Final answer:
Glucagon is released in response to low blood glucose levels, typically due to prolonged fasting. It functions to raise glucose levels in the blood through processes like glycogenolysis and gluconeogenesis.
Step-by-step explanation:
Trigger for the Release of Glucagon
The hormone glucagon is released by the alpha cells of the pancreas when blood glucose levels decline below normal levels. This situation can arise during conditions such as prolonged fasting, or when the body requires more glucose, like during severe exercise or starvation. The primary function of glucagon is to raise blood glucose levels to ensure a steady supply of fuel for the body's cells. This is accomplished through glycogenolysis (the breakdown of glycogen into glucose) primarily in the liver, as well as through gluconeogenesis (the creation of glucose from non-carbohydrate sources), among other mechanisms.
Given the options provided, the correct answer is (1) prolonged fasting. Hyperglycemia, the release of somatostatin, and the release of insulin are not triggers for the secretion of glucagon; instead, they are typically associated with a reduction in glucagon release or the release of other hormones.