The general principle of the structure of the digestive tube, its features in various departments. General plan of the structure of the wall of the digestive tube Sections of the digestive tube

Plan:
1. Departments digestive tube, their composition and functions.
2. General principle structures of the digestive tube, its features in various departments.
3. Origins and embryonic development of the digestive tube.
The digestive system includes the digestive tract and the large glands that lie outside this tube, the large salivary glands. The main function of the digestive tube (HTP) is the mechanical, chemical, enzymatic processing of food, the absorption of nutrients, which are subsequently used as an energy and plastic (building) material.
According to the features of the structure and function in the digestive tube, there are:
1. Anterior section - the oral cavity with its derivatives (lip, tongue, teeth, palate, tonsils and salivary glands) and the esophagus. The function of the anterior part of the HTP is the mechanical processing of food by the dentition and the formation of a food bolus. In addition, the breakdown of carbohydrates by maltase and saliva amylase begins in the oral cavity; a protective function is performed (the tonsils form a pharyngeal lymphoepithelial ring; saliva contains the bactericidal substance lysozyme); perception of taste, texture and temperature of food; and swallowing and transporting the food bolus to the middle part of the HTP; participates in the formation of speech.
2. The middle section is the main section of the HTP and includes the stomach, small and large intestines, the initial section of the rectum, the liver and the pancreas. In the middle section, chemical, enzymatic processing of food takes place, mechanical processing continues, cavity and parietal digestion occurs, absorption of nutrients, feces are formed from undigested food residues. As part of the middle section of the HTP, to perform a protective function, there is a significant amount of lymphoid tissue, for hormonal regulation of local functions (synthesis and secretion of enzymes and hormones by the glands, peristalsis of the HTP, etc.), the epithelium contains single hormone-producing (APUD) cells.
The digestive tube has a general structural plan. The HTP wall consists of 3 membranes: internal - mucous membrane with submucosa, middle - muscular, external - adventitious (loose fibrous sdt) or serous (covered with peritoneum). In each shell, in turn, layers are distinguished.
The mucous membrane consists of 3 layers:
1) epithelium:
a) in the anterior part of the HTP (oral cavity and esophagus), the epithelium is stratified squamous, non-keratinizing - it performs the function of protecting against mechanical damage by solid particles of food;
b) in the stomach - a single-layer prismatic glandular epithelium, plunging into its own mucosal plate, forms gastric pits and gastric glands; the epithelium of the stomach constantly secretes mucus to protect the organ wall from self-digestion, hydrochloric acid and digestive enzymes: pepsin, lipase and amylase;
c) in the small and large intestines, the epithelium is a single-layer prismatic bordered epithelium - it got its name due to epithelial cells - enterocytes: prismatic cells, on the apical surface they have a large number of microvilli (absorption border) - a special-purpose organoid, increase the working surface of the cell, participate in parietal digestion and absorption of nutrients.
This epithelium, plunging into the underlying lamina propria, forms crypts - intestinal glands;
d) in the final sections of the rectum, the epithelium again becomes a multi-layered squamous non-keratinizing.
2) the mucosal lamina propria lies under the epithelium, histologically it is a loose fibrous sdt. The lamina propria contains blood and lymphatic vessels, nerve fibers, and accumulations of lymphoid tissue. Functions: musculoskeletal (for the epithelium), trophism of the epithelium, transportation of absorbed nutrients (through the vessels), protective (lymphoid tissue).
3) muscular plate of the mucosa - represented by a layer of smooth muscle cells - myocytes. Absent in the oral mucosa. The muscular plate of the mucous membrane provides the variability of the relief of the surface of the mucous membrane.
The mucosa is located on the submucosa - consisting of loose fibrous sdt. The submucosa contains blood and lymphatic vessels, nerve fibers and their plexuses, autonomic nerve ganglia, accumulations of lymphoid tissue, and in the esophagus and duodenum there are also glands that secrete a secret into the lumen of these organs. The submucosa ensures the mobility of the mucous membrane in relation to other membranes, participates in the blood supply and innervation of organs, and provides a protective function. The submucosa in some parts of the oral mucosa (back of the tongue, gums, hard palate) is absent.
The muscular coat in most of the AVT is represented by smooth muscle tissue, with the exception of the anterior part of the AVT (up to the middle third of the esophagus) and the anal part of the rectum (sphincter) - in these areas, the muscles are from striated muscle tissue of the skeletal type. The muscular coat ensures the promotion of food masses along the AVT.
The outer shell of the HTP in the anterior (before the thoracic diaphragm) and posterior (after the pelvic diaphragm) is adventitious - consists of a loose fibrous sdt with blood and lymphatic vessels, nerve fibers, and in the abdominal cavity (stomach, small and large intestines) - serous, those. covered with peritoneum.
Sources, laying and development of HTP. At the end of the 3rd week of embryonic development, a flat 3-leaf human embryo folds into a tube, i.e. body is formed. At the same time, the endoderm, the visceral sheet of splanchnotomes and the mesenchyme between them, folding into a tube, form the I intestine - this is a hollow tube closed at the cranial and caudal end, lined inside with endoderm, outside - with a visceral sheet of splanchnotomes, a layer of mesenchyme between them. In the anterior part of the embryo, the ectoderm, invaginating towards the cranial blind end of the I intestine, forms the first oral bay, in the caudal end of the embryo, the ectoderm, invaginating towards the other blind end of the I intestine, forms the anal bay. The lumen of the I intestine from the cavities of these bays is delimited, respectively, by the pharyngeal and anal membranes. The endoderm of the anterior part of the closed first intestine consists of the cellular material of the former prechordal plate of the epiblast, the rest of the endoderm of the first intestine is the material of the hypoblast. In the posterior section of the first intestine, a blind protrusion is formed - the allantois (“urinary sac”) is formed, which is a rudimentary provisional organ of the human embryo. The pharyngeal and anal membranes subsequently rupture and the AVT becomes leaky.
Regarding the question of what level of AVT in an adult corresponds to the line of transition of the ectoderm of the oral bay into the material of the prechordal plate, researchers have no consensus, there are 2 points of view:
1. This border runs along the line of the teeth.
2. The border passes in the region of the posterior part of the oral cavity.
The difficulty in determining this boundary is explained by the fact that in a definite organism, the epithelium (and their derivatives) that develop from the ectoderm of the mouth bay and the prechordal plate do not differ morphologically from each other, since their sources are parts of a single epiblast and, therefore, are not alien to each other. .
The boundary between the epithelium that develops from the material of the prechordal plate and from the material of the hypoblast is clearly traced and corresponds to the line of transition of the stratified squamous non-keratinized epithelium of the esophagus into the epithelium of the stomach.
From the ectoderm of the oral bay, the epithelium of the vestibule of the oral cavity is formed (according to the 2nd point of view - both the epithelium of the anterior and middle parts of the oral cavity and its derivatives: tooth enamel, large and small salivary glands of the oral cavity, adenohypophysis), from the endoderm of the anterior part of the first intestine ( material of the prechordal plate) - the epithelium of the oral cavity and its derivatives (see above), the epithelium of the pharynx and esophagus, the epithelium respiratory system(trachea, bronchial tree and respiratory department of the respiratory system); from the rest of the endoderm (the material of the hypoblast), the epithelium and glands of the stomach and intestines, the epithelium of the liver and pancreas are formed; from the ectoderm of the anal bay, a stratified squamous non-keratinized epithelium and epithelium of the glands of the anal rectum are formed.
From the mesenchyme of the I intestine, a loose fibrous sdt of the mucosal lamina propria, submucosa, advintition and a layer of loose sdt of the muscular membrane, as well as smooth muscle tissue (muscular lamina of the mucous membrane and muscular membrane) are formed.
From the visceral sheet of the splanchnotomes of the I intestine, a serous (peritoneal) cover of the stomach, intestines, liver and partly the pancreas is formed.
The liver and pancreas are laid as a protrusion of the wall of the first intestine, i.e., also from the endoderm, mesenchyme and visceral sheet of splanchnotomes. Hepatocytes, epithelium of the biliary tract and gallbladder, pancreatocytes and epithelium of the excretory tract of the pancreas, cells of the islets of Langerhans are formed from the endoderm; sdt elements and smooth muscle tissue are formed from the mesenchyme, and the peritoneal cover of these organs is formed from the visceral layer of splanchnotomes.
The endoderm of allantois is involved in the development of the transitional epithelium of the bladder

Oorgans of the oral cavity

Oral organs - lip, cheek, tongue, hard and soft palate, gums. The anterior part of the digestive system begins with the oral cavity with its derivatives. The main function of the oral cavity and its derivatives is the capture and mechanical processing of food, i.e. grinding, wetting and the formation of a food lump. Additional functions:
1) the breakdown of carbohydrates by maltase and salivary amylase begins;
2) protective function: immunological protection due to the presence of a lymphoepithelial ring; the presence of bactericidal proteins (lysozyme) in saliva;
3) swallowing a food bolus;
4) participation in the formation of speech;
5) reception of taste, temperature and consistency of food;
6) absorption begins ( medicinal substances such as nitroglycerin).
The general principle of the structure of the wall of the digestive tube, which was discussed in the previous section, is generally observed in the oral cavity, but at the same time there are certain features:
1. Features of the mucous membrane with a submucosal basis:
a) epithelium - in contrast to the middle section of the HTP, the epithelium in the oral cavity is stratified squamous, non-keratinizing, which is due to:
- source of development - ectoderm;
- function - protection against mechanical damage to the mucosa with solid food pieces.
At the same time, it should be noted that this epithelium is partially keratinized in places, as it resists a significant mechanical load:
- filiform papillae of the tongue;
- gum;
- solid sky.
In the lower parts of the PVT, the mucosal lamina propria lies on the mucosal muscular lamina, and in the oral cavity, the mucosal lamina propria is absent, so the mucosal lamina propria passes into the submucosa or attaches to the underlying tissues:
- in the area of ​​the hard palate and on the gums grows together with the periosteum;
- on the back of the tongue - with the muscle tissue of the tongue.
The muscular membrane in the oral cavity is not continuous, but is represented by individual muscles from the skeletal muscles:
- circular muscles of the lips;
- chewing muscles in the thickness of the cheek;
- muscles of the tongue;
- muscles of the pharynx.
Lip. In the lip, the skin part, the transitional and mucous parts are distinguished, and in the thickness of the lip there is a circular muscle of the mouth opening. Outside, the lip is covered with ordinary skin and contains sweat and sebaceous glands, hair. In the transitional part of the lip, sweat glands and hair disappear, the sebaceous glands remain closer to the corners of the mouth, and the keratinized stratified squamous epithelium gradually turns into a non-keratinizing one. The surface of the lip facing the oral cavity is covered with a mucous membrane. Under the stratified squamous non-keratinized epithelium there is a mucosal lamina propria, which, due to the absence of a muscular lamina, gradually passes into the submucosa. In the submucosa are the labial salivary glands (complex muco-protein).
Cheeks. The cheeks, like the lips, are covered with skin on the outside, with a mucous membrane on the inside. The mucous membrane is represented by a layer of stratified squamous non-keratinized epithelium on the surface, under it there is a lamina propria protruding into the epithelium in the form of papillae. The lamina propria passes into the submucosa containing alveolar-tubular muco-protein salivary glands.
Chewing muscles are located in the thickness of the cheeks.
The tongue is a muscular organ, the basis is striated muscle tissue. Muscle fibers are located in 3 mutually perpendicular directions. Between the muscle fibers are layers of loose fibrous sdt with blood vessels, as well as the terminal sections of the lingual salivary glands. These glands, by the nature of the secret in the anterior part of the tongue, are mixed (mucous-protein), in the middle part of the tongue - protein, in the region of the root of the tongue - purely mucous.
The muscular body of the tongue is covered with a mucous membrane. On the lower surface, due to the presence of a submucosal base, the mucous membrane is mobile; there is no submucosa on the back of the tongue, so the mucous membrane is motionless in relation to the muscular body.
On the back of the tongue, the mucous membrane forms papillae: filiform, mushroom-shaped, foliate and grooved papillae are distinguished. Histological structure papillae are similar: the basis is an outgrowth from a loose sdt of the mucosal lamina propria (having the form: filiform, mushroom-shaped, leaflet and anvil), outside the papillae are covered with stratified squamous non-keratinized epithelium. An exception is the filiform papillae - in the region of the tops of these papillae, the epithelium has signs of keratinization or becomes keratinized. The function of the filiform papillae is mechanical, i.e. they work like scrapers. In the thickness of the epithelium of the fungiform, foliate and grooved papillae there are taste buds (or taste buds), which are receptors of the organ of taste. The taste bud has an oval shape and consists of the following types of cells:
1. Taste sensory epitheliocytes - spindle-shaped elongated cells; in the cytoplasm have agranular EPS. Mitochondria have microvilli on the apical surface. Between the microvilli is an electron-dense substance with a high content of specific receptor proteins - sweet-sensitive, acid-sensitive, salt-sensitive and bitter-sensitive. Sensory nerve fibers approach the lateral surface of the sensory epithelial cells and form receptor nerve endings.
2. Support cells - curved spindle-shaped cells that surround and support gustatory sensory epithelial cells.
3. Basal epitheliocytes - poorly differentiated cells, for regeneration of 1 and 2 cells.
The apical surfaces of taste bud cells form taste pits that open into the taste pore. Substances dissolved in saliva enter the taste pits, are adsorbed by the electron-dense substance between the microvilli of sensoepithelial cells, and act on the receptor proteins of the cell membrane, which leads to a change in the electric potential difference between the inner and outer surfaces of the cytolemma, i.e. the cell goes into a state of excitation and this is captured by the nerve endings.
The hard palate is the upper solid wall of the oral cavity and resists significant mechanical stress and is a support for the tongue when mixing and swallowing food. The hard palate is covered with stratified squamous epithelium with signs of keratinization (granules of glycosaminoglycans and keratohyalin). In the hard palate, the muscular lamina of the mucosa and the submucosa are absent, so the mucosal lamina propria is attached to the periosteum of the palatine bones. In the anterior part of the hard palate, lateral to the palatine suture, in the lamina propria there is a significant accumulation of lipocytes - this is the fatty zone of the hard palate, and in the posterior part of the hard palate in the lamina propria there are small salivary glands - this part is called the mucous zone.
The soft palate is a continuation of the hard palate posteriorly, it is mobile and, when swallowing, rising upwards, covers the nasopharynx to prevent food from entering the nose. The upper surface of the soft palate is covered with a single-layer multi-row ciliated epithelium, which is a continuation of the epithelium of the nasal cavity, and the lower surface is a stratified squamous non-keratinized epithelium. Under the epithelium of both surfaces lie their own plates of the mucosa, containing mucous-protein glands, and acquiring the character of an aponeurosis near the hard palate. Between these two own plates is the muscle layer.
The gums are covered with stratified squamous non-keratinized epithelium with signs of keratinization. The lamina propria in the surface layers in the form of papillae protrudes into the epithelium, in the deep layers it is represented by thick bundles of intertwining collagen fibers. There are a lot of mechanoreceptors in the lamina propria of the mucosa, and there are no glands. The muscular plate and submucosa are absent, therefore the mucous membrane fuses directly with the periosteum of the alveolar processes of the jaws. Normally, in a healthy person, the stratified squamous non-keratinizing epithelium of the gums fuses tightly with the cuticle of the enamel of the tooth neck, forming a periodontal junction. If the integrity of the dentogingival connection is violated, a dentogingival pocket is formed, where food particles can linger and become a breeding ground for microorganisms, which in turn can lead to the onset of inflammatory processes in the periodontium and periodontium.

