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The structure of the digestive tube of the middle shell. Sections of the digestive tube. Derivatives of the anterior part of the digestive tube

The wall of the digestive canal along its length has three layers: the inner layer is the mucous membrane, the middle layer is the muscular layer, and the outer layer is the serous layer.

The mucous membrane performs the function of digestion and absorption and consists of its own layer, its own and muscular plates. The proper layer, or epithelium, is supported by loose connective tissue, which includes glands, vessels, nerves and lymphoid formations. The oral cavity, pharynx, and esophagus are covered with stratified squamous epithelium. The stomach and intestines have a single-layer cylindrical epithelium. The lamina propria of the mucous membrane, on which the epithelium lies, is formed by loose fibrous unformed connective tissue. It contains glands, accumulations of lymphoid tissue, nerve elements, blood and lymphatic vessels. The muscular plate of the mucous membrane consists of smooth muscle tissue. Under the muscular plate there is a layer of connective tissue - the submucosal layer, which connects the mucous membrane with the muscular layer lying outward.

Among the epithelial cells of the mucous membrane are goblet-shaped, single-celled glands that secrete mucus. This is a viscous secretion that wets the entire surface of the digestive canal, which protects the mucous membrane from the harmful effects of solid food particles and chemicals and facilitates their movement. The mucous membrane of the stomach and small intestine contains numerous glands, the secretion of which contains enzymes involved in the process of digesting food. According to their structure, these glands are divided into tubular (simple tube), alveolar (vesicle) and mixed (alveolar-tubular). The walls of the tube and vesicle consist of glandular epithelium; they secrete a secretion that flows through the opening of the gland onto the surface of the mucous membrane. In addition, glands can be simple or complex. Simple glands are a single tube or vesicle, while complex glands consist of a system of branched tubes or vesicles that flow into the excretory duct. The complex gland is divided into lobules, separated from each other by layers of connective tissue. In addition to the small glands located in the mucous membrane of the digestive tract, there are large glands: salivary glands, liver and pancreas. The last two lie outside the digestive canal, but communicate with it through their ducts.

The muscular lining of most of the alimentary canal consists of smooth muscle with an inner layer of circular muscle fibers and an outer layer of longitudinal muscle fibers. In the wall of the pharynx and the upper part of the esophagus, in the thickness of the tongue and soft palate, there is striated muscle tissue. When the muscle membrane contracts, food moves through the digestive canal.

The serous membrane covers the digestive organs located in the abdominal cavity and is called the peritoneum. It is shiny, whitish in color, moistened with serous fluid and consists of connective tissue, which is lined with single-layer epithelium. The pharynx and esophagus are covered on the outside not by the peritoneum, but by a layer of connective tissue called adventitia.

The digestive system consists of the oral cavity, pharynx, esophagus, stomach, small and large intestines, as well as two digestive glands - the liver and pancreas (Fig. 23).

Oral cavity

The oral cavity is the initial expanded section of the digestive canal. It is divided into the vestibule of the mouth and the oral cavity itself.

The vestibule of the mouth is the space located between the lips and cheeks on the outside and the teeth and gums on the inside. Through the oral opening, the vestibule of the mouth opens outward. The lips are fibers of the orbicularis oris muscle, covered externally with skin and internally with mucous membrane. At the corners of the mouth opening, the lips pass one into another through adhesions. In a newborn, the oral cavity is small, the gingival margin separates the vestibule from the oral cavity itself, and the lips are thick. The thickness of the lips and cheeks contains facial muscles. The cheeks are formed by the buccal muscles. Children have rounded cheeks with a well-developed fat pad. Part of the fat body atrophies after four years, and the rest goes behind the masticatory muscle. The mucous membrane of the cheeks is a continuation of the mucous membrane of the lips and is covered with multilayered epithelium. On the hard palate it lies on the bone and lacks a submucosa. The mucous membrane, covering the necks of the teeth and protecting them, is fused with the alveolar arches of the jaws, forming gums. A large number of small salivary glands and ducts of the parotid salivary glands open into the vestibule of the mouth.

The oral cavity itself is limited above by the hard and soft palate, below by the diaphragm of the mouth, in front and sides by the teeth, and behind through the pharynx it communicates with the pharynx. The anterior two-thirds of the palate have a bone base and form the hard palate, the posterior third - the soft palate. When a person breathes calmly through the nose, the soft palate hangs obliquely down and separates the oral cavity from the pharynx.

A suture is visible along the midline of the hard palate, and in its anterior part there is a series of transverse elevations that facilitate the mechanical processing of food. The hard palate separates the oral cavity from the nasal cavity. It is formed by the palatine processes of the maxillary bones and horizontal plates of the palatine bones and is covered with a mucous membrane.

The soft palate is located anterior to the hard palate and is a muscular plate covered with mucous membrane. The narrowed and midline posterior part of the soft palate is called the uvula, or “third tonsil.” The real function of the tongue remains unclear, but there is an opinion that it is a reliable barrier to the respiratory tract, preventing a person from choking when swallowing. The child's hard palate is flattened and the mucous membrane is poor in glands. The soft palate is located horizontally, it is wide and short, and does not reach the posterior wall of the pharynx. This ensures the newborn can breathe freely while sucking.

The diaphragm of the mouth (floor of the mouth) is formed by the mylohyoid muscles. At the bottom of the mouth, under the tongue, the mucous membrane forms a fold called the frenulum of the tongue. On both sides of the frenulum there are two elevations with salivary papillae, on which the ducts of the submandibular and sublingual salivary glands open. The pharynx is an opening connecting the oral cavity with the pharynx. It is bounded above by the soft palate, below by the root of the tongue, and on the sides by the palatine arches. On each side there are palatoglossus and palatopharyngeal arches - folds of the mucous membrane, in the thickness of which there are muscles that lower the soft palate. Between the arches there is a recess in the form of a sinus, where the palatine tonsils are located. In total, a person has six tonsils: two palatine, two tubal in the mucous membrane of the pharynx, lingual in the mucous membrane of the root of the tongue, pharyngeal in the mucous membrane of the pharynx. These tonsils form a complex called the lymphoepithelial ring (Pirogov-Waldeyer ring), which surrounds the entrance to the nasopharynx and oropharynx. On top, the tonsil is surrounded by a fibrous capsule and consists of lymphoid tissue that forms follicles of various shapes. The dimensions of the tonsils in the vertical direction are from 20 to 25 mm, in the anteroposterior direction - 15-20 mm, in the transverse direction - 12-15 mm. The medial surface covered with epithelium has an irregular, tuberous outline and contains crypts - depressions.

