Insulin is secreted by the beta cells of the pancreas in response to high blood sugar, although a low level of insulin is always secreted by the pancreas. After a meal, the amount of insulin secreted into the blood increases as the blood glucose rises. Likewise, as blood glucose falls, insulin secretion by the pancreatic islet beta cells decreases.In response to insulin, cells (muscle, red blood cells, and fat cells) take glucose in from the blood, which ultimately lowers the high blood glucose levels back to the normal range
Glucagon is secreted by the alpha cells of the pancreas when blood glucose is low. Blood glucose is low between meals and during exercise. When blood glucose is high, no glucagon is secreted from the alpha cells. Glucagon has the greatest effect on the liver although it affects many different cells in the body. Glucagon's function is to cause the liver to release stored glucose from its cells into the blood. Glucagon also the production of glucose by the liver out of building blocks obtained from other nutrients found in the body, for example, protein [4].