The pictures below show the gastric pit. A gastric pit (GD) is a groove or funnel-shaped invagination of the surface of the epithelium (E).
The surface epithelium consists of high prismatic mucous cells (MCs). lying on a common basement membrane (BM) with their own gastric glands (SG), which open and are visible in the depths of the dimple (see arrows). The basement membrane is often crossed by lymphocytes (L), penetrating from the lamina propria (LP) into the epithelium. In addition to lymphocytes, the lamina propria contains fibroblasts and fibrocytes (F), macrophages (Ma), plasma cells (PC) and a well-developed capillary network (Cap).
The superficial mucous cell, marked with an arrow, is shown at high magnification in Fig. 2.
To adjust the scale of the image of the cells in relation to the thickness of the entire gastric mucosa, the native glands are cut off below their necks. Cervical mucous cell (CMC). marked with an arrow, shown at high magnification in Fig. 3.
On sections of glands, one can distinguish parietal cells (PCs), protruding above the surface of the glands, and constantly rearranging chief cells (GCs). The capillary network (Cap) around one of the glands is also depicted.
PRISMATIC MUCOUS CELLS OF THE STOMACH
Rice. 2. Prismatic mucous cells (MCs) height from 20 to 40 nm, have an elliptical, basally located nucleus (N) with a prominent nucleolus, rich in heterochromatin. The cytoplasm contains rod-shaped mitochondria (M), a well-developed Golgi complex (G), centrioles, flattened cisterns of the granular endoplasmic reticulum, free lysosomes and a varying number of free ribosomes. In the apical part of the cell there are many osmiophilic PAS-positive, single-layer membrane-bound mucus droplets (MSD), which are synthesized in the Golgi complex. Vesicles containing glycosaminoglycans probably leave the cell body by diffusion; in the lumen of the gastric pit, mucigen vesicles are converted into acid-resistant mucus, which lubricates and protects the epithelium of the surface of the stomach from the digestive action of gastric juice. The apical surface of the cell contains several short microvilli covered with glycocalyx (Gk). The basal pole of the cell lies on the basement membrane (BM).
Prismatic mucous cells connected to each other by well-developed junctional complexes (K), numerous lateral interdigitations and small desmosomes. Deeper in the dimple, the superficial mucous cells continue into the cervical mucous cells. The lifespan of mucous cells is about 3 days.
CERVICAL MUCOUS CELLS OF THE STOMACH
Rice. 3. Cervical mucous cells (CMCs) concentrated in the neck area of the stomach's own glands. These cells are pyramidal or pear-shaped and have an elliptical nucleus (N) with a prominent nucleolus. The cytoplasm contains rod-shaped mitochondria (M), a well-developed supranuclear Golgi complex (G), a small number of short cisternae of the granular endoplasmic reticulum, occasional lysosomes and a certain number of free ribosomes. The supranuclear part of the cell is occupied by large PAS-positive, moderately osmiophilic, secretory granules (SGs) surrounded by single-layer membranes, which contain glycosaminoglycans. The surface of the mucous cervical cells, facing the dimple cavity, bears short microvilli covered with glycocalyx (Gk). On the lateral surface there is a good lateral ridge-like interdigitations and junctional complexes are visible (K).The basal surface of the cell is adjacent to the basement membrane (BM).
Cervical mucous cells can also be found in the deep parts of the own gastric glands; they are also present in the cardiac and pyloric parts of the organ. The function of cervical mucous cells is still unknown. According to some scientists, they are undifferentiated replacement cells for superficial mucosal cells or progenitor cells for parietal and chief cells.
In Fig. Figure 1 to the left of the text shows the lower part of the body of the gastric gland (SG), cut transversely and longitudinally. In this case, a relatively constant zigzag direction of the gland cavity becomes visible. This is due to the mutual position of parietal cells (PCs) with chief cells (GCs). At the base of the gland the cavity is usually straight.
Three types of cells can be isolated in the body and base of the gastric gland. Starting from the top, these cells are marked with arrows and are shown on the right side in Fig. 2-4 at high magnification.
MAIN CELLS
Rice. 2. Chief cells (CH) are basophilic, from cubic to low prismatic in shape, localized in the lower third or lower half of the gland. The nucleus (N) is spherical, with a pronounced nucleolus, located in the basal part of the cell. The apical plasmalemma, covered with glycocalyx (Gk), forms short microvilli. Chief cells connect to neighboring cells using junctional complexes (K). The cytoplasm contains mitochondria, developed ergastoplasm (Ep) and a well-defined supranuclear Golgi complex (G).
Zymogen granules (ZGs) originate from the Golgi complex and then transform into mature secretory granules (SGs), accumulating at the apical pole of the cell. Then their contents, by fusion of the granule membranes with the apical plasmalemma, are released by exocytosis into the gland cavity. Chief cells produce pepsinogen, which is a precursor to the proteolytic enzyme pepsin.
PARIETAL CELLS
Rice. 3. Parietal cells (PC)- large pyramidal or spherical cells with bases protruding from outer surface body of the own gastric gland. Sometimes parietal cells contain many elliptical large mitochondria (M) with densely packed cristae, a Golgi complex, several short cisternae of the granular endoplasmic reticulum, a small number of tubules of the agranular endoplasmic reticulum, lysosomes and a few free ribosomes. Branched intracellular secretory tubules (ISCs) with a diameter of 1-2 nm begin as invaginations from the apical surface of the cell, surround the nucleus (N) and almost reach the basement membrane (BM) with its branches.
Many microvilli (MV) protrude into the tubules. A well-developed system of plasmalemmal invaginations forms a network of tubular-vascular profiles (T) with contents in the apical cytoplasm and around the tubules.
Severe acidophilia of parietal cells is the result of the accumulation of numerous mitochondria and smooth membranes. Parietal cells are connected by junctional complexes (J) and desmosomes to neighboring cells.
