Cellular composition of the small intestinal mucosa. Structure of secretory activity. The structure of the intestinal villi

According to morphofunctional characteristics, the intestine is divided into thin and thick sections.

Small intestine(intestinum tenue) is located between the stomach and the cecum. The length of the small intestine is 4-5 m, the diameter is about 5 cm. There are three sections: duodenum, jejunum and ileum. In the small intestine, all types of nutrients are chemically processed - proteins, fats and carbohydrates. The digestion of proteins involves the enzymes enterokinase, kinaseogen and trypsin, which break down simple proteins; Erepsin, which breaks down peptides into amino acids, nuclease digests complex proteins nucleoproteins. Carbohydrates are digested by amylase, maltase, sucrase, lactase and phosphatase, and fats by lipase. In the small intestine, the process of absorption of the products of the breakdown of proteins, fats and carbohydrates into the bloodstream and lymphatic vessels. The intestine performs a mechanical (evacuation) function - it pushes food particles (chyme) towards the colon. The small intestine is also characterized by an endocrine function performed by special secretory cells and consists of the production of biologically active substances - serotonin, histamine, motilin, secretin, enteroglucogon, cholecystokinin, pancreozymin, gastrin.

The wall of the small intestine consists of four membranes: mucous (tunica mucosa), submucosal (tunica submcosa), muscular (tunica muscularis), serous (tunica serosa).

Mucous membrane represented by epithelium (single-layer cylindrical bordered), lamina propria (loose fibrous connective tissue), muscular lamina (smooth muscle cells). A feature of the relief of the mucous membrane of the small intestine is the presence of circular folds, villi and crypts.

Circular folds formed by the mucous membrane and submucosa.

Intestinal villi is a finger-like outgrowth of the mucous membrane 5-1.5 mm high, directed into the lumen of the small intestine. The villus is based on the connective tissue of the lamina propria, in which individual smooth myocytes are found. The surface of the villi is covered with a single-layer cylindrical epithelium, in which three types of cells are distinguished: columnar epithelial cells, goblet cells and intestinal endocrinocytes.

Columnar epithelial cells of the villi(lepitheliocyti columnares) make up the bulk of the epithelial layer of the villi. These are tall cylindrical cells measuring 25 microns. On the apical surface they have microvilli, which under a light microscope look like a striated border. The height of microvilli is about 1 µm, diameter - 0.1 µm. The presence of villi in the small intestine, as well as microvilli of columnar cells, the absorption surface of the mucous membrane of the small intestine increases tens of times. Columnar epithelial cells have an oval nucleus, a well-developed endoplasmic reticulum, and lysosomes. The apical part of the cell contains tonofilaments (terminal layer), with the participation of which end plates and tight junctions are formed, impermeable 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 on their surface and break down food substances with them. This process is called parietal digestion, in contrast to cavity and intracellular digestion, which occurs in the lumen of the intestinal tube. On the surface of the microvilli there is a glycocalyx, represented by lipoproteins and glycosaminoglycans. The products of the breakdown of proteins and carbohydrates - amino acids and monosaccharides - are transported from the apical surface of the cell to the basal surface, from where they enter the capillaries of the connective tissue base of the villi through the basement membrane. This absorption path is also typical for water, mineral salts and vitamins dissolved in it. Fats are absorbed either by phagocytosis of emulsified fat droplets by columnar epithelial cells, or by absorption of glycerol and fatty acids followed by resynthesis of neutral fat in the cell cytoplasm. Lipids enter the lymphatic capillaries through the basal surface of the plasmalemma of columnar epithelial cells.

Goblet exocrinocytes(exocrinocyti caliciformes) are unicellular glands that produce mucous secretion. In the expanded apical part, the cell accumulates secretions, and in the narrowed basal part, the nucleus, endoplasmic reticulum, and Goldky’s apparatus are located. Goblet cells are located singly on the surface of the villi, surrounded by columnar epithelial cells. The secretion of goblet cells serves to moisturize the surface of the intestinal mucosa and thereby promotes the movement of food particles.

Endocrinocytes(endocrinocyti dastrointestinales) are scattered singly among columnar epithelial cells with a border. Among the endocrinocytes of the small intestine, EC-, A-, S-, I-, G-, D-cells are distinguished. The products of their synthetic activity are a number of biologically active substances that have a local effect on secretion, absorption and intestinal motility.

Intestinal crypts- these are tubular depressions of the epithelium into the lamina propria of the intestinal mucosa. The entrance to the crypt opens between the bases of adjacent villi. The depth of the crypts is 0.3-0.5 mm, the diameter is about 0.07 mm. There are about 150 million crypts in the small intestine; together with the villi, they significantly increase the functionally active area of the small intestine. Among the epithelial cells of the crypts, in addition to columnar cells with a border, goblet cells and endocrinocytes, there are also columnar epithelial cells without a border and exocrinocytes with acidophilic granules (Paneth cells).

Exocrinocytes with acidophilic granules or Paneth cells (endocrinocyti cumgranulis acidophilis) are located in groups near the bottom of the crypts. The cells are prismatic in shape, in the apical part of which there are large acidophilic secretory granules. The nucleus, endoplasmic reticulum, and Golgi complex are shifted to the basal part of the cell. The cytoplasm of Paneth cells stains basophilic. Paneth cells secrete dipeptidases (erepsin), which break down dipeptides into amino acids, and also produce enzymes that neutralize hydrochloric acid, which enters the small intestine with food particles.

Columnar epithelial cells without a border or undifferentiated epithelial cells (endocrinocyti nondilferentitati) are poorly differentiated cells that are the source of physiological regeneration of the epithelium of the crypts and villi of the small intestine. In structure, they resemble border cells, but there are no microvilli on their apical surface.

Own record The mucous membrane of the small intestine is formed mainly by loose fibrous connective tissue, where elements of reticular connective tissue are found. In the lamina propria, clusters of lymphocytes form single (solitary) follicles, as well as grouped lymphoid follicles. Large clusters of follicles penetrate through the muscular plate of the mucous membrane into the submucosa of the intestine.

Muscular plate The mucous membrane is formed by two layers of smooth myocytes - the inner circular and outer longitudinal.

Submucosa The walls of the small intestine are formed by loose fibrous connective tissue, which contains a large number of blood and lymphatic vessels and nerve plexuses. In the duodenum, in the submucosa there are the terminal secretory sections of the duodenal (Bruner's) glands. In structure, these are complex branched tubular glands with a mucous-protein secretion. The terminal sections of the glands consist of mucocytes, Paneth cells and endocrinocytes (S-cells). Excretory ducts open into the intestinal lumen at the base of the crypts or between adjacent villi. Excretory ducts are built by cubic mucocytes, which are replaced at the surface of the mucous membrane by columnar cells with a border. The secretion of the duodenal glands protects the mucous membrane of the duodenum from harmful effects gastric juice. Dipeptidases - products of the duodenal glands - break down dipeptides into amino acids, amylase breaks down carbohydrates. In addition, the secretion of the duodenal glands is involved in neutralizing the acidic compounds of gastric juice.

Muscularis The small intestine is formed by two layers of smooth myocytes: internal oblique-circular and external oblique-longitudinal. Between them lie layers of loose fibrous connective tissue, rich in neurovascular plexuses. Function of the muscle membrane: mixing and promoting digestion products (chyme).

Serosa The small intestine is formed by loose fibrous connective tissue, which is covered with mesothelium. Covers the outside of the small intestine on all sides, with the exception of the duodenum, which is covered with peritoneum only in front, and in the remaining parts has a connective tissue membrane.

Colon(intestinum crassum) section of the digestive tube that ensures the formation and passage of feces. Metabolic products, heavy metal salts and others are released into the lumen of the colon. The bacterial flora of the large intestine produces vitamins B and K, and also ensures the digestion of fiber.

Anatomically, the following sections are distinguished in the large intestine: the cecum, the appendix, the colon (its ascending, transverse and descending sections), the sigmoid and rectum. The length of the colon is 1.2-1.5 m, diameter 10 mm. In the wall of the colon there are four membranes: mucous, submucosal, muscular and outer - serous or adventitial.

Mucous membrane The colon is formed by a single-layer prismatic epithelium, connective tissue lamina propria and muscular lamina. The relief of the mucous membrane of the colon is determined by the presence of a large number of circular folds, crypts and the absence of villi. Circular folds are formed on the inner surface of the intestine from the mucous membrane and submucosa. They are located transversely and have a crescent shape. Most of the epithelial cells of the large intestine are represented by goblet cells; there are fewer columnar cells with a striated border and endocrinocytes. At the base of the crypts there are undifferentiated cells. These cells do not differ significantly from similar cells of the small intestine. Mucus covers the epithelium and promotes the sliding and formation of feces.

