Small intestine - body systems (histology). Intestine thin and thick Features of the structure and function of the vessels of the microvasculature of the intestinal villi

12 duodenum (Latin duodnum)- this is the original department, which is located after the stomach. In relation to the human skeleton, the intestine is located at the level of 1,2,3 lumbar vertebrae. The average length of the intestine is from 25 to 30 cm, which corresponds to 12 fingers folded transversely - hence the specificity of the name. The duodenum is unique in its structure, both externally and at the cellular level, and plays an important role in the digestive system. The next after the duodenum is.

This is an organ located directly in the abdominal cavity, along its length often clasps the pancreas, namely its head. The duodenum may not be constant in its location and it depends on gender, age, constitution, fatness, position of the body in space, and so on.

Skeletotopically, taking into account the four sections of the intestine, its upper part starts from the 12th thoracic vertebra, makes the first (upper) bend at the level of the 1st lumbar, then goes down and reaches the 3rd vertebra lumbar of the spine, produces a lower (second) bend, follows from right to left in a horizontal position and, finally, reaches the 2nd lumbar vertebra.

Sections of the duodenum

This organ lies retroperitoneally and has no mesentery. The body is conditionally divided into four main departments:

1. Upper horizontal section. The upper horizontal section may border on the liver, namely its right lobe and is located in the region of the first lumbar vertebra.
2. Descending part (department). The descending division borders on right kidney, bends and can reach the second third lumbar vertebra.
3. Lower horizontal section. The lower horizontal section carries out the second bend and begins with it, is located near the abdominal aorta and inferior vena cava, which are located posterior to duodenum.
4. Ascending department. The ascending section ends with the second bend, rises up and smoothly passes into the jejunum.

The organ is supplied with blood celiac trunk and the superior artery of the mesentery, which, in addition to the intestine, also supplies the base of the pancreatic head.

The structure of the wall of the duodenum 12

The wall is represented by the following layers:

• serous - this is a serous membrane covering the intestine from the outside;
• muscular - represented by muscle fibers (located circularly and along the organ), as well as nerve nodes;
• submucosal - represented by lymphatic and blood vessels, as well as a submucosal membrane having a folded shape with crescents;
• mucous - represented by villi (they are wider and shorter than in other parts of the intestine).

Inside the intestine is a large and small nipples. located approximately 7-7.5 cm directly from the pylorus. The main pancreatic duct and common bile duct enter it. Approximately 8-45 mm from the Vater nipple, a small papilla emerges, an additional pancreatic duct enters it.

Functions

• Motor-evacuation. It is the process of pushing food through the alimentary canal. The organ also serves as a reservoir, it releases bile acids and various pancreatic enzymes.
• Digestive. In the intestine, the initial stage of digestion occurs, due to the action of bile acids and pancreatic enzymes.
• Regulatory. Due to the regulation of bile acids and pancreatic enzymes.
• Acid-alkaline. In the duodenum, the pH of the food lump is brought to optimal values ​​for its further transformation in other parts of the digestive tract.

The wall of the duodenum consists of three membranes: serous (tunica serosa), muscular (tunica muscularis), mucous (tunica mucosa) and submucosa (tela submucosa), separated from the mucous membrane by a muscular plate (lamina muscularis mucosae).

The most significant functional load is borne by the mucous membrane.

In the initial part of the intestine for 5-6 cm, it has no folds.

Distally, sparse low, mostly longitudinal folds appear. In other departments - circular folds. Their height increases as they approach the small intestine. In places of fusion of the intestinal wall with the pancreas, the folds are low, one of them, as already reported, lies longitudinally at the large duodenal papilla (plica. longitudinalis duodeni), and near the flexura duodenojejunalis they go in an oblique direction.

The area of ​​the mucous membrane of the duodenum is significantly increased due to the existence of intestinal villi. At 1 mm, there are from 10 to 40 villi with a height of 200-700 microns.

The most important and numerous cells of the villous epithelium are cylindrical absorptive cells known as enterocytes. There are complex connections between the lateral sides of neighboring enterocytes, and their tops are closely related to each other due to a special connecting complex that maintains the structural unity of the mucous membrane.

most important hallmark Enterocyte should recognize the presence of an apical "brush" border, which consists of regularly arranged microvilli, the height of which is up to 1 µm and the diameter is up to 0.1 µm, and is covered with glycocalyx. It is assumed that the glycocalyx, which contains a large amount of carbohydrates produced by enterocytes, performs not only a protective (immunological) function, but also plays an important role in the modification and retention of intraluminal contents by the absorptive cell due to enzymatic activity.