The lingual tonsil lies in the lamina propria of the mucous membrane of the root of the tongue. It reaches its largest size by the age of 14-20 and consists of 80-90 lymphoid nodules, the number of which is greatest in childhood, adolescence and young adulthood. The paired palatine tonsil is located, as noted above, in the recesses between the palatoglossus and palatopharyngeal arches. The largest number of lymphoid nodules in the palatine tonsils is observed between the ages of 2 and 16 years. By the age of 8-13 years, the tonsils reach their largest size, which persists up to 30 years. The connective tissue inside the palatine tonsil grows especially intensively after 25-30 years, along with a decrease in the amount of lymphoid tissue.

After 40 years, there are practically no lymphoid nodules in the lymphoid tissue. The unpaired pharyngeal tonsil is located in the posterior wall of the pharynx, between the openings of the auditory tubes, in the folds of the mucous membrane. It reaches its largest size at 8-20 years of age; after 30 years, its size gradually decreases. The paired tubal tonsil is located behind the pharyngeal opening of the auditory tube. The tonsil contains only single round lymphoid nodules. It reaches its greatest development at the age of 4-7 years. Its age-related involution begins in adolescence and youth.

Lymphocytes and numerous plasma cells multiplying in all tonsils perform a protective function, preventing the penetration of infection. Since the tonsils are most developed in children, they are affected more often in children than in adults. Enlarged tonsils are often the first sign of tonsillitis, scarlet fever, diphtheria and other diseases. The pharyngeal tonsil in adults is hardly noticeable or disappears completely, but in children it can be of significant size. With pathological growth (adenoids), it makes breathing through the nose difficult.

The tongue is a muscular organ covered with a mucous membrane. The tongue is divided into the tip (apex), body and root. The upper surface (back of the tongue) is convex, much longer than the lower one. The mucous membrane of the tongue is covered with non-keratinizing multilayered epithelium; on the back and edges of the tongue it is devoid of submucosa and is fused with muscles. The tongue has its own muscles and muscles that start from the bones. The intrinsic muscles of the tongue consist of muscle fibers lying in three directions: longitudinal, transverse and vertical. When they are reduced, the shape of the tongue changes. From the bones begin the paired genioglossus, hypoglossus and styloglossus muscles of the tongue, which end in the thickness of the tongue. When contracting, the tongue moves down and up, forward and back. The anterior section of the dorsum of the tongue is dotted with many papillae, which are outgrowths of the lamina propria of the mucous membrane and covered with epithelium. They are filamentous, mushroom-shaped, grooved and leaf-shaped. The filiform papillae are the most numerous and occupy the entire surface of the back of the tongue, giving it a velvety feel. These are tall and narrow outgrowths, 0.3 mm long, covered with stratified squamous, often keratinizing epithelium. Fungiform papillae are scattered over the entire surface of the dorsum of the tongue, with a predominant location at the tip and along the edges of the tongue.

They are rounded, 0.7-1.8 mm long, and shaped like a mushroom. The grooved papillae are surrounded by a ridge and lie on the border between the back and the root of the tongue, where they form a figure in the form of a Roman numeral V. They resemble mushroom-shaped papillae in shape, but their upper surface is flattened, and around the papilla there is a narrow deep groove into which the ducts of the glands open. The number of papillae surrounded by a ridge ranges from 7-12. Leaf-shaped papillae lie along the edges of the tongue in the form of transverse vertical folds or leaves. Their number is 4-8, length 2-5 mm, they are well developed in newborns and infants. On the surface of the mushroom-shaped papillae and in the thickness of the epithelium of the grooved papillae there are taste buds - groups of specialized taste receptor cells. A small number of taste buds are located on the leaf-shaped papillae and in the soft palate.

Teeth are ossified papillae of the mucous membrane. A person's teeth change twice, and sometimes three. The teeth are located in the oral cavity and are strengthened in the cells of the alveolar processes of the jaws. Each tooth has a crown, a neck and a root.

The crown is the most massive part of the tooth, protruding above the level of the entrance to the alveolus. The neck is located on the border between the root and the crown, in this place the mucous membrane comes into contact with the tooth. The root is located in the alveolus and has an apex with a small hole on it. Through this hole, blood vessels and nerves enter the tooth. There is a cavity inside the tooth that goes into the root canal. The cavity is filled with dental pulp - dental pulp, formed by loose connective tissue in which nerves and blood vessels are located. Each tooth has one (incisors, canines), two (lower molars) or three roots (upper molars). The composition of the tooth includes dentin, enamel and cement. The tooth is made of dentin, which is covered with cement in the root area and enamel in the crown area.

Depending on the shape, incisors, canines, small and large molars are distinguished.

The incisors are used for grasping and biting food. There are four of them on each jaw. They have a chisel-shaped crown. The crown of the upper teeth is wide, the lower ones are twice as narrow. The root is single, compressed from the sides of the lower incisors. The root apex is inclined somewhat laterally.

Fangs crush and tear food. There are two of them on each jaw. In humans, they are poorly developed, cone-shaped with a long single root, compressed from the sides and having lateral grooves. A crown with two cutting edges converging at an angle. There is a tubercle on its lingual surface near the neck.

The small molars grind and grind food. There are four of them on each jaw. There are two chewing cusps on the crown of these teeth, which is why they are called double-tubercle. The root is single, but bifurcating at the end.

