The architectonics of the pancreas. The pancreas in its structure belongs to the category of complex alveolar glands. Lobules of the pancreas are separated by layers of loose connective tissue, through which the blood and lymph vessels, nerves and excretory ducts pass. In these layers there are fat cells, sometimes numerous. The pancreas is covered with a thin connective tissue capsule.
The main excretory duct, branching many times, breaks up into small interlobular excretory ducts. Large excretory ducts that arose in the embryo as outgrowths of the intestinal mucosa, like this tube, are lined with a high single-layer cylindrical epithelium, in which goblet-shaped mucous cells are scattered. In places, outgrowths of this epithelial lining give rise to small mucous glands, or crypts, occurring along the main excretory duct near its outlet into the duodenum. Outside, the main excretory duct is surrounded by a layer of dense connective tissue rich in colanic and elastic fibers, which gives it sufficient density, thanks to which, occupying an axial position in the pancreas, it plays to a certain extent the role of a rod supporting the delicate parenchyma of this organ.
The main excretory duct gives off numerous lateral branches (interlobular ducts) passing through thicker connective tissue layers and lined, like the main duct, with a cylindrical epithelium. Interlobular ducts branch into intralobular (small caliber), the epithelium of which is already cubic. Short intralobular ducts finally pass into the intercalary sections, which directly end with the acini. Insertion departments are formed by squamous epithelium.
An electron microscope shows that the apical surface of the epithelial cells of the small excretory ducts, facing their lumen, is elongated into microvilli of various shapes and sizes. The cytoplasm of these cells is electronically light, slightly structured. Ergasto-plasma is weakly expressed and is represented by small vacuoles and pellets of Pelida. Mitochondria are few, round or oval in shape. In places in the cytoplasm there are single, larger vacuoles. Each lobule consists of several acini, tightly pressed against each other and separated only by meager layers of reticular tissue, along which a capillary network braiding acini branches. The acini have a spherical, oval or slightly elongated shape and consist of one layer of glandular epithelial cells, ring-shaped located on a thin basement membrane. The connection of the acini with the insertion departments, which are the beginning of the excretory ducts, can occur in a variety of ways. Sometimes the insertion section at its end directly expands into the acinus, but for the most part, the distal end of the insertion section is pushed into the acinus cavity. In such cases, small epithelial cells are found in the middle of the acinus, lying on the tops of the acinar cells, but belonging to the insertion section. These small cells are called centroacinous; they represent one of the most characteristic structural features of the pancreas. Finally, there are also cases when the acinus is adjacent to the lateral edge of the excretory duct, and then the cross section gives the impression that the lumen of the acinus is limited on one side by acinar cells and, on the other, by excretory duct cells (centroacinous).
The islets of Langerhans stand out in the pancreatic parenchyma in the form of cell clusters, which sharply differ from the surrounding acini by their pale color. The size of the islands varies greatly. Sometimes the islands consist of only a few cells, but, as a rule, they represent large formations, often reaching 175 m or more in diameter and, in any case, significantly exceeding the size of the surrounding acini. The shape of the islands is more or less round (spherical), but often they have irregular angular outlines or protrusions and indentations on their surface.
The islands can be identified due to their ability to perceive some supravital stains more selectively than the rest of the pancreatic parenchyma. If you perfuse a fresh pancreas through its arteries with a weak solution of neutral red or green janus, then against the general background of a pale-colored parenchyma, the islets of Langerhans stand out with a more intense red or blue-green color. The number of islets of Langerhans is very variable, because they are easily formed again, even in an adult organism. However, they clearly predominate in the tail of the pancreas. The total number of islets in the human pancreas ranges from 208,000 to 1,760,000. Age-related changes in the islets cannot be established with sufficient accuracy due to their extreme variability. Apparently, with age, their relative number gradually increases, and after 25 years it begins to gradually decrease. The decorated capsule around the islets is absent, and they are separated from the surrounding acinar parenchyma only by a delicate reticular membrane.
