

The main function of the large intestine is the absorption of water. The process of digestion in the large intestine is partially continued by the juices that have entered it from the small intestine. Favorable conditions for the vital activity of microflora are created in the large intestine. Under the influence of the intestinal microflora, carbohydrates are broken down to volatile fatty acids (acetic - 51 mmol%, propionic - 36 mmol% and oily - 13 mmol%) with the release of gas.

The microflora of the large intestine synthesizes vitamins K, E and group B. With its participation, the suppression of pathogenic microflora occurs, it contributes to the normal functioning of the immune system. Enzymes from the small intestine, especially enteropeptidase, are inactivated with the participation of microorganisms. Carbohydrate feeds contribute to the development of fermentation processes, and protein feeds - putrefactive, with the formation of harmful, poisonous substances for the body - indole, skatole, phenol, cresol and various gases. The decay products of proteins are absorbed into the blood and enter the liver, where they are neutralized with the participation of sulfuric and glucuronic acids. Diets balanced in terms of carbohydrate and protein content balance the processes of fermentation and decay. The resulting large inconsistencies in these processes cause disturbances in digestion and other body functions. In the large intestine, the processes of absorption end, the contents accumulate in it and the formation of feces occurs. The types of contraction of the large intestine and its regulation are almost the same as those of the small intestine.

In the back of the large intestine, fecal matter is formed. Chyme is about 14.5 liters per kilogram of fecal matter.

Excretion of feces (defecation) is a reflex act caused by irritation faecal matter rectal mucosa during its filling. The resulting impulses of excitation along the afferent nerve pathways are transmitted to the spinal center of defecation, from there they go along the efferent parasympathetic pathways to the sphincters, which relax while increasing the motility of the rectum and the act of defecation is carried out.

The act of defecation is facilitated by the appropriate posture of the animal, contractions of the diaphragm and abdominal muscles, which increase intra-abdominal pressure.

5. FEATURES OF BLOOD SUPPLY AND INNERVATION OF THE GASTROINTESTINAL TRACT

The main arteries supplying blood to the stomach and intestines are the celiac artery, as well as the cranial and caudal mesenteric. The celiac artery supplies the stomach, the proximal duodenum, part of the pancreas, and the liver. The short trunk of the celiac artery almost immediately divides into the hepatic and splenic arteries. Cranial mesenteric artery It supplies blood to part of the pancreas and duodenum, jejunum, ileum and proximal colon. The caudal mesenteric artery supplies the distal colon, the rectum, except for its distal section, which is supplied with branches from the internal iliac artery. Venous outflow from the stomach, pancreas, intestines occurs through the portal vein, from the distal part of the rectum through the internal iliac vein. Intestinal vessels form numerous anastomoses, arches, contributing to the formation of collateral circulation. From these collaterals originate vessels that directly supply the circular muscles of the intestinal wall with blood (Fig. 9).

In the submucosa of the stomach, the arteries divide into capillaries, branching in the form of a network and eventually flowing into the venules of the gastric mucosa. These venules, merging, form collective veins, which then flow into the venous plexuses of the submucosal layer.

The small intestine has a wide network of anastomosing arteries and veins that form a plexus in the submucosa. The capillaries of the muscular, submucosal and mucous membranes of the intestine emerge from this plexus. The blood supply to the microvilli includes a system consisting of two arterioles. The first supplies blood to the tip of the villus, dividing into capillaries, the other arteriole supplies blood to the rest of the villus.

In the large intestine, the capillaries after branching are located between the crypts and are drained by venules of the submucosa.

The external innervation of the gastrointestinal tract consists of parasympathetic and sympathetic nerves, which carry out the transmission of information through afferent and efferent fibers. Sensory afferent from the intestine is transmitted along the afferent fibers of the vagus nerve or spinal afferent fibers. The central link of vagal afferentation is located in the nuclei of the solitary tract, and the efferent fibers pass to the periphery as part of the vagus nerve. The central link of spinal afferentation ends at posterior horns spinal cord, and efferent fibers go to the periphery as part of sympathetic nerves. The cell bodies of visceral afferent neurons are localized in the ganglia of the posterior roots. Visceral afferent neurons form synapses with lateral and other neurons at the base of the dorsal roots.