The cells in the crypts are mostly "undifferentiated" precursors of mature absorptive villus cells. As the cells move to the neck of the crypt, they mature. It has been established that approximately three crypts in the normal mucosa supply one villus with cells.

Between the suction cells of the villi and the generative cells of the crypts, being in close contact with them, goblet cells are located. Goblet cells are simple, mucus-secreting structures that cannot divide. Mucus is produced in the endoplasmic reticulum, concentrated in the lamellar complex in the form of droplets, and flows out of the apical part of the cell. Mucin plays an important protective role, and in addition, a change in its secretion can be assessed as a possible marker of the neoplastic process.

The duodenum has specialized glands in the submucosa that connect to the crypts through tributaries. These duodenal glands are thought to be precursors to the gastric-type metaplastic epithelium found in the duodenum in hyperacid conditions.

At the base of the intestinal (Libirkün) crypts, Kulchitsky's cells are found. They have previously been described as argentafine, argyrophilic, or enterochromaffinic cells due to their ability to stain with silver or chromium salts. Currently, they are combined into a large group of specialized neurosecretory (enteroendocrine) cells. The number of subspecies of this group of cells is constantly growing. The ability to secrete hormonally active polypeptides, assimilate and decarboxylate substances - precursors of biogenic amines determined common name these cells - ARID (amine content, precustor uptake, decarboxylation).

One of the best known members of this group are enterochromaffin cells (E-cells) producing 5-hydroxy-tryptamine (serotonin); EG-cells (L-cells) that produce enteroglucagon; C-cells - gastrin; S-cells - secretin.

The lamina propria is the name of the connective tissue of the mucous membrane of the duodenum. The intrinsic layer not only ensures the integrity of the absorptive epithelium with the help of connective tissue fibers and smooth muscle cells, but is an important component of the peripheral or secondary lymphoreticular system. It contains lymphoid and plasma cells, lymphoid accumulations are found. These lymphoid clumps increase in size and number caudally, culminating in the terminal ileum and appendix where they are known as Peyer's patches.

Brunner's duodenal glands are located in the submucosa from the distal pylorus to the major duodenal papilla.

In the upper part of the duodenum, they are also found in the mucous membrane. The terminal sections of the duodenal glands, which have a complex alveolar tubular structure, are formed by large secretory cells containing neutral mucopolysaccharides.

The excretory ducts of the duodenal glands open at the base or on the side walls of the crypts. The epithelium of the ducts is low- or high-prismatic, its cytoplasm contains confluent granules of neutral mucopolysaccharides.

The muscular coat of the duodenum is formed by bundles of smooth muscle cells located in two layers. The outer thinner layer is longitudinal bundles, which are connected to the muscle fibers of the stomach along its lesser curvature, ensuring the continuity of the peristaltic wave along the gastroduodenal junction. The inner layer is made up of circular bundles. Layers and bundles of muscles are separated by layers of loose connective tissue.

The serous membrane consists of fibrous connective tissue and contains a large number of elastic fibers. It is covered with a layer of flat mesothelial cells. Between the serous and muscular membranes there is a subserous layer, represented by loose connective tissue. It is especially well developed in places where the serous cover of the duodenum passes into the ligaments or parietal peritoneum.

Yaitsky N.A., Sedov V.M.

Duodenum(lat. duodenum) - the initial section of the small intestine, following immediately after the pylorus. The continuation of the duodenum is the jejunum.

Anatomy of the duodenum

The figure shows: duodenum (in Fig. English Duodenum), pancreas, as well as bile and pancreatic ducts, through which bile and pancreatic secretion enter the duodenum: the main pancreatic duct (Pancreatic dust), additional (Santorini) pancreatic duct (Accessory pancreatic duct), common bile duct (Common bile-duct), large duodenal (vater) nipple (Orifice of common bile-duct and pancreatic duct).

