What is the primary action of glucagon?

The primary action of glucagon is to increase blood glucose levels, and it does this by stimulating the liver to release stored glycogen. Glycogen is a polysaccharide that serves as a form of glucose storage in the liver. When blood glucose levels drop, such as in instances of hypoglycemia, glucagon is secreted from the alpha cells of the pancreas. This hormone binds to receptors in the liver, promoting the conversion of glycogen back into glucose, allowing it to enter the bloodstream and raise blood glucose levels.

This function is crucial in maintaining homeostasis, particularly during fasting or when the body experiences low sugar levels. By increasing blood glucose, glucagon helps ensure that the body, especially the brain, receives enough energy to function properly.

Other options describe actions that do not accurately reflect glucagon's role. For instance, glucagon does not decrease blood glucose levels or stimulate insulin production; rather, it has the opposite effect and is released in situations where blood sugar needs to be elevated.