6. SUCTION

Absorption is a complex physiological process that ensures the penetration of nutrients through cell membranes and their entry into the blood and lymph. Absorption occurs in all parts of the digestive tract, but with different intensity. In the oral cavity in dogs, absorption is negligible, due to the short stay of food here and the low absorption capacity of the mucous membrane. Water, alcohol, a small amount of salts, amino acids, monosaccharides are absorbed in the stomach. The main section of absorption of all hydrolysis products is the small intestine, where the nutrient transfer rate is exceptionally high. This is facilitated by the peculiarity of the structure of the mucous membrane, which consists in the fact that throughout there are folds and a huge number of villi, which significantly increase the absorption surface. In addition, each epithelial cell contains microvilli, due to which the absorptive surface is additionally increased hundreds of times. The transport of macromolecules can be carried out by phagocytosis and pinocytosis, but in digestive tract mainly micromolecules are absorbed and their absorption is carried out by passive transfer of substances with the participation of diffusion, osmosis and filtration processes. Active transport occurs with the participation of special carriers and energy costs released by macrophages. The substrate (nutrients) combines with the membrane carrier protein, forming a complex compound that moves to the inner layer of the membrane and decomposes into the substrate and carrier protein. The substrate enters the basement membrane and further into the connective tissue, blood or lymphatic vessels. The released carrier protein returns to the surface of the apical membrane for a new portion of the substrate.

Absorption in the intestines is also facilitated by the contraction of the villi, due to which, at this time, lymph and blood are squeezed out of the lymphatic and blood vessels. When the villi relax, a slightly negative pressure is formed in the vessels, which contributes to the absorption of nutrients in them. Stimulators of villi contraction are the products of hydrolysis of nutrients and the hormone villikin, produced in the mucosa of the duodenum and jejunum.

Absorption in the large intestine is insignificant, water is absorbed here, in small amounts of amino acids, glucose, on which the use of deep nutritional enemas in clinical practice is based.

Water is absorbed according to the laws of osmosis, so it can easily pass from the intestine to the blood and back to the intestinal chyme.

Nutrient absorption is influenced by nervous and hormonal factors. Reflex regulation of absorption is carried out with the participation of various receptors of the digestive tract, which provide information to the central nervous system about the secretory-enzymatic, motor and other functions of the digestive organs, with which the absorption activity of the digestive tract is closely related. Hormones of the adrenal glands, pancreas, thyroid, parathyroid glands and posterior pituitary.

LITERATURE

1.Anatomy of domestic animals / A.I. Akayevsky, Yu.F. Yudichev, N.V. Mikhailov, I.V. Khrustalev. - M.: Kolos, 1984. - S.212-254.

3.Joerg M., Steiner. Gastroenterology of dogs and cats. - M.: Mars, 2004. - S. 5-17.

4.Physiology of agricultural animals / A.N. Golikov, N.U. Bazanova, Z.K. Kozhebekov and others - M.: VO Agropromizdat, 1991. - S.87-113.

5. Lineva A. Physiological indicators of the norm of animals. - M.: Aquarium LTD, K.: FGUIPPV, 2003. - S. 153-169.

Service dog / A.P. Mazover, A.V. Krushinnikov and others - M.: D.: VAP, 1994. - 576 p.

7. Liz Palika. The consumer s guide to dog food. - New York: Howell Boo house, 1999. - P. 254.

Digestion is a complex process in which the digestion (mechanical and physico-chemical processing) of feed occurs, the release of undigested residues and the absorption of nutrients by cells. Digestion is the initial stage of metabolism. In addition, the digestive tract performs a number of other important functions.