Functions of the duodenum

Sphincters of the duodenum and the papilla of Vater

Endocrine cells of the duodenum

Short chain fatty acids in the duodenum

• acetic acid - 0.739±0.006 mg
• propionic acid - 0.149±0.003 mg
• butyric acid - 0.112±0.002 mg

duodenum in children

Some diseases and conditions of the duodenum

The material is taken from the site www.hystology.ru

In the small intestine, the chemical processing of food masses, the process of absorption, and the production of biologically active substances continue. With the help of peristaltic contractions of the wall, the contents of the intestine move in the caudal direction.

The intestine develops from the following embryonic rudiments: the inner epithelial lining - from the endoderm, connective tissue and smooth muscle structures - from the mesenchyme, the mesothelium of the serous membrane - from the visceral sheet of non-segmented mesoderm.

As in the stomach, the intestinal wall consists of three membranes: mucous, muscular, serous (Fig. 270). A characteristic feature of its structure is the presence of permanent structures, the function of which is aimed at increasing the suction surface of the epithelial layer of the mucous membrane. These structures are: folds, intestinal villi, crypts, striated border of cells of the epithelial layer. They are formed by the mucous membrane, built from the epithelial layer, the main plate, the muscular plate, the submucosa. All layers of the mucous membrane take part in the formation of intestinal folds. The villi are finger-like outgrowths of the main lamina, covered with an epithelial layer. Crypts are tubular invaginations into the tissue of the main plate of the superficial epithelial layer.

The striated border is built of microvilli, the plasmolemma of the apical pole of epithelial cells.

The cells of the epithelial layer covering the villi develop from the stem cells of the crypts. The main cells of the epithelial layer are enterocytes with a striated border. They are cylindrical in shape with a pronounced polarity: the core

Rice. 270. Small intestine:

1 - mucous membrane; 2 - muscular and 3 - serous membranes; -4 - single-layer epithelium of the villi; 3 - the main plate of the mucous membrane; 6 - villi; 7 - crypts; 8 - muscular plate: 9 - submucosal base; 10 - blood vessels; 11 - submucosal plexus; 12 - an annular layer of the muscular membrane; 13 - longitudinal layer of the muscular membrane; 14 - intermuscular nerve plexus; 15 - mesothelium.

is located in the basal part of the enterocyte, and a striated border lies on the apical pole. The latter consists of numerous protrusions of the cell plasmolemma, clearly visible in an electron microscope (Fig. 271), which increases the suction surface of the mucous membrane by 30 times. Due to the high activity of enzymes located in the striated border, the process of splitting and absorption of substances proceeds here much more intensively than in the intestinal cavity. On the surface of the microvillus is glycocalyx, which is closely associated with the cell membrane. It has the appearance of a thin film and consists of glycoproteins. With the help of the glycocalyx, substances are adsorbed on the surface of enterocytes. In the cytoplasm, under the border lies the cell center, and above the nucleus is the Golgi complex. In the basal part of the cell there are many ribosomes, polysomes, mitochondria.

The apical zones of neighboring enterocytes are interconnected by means of tight contacts and closing plates, thereby closing the intercellular spaces and preventing uncontrolled penetration of substances from the intestinal cavity into them.

In the epithelial layer between the bordered enterocytes are goblet cells. These are unicellular glands that secrete mucus that moisturizes the inner surface of the mucous membrane. After secretion, the goblet cells take on a cylindrical shape. In the process of secretion accumulation, the nucleus and organelles are pushed to the basal pole. developed in the cell

Rice. 271.

BUT- diagram of the structure of a single-layer columnar epithelium:
1 - microvilli of the border; 2 - nucleus; 3 - basement membrane; 4 - connective tissue; B - electron micrograph of the apical pole of the cell.

Golgi complex, smooth endoplasmic reticulum, mitochondria. In the epithelial layer there are endocrine (argyrophilic) cells that produce biologically active substances. All cells of the epithelial layer are located on the basement membrane.

The main plate is built from loose connective tissue, it also contains reticular tissue, lymphocytes, plasma cells, eosinophils. In its central part is a lymphatic vessel. Smooth muscle cells (myocytes) are oriented along it - the contractile component of the villus, blood vessels, and nerves. In the main plate, located below the villi, there are crypts lined with a single-layer cylindrical epithelium. They, like villi, increase the absorption surface of the mucous membrane.