Salivary glands

The surface of the epithelium of the oral cavity is constantly moistened with the secretion of the salivary glands (SG). Salivary glands are numerous. There are small and large salivary glands. Small salivary glands are found in the lips, in the gums, in the cheeks, in the hard and soft palate, in the thickness of the tongue. Major salivary glands include the parotid, submandibular, and sublingual GS. Small SF lie in the mucosa or submucosa, and large SF lie outside these membranes. SF is characterized by an intracellular type of regeneration.
SJ functions:
1. Exocrine function - the secretion of saliva, which is necessary for:
- facilitates articulation;
- formation of a food bolus and its ingestion;
- cleaning the oral cavity from food residues;
- protection against microorganisms (lysozyme);
2. Endocrine function:
- the production of small amounts of insulin, parotin, epithelial and nerve growth factors, a lethality factor.
3. Beginning of enzymatic processing of food (amylase, maltase, pepsinogen, nucleases).
4. Excretory function (uric acid, creatinine, iodine).
5. Participation in water-salt metabolism (1.0-1.5 l / day).
Let's take a closer look at large SJs. All large SF develop from the epithelium of the oral cavity, they are all complex in structure (the excretory duct strongly branches. In large SF, a terminal (secretory) section and excretory ducts are distinguished.
Parotid SF is a complex alveolar protein gland. The terminal sections, according to the structure of the alveoli, are proteinaceous in nature, and consist of serocytes (protein cells). Serocytes are cone-shaped cells with basophilic cytoplasm. The apical part contains acidophilic secretory granules. In the cytoplasm, granular EPS, PC, and mitochondria are well expressed. In the alveoli, outward from the serocytes (as if in a second layer), myoepithelial cells are located. Myoepithelial cells have a stellate or process shape, their processes wrap around the terminal secretory section, and contain contractile proteins in the cytoplasm. When contracting, myoepithelial cells help to move secretions from the terminal section into the excretory ducts. The excretory ducts begin with intercalary ducts - they are lined with low-cubic epithelial cells with basophilic cytoplasm, outside they are wrapped around by myoepithelial cells. Intercalary ducts continue into striated sections. The striated sections are lined with a single-layer prismatic epithelium with basal striation due to the presence of cytolemmal folds in the basal part of the cells and mitochondria lying in these folds. On the apical surface, epitheliocytes have microvilli. The striated sections outside are also covered by myoepitheliocytes. In the striated sections, water is reabsorbed from saliva (saliva thickening) and the salt composition is balanced; in addition, endocrine function is attributed to this section. The striated sections merge into interlobular ducts lined with 2-row epithelium, turning into a 2-layer one. The interlobular ducts drain into the common excretory duct lined with stratified squamous non-keratinized epithelium. The parotid SF is covered on the outside with a connective tissue capsule; interlobular septa are well defined; there is a clear lobulation of the organ. In contrast to the submandibular and sublingual SF, in the parotid SF, the layers of loose fibrous SD inside the lobules are poorly expressed.
The submandibular SF is complex alveolar-tubular in structure, mixed in the nature of the secret, i.e. mucous-protein (with a predominance of the protein component) iron. Most secretory sections are alveolar in structure, and proteinaceous in nature - the structure of these secretory sections is similar to the structure of the terminal sections of the parotid SF (see above). A smaller number of secretory sections are mixed - alveolar-tubular in structure, mucous-protein in nature of the secret. In the mixed end sections in the center there are large light (poorly perceiving dyes) mucocytes. They are surrounded in the form of crescents by smaller basophilic serocytes (protein crescents of Juanici). The terminal sections are surrounded by myoepithelial cells from the outside. In the submandibular SF from the excretory ducts, the intercalary ducts are short, poorly expressed, and the remaining sections have a similar structure to the parotid SF.
The stroma is represented by a capsule and sdt-tissue septa extending from it and interlayers of loose fibrous sdt. Compared to the parotid SF, the interlobular septa are less pronounced (weakly pronounced lobulation). But inside the lobules, layers of loose fibrous sdt are better expressed.
The sublingual SF is a complex alveolar-tubular in structure, a mixed (mucous-protein) gland by the nature of the secretion with a predominance of the mucous component in the secretion. In the sublingual gland, there are a small number of pure protein alveolar end sections (see description in parotid SG), a significant number of mixed mucoprotein end sections (see description in submandibular SG) and purely mucous secretory sections that are tubular in shape and consist of mucocytes with myoepitheliocytes. Of the features of the excretory ducts of the sublingual SF, it should be noted that the intercalary ducts and striated sections are weakly pronounced.
The sublingual SG, as well as the submandibular SF, is characterized by a slightly pronounced lobulation and well-defined layers of loose fibrous sdt inside the lobules.

Esophagus. Stomach

Histological structure. In the esophagus, the general principle of the structure of the wall of the digestive tube is fully respected, i.e. in the wall of the esophagus, 4 membranes are distinguished: mucous, submucosal, muscular and external (mostly adventitious, to a lesser extent serous).
The mucous membrane consists of 3 layers: the epithelium, the lamina propria of the mucosa and the muscular lamina of the mucosa.
1. The epithelium of the esophagus is stratified squamous, non-keratinizing, but signs of keratinization appear in old age.
2. Mucosal lamina propria - histologically, it is a loose fibrous sdt-u, in the form of papillae protrudes into the epithelium. It contains blood and lymphatic vessels, nerve fibers, lymphatic follicles and terminal sections of the cardiac glands of the esophagus - simple tubular branched glands. The cardiac glands of the esophagus are not present throughout the entire length of the esophagus, but only in the upper part (from the level of the cricoid cartilage to the 5th tracheal ring) and in front of the entrance to the stomach. In structure, they are similar to the cardiac glands of the stomach (hence their name). The secretory sections of these glands consist of cells:
a) mucocytes - their majority; in the cytoplasm they have a moderately pronounced agranular EPS and secretory granules with mucin. Mucosocytes do not perceive dyes well, therefore they are light in the preparation. Function: produce mucus;
b) endocrine cells that produce serotonin, melatonin and histamine;
c) parietal exocrinocytes - are found in small numbers; the cytoplasm is oxyphilic, contains a branched system of intracellular tubules and a significant number of mitochondria; function - accumulate and secrete chlorides, which turn into hydrochloric acid in the stomach.
The muscular plate of the mucous membrane consists of smooth muscle cells (myocytes) and elastic fibers, oriented mainly longitudinally. The thickness of the muscle plate increases in the direction from the pharynx to the stomach.
Submucosa - histologically from loose fibrous tissue. Together with the mucous membrane, they form longitudinal folds of the esophagus. In the submucosa are the end sections of the esophageal glands - complex alveolar-tubular branched mucous glands. Secretory sections consist only of mucous cells. These glands are present along the entire length of the organ, but they are most numerous in the upper third on the ventral wall. The secret of these glands facilitates the passage of the food bolus through the esophagus. The submucosa also contains the nerve plexus, a plexus of blood vessels.
Muscular membrane - consists of 2 layers: outer - longitudinal and inner - circular. The muscular membrane in the upper third of the esophagus consists of striated muscle tissue, in the middle third of both striated and smooth muscle tissue, in the lower third - only of smooth muscle tissue. Despite the presence of striated muscle tissue, contraction of the musculature of the esophagus is involuntary, i.e. does not obey the will of man, tk. innervated mainly by parasympathetic nerve fibers of the vagus nerve. Swallowing in the pharynx begins voluntarily, but the continuation of the act of swallowing in the esophagus is involuntary. In the muscular membrane there is a well-defined nerve plexus and blood vessels.
The outer shell in the greater extent of the esophagus is represented by adventitia, i.e. loose fibrous sdt with an abundance of blood vessels and nerves. Below the level of the diaphragm, the esophagus is covered by the peritoneum, i.e. serous membrane.
The stomach is an important organ of the digestive system and performs the following functions:
1. Reservoir (accumulation of food mass).
2. Chemical (HCl) and enzymatic food processing (pesin, chemosin, lipase).
3. Sterilization of food mass (HCl).
4. Mechanical processing (dilution with mucus and mixing with gastric juice).
5. Absorption (water, salts, sugar, alcohol, etc.).
6. Endocrine (gastrin, serotonin, motilin, glucagon).
7. Excretory (excretion from the blood into the cavity of the stomach of ammonia, uric acid, urea, creatinine).
8. Development of an anti-anemic factor (Castle factor), without which the absorption of vitamin B12, which is necessary for normal hematopoiesis, becomes impossible.
Embryonic sources of stomach development:
1. Endoderm - the epithelium of the superficial lining and glands of the stomach.
2. Mesenchyme - sdt elements, smooth muscles.
3. Visceral sheet of splanchnatomes - the serous membrane of the stomach.
Structure. The general principle of the structure of the digestive tube in the stomach is fully respected, that is, there are 4 membranes: mucous, submucosal, muscular and serous.
The surface of the mucous membrane is uneven, forms folds (especially along the lesser curvature), fields, grooves and pits. The epithelium of the stomach is single-layer prismatic glandular - i.e. single-layered prismatic epithelium constantly producing mucus. Mucus liquefies food masses, protects the stomach wall from self-digestion and from mechanical damage. The epithelium of the stomach, plunging into its own plate of the mucous membrane, forms the glands of the stomach, opening into the bottom of the gastric pits - depressions of the integumentary epithelium. Depending on the structural features and functions, cardiac, fundal and pyloric glands of the stomach are distinguished.
The general principle of the structure of the glands of the stomach. By structure, all the glands of the stomach are simple (the excretory duct does not branch) tubular (the end section is in the form of a tube). In the gland, the bottom, body and neck are distinguished. The terminal sections of these glands contain the following types of cells:
1. The main exocrinocytes are prismatic cells with a sharply basophilic cytoplasm. They are located in the region of the bottom of the gland. Under an electron microscope, the granular EPS, the lamellar complex, and mitochondria are well expressed in the cytoplasm; there are microvilli on the apical surface. Function: production of digestive enzymes pepsinogen (in an acidic environment it turns into pepsin, which provides the breakdown of proteins to albumose and peptones), chymosin (breaks down milk proteins) and lipase (breaks down fats).
2. Parietal (covering) exocrinocytes - located in the neck and body of the gland. They have a pear-shaped shape: the wide rounded basal part of the cell is located, as it were, in the second layer - outward from the main exocrinocytes (hence the name - parietal), the apical part of the cell in the form of a narrow neck reaches the lumen of the gland. The cytoplasm is strongly acidophilic. Under an electron microscope in the cytoplasm there is a system of highly branched intracellular tubules and many mitochondria. Functions: accumulation and release of chlorides into the lumen of the gland, which are converted into hydrochloric acid in the cavity of the stomach; production of the anti-anemic Castle factor.
3. Cervical cells - located in the neck of the gland; cells of a low-prismatic form, the cytoplasm is light - it poorly perceives dyes. Organelles are poorly expressed. Mitotic figures are often observed in cells, therefore they are considered poorly differentiated cells for regeneration. Part of the cervical cells produces mucus.
4. Mucocytes - located in the body and neck of the gland. Low prismatic cells with slightly stained cytoplasm. The nucleus is pushed aside to the basal pole, in the cytoplasm there is a relatively weakly expressed granular EPS, a lamellar complex above the nucleus, a few mitochondria, and mucoid secretory granules in the apical part. Function is the production of mucus.
5. Endocrine cells (argentophilic cells - reduce silver nitrite, argerophilic - restore silver nitrate) - a prismatic cell shape with a weakly basophilic cytoplasm. Under the electron microscope, the lamellar complex and EPS are moderately expressed, there are mitochondria. Functions: synthesis of biologically active hormone-like substances: EC cells - serotonin and motilin, ECL cells - histamine, G cells - gastrin, etc. The endocrine cells of the stomach, as well as the entire digestive tube, belong to the APUD system and regulate local functions (stomach, intestines).
Features of the structure of the glands of the stomach.
Cardiac glands of the stomach - a small group of glands, located in a limited area - in a zone 1.5 cm wide at the entrance of the esophagus to the stomach. By structure, simple tubular, highly branched, by the nature of the secret, predominantly mucous. The cellular composition is dominated by mucocytes, few parietal and main exocrinocytes, endocrinocytes.
Fundic (or own) glands of the stomach - the most numerous group of glands, located in the body and fundus of the stomach. In structure, simple tubular unbranched (or slightly branched) glands. The glands are in the form of straight tubes, located very tightly in relation to each other, with very thin layers of sdt. The cellular composition is dominated by the main and parietal exocrinocytes, the remaining 3 types of cells are present, but there are fewer of them. The secret of these glands contains the digestive enzymes of the stomach (see above), hydrochloric acid, hormones and hormone-like substances (see above), mucus.
Pyloric glands of the stomach - located in the pyloric part of the stomach, they are much smaller than the fundic ones. By structure, simple tubular branched, by the nature of the secret, predominantly mucous glands. They are located in relation to each other at a distance (less often), between them there are well-defined layers of loose fibrous sdt. The cellular composition is dominated by mucocytes, a significant number of endocrine cells, there are very few or no main and parietal exocrinocytes.
If we compare the wall of the stomach in the pyloric, fundic and cardial sections, in addition to differences in the structure of the glands, the following should be added: the greatest depth of the pits and the greatest thickness of the muscular membrane in the pyloric section, the smallest depth of the gastric pits and the smallest thickness of the muscular membrane - in the fundic section of the stomach. According to these features, the cardiac department occupies an intermediate (middle) position.
In the muscular membrane of the stomach, 3 layers are distinguished: the inner one is an oblique direction, the middle one is a circular direction, the outer one is the longitudinal direction of myocytes. The outer serous membrane of the stomach without features.

