Glucose is the sugar that fuels your metabolism. After you eat, your digestive tract breaks down carbohydrates into sugar that's absorbed into your bloodstream. Glucose is a vital source of energy for your body's cells. But to provide that energy, glucose must travel from your blood into your cells.
Insulin is the hormone that unlocks the door to your cells. When your blood glucose level rises after you eat, your pancreas springs into action by pouring insulin into your bloodstream. If you produce enough insulin and your cells respond normally, your blood sugar level drops as glucose enters your cells. It is then burned for energy or stored away for future use.