Main functions of the digestive tract:

• secretory - the production and secretion of digestive juices (saliva, gastric and pancreatic juice, bile, intestinal juice) by glandular cells;
• motor (motor) - grinding the feed, mixing it with digestive juices and moving around the gastrointestinal tract *;
• absorption - the transfer of end products of digestion, water, salts and vitamins through the epithelium of the digestive tract into the blood and lymph;
• excretory - excretion of metabolic products, toxins, undigested and excess substances from the body;
• endocrine - synthesis and release of biologically active substances and hormones;
• protective - protection of the internal environment of the body from the ingress of harmful agents (bactericidal, bacteriostatic and detoxification effect);
• immune - about 70% of the body's immune cells are located in the gastrointestinal tract;
• receptor - the implementation of nerve connections, the implementation of visceral and somatic reflexes;
• heat producing;
• homeostatic - maintaining a constant chemical composition of blood plasma.

* GIT - gastrointestinal tract

The digestive system of dogs is very different from the digestive system of humans.

As you can see, the relative volume of the gastrointestinal tract in dogs is less than in humans, therefore, the processes of digestion in our four-legged friends should be much more intense. When eating, a dog, unlike a person, does not chew pieces. There are no enzymes in the saliva of dogs, and the "human" fermentation of the food bolus does not occur. Therefore, eating in humans takes almost 10 times more time than in dogs. But the number of microorganisms in the intestines of dogs is 3 orders of magnitude less than that of humans.

With all this, the digestive tract of our pets works as efficiently as ours! Due to what is this possible? The gastrointestinal tract of dogs "works for wear", with maximum efficiency. And we, responsible owners, should help our pets.

Digestion in the stomach.

The capacity of the stomach in dogs of medium size is 2-2.5 liters. Such a relatively large size is due to the fact that predators eat food in large portions, and the stomach, being a reservoir of food, contributes to the uniform filling of the intestine.

At the reception of 1 kg of feed, from 0.3 to 0.9 liters of gastric juice is allocated. Its acidity is much higher than that of humans (for the digestion of bones and the destruction of dangerous bacteria that have entered the body with food). Due to the high acidity of gastric juice, which is detrimental to microflora, in dogs, fiber in the stomach is almost not digested. Glycogen and starch are not digested in it, since there are no suitable enzymes in saliva and gastric juice. Glucose is absorbed in the stomach.

Food passes through the stomach at different speeds. Rough food stays longer in the stomach. Liquid food passes from the stomach very quickly, a few minutes after eating, and warm faster than cold. Food moves from the stomach to the intestines in batches.

Digestion in the intestines.

The small intestine is the main site of digestion and absorption of nutrients. The contents coming in small portions from the stomach to the intestines undergo further hydrolysis processes in it under the action of the secrets of the pancreas, intestines and bile.

1. Pancreas and its role in digestion

Pancreatic juice is a colorless transparent liquid of an alkaline reaction (pH 7.5-8.5). The inorganic part of the juice is represented by sodium, calcium, potassium, carbonates, chlorides, etc. Organic substances include enzymes for the hydrolysis of proteins, fats and carbohydrates, and various other substances. Proteins are cleaved by proteolytic enzymes - endopeptidases and exopeptidases.

Pancreatic lipase hydrolyzes neutral fats to monoglycerides and fatty acids. Phospholipase A breaks down phospholipids into fatty acids. Amylolytic enzyme (pancreatic alpha-amylase) breaks down starch and glycogen into di- and monosaccharides.

Nucleotic enzymes: ribonuclease, carries out glycolysis of ribonucleic acid, and deoxynuclease hydrolyzes deoxynucleic acid.

2. Digestion in the small intestine

Intestinal juice is produced by cells in the lining of the small intestine. Juice is a cloudy viscous liquid with a specific odor, consisting of dense and liquid parts. The formation of the dense part of the juice occurs by the holocrine type of secretion associated with rejection, desquamation of the intestinal epithelium. The liquid part of the juice is formed by aqueous solutions of organic and inorganic substances. There are more than 20 digestive enzymes in intestinal juice. They act on products already exposed to the action of stomach and pancreatic enzymes.