Parietal cells synthesize hydrochloric acid through an incompletely understood mechanism. Most likely, tubular-vascular profiles actively transport chloride ions through the cell. Hydrogen ions released in the reaction of carbonic acid production and catalyzed by carbonic anhydride cross the plasmalemma by active transport, and then, together with chlorine ions, form 0.1 N. HCI.
Parietal cells produce intrinsic gastric factor, which is a glycoprotein responsible for the absorption of B12 in the small intestine. Erythroblasts cannot differentiate into mature forms without vitamin B12.
ENDOCRINE (ENTEROENDOCRINE, ENTEROCHROMAFFIN) CELLS
Rice. 4. Endocrine, enteroendocrine or enterochromaffin cells (EC) are localized at the base of the gastric glands. The cell body may have a triangular or polygonal nucleus (N), located at the apical pole of the cell. This cell pole rarely reaches the gland cavity. The cytoplasm contains small mitochondria, several short cisterns of the granular endoplasmic reticulum and the infranuclear Golgi complex, from which osmiophilic secretory granules (SG) with a diameter of 150-450 nm are separated. The granules are released by exocytosis from the cell body (arrow) to the capillaries. After crossing the basement membrane (BM), the granules become invisible. The granules produce argentaffin chromaffin reactions simultaneously, hence the term enterochromaffin cells. Endocrine cells are classified as APUD cells.
There are several classes of endocrine cells, with slight differences between them. NK cells produce the hormone serotonin, ECL cells produce histamine, G cells produce gastrin, which stimulates the production of HCl by parietal cells.
Stomach: histology, development and structure
The stomach is one of the main organs of the digestive tract. It processes all the products we consume. This is done thanks to hydrochloric acid, which is present in the stomach. Given chemical compound secreted by special cells. The structure of the stomach is represented by several types of tissues. In addition, the cells that secrete hydrochloric acid and other biologically active substances are not located throughout the organ. Therefore, anatomically, the stomach consists of several sections. Each of them differs in functional significance.
Stomach: organ histology
The stomach is a hollow, pouch-shaped organ. In addition to the chemical processing of chyme, it is necessary for the accumulation of food. To understand how digestion occurs, you should know what gastric histology is. This science studies the structure of organs at the tissue level. As you know, living matter consists of many cells. They, in turn, form tissues. The cells of the body differ in their structure. Therefore, the fabrics are also not the same. Each of them performs a specific function. Internal organs consist of several types of tissues. This ensures their activities.
The stomach is no exception. Histology studies the 4 layers of this organ. The first of these is the mucous membrane. It is located on the inner surface of the stomach. Next there is the submucosal layer. It is represented by adipose tissue, which contains blood and lymphatic vessels, as well as nerves. The next layer is the muscle layer. Thanks to it, the stomach can contract and relax. The last is the serous membrane. It is in contact with the abdominal cavity. Each of these layers is made up of cells that together form tissue.
Histology of the gastric mucosa
Normal histology of the gastric mucosa is represented by epithelial, glandular and lymphoid tissue. In addition, this shell contains a muscular plate consisting of smooth muscle. A feature of the mucous layer of the stomach is that there are many pits on its surface. They are located between the glands that secrete various biological substances. Next there is a layer of epithelial tissue. This is followed by the stomach gland. Together with lymphoid tissue, they form their own plate, which is part of the mucous membrane.
Glandular tissue has a certain structure. It is represented by several formations. Among them:
The secretory department consists of several exo- and endocrinocytes. The excretory duct of the glands of the mucous membrane exits into the bottom of the fossa located on the surface of the tissue. In addition, cells in this section are also capable of secreting mucus. The spaces between the glands are filled with coarse connective fibrous tissue.
Lymphoid elements may be present in the lamina propria of the mucous membrane. They are located diffusely, but throughout the surface. Next comes the muscle plate. It contains 2 layers of circular fibers and 1 layer of longitudinal fibers. He occupies an intermediate position.
Histological structure of the gastric epithelium
The upper layer of the mucous membrane, which is in contact with food masses, is the epithelium of the stomach. The histology of this section of the gastrointestinal tract differs from the structure of the tissue in the intestine. The epithelium not only protects the surface of the organ from damage, but also has a secretory function. This tissue lines the inside of the stomach cavity. It is located over the entire surface of the mucous membrane. Gastric pits are no exception.
The inner surface of the organ is covered with single-layer prismatic glandular epithelium. The cells of this tissue are secretory. They are called exocrinocytes. Together with the cells of the excretory ducts of the glands, they produce secretions.
Histology of the fundus of the stomach
The histology of different parts of the stomach is different. Anatomically, the organ is divided into several parts. Among them:
The fundus of the stomach is of great physiological importance. The histology of this area is complex. The fundus contains the stomach's own glands. Their number is about 35 million. The depth of the pits between the fundic glands occupies 25% of the mucous membrane. The main function of this department is the production of hydrochloric acid. Under the influence of this substance, biological activation occurs active substances(pepsin), digestion of food, and also protects the body from bacterial and viral particles. Proprietary (fundic) glands consist of 2 types of cells - exo- and endocrinocytes.
Histology of the submucous membranes of the stomach
As in all organs, under the mucous membrane of the stomach there is a layer of fatty tissue. In its thickness there are vascular (venous and arterial) plexuses. They supply blood to the inner layers of the stomach wall. In particular, the muscular and submucosal membranes. In addition, this layer contains a network of lymphatic vessels and a nerve plexus. The muscular lining of the stomach is represented by three layers of muscle. This is a distinctive feature of this body. Longitudinal muscle fibers are located outside and inside. They have an oblique direction. Between them lies a layer of circular muscle fibers. As in the submucosa, there is a nerve plexus and a network of lymphatic vessels. The outside of the stomach is covered with a serous layer. It represents the visceral peritoneum.
Benign neoplasms of the stomach and intestines: histology of hemangioma
One of the benign neoplasms is hemangioma. Histology of the stomach and intestines is necessary for this disease. Indeed, despite the fact that the formation is benign, it should be differentiated from cancer. Histologically, hemangioma is represented by vascular tissue. The cells of this tumor are fully differentiated. They are no different from the elements that make up the arteries and veins of the body. Most often, gastric hemangioma forms in the submucosal layer. The typical location for this benign neoplasm is the pyloric region. The tumor can have different sizes.
