Small intestine - body systems (histology). Small and thick intestine Jejunum histology
Duodenum(lat. duodenum) - the initial section of the small intestine, immediately after the pylorus of the stomach. Continuation duodenum is the jejunum.
Anatomy of the duodenum
The duodenum got its name due to the fact that its length is about twelve diameters of the fingers. The duodenum does not have a mesentery and is located retroperitoneally.
The figure shows: duodenum (in the figure, English Duodenum), pancreas, as well as bile and pancreatic ducts, through which bile and pancreatic secretions enter the duodenum: the main duct of the pancreas (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
The duodenum performs secretory, motor and evacuation functions. Duodenal juice is produced by goblet cells and duodenal glands. Pancreatic juice and bile enter the duodenum, ensuring further digestion of nutrients that has begun in the stomach.Sphincters of the duodenum and papilla of Vater
On the inner surface of the descending part of the duodenum, approximately 7 cm from the pylorus, there is a papilla of Vater, in which the common bile duct and, in most cases, the pancreatic duct combined with it, open into the intestine through the sphincter of Oddi. In approximately 20% of cases, the pancreatic duct opens separately. Above the nipple of Vater, 8–40 mm, there may be a nipple of Santorini, through which the additional pancreatic duct opens.Endocrine cells of the duodenum
The liberkühn glands of the duodenum are the largest among other organs. gastrointestinal tract a set of endocrine cells: I-cells producing the hormones cholecystokinin, S-cells - secretin, K-cells - glucose-dependent insulinotropic polypeptide, M-cells - motilin, D-cells - somatostatin, G-cells - gastrin and others.Short-chain fatty acids in the duodenum
In human duodenal contents, the main proportion of short-chain fatty acids (SCFAs) are acetic, propionic and butyric. Their quantity in 1 g of duodenal content is normal (Loginov V.A.):- acetic acid - 0.739±0.006 mg
- propionic acid - 0.149±0.003 mg
- butyric acid - 0.112±0.002 mg
Duodenum in children
The duodenum of a newborn is located at the level of the first lumbar vertebra and has a round shape. By the age of 12, it descends to the III–IV lumbar vertebra. The length of the duodenum up to 4 years is 7–13 cm (in adults up to 24–30 cm). In children early age it is very mobile, but by the age of 7, adipose tissue appears around it, which fixes the intestine and reduces its mobility (Bokonbaeva S.D. et al.).Some diseases and conditions of the duodenum
Some duodenal diseases and syndromes:Duodenum. The wall of the duodenum is divided into membranes: mucous, submucosal, muscular, serous. The mucous membrane forms numerous villi - conical projections with a wide base (1). Between the villi, extending all the way to the muscular layer of the mucous membrane, there are tube-shaped depressions - crypts (3). Both villi and crypts are lined with a single-layer cylindrical bordered epithelium with goblet cells (2). The own layer of the mucous membrane is built from loose fibrous unformed connective tissue with a large number of collagen and reticulin fibers. The muscular layer of the mucous membrane along the entire length of the intestinal tube consists of two layers of smooth muscle: internal circular and external longitudinal (4). The submucosa contains the secretory sections of complex branched mucous glands (5). The muscular layer is constructed of two layers: the inner circular and the outer longitudinal. Staining with picroindigo carmine.
Jejunum. The wall of the jejunum is built in the same way as the wall of the duodenum, but with some differences. The villi in the jejunum are much taller and thinner and have a cylindrical shape. There are no glands in the submucosa.
Vomiting gut. The mucous membrane forms thin, tall villi (1) and tubular depressions - crypts (2), reaching the muscle layer (5). The mucous membrane is covered with a single-layer columnar epithelium with border (3) and goblet (4) cells. Hematoxylin and eosin staining.
Ileum built in the same way as the jejunum. Its peculiarity is that in the caudal section there is a large number of lymphatic follicles that form aggregates. Lymphoid tissue is represented by T- and B-lymphocytes, plasma cells and macrophages. Lymphatic follicles are characterized by proliferation centers with large proliferating B-lymphoblasts selected for IgA synthesis. The areas between the reproductive centers are filled with T-lymphocytes. The intestinal epithelium, in contact with the lymphoid tissue in the stratum propria, does not contain goblet cells, but is infiltrated with numerous lymphocytes.