Intestinal enzymes complete the hydrolysis of nutrient intermediates. The dense part of the juice has a much greater enzymatic activity.

Using the method of layer-by-layer study of the distribution of enzymes in the mucous membrane, it was determined that the main content of intestinal enzymes is concentrated in the upper layers of the duodenal mucosa, and the number of enzymes decreases with distance from it. Secretion of intestinal juice occurs continuously. Reflex influences from the receptors of the oral cavity are weakly expressed.

In the small intestine, along with cavity digestion, carried out by juices and enzymes of the pancreas, bile and intestinal juice, membrane or parietal hydrolysis of nutrients occurs. During abdominal digestion, the initial stage of hydrolysis occurs and large molecular compounds (polymers) are cleaved, and during membrane digestion, the hydrolysis of nutrients is completed with the formation of smaller particles available for absorption. Cavitary hydrolysis is 20-50%, and membrane - 50-80%. Membrane digestion is facilitated by the structure of the intestinal mucosa, which, in addition to villi, has a huge number of microvilli, which form a kind of brush border. Each villus has a central lymphatic capillary that runs through its middle and connects to lymphatic vessels in the submucosal layer of the intestine. In addition, in each villus there is a plexus of blood capillaries, through which the outflowing blood ultimately enters the portal vein.

Although the villi contain both goblet cells and immune cells, the main cells of the villi are enterocytes. At the apical portion of its membrane, each enterocyte is covered with microvilli, which enhance digestion and increase the absorptive surface of the small intestine. Enterocytes live only 3-7 days, then they are renewed. Enterocytes are closely connected to each other, so that almost all absorption takes place in the microvilli, and not through the extracellular space.

The mucus secreted by the cells creates a mucopolysaccharide network on the surface of the brush border - glycocalyx, which prevents the penetration of large molecules of nutrients and microbes into the lumen between the villi, so membrane hydrolysis occurs under sterile conditions. Thus, parietal digestion is the final stage in the hydrolysis of nutrients and the initial stage of their absorption through the membranes of epithelial cells. Chyme (what food has become) moves from the duodenum along the small intestine for complete digestion and absorption by the villi and microvilli.

3. Liver and its role in digestion.

The liver is the largest digestive gland. And bile is the secretion and excretion of liver cells. Bile contains 80-86% water, cholesterol, neutral fats, urea, uric acid, amino acids, vitamins A, B, C, a small amount of enzymes - amylase, phosphatase, protease, etc. The mineral part is represented by the same elements as other digestive juices. Bile pigments (bilirubin and biliverdin) are products of hemoglobin transformations during the breakdown of red blood cells. They give the bile the appropriate color.

The value of bile for the hydrolysis of fats in the gastrointestinal tract lies primarily in the fact that it turns them into a finely dispersed state, thus creating favorable conditions for the action of lipases. Bile acids combine with fatty acids to form a water-soluble complex available for absorption.

The bile that enters the intestine promotes the absorption of fat-soluble vitamins - retinol, carotene, tocopherol, phylloquinone, as well as unsaturated fatty acids.

Bile substances enhance the activity of amylo-, proteo- and lipolytic enzymes of pancreatic and intestinal juices. Bile stimulates the motility of the stomach and intestines and promotes the passage of contents into the intestines. Bile is secreted continuously and enters the bile ducts and gallbladder.