Intestines

General morphofunctional characteristics of the intestine. In the intestine, the small intestine (12 duodenum, jejunum and ileum) and the large intestine (colon, sigma and rectum) are distinguished. The intestine performs a number of important functions:
1. Enzymatic breakdown of nutrients (proteins, fats and carbohydrates) through abdominal,
parietal and membrane digestion.
2. Absorption of split nutrients, water, salts and vitamins.
3. Mechanical function - pushing the chyme through the intestines.
4. Endocrine function - regulation of local functions with the help of hormones of single hormone-producing cells in the composition of the intestinal epithelium.
5. Immune protection due to the presence of single and grouped lymphoid follicles.
6. Excretory function - removal from the blood into the intestinal lumen of some harmful metabolic waste products (indole, skatole, urea, uric acid, creatinine).
The intestinal wall consists of 3 membranes - mucosa with submucosa, muscular and serous. The mucous membrane with the submucosa forms a number of structures that significantly increase the area of ​​​​the working surface - circular folds (T 5 pov. 3 times), villi and crypts (T 8 pov. 10 times).
Circular folds - formed from a duplication of the mucous membrane with a submucosal base, protruding into the intestinal lumen in the form of crescents. Villi - are finger-shaped or leaf-shaped protrusions of the mucous membrane, freely protruding into the intestinal lumen. Crypts are simple tubular unbranched intestinal glands formed by the invagination of the epithelium in the form of tubules into the underlying lamina propria.

To an even greater extent, the increase in the working surface of the intestine is facilitated by the nature of the epithelium - a single-layer prismatic border epithelium - microvilli increase the area of ​​​​the working surface by 20 times. In general, folds, villi, crypts and microvilli increase the surface area by 600 times.
Morphofunctional characteristics of the intestinal epithelium. The epithelium of the intestine along its entire length is a single-layer prismatic limbic. The single-layered prismatic border epithelium of the intestine has
the following cellular composition:
1. Columnar epitheliocytes (border cells, enterocytes) - cells of a prismatic shape, on the apical surface have a large number of microvilli, forming a striated border. Microvilli are covered on the outside with glycocalyx, in the center there are longitudinally located microtubules and actin-high contractile microfilaments, which provide contraction during absorption. In the glycocalyx and cytolemma of the microvilli, enzymes are localized for the breakdown and transport of nutrients into the cytoplasm of the cell. In the apical part of the cells on the lateral surfaces, there are tight contacts with neighboring cells, which ensures the tightness of the epithelium. In the cytoplasm of columnar epitheliocytes there are agranular and granular EPS, the Golgi complex, mitochondria and lysosomes. The function of columnar epitheliocytes is participation in parietal, membrane and intracellular digestion. During parietal digestion, lumps of dense gel are formed from parietal mucus - flocculi, which adsorb digestive enzymes in large quantities. Concentrated digestive enzymes on the surface of floccules significantly increase the efficiency of parietal digestion compared to cavity digestion, in which enzymes work in the intestinal lumen in a solution - chyme. During membrane digestion, digestive enzymes are localized in the glycocalyx and microvillus membrane in a certain orderly order (possibly forming a "conveyor"), which also significantly increases the rate of substrate degradation. Membrane digestion is inextricably completed by the transport of thawed nutrients through the cytolemma into the cytoplasm of columnar epitheliocytes. In the cytoplasm of columnar epithelial cells, nutrients are broken down to monomers in lysosomes (intracellular digestion) and then enter the blood and lymph.
They are localized both on the surface of the villi and in the crypts. The relative content of columnar epitheliocytes decreases in the direction from the duodenum to the rectum
In areas of the epithelium located above the lymphoid follicles, M-cells (with microfolds on the apical surface) are found - a kind of modification of columnar epitheliocytes. M-cells by endocytosis capture A-genes from the intestinal lumen, process and transfer them to lymphocytes,
2. Goblet-shaped exocrinocytes - goblet-shaped cells, like all mucus-producing cells, do not perceive dyes (white), in the cytoplasm they have a Golgi complex, mitochondria and secretory granules with mucin. The function of BE is the production of mucus necessary for the formation of floccules during parietal digestion, facilitating the movement of intestinal contents, gluing undigested particles and forming feces. The number of goblet cells increases in the direction from 12 PCs to the rectum. Localized on the surface of the villi and in the crypts.
3. Paneth cells (cells with acidophilic granularity) - prismatic cells with sharply acidophilic granules in the apical part. The cytoplasm of the basal part of the cells is basophilic, there is a Golgi complex and mitochondria. Function - the production of antibacterial protein lysozyme and digestive enzymes - dipeptidases.
They are localized only at the bottom of the crypts.
4. Endocrinocytes - belong to the APUD system, selectively stained with salts of heavy metals; mostly localized in crypts. There are varieties:
a) EC cells - they synthesize serotonin moplin and substance P;
b) A-cells - synthesize enteroglucogon;
c) S - cells - synthesize secretin,
d) I - riveting - they synthesize cholecystokenin and pancreazimin
e) G-cells - synthesize gastrin; c) D and D1 - cells - synthesize somatostatin and VIP.
5. Cambial cells - low-prismatic cells, organelles are poorly expressed, mitotic figures are often observed in them. Located at the bottom of the crypts. The function of regeneration of the intestinal epithelium (differentiate into all other types of cells). The endocrinocytes and Paneth cells that differentiate from the cambial cells remain and function in the area of ​​the bottom of the crypts, while the columnar epitheliocytes and goblet exocrinocytes, as they mature, gradually rise along the wall of the crypts to the intestinal lumen and end their sporulation there. life cycle and listen.
Finishing the characterization of the intestinal epithelium, it should be concluded that the epithelium in all sections is single-layer prismatic bordered, the ratio of the cell types of this epithelium is different.

The lamina propria is a layer of mucous membrane located just below the epithelium. Histologically, it is a loose, unformed fibrous connective tissue with blood and lymphatic vessels, nerve fibers; lymphoid nodules are common
next layer mucous membrane it is a muscular layer of the mucous membrane - represented
smooth muscle tissue.
Deeper than the mucous membrane is the submucosa - histologically represented by a loose, unformed fibrous connective tissue with blood and lymphatic vessels, nevsh fibers: it contains lymphoid nodules, plexuses of nerve fibers and nerve ganglia.
The muscular layer of the intestine consists of two layers in the inner layer, smooth muscle cells are located mainly circularly, in the outer layer - longitudinally. Between smooth muscle cells are blood vessels and intermuscular nerve plexus.

12 duodenal ulcer.
At 12PC, the breakdown of nutrients by digestive enzymes from the pancreas (trypsin, proteins, amylase, carbohydrates, lipase, fats) and crypts (depiptedases), as well as absorption processes, continue. A feature of the 12PK mucosa is the presence of circular folds, villi, crypts and duodenal glands in the submucosa.
Villi 12PK - unlike toshen, the intestines are short thick, have a leaf-like shape. In the epithelium of the villi, columnar epitheliocytes significantly predominate, a smaller number of goblet cells.
Duodenal glands (Brunner's) - complex in structure, alveolar-tubular, branched, mucous in nature. neutralizes hydrochloric acid, inactivates gastric pencin, participates in the formation of floccules for parietal digestion, protects the intestinal wall from mechanical and chemical-enzymatic damage.
The muscular coat of the 12PC is less pronounced than in the underlying sections. The serosa is absent on the posterior surface.

Jejunum.
In the jejunum, enzymatic cleavage of food substrates, trypsin, pancreatic lipase and amylase, dipeptidases of intestinal crypts, absorption of thawing products, water and salts, mixing and promotion of chyme continue. In the jejunum, endocrinocytes produce biologically active substances and hormones that regulate local functions.
In the small intestine there are circular folds, villi and crypts are well expressed. The villi of the jejunum are long, swampy, finger-shaped, covered with epithelium with a predominance of lateral epitheliocytes. Lymph follicles and lysozyme (Paneth cells) provide control over microorganisms. The muscular and serous membranes of the colon are without features.

Colon.
The structural features of the large intestine are well-defined circular semilunar folds, the absence of villi, the presence of deep crypts with a wide lumen, the predominance of goblet exocrinocytes in the epithelium, an abundance of single and grouped lymphoid follicles. In addition, in the muscular membrane, the longitudinal layer is not continuous, but is represented by three tapes, the length of which is less than the length. of the large intestine, therefore, are formed in the wall of swelling - haustra. Mostly absorbed in the large intestine
water and salts, therefore the intestinal contents thicken. The abundance of goblet cells ensures the production of a large amount of mucus, which glues undigested particles into cat masses and facilitates their pushing through the intestines.
Normally, the lumen of the large intestine contains a significant number of microorganisms, which CAN be considered as a phenomenon of symbiosis. microorganisms break down undigested fiber, and also produce vitamins that are absorbed by the host body. To control the intestinal microflora, there are lymphoid
follicles.
The appendix (appendix) is a blindly ending protrusion of the intestinal wall, opening into the caecum. Building features:
1. In the epithelium, columnar cells, goblet exocrinocytes predominate, there are also many endocrinocytes (2 times more often than in other sections), there are cambial cells.
2. Due to the weak expression of muscular plasticity of the mucosa, the lamina propria without a sharp border passes into the submucosa. The mucosal lamina propria and the submucosa contain a very large number of lymphoid follicles, which allows some authors to attribute this organ to the group of peripheral organs of lymphocytoposis.
3. The muscular coat of the appendix is ​​weakly expressed in comparison with other parts of the intestine.
The fact that the appendix ends blindly, the muscle elements are poorly expressed - are a morphological prerequisite for a possible stagnation of intestinal contents (by the way, rich in microorganisms in this section), and the combination of this with the presence of highly reactive lymphoid tissue in the wall - in turn, is a morphological prerequisite for the likelihood of an inflammatory reaction - this explains the rather high frequency of the disease - appendicitis

Liver and pancreas.

I. General morpho-functional characteristics of the liver.
The liver is the largest gland human body(the mass of the liver of an adult is 1/50 of body weight), performs a number of important functions:
1. Exocrine function - the production of bile, which is necessary in the intestines to emulsify fats and increase peristalsis.
2. Metabolization of hemoglobin - the iron-containing part - heme is transported by macrophages to the red bone marrow and is reused there by erythroid cells for the synthesis of hemoglobin, the globin part is used in the liver for the synthesis of bile pigments and is included in the composition of bile.
3. Detoxification harmful products metabolism, toxins, inactivation of hormones destruction of medicinal substances.

4. Synthesis of blood plasma proteins - fibrinogen, albumins, prothrombin, etc.
5. Purification of blood from microorganisms and foreign particles (stellate macrophages of hemocapillaries).
6. Deposition of blood (up to 1.5 liters).
7. Deposition of glycogen in hepatocytes (insulin and glucagon).
8. Deposition of fat-soluble vitamins-A, D.E.K.
9. Participation in cholesterol metabolism.
10. In the embryonic period - the organ of hematopoiesis.

III. The structure of the liver.
The organ is covered on the outside by the peritoneum and connective tissue capsule. Connective tissue partitions divide the organ into lobes, and lobes into segments consisting of lobules. The morphofunctional units of the liver are the hepatic lobules. For better assimilation of the structure of the lobule, it is useful to recall the features of the blood supply to the liver. The portal vein enters the gates of the liver (collects blood from the intestine - rich in nutrients, from the spleen - rich in hemoglobin from old collapsing red blood cells) and the hepatic vein. artery (blood rich in oxygen). In the organ, these vessels are divided into lobar, then segmental, subsegmental, interlobular. around the lobules. Interlobular arteries and veins in the preparations are located next to the interlobular bile duct and form the so-called hepatic triads. From the perilobular arteries and veins, capillaries begin, which, merging, in the peripheral part of the lobule give rise to sinusoidal hemocapillaries. Sinusoidal hemocapillaries in the lobules run radially from the periphery to the center and merge in the center of the lobule to form the central vein. The central veins flow into the sublobular veins, and the latter merge with each other to form sequentially segmental and lobar hepatic veins that empty into the inferior vena cava.
The structure of the hepatic lobule. The hepatic lobule in space has a classical view. polyhedral prism, in the center of which the central vein passes along the long axis. In the preparation, on a transverse section, the lobule looks like a polyhedron (5-6 sided). In the center of the lobule is the central vein, from which the hepatic beams (or hepatic plates) diverge radially like rays, in the thickness of each hepatic beam there is a bile capillary, and between adjacent beams there are sinusoidal hemocapillaries that run radially from the periphery of the lobule to the center, where they merge into central vein. At the corners of the polyhedron are the interlobular artery and vein, the interlobular bile duct - the hepatic triads. In humans, the connective tissue layer around the lobule is not expressed, the conditional boundaries of the lobule can be determined by the lines connecting neighboring hepatic triads located at the corners of the polyhedron. The proliferation of connective tissue in the liver parenchyma, including around the lobules, is observed with chronic diseases liver, with hepatitis of various etiologies.
The hepatic beam is a strand of 2 rows of hepatocytes running radially from the central vein to the periphery of the lobule. In the thickness of the hepatic beam is a bile capillary. Hepatocytes forming hepatic beams are polygonal cells with 2 poles: the biliary pole is the surface facing the bile capillary, and the vascular pole is the surface facing the sinusoidal hemocapillary. There are microvilli on the surface of the beats of the paired and vascular poles of the hepatocyte. In the cytoplasm of hepatoiites, granular and agranular EPS, a lamellar complex, mitochondria, lysosomes, a cell center are well expressed, there is a large amount of fatty inclusions and inclusions of glycogen. Up to 20% of hepatocytes are 2 or multinucleated. Nutrients and vitamins enter hepatocytes from sinusoidal hemocapillaries. Absorbed into the blood from the intestines; in hepatocytes, detoxification, synthesis of blood plasma proteins, formation and deposition in reserve in the form of inclusions of glycogen, fat and vitamins, synthesis and secretion of bile into the lumen of the bile capillaries occur.
In the thickness of each hepatic beam passes a bile capillary. The gall capillary does not have its own wall; its wall is formed by the cytolemma of hepatocytes. On the biliary surfaces of the cytolemma of hepatocytes there are grooves that, when applied to each other, form a channel - a bile capillary. The tightness of the wall of the bile capillary is provided by desmosomes connecting the edges of the grooves. Bile capillaries begin in the thickness of the hepatic plate closer to the central vein blindly, go radially to the periphery of the lobule and continue into short cholangiols that flow into the interlobular bile ducts. Bile in the bile capillaries flows in the direction from the center to the periphery of the lobule.
A sinusoidal hemocapillary passes between two adjacent hepatic beams. The sinusoidal hemocapillary is formed as a result of the fusion in the peripheral part of the lobule of short capillaries extending from the perilobular artery and vein, i.e. blood in the sinusoidal capillaries is mixed (arterial and venous). Sinusoidal capillaries run radially from the periphery to the center of the lobule, where they merge to form the central vein. Sinusoidal capillaries are sinusoidal type capillaries - they have a large diameter (20 microns or more), the endothelium is not continuous - there are gaps and pores between endotheliocytes, the basement membrane is not continuous - it is completely absent for a long distance. In the inner lining of the hemocapillaries, among the endotsliocytes, there are stellate macrophages (Kupffer cells) - process cells that have mitochondria and lysosomes. Hepatic macrophages perform protective functions - they phagocytize microorganisms, foreign particles. Pit cells (pH cells) are attached to microphages and endotheliocytes from the side of the capillary lumen, performing a 2nd function: on the one hand, they are killers - they kill damaged hepatocytes, on the other hand, they produce hormone-like factors stimulating the proliferation and regeneration of heatocytes. between the hemocapillary and the liver plate there is a narrow space (up to 1 micron) - the space of Disse (pericapillary space) - around the sinusoidal space. In the space of Disse there are argerophilic reticular fibers, a protein-rich fluid, microvilli of hepatocytes. processes of macrophages and perisinusoidal lipocytes. Through space Disse goes between blood and hepatocytes. in the cytoplasm they have many ribosomes, mitochondria and small droplets of fat; function - capable of fiber formation (the number of these cells increases sharply in chronic liver diseases) and deposit fat-soluble vitamins A, D, E, K.
In addition to the classical representation of the liver lobule, there are other models of the lobule - the portal lobule and the liver acinus (see diagram).

