Insulin: how it works
What is insulin?
Insulin is a hormone produced by the pancreas, a large gland that is located in the abdomen, behind your stomach.
Insulin is produced by special cells called pancreatic islets (or islets of Langerhans), which exist as small, isolated clumps of cells within the pancreas. The islets of Langerhans also produce glucagon, another hormone which affects blood glucose levels. Both insulin and glucagon are secreted directly into your bloodstream, and work together to regulate the sugar (glucose) levels in your body.
Glucagon is produced by the alpha cells of the pancreatic islets. It is released when your blood sugar levels are low (for example, if you have been fasting or exercising) stimulating the release of glucose from your body stores. As a result, stored glycogen in the liver is broken down to glucose and enters the bloodstream.
Insulin, on the other hand, is produced by the beta cells of the pancreatic islets. It is released when you have just eaten a meal and the level of glucose in your bloodstream is high. Insulin works by stimulating the cells within your body to take up the glucose in your blood, either for immediate energy or for storing as glycogen in your liver and muscle cells.
Insulin and diabetes
If your pancreas does not produce enough insulin, or if your body's cells fail to respond to the insulin being produced (insulin resistance), then your blood will contain too much glucose (hyperglycaemia). This type of metabolic disorder is known as diabetes mellitus. It is often characterised by excessive thirst or hunger, frequent urination, recurrent infections (such as vaginal thrush or boils) and blurred vision. Other symptoms include slow healing of wounds and cuts, feeling tired or weak, mood swings, headaches, dizziness, leg cramps, and unexplained weight loss (for type 1 diabetes) or weight gain (for type 2 diabetes).
If your body cannot use glucose as its energy source, it will start to break down fat. This releases by-products called ketones into the bloodstream which cause the blood to become acidic (a condition called ketoacidosis). If left untreated, this can lead to diabetic coma and even death.
In type 1 diabetes, the pancreas produces little or no insulin. In type 2 diabetes, the body does not respond to insulin: at first, the pancreas reacts by producing extra insulin (hyperinsulinaemia) but eventually it is unable to produce enough to meet the body's needs.
Achieving normal blood glucose levels
For these reasons it is important that people with diabetes stabilise their blood glucose levels. Ideally, blood glucose levels when fasting or before meals should be between 4 and 6 mmol/L, and blood sugar levels after eating should be between 6 and 8 mmol/L.
In people with type 2 diabetes and people with IGT (impaired glucose tolerance) there either isn’t enough insulin or it does not function correctly which results in the levels of blood glucose being too high after a meal.
People with type 1 diabetes must have daily insulin injections — sometimes several times a day — to achieve their target blood glucose levels, while people with type 2 diabetes can usually control their condition with a healthy diet, sufficient exercise and/or the use of tablets known as oral hypoglycaemic medications. Eventually, however, many people with type 2 diabetes will require insulin injections.