5. Digestion in the large intestine.

The large intestine consists of the caecum, colon, and rectum. The main differences in the structure of the large and small intestines are that the mucous membrane of the large intestines has only simple intestinal glands that secrete mucus that promotes the intestinal contents. Chyme of the small intestine every 30-60 with small portions through the ileocecal sphincter enters the thick section. There are no villi in the mucous membrane of the large intestine. There are a large number of cells that produce mucus. Juice is released continuously under the influence of mechanical and chemical irritations of the mucous membrane. The main function of the large intestine is the absorption of water. The process of digestion in the large intestine is partially continued by the juices that have entered it from the small intestine. Favorable conditions for the vital activity of microflora are created in the large intestine. Under the influence of intestinal microflora, the breakdown of carbohydrates occurs with the release of gas. The microflora of the large intestine synthesizes vitamins K, E and group B. With its participation, the suppression of pathogenic microflora occurs, it contributes to the normal functioning of the immune system.

Suction.

Absorption is a complex physiological process that ensures the penetration of nutrients through cell membranes and their entry into the blood and lymph. Absorption occurs in all parts of the digestive tract, but with different intensity. The main section of absorption of all hydrolysis products is the small intestine, where the nutrient transfer rate is exceptionally high. This is facilitated by the peculiarity of the structure of the mucous membrane, which consists in the fact that throughout there are folds and a huge number of villi, which significantly increase the absorption surface. In addition, each epithelial cell contains microvilli, picture; due to which the suction surface is additionally increased hundreds of times. The transport of macromolecules can be carried out by "swallowing", but in the digestive tract, micromolecules are mainly absorbed and their absorption is carried out by passive transfer of substances with the participation of the diffusion process. Active transport occurs with the participation of special carriers and energy costs released by macrophages. The substrate (nutrients) combines with the membrane carrier protein, forming a complex compound that moves to the inner layer of the membrane and decomposes into the substrate and carrier protein. The substrate enters the basement membrane and further into the connective tissue, blood or lymphatic vessels. The released carrier protein returns to the surface of the cell membrane for a new portion of the substrate. Absorption in the intestines is also facilitated by the contraction of the villi, due to which, at this time, lymph and blood are squeezed out of the lymphatic and blood vessels. When the villi relax, a slightly negative pressure is formed in the vessels, which contributes to the absorption of nutrients in them.

From the foregoing, it becomes clear that the efficiency of absorption of nutrients and vitamins depends on the strength of cell membranes in the small intestine.

First, the cells of the intestinal epithelium are busy producing intestinal juice, which is needed for the breakdown of large molecules, and their transformation for better digestibility. And intestinal juice is part of the membranes and the cytoplasm of these cells (holocrine secretion). The juice is constantly secreted, so the cells all the time need to restore their apical (extending into the intestinal lumen) membranes.

Secondly, all absorption occurs on the surface of the intestinal cells, and the membranes play a major role here. Regardless of the mechanism of absorption (phagocytosis, or "swallowing", diffusion, osmosis), maximum efficiency is achieved only in the presence of strong cell membranes.

And, thirdly, enterocytes live only 3-7 days. That is, 1 or 2 times a week, the intestines are completely renewed from the inside. A huge number of new cells are formed to occupy 4 meters of the intestine! It should also be taken into account that damaging factors and toxins also contribute to the death of intestinal cells.

This is why strong intestinal cell membranes are so important. After all, even balanced diet does not yet guarantee that the nutrients will be beneficial and not transitory.

That is why drugs with a membrane-protective property are used not only in the combined treatment of digestive problems, but also for prevention during stress, and as a permanent supplement to the animal's diet. Prenocan is the first and so far the only veterinary drug designed specifically for dogs. It contains only polyprenyl phosphates and lactose. Polyprenyl phosphates are essential components of cell membranes and are also involved in the processes of protein and carbohydrate metabolism. The main source of entry into the body of animals and humans is plant foods, where polyprenols are in an inactive form. To perform their basic functions in the body, polyprenols undergo a process of phosphorylation, becoming polyprenyl phosphates. When phosphorylated polyprenols enter the body, they are very quickly absorbed by cells and spent on the direct needs of the body. Their effectiveness has been scientifically and clinically proven.

Proper diet, fresh food, a suitable daily routine, lack of stress and additional help with digestion - this is what our assistance to four-legged should be.

