What is the main function of glucose-dependent insulinotropic peptide (GIP)?

Glucose-dependent insulinotropic peptide (GIP) is a hormone released by the K-cells in the duodenum and jejunum in response to food intake, particularly carbohydrates and fats. Its main function is to stimulate insulin secretion from the pancreatic beta cells in a glucose-dependent manner. When blood glucose levels rise after a meal, GIP enhances insulin release, facilitating glucose uptake by tissues and helping to lower blood sugar levels effectively.

The role of GIP is critical in the postprandial (after eating) phase, as it aids in managing blood glucose levels by ensuring that insulin is released only when it is needed, thus promoting metabolic homeostasis. The unique aspect of GIP’s function is its glucose dependency; it is most effective when glucose levels are elevated, which helps prevent hypoglycemia.

Other options relate to various physiological processes but do not accurately describe GIP's primary role. For instance, while glucagon is involved in raising blood glucose levels, GIP specifically promotes insulin secretion. Additionally, GIP does not primarily influence gastric motility or appetite directly, but rather focuses on the regulation of insulin in the context of nutrient intake.