What condition triggers insulin release?

• A. Dehydration
• B. Low blood glucose
• C. Increased cortisol
• D. Elevated blood glucose

Answer: (D)

Elevated blood glucose after a meal is what signals the pancreas to release insulin. Glucose enters the pancreatic beta cells through GLUT2 transporters and is metabolized, raising the ATP/ADP ratio inside the cell. That increase closes ATP-sensitive potassium channels, causing the cell to depolarize. The depolarization opens voltage-gated calcium channels, and the inflow of Ca2+ triggers the release (exocytosis) of insulin-containing granules. The secreted insulin then promotes glucose uptake into liver, muscle, and adipose tissue and suppresses hepatic glucose production, lowering blood glucose back toward normal. Dehydration doesn’t directly trigger insulin release, low blood glucose actually inhibits insulin release and stimulates glucagon, and cortisol raises blood glucose by increasing hepatic glucose production and can cause insulin resistance, but it does not directly trigger insulin release. The key signal for insulin release is high blood glucose.