In the lamina propria of the mucous membrane there are significant accumulations of lymphocytes, which form large single lymphatic follicles that can penetrate the muscular lamina of the mucous membrane and merge with similar formations of the submucosal membrane. Accumulations of dissociated lymphocytes and lymphatic follicles of the digestive tube wall are considered an analogue of the bursa (bursa) of Fabricius in birds, responsible for the maturation and acquisition of immune competence by B lymphocytes.

There are especially many lymphatic follicles in the wall of the appendix. The epithelium of the mucous membrane of the appendix is single-layer prismatic, infiltrated with lymphocytes, with a small content of goblet cells. It contains Paneth cells and intestinal endocrinocytes. The endocrinocytes of the appendix synthesize the bulk of the body's serotonin and melatonin. The lamina propria of the mucous membrane without a sharp boundary (due to the poor development of the muscular lamina mucosa) passes into the submucosa. In the lamina propria and in the submucosa there are numerous large, locally confluent accumulations of lymphoid tissue. The vermiform appendix performs a protective function; lymphoid accumulations are part of the peripheral parts of the immune system of the tissue in it

The muscular plate of the colon mucosa is formed by two layers of smooth myocytes: the inner circular and the outer oblique-longitudinal.

Submucosa The colon is formed by loose fibrous connective tissue, in which there are accumulations of fat cells, as well as a significant number of lymphatic follicles. The submucosa contains the neurovascular plexus.

The muscular layer of the colon is formed by two layers of smooth myocytes: the inner circular and outer longitudinal, between them there are layers of loose fibrous connective tissue. In the colon, the outer layer of smooth myocytes is not continuous, but forms three longitudinal ribbons. Shortening of individual segments of the inner layer of smooth muscle cells contributes to the formation of transverse folds of the colon wall.

The outer lining of most of the large intestine is serous; in the caudal part of the rectum it is adventitial.

Rectum- has a number of structural features. It distinguishes between the upper (pelvic) and lower (anal) parts, which are separated from each other by transverse folds.

The mucous membrane of the upper part of the rectum is covered with single-layer cubic epithelium, which forms deep crypts.

The mucous membrane of the anal part of the rectum is formed by three zones of different structure: columnar, intermediate and cutaneous.

The columnar zone is covered with stratified cubic epithelium, the intermediate zone with stratified squamous non-keratinizing epithelium, and the skin zone with stratified squamous keratinizing epithelium.

The lamina propria of the columnar zone forms 10-12 longitudinal folds, contains blood lacunae, single lymphatic follicles, rudiments: rudimentary anal glands. The lamina propria and the zone are rich in elastic fibers, sebaceous jelly is located here, and there are dissociated lymphocytes. In the lamina propria of the rectum, in its skin part, hair follicles, end sections of apocrine sweat glands, and sebaceous glands appear.

The muscular plate of the rectal mucosa is formed by the inner circular and outer longitudinal layers of smooth myocytes.

The submucosa of the rectum is formed by loose fibrous connective tissue in which the nerves and choroid plexuses are located.

The muscular layer of the rectum is formed by the inner circular outer longitudinal layers of smooth myocytes. The muscular layer forms two sphincters, which play an important role in the act of defecation. The internal sphincter of the rectum is formed by thickening of the smooth myocytes of the inner layer of the muscular layer, the external sphincter is formed by bundles of fibers of striated muscle tissue.

The upper part of the rectum is externally covered with a serous membrane, the anal part is covered with an adventitial membrane.

Small intestinal cancer is a malignant neoplasm of a cell of the intestinal tissue.

Tumors of the small intestine are rare and account for 1% of all intestinal cancers. The length of the loop-shaped small intestine reaches 4.5 m. It consists of intestines: duodenum, jejunum and ileum. In each of these components, under favorable conditions, small intestinal cancer can degenerate from a normal cell.

Malignant tumor of the small intestine

The absence of obvious specific primary symptoms forces patients to seek help from a doctor in the later stages of the disease. In this case, metastasis begins, due to which secondary intestinal cancer develops.

Metastases reach regional lymph nodes and other distant parts of the intestine, so the following cancers can develop:

Causes of small intestine cancer

Specific direct causes of small intestinal cancer have not yet been discovered. Attention is always paid to chronic enzymatic or inflammatory bowel disease; symptoms of cancer can be hidden behind signs of disease, such as diverticulitis, nonspecific ulcerative colitis, enteritis, Crohn's disease, duodenal ulcer. Often the tumor develops against the background of adenomatous polyps, which are prone to degeneration into oncogenic ones.

The duodenum is often affected due to the irritating effect of bile. The initial part of the small intestine is due to the juice of the pancreas and active contact with carcinogenic substances from food, fried foods, alcohol and nicotine.

The first symptoms and signs of small intestine cancer in men and women

If duodenal cancer is suspected, the first symptoms will be similar to peptic ulcer stomach and duodenum and will manifest itself as an aversion to food, dull pain in the epigastric zone with irradiation to the back. At a late stage, duodenal cancer exhibits symptoms associated with poor patency of the bile ducts and intestines due to tumor growth. The patient will suffer from endless nausea and vomiting, flatulence and manifestations of jaundice.

The jejunum and ileum are the first to signal cancer local signs and general dyspeptic disorders:

nausea and vomiting;
bloating;
pain in the intestines;
spasms in the navel and/or epigastrium;
frequent loose stools with mucus.

It has been proven that small intestinal cancer symptoms and manifestations occur more often in men than in women. This fact is associated with the lifestyle of men, nutrition and abuse of malicious habits: alcohol, smoking and drugs. In addition, small intestinal cancer develops; signs and symptoms manifest themselves somewhat differently due to the different structure of the genitourinary system.

Very often, with breast, cervical and ovarian cancer, signs of intestinal cancer appear in women. For tumor metastases prostate gland, testicles may appear symptoms of bowel cancer in men. If the tumor compresses neighboring organs, this leads to the development of pancreatitis, jaundice, ascites, and intestinal ischemia.

Small intestine cancer: symptoms and manifestations

The tumor grows, so the symptoms of oncology in the small intestine intensify:

intestinal patency is impaired;
obvious or hidden intestinal blood loss appears;
perforation of the intestinal wall develops;
the contents enter the peritoneal cavity and peritonitis begins;
intoxication (poisoning) of the body increases due to the breakdown of tumor cells, ulcers and intestinal fistulas appear;
iron deficiency increases;
the functions of the pancreas and liver are impaired.

Cancer does not have a gender identity, so the symptoms of bowel cancer in women and men are largely the same: increasing weakness, weight loss, malaise, anemia and rapid and unexplained fatigue, nervousness, anorexia, difficulty defecating, accompanied by pain, itching , frequent urges.

Classification of stages of small intestinal cancer. Types and Types of Small Bowel Cancer

According to histological classification, oncological formations of the small intestine are:

adenocarcinoma- develops from glandular tissue next to the major papilla of the duodenum. The tumor is ulcerated and covered with a fleecy surface;
carcinoid– develops in any part of the intestine, most often in the appendix. Less often - in the ileum, very rarely - in the rectum. The structure is similar to the epithelial form of cancer.
lymphoma– rare tumor formation (18%) and combines lymphosarcoma and lymphogranulomatosis (Hodgkin’s disease);
leiomyosarcoma– large tumor formation, more than 5 cm in diameter, can be palpated through the peritoneal wall. The tumor creates intestinal obstruction, wall perforation.

Lymphoma of the small intestine can be primary or secondary. If primary lymphoma of the small intestine is confirmed, the symptoms are characterized by the absence of hepatosplenomegaly, enlarged lymph nodes, changes on the sternum x-ray, CT scan, in the blood and bone marrow. If the tumor is large, disturbances in the absorption of food will be observed.

If the retroperitoneal and mesenteric lymph nodes spread tumor cells, then a secondary lymphoma forms in the small intestine. Types of small intestinal cancer include signet ring cell, undifferentiated and unclassified. Growth form – exophytic and endophytic.

Stages of small intestine cancer:

Stage 1 cancer of the small intestine – tumor within the walls of the small intestine, no metastases;
Stage 2 of small intestine cancer – the tumor extends beyond the intestinal wall, begins to penetrate other organs, there are no metastases;
Stage 3 of small intestine cancer - metastasis to the nearest lymph nodes, germination to other organs, no distant metastases;
small intestine cancer stage 4 – metastasis in distant organs (liver, lungs, bones, etc.).

Diagnosis of small intestine cancer

How to recognize colon cancer at an early stage? This determines what treatment will be used, the patient’s condition and the prognosis for survival.

Diagnosis of small intestine cancer is carried out using popular methods:

X-ray examination;
fibrogastroscopy;
angiography of the vessels of the peritoneal cavity;
laparoscopy;
colonoscopy;
CT and MRI;
biopsy examination: determine the type of cells and the degree of their malignancy;
electrogastroenterography: detect disturbances in small intestinal motility characteristic of cancer.