Diagram of the liver acinus Diagram of the portal lobule

The portal hepatic lobule includes segments of 3 neighboring classical lobules and is a triangle in the preparation, on the tops of which there are central veins, and in the center - the hepatic triad

The hepatic acinus is formed by segments of 2 adjacent classical lobules, in the preparation it looks like a rhombus, on the sharp corners of which the central veins are located, and on the obtuse corners - the hepatic triads.

Age-related changes in the liver. The formation of the final structure of the lobules ends by 8-10 years. In the elderly and senile age, the mitonic activity of hepatocytes decreases, and compensatory cell hypertrophy is observed. the content of hepatocytes with polyploidy and mononuclear hepatocytes increases. The pigment lipofuscin and fatty inclusions accumulate in the cytoplasm, the content of glycogen decreases, and the activity of oxidative helium-reducing enzymes decreases. In the liver lobules, the number of hemocapillaries per unit area decreases, which leads to hypoxia and, as a result, to dystrophy and death of hepatocytes in the central parts of the lobules.

IV. gallbladder
thin-walled hollow organ, up to 70 ml. There are 3 membranes in the wall - mucous. muscular and adventitial. The mucous membrane forms numerous folds, consists of a single layer of highly prismatic border epithelium (for the absorption of water and concentration of bile) and its own plate of mucous from loose fibrous connective tissue. In the area of ​​the neck
bubbles in the lamina propria of the mucosa are located alveolar-tubular mucous glands. The muscular membrane is made of smooth muscle tissue, thickening in the neck area to form a sphincter. The outer shell is mostly adventitial (loose fibrous connective tissue). a small area may have a serous membrane.
The gallbladder performs a reservoir function, thickens or concentrates bile, provides portioned flow of bile as needed into the duodenum.

V. Pancreas.
The organ is covered on the outside with a connective tissue capsule, from which partitions thin layers of loose connective tissue extend inward. In the pancreas, the exocrine part (97%) and the endocrine part (up to
The exocrine part of the pancreas consists of terminal (secretory) sections and excretory ducts. The secretory sections are represented by acini - rounded sacs, the wall of which is formed by 8-12 pycreatospamns or acinocytes. Pancretocytes are cone-shaped cells. the basal part of the cells stains basophilically and is called the homogeneous zone - there are granular EPS and mitochondria (RNA in the ribosomes of this organoid is stained with basic dyes and provides basophilia; Above the nucleus there is a lamellar complex, and in the apical part there are oxyphilic secretory granules - the zymogenic zone. In secretory granules are inactive forms of digestive enzymes - trypsin, lipase and amylase.
The excretory ducts begin with intercalary ducts lined with squamous or low-cube epithelium. The intercalary ducts continue into the intralobular ducts with cuboidal epithelium, and then the interlobular ducts and the common excretory duct, lined with prismatic epithelium.
The endocrine part of the pancreas is represented by the islets of Langerhans (or pancreatic islets). Islets are composed of 5 types of enculocytes:
1. B - cells (basophilic cells or b - cells) - make up to 75% of all cells, lie in the central part of the island, stain basophilically, produce the hormone insulin - increases the permeability of the cytolemma of cells (especially liver hepatocytes, muscle fibers in skeletal muscles) for glucose - the concentration of glucose in the blood at the same time decreases, glucose enters the cells and is deposited there in reserve in the form of glycogen. With hypofunction of b-cells develops diabetes- glucose cannot penetrate into the cells, so its concentration in the blood rises and glucose is excreted from the body through the kidneys with urine (up to 10 liters per day).
2. L-cells (a-cells or acidophilic cells) - make up 20-25% of the cells of the islets, are located on the periphery of the islets, contain acidophilic granules with the hormone glucagon in the cytoplasm - an insulin antagonist - mobilizes glycogen from cells - B blood increases the glucose content,
3. D-cells (b-cells or dendritic cells) - 5-10% of cells, located along the edge of the islets, have processes. D-cells produce the hormone somatostatin - it inhibits the release of insulin and glucagon by A- and B-cells, delays the release of pancreatic juice by the exocrine part.
4th D1 cells (argerophilic cells) - small cells, stained with silver salts,
produce VIP - vasoactive polypeptide - reduces arterial pressure, increases the function of the exocrine and endocrine parts of the organ.
5. PP - cells (pancreatic ploypeptide) - 2-5% of cells, located along the edge of the islets, have very small granules with pancreatic polypeptide - enhances the secretion of gastric juice and hormones of the islets of Langerhans.

Regeneration - pancreatic cells do not divide, regeneration occurs through intracellular regeneration - cells constantly renew their worn-out organelles.

DIGESTIVE SYSTEM.

Morpho-functional characteristics of the alimentary canal. Oral cavity: sources of development, the structure of the mucous membrane. The structure of the lips, gums, tongue.

MORPHOFUNCTIONAL CHARACTERISTICS: 3 DIVISIONS

Develops: - from ectoderm- stratified squamous epithelium of the mouth, salivary glands and caudal rectum.

-from endoderm- single-layer prismatic epithelium of the gastric mucosa, small and large intestine, parenchyma of the liver and pancreas

- from mesenchyme- tissues and blood vessels

- visceral leaf of splanchnotome– mesothelium

- visceral peritoneum- serous membrane.

ORAL CAVITY

STRUCTURE:

1. MUCOUS

· Epithelium– multilayer flat

· own record

LIPS: 3 sections: dermal, intermediate and mucous. Mucous - stratified squamous non-keratinized epithelium (some keratin). The lamina propria forms small papillae. There is no muscular plate .. In the submucosa there are salivary labial glands (complex alveolar-tubular and mixed - muco-protein).

BEEKS: Maxillary and mandibular zones (as in the mucosa of the lips). The epithelium is stratified squamous, non-keratinizing, the papillae of the lamina propria are small. The submucosa is well expressed. In the middle zone, the papillae are large. Salivary glands are absent.

GUMS: the mucous membrane is tightly adherent to the periosteum (stratified squamous epithelium, sometimes keratinized). Own plate - long papillae, accumulations of tissue basophils. Muscular plate - no.

LANGUAGE: participates in taste perception, mechanical processing of food and the act of swallowing, the organ of speech.

1. MUCOUS OF THE LOWER SURFACE: the epithelium is stratified squamous, non-keratinizing, the lamina propria forms short papillae. The submucosa is attached to the muscles.

MUCOUS OF THE UPPER AND SIDE SURFACES: immovably fused with muscles, has papillae: filiform, mushroom-shaped, grooved (there is a taste bud under them) and leaf-shaped. The surface of the papillae is formed by a stratified squamous non-keratinized or partially keratinized (filamentous) epithelium lying on the basement membrane. The basis of each papilla is an outgrowth - the primary papilla of its own connective tissue layer of the mucosa. From the top of the primary departs 5-20 secondary papillae, protruding into the epithelium. The connective tissue base of the papillae contains blood capillaries.

ROOT MUCOSA: papillae are absent, there are elevations and depressions (crypts). The collection of lymphoid formations of the root of the tongue is called the lingual tonsil.

1. MUSCLE LAYER: muscle fibers in 3 directions: vertical, longitudinal and transverse. Here are the terminal sections of the salivary glands.

Morpho-functional characteristics of the oral cavity. Sources of development. Large salivary glands, their structure and function. Teeth: structure and development.

MORPHOFUNCTIONAL CHARACTERISTICS: 3 DIVISIONS

1. anterior (oral cavity, pharynx, esophagus) - mechanical processing of food.
2. medium (stomach, thick and small intestine, liver, pancreas) - chemical processing of food.
3. posterior (caudal part of the rectum) - evacuation of undigested residues.

ORAL CAVITY

STRUCTURE:

1. MUCOUS

· Epithelium– multilayer flat

· own record- Loose fibrous connective tissue with blood and lymphatic vessels.

Muscular plate - absent or poorly developed

1. SUBMUCOUS BASIS - absent in some places.
2. MUSCLE COAT - 2 layers: inner - circular, outer - longitudinal.

SALIVARY GLANDS.

STRUCTURE: covered with a connective tissue capsule. From which the partitions depart, dividing the gland into lobules. The glands consist of terminal secretory sections and excretory ducts. excretory ducts distinguish:

1. INTRALOBAL

Intercalary: start from the terminal sections, lined with a flat or cubic epithelium. To-ki are painted basophilically, outside are surrounded by myoepithelial to-mi.

· Striated: lined with cylindrical epithelium stained oxyphilly. There are microvilli on the apical surface, and basal striation on the basal surface.

1. INTERLOBULAR: lined with a 2-layer epithelium. As the ducts enlarge, the epithelium becomes multilayered.
2. DUCTS OF THE GLAND: lined with stratified cuboidal, then stratified squamous non-keratinized epithelium.

Terminal secretory divisions:

1. PROTEIN: consist of cells - serocytes (have a conical shape), surrounded by myoepitheliocytes.

2. MUCOSUS: consist of cells of mucocytes (these are large cells with light cytoplasm and a flattened nucleus), surrounded by myoepitheliocytes.

3. MIXED: the central part is formed by mucous membranes, on the periphery - protein crescents, which are formed by serocytes.

The parotid gland contains only protein end sections, the submandibular gland contains protein and mixed ones, the sublingual gland contains all types of end sections. Intercalary terminal ducts are not detected, as they are subjected to mucus.

STRUCTURE:

• ENAMEL - 97% inorg in-va (phosphate, calcium carbonate). Morphologically, the enamel consists of enamel prisms, which are arranged in bundles perpendicular to the dentin, and have a tortuous course. Each prism consists of a fibrillar network containing hydroxyapatite crystals. Outside, the enamel is covered with a cuticle, which is visible only on the lateral surfaces.
• DENTIN - 28% organic matter (collagen) and 72% calcium phosphate. Consists of the main substance penetrated by tubules. They provide dentin trophism. The collagen fibers of the ground substance have a radial direction in the mantle (outer) dentin, and a tangential direction in the pulp. The border of dentin with enamel has a scalloped appearance, which contributes to their strong connection.
• CEMENT - covers the neck and root of the tooth. It is similar in composition to bone tissue. Distinguish: cell-free cement(consists of collagen fibers and gluing in-va), cell cement(cementocytes + randomly arranged collagen fibers). Cellular cement is compared with coarse fibrous bone tissue. The supply of cement is carried out diffusely, due to the periodontium.
• The pulp is made up of loose connective tissue. Distinguish: peripheral layer(from dentinoblasts), intermediate(formed by poorly differentiated cells - precursors of dentinoblasts), central(fibroblasts, macrophages and collagen fibers)

Digestive canal. The general plan of the wall structure, histofunctional characteristics of the shells of different departments. Physiological regeneration. Esophagus: its structure and functions.

1. mucous membrane

· epithelium The glands are located: endoepithelial exoepithelial- liver, pancreas

· own record

· Muscular plate:

RELIEF: smooth(lips, cheeks ), with grooves folds(all departments) villi(small intestine).

1. muscle membrane, outer - longitudinal.

REGENERATION: regenerates the liver, epithelium, part of the tooth, salivary glands intracellularly and by rare divisions of ductal cells

ESOPHAGUS:

STRUCTURE:

• MUCOUS - epithelium multilayered, flat, non-keratinized. own record mucous- Loose fibrous connective tissue. At level 5 of the tracheal ring and at the entrance to the stomach are the cardiac glands (simple, tubular, branched). The terminal sections contain parietal cells (produce chlorides) and endocrine: EC (serortonin), ECL (histamine), X (unknown). In places of localization of these glands, ulcers, tumors and cysts are often found. ligamentous plate- longitudinally arranged bundles of smooth myocytes.
• SUBMUCOUS: Loose fibrous connective tissue. Here are the own glands of the esophagus (complex branched alveolar-tubular). The terminal sections are mainly composed of mucous cells. The excretory ducts are ampulla-shaped and open on the surface of the epithelium. Due to the mucous and submucosal membranes, longitudinal folds of the esophagus are formed.
• MUSCULAR: internal - circular, external - longitudinal. In the upper third it is striated, in the middle third it is striated and smooth, in the lower third it is smooth. Thickening of the inner layer form sphincters.
• ADVENTIAL - loose fibrous connective tissue that covers most of the esophagus, the abdomen is covered with a serosa.