The glandular cells of the islets are compact clusters or branched cords of irregular shapes. These cords are separated by connective tissue layers, in which wide capillaries - sinusoids - pass. The stroma of the islet consists of reticular fibers associated with these layers.
Finally, in the pancreatic parenchyma there are small blind tubes with a diameter of 12–25 centners, anastomosing between themselves. These tubes are formed by a single-layer epithelium with small cubic cells, among which goblet cells and cells with mucin granules in the cytoplasm are sometimes found. Tubules sometimes end on the islets of Langerhans, especially large ones, at the other end they can be connected with the ducts. Apparently, the tubules are the remnants of epithelial strands that gave rise to islets of Langerhans in embryogenesis, remaining undifferentiated, and in the adult organism they are, in all probability, sources of the formation of new islets, and possibly acini.
Acini and their secretory cycle. Acinar (exocrine) cells have a more or less conical shape and face the apical end to the lumen of the acinus. The lumen of the acinus, which is small during the period of functional rest, the pancreas, increases in the phases of active secretion, stretched by the secretion of liquid secreted from the cells. The tops of acinar cells are covered with a thin apical membrane, and secretory capillaries sometimes opening into the lumen of the acinus are sometimes visible between the lateral surfaces of the contacting cells. The nucleus lies closer to the base of the acinar cell. The apical (supranuclear) part of the cytoplasm is filled with granules of secretion (zymogen), the amount of which is small during the phase of excretion, but in the phase of functional rest, the granules densely fill the entire upper half of the acinar cell. In the same supranuclear zone, with appropriate histological processing, a voluminous and loosely branched Golgi network is revealed, in close contact with the branches of which the maturing granules of the secret lie.
The basal part of the acinar cell differs sharply from the apical in its homogeneity. It is intensively stained with basic colors, in contrast to acidophilic granules of the apical part. Basophilia of the lower part is due to the abundant accumulation of ribosonucleic acid (ribosonucleoproteins), which, obviously, is associated with intensive protein synthesis, leading to the formation of secretion granules. Mitochondria, usually long and thin, often crimped or twisted, are also located in the basal parts of acinar cells.
Rounded large nuclei of acinar cells contain comparatively much chromatin and 1-2 oxyphilic nucleoli. Mitoses in acinar cells are very rare.
Acinar cells have a well-developed ergastoplasm. The use of an electron microscope reveals that the entire cytoplasm of the acinar cell is formed by numerous flattened vesicular membranes that fill the cell almost completely, with the exception of the small supranuclear Golgi zone. The outer surface of a-cytomembranes is seated with numerous ribose nuclei granules (Pelida granules), the abundance of which determines the characteristic basophilia of an acinar cell. Ribosonucleic granules are also scattered along the cytoplasm between the membranes. Bubble-shaped membranes of ergastoplasm are layered more or less parallel around the nucleus of an acinar cell. In the cross section, ergastoplasma has the appearance of chains, crevices and small bubbles, sometimes expanding somewhat. The abundance of rbposonuclein granules makes it possible to intensively synthesize protein products, leading to the formation of secretory zymogen granules that accumulate at the top of the acinar cell.
The secret is secreted only during digestion, therefore the tops of the acinar cells of the pancreas in a starving animal are filled with zymogen granules. In the midst of digestion, a very rapid dissolution of the secretory granules occurs and their secretion into the lumen of the acinus and even into the system of excretory ducts of the pancreas.
In the acinar cell of the pancreas, which produces a secretion of a protein character, the substrate of intensive biosynthesis processes are highly developed ergastoplasma plates, and especially abundant ribosucleic granules, both sitting on these acyte membranes and scattered between them.
By the method of giving the ready-made secret, the exocrine part of the pancreas belongs to typical merocrine glands, the secret of which is secreted in dissolved form by diffusion through the apical membrane, which preserves its integrity. To separate the secret, special nervous or humoral irritation is required, so the secret of the pancreas is secreted only in connection with the ingestion of food into the intestines. Consequently, periods of pancreatic activation (i.e., periods of intense secretion) give off alternating with more or less long periods of functional rest, when secretory products are synthesized in acinar cells, the granules of which accumulate in the upper parts of these cells. Therefore, the meocrine secretion of the pancreas has the character of intermittent, or sporadic, secretion.