How to identify intestinal cancer, the symptoms of which do not manifest themselves in anything specific? During this period, it is very important to confirm or refute the suspicion of cancer, because the sooner treatment begins, the easier it is for the patient to endure its stages, the greater the chance of a positive result. When symptoms appear, the oncological process can be considered advanced, and the moment of early treatment will be missed.

Important! Early symptoms include a “young” state, which should alert any person - this is a reluctance to work or do household chores due to increased weakness and fatigue. Skin become pale and “transparent”. The patient constantly has heaviness in his stomach, he does not feel like eating at all. Following this, dyspeptic disorders appear: nausea, vomiting, pain and heartburn even from water.

When visiting a doctor, a blood test for colon cancer is immediately prescribed and examined. A general basic blood test can reveal anemia, the patient's condition, and the presence of inflammation. According to the level of ESR and hemoglobin - problems in the liver, kidneys and blood. The composition of the blood may indicate certain diseases, including cancer.

Tumor markers for small intestinal cancer are detected in the blood. The most informative and common tumor markers are alpha-fetoprotein, total PSA/free PSA, CEA, CA-15.3, CA-125, CA-19.9, CA-72.4, CYFRA-21.1, hCG and cytokeratin .

For example, using the tumor markers CA 19.9 and CEA (carcinoembryonic antigen), screening diagnostics of colon cancer is carried out. If CEA is determined, then you can find out the staging before surgery and monitor the patient diagnosed with colorectal cancer after it. If the disease progresses, then the level of CEA in the serum will increase. Although it may grow not in connection with a tumor, in later stages colorectal cancer can be detected without an increase in CEA in the blood.

Endoscopic diagnosis and open intestinal biopsy are the main methods for confirming small intestinal oncology.

Treatment of small intestine cancer

Treatment of small intestinal cancer: duodenal, jejunal and ileal intestines is carried out depending on the type of tumor and stage. The main method is bowel resection and removal of tumor formation.

With a confirmed diagnosis of small intestinal cancer, surgery reduces symptoms and increases life expectancy. If it is not possible to delete malignant tumors small intestine at a late stage or it is revealed that the tumor is sensitive to chemotherapy, drugs are used that prevent the growth of cancer cells.

After a palliative operation (alleviating the patient's suffering), treatment is carried out with chemotherapy (polychemotherapy), but without radiation.

After the operation, intestinal motility is additionally diagnosed using electrogastroenterography to prevent the development of a dangerous complication - intestinal paresis.

To alleviate the patient's condition after surgery and chemotherapy in complex therapy introduced ethnoscience for intestinal cancer: alcohol tinctures, infusions and decoctions of medicinal herbs, mushrooms and berries. Appropriate nutrition for intestinal cancer prevents paresis, nausea and vomiting, and improves gastrointestinal motility.

Forecast and prevention of small intestine (bowel) cancer

Prevention of small intestine cancer consists of timely removal of benign neoplasms, polyps, constant monitoring of patients with chronic inflammatory processes of the gastrointestinal tract by specialists, transition to healthy eating and lifestyle, giving up bad habits.

If treatment was given and bowel cancer was removed, how long do people live? If there are no regional or distant metastases, the tumor is removed, survival in the subsequent 5-year period can be 35-40%.

Conclusions! If the tumor is operable, a wide resection of a section of the intestine with lymph nodes and mesentery is performed within the boundaries of healthy tissue. To restore the integrity of the gastrointestinal tract, enteroenteroanastomosis is performed - small intestine into the small intestine or enterocoloanastomosis - small intestine into the large intestine.

For cancer of the duodenum, as part of the small duodenum, duodenectomy and sometimes distal resection of the stomach or pancreas (pancreaticoduodenectomy) are performed. In case of advanced oncology of the small intestine, a bypass anastomosis is performed between loops that remain unaffected. Surgery supplemented with chemotherapy.

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Columnar epithelial cells- the most numerous cells of the intestinal epithelium, performing the main absorption function of the intestine. These cells make up about 90% of the total number of intestinal epithelial cells. A characteristic feature of their differentiation is the formation of a brush border of densely located microvilli on the apical surface of the cells. The length of microvilli is about 1 µm, the diameter is approximately 0.1 µm.

Total number of microvilli per surfaces per cell varies widely - from 500 to 3000. Microvilli are covered on the outside with glycocalyx, which adsorbs enzymes involved in parietal (contact) digestion. Due to microvilli, the active absorption surface of the intestine increases 30-40 times.

Between epithelial cells in their apical part, contacts such as adhesive bands and tight junctions are well developed. The basal parts of the cells contact the lateral surfaces of neighboring cells through interdigitations and desmosomes, and the base of the cells is attached to the basement membrane by hemidesmosomes. Thanks to the presence of this system of intercellular contacts, the intestinal epithelium performs an important barrier function, protecting the body from the penetration of microbes and foreign substances.

Goblet exocrinocytes- These are essentially unicellular mucous glands located among columnar epithelial cells. They produce carbohydrate-protein complexes - mucins, which perform a protective function and promote the movement of food in the intestines. The number of cells increases towards the distal intestine. The shape of the cells changes in different phases of the secretory cycle from prismatic to goblet. In the cytoplasm of cells, the Golgi complex and the granular endoplasmic reticulum are developed - centers for the synthesis of glycosaminoglycans and proteins.

Paneth cells, or exocrinocytes with acidophilic granules, are constantly located in the crypts (6-8 cells each) of the jejunum and ileum. Their total number is approximately 200 million. In the apical part of these cells, acidophilic secretory granules are detected. Zinc and a well-developed granular endoplasmic reticulum are also detected in the cytoplasm. The cells secrete a secretion rich in the enzyme peptidase, lysozyme, etc. It is believed that the secretion of the cells neutralizes the hydrochloric acid of the intestinal contents, participates in the breakdown of dipeptides into amino acids, and has antibacterial properties.

Endocrinocytes(enterochromaffinocytes, argentaffin cells, Kulchitsky cells) - basal granular cells located at the bottom of the crypts. They are well impregnated with silver salts and have an affinity for chromium salts. Among endocrine cells, there are several types that secrete various hormones: EC cells produce melatonin, serotonin and substance P; S cells - secretin; ECL cells - enteroglucagon; I-cells - cholecystokinin; D-cells - produce somatostatin, VIP - vasoactive intestinal peptides. Endocrinocytes make up about 0.5% of the total number of intestinal epithelial cells.

These cells renew themselves much more slowly than epithelial cells. Using historadioautography methods, a very rapid renewal of the cellular composition of the intestinal epithelium was established. This occurs within 4-5 days in the duodenum and somewhat more slowly (5-6 days) in the ileum.

lamina propria of the mucous membrane The small intestine consists of loose fibrous connective tissue, which contains macrophages, plasma cells and lymphocytes. There are also both single (solitary) lymph nodes and larger accumulations of lymphoid tissue - aggregates, or group lymph nodes (Peyer's patches). The epithelium covering the latter has a number of structural features. It contains epithelial cells with microfolds on the apical surface (M-cells). They form endocytotic vesicles with antigen and exocytosis transfer it into the intercellular space where lymphocytes are located.

Subsequent development and plasma cell formation, their production of immunoglobulins neutralizes antigens and microorganisms in the intestinal contents. The muscular plate of the mucous membrane is represented by smooth muscle tissue.

In the submucosa base of the duodenum There are duodenal (Brunner's) glands. These are complex branched tubular mucous glands. The main type of cells in the epithelium of these glands are mucous glandulocytes. The excretory ducts of these glands are lined with border cells. In addition, Paneth cells, goblet exocrinocytes and endocrinocytes are found in the epithelium of the duodenal glands. The secretion of these glands is involved in the breakdown of carbohydrates and neutralization of hydrochloric acid coming from the stomach, mechanical protection of the epithelium.

Muscular lining of the small intestine consists of inner (circular) and outer (longitudinal) layers of smooth muscle tissue. In the duodenum, the muscular layer is thin and, due to the vertical position of the intestine, practically does not participate in peristalsis and the movement of chyme. On the outside, the small intestine is covered with a serous membrane.

SMALL INTESTINE EPITHELIA

Epithelium (E) of the small intestine consists of two types of epithelial cells: absorptive and goblet cells, lying on the basement membrane (BM). The absorptive and goblet cells are connected by junctional complexes (JCs) and multiple lateral interdigitations (LIs). Intercellular gaps (IC) are often formed between the basal parts. Chylomicrons (X, a class of lipoproteins formed in the small intestine during the absorption of lipids) can circulate between these gaps; Lymphocytes (L) penetrate here. Absorbing cells live about 1.5-3.0 days.