In addition to the stomach, hemangiomas can be localized in the small and large intestines. These formations rarely make themselves felt. However, diagnosing hemangiomas is important. At large sizes and constant traumatization (chyme, feces), serious complications can arise. The main one is profuse gastrointestinal bleeding. It is difficult to suspect a benign neoplasm, since in most cases clinical manifestations are missing. An endoscopic examination reveals a dark red or bluish round spot rising above the mucous membrane. In this case, a diagnosis of hemangioma is made. The histology of the stomach and intestines is of decisive importance. In rare cases, hemangioma undergoes malignant transformation.
Gastric regeneration: histology in ulcer healing
One of the indications for histological examination is gastric ulcer. For this pathology, it is carried out endoscopic examination(FEGDS) with taking a biopsy. Histology is required if an ulcer is suspected of malignancy. Depending on the stage of the disease, the tissue obtained may vary. When the ulcer heals, the stomach scar is examined. In this case, histology is needed only if there are symptoms due to which malignant degeneration of the tissue can be suspected. If there is no malignancy, then the analysis reveals cells of coarse connective tissue. When a gastric ulcer becomes malignant, the histological picture may be different. It is characterized by changes in the cellular composition of the tissue and the presence of undifferentiated elements.
What is the purpose of gastric histology?
One of the organs of the digestive tract in which neoplasms often develop is the stomach. Histology should be performed if there is any change in the mucous membrane. The following diseases are considered indications for this study:
The listed pathologies refer to precancerous diseases. This does not mean that the patient has malignant tumor, and its localization is the stomach. Histology helps determine exactly what changes are observed in the tissues of the organ. To prevent the development of malignant degeneration, it is worth conducting research as early as possible and taking action.
Gastric histology results
The results of histological examination may vary. If the organ tissue is not changed, then microscopy reveals normal prismatic single-layer glandular epithelium. When taking a biopsy of deeper layers, you can see smooth muscle fibers and adipocytes. If the patient has a scar from a protracted ulcer, then rough fibrous connective tissue is found. For benign formations, histological results may be different. They depend on the tissue from which the tumor developed (vascular, muscle, lymphoid). The main feature of benign formations is cell maturity.
Sampling of stomach tissue for histology: methodology
To perform a histological examination of stomach tissue, it is necessary to perform a biopsy of the organ. In most cases, it is performed using endoscopy. The apparatus for performing FEGDS is placed into the lumen of the stomach and several pieces of organ tissue are cut off. It is advisable to take biopsies from several distant sites. In some cases, tissue for histological examination is taken during surgical intervention. After this, thin sections from the biopsy are taken in the laboratory and examined under a microscope.
How long does a histological analysis of stomach tissue take?
If you suspect oncological diseases gastric histology is required. How long does this analysis take? Only the attending physician can answer this question. On average, histology takes about 2 weeks. This applies to planned studies, for example, when removing a polyp.
During surgery, urgent histological examination of the tissue may be necessary. In this case, the analysis takes no more than half an hour.
Which clinics perform histological analysis?
Some patients are interested in: where can gastric histology be done urgently? This study is carried out in all clinics that have the necessary equipment and laboratory. Urgent histology is carried out in oncology clinics and some surgical hospitals.
Atrophy of the gastric mucosa
Atrophy of the gastric mucosa - pathological process, developing as a result of inflammation. With atrophy, there is a gradual death of functioning cells and their replacement with scar tissue, and then its thinning.
Foci of atrophy can be detected with any gastritis, but in the classification of gastric diseases it stands out special shape- atrophic gastritis, for which such changes are most characteristic. It is important that this disease is a precancerous pathology. Therefore, all patients require treatment and medical supervision.
In the International Classification, chronic atrophic gastritis is taken into account under code K 29.4.
Characteristics of the atrophy process
The most common location for atrophy of the gastric mucosa is the lower third of the body or antrum. One of the main damaging factors is considered to be Helicobacter, which lives closer to the pyloric zone.
At the initial stage, glandular (goblet) cells produce hydrochloric acid even in excess. Perhaps this process is associated with the stimulating effect of the bacterial enzyme system.
Then the synthesis of gastric juice is replaced by mucus, and the acidity gradually decreases.
By this time, the protective role of the mucous membrane is lost. Any food chemicals can harm the cells lining the inside of the stomach. Toxic products and remnants of destroyed cells become foreign to the body.
The autoimmune mechanism is involved in the destruction process. Antibodies are produced against damaged cells, which continue to fight their own epithelium. Important role plays a role in blocking recovery processes.
In a healthy stomach epithelial layer updated completely every 6 days. Here, old dysfunctional cells remain in place or they are replaced with connective tissue.
On histology, instead of clear outlines of the epithelium (look at top edge) destroyed cells are visible, piriform glands are absent
In any case, the atrophied mucosa cannot replace gastric juice with mucus. There is a gradual thinning of the stomach wall. In practice, the organ is excluded from digestion, and gastrin production increases. The bolus of food enters the small intestine unprepared, which leads to failure of other successive stages.
The process doesn't end there. The most dangerous period of atrophic changes begins: the epithelium begins to produce similar, but not true, cells. Most often they can be classified as intestinal. They are not able to produce gastric secretions. This process is called metaplasia and dysplasia (transformation), and precedes cancerous degeneration.
Atrophied areas on the mucous membrane cannot be completely restored, but with the help of treatment there is still a chance to support the remaining functioning cells, compensate for the lack of gastric juice and prevent disruption of the overall digestive process.
Causes
Most common reasons diseases are considered: exposure to Helicobacter and autoimmune factors. Researchers have proposed distinguishing external (exogenous) and internal (endogenous) damage factors that can cause atrophic changes mucous membrane. External ones include toxic substances entering the stomach and malnutrition.