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, predominantly longitudinal folds appear. In other sections there are circular folds. Their height increases as they approach the small intestine. In the 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 duodenal mucosa is significantly increased due to the existence of intestinal villi. There are from 10 to 40 villi with a height of 200-700 microns per 1 mm.
The most important and numerous cells of the villous epithelium are columnar absorptive cells known as enterocytes. There are complex connections between the lateral sides of neighboring enterocytes, and their apices are closely adjacent to each other thanks to a special connective complex that maintains the structural unity of the mucous membrane.
The most important distinguishing feature of the enterocyte is the presence of an apical “brush” border, which consists of regularly spaced microvilli, the height of which is up to 1 μm and the diameter of up to 0.1 μm, and is covered with glycocalyx. It is assumed that the glycocalyx, containing 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 cells of the villi. As cells move toward the neck of the crypt, they mature. It has been established that in a normal mucous membrane, approximately three crypts “supply” one villus with cells.
Between the absorptive 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 from the apical part of the cell. Mucin plays an important protective role, and in addition, changes in its secretion can be assessed as a possible marker of the neoplastic process.
The duodenum has specialized glands in the submucosal layer that connect to the crypts through tributaries. It is assumed that these duodenal glands are the precursors of the metaplastic epithelium of the gastric type found in the duodenum during hyperacid conditions.
Kulchitsky cells are found at the base of the intestinal (libyrkun) crypts. They were previously described as argentafine, argyrophilic, or enterochromaffin cells because of 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 the general name of these cells - ARID (amine content, precustor uptake, decarboxilation).
Some of the best known members of this group are enterochromaffin cells (E cells), which produce 5-hydroxy-tryptamine (serotonin); EG cells (L cells), which 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 stratum propria 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, and lymphoid aggregates are found. These lymphoid collections increase in size and number caudally, reaching a maximum in the terminal ileum and appendix, where they are known as Peyer's patches.
Bruner'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 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 highly prismatic; its cytoplasm contains confluent granules of neutral mucopolysaccharides.
The muscular layer of the duodenum is formed by bundles of smooth muscle cells arranged in two layers. The outer thinner layer consists of longitudinal bundles that connect 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 consists of circular bundles. Layers and bundles of muscles are separated by layers of loose connective tissue.
The serosa consists of fibrous connective tissue and contains a large number of elastic fibers. It is covered with a layer of squamous mesothelial cells. Between the serous and muscular layers there is a subserosal layer, represented by a loose connective tissue. It is especially well developed in the places of transition of the serous covering of the duodenum into the ligaments or parietal peritoneum.
Yaitsky N.A., Sedov V.M.
Material taken from the site www.hystology.ru
In the small intestine, 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 intestinal contents move in the caudal direction.
The intestine develops from the following embryonic rudiments: the internal epithelial lining - from the endoderm, connective tissue and smooth muscle structures - from the mesenchyme, the mesothelium of the serous membrane - from the visceral layer of unsegmented mesoderm.
As in the stomach, the intestinal wall consists of three membranes: mucous, muscular, serous (Fig. 270). Feature its structure is the presence of permanent structures, the function of which is aimed at increasing the absorption surface of the epithelial layer of the mucous membrane. These structures are: folds, intestinal villi, crypts, and a striated border of cells of the epithelial layer. They are formed by the mucous membrane, built from the epithelial layer, the main lamina, the muscular lamina, and the submucosa. All layers of the mucous membrane take part in the formation of intestinal folds. The villi are finger-shaped outgrowths of the main plate, covered with an epithelial layer. Crypts are tube-shaped invaginations into the tissue of the main lamina of the superficial epithelial layer.
The striated border is built from microvilli, the plasmalemma of the apical pole of epithelial cells.
