Insulin Resistance Vs. Insulin Sensitivity Definition

Disposal of glucose from circulation into skeletal muscle is performed by insulin.

Insulin attaches to a receptor on the surface of muscle tissue and drives a complex change within the interior compartment of the tissues which allows glucose to enter.

Tissue responsiveness to insulin, meaning how successfully the receptor operates to permit glucose clearance, is termed insulin sensitivity. In the case of optimal insulin sensitivity, after a high sugar meal, insulin rises sharply, pushing glucose into the tissues rapidly, then dissipates. In the case of poor insulin sensitivity, however, insulin's elevation is sustained due to an inability to force glucose into muscle tissues.

Poor receptor sensitivity indicates a failure in the communication between insulin and the internal cellular machinery. Locked out of the muscles, glucose remains elevated in circulation. Because glucose remains high, the pancreas must generate additional insulin or insulin will need to be injected to complete circulatory glucose disposal.

Abnormally low insulin sensitivity is called insulin resistance. In this case, tissues resist the activity of insulin on a regular basis, disabling efforts to remove glucose from circulation and eventually requiring medical intervention.

Insulin resistance also occurs at the liver and adipose tissues. When these tissues do not properly respond to insulin, glucose and fat are released into circulation. Sustained elevation of circulatory glucose and triglyceride causes cardiovascular diseases and obesity.