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FEATURES OF DIGESTION IN DOGS

Dogs are carnivores. However, as a result of long-term human influence, their body has adapted to eating and absorbing the nutrients of a diet consisting of meat, fish, dairy, vegetable and grain feed.

In the process of digestion, proteins, fats and carbohydrates of feed undergo significant changes: proteins break down into amino acids, carbohydrates into glucose, fats into glycerol and fatty acids. These substances are absorbed into the blood and lymph and are used both for building the body and as energy sources.

Changes in feed in the digestive tract occur as a result of their physical (grinding, moisturizing, etc.), chemical (with the help of digestive gland juices containing enzymes) and biological (with the participation of microflora) processing.

Digestion begins in the mouth. Simultaneously with chewing food in the oral cavity, food is wetted with saliva, which, in addition to water, proteins, chlorides, phosphates, bicarbonates, etc., contains lysozyme, a substance that kills bacteria. This seems to be related to dogs licking their wounds. The intensity of secretion and the nature of saliva vary depending on the food. More saliva is secreted for dry food, less for watery food. Saliva is secreted on food substances thick, viscous, with a high content of mucin. The saliva secreted by rejected substances (pepper, acid, soda, etc.) is liquid, the so-called "washing" saliva. Especially developed in dogs is the secretion of saliva in response to mental excitations. For example, if a dog is familiar with some food substance, then when he sees (shows) it, he always reacts with salivation. Unlike other animals, in the oral cavity of a dog, food is almost not subjected to chemical digestion.

Digestion of food begins in the stomach. Normal stomach capacity in medium-sized dogs is 2–2.5 liters. The stomach in dogs is single-chamber, gastric juice is secreted in it. Pure gastric juice has an acidic reaction due to the presence of hydrochloric acid, the content of which depends on the nature of the food. Gastric juice contains enzymes that digest food. Pepsin digests proteins in the presence of hydrochloric acid. Different feed proteins are digested differently by pepsin. For example, meat proteins are digested quickly, egg white is much slower. The optimal concentration of hydrochloric acid for protein digestion is 0.1-0.2%, a high concentration (0.6%), as well as a low one, reduces the effect of pepsin. The second enzyme of gastric juice is chymosin. It converts milk caseinogen into casein. Under the action of this enzyme, milk curdles in the stomach and is digested by the enzymes of gastric juice. Puppies have relatively more chymosin and less pepsin and hydrochloric acid; adult dogs, on the contrary, have more pepsin and hydrochloric acid and less chymosin. In the gastric juice there is also lipase, which breaks down fats, but its amount is small. More lipase in the gastric juice of young dogs, in which it digests milk fat.

In the absence of food, the gastric glands are at rest. But as soon as the dog begins to eat or sees familiar food, it enters a state of food excitement, and after 5-6 minutes, the secretion of gastric juice begins in its stomach. The emotional arousal of the dog also affects the juice secretion. If a cat is shown to a dog in the midst of gastric secretion, this will infuriate her and the secretion of juice stops.

Juice differs in acidity and digesting power for different foods. The acidity of the juice is the highest when eating meat - an average of 0.56%, milk - 0.49%, bread - 0.47%. The digestive power of juice is greatest when eating bread - an average of 6.6 mm, meat - 4 mm, milk - 3.3 mm. The secretion of the glands of the stomach largely depends on the quality of the feed, especially its taste.

Thus, the quantity and quality of digestive juice depends on the composition of the diet. So, for example, when feeding dogs only meat, a small amount of viscous saliva is released, bread - a large amount of liquid saliva. The separation of gastric juice proceeds in a similar way: the gastric juice richest in enzymes is separated for bread, but with a small amount acids, for meat - the richest in acid.

In the study of gastric juice, it turned out that various feed substances not only cause the separation of gastric juice of different composition, which has different digesting power and acidity, but there are differences in the very nature of the separation of juice.

When feeding bread, the maximum amount of gastric juice is secreted in the first hour, then during the second hour the secretion drops significantly and gradually approaches zero.