Digestive canal. General plan of the wall structure, innervation and vascularization. Morpho-functional characteristics of the endocrine and lymphoid apparatus. Physiological regeneration.

GENERAL PLAN OF THE STRUCTURE OF THE DIGESTIVE TUBE:

1. mucous membrane

· epithelium: in the anterior and posterior sections - multi-layer flat, on the average - single-layer prismatic. The glands are located: endoepithelial(goblet cells in the intestines), exoepithelial(lamina propria - esophagus, stomach; submucosa - esophagus, duodenum); outside the alimentary canal- liver, pancreas

· own record: separated by a basement membrane, it is a loose fibrous connective tissue. There are blood and lymphatic vessels, nerve elements, lymphoid tissue.

· Muscular plate: 1-3 layers of smooth muscle cells. In some departments (tongue, gums), nasty muscle cells are absent.

RELIEF: smooth(lips, cheeks ), with grooves(dimples in the stomach, crypts in the intestines), folds(all departments) villi(small intestine).

1. submucosa: loose fibrous connective tissue. Provides mobility of the mucous membrane, forming folds. There are plexuses of blood and lymphatic vessels, accumulations of lymphoid tissue, submucosal nerve plexuses.
2. muscular coat : 2 layers: inner - circular, outer - longitudinal. In the anterior and posterior sections of the digestive tube - striated muscles, on average - smooth. Function - movement and promotion of food.

LYMPHOID DEVICE:

Lymphatic capillaries form networks under the epithelium, around the glands and in the muscular membrane, lymphatic vessels form plexuses of the submucosa and muscularis, and sometimes the outer membrane (esophagus). The largest plexuses of vessels are located in the submucosa.

ENDOCRINE APPARATUS:

In the epithelium of the mucous membrane and glands of the PS, but especially in its middle section, there are single endocrine cells. The biologically active substances they secrete - neurotransmitters and hormones - have both a local effect (regulating the functions of the glands and vascular smooth muscles), and a general effect on the body.

• EU – serotonin melatonin
• ECL – histamine(increases the synthesis of chlorides)
• G – gastrin
• P – bombesine
• D – somatostatin
• D1 – VIP(vaso-intestinal polypeptide) (dilates blood vessels, stimulates the pancreas)
• A – glucagon(increases blood glucose levels)
• X- function unknown
• S- in the small intestine, hormone secretin
• K- in the small intestine gastroinhibitory polypeptide
• L- small intestine - glycentine
• I- small intestine - cholecystokin
• M0 - small intestine - motilin

Stomach. General morpho-functional characteristics. Features of the structure of various departments. Histophysiology of the glands. Innervation and vascularization. Physiological regeneration. Age features.

FUNCTIONS: serketory, mechanical, production of anti-anemic factor (Castle), suction, excretory, endocrine.

STRUCTURE:

• MUCOUS - epithelium- single-layered, prismatic, glandular. All cells secrete a mucus-like secret that performs a protective function. lamina propria mucosa- loose connective tissue, the glands of the stomach are located here, lymphoid formations are found. Muscular plate - three layers: inner and outer - circular, middle - longitudinal.
• SUBMUCOUS - loose connective tissue, vessels and nerve plexuses of Meissner.
• MUSCLE - three layers, outer, longitudinal, middle circular - continuation of the layers of the esophagus. The inner layer is an oblique arrangement of muscle cells. Intermuscular nerve plexuses of Auerbach.
• SEROUS - loose connective tissue covered with mesothelium.

RELIEF OF THE STOMACH: gastric folds gastric fields - limited to the superficial veins of the stomach, correspond to groups of glands, stomach pits - deepening of the epithelium in the lamina propria of the mucosa. In the cardial section and the body of the stomach, they occupy ½ of the thickness of the mucosa, in the pyloric they are deeper.

GLANDS OF THE STOMACH -

own glands: located in the area of ​​the body and bottom, simple tubular, unbranched, open at the bottom of the dimples. In the gland, the isthmus and neck are distinguished - correspond to the excretory duct, body and bottom - corresponds to the secretory part.

Five types of glandular cells:

• The main exocrinocytes secrete pepsinogen, which is converted to pepsin in the presence of HCl.
• PARIETAL (cooking) EXOCRINOCYTES - located outside of the main and mucous cells. Large cells with oxyphilic cytoplasm, intracellular tubules, passing into intercellular. Synthesize chloride.
• MUCOUS - nuclei in the basal part, secretion granules in the apical part.
• CERVICAL MUCOUS CELLS - in the region of the neck of the gland. Source of regeneration of the secretory epithelium of the glands and the epithelium of the gastric pits.
• ENDOCRINE
  • EU – serotonin(stimulates the secretion of mucus, enzymes, enhances gastric motility), melatonin(regulates the photoperiodicity of the process)
  • ECL – histamine(increases the synthesis of chlorides)
  • G – gastrin(stimulates secretion of pepsinogen, HCl and gastric motility)
  • P – bombesine(increases the production of chlorides, stimulates the pancreas, increases the contraction of the gallbladder)
  • D – somatostatin(inhibits protein synthesis in the cell). They are located in the pyloric glands.
  • D1
  • A
  • X- function unknown

Pyloric glands - located in the pyloric part of the stomach, branched, have wide terminal sections, practically devoid of parietal cells, terminal sections mainly consist of mucous cells.

cardiac glands - simple tubular, branched end sections, contain mucous cells, rarely - main and parietal.

FEATURES OF THE STRUCTURE OF DIFFERENT PARTS OF THE STOMACH:

G- mainly in the pyloric and cardiac glands

DandD1 - more common in pyloric

ECL- body and bottom of own glands

Small intestine. General morpho-functional characteristics. Sources of development. Histophysiology of the crypt-villus system. Features of the structure of various departments. Innervation and vascularization. Age features.

STRUCTURE:

RELIEF: circular folds- Made up of mucosa and submucosa intestinal villus - mucosal protrusion, crypts- depressions in the mucous membrane

SHELLS:

• MUCOUS - epithelium single-layer cylindrical border.

ü LIMBED CYLINDRICAL ENTEROCYTES - on the apical surface of the microvilli, which form a striated border - active absorption and breakdown of substances (parietal digestion), a variety - M cells– on the apical surface, in addition to microvilli, there are microoutgrowths. Located in the epithelium above the lymphatic follicles, capable of capturing the antigen, stimulate the immune response.

ü Goblet-shaped - the amount increases in the direction from the duodenum 12. In the phase of secretion accumulation, the nucleus is flattened, there are drops of mucus above it. After secretion, the cell becomes narrow.

ü ENDOCRINE

§ S- in the small intestine, hormone secretin(secretion of bicarbonates and water in the pancreas and biliary tract)

§ K- in the small intestine gastroinhibitory polypeptide(GIP) - inhibition of the secretion of hydrochloric acid in the stomach

§ L- small intestine - glycentine(glucagon-like substance - hepatic glycogenolysis)

§ I- small intestine - cholecystokin(secretion of pancreatic enzymes, contraction of the gallbladder)

§ M0 - small intestine - motilin(increased intestinal motility)

§ EU – serotonin(stimulates the secretion of mucus, enzymes, enhances gastric motility), melatonin(regulates the photoperiodicity of the process)

§ A – glucagon (increases blood glucose levels)

§ G – gastrin(stimulates secretion of pepsinogen, HCl and gastric motility)

§ D – somatostatin(inhibits protein synthesis in the cell). They are located in the pyloric glands.

§ D1 – VIP (vaso-intestinal polypeptide) (expands blood vessels, stimulates the pancreas)

ü UNDIFFERENTIATED (poorly differentiated) - a source of regeneration of the epithelium

ü CELLS WITH ACIDOPHILIAN GRAIN - Pannet's cells - are located at the bottom of the crypts, in the apical part there are acidophilic granules. Either dipeptidases are isolated (they break down polypeptides into amino acids), or a substance that neutralizes HCl.

The crypt epithelium contains all 5 cell types. On the villus, only limbic, goblet and endocrine. The epithelium of the crypts and villi is a single system. All cells are descendants of one SC.

PROPER PLATE OF THE MUCOUS - represented by loose connective tissue, there are lymphatic follicles

MUCOUS MUSCULAR PLATE - two layers: inner circular, outer - longitudinal

• SUBMUCOUS - loose connective tissue,
• MUSCLE - internal circular, external longitudinal
• SEROUS - covers the small intestine from all sides, with the exception of the duodenum 12.

FEATURES OF THE STRUCTURE OF DIFFERENT DEPARTMENTS:

• DUODENAL - the villi are wide and low, in the submucosa - duodenal glands (complex, tubular, branched), in the terminal sections, mucous cells predominate, there are Pannet cells, endocrine, rarely parietal. These glands are involved in the formation of intestinal juice. It contains dipeptidases, amylase, mucoids that neutralize HCl.
• SKINNY - the villi are long, with a large number of goblet cells, in the mucosal lamina propria - a large number of solitary (single) follicles.
• ILIAC - the villi are short and sparsely located. In the lamina propria of the mucosa there are aggregates of lymphoid follicles.

Colon. Appendix. Rectum. General morpho-functional characteristics. Structure. Age features. Physiological regeneration.

STRUCTURE: has the same shells as the thin one.

Peculiarities:

• There are no villi, crypts are well developed.
• The cellular composition of the epithelium, as in the small intestine, more goblet cells, few Pannet cells, the border cells have a less thin striated border.
• The lamina propria contains a large number of lymph nodes.
• The muscular coat has 2 layers, but the outer layer goes in 3 ribbons, swellings are formed.

APPENDIX:

The epithelium of the crypts contains a small amount of goblet cells, ECL cells and Pannett cells are more common than in other departments. The lamina propria passes into the submucosa. The muscular plate is practically absent. In the connective tissue of the lamina propria and submucosa there are a large number of lymphatic follicles → because of this, the appendix is ​​called the intestinal tonsil. Muscular and serous membranes - without features.

RECTUM: consists of the same membranes as other departments. In the pelvic part, due to the submucosa and the inner layer of the muscular membrane, 3 transverse folds are formed. In the anal part, 3 zones are distinguished: columnar, intermediate and skin. In the upper sections there are crypts, in the lower sections they disappear. The mucosal epithelium in the upper section is single-layer prismatic; in the columnar zone - multilayer cubic; in the intermediate - multilayer flat non-keratinizing; in the skin - multilayered flat keratinizing.

In the lamina propria, there are single lymphatic nodules. In the region of the columnar zone there is a network of thin-walled blood lacunae, from which blood flows into the hemorrhoidal veins.

The muscularis mucosa contains 2 layers. The submucosa contains plexuses of hemorrhoidal veins. The columnar zone contains vestigial anal glands. In pathology, they can serve as a site for the formation of fistulas. The muscular membrane contains 2 layers: the inner circular forms sphincters.

Pancreas. General morpho-functional characteristics. The structure of the exo- and endocrine parts, their histophysiology. Physiological regeneration. Age changes. The concept of gastroenteropancreatic (GEP) endocrine system.

Pancreas- mixed secretion, the exocrine part produces pancreatic juice containing trypsin, amylase and lipase. The endocrine part produces insulin, glucagon, self-tostatin and pancreatic polypeptide.

Structure: covered with a peritoneum and a connective tissue capsule, from which septa extend, dividing the gland into lobules. The lobule consists of exo- and endocrine parts.

EXOCRINE PART - structural and functional unit is pancreatic acinus - consists of a secretory section and an intercalary duct. The composition of the secretory section includes 8-12 exocrine pancreatocytes (acinocytes) located on the basement membrane. Acinocytes are cells of a conical shape, on the basal surface - folds, on the apical surface - microvilli. The apical part contains granules with a secret - zymogenic zone(oxyphilic). The basal part contains granular ER, CG - homogeneous zone(basophilic). The secret released from the acinocytes enters the intercalary duct. Small cells of the intercalary duct may adjoin acinocytes laterally and have a common basement membrane with them. In addition, they can be located on the apical part of the acinocyte, with such localization they are called - centroacinous cells. After the intercalary duct, the secret enters interacinous ducts which are lined by single layered cuboidal epithelium → into larger intralobular ducts (cubic epithelium) → interlobular ducts (single columnar epithelium, goblet cells, endogrine cells) → common pancreatic duct (columnar epithelium)

ENDOCRINE PART - represented by the islets of Langerhans. The islets are composed of insulocytes. The cells are well developed CG, mitochondria, many secretory granules.

There are five types of insulocytes:

• B - 70-75%, contain basophilic granules, which contain insulin.
• A - 20-25%, on the periphery of the islet, glucagon - hyperglycemic effect
• D - somatostatin - inhibits the work of A and B cells, acinocytes
• D1 - VIP, dilates blood vessels, reduces pressure, stimulates the secretion of pancreatic juice.
• PP - pancreatic polypeptide, stimulates the secretion of gastric and pancreatic juice.

GEO system: diffuse endocrine system digestive organs - single hormone-producing cells.

Liver. General morpho-functional characteristics. Features of the blood supply. The structure of the classical hepatic lobule. Representation of the portal lobule and acinus. Structural and functional characteristics of hepatocytes, lipocytes, cells of sinusoidal hemocapillaries. physiological regeneration. Gallbladder, structure and functions.

LIVER - the largest gland, participates in the neutralization of harmful metabolic products, in the inactivation of hormones, protective function (Kupffer cells protect against microorganisms), glycogen depot, synthesis of blood plasma proteins, bile formation, participation in cholesterol metabolism, metabolism of vitamins (A, D, E, TO).

STRUCTURE: from the surface of the connective tissue capsule. The parenchyma is formed by hepatic lobules.

CLASSIC HEPATIC LOBE: shaped like hexagonal prisms with a flat base and convex apex. Between the lobules are layers of connective tissue, which forms the stroma of the organ. Connective tissue contains blood vessels and bile ducts. It consists of hepatic beams, in the center is an intralobular sinusoidal capillary. Beams - formed by two rows of hepatocytes. The flow of bile is directed to the periphery, where it enters the hollangioles - narrow tubes that flow into the interlobular bile ducts.

