pancreatic islets. What are the advantages and disadvantages of allotransplantation of pancreatic islets? Islet cell transplant

Hormones of the pancreas. Islets of Langerhans. Somatostatin. Amylin. Regulatory functions of pancreatic hormones.

endocrine function in pancreas do not perform accumulations of cells of epithelial origin, called islets of Langerhans and making up only 1-2% of the mass of the pancreas - an exocrine organ that forms the pancreatic digestive juice. The number of islets in the gland of an adult is very large and ranges from 200 thousand to one and a half million.

In the islets, several types of hormone-producing cells are distinguished: alpha cells form glucagon, beta cells - insulin, delta cells - somatostatin, ji-cells - gastrin and PP or F cells - pancreatic polypeptide. In addition to insulin, hormones are synthesized in beta cells. amylin, which has the opposite effect of insulin. The blood supply to the islets is more intense than the main parenchyma of the gland. Innervation is carried out by postganlion sympathetic and parasympathetic nerves, and among the cells of the islets are located nerve cells that form neuroinsular complexes.

Insulin is synthesized in the endoplasmic reticulum beta cells first in the form of pre-proinsulin, then the 23-amino acid chain is cleaved from it and the remaining molecule is called proinsulin. In the Golgi complex proinsulin It is packaged in granules, in which proinsulin is cleaved into insulin and a connecting peptide (C-peptide). In granules insulin deposited in the form of a polymer and partially in a complex with zinc. The amount of insulin deposited in granules is almost 10 times higher than daily requirement in hormone. Insulin secretion occurs by exocytosis of the granules, while an equimolar amount of insulin and C-peptide enters the blood. Determining the content of the latter in the blood is an important diagnostic test for assessing the secretory ability (3-cells.

secretion of insulin is a calcium dependent process. Under the influence of a stimulus - an increased level of glucose in the blood - the membrane of beta cells is depolarized, calcium ions enter the cells, which starts the process of contraction of the intracellular microtubular system and the movement of granules to the plasma membrane, followed by their exocytosis.

secretory function of various islet cells is interconnected, depends on the effects of the hormones they form, in connection with which the islets are considered as a kind of "mini-organ" (Fig. 6.21). Allocate two types of insulin secretion: basal and stimulated. Basal insulin secretion carried out constantly, even during fasting and blood glucose levels below 4 mmol / l.

Stimulated secretion of insulin is the answer beta cells islets on elevated level D-glucose in the blood flowing to beta cells. Under the influence of glucose, the energy receptor of beta cells is activated, which increases the transport of calcium ions into the cell, activates adenylate cyclase and the pool (fund) of cAMP. Through these mediators, glucose stimulates the release of insulin into the blood from specific secretory granules. Enhances the response of beta cells to the action of glucose hormone duodenum- gastric inhibitory peptide (GIP). In the regulation of insulin secretion, the vegetative nervous system. Nervus vagus and acetylcholine stimulate insulin secretion, while sympathetic nerves and norepinephrine inhibit insulin secretion through alpha-adrenergic receptors and stimulate glucagon release.

A specific inhibitor of insulin production is the hormone of the delta cells of the islets - somatostatin. This hormone is also formed in the intestine, where it inhibits glucose absorption and thereby reduces the response of beta cells to a glucose stimulus. The formation in the pancreas and intestines of peptides similar to mosgos, such as somatostatin, confirms the existence of a unified APUD system in the body. Glucagon secretion is stimulated by a decrease in blood glucose levels, hormones gastrointestinal tract(GIP gastrin, secretin, cholecystokinin-pancreozymin) and with a decrease in Ca2 + ions in the blood. Insulin, somatostatin, blood glucose and Ca2+ suppress the secretion of glucagon. In the endocrine cells of the intestine, glucagon-like peptide-1 is formed, which stimulates the absorption of glucose and the secretion of insulin after a meal. Cells of the gastrointestinal tract that produce hormones are a kind of "early warning device" of the cells of the pancreatic islets about the intake nutrients in the body, requiring for the utilization and distribution of the participation of pancreatic hormones. This functional relationship is reflected in the term " gastro-entero-pancreatic system».

What hormones does the pancreas produce?

The pancreas plays a major role in the production of digestive juices, which are made up of powerful enzymes. Enzymes are released into small intestine after eating to digest incoming food.

Iron also produces various hormones that control blood glucose levels.

