Insulin (from the Latin. Insula "island") is a polypeptide hormone of the pancreas, the function of which is to supply the body cells with energy. The place of synthesis of insulin are 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 is sufficiently studied in its structure. A connection was found between the hormone and protein metabolism, which is insufficiently developed in diabetics, which leads to early cell deterioration. The role of insulin in protein synthesis is to enhance the uptake of amino acids by the cells from the blood and then create proteins from them.
In addition, it is insulin that inhibits the decomposition of proteins in cells. Insulin also affects lipids in such a way that with its deficiency acidosis and atherosclerosis develop. Why is insulin linked to cell energy? Because with a plentiful 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 to glycogen, which accumulates in the liver and muscles. It is needed when other sources of energy are depleted. There is a direct relationship between insulin and glycogen synthesis. And even when there is a lot of glycogen, sugar is converted to fat (4 molecules of fat are obtained from 1 sugar molecule) - it is deposited on the sides.
Discovery story
In 1869, in Berlin, the very young, 22-year-old medical student Paul Langerhans, while studying the pancreas under a microscope, noticed groups of cells scattered across the gland, later called islets of Langerhans.
Their role was initially unclear. Later E. Lagus said that these cells are involved in digestion. In 1889, the German physiologist Oscar Minkowski disagreed with him and, as evidence, removed the pancreas from the experimental dog.
Minkowski's assistant laboratory assistant noted that the urine of the operated dog attracted many flies. In her study, sugar was found. This was the first experience to link the pancreas with diabetes.
In 1900, the Russian scientist Leonid Vasilievich Sobolev (1876-1919) from the laboratory of IP Pavlov experimentally proved that the islets of Langerhans participate in the metabolism of carbohydrates.
Hormone structure
Human insulin is a protein with a molecular weight of 5808, consisting of 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 human. This allowed the creation of synthetic insulin for the treatment of diabetes. The most commonly used pig insulin, which differs from human only one amino acid.
Bovine - has 3 amino acids. Determining the exact sequence of all amino acids in the composition of insulin was made by the English microbiologist Frederick Senger. For this decoding in 1958 he received the Nobel Prize in chemistry.
Some more history
Isolation of insulin for practical use was made in 1923 by scientists of the University of Toronto F. Bunting and Best, who also received the Nobel Prize. It is known that Bunting fully agreed with Sobolev's theory.
A bit of anatomy
The pancreas is unique in its structure. This refers to the fact that it is both an endocrine gland and an exocrine gland. Its exofunction is involved 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 total area of ββthe gland.
And only 5% are in the islets of Langerhans. This indicates the power of the gland and its huge work in the body. The islands are localized around the perimeter. 5% are millions of islets, 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 BZHU from incoming food. The synthesis of insulin occurs in b-cells.
How does this happen
The detailed insulin production process has not been precisely established to this day. For this reason, diabetes refers to incurable pathologies. When establishing the mechanism of insulin formation, diabetes can also be controlled, 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. Simplification scheme: precursor - preproinsulin - proinsulin - active insulin.
Synthesis
The synthesis of insulin in the cell in a simplified scheme looks like this:
- Beta cells form an insulin substance that 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 displays the desired compounds through the membrane.
- The transformation of all stages leads to the appearance of a capable hormone.
- Now insulin is packed in special secretory granules. It is stored on demand and matures. The C-peptide, zinc ions, amylin and proinsulin residues are also stored in granules. The synthesis and secretion of insulin begins during a meal: digestive enzymes arrive, a completely prepared granule merges with the cell membrane, and its contents are completely squeezed out of the cell into the blood.
- When hyperglycemia develops, insulin is on its way - it is released and begins to act. It seeps into the capillaries of the pancreas, of which there is a mass, they penetrate the gland through.
The regulation of insulin synthesis occurs due to the glucose-sensor system of beta cells. It completely regulates the balance between sugar intake and insulin production.
Summary: insulin synthesis in the body is activated with hyperglycemia. But insulin during food only rises, but it is produced around the clock.