Suction cells (AC)- tall prismatic cells with an elliptical, often with invaginations, nucleus (N), located in the lower part of the cell body. The nucleoli, Golgi complex (G) and mitochondria are well developed. The granular endoplasmic reticulum often continues into the granular one. The cytoplasm contains a certain amount of lysosomes and free ribosomes.

The apical pole of the cell is polygonal in shape. Microvilli (Mv) are covered with a thick layer of glycocalyx (Gk), in some places in the figure it is partially removed. Microvilli and glycocalyx form the brush border (BBC), which increases the intestinal absorption surface to 900 m2.

Goblet cells (GC)- basophilic cells scattered among absorptive cells. In active cells, the nucleus is cup-shaped and located at the basal pole of the cell. The cytoplasm contains mitochondria, a well-developed supranuclear Golgi complex, several cisternae of the granular endoplasmic reticulum oriented parallel to each other, and many free ribosomes.

The last two structures are responsible for goblet cell basophilia. From the Golgi complex, numerous mucous droplets (MDs) surrounded by a single-layer membrane arise, filling the entire supranuclear cytoplasm and giving the cells a goblet shape. Droplets are released from cells by fusion of the surrounding membranes with the apical plasmalemma. Once mucus droplets are released, the goblet cells become invisible under a light microscope. Goblet cells are capable of replenishing the cytoplasm with mucus droplets during 2-3 secretory cycles, since their life lasts about 2-4 days.

Products goblet cells CHIC-positive and metachromatic, as it consists of glycoproteins and glycosaminoglycans; it serves to lubricate and protect the absorption cells. Networks of capillaries (Cap) and reticular fibrils (RF) belonging to the lamina propria (LP) of the mucosa are located immediately below the epithelial basement membrane (BM). Reticular fibers serve, among other things, to attach thin, vertically oriented smooth muscle cells (SMCs) to the basement membrane. Their contractions shorten the intestinal villi. At some distance from the epithelium, blind dilations of the lacteal vessels (ML) begin. Numerous openings (O) are visible between the endothelial cells, through which chylomicrons enter the lymphatic circulation. Anchoring filaments (AF) are also noted, attaching the lacteal vessels to the network of collagen fibers.

A large number of collagen (KB) and elastic (EF) fibers pass through the lamina propria of the mucous membrane. In the network of these fibrils there are lymphocytes (L), plasma cells (PC), histiocytes (H) and eosinophilic granulocytes (EG). Fibroblasts, fibrocytes (F) and some reticular cells belong to the permanent cells of the lamina propria of the mucous membrane.

ABSORPTION (ABSORPTION) OF LIPIDS IN THE SMALL INTESTINE

The function of absorptive cells is to absorb nutrients from the intestinal cavity. Since the absorption of proteins and polysaccharides is difficult to detect morphologically, we will describe lipid absorption.

Mechanism lipid absorption is divided into the enzymatic breakdown of fats into fatty acids and monoglycerides and the entry of these products into absorptive cells, where the resynthesis of new lipid droplets - chylomicrons (X) occurs. They are then released into the basal intercellular clefts, cross the basal lamina and enter the lacteal vessel (ML).

Chylomicrons are emulsified droplets of fat that have a milky color, which is why all lymphatic intestinal vessels are called lacteal.

Colon contains a mucous membrane that does not form folds, with the exception of its distal (rectal) section. There are no villi in this part of the intestine. The intestinal glands are long and characterized by a large number of goblet and border cells and a low content of enteroendocrine cells.

Limb cells- columnar, with short microvilli of irregular shape. The large intestine is well adapted to perform its main functions: absorbing water, forming fecal matter and producing mucus. Mucus is a highly hydrated gel that not only acts as a lubricant on the surface of the intestine, but also coats bacteria and various particles. Water absorption occurs passively following the active transport of sodium through the basal surfaces of epithelial cells.

Colon histology

Own plate rich in lymphoid cells and nodules, which often continue into the submucosa. Such a powerful development of lymphoid tissue (KALT) is associated with a huge population of bacteria in the colon. The muscular layer includes longitudinal and circular layers.

This shell differs from that in the small intestine, because bundles of smooth muscle cells of the outer longitudinal layer are collected into three thick longitudinal belts - intestinal ribbons (lat. teniae coli). In the intraperitoneal areas of the large intestine, the serous membrane contains small hanging protrusions consisting of adipose tissue - fatty appendages (lat. appendices epiploicae).

Gland in the colon. Its bordered and mucous goblet cells are visible. Please note that the goblet cells secrete a secretion and begin to fill the lumen of the gland with it. Microvilli on the border cells are involved in the process of water absorption. Staining: pararosaniline-toluidine blue.

IN anal(anal) area, the mucous membrane forms a series of longitudinal folds - rectal columns of Morgagni. Approximately 2 cm above the anus, the intestinal mucosa is replaced by stratified squamous epithelium. In this area, the lamina propria contains a plexus formed by large veins, which, when excessively dilated and varicose, give rise to hemorrhoids.

Small intestine cancer: characteristic signs and symptoms

What are the signs and symptoms when diagnosed with small bowel cancer? What is the etiology of the disease and principles of treatment?

Small bowel cancer

The small intestine consists of several sections. Depending on which of them the cancer develops, there are:

The most common type of cancer is the duodenum.

Cancer develops from various intestinal tissues and can spread to other organs. Depending on the tissue from which the tumor developed, several histological types are distinguished:

Lymphoma that develops from tissues rich in immune cells.
Sarcoma developing from smooth muscles that provide peristalsis of the small intestine.
Adenocarcinoma developing from mucosal cells. This is the most common form.

Different types of cancer have different etiologies and clinical manifestations, suggest different treatment approaches and prognoses.

Clinical manifestations

Based on the degree of development of the disease, there are several stages of cancer development, which are manifested by certain symptoms:

The tumor develops in the tissue area of the intestinal walls. There is no spread to other organs or metastases. At this stage, most often there are no symptoms that may cause concern to the patient.
The tumor begins to spread to neighboring organs. There are no metastases.
The appearance of metastases in the nearest lymph nodes and in organs is absent.
The presence of metastases in distant organs.

The first symptoms of the disease appear with the development of severe narrowing of the intestine or ulceration of the tumor, which are prolonged pain in the epigastric region. This is accompanied by the following symptoms:

weight loss;
anemia (a drop in hemoglobin levels), which causes weakness and dizziness;
vomiting if the tumor is localized in the upper parts of the jejunum;
loose stools with mucus;
signs of intestinal obstruction;
obvious or hidden blood loss, especially often manifested in sarcoma;
increased bilirubin levels with liver metastases;
yellow skin color;
sclera of the eyes.

Causes of small intestinal cancer

The exact causes of small intestinal cancer have not been identified. Based on clinical studies and statistical data, it is known that the risk of developing the disease is highest in the following cases:

in cases of small intestinal cancer observed in direct relatives;
in the presence of chronic inflammatory diseases of the small intestine that destroy the mucous membrane (Crohn's disease, celiac disease);
in the presence of polyps in the intestines;
in the presence of cancer of other organs;
when exposed to radiation;
when smoking, alcohol abuse, regular consumption of dried, salted, smoked foods, with a high content of animal fat (fatty meats, lard).

Small bowel cancer is more common:

in developing countries in Asia;
in blacks;
among men;
among persons over 60 years of age.

Diagnosis and treatment methods

If you notice any unpleasant symptoms, you should contact a qualified specialist as soon as possible. In the presence of cancer, early diagnosis is the most important condition for a favorable prognosis.

Research methods that allow diagnosing the presence of cancer, the degree of its development and spread:

FGDS (fibrogastroduodenoscopy) is a method of instrumental examination of the inner surface of the esophagus, stomach and duodenum by inserting a probe through the nasal sinuses or mouth.
Colonoscopy is a method of instrumental examination of the inner surface of the large intestine by inserting a probe through the anus.
Laparoscopy is an examination or surgical procedure in which a skin incision is made in the desired area and a miniature camera and surgical instruments are inserted into the abdominal area.
Ultrasound ( ultrasonography) abdominal organs.
CT (computed tomography), MRI (magnetic resonance imaging) of the small intestine.
Blood chemistry.
X-ray examination of the chest organs.
Bone tissue centigraphy.

When conducting such instrumental examinations, like FGDS, colonoscopy, laparoscopy, biopsy is performed (taking a tissue sample for detailed laboratory research) for detailed examination of tissues for the presence of cancer cells and determining the type of tumor.

Surgery is the most effective treatment for small intestinal cancer. The operation consists of removing (ectomy) the tumor and affected tissues and lymph nodes. Artificial restoration of removed tissue can also be carried out in several ways:

Enteroanastomosis is a surgical connection between intestinal loops.
Enterocoloanastomosis is a surgical connection between the loops of the large and small intestines.