Toxic to the stomach are:
- nicotine, a decomposition product of tobacco products;
- dust particles of coal, cotton, metals;
- arsenic, lead salts;
- alcohol-containing liquids;
- medications from the Aspirin group, sulfonamides, corticosteroids.
- a person eats irregularly, periods of hunger alternate with overeating;
- mainly eat fast food, spicy and fatty dishes, “dry food”;
- cold or too hot food (ice cream, tea) enters the stomach;
- insufficiently chewed food in the mouth due to diseases of the teeth, gums, poor prosthetics, lack of teeth in old age.
- any disorders of the neuroendocrine regulation of secreting cells, leading to disruption of regeneration processes (stress, chronic diseases nervous system, myxedema, diabetes, dysfunction of the pituitary gland and adrenal glands);
- general human diseases that disrupt blood flow in the wall of the stomach and regional vessels (thrombosis, severe atherosclerosis), congestion in the veins against the background of increased pressure in the portal system;
- cardiac and respiratory failure, accompanied by tissue hypoxia (lack of oxygen);
- deficiency of vitamin B 12 and iron in the body;
- hereditary predisposition - consists of a genetically determined lack of factors to restore the cellular composition of the mucosa.
- weight loss;
- symptoms of vitamin deficiency (dry skin, hair loss, bleeding gums, mouth ulcers, headaches);
- hormonal problems, expressed in men as impotence, in women as impaired menstrual cycle, infertility;
- increased irritability, tearfulness, insomnia.
- focal atrophy - areas of atrophy with normal tissue alternate on the mucosa; this process is most favorable for treatment, because there are still cells capable of taking on a compensatory function;
- diffuse - a severe widespread process, covers the entire antrum and rises to the cardia, almost all cells are affected, instead of a mucous layer, continuous fibrosis appears.
Food can turn into exogenous damage factors if:
This "workaholic's dream" saturates the body, but is not a healthy food
Internal reasons include:
Signs of atrophy
Symptoms of atrophy of the gastric mucosa appear late, when acidity reaches zero. Young and middle-aged men are more often affected. Pain syndrome is absent or very weakly expressed, which is why they consult a doctor at an advanced stage of the process.
Signs of atrophy do not differ from the general symptoms of gastric disorders. Patients note a feeling of heaviness in the epigastrium immediately after eating, sometimes nausea, belching, bloating, loud rumbling, bad smell from the mouth and unstable stool.
Attacks of nausea and dyspeptic disorders are symptoms of pathology
The presence of signs of impaired digestion is indicated by:
Diagnostics
Atrophy of the gastric mucosa can only be diagnosed visually. It used to be determined by a pathologist or surgeon, but nowadays the widespread use of fibrogastroscopic technology makes it possible not only to record the picture in different parts of the stomach, but also to take material for histological examination, to divide the process into types and degrees of functional disorders.
Histologically, the infiltration of cells of the mucous layer by lymphocytes, destruction of the glandular epithelium, thinning of the wall, and impaired folding are revealed. Cracks and erosions may appear.
Depending on the size of the affected area, the following are distinguished:
Based on the number of lost and remaining healthy cells, the degrees of atrophic changes are distinguished:
With subatrophy, shortening of the cells of the epithelial layer is observed
Depending on the severity of the atrophic process, histological changes are assessed as:
In diagnosing pathology, it is not enough to establish that the gastric mucosa is atrophic; in order to try to stop the process, the doctor needs to know the cause of the changes, the degree of dysfunction of the organ.
To do this, the patient undergoes the following studies: detection of antibodies to Helicobacter and to Castle factor (components of parietal cells) in the blood, determination of the ratio of pepsinogen I, pepsinogen II (protein components for the production of hydrochloric acid), the method is considered a marker of atrophy, since it allows one to judge the remainder of intact epithelial glands.
It is also necessary to study gastrin 17, a hormonal substance responsible for endocrine regulation secretion of epithelial cells, their restoration and motility of gastric muscle tissue and daily pH-metry to identify the nature of acid formation.
To identify Helicobacter, all patients with atrophic gastritis are prescribed a urease breath test by the attending physician.
What types of gastritis develop based on epithelial atrophy?
Depending on the degree of development and localization of the inflammation process in the stomach with mucosal atrophy, it is customary to distinguish several types of gastritis.
Surface
The mildest form of the disease. The acidity of gastric juice is almost normal. Happening copious discharge mucus glands, so protection is maintained. Histology shows signs of degeneration.
Focal
Acidity is maintained by areas of healthy epithelium. The mucosa shows alternating areas of atrophy and sclerosis with healthy tissue. Symptoms include intolerance to milk and eggs. This suggests a role for immune dysfunction.
Diffuse
The surface of the stomach is covered with a proliferation of immature cells, pits and ridges, and the structure of the mucosal glands is disrupted.
Erosive
In the atrophy zone, circulatory disturbance occurs, which gives a picture of spotty hemorrhages and accumulation of blood vessels. The course is severe with gastric bleeding. More often observed in alcoholics and people who have had a respiratory infection.
Antral
Named for the predominant localization of the lesion. It is characterized by cicatricial changes in the antral zone, narrowing of the pyloric region, and a tendency to develop into an ulcerative process.
Treatment
The problem of how to treat mucosal atrophy depends on the predominant aggressive action, the identified cause of the process, and the residual ability to recover (reparation). Given the absence of severe symptoms, patients are often treated on an outpatient basis. Mandatory recommendations include: regimen and diet.
It is not recommended to engage in strenuous sports; it is necessary to reduce physical activity to moderate. It is required to stop smoking and drinking alcoholic beverages, including beer. It is prohibited to take any medications without permission, including those for headaches and flu.
Diet Requirements
The patient's diet includes choosing foods that do not damage or irritate the gastric mucosa. Therefore, it is strictly prohibited:
The patient is advised to maintain meals in small, frequent meals. Use stewed, boiled, steamed, baked dishes. In case of pain, it is advised to switch to semi-liquid pureed food for several days (meatballs, low-fat broths, oatmeal on water, jelly).