Hepatocyte - has an irregular polygonal shape - one or two nuclei, large, often polyploid cells, all organelles are well developed, glycogen, lipids and pigments predominate from inclusions. Work: cells take oxygen, glucose and other nutrients from the blood, and release urea, proteins and lipids into the flowing blood. Between hepatocytes in the same row there are tight contacts that do not allow bile and blood to connect. Hepatocytes have two surfaces - vascular(facing the sinusoidal capillary) and biliary(directed towards the bile duct). The wall of the bile duct is formed by the biliary surface of the hepatocyte.

Sinusoidal hemocapillaries- lined with flat endotheliocytes with pores that form reticular zones. Kupffer cells- monocyte-macrophage system. pit cells- cells of the type of lymphocytes, stimulate the division of liver cells, killers. The basement membrane is absent for a large extent. The capillaries are surrounded by a sinusoidal space (Disse space). Here are microvilli of hepatocytes, argyrophilic fibers and lipocytes- fat cells.

BLOOD SUPPLY:

INFLOW SYSTEM: The portal vein and hepatic artery in the liver branch into lobar → segmental → interlobular → perilobular arteries. Next to the vessels are the bile ducts of the same name. As a result of this, liver triad: artery, vein and bile duct.

CIRCULATION SYSTEM: from the perilobular arteries and veins, intralobular blood capillaries begin, in their structure they are sinusoidal capillaries. They have mixed blood. The direction of blood flow from the periphery of the lobule to the center.

OUTFLOW SYSTEM: central vein (muscleless type)→collective or sublobular veins (large, single)→hepatic veins (3-4)→inferior vena cava

HEPATIC ACINUUS - wide plates anastomosing with each other, between them lie blood lacunae.

PORTAL HEPATIC LOBE - includes 3 segments of adjacent hepatic lobes, in the center - a triad, and along the tops - the central veins

GALL BLADDER: 40-70 ml, mucosa (single-layer, high prismatic, bordered epithelium), muscular coat - smooth bundles of circularly lying fibers), adventitial

REGENERATION: high capacity for physiological regeneration. Occurs by compensatory hypertrophy and reproduction of hepatocytes. Stimulates the regeneration of food rich in carbohydrates and proteins.

HISTOGENESIS OF THE STRUCTURAL COMPONENTS OF THE DIGESTIVE TUBE

Endoderm gives rise to the epithelial lining of the middle part of the digestive tube (single-layer prismatic epithelium of the mucous membranes of the stomach, small intestine and most of the large intestine), as well as the glandular parenchyma of the liver and pancreas.

The ectoderm is the source of the formation of a multilayer, squamous epithelium of the oral cavity, the parenchyma of the salivary glands, and the epithelium of the caudal rectum.

Mesenchyme is the source of development of connective tissues, blood vessels and smooth muscles of the wall of the digestive tube.

Mesodermal origin are: striated skeletal muscles of the anterior and posterior parts of the digestive tube (the source of development is the somite myotomes) and the mesothelium of the serous membranes (the source of development is the visceral leaf of the splanchnotome).

The nervous apparatus of the wall of the digestive tract has neural origin (neural crest).

GENERAL PLAN OF THE STRUCTURE OF THE DIGESTIVE TUBE

The wall of the digestive tube consists of 4 main shells (Fig. 1).

I. Mucous membrane(tunica mucosa);

II. Submucosa(tela submucosa);

III. Muscular membrane(t.muscularis);

I.Y. Serous or adventitial membranes (t.serosa - t.adventitia).

Rice. 1. Scheme of the structure of the digestive tube on the example of the middle section.

I. MUCOUS MEMBRANE.

The name of this shell is due to the fact that its surface is constantly moistened by the secreted glands. slime(mucus is a viscous mixture of glycoproteins such as mucus and us). The mucus layer provides moisture and elasticity of the membrane, plays an important protective role, especially in a single-layer epithelium, is a medium and an adsorbent in the processes of parietal digestion. Throughout the digestive tube, from one end to the other, there are many either individual cells or glands that secrete mucus.

The mucous membrane, as a rule, consists of 3 layers (plates):

1) epithelium.

The type of epithelium varies depending on the function that this section of the digestive tube performs (Table 2):

- stratified squamous epithelium in the anterior and posterior sections (the protective role prevails);

- single layer prismatic epithelium- in the middle section (the main function is secretory or suction).

table 2

III. MUSCLE COVER.

The muscular layer is formed striated skeletal tissue- in the anterior part and in the posterior part digestive tube or smooth muscle tissue - in the middle section. The change of skeletal muscles to smooth occurs in the wall of the esophagus, thus, in the upper third of the human esophagus, the muscular membrane is represented by skeletal muscles, in the middle part - by skeletal and smooth muscle tissue in equal proportions, in the lower third - by smooth muscles. As a rule, muscle bundles form 2 layers:

internal - with a circular arrangement of muscle fibers;

external - with a longitudinal arrangement of muscle fibers.

The muscle layers are separated by connective tissue layers, in which the vessels and intermuscular ( Aerobakhovo) nerve plexus.

The function of the muscular membrane is peristaltic contractions of the muscles, which contribute to the mixing of the food mass and its movement in the distal direction.

I.Y. OUTER SHELL

The outer shell can be serous or adventitious.

The part of the digestive tract that is located inside the abdominal cavity (intraperitoneally) has serosa, consisting of connective tissue base(contains vascular, nervous elements, including serous nerve plexuses, lobules of adipose tissue), covered mesothelium- single-layered squamous epithelium of the visceral peritoneum.

In those departments where the tube is connected to the surrounding tissues (mainly in the anterior and posterior regions), the outer sheath is adventitial: there is only a connective tissue base that merges with the connective tissue of the surrounding structures. Thus, the outer shell of the esophagus above the diaphragm is adventitious, below the diaphragm it is serous.

SUBMUCOUS BASIS

The submucosa provides the mobility of the mucous membrane and attaches it to the underlying muscles or bones that perform a supporting function.

The submucosa is formed by loose connective tissue, more fibrous than the lamina propria of the mucosa, often contains accumulations of fat cells and terminal sections of small salivary glands.

In some parts of the oral cavity - where the mucous membrane is firmly fused with the underlying tissues and lies directly on the muscles (upper and lateral surfaces of the tongue) or on the bones (hard palate, gums) - the submucosa missing.

STRUCTURES OF THE MOUTH

LIP

The lip is a transition zone skin face in the mucous membrane of the digestive tract. The central part of the lip is occupied by the striated muscle tissue of the annular muscle of the mouth.

Three sections are distinguished in the lip (Fig. 4):

• cutaneous(outer)
• intermediate (red border)
• slimy(interior).

Cutaneous the department has a skin structure: it is lined with stratified squamous keratinized epithelium (epidermis), contains hair roots, sweat and sebaceous glands. Muscle fibers are woven into the dermis.

Intermediate section (red border)- in this zone, the epithelium thickens sharply; the stratum corneum is thin, transparent; hair roots and sweat glands disappear; but there are still single sebaceous glands that open with ducts to the surface of the epithelium. High papillae with numerous capillary networks come very close to the epithelium layer - the blood shines through the epithelium layer, causing the red color of this section. An abundance of nerve endings is characteristic, which determines the high sensitivity of this zone. In the intermediate section, two zones are distinguished: the outer one is smooth and the inner one is villous. In newborns, this part of the lip is covered with epithelial outgrowths - villi.

Fig.4. The scheme of the structure of the lip

KO - skin section; PRO - intermediate department; CO - mucous section;

MO - muscular basis; EPD - epidermis; D - dermis; PZh - sweat gland;

SJ - sebaceous gland; B - hair; MPNE - stratified squamous nonkeratinized epithelium; SP, lamina propria; AT - adipose tissue;

SGZh - mixed labial glands. The arrow indicates the boundary between the dermal and intermediate sections of the lip.

Mucous department- large thickness, lined with stratified squamous non-keratinized epithelium c. very large, polygonal cells of the spinous layer. Irregular papillae of the lamina propria have different heights. In the lamina propria of the mucous membrane, it smoothly passes into the submucosa adjacent to the muscles. Connective tissue is characterized by numerous elastic fibers. The submucosal base contains a large number of vessels, adipose tissue and terminal sections of complex alveolar-tubular mucous and proteinaceous-mucous salivary glands, the excretory ducts of which open into the vestibule.

CHEEK

The basis of the cheek is the striated muscle tissue of the buccal muscle.

The cheek consists of 2 sections - skin (external) and mucous (internal).

Outside, the cheek is covered with thin skin with well-developed subcutaneous fatty tissue.

The inner mucous membrane is smooth and elastic, similar in structure to the similar mucous section of the lip. In the mucous section of the cheek, 3 zones:

· upper (maxillary);

· lower (mandibular);

· intermediate- between the upper and lower, along the line of closing of the teeth from the corner of the mouth to the branch of the lower jaw.

In the buccal mucosa there are papillae of various heights and shapes - mostly low, they often bend and branch. The connective tissue of the cheek is characterized by a high content of collagen fibers. Separate thick strands of dense connective tissue are pulled through the submucosa, attaching their own plate to the underlying muscle tissue. Due to this, the mucosa does not form large folds that could constantly bite. In the submucosal base, the terminal sections of the mixed salivary glands lie in groups, often they are immersed in the muscle tissue. In addition, the submucosa contains lobules of adipose tissue.

V intermediate zone the epithelium is partially keratinized, so this part of the cheek has a paler color and is called white line. There are no salivary glands in this zone, but there are sebaceous glands located subepithelially. In newborns, epithelial outgrowths are determined in this zone, similar to those in the inner zone of the intermediate section of the lip.

The tongue has a body, tip and root.

The basis of the tongue is bundles of fibers of striated muscle tissue located in three mutually perpendicular directions; between them are layers of loose connective tissue with vessels and nerves and fatty lobules.

The tongue is covered with a mucous membrane. The relief and structure of the mucous membrane of the lower (ventral) surface of the tongue differs from the structure of the upper (dorsal) and lateral surfaces (Fig. 4).

Fig.5. Diagram of the structure of the tip of the tongue

VP - upper surface; NP - lower surface; MO - muscular basis;

E - epithelium; SP, lamina propria;

PO, submucosa; NS - filiform papillae; HS - fungiform papillae; SG - mixed salivary glands; VPZh - excretory duct of the gland.

The simplest structure has a mucous membrane on bottom surface language. It is covered with stratified squamous non-keratinized epithelium, the lamina propria protrudes into the epithelium with short papillae. The submucosa is adjacent to the muscles. Sublingual administration of drugs leads to their rapid entry into the blood, because in this area there is a dense plexus of blood vessels, and the thin epithelium and lamina propria are highly permeable.

On the top and side surfaces tongue, the mucous membrane is fixedly fused with the muscular body (muscle perimysium), and the submucosa is absent. On the mucous membrane there are special formations - papillae- outgrowths of the connective tissue of the lamina propria, covered with stratified epithelium. From the top of the primary papilla, thinner and shorter secondary papillae extend into the epithelium in the form of scallops. Connective tissue contains numerous capillaries.

There are several types of papillae:

filiform (papillae filiformes)

mushroom-shaped (papillae fungiformes)

foliate (papillae foliatae)

grooved (papillae vallatae)

Filiform papillae(Fig.6) - the most numerous and the smallest, evenly distributed over the surface of the tip and body. They have the appearance of cone-shaped protrusions lying parallel to each other. The papillae are covered with epithelium, the thin stratum corneum of which forms pointed protrusions facing the pharynx. The thickness of the stratum corneum decreases from the top of the papilla to its base. In some animals that feed on roughage, the thickness of the stratum corneum is significant. The connective tissue base of the papillae is characterized by a high content of collagen fibers, blood vessels and nerve fibers. For a number of diseases gastrointestinal tract, with an increase in temperature, the rejection ("desquamation") of the horny scales slows down, which gives a picture of a "white coating" on the back of the tongue. Between the papillae, the mucosa is lined with a more flexible non-keratinized epithelium.

fungiform papillae(Fig. 7) few, scattered among the filiform papillae, mainly on the tip of the tongue and along its sides. Larger in size. The shape of the papillae is characteristic - a narrow base - "leg" and a flat, expanded "hat". There are a lot of vessels in the connective tissue base - the blood in them shines through the thin epithelium, giving the papillae a red color. Taste buds can be located in the epithelium of fungiform papillae.

Grooved or walled papillae(Fig. 8) are located between the body and the root of the tongue, along their V-shaped groove border in the number 6-12. They are large (diameter 1-3 mm). The papillae do not protrude above the surface, since they are surrounded by a deep groove that separates the papilla from the thickening of the mucous membrane - the roller. Numerous taste buds are present in both the epithelium of the papilla and the ridge. In the connective tissue, they have bundles of smooth myocytes, which makes it possible for the roller and papilla to come together for contact of nutrients. The ducts of the serous salivary glands (Ebner) flow into the groove, the secret of which washes the groove.

Foliate papillae(Fig. 9) in humans are well developed only in early childhood; in adults they are atrophied. They are located in the amount of 3-8 on each of the lateral surfaces of the tongue on the border of the root and body. They are formed by parallel folds of the mucous membrane of a leaf-shaped form, separated by slits into which the excretory ducts of the serous salivary glands open. On the lateral surface, the epithelium contains taste buds.

There are no papillae in the mucous membrane of the root of the tongue. The mucous membrane of the root of the tongue has an uneven relief due to the lymph nodes of the lingual tonsil and crypts.

SOFT PALATE (Palatum molle)

The soft palate is a mucosal fold with a muscular fibrous base that separates the oral cavity from the pharynx. It differs in a more red color, due to the fact that there are many blood vessels in the lamina propria of the mucosa, which shine through a relatively thin layer of non-keratinized epithelium.

There are two surfaces in the soft palate:

anterior (oral, oropharyngeal)) surface

back (nasal, nasopharyngeal) surface .

The free edge of the soft palate is called the tongue (uvula palatine).

Anterior oropharyngeal the surface, like the uvula, is lined with a thin stratified squamous non-keratinizing epithelium. The lamina propria forms numerous high and narrow papillae, below there is a dense layer of intertwining elastic fibers, which is associated with the mobility of this section of the palate. The very thin submucosa includes the terminal sections of the minor salivary glands, lobules of adipose tissue, and is fused with muscles.

