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Causes
By Mayo Clinic staffType 2 diabetes develops when the body becomes resistant to insulin or when the pancreas stops producing enough insulin. Exactly why this happens is unknown, although excess weight and inactivity seem to be important factors.
Insulin is a hormone that comes from the pancreas, a gland located just behind the stomach. When you eat, the pancreas secretes insulin into the bloodstream. As insulin circulates, it acts like a key by unlocking microscopic doors that allow sugar to enter your cells. Insulin lowers the amount of sugar in your bloodstream. As your blood sugar level drops, so does the secretion of insulin from your pancreas.
Glucose — sugar — is a main source of energy for the cells that make up muscles and other tissues. Glucose comes from two major sources: the food you eat and your liver. After intestinal digestion and absorption, sugar is absorbed into the bloodstream. Normally, sugar then enters cells with the help of insulin.
The liver acts as a glucose storage and manufacturing center. When your insulin levels are low — when you haven't eaten in a while, for example — the liver metabolizes stored glycogen into glucose to keep your glucose level within a normal range.
In type 2 diabetes, this process works improperly. Instead of moving into your cells, sugar builds up in your bloodstream. This occurs when your pancreas doesn't make enough insulin or your cells become resistant to the action of insulin.
In type 1 diabetes, which is much less common, the pancreas produces little or no insulin.
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