If pain does not play a serious role in the clinic, then the diet should be varied, taking into account the given restrictions. Allowed:
About mineral water the patient needs to consult a doctor, since the choice depends on the acidity of the gastric juice, and it can vary during the process of atrophy.
Drug therapy
To restore the gastric mucosa, it is necessary to get rid of the harmful effects of Helicobacter, if present, and block a possible autoimmune process. To combat bacterial infection a course of eradication is used.
A combination of tetracycline and penicillin antibiotics with Metronidazole (Trichopol) is prescribed. The course and dosage are chosen by the doctor individually.
Good results are accompanied by treatment with De-Nol (based on bismuth citrate)
To confirm the effectiveness, control studies are carried out on Helicobacter. In the initial stage of atrophy, when acidity may be increased, proton pump inhibitor drugs are recommended. They suppress the mechanism of hydrochloric acid production.
The group includes:
When hypo- and anacid states occur, these drugs are contraindicated. Acidin-pepsin and gastric juice are prescribed to replace one's own secretion. Stimulates the regeneration process Solcoseryl, Aloe in injections. Domperidone and prokinetics can support and improve gastric motor function.
Preparations based on bismuth and aluminum (Vicalin, Kaolin, bismuth nitrate) protect the mucous membrane from chemicals and bacteria from food products. If during the diagnostic process it becomes obvious that the body is in an autoimmune state, the patient is prescribed corticosteroid hormones to suppress an excessive immune reaction.
In severe cases of atrophy, the pathology is supplemented by a disruption in the production of enzymes by all organs involved in digestion. Therefore, enzymatic agents may be required: Panzinorm, Festal, Creon.
In case of connection B 12 -deficiency anemia courses of vitamin B 12 and folic acid.
So far, the fibrogastroscopic method is the only most accessible way for patients to confirm the diagnosis of atrophy
Folk and herbal remedies
The traditional method of treatment should be approached with caution, taking into account acidity. With normal secretory function, you can take decoctions of chamomile and calendula.
If it is reduced, rosehip decoction and diluted juices of tomatoes, lemon, and potatoes are recommended to stimulate acid formation. At the pharmacy you can buy herbal teas with plantain, thyme, wormwood, and St. John's wort. It is convenient to use the herbal medicine Plantaglucid. It consists of granulated plantain extract, diluted in warm water before taking.
The most significant problem modern medicine is to identify patients and prevent cancer transformation. It is difficult to organize fibrogastroscopic examinations of patients if they have little concern. Members of a family in which more than one case of atrophic gastritis has been identified are much more attentive to prevention and have deaths from stomach cancer.
Such patients should undergo fibrogastroscopy once a year, follow a diet, stop smoking and drinking alcohol. No one can be sure what difficulties these people will have to overcome in life, and how their stomach will tolerate genetic predisposition.
The structure of the stomach wall
For readers of my blog interested in Human anatomy and physiology, we will present in detail structure of the stomach wall .
The stomach wall consists of the following layers:
I.Mucous membrane.
II. Submucosal layer.
III. Muscular membrane.
IV. Serous membrane.
I. Let's talk about the gastric mucosa.
The mucous membrane is represented by:
1. Single-layer, single-row, prismatic glandular (superficial pitted) epithelium.
2. Own muscle plate.
3. Basement membrane (lamina propria).
Note that the mucous membrane of the stomach is a continuation of the mucous membrane of the esophagus. At the junction of the esophagus with the stomach there is a serrated strip, which is the boundary between the multilayered epithelium of the mucous membrane of the esophagus and the single-layered columnar epithelium of the stomach. The surface of the cells is covered with mucus synthesized by mucocytes.
Outwardly, it is noticeable that the mucous membrane is divided into small, 1-6 mm in diameter, protruding areas, which are called gastric fields. They have a polygonal shape and are separated from each other by grooves in which there are layers of connective tissue and superficial veins. In these fields there are special depressions - gastric dimples, 0.2 mm in diameter, surrounded by villous folds. These folds are most pronounced in the pyloric region. The openings of 1-2 ducts of the gastric glands open into each dimple.
Let's give some numbers. The thickness of the normal gastric mucosa is 0.25-1.5 mm. the total area is 500-800 cubic centimeters, and the number of glands can be from 4 to 25 million. On one square centimeter of the mucous membrane there are up to 60 gastric pits, and each pit contains 4-5 glands. The microvasculature of the gastric mucosa makes up 67-72% of the total blood flow of the stomach, the submucosal layer accounts for 13%, and muscle layer – 15%.
The mucous membrane forms folds that have different directions in different sections: along the lesser curvature there are longitudinal folds, in the area of the fundus and body of the stomach - transverse, oblique and longitudinal. They allow you to significantly increase the surface of the stomach, increase the area of contact of food with the mucous membrane and promote more efficient digestion.
Microscopically, three zones are distinguished in the gastric mucosa: cardiac, fundic and pyloric. The boundaries of these zones are unclear and they gradually transform into one another, with the width of the intermediate zones being about 1 cm. The zones generally coincide with the anatomical sections, but not completely. Each zone contains characteristic types of glands:
- cardiac glands are located in the cardia region;
- the main glands of the stomach - in the area of the fundus and body of the stomach;
- intermediate gastric glands - in the mucous membrane of the intermediate part of the stomach, between the body and the pylorus;
- pyloric glands of the stomach - in the mucous membrane of the pylorus.
The superficial pitted epithelium of the mucosa is represented by cylindrical (prismatic) epithelial cells (mucocytes), arranged in one layer. The epithelial layer contains:
a) cells of the APUD system, in which biogenic amines and peptide hormones are synthesized, regulating the secretory and motor activity of the digestive organs, depending on the quantitative and qualitative composition of food;
b) intraepithelial lymphocytes: collect and transmit information about the antigenic properties of food to other cells of the immune system, have a cytotoxic effect against bacteria supplied with food.
