Insulin and glucagon are peptide hormones that maintain homeostasis, or balance, in blood glucose levels within the body. Beta cells produce the inactive form of insulin and glucagon is produced by alpha cells. That inactive form of insulin, proinsulin, is converted into insulin during circulation, and insulin and glucagon are then secreted by the endocrine portion of the pancreas and work synergistically to keep blood glucose concentrations within a very tight normal range.

Normal blood glucose levels should stay between 70 milligrams of glucose per 100 milliliters of blood (mg/dl) and 110 mg/dl. Hypoglycemia is the term given to blood glucose levels below 70 mg/dl. Levels above 110 mg/dl can be considered normal right after a meal but should always remain below 180 mg/dl, even after eating. A blood glucose level above 180 mg/dl means there is too much glucose in the blood and is referred to as hyperglycemia.

When blood sugar levels rise in the blood, insulin is secreted by the beta cells of the pancreas. A low level of insulin is always being secreted, but the amount of insulin secreted into the bloodstream increases after a meal. As the blood glucose level rises, so does the amount of insulin secreted. The release of insulin causes muscle cells, red blood cells and fat cells to take in glucose from the blood, lowering blood glucose levels back to within the normal range. As the blood glucose level falls, insulin secretion decreases.

Hyperglycemia can be a temporary condition that shows no symptoms. Chronic hyperglycemia, however, can cause long-term debilitating complications including a loss of eyesight, and heart, nerve and kidney damage. Those most likely to suffer from hyperglycemia are people with diabetes mellitus. This is why diabetes treatment often involves using insulin to keep blood glucose levels within a normal range and fairly balanced.

Blood glucose levels typically decline between meals and during exercise. When blood glucose is too low, the alpha cells of the pancreas secrete glucagon to help raise those levels. Similar to insulin, glucagon affects many cells within the body, but the liver is glucagon’s key receptor.

The liver stores glucose in the form of glycogen. Secreted glucagon causes the liver to convert this stored glycogen into glucose and release it into the bloodstream, raising blood glucose levels in the process. Glucagon also triggers the liver, muscle cells and other cells to make glucose using building blocks acquired from the body’s other nutrients, such as protein. This process is called gluconeogenesis and helps to maintain blood glucose concentrations during periods of vigorous exercise or starvation. By working together, insulin and glucagon use their two very different functions to help keep the body working properly.