As noted above, pancreatic islets vary greatly in size and in the frequency of their distribution in the parenchyma. Usually they have a more or less rounded shape and are distinguished by a relatively compact arrangement of cells in the form of improperly branched strands. Specific islet cells are represented by two main varieties. Most islet cells contain small granules, soluble in alcohol, but retained in aqueous fixatives. On the contrary, the granules of other cells dissolve in water, but are preserved by alcohol fixatives. The cells of the first group are called B-cells (P-cells), while the cells of the second type with alkanol-resistant granules are designated as A-cells (a-cells). As one of the common methods for differentiating islet cells, Gomori chromate hematoxylin and phloxin staining is usually used (O.Soshop, 1941). In addition, granules of A cells, revealing a distinct argyrophilia, are selectively blackened with ammonia silver.
The distribution of A and B cells over the islet may be different. B cells are located in compact cords, being in direct contact with capillaries. These cells have a more or less prismatic shape and are closely adjacent to each other. Their nuclei are rounded or slightly oval, relatively rich in chromatin. Rounded or angular A-cells, larger in size than B-cells, in some cases lie in irregular clusters on the periphery of the islet (in rodents), in others they are scattered throughout the islet, and they are collected in small groups in the center of the islet (in humans, predators ) The nuclei of A-cells are vesicular, large, light stained, have a large oxyphilic nucleolus.
In addition to A- and B-cells, which make up the bulk of the island, a small number also contains cells lacking granules (the so-called C-cells). Along with them, cells of type B are sometimes detected, which are distinguished by a pale blue color of granules when applying staining according to Mallory or by the method of azan, the functional significance of cells C and B is unknown. It is possible that C cells represent reserve, slightly differentiated stages of the development of B cells, and the cells are attributed a similar value with respect to A cells, because, like the latter, they exhibit some cytoplasmic argyrophilia.
Islet cells sharply differ from acinar cells in the structure of their ergastoplasmic formations. While acinar cells are characterized by abundant development of acitomembranes, which densely fill the entire cytoplasm in parallel rows, in islet cells of ergastoplasm (the “endoplasmic reticulum”) is represented by relatively small, without noticeable order, vesicles seated on the outside with ribosonucleic granules. Moreover, in B cells, such elements of ergastoplasm are developed somewhat more strongly, sometimes parallel grouping of acitomembranes is even observed in separate zones of the cytoplasm. Ergastoplasma A-cells are more scarce, and its vesicles, irregularly shaped and of varying sizes, are scattered loosely.
Specific granules of B and A cells are very similar electronically. They lie inside the vesicles of ergastoplasm and are surrounded by its membranes.
Chondriosomes in islet cells, in contrast to the long filamentous mitochondria characteristic of acinar cells, have the form of short rods, often of irregular shape and have a relatively high electron-optical density. Chondriosomes of islet cells approach the chondriosomes of duct cells. In B cells, chondriosomes are more numerous than in A cells. The Golgi network in islet cells is less developed than in acinar cells. It is represented mainly by a system of large vacuoles, while double plates (y-cytomasmbranes) are weakly expressed. The Golgi network lies in that part of the islet cell that faces the capillary. Sometimes, in A-cells with ordinary stains, an annular structure (macula) is found, which represents a negative image of the Golgi network.
In the wall of capillaries branching in islands, an electron microscope reveals peculiar pores that penetrate the endothelial lining and are covered with a thin membrane. Between the capillary and adjacent islet cells, a narrow free slit-like space remains.