The muscular plate of the mucous layer, together with the submucosal layer, creates the basis for the formation of numerous folds by the mucous membrane.
The basement membrane or lamina propria (stroma of the mucous membrane) is its own layer of loose connective tissue, in which blood and lymphatic vessels are located, forming the microvasculature, arteriole-venular shunts, fenestrated capillaries, gastric glands, intercellular substance represented by reticular, precollagen and collagen fibers and numerous cells:
- cells of lymphoid tissue - fibroblasts, reticular, mast cells, plasma cells, lymphocytes varying degrees maturity and granulocytes, united into reticular tissue or which can be represented by single and group follicles;
- granulocytes and lymphocytes migrating from the blood. They provide antibacterial and antitoxic effects and are involved in digestive leukopidesis. Let us dwell on digestive leukopidesis in more detail.
It is known that at the height of digestion in the lamina propria the number of basophils, neutrophils, eosinophils and lymphocytes increases significantly. Wherein:
- basophils secrete compounds that increase vascular permeability and the number of intercellular substance. This causes swelling and loosening of the lamina propria, which promotes cell migration;
- neutrophils secrete hydrolytic enzymes (lysozyme, lactoferrin), which have an antibacterial effect;
— eosinophils and lymphocytes neutralize toxic substances due to their participation in local immune reactions.
Let's look at the functions of the eigenplate:
1. Support-mechanical.
Maintains the structure of the epithelial layer.
2. Transport-trophic.
Ensuring the diffusion of various compounds from the surface and epithelial cells into the blood.
3. Participates in digestive leukopidesis.
4. Lymphoid tissue of the lamina propria provides local protection against antigens of various natures (toxins, viruses, bacteria) that enter with food, carrying out phagocytosis and synthesis of immunoglobulins A.
II. The submucosal layer of the stomach wall is involved in the formation of folds and promotes stretching of the organ.
III. The muscular layer ensures gastric peristalsis, which allows for rhythmic movement of food. It is represented by three layers:
1. Longitudinal layer of muscles. It is a continuation of the longitudinal muscles of the esophagus and is located in the fundus and body of the stomach. More powerful bundles are located along the lesser curvature and especially increase in the area of the pylorus.
2. Circular layer. It is also a continuation of a similar layer of muscles of the esophagus, evenly covers the entire stomach, becomes thinner in the fundus and thickens in the area of the pylorus, thereby forming the pyloric sphincter.
3. Inner oblique layer. Does not completely cover the stomach. Its main part first runs longitudinally, then forms an arc and goes to the greater curvature of the stomach. In the bottom area, the beams of this layer are mixed with the beams of the circular layer. One of the powerful muscle groups of this layer covers the cardia, and the other, the longest and most developed, is directed to the border between the body and the sinus and is called the lower segmental loop, which ensures the motor activity of the stomach during digestion.
IV. Serous membrane. or mesothelium, ensures the mobility of the stomach and reduces resistance to friction of organs abdominal cavity. It covers the entire anterior and posterior walls of the stomach, with the exception of a small area on back wall at the cardia itself and along the greater and lesser curvature, as well as at the points of attachment of the ligaments - there the peritoneum covering the stomach passes onto the ligaments and forms a duplication.
The human stomach contains glands that digest food. These include parietal cells. During normal functioning of the glands, a person does not experience unpleasant or pain. Proper nutrition is required for the body to function properly. If a person often eats unhealthy food, the glands of the stomach, including the parietal cells, suffer.
Digestion in the stomach
The stomach consists of three parts:
- cardiac - located near the esophagus;
- fundamental - the main part;
- pyloric - near the duodenum.
Inside there is a mucous membrane that is the first to come into contact with food coming from the esophagus. In addition, there is a muscular and serous membrane. They are responsible for motor and protective functions.
The mucous membrane contains an epithelial layer, which contains a large number of glands. They secrete a secretion that allows them to digest food. Gastric juice is produced constantly, but its amount is influenced by hormones and the brain. Thoughts about food and the smell make the glands work more actively. Thanks to this, up to 3 liters of secretion are produced per day.
Types of stomach glands
The glands in the stomach have a variety of shapes. The number is in the millions. Each gland has its own function. They come in the following types:
What is a parietal cell
The cell is shaped like a cone or pyramid. The number is higher in men than in women. Parietal cells secrete hydrochloric acid. For the process to occur, the participation of histamine, gastrin and acetylcholine is required. They act on the cell through special receptors. The amount of hydrochloric acid is regulated by the nervous system.
Previously, in case of gastric ulcer, part of the organ was removed for better functioning. But in practice it turned out that if the part in which the parietal cells were located was cut out, then digestion slowed down. The patient had complications after surgery. At the moment, this method of treatment has been abandoned.
Features and Functions
A distinctive feature of parietal cells is their single location outside the mucous cells. They are larger than other epithelial cells. Appearance they are asymmetrical; the cytoplasm contains one or two nuclei.
Inside the cells there are tubules responsible for transporting ions. From the inside, the channels pass into the external environment of the cell and open the lumen of the gland. There are villi on the surface, microvilli are located inside the tubules. Another feature of cells is a large number of mitochondria. The main function of parietal cells is to produce ions that contain hydrochloric acid.
Hydrochloric acid is required to destroy pathogenic bacteria and reduce the rotting of food debris. Thanks to it, the digestion process goes faster, proteins are absorbed more easily.
Factors affecting the functioning of the glands
The following factors influence the proper functioning of the gastric glands:
- healthy eating;
- emotional condition person;
- stressful situations;
- chronic diseases of the liver and gall bladder;
- alcohol abuse;
- long-term use of medications that irritate receptors;
- chronic gastritis;
- stomach ulcer;
- smoking.
When work is disrupted, chronic diseases occur. Non-compliance with the rules healthy image life provokes the risk of degeneration of healthy cells into malignant neoplasms. Stomach cancer is not immediately recognized. The fact is that the process begins gradually, and the patient does not see a doctor for a long time.