Not only glucose regulates the synthesis and secretion of insulin. During the meal, there are additional stimuli: 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 an 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 converted to glucose. Over time (with age), the strength and activity of pancreatic islets decreases, which becomes noticeable after 40 years.
The lack of synthesis of insulin causes irreversible changes in many organs and systems. The norm of insulin in the blood in an adult is 3-25 ΞΌE / ml, after 58-60 years - 7-36 ΞΌE / ml. Also, insulin is always elevated in pregnant women.
In addition to regulating hyperglycemia, insulin has anabolic and anti-catabolic function. In other words, both of these processes are participants in the metabolism. One of them activates, the other inhibits the metabolic process. Their consistency allows you to maintain the constancy of the body's homeostasis.
Insulin function
Insulin forms some mechanisms of fermentation in cells, supporting metabolism. When excreted, 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. For this, glucose needs to be distributed somewhere, therefore, insulin also 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:
- Increased ability of cells to capture amino acids (leucine and valine).
- Increased 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. Anticatabolic function.
- Decrease in protein breakdown by blocking the process of their decomposition to amino acids (hydrolysis).
- Decreased lipid decomposition (lipolysis, as a result of which usually fatty acids enter the bloodstream).
Elimination (excretion) of insulin
This process occurs in the liver and kidneys. More than half of it is excreted by the liver. There is a special enzyme, insulinase, which inactivates insulin by breaking down its structural bonds to amino acids. 35% of insulin is decomposed in the kidneys. This process occurs in the lysosomes of the renal tubule epithelium.
Insulin may increase or decrease in production. This occurs with various pathologies. If such violations are prolonged, irreversible changes in the vital systems of the body develop.
The interaction of glucose and insulin
Glucose is the ubiquitous compound in body tissues. Almost any carbohydrate coming from food is converted into it. The most important property of glucose is to serve as a source of energy, especially its lack of muscle and brain immediately notice.
In order to avoid a lack of glucose in the cells, insulin is needed. It acts as a key for cells. Without it, glucose cannot penetrate into the 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 fond of myocytes and adipocytes (fat cells), 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 neutralization of glucose by insulin
Also a multifaceted process, is developing in stages. The first proteins to be activated are transporters, the role of which is to capture glucose molecules and transfer them through the membrane.
The cell is saturated with sugar. Part of the glucose goes to hepatocytes, where it is converted to glycogen. Its molecules already go to other tissues. What causes an insulin deficiency in the body.
Insulin synthesis deficiency 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 monotonous. The latter contain pancreatic extract of one animal.
Combined - combine extracts of the glands of several animal species. Virtually not applicable 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 - pork, differs in only one amino acid.
In Russia, insulin is not used from cattle (it differs by 3 amino acids).
According to the degree of purification, insulin is traditional (it contains impurities of other pancreatic hormones), monopic (MP) is additionally filtered on a gel, its impurities are no more than 1 β’ 10β3, monocomponent (MK) is ascending. The latter - the purest - 99% purification (1 β’ 10β6 impurities).
Also, insulin differs in its beginning, peak and duration of action - it is ultrashort, short, medium and prolonged - long and ultra-long. The choice is up to the doctor.
How to replenish insulin
Surgical and physical methods of recovery have not been created to date. It is possible to use insulin only in injections. PSSP can support the depleted pancreas - they reduce hyperglycemia. Sometimes insulin therapy can supplement HRT - these are medical methods.
But there are enough improvised ways of influencing insulin production: a diet with a reduced amount of carbohydrates, which implies fractional nutrition and food intake at the same time, the frequency of intake is 5-6 times a day. Useful spices, the rejection of simple carbohydrates and the transition to complex ones with low GI, increased fiber in the diet, green tea and more seafood, the right protein and herbal medicine. Aerobic exercises and other moderate physical activity are recommended, and this is avoiding physical inactivity, obesity, because, as you know, physical exercises help to avoid many problems.