The cells of the epithelial layer covering the villi develop from crypt stem cells. 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 membrane; -4 - single-layer villous epithelium; 3 - main lamina of the mucous membrane; 6 - villi; 7 - crypts; 8 - muscle plate: 9 - submucosa; 10 - blood vessels; 11 - submucosal plexus; 12 - annular layer of the muscular layer; 13 - longitudinal layer of the muscle membrane; 14 - intermuscular nerve plexus; 15 - mesothelium.
is located in the basal part of the enterocyte, and at the apical pole lies a striated border. The latter consists of numerous protrusions of the cell plasmalemma, clearly visible in an electron microscope (Fig. 271), which increases the absorption surface of the mucous membrane by 30 times. Due to the high activity of enzymes located in the striated rim, the process of breakdown and absorption of substances occurs here much more intensely than in the intestinal cavity. On the surface of the microvillus there is a glycocalyx, closely associated with the cell membrane. It looks like 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, and mitochondria.
The apical zones of neighboring enterocytes are connected to each other using tight junctions and end plates, thereby closing the intercellular spaces and preventing the uncontrolled penetration of substances into them from the intestinal cavity.
In the epithelial layer between the bordered enterocytes there are goblet cells. These are single-celled 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 towards the basal pole. Developed in the cell
Rice. 271.
A- diagram of the structure of single-layer columnar epithelium:
1
- microvilli of the border; 2
- core; 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 lamina is built of loose connective tissue and also contains reticular tissue, lymphocytes, plasma cells, and eosinophils. In its central part there is a lymphatic vessel. Smooth muscle cells (myocytes) are oriented along it - the contractile component of the villi, blood vessels, and nerves. In the main plate, located below the villi, there are crypts lined with single-layer columnar epithelium. They, like villi, increase the absorption surface of the mucous membrane.
Among the epithelial cells there are bordered and borderless enterocytes, goblet cells, Paneth cells, and endocrine cells. The structure of bordered enterocytes (columnar cells) and goblet cells is similar to the cells of the villus. Borderless enterocytes are columnar in shape and characterized by high mitotic activity. Due to their division, physiological replacement of dying cells of the epithelial cover occurs. Paneth (apical granular) cells are located at the bottom of the crypts; they are distinguished by large oxyphilic granules, as well as the presence of an electron-dense membrane. These cells produce a secretion that affects the process of protein breakdown. It is believed that it neutralizes the hydrochloric acid of 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 and lymphatic vessels, submucosal nerve plexus. In the duodenum, this layer contains 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. Excretory ducts, built from smaller cubic or cylindrical cells, open into the crypts or spaces between the villi. In the duodenal glands there are individual endocrine, parietal, Paneth, and goblet cells. The duodenal glands produce secretions involved in the expansion of carbohydrates and neutralization of hydrochloric acid.
The muscularis propria is formed by two layers of smooth muscle cells: inner and outer. The inner layer is more developed and its cells lie circular in relation to the lumen of the organ. The outer layer consists of longitudinally oriented cells. Between these layers of loose connective tissue is the muscular nerve plexus. Due to the contraction of the muscular membrane, food material moves along the intestines.
The serosa usually consists of loose connective tissue and mesothelium.
It contains the small and large intestines. The small intestine includes the duodenum, jejunum and ileum.
Small intestine
Saves mechanical function - ensures the advancement of chyme, increases sharply hydrolysis food products, which is carried out using intestinal juice. It is saturated with hydrolytic enzymes that are capable of breaking down almost all known biological substances. All enzymes act at pH=8.5-9.
Proteins - trypsin, dipeptidase, enterokinase, nuclease, chemotrypsin.
Carbohydrates - maltase, amylase, sucrase.
Lipids - lipase.
The formation of intestinal juice involves the pancreas, duodenal glands and intestinal glands - a set of cellular glandular elements that are contained in the intestines.
Available suction function, and little water is absorbed, mainly nutrients. excretory the function is characteristic of the intestines to a small extent. The intestines also provide local immune protection.
The wall contains 4 shells along its entire length.