The gland produces hormones from endocrine cells - these cells are collected in clusters known as the islets of Langerhans and control what happens in the blood with them.

Cells can release hormones directly into the blood when needed.

In particular, when blood sugar levels rise, cells produce hormones, in particular insulin.

So, the pancreas produces the hormone insulin.

This hormone helps the body lower blood glucose levels and directs sugar to fat, muscle, liver, and other body tissues where it can be used for energy when needed.

The "alpha cells" in the islets of Langerhans produce another important hormone, glucagon. It has the opposite effect of insulin, helping to release energy into the bloodstream by raising blood sugar levels.

Glucagon and insulin work together to control blood glucose balance.

general characteristics

The main job of the pancreas is the production of pancreatic enzymes. It regulates with their help the processes of digestion.

They help to break down proteins, fats and carbohydrates from food. More than 97% of gland cells are responsible for their production.

And only about 2% of its volume is occupied by special tissues, called "islets of Langerhans". They are small groups of cells that produce hormones.

These accumulations are located evenly throughout the pancreas.

The cells of the endocrine part of the gland produce some important hormones. They have a special structure and physiology.

These areas of the gland, where the islets of Langerhans are located, do not have excretory ducts. Only a lot of blood vessels, where the received hormones directly enter, surround them.

In various pathologies of the pancreas, these accumulations of endocrine cells are often damaged. Because of this, the amount of hormones produced may decrease, which negatively affects general condition organism.

The structure of the islets of Langerhans is heterogeneous. Scientists divided all the cells that make them up into 4 types and found out that each produces certain hormones:

• approximately 70% of the volume of the islets of Langerhans is occupied by beta cells that synthesize insulin;
• in second place in importance are alpha cells, which make up 20% of these tissues, they produce glucagon;
• delta cells produce somatostatin, they make up less than 10% of the area of ​​the islets of Langerhans;
• least of all, PP cells are located here, which are responsible for the production of pancreatic polypeptide;
• Besides, in a small amount the endocrine part of the pancreas synthesizes other hormones: gastrin, thyroliberin, amylin, c-peptide.

Possible hormonal problems

Between meals, the pancreas does not produce insulin, and this allows the body to gradually release stored energy back into the blood as needed.

Blood glucose levels remain very stable at all times, allowing the body to have a constant supply of energy. This energy is needed for his metabolism, exercise and as "fuel" for the brain, which "works" on glucose.

This ensures that the body does not starve between meals.

Also, hormones released during the period acute stress, such as adrenaline, stop the release of insulin, leading to an increase in blood glucose levels.

When the cells in the pancreas that produce insulin become ineffective, or stop working altogether, and do not produce enough insulin, it causes diabetes.

Insulin

This is the main hormone of the pancreas, which has a serious effect on carbohydrate metabolism in the body. It is he who is responsible for the normalization of glucose levels and the rate of absorption by different cells. Hardly a common person, far from medicine, knows what hormones the pancreas produces, but everyone knows about the role of insulin.

This hormone is produced by beta cells, which are abundant in the islets of Langerhans. It is not produced anywhere else in the body. And as a person ages, these cells gradually die, so the amount of insulin decreases. This may explain why the number of people with diabetes increases with age.

The hormone insulin is a protein compound - a short polypeptide. It doesn't work out the same way all the time.

Stimulates its production by increasing the amount of sugar in the blood. Indeed, without insulin, glucose cannot be absorbed by the cells of most organs.

And its main functions are precisely to accelerate the transfer of glucose molecules to cells. This is a rather complex process, aimed at ensuring that glucose is not present in the blood, but goes where it is really needed - to ensure the work of cells.

The role of hormones

Insulin, the main hormone of the pancreas, is tightly regulated in healthy body person to balance food intake and metabolic needs of the body.

Insulin regulates metabolism by promoting the absorption of carbohydrates. Glucose absorbed by tissues is converted into glycogen through glycogenesis, or into fats (triglycerides) through lipogenesis.

The actions of the hormone at the level of human metabolism include:

• increased cellular uptake of certain substances, most notably in glucose uptake by muscle and adipose tissue (approximately two-thirds of all cells in the body);
• increased DNA replication and protein synthesis by controlling amino acid uptake;
• changes in the activity of numerous enzymes.