Large molars - six on each jaw, decreasing in size from front to back. The last, smallest one, erupts late and is called a wisdom tooth. The shape of the crown is cuboidal, the closure surface is square. They have three or more tubercles. The upper molars have three roots, the lower ones have two. The three roots of the last molar merge into one conical shape.

As noted earlier, a person has two sets of teeth, depending on which they distinguish between milk and permanent teeth. There are only 20 milk teeth. Each half of the upper and lower dentition has 5 teeth: 2 incisors, 1 canine, 2 molars. Milk teeth erupt between the ages of 6 months and 2.5 years in the following order: middle incisors, lateral incisors, first molars, canines, second molars. The number of permanent teeth is 32: on each half of the upper and lower dentition there are 2 incisors, 1 canine, 2 small molars and 3 large molars. Permanent teeth erupt between the ages of 6-14 years. The exception is wisdom teeth, which appear at the age of 17-30 years, and sometimes are completely absent. The first of the permanent teeth to erupt are the first large molars (at the 6-7th year of life). The order of appearance of permanent teeth is as follows: first large molars, middle incisors, lateral incisors, first small molars, canines, second small molars, second large molars, wisdom teeth. The closure of the upper incisors with the lower ones is called a bite. Normally, the teeth of the upper and lower jaws do not completely correspond to each other, and the teeth of the upper jaw somewhat overlap the teeth of the lower jaw.

The ducts of three pairs of large salivary glands open into the oral cavity: parotid, submandibular, sublingual. The parotid gland is the largest (weight 20-30 g), has a lobular structure, covered on top with a connective tissue capsule. Located on the lateral surface of the face, in front and below the auricle. The duct of this gland runs along the outer surface of the masticatory muscle, pierces the buccal muscle and opens into the vestibule of the mouth on the mucous membrane of the cheek. By structure it belongs to the alveolar glands. The submandibular gland has a mass of 13-16 g and is located under the diaphragm of the mouth in the submandibular fossa. Its duct opens into the oral cavity. It is a mixed gland. The sublingual gland is the smallest (weight 5 g), narrow, elongated. Located on the upper surface of the diaphragm of the mouth. The top is covered with a mucous membrane, which forms a sublingual fold above the gland. The gland has one large duct and several small ones. The large excretory duct opens together with the duct of the submandibular gland, small ducts open on the sublingual fold.

Digestive tube

1. Small medical encyclopedia. - M.: Medical encyclopedia. 1991-96 2. First aid. - M.: Great Russian Encyclopedia. 1994 3. Encyclopedic Dictionary of Medical Terms. - M.: Soviet Encyclopedia. - 1982-1984.

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DIGESTIVE SYSTEM- DIGESTIVE SYSTEM, b. or m. a complex system of cavities lined with epithelium, which is supplied in certain parts with glands secreting various enzymes, due to which the breakdown and dissolution of food materials absorbed occurs ... Great Medical Encyclopedia

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The digestive, gastrointestinal tract (GIT), or food tube, is an organ system in real multicellular animals, designed to process and extract nutrients from food, absorb them into the blood and excrete them from the body... ... Wikipedia

AND; pl. genus. side, dat. bkam; and. 1. Decrease to Pipe (1 digit). Rubber, plastic t. 2. Object, device, device of a pipe-like shape. Roll the paper into a tube. Glassblowing t. Remote t. X-ray t. (device for obtaining... ... encyclopedic Dictionary

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And, gen. pl. side, dat. bkam, w. 1. decrease to pipe (in 1 value); small section pipe. Rubber tube. Steam pipe. □ This man has a silver tube inserted down his throat. Paustovsky, Kara Bugaz. Huge argon tubes flared up... ... Small academic dictionary

- (Insecta), the largest class of animals, uniting more species than all other groups combined. Belongs to arthropod invertebrates. Like all these animals, insects have a segmented body with jointed appendages, covered... ... Collier's Encyclopedia

digestive tube

Lecture outline:

1. General characteristics and functions of the digestive system.

2. General plan of the structure of the digestive tube.

3. Oral cavity. Structural and functional organization.

4. Pharynx.

5. Esophagus.

6. Stomach.

7. Small intestine

8. Colon.

The digestive system unites a number of organs, which together ensure the body’s absorption from the external environment of substances necessary to fulfill its plastic and energy needs. It includes the digestive tube and the glands located outside it, the secretion of which helps digest food particles: three pairs of large salivary glands, the liver and the pancreas.

The digestive tube has anterior, middle and posterior sections. The anterior section includes the oral cavity, pharynx and esophagus. The secretions of the major and minor salivary glands are released into the oral cavity. The main function of the anterior part of the digestive tube is the mechanical and initial chemical processing of food. The middle section of the digestive tube includes the stomach, small intestine, and part of the large intestine (towards its caudal part). The excretory ducts of the liver and pancreas flow into the small intestine (its section called the duodenum). The main functions of the middle section of the digestive tube are chemical processing (digestion) of food, absorption of substances and the formation of feces from undigested food debris. The posterior section of the digestive tube, the caudal part of the rectum, ensures the removal of undigested food particles outside the body.

Language ( lingua) - muscular n than organ that, in addition to participating in the mechanical processing of food and swallowing, also provides articulation (sound production) and tasting. There are lower, lateral and upper surfaces of the tongue, which have a number of structural features.

The lower surface of the tongue is covered with a multilayer flat non-keratinizing epithelium. It has a well-developed lamina propria and submucosa, the presence of which determines the displacement of the mucous membrane relative to the muscular base of the tongue. On the lower surface of the tongue, on both sides of its frenulum, the excretory ducts of the sublingual and submandibular salivary glands flow into the oral cavity. Due to the rich vascularization the lower surface of the tongue and the high penetration of its epithelium for a variety of chemical compounds, medications (validol, nitroglycerin) are placed under the tongue to ensure their rapid absorption and entry into the blood. The upper and lateral surfaces of the tongue are covered with a mucous membrane, motionlessly fused with the muscular base of the tongue. The epithelium and the lamina propria of the mucous membrane form here protrusions with a characteristic structure, which are called the papillae of the tongue. There are filamentous, conical, leaf-shaped, mushroom-shaped and e frontal papillae.