The work of the glands is important for the digestion of food, so it is important to prevent the development of stomach diseases and undergo regular medical examinations and avoid as much as possible surgical intervention.
Autoimmune gastritis
Sometimes a person develops a Disease in which the body perceives its own cells as enemies and begins to destroy them. In practice, such gastritis is rare and is characterized by the death of the gastric mucosa and the destruction of the gastric glands.
As a result of a malfunction in the body, the production of gastric juice is reduced, and problems arise with the digestion of food. At the same time, the level decreases internal factor Castle and vitamin B12 deficiency appears, which leads to the development of anemia.
Typically, autoimmune gastritis develops into a chronic form. In this case, the patient experiences accompanying illnesses thyroid gland. The disease is difficult to diagnose and cannot be completely cured. Patients take medications throughout their lives.
The appearance of antibodies to Castle factor and parietal cells is detected by immunoglobulins, which indicate that vitamin B12 has ceased to be absorbed.
Causes and symptoms of autoimmune gastritis
The exact reasons for the development are still unknown of this disease. But there are a number of assumptions explaining what can trigger the process of self-destruction in the body:
The symptoms of the disease differ little from other diseases of the gastrointestinal tract. First of all, patients pay attention to:
- pain in the stomach;
- heaviness and discomfort after eating;
- nausea;
- bowel dysfunction;
- burping;
- rumbling in the stomach;
- constant flatulence.
In addition to the main signs, a person may be tormented by symptoms to which he does not attach importance. Low blood pressure, constant fatigue, sweating, weight loss and pale skin are secondary signs of the disease. For doctors, the main reason indicating autoimmune gastritis is the condition that antibodies to parietal cells are elevated.
Diagnosis and treatment of autoimmune gastritis
To make a diagnosis, the doctor collects data about the patient. Anamnesis and current complaints suggest what disease is tormenting the person. To confirm or refute the diagnosis, the following measures are required:
- general and biochemical blood test;
- immunological analysis for antibodies to parietal cells;
- level of gastric juice secretion;
- FGDS;
- Ultrasound of internal organs;
- determination of vitamin B12 levels.
Based on the examination, the doctor determines the diagnosis. Autoimmune gastritis cannot be treated. All drugs are aimed at reducing discomfort and improving quality of life.
At severe pain painkillers and antispasmodics are prescribed. Additionally, it is necessary to take enzymes to improve food digestion. A course of B vitamins and folic acid is taken. A diet is prescribed with the exclusion of foods that have Negative influence on the gastric mucosa.
The wall of the small intestine is composed of mucous membrane, submucosa, muscular and serous membranes.
The inner surface of the small intestine has a characteristic relief due to the presence of a number of formations - circular folds, villi and crypts (intestinal glands of Lieberkühn). These structures increase the overall surface small intestine, which contributes to the performance of its basic digestive functions. Intestinal villi and crypts are the main structural and functional units of the mucous membrane of the small intestine.
The mucous membrane of the small intestine consists of a single-layer prismatic bordered epithelium of the own layer of the mucous membrane and the muscular layer of the mucous membrane.
The epithelial layer of the small intestine contains four main cell populations:
- * columnar epithelial cells,
- * goblet exocrinocytes,
- * Paneth cells, or exocrinocytes with acidophilic granules,
- * endocrinocytes, or K-cells (Kulchitsky cells),
- * as well as M-cells (with microfolds), which are a modification of columnar epithelial cells.
The small intestine includes three sections: duodenum, jejunum and ileum.
In the small intestine they undergo chemical treatment all types nutrients- proteins, fats and carbohydrates.
Enzymes of pancreatic juice (trypsin, chymotrypsin, collagenase, elastase, carboxylase) and intestinal juice (aminopeptidase, leucine aminopeptidase, alanine aminopeptidase, tripeptidase, dipeptidase, enterokinase) are involved in the digestion of proteins.
Enterokinase is produced by cells of the intestinal mucosa in an inactive form (kinazogen) and ensures the conversion of the inactive enzyme trypsinogen into active trypsin. Peptidases provide further sequential hydrolysis of peptides, which began in the stomach, to free amino acids, which are absorbed by intestinal epithelial cells and enter the blood.
In the small intestine, the process of absorption of the breakdown products of proteins, fats and carbohydrates into the blood and lymphatic vessels occurs. In addition, the intestine performs a mechanical function: it pushes chyme in the caudal direction. This function is carried out due to peristaltic contractions of the muscular lining of the intestine. The endocrine function performed by special secretory cells is the production of biologically active substances - serotonin, histamine, motilin, secretin, enteroglucagon, cholecystokinin, pancreozymin, gastrin and gastrin inhibitor.
Intestinal juice is a cloudy, viscous liquid, a product of the activity of the entire mucous membrane of the small intestine, has a complex composition and different origins. A person secretes up to 2.5 liters of intestinal juice per day. (Potyrev S.S.)
The crypts of the mucous membrane of the upper part of the duodenum contain duodenal, or Brunner's, glands. The cells of these glands contain secretory granules of mucin and zymogen. The structure and function of Brunner's glands are similar to the pyloric glands. The juice of Brunner's glands is a thick, colorless liquid of a slightly alkaline reaction, which has little proteolytic, amylolytic and lipolytic activity. Intestinal crypts, or Lieberkühn's glands, are located in the mucous membrane of the duodenum and the entire small intestine and surround each villi.
Many epithelial cells of the crypts of the small intestine have secretory ability. Mature intestinal epithelial cells develop from undifferentiated borderless enterocytes, which predominate in the crypts. These cells have proliferative activity and replenish intestinal cells that are desquamated from the tips of the villi. As they move toward the apex, the borderless enterocytes differentiate into absorptive villous cells and goblet cells.
Intestinal epithelial cells with striated borders, or absorptive cells, cover the villus. Their apical surface is formed by microvilli with outgrowths of the cell membrane, thin filaments that form the glycocalyx, and also contains many intestinal enzymes translocated from the cell where they were synthesized. Lysosomes located in the apical part of cells are also rich in enzymes.