Among the cells of the epithelium, there are bordered and borderless enterocytes, goblet cells, Paneth cells, endocrine cells. The structure of the border enterocytes (columnar cells) and goblet cells is similar to the cells of the villus. Borderless enterocytes are columnar, characterized by high mitotic activity. Due to their division, the physiological replacement of dying cells of the epithelial cover takes place. Panetovskie (apical-granular) cells are located at the bottom of the crypts, they are distinguished by large oxyphilic granularity, as well as the presence of an electron-dense membrane. These cells produce a secret that affects the process of protein breakdown. It is believed that it neutralizes the hydrochloric acid of the chyme.

The muscular plate of the mucous membrane consists of smooth muscle cells that form the inner circular and outer longitudinal layers.

The submucosa is represented by loose, unformed connective tissue. Here are the blood vessels lymphatic vessels, submucosal nerve plexus. In the duodenum in this layer are complex branched tubular duodenal (submucosal) glands.

The cells of the terminal section have a light cytoplasm containing mucous inclusions and a dark nucleus located at the base of the cell. The excretory ducts, built from smaller cubic or cylindrical cells, open into crypts or into the spaces between the villi. In the duodenal glands, there are separate endocrine, parietal, Panetian, goblet cells. The duodenal glands produce secretions involved in the expansion of carbohydrates and the neutralization of hydrochloric acid.

The muscular coat is formed by two layers of smooth muscle cells: inner and outer. The inner layer is more developed and its cells lie circularly in relation to the lumen of the organ. The outer layer consists of longitudinally oriented cells. Between these layers in the loose connective tissue is the muscular nerve plexus. Due to the contraction of the muscular membrane, the food material moves along the intestines.

The serous membrane usually consists of loose connective tissue and mesothelium.

SMALL INTESTINE

Anatomically, the small intestine is divided into the duodenum, jejunum, and ileum. In the small intestine, proteins, fats, carbohydrates undergo chemical processing.

Development. The duodenum is formed from the end of the foregut initial department middle, a loop is formed from these rudiments. The jejunum and ileum are formed from the remainder of the midgut. 5-10 weeks of development: a loop of growing intestine is "pushed" out of the abdominal cavity into the umbilical cord, and the mesentery grows up to the loop. Further, the loop of the intestinal tube "returns" to abdominal cavity, it rotates and grows further. The epithelium of the villi, crypts, duodenal glands are formed from the endoderm of the primary intestine. Initially, the epithelium is single-row cubic, 7-8 weeks - single-layer prismatic.

8-10 weeks - the formation of villi and crypts. 20-24 weeks - the appearance of circular folds.

6-12 weeks - differentiation of epitheliocytes, columnar epitheliocytes appear. The beginning of the fetal period (from 12 weeks) is the formation of a glycocalyx on the surface of epitheliocytes.

Week 5 - differentiation of goblet exocrinocytes, week 6 - endocrinocytes.

7-8 weeks - the formation of the own plate of the mucous membrane and submucosa from the mesenchyme, the appearance of the inner circular layer of the muscular membrane. 8-9 weeks - the appearance of the outer longitudinal layer of the muscular membrane. 24-28 weeks there is a muscular plate of the mucous membrane.

The serous membrane is laid at the 5th week of embryogenesis from the mesenchyme.

The structure of the small intestine

In the small intestine, the mucous membrane, submucosa, muscular and serous membranes are distinguished.

1. Structural and functional unit of the mucous membrane are intestinal villi- protrusions of the mucous membrane, freely protruding into the intestinal lumen and crypts(glands) - deepening of the epithelium in the form of numerous tubules located in the lamina propria of the mucous membrane.

mucous membrane consists of 3 layers - 1) a single-layer prismatic border epithelium, 2) its own layer of the mucous membrane and 3) the muscular layer of the mucous membrane.

1) Several populations of cells are distinguished in the epithelium (5): columnar epitheliocytes, goblet exocrinocytes, exocrinocytes with acidophilic granules (Paneth cells), endocrinocytes, M cells. The source of their development is stem cells located at the bottom of the crypts, from which progenitor cells are formed. The latter, mitotically dividing, then differentiate into a specific type of epithelium. Progenitor cells, being in the crypts, move in the process of differentiation to the top of the villus. Those. the epithelium of crypts and villi represents a single system with cells at various stages of differentiation.