Composed of the epithelium of the lateral surfaces of the leaf-shaped, mushroom-shaped and groove O prominent papillae contain taste buds - the so-called taste budsbulbs, therefore, the role of these types of tongue papillae is associated primarily with tasting. The body of the tongue is formed by bundles of striated muscle fibers, which are located in three mutually perpendicular planes. The dense connective tissue median septum divides the tongue muscle into right and left halves. Between the muscular base of the tongue and the lamina propria of the mucous membrane of its back, a dense plexus of collagen and elastic fibers forms the so-called reticular layer, which plays the role of the aponeurosis of the tongue. In the connective tissue of the root of the tongue there is a cluster of lymphocytes that form the lingual tonsil. Lymphocytes form a spherical cluster.

Between the bundles of striated muscle fibers of the tongue there are a large number of small salivary glands, which produce protein, mucous or protein-mucus secretion. Glands that produce protein secretions are located mainly near the leaf-shaped and grooved papillae. These are complex alveolar branched glands. Mucous glands are located in the root area and on the lateral surfaces of the tongue. These are complex alveolar-tubular branched glands, the secretion of which is rich in mucins. The excretory ducts of the mucous glands of the root of the tongue open into the crypts of the lingual tonsil. Mixed protein-mucosal glands are localized mainly in the anterior parts of the tongue; their excretory ducts open on the lower surface of the tongue along the folds of its mucous membrane.

Sky ( palatum) is the partition between the nasal and oral cavities. There are hard and soft e Bo, the latter in its rear part turns into a tongue. At the heart of solid e ba there are bone plates fused in the midline. On the side of the oral cavity, the hard palate is covered with a mucous membrane, covered with a multilayered flat non-keratinizing epithelium into which tall connective tissue papillae of the lamina propria grow. Topographically, in the composition of solid e ba there are four zones: fatty, glandular, marginal and zone n e long seam. The area of adipose tissue covers the anterior part of the hard tissue. e ba. In this area, under the mucous membrane, there is fatty tissue, which is an analogue of the submucosa of other parts of the oral cavity. The glandular zone occupies the posterior part of the hard tissue. e ba. In this area between the mucous membrane and the periosteum of the bone plates, groups of small salivary glands are localized, which produce a mucous-protein secretion.

The marginal zone in the form of an arc covers the solid surface. e Bo and is the place of transition of its mucous membrane into the gums of the upper jaw. In the marginal zone, the mucous membrane of the hard tissue e batightly fused with the periosteum of the base of the alveolar processes. Along the midline of the hard e ba passes zone n e long seam. In this area, as in the marginal zone, the mucous membrane is tightly fused with the periosteum of the bone plates. Epithelium in the suture area of the hard n e ba forms characteristic thickenings, especially well developed in childhood: then they look like concentric layers of epithelial cells and are called epithelial bodies n e ba. The tight fusion of the mucous membrane with the periosteum in the suture area and the marginal zone determines its real estate.

Soft nyo bo and tongue is a continuation of the back of the hard n e ba, however, if based on solid n e ba bone plates lie, then soft n e Bo and uvula have a mucous membrane. In the mucous membrane of the soft tissue e ba and uvula distinguish two surfaces - oral and nasal, as well as a transition zone. In fetuses and newborns, the boundary between these surfaces lies on the line of bending of the mucous membrane from the nasal to the oral surface. In adults, this border shifts towards the nasal surface so that the entire uvula is covered with epithelium characteristic of the oral cavity. The oral surface of the mucous membrane of the soft tissue e ba and tongue are covered with multi-layer flat non-keratinizing epithelium. The lamina propria forms high papillae; the muscular lamina mucosa is absent. In soft n e The uvula and uvula have a well-developed submucosa, which contains salivary glands that produce mucous secretion. Nasal mucosal surface e The ba is covered with a single-layer multirow ciliated epithelium, which is characteristic of the upper respiratory tract. On its surface, ducts of small glands open that produce mucus. In the transition zone, the epithelium turns from multilayer squamous into multirow prismatic, and the latter turns into single-layer multirow ciliated.

The palatine tonsils are located between the palatoglossal and velopharyngeal arches. The structure of the tonsil is based on the folds of the mucous membrane. In the depths of the folds of epithelium growing into the lamina propria of the mucous membrane, 10-20 slits are formed - crypts. When crypts branch, secondary crypts are formed. Around the crypts there are spherical accumulations of lymphocytes - lymph nodes with light (reactive) centers. The nodules are formed predominantly by B-lymphocytes and plasmacytes. The loose connective tissue of the lamina propria of the mucous membrane merges with the submucosa, where the final secretory sections of the mucous glands of the pharynx are located. The muscular coat is formed by cross-striated muscle tissue and forms two layers - the outer circular and the inner longitudinal. The adventitia is formed by loose fibrous connective tissue.

The pharynx (throat, pharynx) is a cone-shaped canal 12...14 cm long that connects the oral cavity with the esophagus. The digestive and respiratory tracts intersect at the pharynx. The wall of the pharynx is made up of four membranes - mucous, submucosal, muscular and adventitial Noah. There are three sections of the pharynx - nasal, oral and laryngeal.

The mucous membrane of the nasal section is covered with a single-layer multirow ciliated epithelium (respiratory type). In the area where the cardiac glands are localized, diverticula, ulcers and tumors of the esophagus often occur. The muscular plate of the mucous membrane is formed by longitudinally oriented bundles of smooth myocytes, between whichareplexus of elastic fibers. The submucosa of the esophagus is formed by loose connective tissue, in which the final secretory sections of the own glands of the esophagus are located. In structure, these are complex branched alveolar-tubular glands with a mucous type of secretion. Proper glands are concentrated mainly on the ventral surface of the upper third of the esophagus. Multilayer flat non-keratinizing the epithelium of the tonsil crypts is dense infiltrated numerous lymphocytes and neutrophilic granulocytes, as a result of which it received the name reticular epithelium. In the crypt space you can see exfoliated epithelial cells, lymphocytes that migrated here from the follicles, as well as foreign particles. Inflammation of the tonsils is called tonsillitis.