The physiological significance of B and A cells. Already from the fact that insulin can be extracted from the pancreas with acidified alcohol, and B-cell granules selectively dissolve in alcohol, it can be concluded that these cells produce insulin.With a prolonged load of the test animal with glucose, the increased need for insulin manifests itself at the first moment by the quick release of granules from B cells, and then their hypertrophy and hyperplasia, when they are again filled with specific granules. Finally, decisive evidence comes from the use of alloxan. This substance causes selective B-cell necrosis only (A-cells remain normal), and at the same time short-term hypoglycemia occurs first (due to the fact that the entire supply of insulin contained in them is immediately released from the destroyed B-cells), followed by persistent hyperglycemia and glycosuria. On the contrary, under the action of synthetic sugar-lowering substances of the sulfanilamide group (B 255, nadisan, rastinone), islet hypertrophy and hyperplasia are observed, accompanied by swelling of B cells, an increase in the number of mitoses in them and the release of their granules, which indicates an increase in their secretory activity. Only with prolonged use of these antidiabetic drugs can depletion of B cells occur, leading to their hydropic degeneration. Thus, the significance of B cells as producers of insulin has been established with exhaustive certainty.
The pancreas of cattle contains about 150 mg / kg of insulin. According to Barnett and his staff, total insulin production in humans reaches about 2 mg per day.
It was found that to restore normal blood sugar levels in animals exposed to alloxan, larger amounts of insulin are required than to normalize the sugar curve in a depancreatized animal. It follows that in the pancreas, which has lost B cells, a certain substance is produced that exerts a hyperglycemic effect, i.e. acting opposite to insulin. The desired product (“hyperglycemic glycogenolytic factor”, or “NOG”) was isolated from the pancreas by Merlin and received the name glucagon. Glucagon preparations increase blood sugar.
Just as B cells are selectively affected by alloxan, cells A experience a similar sensitivity to cobalt salts and especially cadmium, which cause the return of accumulated granules of secretion from these cells. In this case, a decrease in blood sugar is detected. Prolonged administration of cadmium sulfate is accompanied by an increase in the number of A cells and hyperglycemia. These data indicate the connection of A-cells with the formation of glucagon. On the other hand, injections of exogenous glucagon lead to selective atrophy of A-cells while maintaining B-cells intact, which confirms the conclusion about the glucocagon-forming activity of A-cells.
Thus, the islets of Langerhans participate in the regulation of carbohydrate metabolism, producing two hormones - insulin glucagon - with an antagonistic effect. Each of these hormones is produced by special specialized cells. Therefore, the quantitative ratio between A- and B-cells should be essential for the regulation of blood sugar. Normally, in an adult, this ratio varies somewhat, but on average it stays at about 1: 3.5–1: 4. Therefore, the B cell significantly predominates quantitatively. In embryogenesis, in some animals, A-cells are the first to differentiate, in others, B-cells first appear, in fetuses and newborns, the ratio the numbers
Pancreas: Its structure and role in the body
Everyone knows that there is such a gland called the pancreas. As soon as it begins to poorly fulfill its role, a person is struck by diseases such as pancreatitis, possibly even diabetes.
Despite the fact that these are completely different diseases, and the causes of their occurrence may also differ, but everything revolves around the pancreas. Due to its special structure, and a dual role in the body, it is able to digest food in time and release insulin into the blood.
The pancreas itself is reliably located in the abdominal cavity, and is located between the stomach itself and the small intestine. It has significantly low weight, only 80 grams, but plays a very important role in the body.
First of all, it is a mixed gland - endocrine and exocrine, and during the digestion of food it produces the enzymes and hormones necessary for humans. So, it works in the body to fulfill the following role:
- During the process of digesting food, the pancreas produces enzymes, which then enter the duodenum 12 for further processing.
- The normal functioning of the pancreas provides the body with insulin and glucagon in sufficient quantities.
As already noted, this segment of the holistic system of the body consists of two completely different in structure and functionality parts - Endo - and Exocrine. Each of which performs its important role.
- Endocrine - performs the secretory function inside.
- Exocrine is an externally secretory function.
Externally, the secretory function is aimed at the production of pancreatic juice. And it contains such enzymes - nuclease, amylase, lipase, steapsin, protease. With the help of these enzymes, all food gets into the stomach, breaks down into small particles. Each of these enzymes is also responsible for certain compounds, fats and allows you to process everything well.