Actions of insulin, direct and indirect:

• stimulation of glucose uptake - insulin reduces the concentration of glucose in the blood by inducing the consumption of glucose by the cell;
• induces glycogen synthesis – when glucose levels are high, insulin induces glycogen formation by activating the hexokinase enzyme. In addition, insulin activates the enzymes phosphofructokinase and glycogen synthase, which are responsible for the synthesis of glycogen;
• increase in potassium absorption - stimulation of cells to increase the content of intracellular water;
• decrease in gluconeogenesis and glycogenolysis, which reduces the production of glucose from non-carbohydrate substrates, mainly in the liver;
• an increase in lipid synthesis - insulin causes fat cells take in blood glucose, which turns into triglycerides, lowering insulin causes the opposite effect;
• increased esterification of fatty acids adipose tissue synthesize neutral fats (for example, triglycerides), a decrease in insulin causes the opposite effect;
• decrease in lipolysis - the process of splitting fats into their constituents fatty acid under the action of the enzyme lipase;
• decrease in proteolysis - decrease in protein breakdown;
• decrease in autophagy – decrease in the level of degradation of damaged organelles;
• increased absorption of amino acids - provokes cells to absorb circulating amino acids, a decrease in insulin inhibits absorption;
• toning the arterial muscles - forces the muscles arterial wall relax by increasing blood flow, especially in micro-arteries, reducing insulin allows the muscle to contract;
• increased secretion of hydrochloric acid parietal cells in the stomach;
• decreased renal excretion of sodium.

Insulin also affects other bodily functions such as vascular compliance and cognitive ability. After insulin enters human brain, it improves the learning and benefits of human verbal memory.

The hormone also has a stimulating effect on the release of the gonadotropin hormone from the hypothalamus, which favors reproductive function.

The hormones pancreatic polypeptide and somatostatin produced by the pancreas are thought to play a role in the regulation and fine-tuning of insulin and glucagon-producing cells.

Glucagon

It is the second most important hormone in the pancreas. It is produced by alpha cells, which occupy about 22% of the volume of the islets of Langerhans. In structure, it is similar to insulin - it is also a short polypeptide. But it performs exactly the opposite functions. It does not reduce, but increases the level of glucose in the blood, stimulating its release from storage sites.

The pancreas releases glucagon when the amount of glucose in the blood decreases. After all, it, together with insulin, inhibits its production. In addition, the synthesis of glucagon increases in the presence of an infection in the blood or an increase in the level of cortisol, with increased physical activity or an increase in protein intake.

Pancreatic polypeptide

There are even less important pancreatic hormones, of which very little is produced. One of them is a pancreatic polypeptide.

It was discovered recently, so its functions are not yet fully understood. This hormone is produced only by the pancreas - its PP-cells, as well as in the ducts.

It secretes it when eating a large amount of protein foods or fats, with increased physical exertion, fasting, and also with severe hypoglycemia.

When this hormone enters the bloodstream, the production of pancreatic enzymes is blocked, the release of bile, trypsin and bilirubin is slowed down, and the muscles of the gallbladder are relaxed. It turns out that the pancreatic polypeptide saves enzymes and prevents bile loss.

In addition, it regulates the amount of glycogen in the liver. It is noticed that in obesity and some other metabolic pathologies there is a lack of this hormone.

And an increase in its level can be a sign of diabetes or hormone-dependent tumors.

Hormone dysfunction

Inflammatory processes and other diseases of the pancreas can damage the cells that produce hormones. This leads to the appearance various pathologies associated with violation metabolic processes. Most often, with hypofunction of endocrine cells, there is a lack of insulin and diabetes mellitus develops. Because of this, the amount of glucose in the blood rises, and it cannot be absorbed by the cells.

For diagnostics endocrine pathologies pancreas is used to analyze blood and urine for glucose. It is very important to consult a doctor for examination at the slightest suspicion of dysfunction of this organ, since early stages any pathology is easier to treat.

A simple determination of the amount of glucose in the blood does not always indicate the development of diabetes. If this disease is suspected, a biochemistry test, glucose tolerance tests, and others are done.

But the presence of glucose in the urine is a sign severe course diabetes mellitus.

Lack of other pancreatic hormones is less common. Most often this happens in the presence of hormone-dependent tumors or the death of a large number of endocrine cells.

The pancreas performs very important features. It not only provides normal digestion. The hormones that are produced by its cells are necessary to normalize the amount of glucose and ensure carbohydrate metabolism.