Posterior nasopharyngeal surface covered with a single-layer multi-row prismatic ciliated epithelium. In the lamina propria, rich in elastic fibers, the terminal sections of the glands are located, and single lymphatic nodules are often found. The mucous membrane is separated from the muscle tissue by a layer of elastic fibers.

TONGALINS

tonsils – peripheral organs of immunity, which are located on the border of the oral cavity and the esophagus - in the area of ​​​​the entrance gate of infection - and protect the body from the penetration of foreign agents. Tonsils are called lymphoepithelial organs, since they have a close interaction between the epithelium and lymphocytes. Pairs are distinguished palatine- and solitary - pharyngeal and lingual- almonds. In addition, there are accumulations of lymphoid tissue in the area of ​​the auditory tubes (tubal tonsils) and on the anterior wall of the larynx, at the base of the epiglottal cartilage (laryngeal tonsils). All these formations form Pirogov-Waldeyer lymphoepithelial ring surrounding the entrance to the respiratory and digestive tracts.

Functions of the tonsils:

Antigen-dependent differentiation of T- and B-lymphocytes (hematopoietic);

Barrier-protective (phagocytosis and specific immune reactions);

control over the state of food microflora.

The development of the tonsils occurs through the interaction of the epithelium, reticular tissue and lymphocytes. In the places where the palatine tonsils are laid, the epithelium is initially multi-row ciliated, then it becomes multi-layered squamous non-keratinizing. In the reticular tissue lying under the epithelium, which is formed from the mesenchyme, lymphocytes are infused. B-lymphocytes form lymphoid nodules, and T-lymphocytes inhabit the internodular tissue. This is how the T- and B-zones of the tonsils are formed.

palatine tonsils. Each palatine tonsil consists of several folds of mucous membrane. Stratified squamous non-keratinizing epithelium forms 10-20 depressions in the lamina propria called crypts or lacunae. The crypts are deep and branch heavily. The epithelium of the tonsils, especially the lining of the crypts, is abundantly populated ( infiltrated) lymphocytes and granular leukocytes. With inflammation in the crypts, pus can accumulate, containing dead leukocytes, epithelial cells, and microorganisms. In the lamina propria of the mucous membrane there are lymphoid nodules (follicles), which consist of a large reproduction center and a mantle zone (crown) containing B-lymphocytes. The follicles contain macrophages and follicular dendritic cells that perform antigen-presenting functions. The internodular zones are T-zones. Here are postcapillary venules with high endothelium for lymphocyte migration. The supra-nodular connective tissue of the lamina propria contains a large number of diffusely located lymphocytes, plasma cells and macrophages. Outside, the tonsil is covered with a capsule, which, in fact, is a compacted internal

part of the submucosa. The submucosa contains the terminal sections of the mucous membranes of the small salivary glands. Outside of the submucosa lie the muscles of the pharynx.

The remaining tonsils are similar in structure to the palatine ones, differing in some details. Thus, the epithelium of the lingual tonsil forms up to 100 short, slightly branching, shallow crypts. The epithelium in the region of the tubal, laryngeal, and partly pharyngeal (in children) tonsils is multi-row prismatic. In childhood and young age, the pharyngeal tonsil (adenoids) may grow, which leads to difficulty in nasal breathing.

Clearance of the crypt

Lymphoid nodules

SECTIONS OF THE DIGESTIVE TUBE

General characteristics, development, membranes of the digestive tube

Introduction

The digestive system includes digestive tube(GIT, or gastrointestinal tract) and related major glands: salivary, liver and pancreas. A huge number of small digestive glands are part of the wall of the digestive tube.

In the process of digestion, mechanical and chemical processing of food and the subsequent absorption of its breakdown products occur.

The digestive system is conventionally divided into three main sections: anterior, middle and posterior.

Anterior section includes the organs of the oral cavity, pharynx and esophagus. This is where food processing takes place. middle department consists of the stomach, small and large intestines, as well as the liver and pancreas. In this department, mainly the chemical processing of food, the absorption of its breakdown products and the formation of feces are carried out. Back department It is represented by the caudal part of the rectum and provides the function of evacuating undigested food residues from the alimentary canal.

In addition to the actual digestive function, this system also performs excretory, immune, endocrine functions. The excretory function is to release harmful substances through the wall of the digestive tract, which is especially important in case of impaired renal function. The immune function consists in the capture, processing and transport of antigens from food, with the subsequent development of immune reactions. The endocrine function consists in the production of a large number of various hormones with local and systemic effects.

Development

The epithelial lining of the digestive tube and gland develop from the endoderm and ectoderm.

From endoderm a single-layer prismatic epithelium of the mucous membrane of the stomach, small and most of the large intestine, as well as the glandular parenchyma of the liver and pancreas are formed.

From the ectoderm the oral and anal bays of the embryo form a stratified squamous epithelium of the oral cavity, salivary glands and the caudal rectum.

mesenchyme is a source of development of connective tissue and blood vessels, as well as smooth muscles of the digestive organs. From the mesoderm- visceral sheet of splanchnotoma - a single-layer squamous epithelium (mesothelium) of the outer serous membrane (visceral sheet of the peritoneum) develops.

General plan of the structure of the digestive tube

The digestive tube in any of its departments consists of four shells:

internal - mucous membrane ( tunica mucosa),

The submucosa ( tela submucosa),

the muscular layer ( tunica muscularis) and

The outer shell, which is represented by either the serous membrane ( tunica serosa), or adventitial sheath ( tunica adventitia).

It should be noted that the submucosa is often considered as part of the mucosa (and then we are talking about three membranes in the gastrointestinal wall). The serous membrane is sometimes regarded as a type of adventitial membrane.

mucous membrane

It got its name due to the fact that its surface is constantly moistened with mucus secreted by the glands. This shell consists, as a rule, of three plates:

epithelial plate (epithelium),

The lamina propria of the mucosa ( lamina propria mucosae) and

The muscularis mucosa ( lamina muscularis mucosae).

The epithelium in the anterior and posterior sections of the digestive tube is stratified squamous, and in its middle section it is single-layer prismatic.

In relation to the epithelium, the digestive glands are located either endoepithelial(for example, goblet cells in the intestine), or exoepithelial: in the lamina propria (esophagus, stomach) and in the submucosa (esophagus, duodenum) or outside the alimentary canal (liver, pancreas).

The lamina propria lies under the epithelium, separated from it by a basement membrane and represented by loose fibrous connective tissue. Here are blood and lymphatic vessels, nerve elements, accumulations of lymphoid tissue. In some departments (e.g. esophagus, stomach), simple glands can be located here.

The muscular plate of the mucous membrane is located on the border with the submucosa and consists of 1-3 layers formed by smooth muscle cells. In some departments (tongue, gums), smooth muscle cells are absent.

The relief of the mucosa shell throughout the alimentary canal is heterogeneous. Its surface can be smooth (lips, cheeks), form depressions (pits in the stomach, crypts in the intestines), folds (in all departments), villi (in the small intestine). The relief of the mucosa depends on the muscular plate of the mucosa, as well as on the severity of the submucosa.

Submucosa

Consists of loose fibrous connective tissue. The presence of a submucosal base ensures the mobility of the mucous membrane, the formation of folds. In the submucosa there are plexuses of blood and lymphatic vessels, accumulations of lymphoid tissue and Meissner's submucosal nerve plexus ( plexus nervorum submucosus). two parts of the gastrointestinal tract, the esophagus and duodenum- glands are located in the submucosa.

Muscular membrane

It consists, as a rule, of two layers - the outer longitudinal and the inner circular. In the anterior and posterior sections of the alimentary canal, the muscle tissue is predominantly striated, and in the middle (larger) section it is smooth. The muscle layers are separated by connective tissue, which contains blood and lymphatic vessels and Auerbach's intermuscular nerve plexus ( plexus nervorum intermuscularis s. myenteric). Contractions of the muscle membrane help to mix and move food during digestion.

outer shell

Most of the digestive tube is covered serosa- visceral peritoneum. The peritoneum consists of a connective tissue base (i.e., the adventitia proper), in which the vessels and nerve elements are located, and is covered with a single-layer squamous epithelium - mesothelium. Damage to the mesothelium leads to the formation of adhesions - i.e. fusion of the underlying connective tissue of adjacent organs and impaired mobility.

In the esophagus and part of the rectum, the serous membrane is absent. In such places, the digestive tube is covered on the outside adventitia consisting only of loose connective tissue.

Vascularization. The wall of the digestive tube is richly supplied with blood and lymphatic vessels throughout. The arteries form the most powerful plexuses in the submucosa, which are closely related to the arterial plexuses lying in the lamina propria. In the small intestine, arterial plexuses are also formed in the muscular membrane. Networks of blood capillaries are located under the epithelium of the mucous membrane, around the glands, crypts, gastric pits, inside the villi, papillae of the tongue and in muscle layers. Veins also form plexuses of the submucosa and mucosa.

The presence of arteriovenular anastomoses ensures the regulation of blood flow to various parts of the digestive tract, depending on the phase of digestion.

Lymphatic capillaries form networks under the epithelium, around the glands, and in the muscle sheath. Lymphatic vessels form plexuses of the submucosa and muscle membrane, and sometimes the outer membrane (esophagus). The largest plexuses of vessels are located in the submucosa.

innervation. Efferent innervation is provided by the ganglia of the autonomic nervous system located either outside the digestive tube (extramural sympathetic ganglia), or in its thickness (intramural parasympathetic ganglia). The extramural ganglia include the superior cervical, stellate and other nodes of the sympathetic chain that innervate the esophagus, the ganglia of the solar (celiac) and pelvic plexuses innervating the stomach and intestines. Intramural are the ganglia of the intermuscular (Auerbach), submucosal (Meissner) and subserous, or adventitious, plexuses. Axons of efferent neurons of sympathetic and parasympathetic plexuses innervate muscles and glands.

Afferent innervation is carried out by the endings of the dendrites of sensory nerve cells that are part of the intramural ganglia, and by the endings of the dendrites of the sensory cells of the spinal ganglia. Sensitive nerve endings are located in the muscles, epithelium, fibrous connective tissue. Afferent endings in the wall of the alimentary canal can be polyvalent, i.e. simultaneously innervate various tissues - epithelial, muscle, connective, as well as blood vessels.

In the epithelium of the mucous membrane and glands of all parts of the digestive system, but especially in its middle part, there are single endocrine cells - apudocytes. The biologically active substances they release (neurotransmitters and hormones) have both a local effect, regulating the function of the glands and vascular smooth muscles, and a general effect on the body.

In the digestive organs, their totality is sometimes called the gastroenteropancreatic system (GEP system). There are more than 10 types of main cells in this system of the gastrointestinal tract.

Some terms from practical medicine:

· gastroenterology (gastroenterology; gastro - Greek gaster, gasteros or gastros stomach + greek entera intestines, intestines + logos doctrine) - a section of internal diseases that studies the etiology, pathogenesis and clinical forms of predominantly non-infectious diseases of the gastrointestinal tract, developing methods for their diagnosis, treatment and prevention;

· spike(s) [commissura(-ae); synonym: commissure, synechia, mooring] in pathology - a fibrous cord formed between adjacent surfaces of organs as a result of an injury or inflammatory process;

digestive tube

Lecture plan:

1. General characteristics and functions of the digestive system.

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

3. Oral cavity. Structural-functional organization.

4. Pharynx.

5. Esophagus.

6. Stomach.

7. small intestine

8. Colon.

The digestive system combines a number of organs, which together ensure the assimilation by the body from the external environment of substances necessary for the realization of its plastic and energy needs. It includes the digestive tube and the glands located outside it, the secret of which contributes to the digestion of food particles: three pairs of large salivary glands, the liver and the pancreas.

The alimentary canal has anterior, middle, and posterior sections. The anterior section includes the oral cavity, pharynx and esophagus. The secret of large and small salivary glands is excreted into the oral cavity. The main function of the anterior alimentary canal 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 (to its caudal part). The excretory ducts of the liver and pancreas flow into the small intestine (its department, which is called the duodenum). The main functions of the middle part of the digestive tube are the chemical processing (digestion) of food, the absorption of substances and the formation of feces from undigested food residues. The posterior part of the digestive tube is the caudal part of the rectum, which ensures the removal of undigested food particles from the body.

Language ( lingua) - muscles 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 multi-layered flat non-keratinizing epithelium. It has a well-developed lamina propria and a submucosa, the presence of which predetermines 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 permeability of its epithelium for a variety of chemical compounds, drugs (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 that is immobilely fused with the muscular base of the tongue. The epithelium and the lamina propria form here protrusions with a characteristic structure, which are called papillae of the tongue. Distinguish filiform, conical, leaf-shaped, mushroom-shaped and e frontal papillae.

As part of the epithelium of the lateral surfaces of leaf-shaped, mushroom-shaped and gutter O prominent papillae placed taste buds - the so-called tastebulbs, therefore, the role of these types of papillae of the tongue is associated mainly with tasting. The body of the tongue is formed by bundles of striated muscle fibers, which are located in three mutually perpendicular planes. A dense connective tissue median septum divides the muscle of the tongue into right and left halves. Between the muscular base of the tongue and its own plate of the mucous membrane of its back, a dense plexus of collagen and elastic fibers forms the so-called mesh layer, which plays the role of the aponeurosis of the tongue. In the connective tissue of the root of the tongue there is an accumulation of lymphocytes that form the tongue tonsil. Lymphocytes form a cluster of spherical shape.

Between the bundles of striated muscle fibers of the tongue, a large number of small salivary glands are localized, which produce a protein, mucous or protein-mucous secret. Glands that produce a protein secret, located mainly near the foliate and trough papillae. These are complex alveolar branched glands. Glands of the mucous type are located in the root area and on the lateral surfaces of the tongue. These are complex alveolar-tubular branched glands, the secret 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 tongue tonsil. Mixed protein-mucous 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 a partition between the nasal and oral cavities. Distinguish between hard and soft yo bo, the latter in its back passes into the tongue. At the heart of solid n yo ba lie bone plates fused in the midline. From the side of the oral cavity, the hard palate is covered with a mucous membrane covered with a multi-layered flat non-keratinizing epithelium into which high connective tissue papillae of the lamina propria grow. Topographically as part of a solid yo ba distinguish four zones: fatty, glandular, marginal and zone n yo big seam. The zone of adipose tissue covers the anterior part of the solid n yo ba. In this area, under the mucous membrane, fatty tissue is located, which is an analogue of the submucosa of other parts of the oral cavity. The glandular zone occupies the back of the solid yo 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 secret.

