What is Diabetes?
Diabetes mellitus includes a group of conditions characterized by a high level of blood glucose, commonly referred to as blood sugar. Too much sugar in the blood can cause serious, sometimes life-threatening health problems.
There are two types of chronic (lasts for life) diabetic conditions : type 1 diabetes and type 2 diabetes. Pregnant women may acquire a transient form of the disease called gestational diabetes which usually resolves after the birth of baby. Prediabetes is when your blood sugar is at the borderline : higher than normal, but lower than in diabetics. Prediabetes may or may not progress to diabetes.
Insulin and Metabolism of Glucose
In order to understand diabetes we should first understand glucose metabolism and role of insulin. Carbohydrate (carb) in food breaks down to glucose which is carried by the bloodstream to various organs of the body where it is either consumed as an energy source (e.g. in muscles), or is stored for later use (in the liver). Insulin is a hormone produced by beta cells of the pancreas and is necessary for glucose intake by the target cells. In other words, when insulin is deficient, muscle or liver cells won’t be able to use or store glucose and as a result, glucose will accumulate in the blood (Fig. 1).
How blood glucose is regulated ? A feedback loop is in place to ensure that glucose level in the blood is never too high or too low, i.e. in normal range. Shortly after a meal, level of glucose in the blood is up. High glucose level stimulates beta cells to secrete insulin into the bloodstream. Insulin and glucose travel in bloodstream to reach target organs (e.g. muscles, liver,..). In target organs, insulin induces cells to take up glucose for use as energy or store for later use. As glucose is consumed by target organs, its concentration in the blood goes down and no more insulin is secreted from beta cells, insulin level goes down, glucose is no longer taken into cells, this prevents glucose level from going down further. When blood sugar level is too low (e.g. before meal time), previously stored glucose in the liver is released back into the bloodstream thanks to the action of another pancreatic hormone called glucagon. In short, insulin lowers blood sugar level while glucagon increases it. Regulation and ratio of these two hormones are vital for maintaining blood glucose levels within normal range.
Type 1 and type 2 Diabetes
Type 1 diabetes = insulin dependent : The pancreas does not produce enough insulin due to lack of beta cells. Not enough beta cells in the pancreas => not enough insulin => organs can not use or store glucose => glucose accumulates in the bloodstream. Type 1 is characterized by early (juvenile) onset, symptoms commonly start suddenly and before the age of 20. Type 1 diabetes is normally managed with insulin injection.
Fig. 1: Type 1 diabetes. The pancreas produces less insulin, liver and muscle cells absorb less glucose, glucose stays in the blood, blood sugar level increased. Click on image to see a larger version on Alila Medical Media website where the image is also available for licensing.
Type 2 diabetes = insulin resistant : Insulin is produced normally by the pancreas, but for some reasons, the cells of target organs (e.g. muscles, liver,..) do not response to insulin and therefore can not use or store glucose, glucose accumulates in the blood (Fig. 2). Type 2 is characterized by adult onset, symptoms usually appear gradually and start after the age of 30. Type 2 diabetes accounts for about 80-90% of all diabetics. Management focuses on weight loss and includes a low-carb diet.
Fig. 2: Type 2 diabetes. The pancreas produces the same amount of insulin but organs are unresponsive, glucose can not be used and stays in the blood, blood sugar level increased. Click on image to see a larger version on Alila Medical Media website where the image is also available for licensing.
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