Goblet cells are called unicellular glands. The cell overflowing with mucus has the characteristic appearance of a glass. Mucus secretion occurs through breaks in the apical plasma membrane. The secretion has enzymatic, including proteolytic, activity. (Potyrev S.S.)
Enterocytes with acidophilic granules, or Paneth cells, also have morphological characteristics secretion. Their granules are heterogeneous and are released into the lumen of the crypts according to the type of merocrine and apocrine secretion. The secretion contains hydrolytic enzymes. The crypts also contain argentaffin cells that perform endocrine functions.
Even in the cavity of the small intestinal loop, isolated from the rest of the intestine, the contents are the product of many processes (including desquamation of enterocytes) and two-way transport of high- and low-molecular substances. This, in fact, is intestinal juice.
Properties and composition of intestinal juice. During centrifugation, intestinal juice is divided into liquid and dense parts. The ratio between them varies depending on the strength and type of irritation of the mucous membrane of the small intestine.
The liquid part of the juice is formed by secretions, solutions of inorganic and organic substances transported from the blood, and partly by the contents of destroyed intestinal epithelial cells. The liquid part of the juice contains about 20 g/l of dry matter. Inorganic substances (about 10 g/l) include chlorides, bicarbonates and phosphates of sodium, potassium, and calcium. The pH of the juice is 7.2-7.5, with increased secretion it reaches 8.6. Organic matter The liquid part of the juice is represented by mucus, proteins, amino acids, urea and other metabolic products.
The dense part of the juice is a yellowish-gray mass that looks like mucous lumps and includes undestroyed epithelial cells, their fragments and mucus - the secretion of goblet cells has a higher enzymatic activity than the liquid part of the juice (G.K. Shlygin).
In the mucous membrane of the small intestine, a continuous change in the layer of surface epithelial cells occurs. They are formed in the crypts, then move along the villi and are exfoliated from their tips (morphokinetic, or morphonecrotic, secretion). Complete renewal of these cells in humans occurs in 1-4-6 days. Such a high rate of formation and rejection of cells ensures a fairly large number of them in the intestinal juice (about 250 g of epithelial cells are rejected per day in a person).
Mucus forms a protective layer that prevents excessive mechanical and chemical exposure chyme onto the intestinal mucosa. The activity of digestive enzymes is high in mucus.
The dense part of the juice has significantly greater enzymatic activity than the liquid part. The bulk of enzymes are synthesized in the intestinal mucosa, but some of them are transported from the blood. Intestinal juice contains more than 20 different enzymes that take part in digestion.
The main part of intestinal enzymes takes part in parietal digestion. Carbohydrates are hydrolyzed by b-glucosidases, b-galactasidase (lactase), glucoamylase (g-amylase). β-glucosidases include maltase and trehalase. Maltase hydrolyzes maltose, and trehalase hydrolyzes trehalose into 2 glucose molecules. b-Glucosidases are represented by another group of disaccharidases, which includes 2-3 enzymes with isomaltase activity and invertase, or sucrase; with their participation, monosaccharides are formed. (Briefly T.F.)
The high substrate specificity of intestinal disaccharidases when they are deficient causes intolerance to the corresponding disaccharide. Genetically fixed and acquired lactase, trehalase, sucrase and combined deficiencies are known. A significant population of people, especially the peoples of Asia and Africa, have been diagnosed with lactase deficiency.
In the small intestine, the hydrolysis of peptides continues and is completed. Aminopeptidases constitute the bulk of enterocyte brush border peptidase activity and cleave the peptide bond between two specific amino acids. Aminopeptidases complete membrane hydrolysis of peptides, resulting in the formation of amino acids - the main absorbable monomers.
Intestinal juice has lipolytic activity. Intestinal monoglyceride lipase is of particular importance in the parietal hydrolysis of lipids. It hydrolyzes monoglycerides of any hydrocarbon chain length, as well as short-chain di- and triglycerides, and to a lesser extent medium-chain triglycerides and cholesteryl esters. (Potyrev S.S.)
A number of food products contain nucleoproteins. Their initial hydrolysis is carried out by proteases, then the RNA and DNA cleaved from the protein part are hydrolyzed by RNA and DNases, respectively, to oligonucleotides, which, with the participation of nucleases and esterases, are degraded to nucleotides. The latter are attacked by alkaline phosphatases and more specific nucleotidases, releasing nucleosides that are then absorbed. The phosphatase activity of intestinal juice is very high.
The enzyme spectrum of the mucous membrane of the small intestine and its juice changes under the influence of certain long-term diets.
Regulation of intestinal secretion. Food intake, local mechanical and chemical irritation of the intestine increase the secretion of its glands using cholinergic and peptidergic mechanisms.
In the regulation of intestinal secretion, local mechanisms play a leading role. Mechanical irritation of the mucous membrane of the small intestine causes an increase in the secretion of the liquid part of the juice. Chemical stimulators of secretion of the small intestine are products of the digestion of proteins, fats, pancreatic juice, hydrochloric and other acids. Local impact products of digestion of nutrients causes the separation of intestinal juice rich in enzymes. (Briefly T.F.)
The act of eating does not significantly affect intestinal secretion, at the same time, there is evidence of the inhibitory effects on it of irritation of the antrum of the stomach, the modulating effects of the central nervous system, the stimulating effect on the secretion of cholinomimetic substances and the inhibitory effect of anticholinergic and sympathomimetic substances. Stimulates intestinal secretion of GIP, VIP, motilin, inhibits somatostatin. The hormones enterocrinin and duocrinin, produced in the mucous membrane of the small intestine, stimulate the secretion of intestinal crypts (Lieberkühn's glands) and duodenal (Brunner's) glands, respectively. These hormones are not isolated in purified form.
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 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), stimulation of the vagus nerve, gastrointestinal hormones (especially cholecystokinin and secretin). Secretion is inhibited by influences from the sympathetic nervous system.
Secretory function 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 the digestive tract are converted 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. Behind a short time stay of food in 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 duodenum to 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 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.
