What is insulin: Definition and 18 Discussions

Insulin (, from Latin insula, 'island') is a peptide hormone produced by beta cells of the pancreatic islets encoded in humans by the INS gene. It is considered to be the main anabolic hormone of the body. It regulates the metabolism of carbohydrates, fats and protein by promoting the absorption of glucose from the blood into liver, fat and skeletal muscle cells. In these tissues the absorbed glucose is converted into either glycogen via glycogenesis or fats (triglycerides) via lipogenesis, or, in the case of the liver, into both. Glucose production and secretion by the liver is strongly inhibited by high concentrations of insulin in the blood. Circulating insulin also affects the synthesis of proteins in a wide variety of tissues. It is therefore an anabolic hormone, promoting the conversion of small molecules in the blood into large molecules inside the cells. Low insulin levels in the blood have the opposite effect by promoting widespread catabolism, especially of reserve body fat.
Beta cells are sensitive to blood sugar levels so that they secrete insulin into the blood in response to high level of glucose, and inhibit secretion of insulin when glucose levels are low. Insulin enhances glucose uptake and metabolism in the cells, thereby reducing blood sugar level. Their neighboring alpha cells, by taking their cues from the beta cells, secrete glucagon into the blood in the opposite manner: increased secretion when blood glucose is low, and decreased secretion when glucose concentrations are high. Glucagon increases blood glucose level by stimulating glycogenolysis and gluconeogenesis in the liver. The secretion of insulin and glucagon into the blood in response to the blood glucose concentration is the primary mechanism of glucose homeostasis.Decreased or absent insulin activity results in diabetes mellitus, a condition of high blood sugar level (hyperglycaemia). There are two types of the disease. In diabetes mellitus type 1, the beta cells are destroyed by an autoimmune reaction so that insulin can no longer be synthesized or be secreted into the blood. In diabetes mellitus type 2, the destruction of beta cells is less pronounced than in type 1, and is not due to an autoimmune process. Instead, there is an accumulation of amyloid in the pancreatic islets, which likely disrupts their anatomy and physiology. The pathogenesis of type 2 diabetes is not well understood but reduced population of islet beta-cells, reduced secretory function of islet beta-cells that survive, and peripheral tissue insulin resistance are known to be involved. Type 2 diabetes is characterized by increased glucagon secretion which is unaffected by, and unresponsive to the concentration of blood glucose. But insulin is still secreted into the blood in response to the blood glucose. As a result, glucose accumulates in the blood.
The human insulin protein is composed of 51 amino acids, and has a molecular mass of 5808 Da. It is a heterodimer of an A-chain and a B-chain, which are linked together by disulfide bonds. Insulin's structure varies slightly between species of animals. Insulin from non-human animal sources differs somewhat in effectiveness (in carbohydrate metabolism effects) from human insulin because of these variations. Porcine insulin is especially close to the human version, and was widely used to treat type 1 diabetics before human insulin could be produced in large quantities by recombinant DNA technologies.Insulin was the first peptide hormone discovered. Frederick Banting and Charles Herbert Best, working in the laboratory of J. J. R. Macleod at the University of Toronto, were the first to isolate insulin from dog pancreas in 1921. Frederick Sanger sequenced the amino acid structure in 1951, which made insulin the first protein to be fully sequenced. The crystal structure of insulin in the solid state was determined by Dorothy Hodgkin in 1969. Insulin is also the first protein to be chemically synthesised and produced by DNA recombinant technology. It is on the WHO Model List of Essential Medicines, the most important medications needed in a basic health system.

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  1. mktsgm

    What is the role of insulin other than translocating GLUT-4 proteins?

    Insulin's role in glucose metabolism by translocating GLUT-4 proteins into the plasma membrane (thereby regulating the uptake of glucose), in the adipose and skeletal muscle cells, is rather well known. And in the liver, insulin aids to regulate gluconeogenesis and promoting glycogen synthesis...
  2. mktsgm

    Normally insulin levels are not measured in type-2 diabetes. Why?