Pancreatic islets of Langerhans or pancreatic islets are polyhormonal endocrine cells that are responsible for hormone production. Their size varies from 0.1 to 0.2 mm, total in adults, from 200 thousand to two million.

Entire groups of cell clusters were discovered by the German scientist Paul Langerhans in the middle of the 19th century - they were named after him. Within 24 hours, the pancreatic islets produce about 2 milligrams of insulin.

Most of the cells are localized in the tail of the pancreas. Their mass does not exceed 3% of the total organ volume. digestive system. With age, the weight of cells with endocrine activity decreases significantly. By the age of 50, they remain 1-2%.

Consider why the islet apparatus of the pancreas is needed, and what cells does it consist of?

What cells make up islets?

Pancreatic islets are not a cluster of identical cell structures, they include cells that differ in functionality and morphology. endocrine department The pancreas consists of beta cells, their total specific gravity is about 80%, they secrete amelin and insulin.

The alpha cells of the pancreas produce glucagon. This substance acts as an insulin antagonist, increases glucose in circulatory system. They occupy about 20% in relation to total mass.

Glucagon has a wide range of functions. It affects the production of glucose in the liver, stimulates the breakdown of adipose tissue, lowers the concentration of cholesterol in the body.

Also, this substance promotes the regeneration of liver cells, helps to release insulin from the body, increases blood circulation in the kidneys. Insulin and glucagon have different and opposite functions. Other substances such as adrenaline, somatotropin, cortisol help to regulate this situation.

Langerhans cells of the pancreas consist of the following clusters:

• The accumulation of "delta" provides the secretion of somatostatin, which can inhibit the production of other components. Of the total mass of this hormonal substance, about 3-10%;
• PP cells are able to secrete a pancreatic peptide, which enhances gastric secretion and suppresses excessive activity of the organ of the digestive system;
• The Epsilon cluster synthesize a special substance responsible for the feeling of hunger.

The islets of Langerhans are a complex and multifunctional microorganism that has a certain size, shape, and a characteristic distribution of endocrine components.

It is the cellular architecture that influences intercellular connections and paracrine regulation, which helps to release insulin.

The structure and function of the pancreatic islets

The pancreas is a fairly simple organ in terms of structure, but its functionality is quite extensive. The internal organ produces the hormone insulin, which regulates blood sugar. If its relative or absolute insufficiency is observed, then a pathology is diagnosed - type 1 diabetes mellitus.

Since the pancreas belongs to the organs of the digestive system, it takes an active part in the production of pancreatic enzymes that promote the breakdown of carbohydrates, fats and proteins that come with food. If this function is violated, pancreatitis is diagnosed.

The main function of the pancreatic islets is to maintain the required concentration of carbohydrates and control other internal organs. The accumulation of cells is abundantly supplied with blood, they are innervated through the sympathetic and vagus nerves.

The structure of the islands is quite complex. We can say that each cluster of cells is a full-fledged formation that has its own functionality. Thanks to this structure, the exchange between the components of the parenchyma and other glands is ensured.

The cells of the islets are arranged in the form of a mosaic, that is, randomly. The mature islet is characterized proper organization. It consists of lobules, they are surrounded by connective tissues, the smallest blood vessels. In the center of the lobules are beta cells, others are located on the periphery. The size of the islands depends on the size of the last clusters.

When the components of the islands begin to interact with each other, this is reflected in other cells that are localized nearby. This can be described in the following nuances:

1. Insulin promotes the secretory activity of beta cells, but at the same time inhibits the working functionality of alpha clusters.
2. In turn, the alpha cells “tone” glucagon, and it affects the delta cells.
3. Somatostatin equally inhibits the functionality of both beta and alpha cells.

If a failure is detected in the inherent nature of the chain, associated with immune disorders, then beta cells are attacked by their own immunity.

They begin to collapse, which provokes serious and dangerous disease- diabetes.

Cell transplant

is chronic and incurable disease. Endocrinology has not come up with a way to cure a person forever. Through medications and healthy lifestyle life, you can achieve stable compensation for the disease, but nothing more.

Beta cells do not tend to regenerate. However, in modern world there are certain ways to help them "restore" - replace. Along with transplantation of the pancreas or the establishment of an artificial internal organ transplantation of pancreatic cells.

This is the only chance for diabetics to restore the structure of the destroyed islets. Numerous scientific experiments were carried out, during which beta cells were transplanted from a donor to type 1 diabetics.

