This negative feedback loop (something's wrong, fix it) is regulated by the release of insulin and glucagon through the islets in the pancreas. Insulin secretion is triggered by a high level of glucose in blood. Insulin causes a reaction in a numbers of cells, including muscle cells, red blood cells and fat cells to begin taking in and storing excess blood glucose, lowering the level of free glucose in the blood. Glucagon secretion, on the other hand, is triggered by a low level of glucose in blood. Glucagon causes a direct reaction in the liver, causing it to release excess glucose stored in its cells into the bloodstream, which raises the level of glucose. It also has the effect of instructing the liver and muscle cells, among others, to begin actually creating new glucose molecules out of the building blocks of other nutrients in the body.