Resection (excision) is prescribed only by a doctor in the absence of contraindications. The type of surgical intervention depends on the stage of development of the disease and the extent of spread.

In advanced stages of cancer, when extensive resection is not possible, surgical implantation of a bypass anastomosis in a healthy area of the organ is prescribed.

The earlier the stage of cancer development, the pathological tissue is removed, the more favorable the prognosis for the patient.

Conservative treatment. An addition to surgical treatment for small intestinal cancer is chemotherapy or radiation therapy. Radiation therapy involves exposing malignant cells to high-frequency radiation. Chemotherapy is the intravenous or oral administration of drugs into the body.

The listed procedures cause many side effects, including general weakness and malaise, nausea, vomiting, diarrhea, headaches, hair loss, hematopoietic disorders, weakness, diarrhea, the appearance of ulcers on the mucous membrane oral cavity, disruption of the immune system.

An important condition for the treatment of small intestinal cancer is proper nutrition, which includes compliance with the following conditions:

Exclusion from the diet of foods containing animal fats.
Inclusion in the diet of foods with sufficient fiber content, fish oil, soy, indole-3 carbinol.
Quitting alcohol and cigarettes.

In advanced cancer cases, when surgery is not advisable due to its ineffectiveness, radiation and chemotherapy may be prescribed. Radiation therapy may be given to relieve symptoms.

Preventive actions

At early diagnosis and treatment is possible complete cure. Small intestinal cancer develops long time and does not metastasize for a long time due to the fact that it is poorly supplied with blood and cancer cells do not spread so quickly throughout the body.

Even after the operation, the patient must undergo regular examination by an oncologist and undergo the necessary tests. It is also necessary to closely monitor the health status of persons at risk.

These tumors are observed in all parts of the small intestine;

14 % malignant neoplasms constitute sarcomas. The incidence of sarcomas does not depend on gender, with a peak incidence in the sixth to eighth decades of life. Typically, mesenchymal tumors of this location develop in younger patients than cancer, and are more common than AK and carcinoid. A common complication of mesenchymal tumors of the small intestine is intussusception. The prognosis for sarcoma depends on the mitotic index, size, depth of invasion, and the presence or absence of metastases. The 5-year life expectancy of patients is 45% (for carcinoid - 92%; for AK - 63%). With sarcoma of the small intestine, the prognosis is worse than with similar tumors of the colon, stomach, and esophagus. The macroscopic appearance, histological structure and cytological diagnostic capabilities are given in Chapter. about the stomach.

Gastrointestinal stromal tumors (GISTs) are of significant importance; leiomyoma, leiomyosarcoma, Kaposi's sarcoma, angiosarcoma rarely found in the small intestine (the histological and cytological picture is similar to tumors of the esophagus and stomach, see Chapters IV and V). Leiomyoma is most often localized intramural, large tumors bulge into the lumen, ulcerate and bleed.

Genetic features. In small, especially malignant gastrointestinal tract tumors, as in similar stomach tumors, mutations of the c-kit gene in exon 11 are detected. Using comparative genomic hybridization, deletions were identified on chromosomes 14 and 22, which is also characteristic of gastric GI tract. The fundamental criterion for the diagnosis of AK is the presence of invasion of the muscular plate of the mucous membrane, which in practice is not always easy to determine, because well-differentiated AK mimics an adenoma. On the other hand, in some adenomas, acellular mucus penetrates the intestinal wall, mimicking invasion. If the wall of the appendix contains acellular mucus, then the diagnosis of adenoma is possible only if the muscular plate is intact. Sometimes AK is so highly differentiated that it is difficult to verify it as a malignant tumor. Well-differentiated AC of the appendix grows slowly, clinically creating a picture of pseudomyxoma peritonei. Most appendiceal AKs are mucous. If there are >50% signet ring cells, the tumor is called signet ring cell. Non-mucous tumors proceed in the same way as in the colon. Metastases in the lymph nodes are observed late.

The 5-year life expectancy rate for localized AK of the appendix is 95%, for mucinous cystadenocarcinoma - 80%; for distant metastases of these tumors - 0% and 51%, respectively. An advanced stage, a high degree of malignancy, and a non-mucous tumor are associated with a poor prognosis for AK of the appendix. With complete removal of the tumor, an extension of life expectancy is noted.

The histological and cytological picture of AK is similar to that of similar tumors of other locations.

Pseudomyxoma peritonei represented by mucus on the surface of the peritoneum. A clear picture is due to the highly differentiated mucous membrane of the AK (Fig. 175-182), and there are few cells, cellular component grows slowly, but the mucus arrives quickly. The tumor is poorly manifested on the surface of the peritoneum, while large volumes of mucus are located in the omentum, on the right under the diaphragm, in the renal space, in the ligament of Treitz, in the left parts of the colon, in the pelvic cavity. Occasionally, mucous cysts are found in the spleen. In these cases, the tumor tends to remain in the abdominal cavity for many years.

Most cases of pseudomyxoma peritonei arise from primary cancer of the appendix, but occasionally it can spread from the ovary, gallbladder, stomach, PTC, pancreas, fallopian tubes, urachus, lung, and breast. With pseudomyxoma peritonei, weight loss, a high degree of malignancy on histological examination, and morphological invasion of underlying structures are factors for an unfavorable prognosis.

In half of the cases of pseudomyxoma peritonei, loss of heterozygosity for one or two polymorphic microsatellite loci was detected, which indicates the monoclonality of the tumor. If the clinical picture matches cytological diagnosis establish reliably: “pseudomyxoma”.

Carcinoid tumor is the most common (50-75%) primary tumor of the appendix; -19% of all gastrointestinal carcinoids are localized in the appendix, mainly in its distal part; the tumor is more often diagnosed in women. Tubular carcinoid is observed at a much younger age than goblet cell carcinoid ( average age 29 years and 53 years respectively). Asymptomatic lesions are often observed (a single tumor nodule is discovered accidentally in the appendectomy material). Rarely, carcinoid can cause obstruction of the lumen of the appendix, leading to appendicitis. Carcinoid syndrome occurs extremely rarely, always with metastases in the liver and retroperitoneum.

EC cell carcinoid of the appendix is a clearly demarcated dense nodule, matte, grayish-white on section, the size<1 см. Опухоли >2 cm are rare, most located at the apex of the appendix. Goblet cell carcinoid and carcinoid-AC are found in any part of the appendix in the form of a diffuse infiltrate, measuring 0.5-2.5 cm.

In most cases, appendiceal carcinoid has a favorable prognosis. Tumors and metastases often grow slowly. Clinically non-functioning lesions of the appendix that do not grow into blood vessels, size<2 см, обычно излечивают полной местной эксцизией, в то время как размеры >2 cm, invasion of the mesentery of the appendix and metastases indicate aggressiveness of the lesion. Localization of the tumor at the base of the appendix involving the edge of the incision or the cecum is prognostically unfavorable and requires at least partial resection of the cecum in order to avoid residual tumor and relapse. The frequency of regional metastases of appendiceal carcinoid is 27%, distant metastases - 8.5%. The 5-year life expectancy rates for local appendiceal carcinoid are 94%, for regional metastases 85%, and for distant metastases 34%. Goblet carcinoid is more aggressive than regular carcinoid but less aggressive than appendiceal carcinoid; tubular carcinoid, on the contrary, has a favorable prognosis.

Histological picture: Most appendiceal carcinoids are EC cell enterochromatin tumors; L-cell carcinoids and mixed endocrine-exocrine cancers are rare.

The structure of the EC-cell argentaffin carcinoid of the appendix is similar to the structure of a similar carcinoid of the small intestine (see above). Most tumors invade the muscular layer, lymphatic vessels and perineurium, and in 2/3 cases - the mesentery of the appendix and the peritoneum, however, they rarely metastasize to the lymph nodes and distant organs, unlike ileal carcinoid. In appendix carcinoids, supporting cells are visible around nests of tumor cells; in contrast, supporting cells are absent in EC cell carcinoids of the ileum and colon.

L-cell carcinoid producing glucagon-like peptides (GLP-1 and GLP-2, enteroglucagon glycentin, oxyntomodulin) and PP/PYY is non-argentaffin; most often measures 2-3 mm; characterized by tubular structures made of small cylindrical cells and trabecular structures in the form of long cords (type B); similar carcinoids are often found in the rectum.