Physiological regeneration is provided by mitotic division of progenitor cells. Reparative regeneration - a defect in the epithelium is also eliminated by cell reproduction, or - in case of gross damage to the mucosa - is replaced by a connective tissue scar.

In the epithelial layer in the intercellular space there are lymphocytes that carry out immune protection.

The crypt-villus system plays an important role in the digestion and absorption of food.

intestinal villus – from the surface it is lined with a single-layer prismatic epithelium with three main types of cells (4 types): columnar, M-cells, goblet, endocrine (their description is in the Crypt section).

Columnar (border) epithelial cells of the villi- on the apical surface, a striated border formed by microvilli, due to which the suction surface increases. There are thin filaments in the microvilli, and on the surface there is a glycocalyx, represented by lipoproteins and glycoproteins. The plasmalemma and glycocalyx contain a high content of enzymes involved in the breakdown and transport of absorbable substances (phosphatases, aminopeptidases, etc.). The processes of splitting and absorption occur most intensively in the region of the striated border, which is called parietal and membrane digestion. The terminal network present in the apical part of the cell contains actin and myosin filaments. There are also connecting complexes of dense insulating contacts and adhesive belts that connect neighboring cells and close the communication between the intestinal lumen and intercellular spaces. Under the terminal network there are tubules and cisterns of the smooth endoplasmic reticulum (fat absorption processes), mitochondria (energy supply for absorption and transport of metabolites).

In the basal part of the epitheliocyte there is a nucleus, a synthetic apparatus (ribosomes, granular ER). Lysosomes and secretory vesicles formed in the area of ​​the Golgi apparatus move to the apical part and are located under the terminal network.

Secretory function of enterocytes: production of metabolites and enzymes necessary for parietal and membrane digestion. The synthesis of products occurs in the granular ER, the formation of secretory granules occurs in the Golgi apparatus.

M cells- cells with microfolds, a type of columnar (marginal) enterocytes. They are located on the surface of Peyer's patches and single lymphatic follicles. On the apical surface of microfolds, with the help of which macromolecules are captured from the intestinal lumen, endocytic vesicles are formed, which are transported to the basal plasmolemma, and then to the intercellular space.

goblet exocrinocytes located singly among columnar cells. By the end of the small intestine, their number increases. Changes in cells proceed cyclically. The secret accumulation phase - the nuclei are pressed to the base, near the nucleus, the Golgi apparatus and mitochondria. Drops of mucus in the cytoplasm above the nucleus. The formation of the secret occurs in the Golgi apparatus. At the stage of accumulation of mucus in the cell, altered mitochondria (large, light with short cristae). After secretion, the goblet cell is narrow; there are no secretion granules in the cytoplasm. The secreted mucus moisturizes the surface of the mucosa, facilitating the movement of food particles.

2) Under the epithelium of the villi is the basement membrane, behind which is loose fibrous connective tissue of the lamina propria. It contains blood and lymph vessels. Blood capillaries are located under the epithelium. They are of the visceral type. Arteriole, venule and lymphatic capillary are located in the center of the villus. In the stroma of the villus there are separate smooth muscle cells, the bundles of which are entwined with a network of reticular fibers that connect them with the stroma of the villus and the basement membrane. The contraction of smooth myocytes provides a "pumping" effect and enhances the absorption of the contents of the intercellular substance into the lumen of the capillaries.

intestinal crypt . Unlike villi, it contains, in addition to columnar epitheliocytes, M-cells, goblet cells, stem cells, progenitor cells, differentiating cells on different stages development, endocrinocytes and Paneth cells.

Paneth cells located singly or in groups at the bottom of the crypts. They secrete a bactericidal substance - lysozyme, an antibiotic of a polypeptide nature - defensin. In the apical part of the cells, strongly refracting light, sharply acidophilic granules when stained. They contain a protein-polysaccharide complex, enzymes, lysozyme. In the basal part, the cytoplasm is basophilic. The cells revealed a large amount of zinc, enzymes - dehydrogenases, dipeptidases, acid phosphatase.

