Why does glucagon promote insulin secretion?

Glucagon and insulin are hormones secreted by different types of cells in the pancreas (alpha cells and beta cells, respectively). The primary function of glucagon is to elevate blood glucose levels, whereas insulin acts to lower blood glucose levels.

1. Effect of blood glucose concentration: When blood glucose levels decrease in the body, pancreatic alpha cells secrete glucagon, which breaks down glycogen to raise blood glucose levels. This process of increasing blood glucose stimulates pancreatic beta cells to secrete insulin.

2. Direct stimulatory effect: Glucagon can stimulate insulin secretion from beta cells by directly acting on them. This stimulation helps maintain blood glucose within a relatively stable range and prevents blood glucose levels from dropping too low.

3. Indirect effects: In regulating blood glucose balance, insulin and glucagon work synergistically. Insulin primarily lowers blood glucose levels, while glucagon mainly raises them. When blood glucose levels decrease, glucagon secretion increases, stimulating insulin secretion to maintain stable blood glucose levels.

Glucagon-induced insulin secretion is part of the regulatory mechanism for blood glucose homeostasis, maintaining blood glucose levels within a stable range through both direct and indirect pathways, thus helping the body maintain normal blood glucose levels under various physiological conditions.