Final answer:
The hormone secreted by the pancreas that opposes the effect of insulin is glucagon, which is produced by alpha cells and increases blood glucose by stimulating glycogen conversion in the liver.
Step-by-step explanation:
The hormone secreted by the pancreas that opposes the effect of insulin is glucagon. Alpha (a) cells in the pancreatic islets produce glucagon, which serves to increase the level of glucose in the blood. This is achieved by stimulating the liver to convert stored glycogen into glucose that is then released into the bloodstream. In contrast, insulin, which is secreted by beta (B) cells, decreases the blood glucose levels by promoting the absorption of glucose into cells. Therefore, glucagon and insulin have opposing effects in regulating blood glucose levels.