The inner surface of the small intestine is extremely uneven - there are circular folds that are formed by the mucous and submucosal base; they divide the small intestine into segments, increasing the working surface of the intestine and creating conditions for digestion. Chyme passes through 7 meters of intestine in a few hours, that is, folds ensure discrete passage of chyme. There are about 4 million intestinal villi. These are finger-like thin outgrowths of the mucous membrane into the lumen of the small intestine; the maximum frequency of villi is in the duodenum. There they are wide and low. Then, as the small intestine progresses, they occur less frequently, but become thin and long. There are up to 150 million crypts - intestinal glands. The crypt is a depression of the mucosal epithelium into the underlying connective tissue. Around each villus there are several crypts.
The mucous membrane is lined with single-layer prismatic bordered epithelium. The epithelium lining the intestinal villi contains bordered enterocytes. These are tall cylindrical cells with moderately developed organelles. At the top it contains up to 3 thousand microvilli. Between and above the microvilli there is a network of thin fibrils - the glycocalyx. The fibrils contain hydrolytic and transport enzymes that provide parietal digestion and transport of substances from the border zone into the cells. Microvilli increase the absorption surface by 10-40 times (maximum in the duodenum) and prevent the penetration of organisms, especially E. coli. Between the bordered enterocytes lie in significantly smaller numbers goblet cells. They produce and secrete a mucous secretion onto the surface of the intestine. Between these cells are located endocrine cells diffuse endocrine system. Therefore, the small intestine is characterized by endocrine function. The number of endocrine cells is maximum in the duodenum and decreases in the underlying sections.
In the upper half of the crypt epithelium there are cylindrical cells with a weakly defined border. The lower half of the crypts contains a large number of goblet cells. At the bottom of the crypts there are a large number of endocrine cells and the so-called acidophilic granular cells. They contain protein secretory granules and produce and secrete enzymes that break down proteins, mainly dipeptidases. In the epithelium of the lower part of the crypts there are poorly differentiated stem cells. They proliferate and differentiate - some into acidophilic granular cells, endocrine cells, and goblet cells. A large number of young cells move along the basement membrane in top part crypts and differentiates into bordered enterocytes, then move along the surface of the villi, reaching maximum differentiation in the middle third of the intestinal villi. Then they move to the top of the intestinal villi. Here they die and desquamate into the intestinal lumen. Complete renewal of the intestinal villi epithelium occurs in 3-6 days. The stroma of the intestinal villi is composed of loose connective tissue - part of the lamina propria, which contains dense capillary network-- closer to the basement membrane, there is a lymphatic capillary in the center and a bundle of smooth muscle cells passes through the center.
Along the course of the small intestine, the number of mucous cells in the epithelium increases, the number of bordered enterocytes, endocrine cells and cells with acidophilic granules decreases.
The lamina propria of the mucous membrane of loose connective tissue forms the stroma of the intestinal villi and is located in narrow layers between the intestinal crypts. Contains blood and lymphatic capillaries, thin nerve fibers, up to 10 thousand lymph nodes, which form clusters in the ileum. In the epithelium opposite the lymph nodes there are so-called M cells-- microfolded cells. They are lower than the bordered enterocytes, they have short microvilli, they are wider and form depressions (folds) in which immunocompetent cells are located - usually lymphocytes. M cells are arranged in microfields. These cells absorb antigens from the intestinal lumen and transfer the antigens to the lymph nodes.
The muscular plate contains an inner circular layer and an outer longitudinal one. Bundles of smooth muscle cells extend from it into the intestinal villi. It helps reduce intestinal villi. Contraction of the mucous membrane and secretion of secretions from the intestinal villi.
The submucosa is formed by loose, unformed connective tissue. Contains large vascular and nerve plexuses. The widest is in the duodenum and contains the duodenal glands. These are complex, branched tubular glands that open into intestinal crypts. Their secretory compartment contains mucous cells, goblet cells, acidophilus granule cells, chief cells and parietal cells. These glands are involved in the formation of intestinal juice. Everywhere except the duodenum, the submucosa is thin.
The muscular layer is made of smooth muscle tissue. The inner circular and outer longitudinal layers are well developed. Between them lies the intermuscular nerve plexus. Contraction of the muscle membrane ensures the movement of chyme through the small intestine.
The outer shell is represented by a layer of peritoneum, which contains a lot of nerve receptors and nerve plexuses. On the surface, the serous membrane is moistened with mucous secretion and is constantly in motion.