Esophagus (esophagus) is a section of the digestive tube about 30 cm long that connects the pharynx with the stomach cavity. The esophagus is located between the sixth cervical and eleventh thoracic vertebrae. The wall of the esophagus is formed by four membranes: mucous, submucosal, muscular and external ( adventitial noisy or serous). The esophageal mucosa has three layers; epithelium, lamina propria and muscularis lamina. Esophageal stratified squamous epithelium non-keratinizing; In old age, keratinization is possible. During the transition to the stomach, the stratified squamous epithelium of the esophagus is replaced by a single-layer prismatic one. lamina propriashellThe esophagus is formed by loose connective tissue, the ingrowth of which into the epithelium forms papillae.

As part of the lamina propria of the mucous membrane at the level signet-shaped cartilage of the larynx and in the area of the transition of the esophagus to the stomach the final sections of the cardiac glands lie. These are simple tubular or tubulo-alveolar branched glands that produce primarily mucus. In addition to mucocytes, they include a significant number of endocrine cells, as well as single parietal cells, about the cake produce H + - ions. The ducts of the cardiac glands are formed by single-layer cylindrical epithelium, which directly transforms into multilayered epithelium. The muscular layer of the upper third of the esophagus is formed by transversely striated muscle tissue. In the middle third of the organ, smooth myocytes join the cross-striated muscle fibers. The muscular lining of the lower third of the esophagus is formed by smooth muscle tissue. There are internal circular and external longitudinal layers of the muscular lining of the esophagus, although individual muscle bundles may have an oblique longitudinal direction. Thickening of the inner layer of the muscular lining of the esophagus at the level signet-shaped The cartilage of the larynx forms the upper sphincter of the esophagus, and when the latter passes into the stomach, the lower sphincter. The outer lining of the esophagus above the diaphragm is formed by loose connective tissue (tunica adventitia). Under the diaphragm, the adventitial membrane becomes serous: the loose connective tissue here is covered with a single layer of mesothelial cells.

Stomach ( gaster, ventriculus) - a sac-like expansion of the digestive tube with a volume of 1.7...2.5 liters, into which food crushed and moistened in the oral cavity enters through the esophagus. The wall of the stomach is formed by four membranes - mucous, submucosal, muscular serous. A feature of the relief of the gastric mucosa is the presence of folds, fields and pits. The mucous membrane is constructed of three layers - the epithelium, the lamina propria and the muscularis lamina. The gastric mucosa produces an internal antianemic factor necessary for the absorption of vitamin B12, which enters the stomach with nutrients. The plasmalemma of the apical surface of epithelial cells forms microvilli. In the apical part of the cell, granules of mucous secretion accumulate, which, when secreted, cover the surface of the mucous membrane and protect it from the digestive action of gastric juice. Consequently, the gastric mucosa can be considered as a continuous glandular field. Near the bottom of the gastric pits, which are ingrowths of the surface epithelium into the lamina propria of the mucous membrane, there are poorly differentiated, actively proliferating cells. As they differentiate and age, they move toward the surface of the mucous membrane, followed by exfoliation into the lumen of the stomach.

The lamina propria of the gastric mucosa is built from loose connective tissue in which the gastric glands lie. There are three types of glands: intrinsic, cardiac and pyloric. The proper glands of the stomach are simple tubular, unbranched or weakly branched, located in the area of the fundus and body of the stomach. The final secretory section is formed by the bottom and body of the own gland, the excretory duct is formed by the isthmus and neck. The secretion of several of the stomach's own glands flows into the gastric pit. Each gland is built from five types of cells: main exocrinocytes, parietal exocrinocytes, cervical and accessory mucocytes, and endocrinocytes.

The secretory products of the main cells - pepsinogen and chymosin - are localized in the apical part of the cells in the form of zymogenic granules (the so-called Langley granules). The latter have oxyphilic properties and refract light well. In the apical (closer to the lumen of the gland) part of the cells, granules of protein secretion accumulate. The plasmalemma of the apical surface of the main exocrinocytes forms microvilli. The basal part of the cell contains a round nucleus and well-defined elements of the Golgi complex. Chymosin breaks down milk proteins and is produced primarily in childhood.

Parietal exocrinocytes of the gastric glands secrete H-ions, resulting in an acidic environment in the stomach. Parietal cells are located alone in the area of the bottom and body of the own glands, between basolateral parts of the main exocrinocytes. These are large cells of irregular round shape with one or two nuclei and oxyphilic cytoplasm. The latter contains a significant number of mitochondria and is penetrated by a branched system of intracellular tubules, through which secretory products enter the intercellular tubules, and from there into the lumen of the gland.Cervical mucocytes form the excretory ducts of their own glands. These are cubic or prismatic cells, in the basal part of which the nuclei are localized, and secretory mucus granules accumulate in the apical part. Among cervical mucocytes there are poorly differentiated cells that are the source of physiological regeneration of gastric glandulocytes and cells of the gastric pits. Accessory mucocytes, scattered singly in the glands, resemble cervical mucocytes in structure and function.

Endocrinocyteslocalized alone between the main cells, mainly in the area of the bottom and body of the glands. They belong to dissociated endocrine system of the gastrointestinal tract, or APUD system. The cardiac and pyloric glands are located in the same areas of the stomach. In structure, these are simple tubular, highly branched glands. The pyloric glands lack chief and parietal cells; the cardiac glands have them in small quantities. The cardiac and pyloric glands also contain a significant number of endocrine cells. In the lamina propria of the mucous membrane between the gastric glands, there are accumulations of lymphocytes in the form of diffuse infiltrates or single lymphatic follicles. The number of the latter increases in the pyloric part of the stomach.