Goblet cell carcinoid, usually 2–3 mm in size, grows in the submucosal layer, concentrically invades the wall of the appendix, and consists of small, round nests of signet ring cells resembling normal intestinal goblet cells, except for the compressed nuclei. Some of the cells are located in isolation; Pannet cells with lysosomes and foci resembling Brunner's glands are visible. When individual goblet cells fuse, extracellular “lakes” of mucus are formed. The picture is difficult to distinguish from mucous AK, especially with tumor invasion into the wall and distant metastases. There are argentaffin and argyrophilic tumors. Immunohistochemically, the endocrine component gives a positive reaction to chromogranin A, serotonin, enteroglucagon, somatostatin and PP; goblet cells express carcinoembryonic antigen. With EM, dense endocrine granules, mucus droplets, and sometimes both components are visible in the cytoplasm of the same cell.

Tubular carcinoid is often misdiagnosed as AK metastases, because the tumor is represented by small discrete tubes, sometimes with mucus in the lumen. Short trabecular structures are common; Solid nests are usually absent. In isolated cells or in small groups of cells, a positive argentaffin and argyrophilic reaction is often detected. Unlike cancer, it is characterized by an intact mucous membrane, orderly structures, and the absence of cell atypia and mitoses. The tumor is positive for chromogranin A, glucagon, serotonin, IgA and negative for protein S 100. An exocrine-endocrine tumor consists of goblet cells and structures characteristic of carcinoid and AK.

Genetic features: In contrast to AK of the colon, mutations of the KRAS gene were not found in typical carcinoid and goblet cell carcinoid of the appendix; in the latter, TP53 mutations were found in 25% of cases (mainly G:C->A:T transitions).

Cytological diagnosis: on routine smears, EC-cell and L-cell carcinoids are cytologically diagnosed as typical carcinoid NOS. Goblet cell carcinoid, tubular carcinoid, and exocrine-endocrine carcinoid cannot be identified as such cytologically. Small cell carcinoma has properties similar properties of this tumor in other parts of the gastrointestinal tract.

Rare tumors of the appendix: In the mucosa and submucosa, a non-urinoma is found, and occasionally an axial neuroma, which causes obliteration of the appendix lumen. Histological structure similar to neuron of other localizations. Gastrointestinal tract infections are rarely found in the appendix. Kaposi's sarcoma in this organ may be part of an acquired immunodeficiency syndrome. Primary PL of the appendix (Burkitt's PL) is very rare; more often, tumors of neighboring organs spread to the appendix.

Secondary tumors are not typical for the appendix: isolated cases of metastases from cancer of the gastrointestinal tract, gall bladder, genitourinary tract, breast, lungs, thymoma, melanoma have been published. Involvement of the serosa of the appendix is often associated with transintestinal spread. The cytological picture of tumors is similar to that of tumors of other organs.

Stomach Secretory. The function is to produce gastric juice by the glands. Mechanical function

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In the large intestine, water is absorbed from the chyme and feces are formed. In the large intestine

In the small intestine, the process of absorption of the breakdown products of proteins, fats and carbohydrates into the blood and lymphatic vessels also occurs. The small intestine also performs a mechanical function: it pushes chyme in the caudal direction.

Structure. The wall of the small intestine consists of the mucosa, submucosa, muscular and serous membranes.

On the surface, each intestinal villi is lined with single-layer columnar epithelium. There are three types of cells in the epithelium: bordered, goblet and endocrine (argyrophilic).

Enterocytes with a striated border make up the bulk of the epithelial layer covering the villus. They are characterized by a pronounced polarity of structure, which reflects their functional specialization: ensuring the resorption and transport of substances supplied with food.

Intestinal goblet cells are typical mucous cells in structure. They experience cyclical changes associated with the accumulation and subsequent secretion of mucus.

The epithelial lining of the intestinal crypts contains the following types of cells: bordered, borderless intestinal cells, goblet, endocrine (argyrophilic) and intestinal cells with acidophilic granularity (Paneth cells).

The lamina propria of the mucous membrane of the small intestine mainly consists of a large number of reticular fibers. They form a dense network throughout the lamina propria and, approaching the epithelium, participate in the formation of the basement membrane.

The submucosa contains blood vessels and nerve plexuses.

The muscular layer is represented by two layers of smooth muscle tissue: internal (circular) and external (longitudinal).

The serous membrane covers the intestine on all sides, with the exception of the duodenum. The lymphatic vessels of the small intestine are represented by a very widely branched network. Each intestinal villi has a centrally located lymphatic capillary that blindly ends at its apex.

Innervation. The small intestine is innervated by sympathetic and parasympathetic nerves.

Afferent innervation is carried out by the sensitive myenteric plexus, formed by the sensory nerve fibers of the spinal ganglia and their receptor endings.

Efferent parasympathetic innervation is carried out through the musculo-intestinal and submucosal nerve plexuses.

Structure thin guts. Thin intestine(intestinum tenue) – the next section of the digestive system after the stomach.

Thin intestine. IN thin gut All types of nutrients are chemically processed: proteins, fats and carbohydrates.

If you have symptoms of bloat thin guts it is necessary to immediately perform the operation, without waiting for the full classical picture of the disease to appear.

Ileum intestine- continuation of the skinny, its loops lie in the lower right part of the abdominal cavity. The last loops lie in the pelvic cavity thin guts.

Practically thin intestine can be implemented in thin, thin to thick and thick to thick. The most common type is ileocecal intussusception.

Fat intestine. In thick gut water is absorbed from the chyme and feces are formed.

Crypts in the colon gut better developed than in thin.

Colon intestine located around the hinges thin guts, which are located in the middle of the bottom.

Colonic structure guts. Colon intestine located around the hinges thin guts, which are located in the middle of the lower floor of the abdominal cavity.

The structure of the thick and blind guts. Fat intestine(intestinym crassum) – continued thin guts; is the final section of the digestive tract.

Thin intestine(intestinum tenue) – the section of the digestive system next after the stomach; zakan.

Every day, up to 2 liters of secretion are formed in the small intestine ( intestinal juice) with a pH of 7.5 to 8.0. Sources of secretion are the glands of the submucosal membrane of the duodenum (Brunner's glands) and part of the epithelial cells of the villi and crypts.

· Brunner's glands secrete mucus and bicarbonates. The mucus secreted by Brunner's glands protects the wall of the duodenum from the action of gastric juice and neutralizes hydrochloric acid coming from the stomach.

· Epithelial cells of villi and crypts(Fig. 22–8). Their goblet cells secrete mucus, and their enterocytes secrete water, electrolytes and enzymes into the intestinal lumen.

· Enzymes. On the surface of enterocytes in the villi of the small intestine there are peptidases(break down peptides into amino acids), disaccharidases sucrase, maltase, isomaltase and lactase (break down disaccharides into monosaccharides) and intestinal lipase(breaks down neutral fats into glycerol and fatty acids).

· Regulation of secretion. Secretion stimulate mechanical and chemical irritation of the mucous membrane (local reflexes), excitement vagus nerve, gastrointestinal hormones (especially cholecystokinin and secretin). Secretion is inhibited by influences from the sympathetic nervous system.

Secretory function of the colon. The crypts of the colon secrete mucus and bicarbonates. The amount of secretion is regulated by mechanical and chemical irritation of the mucous membrane and local reflexes of the enteric nervous system. Excitation of the parasympathetic fibers of the pelvic nerves causes an increase in mucus secretion with simultaneous activation of colon peristalsis. Strong emotional factors can stimulate acts of defecation with periodic release of mucus without fecal contents (“bear disease”).

Digestion of food

Proteins, fats and carbohydrates in digestive tract turn into products that can be absorbed (digestion, digestion). Digestive products, vitamins, minerals and water pass through the epithelium of the mucous membrane and enter the lymph and blood (absorption). The basis of digestion is the chemical process of hydrolysis carried out by digestive enzymes.

· Carbohydrates. Food contains disaccharides(sucrose and maltose) and polysaccharides(starches, glycogen), as well as other organic carbohydrate compounds. Cellulose it is not digested in the digestive tract, since humans do not have enzymes capable of hydrolyzing it.

à Oral cavity and stomach. a-Amylase breaks down starch into the disaccharide maltose. During the short time that food remains in the oral cavity, no more than 5% of all carbohydrates are digested. In the stomach, carbohydrates continue to be digested for an hour before the food is completely mixed with gastric juices. During this period, up to 30% of starches are hydrolyzed to maltose.

à Small intestine. a-Amylase of pancreatic juice completes the breakdown of starches into maltose and other disaccharides. Lactase, sucrase, maltase and a-dextrinase contained in the brush border of enterocytes hydrolyze disaccharides. Maltose is broken down into glucose; lactose - to galactose and glucose; sucrose - to fructose and glucose. The resulting monosaccharides are absorbed into the blood.

· Squirrels

à Stomach. Pepsin, active at pH 2.0 to 3.0, converts 10–20% of proteins into peptones and some polypeptides.

