Final answer:
When blood glucose falls, pancreatic alpha cells release glucagon, which raises blood glucose levels by stimulating glycogen breakdown (glycogenolysis) and glucose synthesis (gluconeogenesis).
Step-by-step explanation:
When blood glucose falls, pancreatic alpha cells release glucagon into circulation, where it binds to receptors on target cells, initiating pathways that cause them to release glucose, thus causing blood glucose to rise.
Receptors in the pancreas can sense the decline in blood glucose levels, and in response, the alpha cells secrete the hormone glucagon. This process leads to several effects that increase blood glucose levels, primarily by stimulating the breakdown of glycogen to glucose in the liver and skeletal muscle cells, a process known as glycogenolysis. Additionally, glucagon promotes gluconeogenesis, where the liver converts amino acids to glucose, and stimulates adipose cells to release fatty acids. These actions work together to raise blood glucose levels to normal homeostatic ranges.