Metabolism on-line - the virtual tutorial room
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An unusual cause of diabetes - how the pancreas senses a rise in blood glucose
There are two common types of diabetes mellitus
Type 1 diabetes (also known as insulin-dependent diabetes or juvenile onset diabetes)
Here the problem is one of failure to secrete adequate amounts of insulin, and patients are dependent on injection of insulin to maintain control over their blood glucose concentration. The condition usually develops in childhood and progresses with loss of pancreatic beta islet cells until there is almost no secretion of insulin.
Type 2 diabetes (also known as non-insulin-dependent diabetes or maturity onset diabetes)
Here the problem is one of loss of sensitivity of tissues to insulin action; the secretion of insulin may be normal or greater than normal. Although injection of insulin helps to maintain good control over blood glucose concentration, patients are not strictly dependent on an exogenous source of insulin. The problem usually develops in adult life and is commonly associated with obesity, especially abdominal obesity.
What are the main ways in which insulin acts to lower blood glucose?
Insulin stimulates uptake of glucose into muscle and adipose tissue. It achieves this by recruitment of glucose transporters from intracellular vesicles to the cell surface.
In the presence of insulin, glucose becomes major fuel for muscle contraction. There is increased synthesis of glycogen as a result of activation of glycogen synthase and inactivation of glycogen phosphorylase.
In adipose tissue, glucose is used for the synthesis of fatty acids and and the triacylglycerol for storage, as a result of increased activity of fatty acid synthase and decreased activity of hormone-sensitive lipase.
Liver uptake of glucose is not affected by insulin, but insulin stimulates the synthesis of glycogen from glucose, as in muscle, as a result of activation of glycogen synthase and inactivation of glycogen phosphorylase.