The edge zone in the form of an arc covers a solid surface yo more and is the place of transition of its mucous membrane into the gum upper jaw. In the marginal zone, the mucous membrane of the solid yo badensely fused with the periosteum of the base of the alveolar processes. Along the median line of the solid n yo ba pass zone n yo big seam. In this area, as well as in the marginal zone, the mucous membrane is tightly fused with the periosteum of the bone plates. The epithelium in the area of ​​the suture of the hard n yo ba forms characteristic thickenings, especially well developed in childhood: then they look like concentric layers of epitheliocytes and are called epithelial bodies n yo ba. Dense fusion of the mucous membrane with the periosteum in the area of ​​the suture and the marginal zone predetermines its real estate.

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

The palatine tonsils are located between the palatoglossal and palatopharyngeal arches. The structure of the tonsil is based on the folds of the mucous membrane. In the depth of the folds, the ingrowth of the epithelium into the lamina propria of the mucous membrane forms 10-20 slits - crypts. When crypts branch, secondary crypts are formed. Around the crypts are spherical clusters of lymphocytes - lymphatic nodules with light (reactive) centers. The nodules are formed mainly by B-lymphocytes and plasmocytes. The loose connective tissue of the lamina propria merges with the submucosa, where the final secretory sections of the mucous glands of the pharynx are located. The muscular coat is formed by transversely striated muscle tissue and forms two layers - the outer circular and the inner longitudinal. The adventitial membrane is formed by loose fibrous connective tissue.

Pharynx (throat, pharynx) - a cone-shaped canal 12 ... 14 cm long that connects the oral cavity with the esophagus. The pharynx intersects the digestive and respiratory tract. The wall of the pharynx is built 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 region is covered with a single layer of multi-row ciliated epithelium (respiratory type). In the localization of the cardiac glands, diverticula, ulcers and tumors of the esophagus often occur. The muscularis mucosa 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, which houses the final secretory sections of the esophageal glands. By structure, these are complex branched alveolar-tubular glands with a mucous type of secretion. Own glands are concentrated mainly on the ventral surface of the upper third of the esophagus. Layered flat non-keratinizing epithelium of the crypts of the tonsils densely infiltrated numerous lymphocytes and neutrophilic granulocytes, as a result of which it received the name reticular epithelium. In the space of the crypts, one can see exfoliated epitheliocytes, lymphocytes that migrated here from the follicles, as well as foreign particles. Inflammation of the palatine tonsils is called tonsillitis.

Esophagus (esophagus) - a section of the digestive tube about 30 cm long, which 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 noah or serous). Three layers are distinguished in the mucous membrane of the esophagus; epithelium, lamina propria, and lamina propria. The epithelium of the esophagus is stratified squamous non-keratinizing; in old age, keratinization is possible. When passing into the stomach, the stratified squamous epithelium of the esophagus is replaced by a single-layer prismatic epithelium. lamina propria mucosashellsThe esophagus is formed by loose connective tissue, which grows into the epithelium to form papillae.

As part of the lamina propria of the mucous membrane at the level cricoid the cartilage of the larynx and in the area of ​​​​the transition of the esophagus to the stomach lie the final sections of the cardiac glands. These are simple tubular or tubular-alveolar branched glands that produce predominantly 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 a single-layer cylindrical epithelium, which directly passes into a multi-layered one. The muscular membrane 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 transversely striated muscle fibers. The muscular layer of the lower third of the esophagus is formed by smooth muscle tissue. Distinguish between the inner circular and outer longitudinal layers of the muscular membrane of the esophagus, although individual muscle bundles may have an oblique direction. Thickening of the inner layer of the muscular membrane of the esophagus at the level cricoid 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 shell of the esophagus above the diaphragm is formed by loose connective tissue (adventitial shell). Under the diaphragm, the adventitial membrane passes into the serous one: loose connective tissue is covered here with one layer of mesothelial cells.

Stomach ( gaster, ventriculus) - a bag-like extension of the digestive tube with a volume of 1.7 ... 2.5 liters, where 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 built of three layers - epithelium, proper and muscular plates. The mucous membrane of the stomach produces an internal anti-anemic factor necessary for the absorption of vitamin B 12, which enters the stomach with nutrients. The plasmalemma of the apical surface of epitheliocytes forms microvilli. In the apical part of the cell, granules of mucous secretion accumulate, which, when released, covers the surface of the mucous membrane and protects it from the digestive action of gastric juice. Therefore, 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. With differentiation and aging, their movement towards the surface of the mucous membrane is observed, followed by exfoliation into the lumen of the stomach.

The lamina propria of the gastric mucosa is made up of loose connective tissue in which the gastric glands lie. There are three types of glands: own, cardiac and pyloric. Own glands of the stomach - simple tubular unbranched or slightly branched - located in the area of ​​the bottom and body of the stomach. The final secretory section is formed by the bottom and body of its own gland, the excretory duct is formed by the isthmus and neck. The secret of several own glands of the stomach flows into the gastric fossa. Each gland is built from five types of cells: main exocrinocytes, parietal exocrinocytes, cervical and additional mucocytes, and endocrinocytes.

The secretory products of the chief 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 the properties of oxyphilia, they 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, well-defined elements of the Golgi complex. Chymosin breaks down milk proteins, it is produced mainly in childhood.

Parietal exocrinocytes of the gastric glands secrete H-ions, as a result of which an acidic environment is created in the stomach. Parietal cells are located alone in the area of ​​the bottom and body of their 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 cells of a cubic or prismatic shape, in the basal part of which the nuclei are localized, and in the apical part secretory granules of mucus accumulate. Among the cervical mucocytes occur poorly differentiated cells that are the source of physiological regeneration of gastric glandulocytes and cells of gastric pits. Additional mucocytes, scattered alone in the glands, are similar in structure and function to cervical mucocytes.

endocrinocytesare localized 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. Cardiac and pyloric glands are located in the same areas of the stomach. In structure, these are simple tubular highly branched glands. In the pyloric glands, the main and parietal cells are absent, in the cardiac glands they are in small quantities. The composition of the cardiac and pyloric glands also includes a significant number of endocrine cells. In the lamina propria 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 caecum. 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 becomes thinner in diameter up to 3 cm. It has three sections: the duodenum, the hungry and the longitudinal intestine. The duodenum has the shape of a horseshoe, approximately 30 cm long. Concluding the characterization 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 ( Shabadash) and internal ( Meissner). The muscular layer of the stomach is formed by three layers of smooth myocytes: external longitudinal, middle circular and internal oblique.

The wall of the small intestine is formed by four membranes: mucous, submucosal, muscular and serous. The mucous membrane consists of three layers - epithelium, proper and muscular plates. The epithelium of the mucous membrane of the small intestine is a 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.

A 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 villus is covered with a cylindrical epithelium, which contains three types of epithelial cells: columnar epitheliocytes, goblet cells and intestinal endocrinocytes. Columnar epithelial cells of the villi make up the bulk of the epithelial layer of the villus. It's high cylindrical cells measuring 8x25 µm. 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 microvilli are about 1 µm high and 0.1 µm in diameter. Due to the presence of both villi and microvilli, the absorptive surface of the small intestinal mucosa grows hundreds of times. Columnar epitheliocytes have an oval nucleus, a 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 breakdown products 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 basal 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 following resynthesis of neutral fat in the cytoplasm of cells. Goblet cells are single-celled glands that produce mucus. The shape of the cells is characterized by their name: in the expanded apical part they accumulate secretory products, in the narrowed lower part of the cell, similar to the stem of the glass, the nucleus, endoplasmic reticulum, Golgi complex are located. Single goblet cells are scattered on the surface of the villi, surrounded by columnar epithelial cells with a border. The secret of goblet cells moisturizes the surface of the mucous membrane, thereby promoting the movement of food particles to the large intestine.

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 have a local regulatory effect on the secretion, absorption and motility of the intestine. Hormones that are produced by the endocrinocytes of the small intestine enter the hemocapillaries of the connective tissue base of the villi and reach their target cells with blood: columnar epithelial cells with a border, goblet cells, smooth myocytes of the vascular wall of the intestinal mucosa and muscular membranes.

Crypts are tubular ingrowths of the epithelium into the lamina propria of the intestinal mucosa. The entrance to the crypt opens between the bases of neighboring 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 epithelial cells of the crypts, in addition to the cells previously characterized in the composition of the villi (columnar cells with a border, goblet cells and endocrinocytes), there are also columnar cells without a border and exocrinocytes with acidophilic granularity ( Paneth cells). A feature of columnar epitheliocytes with a border in the composition of the crypts is their somewhat lower height compared to similar cellular elements of the villi, as well as pronounced basophilia of the cytoplasm. Goblet cells of 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 granularity 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. In structure, these cells resemble columnar cells with a border, but their apical surface lacks microvilli.

The lamina propria of the mucous membrane of the small intestine is formed by loose connective tissue, in which there are many elastic and reticular fibers, hemo- and lymphocapillaries. Accumulations of lymphocytes here form single and grouped lymphatic follicles, the number of which grows 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 of localization of grouped lymphatic follicles, 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, in the connective tissue of the lamina propria there are eosinophilic granulocytes, plasmocytes. The muscular plate of the mucous membrane is formed by two layers of smooth myocytes - the inner circular and the outer longitudinal.

The submucosa of the wall of the small intestine is formed by loose connective tissue, in which there is a significant amount of blood and lymphatic vessels, nerve plexuses. In the duodenum, in the submucosa, the final secretory sections of the duodenal (Bruner) glands lie. In structure, these are complex branched tubular glands with a mucous-protein secret, which resemble the pyloric glands of the stomach. The final secretory sections of the duodenal glands are built from mucocytes, Paneth cells and endocrinocytes (S-cells). The excretory ducts of the Bruner glands open near the base of the crypts or between adjacent villi. The excretory ducts of the glands are built of cubic or prismatic mucocytes, 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 membrane 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 (intestіnum erassum) - part of the digestive tube, which ensures the formation and excretion of feces. Excretory substances (products of metabolism), 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 large intestine is formed by a single-layer cylindrical epithelium, a connective tissue lamina propria, and a muscular lamina built from smooth muscle tissue. A feature of the relief of the mucous membrane of the colon is the presence of a large number of crypts and the absence of villi. The vast majority of cells of the epithelial layer of the mucous membrane of the colon are goblet cells, much less here are columnar epitheliocytes with a striated border and endocrinocytes. Goblet cells produce a large amount of mucus, which coats the surface of the mucous membrane, and, mixing with undigested food particles, promotes the passage of stool in the caudal direction. Near the base of the crypts are placed undifferentiated cells, as a result of the proliferation of which the physiological regeneration of the epithelium is carried out. Occasionally, Pannet cells may be found in crypts. These cell populations do not differ significantly from similar cellular elements of the small intestine.

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

The muscular plate of the mucous membrane of the large intestine 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 colon has an unequal development: in the worm-like process, for example, it is poorly developed. The submucosa of the large intestine 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 plexus is located in the submucosa.

The muscular membrane of the large intestine is formed by two layers of smooth myocytes: internal circular and 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 bands. The contraction of individual segments of the inner circular layer of smooth muscle membrane myocytes provides the formation of transverse folds of the colon wall. The outer shell of the vast majority of the large intestine 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 muscular membrane take part in the formation of the latter. The mucous membrane of the upper part of the rectum is covered with a single layer of cubic epithelium, which forms numerous deep crypts. The mucous membrane of the anal part of the rectum consists of three distinct zones: columnar, intermediate, and cutaneous. The columnar zone is covered with multilayer cubic, the intermediate zone is covered with multilayer flat non-keratinizing, skin - stratified squamous keratinized epithelium. The lamina propria of the columnar zone forms 10-12 longitudinal folds, contains many blood lacunae, from which blood will flow into the hemorrhoidal veins. Here are located single lymphatic nodules, 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; here are the final sections of the sebaceous glands. Hair follicles, terminal sections of apocrine sweat glands, and sebaceous glands appear in the connective tissue proper plate of the mucous membrane of the skin zone. The muscular plate of the mucous membrane of the rectum is formed by the inner circular and outer longitudinal layers of smooth myocytes.

The submucosa of the rectum is formed by loose connective tissue, which houses the nerve and choroid plexus. Among the latter, one should single out the plexus of hemorrhoidal veins, with a 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 well as in the lamina propria of its mucosa, the terminal sections of the rudimentary anal glands are located. These are six to eight branched tubular epithelial formations that reach the inner circular layer of the muscular membrane from the surface of the mucous membrane. The anal glands, when they become inflamed, can cause the appearance of rectal burrows.

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

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

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 fixed on loose connective tissue, which includes glands, vessels, nerves, and lymphoid formations. The oral cavity, pharynx, esophagus are covered with stratified squamous epithelium. The stomach, intestines have a single-layer cylindrical epithelium. The lamina propria, 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 is composed of smooth muscle tissue. Under the muscular plate is a layer of connective tissue - the submucosal layer, which connects the mucous membrane with the muscular membrane lying outward.

Among the epithelial cells of the mucous membrane are goblet, unicellular glands that secrete mucus. This is a viscous secret that wets the entire surface of the digestive canal, which protects the mucous membrane from harmful effects solid food particles, chemicals and facilitates their movement. In the mucous membrane of the stomach and small intestine there are numerous glands, the secret of which contains enzymes involved in the process of digestion of food. By structure, these glands are divided into tubular (simple tube), alveolar (vesicle) and mixed (alveolar tubular). The walls of the tube and vesicle consist of a glandular epithelium, secrete a secret that flows through the opening of the gland to the surface of the mucous membrane. In addition, the glands are simple and 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. A 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, liver and pancreas. The last two lie outside the alimentary canal, but communicate with it through their ducts.

The muscular coat over most of the alimentary canal is composed 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 upper part of the esophagus, in the thickness of the tongue and soft palate is striated muscle tissue. When the muscle membrane contracts, food moves through the alimentary 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 a single layer of epithelium. The pharynx and esophagus are not covered on the outside by the peritoneum, but by a layer of connective tissue called the adventitia.

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