What is the effect of glucagon in the body?

Glucagon is a hormone produced by the alpha cells of the pancreas, and its primary role in the body is to increase blood glucose levels. It does this by promoting gluconeogenesis and glycogenolysis in the liver. During periods of fasting or between meals, when blood glucose levels are low, glucagon is released into the bloodstream to mobilize glucose stored in the liver.

Specifically, glucagon stimulates the breakdown of glycogen, which is the stored form of glucose, into glucose molecules that are then released into the bloodstream. It also encourages the liver to convert non-carbohydrate substrates, such as amino acids and glycerol, into glucose through the process of gluconeogenesis, further increasing the availability of blood glucose.

In contrast, the other choices either describe functions that are contrary to glucagon’s effects or relate to different hormones. For example, decreasing blood glucose levels is primarily a function of insulin rather than glucagon, and stimulating glycogen synthesis also relates to insulin's action, which promotes the storage of glucose rather than its release. Enhancing metabolic rate can involve various hormones, but it is not the principal action of glucagon in terms of blood glucose regulation.