Small intestine (intestinum tenue) - part of the digestive tube located in the lower part of the abdominal cavity between the stomach and the cecum. The length of the small intestine is 4...5 m, the diameter in the proximal section is 5 cm, in the distal direction the intestine thins in diameter to 3 cm. It has three sections: the duodenum, the hungry intestine and the longitudinal intestine. The duodenum has the shape of a horseshoe, approximately 30 cm long. Completing the characteristics of the gastric mucosa, it should be noted that in its pyloric part the gastric pits deepen significantly.

The submucosal base of the stomach is formed by loose connective tissue in which the submucosal nerve plexuses are located - external (Shabadasha) and internal (Meissner). The muscular lining of the stomach is formed by three layers of smooth myocytes: outer longitudinal, middle circular and inner oblique longitudinal.

The wall of the small intestine is formed by four membranes: mucous, submucosal, muscular and serous. The mucous membrane consists of three layers - the epithelium, the lamina propria and the muscularis lamina. The epithelium of the mucous membrane of the small intestine is single-layer cylindrical. The lamina propria is formed by loose connective tissue, the muscular lamina is formed by smooth myocytes. A feature of the relief of the mucous membrane of the small intestine is the presence of circular folds, villi and crypts.

The villus is a finger-shaped protrusion of the mucous membrane with a height of 0.5.., 1.5 mm directed into the lumen of the small intestine. The villus is based on the connective tissue of the lamina propria, in which single smooth myocytes occur. The surface of the villi is covered with columnar epithelium, which contains three types of epithelial cells: columnar epithelial cells, goblet cells and intestinal endocrinocytes. Columnar epithelial cells of the villi make up the bulk of the epithelial layer of the villi. It's high cylindrical cells measuring 8x25 microns. On the apical surface they contain microvilli (the latter should not be confused with the villi of the small intestine), which under a light microscope have a characteristic appearance of a striated frame. The height of microvilli is about 1 µm, diameter - 0.1 µm. Thanks to the presence of both villi and microvilli, the absorption surface of the mucous membrane of the small intestine increases a hundred times. Columnar epithelial cells have an oval nucleus, well-developed ergastoplasm, and a lysosomal apparatus. The apical part of the cells contains tonofilaments, with the participation of which obturator plates and tight junctions are formed, permeable to substances from the lumen of the small intestine.

Columnar epithelial cells of the villi are the main functional element of the processes of digestion and absorption in the small intestine. The microvilli of these cells adsorb enzymes and the nutrients they break down on their surface. The products of the breakdown of proteins and carbohydrates - amino acids and monosaccharides - are transported from the apical to the basal part of the cells, from where they enter the capillaries of the connective tissue base of the villi through the basement membrane. A similar absorption path is also characteristic of water, mineral salts and vitamins dissolved in it. Fats are digested either by phagocytosis of droplets emulsified fat (chylomicrons), columnar epithelial cells, or by absorption of glycerol and fatty acids (the latter are formed from neutral fats under the action of lipases) with the subsequent resynthesis of neutral fat in the cytoplasm of the cells. Goblet cells are single-celled glands that produce mucous secretions. The shape of the cells is characterized by their name: in the expanded apical part they accumulate secretory products, in the lower part of the cell, narrowed like the stem of a glass, the nucleus, endoplasmic reticulum, and Golgi complex are located. Single goblet cells are scattered on the surface of the villi surrounded by columnar epithelial cells with a border. The secretion of goblet cells moisturizes the surface of the mucous membrane, thereby promoting the movement of food particles to the colon.

Endocrinocytes, as well as goblet cells scattered alone among columnar epithelial cells with a border. Among the endocrinocytes of the small intestine, EC-, A-, S-, I-, G-, D-, D1-cells are distinguished. The products of their synthetic activity are a number of biologically active substances that exert a local regulatory effect on secretion, absorption and intestinal motility. Hormones that are produced by endocrinocytes of the small intestine enter the hemocapillaries of the connective tissue base of the villi and are transported with the blood to their target cells: columnar epithelial cells with a border, goblet cells, smooth myocytes of the vascular wall of the mucous and muscular membranes of the intestine.

Crypts are tubular ingrowths of epithelium into the lamina propria of the intestinal mucosa. The entrance to the crypt opens between the bases of adjacent villi. The depth of the crypts is 0.3..0.5 mm, the diameter is about 0.07 mm. There are over 150 million crypts in the small intestine, which, like villi, significantly increase the functionally active area of the small intestine. Among the crypt epithelial cells, in addition to the cells previously characterized as part of the villi (columnar cells with a border, goblet cells and endocrinocytes), there are also columnar cells without a border and exocrinocytes with acidophilic granules (Paneth cells). The peculiarity of columnar epithelial cells with a border as part of the crypts is their slightly lower height compared to similar cellular elements of the villi, as well as pronounced basophilia of the cytoplasm. The goblet cells of the villi and crypts do not differ significantly. The number of endocrinocytes in the crypts is higher than on the villi; the functional activity of the endocrinocytes of the villi and crypts is the same.

The secretory products of Paneth cells are dipeptidases - enzymes that break down dipeptides into amino acids. It is also believed that cells with acidophilic granules produce enzymes that neutralize the acidic components of gastric juice that enter the small intestine along with food particles. Columnar epithelial cells without borderrepresent a population of poorly differentiated cells that are the source of physiological regeneration of the epithelium of the crypts and villi of the small intestine. The structure of these cells resembles columnar cells with a border, but there are no microvilli on their apical surface.

The lamina propria of the mucous membrane of the small intestine is formed by loose connective tissue, which contains a lot of elastic and reticular fibers, hemo- and lymphocapillaries. Clusters of lymphocytes form here single and grouped lymphatic follicles, the number of which increases in the direction from the duodenum to the hungry intestine. The largest accumulations of lymphatic follicles pass through the muscular plate of the mucous membrane into the submucosa of the intestine. In places where grouped lymphatic follicles are localized, villi of the mucous membrane are usually absent. The maximum number of lymphatic accumulations in the wall of the small intestine is found in children; with age, their number decreases. In addition to lymphocytes, the connective tissue of the lamina propria of the mucous membrane contains eosinophilic granulocytes and plasmacytes. The muscular plate of the mucous membrane is formed by two layers of smooth myocytes - the inner circular and outer longitudinal.