Endocrinocytes. There are more of them than in the villi. EC-cells secrete serotonin, motilin, substance P. A-cells - enteroglucagon, S-cells - secretin, I-cells - cholecystokinin and pancreozymin (stimulate the functions of the pancreas and liver).

lamina propria of the mucous membrane contains a large number of reticular fibers forming a network. They are closely related to process cells of fibroblastic origin. There are lymphocytes, eosinophils, plasma cells.

3) Muscular plate of the mucosa consists of an inner circular (individual cells go into the lamina propria) and an outer longitudinal layer.

2. Submucosa It is formed by loose fibrous irregular connective tissue and contains lobules of adipose tissue. It contains the vascular collectors and the submucosal nerve plexus. .

Accumulation of lymphoid tissue in the small intestine in the form of lymphatic nodules and diffuse accumulations (Peyer's patches). Solitary throughout, and diffuse - more often in the ileum. Provide immune protection.

3. Muscular membrane. Inner circular and outer longitudinal layers of smooth muscle tissue. Between them is a layer of loose fibrous connective tissue, where the vessels and nodes of the nervous musculo-intestinal plexus. Carries out mixing and pushing the chyme along the intestine.

4. Serous membrane. Covers the intestine from all sides, with the exception of the duodenum, covered with peritoneum only in front. It consists of a connective tissue plate (PCT) and a single-layer, squamous epithelium (mesothelium).

Duodenum

The feature of the structure is the presence duodenal glands in the submucosa, these are alveolar-tubular, branched glands. Their ducts open into crypts or at the base of the villi directly into the intestinal cavity. Glandulocytes of the terminal sections are typical mucous cells. The secret is rich in neutral glycoproteins. In glandulocytes, synthesis, accumulation of granules and secretion are simultaneously noted. Secret function: digestive - participation in the spatial and structural organization of hydrolysis and absorption processes and protective - protects the intestinal wall from mechanical and chemical damage. The absence of a secret in the chyme and parietal mucus changes their physicochemical properties, while the sorption capacity for endo- and exohydrolases and their activity decrease. The ducts of the liver and pancreas open into the duodenum.

Vascularization small intestine . Arteries form three plexuses: intermuscular (between the inner and outer layers of the muscular membrane), wide-looped - in the submucosa, narrow-looped - in the mucous membrane. Veins form two plexuses: in the mucosa and submucosa. Lymphatic vessels - in the intestinal villus, a centrally located, blindly ending capillary. From it, the lymph flows into the lymphatic plexus of the mucous membrane, then into the submucosa and into the lymphatic vessels located between the layers of the muscular membrane.

innervation small intestine. Afferent - muscular-intestinal plexus, which is formed by sensitive nerve fibers spinal ganglia and their receptor endings. Efferent - in the thickness of the wall, the parasympathetic musculo-intestinal (most developed in the duodenum) and submucosal (Meisner) nerve plexus.

DIGESTION

Parietal digestion, carried out on the glycocalyx of columnar enterocytes, accounts for about 80-90% of the total digestion (the rest is cavitary digestion). Parietal digestion takes place under aseptic conditions and is highly conjugated.

Proteins and polypeptides on the surface of microvilli of columnar enterocytes are digested to amino acids. Being actively absorbed, they enter the intercellular substance of the lamina propria, from where they diffuse into the blood capillaries. Carbohydrates are digested to monosaccharides. Also actively absorbed and enter the blood capillaries of the visceral type. Fats are broken down into fatty acids and glycerides. They are captured by endocytosis. In enterocytes, they endogenize (change the chemical structure in accordance with the body) and resynthesize. Transport of fats is carried out mainly through the lymphatic capillaries.

Digestion includes further enzymatic processing of substances to final products, their preparation for absorption and the absorption process itself. In the intestinal cavity, extracellular cavitary digestion, near the intestinal wall - parietal, on the apical parts of the plasmolemma of enterocytes and their glycocalyx - membrane, in the cytoplasm of enterocytes - intracellular. Absorption is understood as the passage of the products of the final breakdown of food (monomers) through the epithelium, basement membrane, vascular wall and their entry into the blood and lymph.