When feeding with meat during the first two hours, the secretion remains almost the same, then it quickly falls and reaches zero in 2-3 hours.

The amount of juice secretion of the gastric glands is directly dependent on the nature of a particular feeding regime. A long-term, protein-rich meat regimen leads to an increase in the absolute amount of gastric juice rich in proteins and enzymes, while a long-term carbohydrate (bread) diet causes a sharp decrease in the amount of gastric juice. Given this situation, in no case should you change the feed rations of dogs abruptly, the transition from one feed ration to another should be carried out gradually.

Different foods pass through the stomach at different speeds. Coarse food stays longer in the stomach, liquid food leaves the stomach a few minutes after eating, and warm food is faster than cold food. Food passes from the stomach to the intestines in portions.

Dogs exhibit vomiting. Vomiting appears as a result of irritation of the mucous membrane of the stomach or intestines by toxic substances that have entered the stomach with food, or as a result of strong mechanical irritation of the pharynx of the esophagus by solid particles of food. In these cases, vomiting should be considered as a protective reaction of the body. But vomiting occurs, for example, with an increase in intracranial pressure or with the appearance in the blood of substances that irritate the vomiting center. Such substances can be bacterial toxins and products of abnormal metabolism. Vomiting can be caused by administering apomorphine to a dog.

From the stomach, food masses gradually enter the intestinal, where intestinal juice, pancreatic juice and bile are poured onto them. All these juices have a powerful digestive effect. The reaction of these juices and intestinal contents is generally alkaline. Pancreatic juice is rich in enzymes. Trypsin breaks down proteins and peptides into amino acids. To digest carbohydrates, pancreatic juice contains amylase, which digests starch and glycogen to glucose. It also contains a nuclease that digests nucleic acids. Pancreatic lipase breaks down fats into glycerol and fatty acids. The composition of pancreatic enzymes varies with the nature of the diet. In total, more pancreatic juice is secreted when feeding with bread, less when feeding with milk. The duration of secretion is greatest when eating bread, in the shortest time the juice is separated for meat. The greatest amount of trypsin is contained in the juice allocated to milk; when bread is fed, a lot of amylase is released in the juice. The feeding regimen greatly affects the activity of the pancreas. An abrupt transition to a different diet can cause an upset in the activity of the pancreas.

In the lumen of the duodenum, in addition to pancreatic juice, bile is secreted during digestion - the secret of the liver, which also takes part in the digestion of food. Bile is constantly produced in the liver, as it is not only digestive juice, but also a secret with which unnecessary substances are removed from the body. Outside the period of digestion, bile enters the gallbladder, which is its reservoir. Bile enters the intestines from both the bladder and the liver only during digestion. After intensive digestion, the bladder may be empty. Bile in the process of digestion enhances the action of lipase of the pancreatic and intestinal juices, contributing to the digestion of fats. When feeding dogs with meat, bile begins to flow into the intestines after 5-8 minutes.

The digestion of food is also influenced by intestinal juice, which contains enzymes that complete the breakdown of complex organic substances of food into simpler ones. The composition of intestinal juice also varies depending on the nature of the food.

The time of passage of food through the digestive canal in dogs depends mainly on the composition of the diet and averages 12–15 hours. Vegetable food causes stronger intestinal motility and therefore passes through the alimentary canal faster than meat food, after 4-6 hours.

Digestibility of nutrients of different feeds is not the same. Meat in dogs after 2 hours is digested by half, after 4 hours - by 3/5, after 6 hours - by 7/8, and after 12 hours - everything. Rice is digested as follows: after an hour - 8%, after 2 - 25%, after 2 - by 50%, after 2 - by 75%, after 6 - by 90%, after 8 hours - by 98%.

With excessive feeding, the amount of feces excreted by the dog increases, since part of the food is not digested. When moving, the act does not occur in dogs. In a normal feeding regimen, dogs empty their rectum 2-3 times a day.