The submucosa of the wall of the small intestine is formed by loose connective tissue, which contains a significant number of blood and lymphatic vessels and nerve plexuses. In the duodenum, the terminal secretory sections of the duodenal (Bruner's) glands lie in the submucosa. In structure, these are complex branched tubular glands with a mucous-protein secretion, which resemble the pyloric glands of the stomach. The terminal secretory sections of the duodenal glands are built from mucocytes, Paneth cells and endocrinocytes (S-cells). The excretory ducts of the Brunerian glands open near the base of the crypts or between adjacent villi. The excretory ducts of the glands are built from mucocytes of cubic or prismatic shape, which are replaced near the surface of the mucous membrane by columnar cells with a border. There are especially many lymphatic follicles in the wall of the appendix, which, due to its high saturation with lymphoid elements, is sometimes also called the tonsil of the abdominal cavity. The epithelium of the mucous membrane of the appendix is single-layer prismatic. The muscular layer of the small intestine is formed by two layers of smooth myocytes: internal oblique-circular and external oblique-longitudinal. Between both layers of muscle tissue lie layers of connective tissue rich in neurovascular plexuses.

Large intestine ( intestinum erassum) - part of the digestive tube that ensures the formation and excretion of feces. Excretory substances (metabolic products), salts of heavy metals, and the like accumulate in the lumen of the colon. The bacterial flora of the colon produces vitamins B and K, and also ensures the digestion of fiber. The mucous membrane of the colon is formed by a single-layer columnar epithelium, a connective tissue lamina propria, and a muscular lamina constructed of smooth muscle tissue. A feature of the relief of the colon mucosa is the presence of a large number of crypts and the absence of villi. The vast majority of cells in the epithelial layer of the colon mucosa are goblet cells; there are significantly fewer columnar epithelial cells with a striated border and endocrinocytes. Goblet cells produce a large amount of mucus, which envelops the surface of the mucous membrane, and, mixing with undigested food particles, promotes the passage of feces in the caudal direction. Near the base of the crypts are located undifferentiated cells, as a result of proliferation of which physiological regeneration of the epithelium occurs. Sometimes Pannett cells can be found in crypts. The named cell populations do not differ significantly from similar cellular elements of the small intestine.

In the loose connective tissue of the lamina propria of the mucous membrane there are significant accumulations of lymphocytes. It contains a large number of Pannett cells and intestinal endocrinocytes. The latter synthesize the bulk of endogenous serotonin and melatonin in the body. This fact, as well as the high content of lymphoid elements, obviously explains the important place that the vermiform appendix occupies in the immune defense system of the human body.

The muscular plate of the colon mucosa is formed by two layers of smooth myocytes: internal circular and external oblique. The muscular plate of the mucous membrane in different parts of the large intestine has unequal development: in the vermiform in the process, for example, it is poorly developed. The submucosa of the colon is formed by loose connective tissue, in which there is an accumulation of fat cells, as well as a significant number of lymphatic follicles. The neurovascular plexuses are located in the submucosa.

The muscular layer of the colon is formed by two layers of smooth myocytes: the internal circular and the external longitudinal, between which lie layers of loose connective tissue. In the colon, the outer layer of smooth myocytes is not continuous, but forms three longitudinal ribbons. The contraction of individual segments of the internal circular layer of smooth myocytes of the muscularis mucosa ensures the formation of transverse folds of the colon wall. The outer lining of the vast majority of the colon is serous; in the caudal part of the rectum, the serous membrane passes into the adventitia. The rectum has a number of structural features that should be considered in more detail. It distinguishes between the upper (pelvic) and lower (anal) parts, which are separated from one another by transverse folds. The submucosa and the inner circular layer of the muscularis are involved in the formation of the latter. The mucous membrane of the upper part of the rectum is covered with a single-layer cubic epithelium, which forms numerous deep crypts. The mucous membrane of the anal part of the rectum is made up of three zones of different structure: columnar, intermediate and cutaneous. The columnar zone is covered with multilayer cubic, the intermediate zone is covered with multilayer flat non-keratinizing, skin - multilayered squamous keratinizing epithelium. The lamina propria of the columnar zone forms 10-12 longitudinal folds and contains many blood lacunae, the blood from which will flow into the hemorrhoidal veins. Here are located single lymph nodes, the final sections of the rudimentary anal glands. The latter pass into the submucosa. The lamina propria of the intermediate zone is rich in elastic fibers, lymphocytes and tissue basophils; The terminal sections of the sebaceous glands are located here. In the connective tissue lamina propria of the mucous membrane of the skin area, hair follicles, the terminal sections of apocrine sweat glands, and sebaceous glands appear. The muscular plate of the rectal mucosa is formed by the inner circular and outer longitudinal layers of smooth myocytes.

The submucosa of the rectum is formed by loose connective tissue in which the nerve and vascular plexuses are located. Among the latter, we should highlight the plexus of hemorrhoidal veins, with the loss of wall tone of which hemorrhoidal bleeding can occur. In the submucosa of the rectum there are a large number of baroreceptors (Vater-Pacini bodies), the irritation of which plays a significant role in the mechanisms of defecation. In the submucosa of the columnar zone, as in the lamina propria of its mucous membrane, the terminal sections of the rudimentary anal glands are located. These are six to eight branched tubular epithelial formations that from the surface of the mucous membrane reach the inner circular layer of the muscular layer. When the anal glands become inflamed, they can cause rectal orifices.

The muscular layer of the rectum is formed by internal circular and external longitudinal layers of smooth myocytes, between which lie layers of connective tissue. The muscularis propria forms two sphincters, which play a significant role in the act of defecation. The internal sphincter of the rectum is formed by thickening of the smooth myocytes of the inner layer of the muscular layer, the external sphincter is formed by bundles of fibers of striated skeletal muscle tissue. The upper part of the rectum is covered with a serous membrane, the anal part with an adventitial membrane.