The research results showed that surgical intervention contributes to the restoration of the concentration of carbohydrates in human body. In other words, there is a solution to the problem, which is a big plus. However, the minus include lifelong immunosuppressive therapy - the use of medicines that prevent rejection of donor biological material.

As an alternative to a donor source, the use of stem cells is allowed. This option is quite relevant, since the pancreatic islets of donors have a certain reserve.

Restorative medicine is developing rapidly, but we need to learn not only to transplant cells, but also to prevent their subsequent destruction, which happens in any case in the body of diabetics.

Pancreatic transplantation from a pig has a certain perspective in medicine. Before the discovery of insulin, extracts from the gland of an animal were used for. As you know, the difference between human and porcine insulin is only in one amino acid.

The study of the structure and functionality of the pancreatic islets is characterized by great prospects, since the "sweet" disease occurs due to damage to their structure.

The work of the pancreas is described in the video in this article.

The picture next to the text provides a generalized description of the endocrine cells of the islet of Langerhans, without specifying their actual position within it. The figure also shows the structure of fenestrated capillaries and autonomous capillaries present in the pericapillary space. nerve fibers(HB) and nerve endings(BUT).

Groups of such cells were discovered back in 1869 by the scientist Paul Langerhans, after whom they are named. The cells of the islets are concentrated mainly in the tail of the pancreas and make up 2% of the mass of the organ. In total, there are about 1 million islets in the parenchyma.

What cells make up islets?

The islets of Langerhans contain different, morphologically and functionally, cells.

The endocrine segment of the pancreas includes:

• Alpha cells - produce glucagon, which is an antagonist of insulin and provides an increase in blood glucose levels. Occupy 20% of the mass of the remaining cells.
• Beta cells - synthesize insulin and amelin. They make up 80% of the mass of the island.
• Delta cells - provide the production of somatostatin, which can inhibit the secretion of other glands. These cells are from 3 to 10% of the total mass.
• PP cells produce pancreatic polypeptide. It is responsible for enhancing gastric secretion and suppressing pancreatic function.
• Epsilon cells - secrete ghrelin, which is responsible for the onset of hunger.

Why are islands needed and how are they arranged?

The islets of Langerhans are responsible for maintaining the balance of carbohydrates in the body and the work of others. endocrine organs. They have an abundant blood supply, innervated by vagus and sympathetic nerves. Among the islets are neuroinsular complexes. Ontogenetically, islet cells are formed from epithelial tissue.

The islet has complex structure and each of them is a full-fledged functionally active formation. Its structure promotes the exchange of biologically active substances between other glands for the simultaneous secretion of insulin. The cells of the islets are placed in the form of a mosaic, that is, they are mixed with each other. The exocrine structure of the pancreas can be represented by clusters of several cells and large islets.

It is known that a mature island in the parenchyma has an ordered organization. He is surrounded connective tissue, has lobules, and inside are blood capillaries. The center of the lobule is filled with beta cells, and alpha and delta cells are located on the periphery. We can say that the structure of the island is directly related to its size.

What is endocrine function islets and why antibodies are formed against them?
When islet cells interact, a mechanism is formed feedback. Cells affect adjacent ones:

• Insulin has an activating effect on beta cells and inhibits alpha cells.
• Glucagon activates alpha cells, which in turn act on delta cells.
• Somatostatin inhibits the work of alpha and beta cells.

If the immune mechanisms against beta cells are disrupted, antibodies are formed that destroy them and lead to the development of diabetes mellitus.

Why do islet transplants?

Islet transplantation is a viable alternative to pancreas transplantation or artificial organ. This intervention gives diabetic patients a chance to restore the structure of beta cells. were held clinical researches in which patients with type 1 diabetes were transplanted with islet cells from donors. As a result of the tests, it was revealed that such an intervention leads to the restoration of the regulation of carbohydrate levels. Patients with diabetes undergo powerful immunosuppressive therapy to prevent rejection of donor tissues.

Has the prospect of xenotransplantation - transplantation of the pancreas from a pig. Before the discovery of insulin, extracts from porcine pancreas were used to treat diabetes. Human and porcine insulin are known to differ in only one amino acid.
The study of the structure and function of the islets of Langerhans has great prospects, since diabetes mellitus develops due to damage to their structure.

Useful video about the pancreas