As a result of all processes in the digestive tract, pancreatic juice is produced. Such factors as the type of food, its smell, chewing process, and swallowing are capable of enhancing its secretion. In a word, the allocation of pancreatic juice directly depends on food intake.
And also hormones of the thyroid gland, adrenal glands, and the brain can influence the excretion of pancreatic enzymes. If changes or violations have occurred in this chain, then this immediately affects the work of the pancreas.
The endocrine function, or as it is also called “Langerhans Islands”, gives the body the necessary hormones - insulin, samatostatin, polypeptide. Insulin is absorbed by glucose cells. This process affects muscle and adipose tissue. This hormone is able to turn glucose into glycogen, which is stored in liver cells and muscles.
The body itself, if necessary, spends the right amount of glycogen. If insulin production occurs in insufficient quantities, then diabetes mellitus develops. In addition, with poor pancreatic function, other diseases develop.
Causes of pancreatic disease
If our stomach starts to hurt, then we naturally associate this with poor nutrition, rest, constant stress. It is also worth noting a number of other factors that can damage the digestive tract and cause pancreatic disease:
- Excessive use of alcohol and tobacco.
- Medications, a long course of treatment.
- Hereditary pancreatitis.
- Infectious diseases - hepatitis of various forms, mumps.
- Pancreatic cancer.
Recently, it is noted that cases of pancreatic disease due to viruses and bacteria have become more frequent. The penetration of these elements into the pancreas is very dangerous, since they form a focus in the pancreas, which then spreads throughout the body.
An acute attack of pain can occur suddenly, and practically take a person by surprise. And it can happen anywhere. Moreover, any cause that caused the disease is accompanied by acute pain, and it becomes intolerable with every minute.
At this point, it is urgent to call an ambulance team, as home remedies will not help relieve pain. Alcohol addiction, smoking, can cause an attack of pancreatitis. Proper nutrition, walks in the fresh air, physical exercises, can have a positive impact on the work of the pancreas.
Analysis for pancreatic histology: To whom it is prescribed that they check
Histology studies the structure of cells in the body, and this study can determine the presence of life-threatening cells and tumors.
This method of pancreatic research allows to determine pathological changes with high accuracy. Very often, gynecologists use this method of researching the body to detect cervical cancer.
For the study of the pancreas, histological analyzes were also used. Since this is one hundred percent result. Who is assigned this analysis? One answer can be given to those patients who have suspected pancreatic oncology.
Despite the fact that this disease is less common than malignant tumors of the stomach, but unfortunately, it is more common than oncology of the lungs and liver. Every year, the incidence of pancreatic cancer increases by about two percent. The following signs may be a consequence of the development of pancreatic oncology:
- Chronic pancreatitis.
- Poor quality products and synthetic additives.
- Alcohol abuse.
Histology allows early detection of the presence of a pathological tumor and timely assistance to the patient. Every person knows that the disease is easier to prevent than to treat in the future. Take good care of your health, eat right, do not abuse alcohol and exercise. A healthy lifestyle allows you to live a full, interesting life without pain, illness and the complications associated with them.
Gland anatomy and function
The pancreas consists of connective tissue and is contained in a dense capsule. It has many capillaries necessary for proper blood supply, so its damage can lead to dangerous internal bleeding.
The pancreas is located in the retroperitoneal cavity of the human body. In front of her is the stomach, which is separated by a sebaceous bag, behind - the spine. Lymph nodes, celiac plexus and abdominal aorta are localized in the back of the gland. It is with this arrangement of the organ that the load on it is distributed optimally.
The shape of the organ is elongated, it looks like a comma. It is conditionally divided into parts:
- Head (up to 35 millimeters in length) - located near the duodenum and adjoins it tightly.
- The body (up to 25 millimeters) is localized in the region of the first lumbar vertebra.
- Tail (up to 30 millimeters).
Thus, the length of the organ itself of an adult is, as a rule, no more than 230 millimeters.
The anatomy of an organ is complex. The pancreas is one of the organs of the endocrine system. Its tissues according to the type of structure and structure are divided into two types: exocrine and endocrine.
