Insulin: how it works

Insulin is a hormone that helps your body control the amount of sugar (glucose) in your blood. It is produced by the pancreas, a large gland that is located in the abdomen behind your stomach.

How does insulin work?

Insulin is produced in the islets of Langerhans (pancreatic islets), which are small isolated clumps of special cells in the pancreas. Insulin works alongside glucagon, another hormone produced by the pancreas, to manage the levels of glucose in your blood.

Both insulin and glucagon are secreted directly into your bloodstream, and work together to regulate your blood glucose levels. Insulin should stop your blood sugar from rising too high and glucagon should prevent it from becoming too low.

Insulin is produced by the beta cells of the pancreatic islets. Insulin is released when you have just eaten a meal and the level of glucose in your bloodstream is high. It works by stimulating the uptake of glucose into cells, lowering your blood sugar level. Your liver and muscles can take up glucose either for immediate energy or to be stored as glycogen until it’s needed.

Glucagon is produced by the alpha cells of the pancreatic islets. It is released when your blood sugar levels are low (for example overnight, or if you have been fasting or exercising). Glucagon stimulates cells in the liver and muscles to convert stored glycogen to glucose. The glucose is then released into the bloodstream, raising your blood sugar level.

What is insulin resistance?

Insulin resistance is when the liver and muscle cells stop responding properly to insulin.

The initial response of the pancreas is to make more insulin to help glucose enter cells, but the pancreas usually cannot keep making more and more insulin to overcome the insulin resistance. Eventually the insulin-producing cells of the pancreas start to burn themselves out and blood glucose levels start to rise (hyperglycaemia).

After some time, insulin resistance can cause type 2 diabetes, because there are no longer enough insulin-producing cells and also, the remaining ones are not as effective.

What is pre-diabetes?

Pre-diabetes is the condition when blood sugar levels are raised, but are not high enough for a diagnosis of type 2 diabetes to be made. Insulin resistance is the process by which pre-diabetes comes about.

People with pre-diabetes have so-called impaired fasting glucose (IFG) or impaired glucose tolerance (IGT).

  • Impaired fasting glucose (IFG) is when your blood sugar levels are raised after fasting (not eating) but the levels are not high enough to diagnose diabetes. IFG is due to the liver releasing too much glucose into the blood when you are fasting overnight because it has become resistant to the effects of insulin.
  • Impaired glucose tolerance (IGT) is when blood glucose levels are higher than normal (and also higher than in IFG) but still not high enough to make a diagnosis of diabetes. In IGT, blood glucose levels may be raised after meals or at other times. IGT happens when the body’s cells stop responding properly to insulin (insulin resistance) and/or there is not enough insulin to meet the body’s needs.

Your risk of developing pre-diabetes is increased if you are overweight or don’t get enough physical activity. Pre-diabetes risk factors are similar to those for type 2 diabetes.

Many people with pre-diabetes go on to develop type 2 diabetes. However, making lifestyle changes, such as eating a healthy balanced diet, losing weight and getting regular physical activity, can stop pre-diabetes from progressing to type 2 diabetes.

Insulin and diabetes

Diabetes mellitus is a condition where the blood contains too much glucose. The high blood glucose can be due to the pancreas not producing enough insulin, or to insulin resistance, where the body’s cells are not responding to the insulin being produced.

The most common types of diabetes include:

  • type 1 diabetes, where the pancreas produces little or no insulin because the beta cells have been destroyed by the immune system;
  • type 2 diabetes, where the body stops responding to insulin - at first, the pancreas reacts by producing extra insulin (hyperinsulinaemia), but eventually it is unable to make enough to meet the body's needs; and
  • gestational diabetes, where diabetes develops during pregnancy.

Achieving normal blood glucose levels

People with type 1 diabetes must take daily insulin to control their blood glucose levels. Insulin is usually given by injection (using a needle and syringe or insulin pen) or via an insulin pump.

People with type 2 diabetes can often control their blood sugar levels with a healthy diet, sufficient exercise and/or the use of tablets known as oral hypoglycaemic medicines, such as metformin. Eventually, however, many people with type 2 diabetes will also require insulin injections to keep their blood sugar levels steady.

People with diabetes need to monitor their blood sugar levels regularly. Your general practitioner (GP), endocrinologist (diabetes specialist) and diabetes educator will work with you to set goals for your optimum blood glucose levels before and after meals.

Blood sugar level targets, or goals, are usually set specifically for an individual. Factors that help work out your personalised target blood sugar levels include the type of diabetes you have and whether you are prone to episodes of low blood sugar (hypoglycaemia).

Last Reviewed: 28 August 2017
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References

1. Diabetes: Detection and diagnosis (published Nov 2013; amended Feb 2015). In: eTG complete. Melbourne: Therapeutic Guidelines Limited; 2017 Jul. https://tgldcdp.tg.org.au/etgcomplete(accessed Aug 2017).
2. Management of type 1 diabetes (published Nov 2013). In: eTG complete. Melbourne: Therapeutic Guidelines Limited; 2017 Jul. https://tgldcdp.tg.org.au/etgcomplete (accessed Aug 2017).
3. Management of type 2 diabetes (published Nov 2013). In: eTG complete. Melbourne: Therapeutic Guidelines Limited; 2017 Jul. https://tgldcdp.tg.org.au/etgcomplete (accessed Aug 2017).
4. Diabetes Australia. Insulin (published June 2016). http://diabetesnsw.com.au/useful-tools/information-sheets/ (accessed Aug 2017).
5. National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK). What is diabetes? (updated Nov 2016). https://www.niddk.nih.gov/health-information/diabetes/overview/what-is-diabetes (accessed Aug 2017).
6. Diabetes NSW. Pre-diabetes (IFG and ICT) (revised 2012). https://diabetesnsw.com.au/wp-content/uploads/2014/12/DA-29-Pre-diabetes.pdf (accessed Aug 2017).
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