To understand what diabetes is, you must first understand how glucose (blood sugar) is normally processed in the body.
How Insulin Works
Insulin is a hormone that comes from the pancreas, a gland situated behind and below the stomach. The pancreas releases insulin into the bloodstream. Insulin allows sugar to enter your cells and lowers the amount of sugar that is in your bloodstream. As your blood sugar level drops, so does the amount of insulin released from your pancreas.
The Role of Glucose
Glucose is a blood sugar. It is the main source of energy for the cells that make up muscles and other tissues in the body. Glucose comes from two major sources: food and your liver. Glucose is absorbed into the bloodstream and, where it enters the cells with the help of insulin. Your liver stores and makes glucose. When your insulin levels are low, such as when you haven't eaten in a while, the liver breaks down glycogen (which is the main form of glucose that is stored in the body) into glucose to keep your glucose level within a normal range.
Causes of Type 1 Diabetes
Your immune system normally fights harmful bacteria or viruses. In type 1 diabetes, it attacks and destroys the insulin-producing cells in the pancreas. This leaves you with little or no insulin; instead of going into your cells, sugar builds up in your bloodstream. Type 1 diabetes is thought to be caused by a combination of genetic and environmental factors. However, exactly what many of those factors are is still unclear.
Causes of Prediabetes and Type 2 Diabetes
In prediabetes and type 2 diabetes, your cells become resistant to insulin. When this happens, your pancreas is unable to make enough insulin to overcome this resistance. Instead of moving into your cells where it's needed for energy, sugar builds up in your bloodstream. Exactly why this happens is uncertain but it's believed that genetic and environmental factors play a role. Being overweight is a strong risk factor for the development of type 2 diabetes.
Causes of Gestational Diabetes
During pregnancy, the placenta makes hormones you will need to carry on your pregnancy. These hormones make your cells more resistant to insulin. As your placenta grows larger in the second and third trimesters, it creates more of these hormones, making it even harder for insulin to do its job. Normally, your pancreas produces enough extra insulin to beat this resistance. But sometimes, the pancreas can't keep up. When this happens, not enough glucose gets into the cells and too much stays in the blood. This is gestational diabetes