Final answer:
Insulin is the hormone that has the opposite effect of glucagon. While glucagon raises blood glucose levels, insulin lowers them as part of a negative-feedback system, thus maintaining blood glucose homeostasis.
Step-by-step explanation:
The hormone that has the opposite effect of glucagon is insulin. Glucagon, produced by the alpha cells of the pancreas in response to low blood glucose levels, has a hyperglycemic effect; it raises blood glucose levels by promoting glycogenolysis, gluconeogenesis, and the release of fatty acids from adipose tissue. In contrast, insulin, which is secreted by the beta cells of the pancreas when blood glucose levels are high, reduces blood glucose levels by promoting the uptake of glucose by cells and the conversion of glucose into glycogen. These two hormones are part of a complex negative-feedback system that regulates blood glucose homeostasis.
Conditions like diabetes mellitus can result if there is target cell resistance to insulin, leading to chronically high blood glucose levels. Insulin actively lowers blood glucose by facilitating the uptake of glucose into target cells and inhibiting the breakdown of glycogen to glucose. The actions of insulin and glucagon are finely balanced to maintain blood glucose levels within a narrow range, thereby providing a stable supply of energy to the body.