Insulin (from the Latin insula "island") is a polypeptide hormone of the pancreas, the function of which is to supply the cells of the body with energy. The site of insulin synthesis is in the pancreatic islets of Langerhans, their beta cells. Insulin is involved in the metabolism of all tissue cells, although at the household level it is associated only with diabetes.
General information
Today, insulin has been sufficiently studied in its structure. The connection of the hormone with the metabolism of proteins, which are produced in insufficient quantities in diabetics, is revealed, which leads to early wear of cells. The role of insulin in protein synthesis is to increase the uptake of amino acids from the blood by cells and then to create proteins from them.
Besides this, it is insulin that inhibits the decomposition of proteins in cells. Insulin also affects lipids in such a way that acidosis and atherosclerosis develop with its deficiency. Why bindinsulin with cell energy? Because with a hearty meal, insulin synthesis increases markedly, sugar is transported into the cells, and they store energy. At the same time, the level of glucose in the blood decreases - this is the main property of insulin. With an excess of glucose, insulin converts it into glycogen, which accumulates in the liver and muscles. It is needed when other energy sources are depleted. There is a direct link between insulin and glycogen synthesis. And when there is a lot of glycogen, sugar is converted into fat (4 molecules of fat are obtained from 1 molecule of sugar) - it is deposited on the sides.
Discovery history
In 1869 in Berlin, a very young, 22-year-old medical student Paul Langerhans, while studying the pancreas under a microscope, noticed groups of cells scattered throughout the gland, later called the islets of Langerhans.
Their role was unclear at first. Later, E. Lagus stated that these cells are involved in digestion. In 1889, the German physiologist Oskar Minkowski disagreed and removed the pancreas from an experimental dog as proof.
Lab assistant Minkowski noticed that the urine of an operated dog attracts a lot of flies. During her research, sugar was found. This was the first experience to link the pancreas to diabetes.
In 1900, the Russian scientist Leonid Vasilyevich Sobolev (1876-1919) from the laboratory of I. P. Pavlov experimentally proved that the islets of Langerhans are involved in the metabolism of carbohydrates.
The structure of the hormone
Human insulin is a protein with a molecular weight of 5808, consistingof 51 amino acids connected in 2 peptide chains: A - contains 21, chain B - 30 amino acids.
Their bond is supported by 2 disulfide bonds. When these bridges are destroyed, the hormone is inactivated. It is structured, like any ordinary protein, in B-cells.
Some animals have insulin, similar in structure to the human. This allowed the creation of synthetic insulin for the treatment of diabetes. The most commonly used is porcine insulin, which differs from human insulin in only one amino acid.
Bovine - differs by 3 amino acids. The determination of the exact sequence of all amino acids in the composition of insulin was made by the English microbiologist Frederick Sanger. For this decoding in 1958, he received the Nobel Prize in Chemistry.
A little more history
Isolation of insulin for practical use was made in 1923 by University of Toronto scientists F. Banting and Best, who also received the Nobel Prize. It is known that Banting fully agreed with Sobolev's theory.
A bit of anatomy
The pancreas is unique in its structure. This means that it is both an endocrine gland and an exocrine gland. Its exofunction lies in participation in digestion. It produces valuable digestive enzymes - proteases, amylases and lipases, which are secreted through the ducts into its cavity. The exocrine part occupies 95% of the entire area of the gland.
And only 5% falls on the islets of Langerhans. This indicates the power of the gland and its tremendous work in the body. Islets are localized along the entire perimeter. 5% is millions of islands, although their total mass is only 2 g.
Each islet contains cells A, B, D, PP. They all produce their compounds involved in the exchange of BJU from incoming food. Insulin synthesis occurs in B cells.
How it happens
The detailed process for the production of insulin is not exactly established today. For this reason, diabetes is classified as an incurable pathology. By establishing the mechanism of insulin production, it will be possible to control diabetes by initially influencing the process of insulin synthesis.
The complexity of the multi-stage process. With it, several transformations of substances occur, as a result of which inactive insulin becomes active. Simplified scheme: precursor - preproinsulin - proinsulin - active insulin.
Synthesis
Insulin synthesis in a cell in a simplified scheme looks like this:
- Beta cells form an insulin substance, which is sent to the Golgi apparatus of the cell. Here it is further processed.
- The Golgi complex is such a structure of the cell membrane that accumulates, synthesizes, and then removes the necessary compounds through the membrane.
- The transformation of all stages leads to the appearance of a capable hormone.
- Insulin is now packaged in special secretory granules. Stored until demand and ripens. The granules also store C-peptide, zinc ions, amylin, and proinsulin residues. Synthesis and secretion of insulin begin during meals:digestive enzymes enter, the fully prepared granule fuses with the cell membrane, and its contents are completely squeezed out of the cell into the blood.
- When hyperglycemia develops, insulin is already on the way - it is released and begins to act. It seeps into the capillaries of the pancreas, of which there are a lot, they penetrate the gland through and through.
Insulin synthesis is regulated by the glucose-sensing system of beta cells. It completely regulates the balance between sugar intake and insulin production.
Summary: Insulin synthesis in the body is activated during hyperglycemia. But insulin only rises with meals, but it is produced around the clock.