COLON

Anatomically, the large intestine is divided into the caecum with appendix, ascending, transverse, descending and sigmoid colon and rectum. In the large intestine, electrolytes and water are absorbed, fiber is digested, and stool. The secretion of large amounts of mucus by the goblet cells promotes the evacuation of stool. Starring intestinal bacteria Vitamins B12 and K are synthesized in the large intestine.

Development. Epithelium colon and the pelvic part of the rectum is a derivative of the endoderm. It grows at 6-7 weeks of fetal development. The muscular layer of the mucous membrane develops at the 4th month of intrauterine development, and the muscularis a little earlier - at the 3rd month.

The structure of the colon wall

Colon. The wall is formed by 4 membranes: 1. mucous, 2. submucosal, 3. muscular and 4. serous. The relief is characterized by the presence of circular folds and intestinal crypts. No villi.

1. Mucous membrane has three layers - 1) epithelium, 2) lamina propria and 3) muscular lamina.

1) Epithelium single layer prismatic. Contains three types of cells: columnar epitheliocytes, goblet, undifferentiated (cambial). Columnar epitheliocytes on the surface of the mucous membrane and in its crypts. Similar to those in the small intestine, but have a thinner striated border. goblet exocrinocytes contained in large quantities in crypts, secrete mucus. At the base of the intestinal crypts are undifferentiated epitheliocytes, due to which the regeneration of columnar epitheliocytes and goblet exocrinocytes occurs.

2) Own plate of the mucous membrane- thin connective tissue layers between the crypts. There are solitary lymphatic nodules.

3) Muscular plate of the mucous membrane better expressed than in the small intestine. The outer layer is longitudinal, muscle cells are located more loosely than in the inner - circular.

2. Submucosal base. Presented by RVST, where there are a lot of fat cells. Vascular and nervous submucosal plexuses are located. Many lymphoid nodules.

3. Muscular membrane. The outer layer is longitudinal, assembled in the form of three ribbons, and between them a small number of bundles of smooth myocytes, and the inner layer is circular. Between them is a loose fibrous connective tissue with vessels and a nervous musculo-intestinal plexus.

4. Serous membrane. Covers different departments differently (completely or on three sides). Forms outgrowths where adipose tissue is located.

Appendix

An outgrowth of the large intestine is considered a rudiment. But it performs a protective function. Characterized by the presence of lymphoid tissue. Has a light. Intensive development of lymphoid tissue and lymphatic nodules is observed at 17-31 weeks of fetal development.

mucous membrane has crypts covered with a single layer of prismatic epithelium with a small amount of goblet cells.

lamina propria mucosa without a sharp border, it passes into the submucosa, where numerous large accumulations of lymphoid tissue are located. AT submucosal located blood vessels and submucosal nerve plexus.

Muscular membrane has outer longitudinal and inner circular layers. The outside of the appendix is ​​covered serous membrane.

Rectum

The shells of the wall are the same: 1. mucous (three layers: 1)2)3)), 2. submucosal, 3. muscular, 4. serous.

1 . mucous membrane. Consists of epithelium, own and muscular plates. one) Epithelium in the upper section it is single-layered, prismatic, in the columnar zone - multi-layered cubic, in the intermediate zone - multi-layered flat non-keratinizing, in the skin - multi-layered flat keratinizing. In the epithelium there are columnar epitheliocytes with a striated border, goblet exocrinocytes and endocrine cells. The epithelium of the upper part of the rectum forms crypts.

2) Own record participates in the formation of folds of the rectum. Here are single lymphatic nodules and vessels. Columnar zone - lies a network of thin-walled blood lacunae, blood from them flows into the hemorrhoidal veins. Intermediate zone - a lot of elastic fibers, lymphocytes, tissue basophils. single sebaceous glands. Skin zone - sebaceous glands, hair. Appear sweat glands of the apocrine type.

3) Muscular plate The mucous membrane consists of two layers.

2. Submucosa. The nerve and vascular plexuses are located. Here is the plexus of hemorrhoidal veins. If the wall tone is disturbed, varicose veins appear in these veins.

3. Muscular membrane consists of outer longitudinal and inner circular layers. The outer layer is continuous, and thickenings of the inner form sphincters. Between the layers there is a layer of loose fibrous unformed connective tissue with vessels and nerves.

4. Serous membrane covers the rectum in the upper part, and in the lower parts of the connective tissue membrane.