    Type-2 diabetes patients generally display higher levels of glucose circulating in their blood. While type-1 is considered a lack of insulin disease, in type-2 it is considered that insulin may be present, but it is not working properly. It is called Insulin-resistance. Most of the drugs for...
  3. mktsgm

    Medical Insulin vs Glucagon: How the Body Balances Glucose Levels

    We know that insulin and Glucagon are considered antagonistic hormones as they help us to maintain the homeostatic glucose level for our cells. When the concentration of blood glucose rises (after eating, for example), beta cells of the pancreas secrete insulin into the blood. Insulin helps to...
  4. bhobba

    Metabolic Syndrome Without Insulin Resistance

    Hi Guys I have metabolic syndrome, amongst other things. A friend has all the signs - sleep apnia, low testosterone, high AST, high ferritin, high blood pressure, horrid cholesterol, belly fat etc. Yet despite test after test he does not have insulin resistance. Me I am way insulin...
  5. mktsgm

    Medical Insulin dependent glucose uptake

    We know that type 2 diabetes is caused by insulin insufficiency/resistance. Normally Insulin causes GLUT4 in the liver and muscle/adipose cells to surface at their cell membrane, to facilitate the transport of glucose from the circulating blood. Type2DM lacks this action and hence glucose...
  6. infinite.curve

    Insulin Resistance and Cell Signaling

    Well, I am confused on insulin resistance and cellular signaling. Know... Below is my understand: Insulin resistance happens either when the paceraes does not produce enough of the protein insulin and another way resistance occurs is when the receptor is not functioning properly. Are there...
  7. haael

    How can bacteria synthesize human insulin?

    I have just read that genetically modified e. coli can synthesize human insulin. But I wonder. Human (eucaryotic) genes have all kinds of introns, regulators, starting sequences etc. Bacteria don't have all of those. How can a procaryota produce an eucaryotic peptide? Has the insulin gene been...
  8. T

    Why doesn't decreased insulin secretion during stress cause problems?

    During fight-or-flight situations, alpha 2 receptors ( which are inhibitory receptors ) of the pancreatic beta cells are stimulated, and as a result there's decreased insulin production. While it benefits the body by producing increased blood sugar level, I don't understand why Insulin doesn't...
  9. bohm2

    Can high insulin make you fat?

    Can high insulin make you fat directly? I thought this was a very interesting study because it seems to question the usual relationship between insulin levels, insulin resistance and obesity: Hyperinsulinemia Drives Diet-Induced Obesity Independently of Brain Insulin Production...
  10. B

    Glucose effectiveness and insulin sensitivity

    I'm reading an article about glucose dynamics and there were two terms I wasn't sure about. I'm guessing insulin sensitivity is how much glucose is absorbed by a certain amount of insulin, but what is glucose effectiveness? Any help is appreciated.
  11. Z

    Questions about Diabetes: Insulin Needles, Type 2 & Autoimmune Diseases

    I've been recently reading up on diabetes and there's some questions I can't find the answers to so if anyone here know please help Are insulin needles used for type 2 diabetes? -I keep hearing ppl saying that they are but isn't type 2 when the body doesn't respond to insulin? Type 2...
  12. M

    What are the characteristics of insulin

    What are the characteristics of insulin produced by the enzyme Genetic Engineering ? Is identical of the human insulin ?
  13. E

    Medical How is fat metabolized and related to insulin?

    I'm what you would, in the bodybuilding world, call a hardgainer. No matter what I do I can't gain weight. I used to eat lots of carbs on a 4000 Calorie diet and nothing happened as far as weight gain. I would just get frequent urination and a fruitish odor in the back of my mouth and would...
  14. P

    Does anyone know how insulin is produced nowadays?

    Does anyone know how insulin is produced nowadays? I know that bacteria get a human gene which codes for the production of insulin, but I'd like to get some more in-depth information because we have to make a folder at school.
  15. M

    Half Life of radioactive insulin

    In my assay of 50uL of 125-I-insulin I have 20,000 cpm at the expiry date. The half life of 125-I-Insulin is 60 days. So how can I calculate how many counts a 50uL sample of 125-I-labelled insulin would contained at 4 months past the expiry date? cheers
  16. N

    Insulin and GLUT4 glucose transporters

    The presence of insulin increases the activity of the GLUT4 glucose transporters and not the actual number of the transporters. In a freeze fracture, it appeared that the GLUT4s moved from the internal membrane into the plasma membrane. I am asked to deduce the mechanism by which glucose...
  17. Y

    Which Kidney Hormones: Insulin, Adrenaline, Growth Hormone, EPO or Thyroxine?

    I have a question that says: Which of the following hormons are produced in the kidneys: Insulin, adrenaline, growthhormon, EPO or thyroxine ? Thanks again :D
  18. J

    GI, Insulin and Fat: Exploring Effects on Body Weight

    I'm trying to understand what a person said (from ahttp://forums.whirlpool.net.au/forum-replies.cfm?t=162168&p=4 . Later on, he goes to say that without insulin, eating excess fat would not cause you to get fat (near the bottom of the page). I'm confused... I'm sure insulin regulated the...