Which of the following hormones can raise blood glucose levels?

Glucagon is a hormone produced by the alpha cells of the pancreas that plays a crucial role in regulating blood glucose levels. When blood glucose levels drop, glucagon is released into the bloodstream. Its primary function is to stimulate the liver to convert glycogen, the stored form of glucose, back into glucose through a process known as glycogenolysis. Additionally, glucagon promotes gluconeogenesis, which is the synthesis of glucose from non-carbohydrate sources such as proteins and fats.

By increasing the availability of glucose in the bloodstream, glucagon helps restore normal blood sugar levels, especially during fasting or between meals. This action is critical for maintaining energy homeostasis in the body, particularly for tissues that rely heavily on glucose, such as the brain.

In contrast, insulin, another hormone produced by the pancreas, lowers blood glucose levels by facilitating the uptake of glucose by cells and promoting its storage as glycogen. Histamine is involved in immune responses and does not directly influence blood glucose levels, while prolactin primarily regulates lactation and reproductive functions rather than glucose metabolism. Thus, glucagon is the key hormone that effectively raises blood glucose levels when needed.