Glucose Metabolism and Insulin Resistance
A stable level of glucose in the blood is necessary to provide energy to the brain, muscles, and organs; and excess energy is stored in fat tissue. When glucose levels in the blood decrease, pancreatic beta cells produce glucagon, which stimulates the liver to mobilize glycogen stores to release glucose into the bloodstream. When glucose levels rise, pancreatic alpha cells produce insulin, which inhibits glucose output from the liver and stimulates muscle and fat tissue to absorb glucose from the blood.
In insulin resistance the liver, muscle, and fat do not respond to the presence of insulin, which in turn leads to elevated blood glucose levels. This increases signaling to tissue receptors, which respond, although at a minimal level, allowing glucose levels to remain elevated. In type II diabetes, however, tissue receptors are desensitized to glucose stimuli and blood sugar levels rise, leading to symptoms of diabetes and, if left uncontrolled, to diabetic complications.