Not only glucose regulates the synthesis and secretion of insulin. During meals, additional stimuli also take place: proteins contained in food (amino acids leucine and arginine), estrogens and cholecystokinin, K, Ca ions, fatty acids from fats. A decrease in insulin secretion is noted with an increase in the blood of the insulin antagonist - glucagon. It is produced in the same pancreatic islets, but in alpha cells. The role of glucagon in the breakdown and consumption of glycogen. The latter is then converted to glucose. Over time (with age), the strength and activity of the pancreatic islets decreases, which becomes noticeable after 40 years.
Lack of insulin synthesis causes irreversible changes in many organs and systems. The rate of insulin in the blood of an adult is 3-25 μU / ml, after 58-60 years - 7-36 μU / ml. Also, insulin is always elevated in pregnant women.
Besides regulationhyperglycemia, insulin has an anabolic and anti-catabolic function. In other words, both of these processes are participants in metabolism. One of them activates, the other inhibits the metabolic process. Their consistency allows you to maintain the constancy of the body's homeostasis.
Functions of insulin
Insulin forms some of the mechanisms of fermentation in cells, supporting metabolism. When released, it increases the intake and use of glucose by tissues, its storage by muscles and liver and adipose tissue.
Its main purpose is to achieve normoglycemia. To do this, glucose needs to be distributed somewhere, so insulin increases the ability of cells to absorb glucose, activates enzymes for its glycolysis, increases the intensity of glycogen synthesis, which goes to the liver and muscles, and reduces gluconeogenesis in the liver, in which glucose stores in the liver decrease.
Anabolic functions
Anabolic functions include:
- Increasing the ability of cells to capture amino acids (leucine and valine).
- Increasing the supply of minerals to cells - K, Ca, Mg, P.
- Activation of protein synthesis and DNA duplication.
- Participation in the formation of esters (esterification) from fatty acids necessary for the appearance of triglycerides. Anti-catabolic function.
- Reducing the breakdown of proteins by blocking the process of their decomposition to amino acids (hydrolysis).
- Reduce lipid breakdown (lipolysis, which normally releases fatty acids into the blood).
Elimination (removal) of insulin
This process takes place in the liver and kidneys. More than half of it is excreted by the liver. There is a special enzyme here - insulinase, which inactivates insulin by destroying its structural bonds to amino acids. 35% of insulin decomposes in the kidneys. This process occurs in the lysosomes of the epithelium of the renal tubules.
Insulin can increase or decrease in production. It occurs in various pathologies. If such violations are prolonged, irreversible changes in the vital systems of the body develop.
Interaction between glucose and insulin
Glucose is a ubiquitous compound in body tissues. Almost any carbohydrates that come with food are converted into it. The most important property of glucose is to serve as a source of energy, especially the muscles and brain immediately notice its lack.
In order for there to be no shortage of glucose in the cells, insulin is needed. It acts as a key for cells. Without it, glucose cannot enter cells, no matter how much sugar you eat. On the surface of the cells there are special protein receptors for binding to insulin.
The hormone is especially loved by myocytes and adipocytes (fat cells), and they are called insulin-dependent. They make up almost 70% of all cells. The processes of respiration, blood circulation, movement are provided by them. For example, a muscle without insulin will not work.
Biochemistry of insulin neutralization of glucose
Also a multifaceted process, it develops in stages. Proteins are the first to be activated immediately - transporters, whose role is to capture glucose molecules and transport them through the membrane.
The cell is saturated with sugar. Part of the glucose is sent to hepatocytes, where it is converted into glycogen. Its molecules are already going to other tissues. What causes lack of insulin in the body.
Lack of insulin synthesis causes type 1 diabetes. If the production of the hormone is sufficient, but the cells do not respond to it due to the appearance of insulin resistance in them, type 2 diabetes develops.
Classification of insulin preparations
They are combined and single-species. The latter contain an extract from the pancreas of one animal.
Combined - combine extracts of the glands of several animal species. Almost never used today.
By origin or species, insulin is used by human and pig, cattle or whale. They differ in some amino acids. The most preferred after the human - pig, differs in only one amino acid.
In Russia, insulin from cattle is not used (it differs by 3 amino acids).
According to the degree of purification, insulin can be traditional (contains impurities of other pancreatic hormones), monopeak (MP) - additionally filtered on the gel, impurities in it are not more than 1•10−3, monocomponent (MK) - in ascending order. The last one is the purest - 99% purification (1•10−6 impurities).
Insulin also differs in onset, peak and duration of action - it can be ultrashort, short, medium andprolonged - long and extra long. The choice is up to the doctor.
How to replenish insulin
Surgical and physical recovery methods have not been created to date. It is possible to use insulin only in injections. PSSP can also support an exhausted pancreas - they reduce hyperglycemia. Sometimes insulin therapy can be supplemented with HRT - these are medication methods.
But there are enough improvised ways to influence the production of insulin: a diet with a reduced amount of carbohydrates, which implies the fragmentation of nutrition and eating at the same time, the frequency of intake is 5-6 times a day. It is useful to use spices, avoid simple carbohydrates and switch to complex ones with low GI, increase fiber in the diet, green tea and more seafood, proper protein and herbal medicine. Aerobic exercises and other moderate physical activity are recommended, and this is a departure from hypodynamia, obesity, because, as you know, physical exercises help to avoid many problems.