The exocrine part of the gland forms and secretes the enzymes required in digestion in the duodenum. They help to digest the main food components in food. The endocrine part produces hormones and metabolizes.
Despite the fact that the pancreas is a whole organ, its anatomy and histology are significantly different from others.
The histological structure of the pancreas
Histology is a scientific section of biology that studies the structure and functions of the components of the body, tissues and organs. The pancreas is the only organ in the body that forms and secretes both internal and external secretions. Therefore, the histological structure of the pancreas has a rather complex structure.
In order to conduct a complete and detailed examination of tissues using histological preparations. They are pieces of tissue stained with special compounds for examination under a microscope.
Exocrine pancreatic tissue consists of acini, which form digestive enzymes, and ducts, which excrete them. Acini densely located to each other and connected with a thin layer of loose tissue containing blood vessels. The cells of the exocrine region of the gland have a triangular shape. The cell nucleus is round.
Acini themselves are divided into two parts: basal and apical. The basal contains a membrane of the granular network. When using a histological preparation, the staining of this part will be quite uniform. The apical, in turn, takes on acidic hues. With the help of a histological preparation, one can also consider well-developed mitochondria and the Golgi complex.
The ducts for excretion of enzymes also have several types:
- General - is formed from interlobular, interconnected.
- Insertion - localized in the area of the insertion part of the acinus. They have a flat and cubic epithelium.
- Interlobular - covered with a single-layer shell.
- Interacinous (intralobular).
It is with the help of the shells of these ducts that bicarbonates are secreted, which forms an alkaline environment in the juice of the pancreas.
This part of the pancreas is formed from the so-called islets of Langerhans, consisting of a collection of cells that have a round and oval shape. This tissue is well supplied with blood due to numerous capillary networks. Her cells stain poorly when using a histological preparation.
As a rule, the following types are distinguished:
- A - are produced in peripheral areas and are considered an antagonist of insulin. They can be fixed with alcohol and dissolved in water. Glucagon is produced.
- B - represent the most numerous population and are located in the very center of the islands. They are the source of insulin, which lowers blood sugar. Well soluble in alcohol. Poorly stained with the drug.
- D - form and release the hormone somatostatin, which slows down the synthesis of cells A and B. They have an average level of density and size, are located on the periphery.
- D-1 - produce a polypeptide and represent the most small group of cells. Responsible for reducing pressure, activating the secretion of the gland. They have a high density.
- PP cells - synthesize a polypeptide and enhance the production of pancreatic juice. They are also located in the periphery.
The hormones that are formed by the islets of Langerhans are sent immediately to the blood because they do not have ducts. Moreover, the largest part of these sites is located in the "tail" of the pancreas. Their number, as a rule, changes over time. So, during the period of active growth of the body, it increases, and after twenty-five years it gradually begins to decrease.
The smaller endocrine part is formed by pancreatic islets or islets of Langerhans (insulae pancreaticae, insula - islet) located between the acini of the predominantly caudal part of the gland.
The islands are separated from the acini by a thin connective tissue layer and are round-shaped cell clusters penetrated by a dense network of capillaries with a diameter of about 0.3 mm.
Their total number is approximately 1 million. Endocrinocytes in strands surround the capillaries of the islets, in close contact with the vessels either through the cytoplasmic processes, or adjacent to them directly.
The physicochemical and morphological properties of granules of endocrinocytes secrete five types of secretory cells:
- alpha cells (10-30%) produce glucagon,
- beta cells (60-80%) synthesize insulin,
- delta and D1-cells (5-10%) form a somatostatin vaso-intestinal peptide (VIP),
- PP cells (2-5%) produce pancreatic polypeptide.
Beta cells are located mainly in the central zone of the islet, while the remaining endocrinocytes are located on its periphery.
In addition to the main species, a special type of cells is located in the islet region - acinoislet (mixed or transient) cells that perform both endocrine and exogenous functions. In addition, local endocrine regulation cells producing gastrin, thyroliberin and somatoliberin were found in the islets.