à Small intestine(Fig. 22–8)

Ú Pancreatic enzymes trypsin and chymotrypsin in the intestinal lumen They break down polypeptides into di- and tripeptides; carboxypeptidase cleaves amino acids from the carboxyl end of polypeptides. Elastase digests elastin. Overall, few free amino acids are produced.

Ú On the surface of the microvilli of bordered enterocytes in the duodenum and jejunum there is a three-dimensional dense network - the glycocalyx, in which numerous peptidases are located. It is here that these enzymes carry out the so-called parietal digestion. Aminopolypeptidases and dipeptidases break down polypeptides into di- and tripeptides, and convert di- and tripeptides into amino acids. Amino acids, dipeptides and tripeptides are then easily transported into the enterocytes through the microvilli membrane.

Ú In bordered enterocytes there are many peptidases specific for bonds between specific amino acids; within a few minutes, all remaining di- and tripeptides are converted into individual amino acids. Normally, more than 99% of the products of protein digestion are absorbed in the form of individual amino acids. Peptides are very rarely absorbed.

Rice. 22–8 . Villi and crypt of the small intestine. The mucous membrane is covered with single-layer columnar epithelium. Border cells (enterocytes) are involved in parietal digestion and absorption. Pancreatic proteases in the lumen of the small intestine break down polypeptides coming from the stomach into short peptide fragments and amino acids, followed by their transport into enterocytes. The breakdown of short peptide fragments into amino acids occurs in enterocytes. Enterocytes transfer amino acids to their own layer of the mucous membrane, from where the amino acids enter the blood capillaries. Disaccharidases associated with the glycocalyx of the brush border break down sugars into monosaccharides (mainly glucose, galactose and fructose), which are absorbed by enterocytes and subsequently released into the stratum propria and entering the blood capillaries. Digestive products (except triglycerides), after absorption through the capillary network in the mucous membrane, are sent to the portal vein and then to the liver. Triglycerides in the lumen of the digestive tube are emulsified by bile and broken down by the pancreatic enzyme lipase. The resulting free fatty acids and glycerol are absorbed by enterocytes, in the smooth endoplasmic reticulum of which triglycerides are resynthesized, and in the Golgi complex the formation of chylomicrons, a complex of triglycerides and proteins, occurs. Chylomicrons undergo exocytosis on the lateral surface of the cell, pass through the basement membrane and enter the lymphatic capillaries. As a result of contraction of SMCs located in the connective tissue of the villi, lymph moves into the lymphatic plexus of the submucosal membrane. In addition to enterocytes, the bordered epithelium contains goblet cells that produce mucus. Their number increases from the duodenum to the ileum. In the crypts, especially in the area of their bottom, there are enteroendocrine cells that produce gastrin, cholecystokinin, gastric inhibitory peptide, motilin and other hormones.

· Fats are found in food mainly in the form of neutral fats (triglycerides), as well as phospholipids, cholesterol and cholesterol esters. Neutral fats are found in foods of animal origin; they are much less in plant foods.

à Stomach. Lipases break down less than 10% of triglycerides.

à Small intestine

Ú Digestion of fats in the small intestine begins with the transformation of large fat particles (globules) into small globules - emulsification of fats(Fig. 22–9A). This process begins in the stomach under the influence of mixing fats with gastric contents. In the duodenum, bile acids and the phospholipid lecithin emulsify fats to particle sizes of 1 micron, increasing the total surface area of fats by 1000 times.

Ú Pancreatic lipase breaks down triglycerides into free fatty acids and 2-monoglycerides and is capable of digesting all chyme triglycerides within 1 minute if they are in an emulsified state. The role of intestinal lipase in the digestion of fats is small. The accumulation of monoglycerides and fatty acids at the sites of fat digestion stops the hydrolysis process, but this does not happen because micelles, consisting of several dozen molecules of bile acids, remove monoglycerides and fatty acids at the moment of their formation (Fig. 22-9A). Cholate micelles transport monoglycerides and fatty acids to the microvilli of enterocytes, where they are absorbed.

Ú Phospholipids contain fatty acids. Cholesterol esters and phospholipids are broken down by special lipases of pancreatic juice: cholesterol esterase hydrolyzes cholesterol esters, and phospholipase A 2 breaks down phospholipids.

Table 5-10.

(From: Centers for Disease Control. Foodborne disease outbreaks, annual summary, 1982. Atlanta: Centers for Disease Control, 1986; St. ME. Waterrelated disease outbreaks, 1985 MMWR CDC Surveillance Summary 1988; 37 (55-2); Yamada T ., Alpers D. H., Owyand C., Polvell D. W., Silverstein F. E., eds. Textbook of Gastroenterology, 2nd ed. Philadelphia: J. B. Lippincott, 1995: 1609.)

The mucous membrane of the small intestine consists of villi and crypts (Fig. 5-9). Crypt cambial cells are the source of enterocytes and other specialized epithelial cells that, upon differentiation, migrate along the crypt-villus axis. As they move along the villi, the cells age and slough off. In humans, such migration of enterocytes takes about 3-5 days. The cells of the villi are predominantly absorptive, and the cells of the crypts are secreting, therefore, when the villi are damaged or lost, the remaining cells are stored only in the crypts, thus , secretion begins to overall prevail over absorption, which leads to the development of secretory diarrhea. Due to damage to the mucous membrane, the absorption of nutrients from food is impaired, so unabsorbed substances also cause osmotic diarrhea. With inflammation (some infections, ulcerative colitis, disease Crohn's) enterocytes are damaged, which stimulates secretion, in addition, it is stimulated by such inflammatory mediators as prostaglandins E1 and E2, hydroxyeicosotetraenoic and hydroxyperoxyeicosotetraenoic acids. Ischemia of the small or large intestine, the effect of radiation also lead to damage and death of the epithelium, which is often accompanied by bloody stool (ischemic or radiation colitis). The term "colitis" in in this case is not entirely accurate, since the main mechanism of damage here is vascular disorders, and not inflammation. The causes of damage to the intestinal mucosa are given in table. 5-11.

Rice. 5-9.

At the base of each villi there are from 6 to 14 crypts (fewer in the proximal sections and more in the distal). In the lower parts of the crypts there are 40-50 cells with an average proliferation cycle time of 26 hours and 20-30 non-proliferating Napet cells. Cambial (fixed) cells have maximum proliferative activity. Cells from this place migrate both towards the villi and towards the base of the crypts to Paneth cells. The upper sections of the crypts contain proliferating cells that migrate to the villi. 275 cells approach the base of the villus from each crypt. The cells migrate to the tip of the villus, where they are then desquamated. (From: Yamada T., Alpcrs D.H., Owyang S., Powell D.W., Silverstein F.E., eds. Textbook of Gastroenterology, 2nd ed. Philadelphia: J.B. Lippincott, 1995:562.)

The structure of the wall of the small intestine

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The structure of the wall of the small intestine is similar in all sections. It consists of the mucous membrane, submucosa, muscular and serous membranes.

Mucous membrane

The mucous membrane has a characteristic relief due to macro- and microscopic formations, characteristic only of the small intestine. These are circular folds (more than 600), villi and crypts.

Spiral or circular folds protrude into the intestinal lumen by no more than 1 cm. The length of such folds is from half to two-thirds, sometimes up to the entire circumference of the intestinal wall. When the intestine is filled, the folds do not smooth out. As you move toward the distal end of the intestine, the size of the folds decreases and the distance between them increases. The folds are formed by the mucous membrane and submucosa (see Atl.).

Rice. 4.15. Intestinal villi and crypts of the small intestine

Rice. 4.15. Intestinal villi and crypts of the small intestine:
A - scanning microscopy;
B and C - light microscopy:
1 — villi in a longitudinal section;
2 - crypts;
3 - goblet cells;
4 - Paneth cells

The entire surface of the mucous membrane in the folds and between them is covered intestinal villi(Fig. 4.15; see Atl.). Their total number exceeds 4 million. These are miniature leaf-shaped or finger-shaped outgrowths of the mucous membrane, reaching a thickness of 0.1 mm, and a height from 0.2 mm (in the duodenum) to 1.5 mm (in the ileum). The number of villi is also different: from 20-40 per 1 mm 2 in the duodenum to 18-30 per 1 mm 2 in the ileum.

Each villus is formed by a mucous membrane; the muscular plate of the mucosa and submucosa do not penetrate into it. The surface of the villi is covered with single-layer columnar epithelium. It consists of absorptive cells (enterocytes) - about 90% of cells, between which are interspersed goblet cells that secrete mucus and enteroendocrine cells (about 0.5% of all cells). An electron microscope revealed that the surface of enterocytes is covered with numerous microvilli, forming a brush border. The presence of microvilli increases the absorption surface of the mucous membrane of the small intestine to 500 m2. The surface of the microvilli is covered with a layer of glycocalyx, which contains hydrolytic enzymes that break down carbohydrates, polypeptides and nucleic acids. These enzymes ensure the process of parietal digestion. The broken down substances are transported through the membrane into the cell and are absorbed. After intracellular transformations, the absorbed substances are released into the connective tissue and penetrate into the blood and lymphatic vessels. Side surfaces epithelial cells are firmly connected to each other using intercellular contacts, which prevents substances from entering the intestinal lumen into the subepithelial connective tissue. The number of scattered individual goblet cells gradually increases from the duodenum to the ileum. The mucus secreted by them wets the surface of the epithelium and promotes the movement of food particles.