Digestive system – I. Organs of the oral cavity

The digestive system consists of the digestive tube and the large digestive glands located outside it (salivary, liver and pancreas), the secretion of which contributes to the process of breaking down consumed food.

Main functions The digestive system is mechanical and chemical processing of food, secretory, resorptive (absorption), excretory, barrier-protective and evacuation. The digestive system as a whole ensures that the body absorbs substances received from the external environment that are necessary to fulfill its plastic and energy needs.

In the digestive system there are three departments: front(organs of the oral cavity, pharynx, esophagus), average(stomach, intestines, liver, pancreas) and rear(anal part of the rectum).

The digestive tube consists from tubular organs . Their wall consists of three shells: mucosa, muscular and serous (adventitial).

Mucous membrane(internal ) consists of several layers: epithelial, lamina propria and lamina muscularis. The surface of the mucous membrane is uneven: its relief in the stomach is represented by folds, fields and pits. In the small intestine, in addition to folds, specific outgrowths are formed - villi and tubular depressions - crypts. The presence of villi and crypts increase the area of contact of the mucous membrane with food particles undergoing chemical processing. This facilitates the processes of digestion and absorption of products of enzymatic breakdown of food. There are no villi in the large intestine, and therefore the absorption of food digestion products there is sharply reduced.

Epithelium of the mucous membrane different in different parts of the digestive tube. In the anterior and posterior sections, it is multilayered, flat, non-keratinizing and primarily performs a protective function (protects against mechanical damage from rough food and feces). In the middle section the epithelium is single-layer prismatic. Moreover, in the stomach there is a single-layer prismatic glandular(secretes mucus), and in the intestines - a single-layer prismatic edged(absorbs food breakdown products).

lamina propria of the mucous membrane formed by loose fibrous connective tissue in which the neurovascular plexuses, simple glands (in the esophagus, stomach), crypts (intestines), and lymphatic follicles are located.

Muscular plate formed by one to three layers of smooth muscle tissue myocytes. It is absent from the oral mucosa.

Submucosa(often described as an independent shell) is formed by loose fibrous connective tissue. In some parts of the oral cavity it is absent. In the submucosa of the esophagus, stomach and intestines are located submucosal vascular and nervous (Meissner) plexuses, clusters of lymphatic follicles And terminal sections of complex exocrine glands(in the esophagus and duodenum).

Muscularis(middle) is represented by two (in the stomach there are three) layers of muscles: internal - circular and external - longitudinal. In the initial and final sections of the digestive tube, the muscular membrane is formed striated muscle tissue, and on average - smooth. Between the layers of muscles in the intermuscular connective tissue are the intermuscular nerve (Auerbach) and choroid plexuses. Contractions of the muscular membrane ensure the mixing of food with the secretion of the glands and the movement of food and feces in the caudal direction.

Outer shell (serous or adventitial). The part of the digestive tube located in the abdominal cavity (stomach, intestines) is covered serosa, consisting of a connective tissue base covered with mesothelium. Under the serous membrane are located subserous nervous and choroid plexuses. The function of the serous membrane is reduced to the secretion of serous fluid, which provides moisture and easy mobility of the digestive tube. Damage to the serous membrane during inflammatory processes or damage during surgical operations leads to the development of adhesions, impaired intestinal motility and intestinal obstruction. The alimentary canal in the anterior (above the diaphragm) and posterior sections is covered adventitia, formed by loose fibrous connective tissue.

The wall of the digestive canal along its length has three layers: the inner layer is the mucous membrane, the middle layer is the muscular layer, and the outer layer is the serous layer.

The mucous membrane performs the function of digestion and absorption and consists of a layer of its own, the lamina propria and the muscularis laminae. The proper layer, or epithelium, is supported by loose connective tissue, which includes glands, blood vessels, nerves and lymphoid formations. The oral cavity, pharynx, and esophagus are covered with stratified squamous epithelium. The stomach and intestines have a single-layer cylindrical epithelium. The lamina propria of the mucous membrane, on which the epithelium lies, is formed by loose fibrous unformed connective tissue. It contains glands, accumulations of lymphoid tissue, nerve elements, blood and lymphatic vessels. The muscularis mucosa consists of smooth muscle tissue. Under the muscular plate there is a layer of connective tissue - the submucosal layer, which connects the mucous membrane with the muscular layer lying outward.

Among the epithelial cells of the mucous membrane are goblet-shaped, single-celled glands that secrete mucus. This is a viscous secretion that wets the entire surface of the digestive canal, which protects the mucous membrane from the harmful effects of solid food particles and chemicals and facilitates their movement. The mucous membrane of the stomach and small intestine contains numerous glands, the secretion of which contains enzymes involved in the process of digesting food. According to their structure, these glands are divided into tubular (simple tube), alveolar (vesicle) and mixed (alveolar-tubular). The walls of the tube and vesicle consist of glandular epithelium; they secrete a secretion that flows through the opening of the gland onto the surface of the mucous membrane. In addition, glands can be simple or complex. Simple glands are a single tube or vesicle, while complex glands consist of a system of branched tubes or vesicles that empty into the excretory duct. The complex gland is divided into lobules, separated from each other by layers of connective tissue. In addition to the small glands located in the mucous membrane of the digestive tract, there are large glands: salivary glands, liver and pancreas. The last two lie outside the digestive canal, but communicate with it through their ducts.

The muscular lining of most of the alimentary canal consists of smooth muscle with an inner layer of circular muscle fibers and an outer layer of longitudinal muscle fibers. In the wall of the pharynx and the upper part of the esophagus, in the thickness of the tongue and soft palate there is striated muscle tissue. When the muscle membrane contracts, food moves through the digestive canal.

The digestive system consists of the mouth, pharynx, esophagus, stomach, small and large intestines, as well as two digestive glands - the liver and pancreas