The base of the villi consists of loose connective tissue of its own layer of the mucous membrane with a mesh of elastic fibers; blood vessels and nerves branch in it. In the center of the villus there runs a lymphatic capillary that blindly ends at the apex and communicates with the plexus of lymphatic capillaries of the submucosal layer. Along the villus there are smooth muscle cells connected by reticular fibers to the basement membrane of the epithelium and the stroma of the villus. During digestion, these cells contract, the villi shorten, thicken, and the contents of their blood and lymph vessels are squeezed out and go into the general blood and lymph flow. When the muscle elements relax, the villus straightens, swells, and absorbed through the marginal epithelium nutrients enter the vessels. Absorption is most intense in the duodenum and jejunum.

Between the villi there are tubular invaginations of the mucous membrane - crypts, or intestinal glands (Fig. 4.15; Atl.). The walls of the crypts are formed by secretory cells of various types.

At the base of each crypt are Packet cells containing large secretory granules. They contain a set of enzymes and lysozyme (a bactericidal substance). Between these cells there are small, poorly differentiated cells, due to the division of which the epithelium of the crypts and villi is renewed. It has been established that renewal of intestinal epithelial cells in humans occurs every 5-6 days. Above the Packet cells are mucus-secreting cells and enteroendocrine cells.

In total, there are more than 150 million crypts in the small intestine - up to 10 thousand per 1 cm2.

In the submucosal layer of the duodenum there are branched tubular duodenal glands that secrete a mucous secretion into the intestinal crypts, which participates in the neutralization of hydrochloric acid coming from the stomach. Some enzymes (peptidases, amylase) are also found in the secretions of these glands. The largest number of glands is in the proximal parts of the intestine, then it gradually decreases, and in distal section they disappear completely.

In the lamina propria of the mucous membrane there are many reticular fibers that form the “framework” of the villi. The muscular plate consists of an inner circular and outer longitudinal layer of smooth muscle cells. From the inner layer, individual cells extend into the connective tissue of the villi and into the submucosa. In the central part of the villus lies a blindly closed lymphatic capillary, often called the lacteal vessel, and a network of blood capillaries. The nerve fibers of the Meissner plexus are located in a similar way.
Throughout the small intestine, lymphoid tissue forms small single follicles in the mucous membrane, up to 1–3 mm in diameter. In addition, in the distal ileum, on the side opposite to the attachment of the mesentery, there are groups of nodules that form follicular plaques (Peyer's patches) (Fig. 4.16; Atl.).

Rice. 4.16. Structure of the small intestine

Rice. 4.16. Structure of the small intestine:
1 - muscular layer;
2 - mesentery;
3 - serous membrane;
4 - single follicles;
5 - circular folds;
6 - mucous membrane;
7 - follicular plaque

These are flat plates elongated along the intestine, reaching several centimeters in length and 1 cm in width. Follicles and plaques, like lymphoid tissue in general, play a protective role. In children aged 3 to 15 years, there are about 15,000 single lymph nodes. In old age, their number decreases. The number of plaques also decreases with age from 100 in children to 30-40 in adults; they are almost never found in old people. In the area where plaques are located, intestinal villi are usually absent.

Submucosa

Accumulations of fat cells are often found in the submucosa. The choroid and nerve plexuses are located here, and the secretory glands lie in the duodenum.

Muscularis

The muscular layer of the small intestine is formed by two layers of muscle tissue: the inner, more powerful, circular and the outer, longitudinal. Between these layers lies the myenteric nerve plexus, which regulates contractions of the intestinal wall.

The motor activity of the small intestine is represented by peristaltic, wave-like movements, and rhythmic segmentation (Fig. 4.17).

Rice. 4.17. Motility of the small intestine:
A - pendulum-like movement (rhythmic segmentation); B - peristaltic movements

They arise due to contraction of the circular muscles, spread through the intestine from the stomach to the anus and lead to the movement and mixing of chyme. Areas of contraction alternate with areas of relaxation. The frequency of contractions decreases in the direction from the upper intestines (12/min) to the lower (8/min). These movements are regulated by the autonomic nervous system and hormones, most of which are formed in the gastrointestinal tract itself. The sympathetic nervous system inhibits the motor activity of the small intestine, and the parasympathetic enhances it. Intestinal movements are preserved after destruction of the vagus and sympathetic nerves, but the strength of contractions is reduced, which indicates that these contractions depend on innervation; this is also true for peristalsis. Segmentation is associated with intestinal smooth muscle, which can respond to local mechanical and chemical stimuli. One such chemical is serotonin, which is produced in the intestines and stimulates its movement. Thus, contractions of the small intestine are regulated by external nerve connections, the activity of the smooth muscle itself, and local chemical and mechanical factors.

In the absence of food intake, peristaltic movements predominate, promoting the advancement of chyme. Eating slows them down - movements associated with mixing the intestinal contents begin to predominate. The duration and intensity of motor activity depends on the composition and calorie content of food and decreases in the order: fats - proteins - carbohydrates.

Serosa

The serosa covers the small intestine on all sides, with the exception of the duodenum, which is covered by peritoneum only in front.

Duodenum

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Duodenum (duodenum) has a horseshoe shape (see Atl.). The initial segment of the intestine is covered with peritoneum on three sides, i.e. located intraperitoneally. The remaining large part is attached to the posterior abdominal wall and is covered with peritoneum only in front. The remaining walls of the intestine have a connective tissue (adventitia) membrane.

In the intestine, there is an upper part, starting from the pylorus of the stomach and lying at the level of the first lumbar vertebra, a descending part, which descends on the right along the spine to the level of the third lumbar vertebra, and a lower part, passing after a slight bend upward, at the level of the second lumbar vertebra, into the jejunum. The upper part lies under the liver, in front of the lumbar part of the diaphragm, the descending part is adjacent to the right kidney, is located behind the gallbladder and transverse colon, and the lower part lies near the aorta and the inferior vena cava, in front of it the root of the mesentery of the jejunum crosses it.

The head of the pancreas is located in the flexure of the duodenum. The excretory duct of the latter, together with the common bile duct, obliquely penetrates the wall of the descending part of the intestine and opens at an elevation of the mucous membrane, which is called the major papilla. Very often 2 cm higher major papilla the small one protrudes, on which the accessory duct of the pancreas opens.

The duodenum is connected by ligaments to the liver, kidneys and transverse colon. The hepatoduodenal ligament contains the common bile duct, portal vein, hepatic artery and lymphatic vessels of the liver. The remaining ligaments contain arteries that supply blood to the stomach and mesenteries.

Jejunum and ileum

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The jejunum and ileum (ileum) intestines (see Atl.) are covered on all sides with a serous membrane (peritoneum) and are movably suspended from the posterior wall of the abdomen on the mesentery. They form many loops, which in a living person, thanks to peristaltic contractions, constantly change their shape and position, filling most peritoneal cavity.

There is no anatomical boundary between the jejunum and ileum; the loops of the first lie predominantly in the left part of the abdomen, and the loops of the second occupy its middle and right parts. In front of the small intestines is the greater omentum. In the right lower part of the abdomen (in the iliac fossa), the ileum opens into the initial part of the colon. The mesentery supplies blood vessels and nerves to the intestine.

Blood supply to the small intestine

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The blood supply to the small intestine is through the mesenteric arteries and the hepatic artery (duodenum). The small intestine is innervated by the plexuses of the autonomic nervous system of the abdominal cavity and the vagus nerve.

Causes of small intestine cancer

The first symptoms and signs of small intestine cancer in men and women

Classification of stages of small intestinal cancer. Types and Types of Small Bowel Cancer

Stages of small intestine cancer:

Diagnosis of small intestine cancer

Treatment of small intestine cancer

Forecast and prevention of small intestine (bowel) cancer

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SMALL INTESTINE EPITHELIA

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Small intestine cancer: characteristic signs and symptoms

Small bowel cancer

Clinical manifestations

Causes of small intestinal cancer

Diagnosis and treatment methods

Preventive actions

More on the topic Damage to the mucous membrane (desquamation of villous cells and inflammation):

The structure of the wall of the small intestine

Mucous membrane

Submucosa

Muscularis

Serosa

Duodenum

Jejunum and ileum

Blood supply to the small intestine