Which cells secrete insulin?

• A. Beta cells
• B. Alpha cells
• C. Delta cells
• D. Acinar cells

Answer: (A)

Insulin is produced and secreted by the beta cells of the pancreatic islets. These cells detect rising blood glucose after a meal and release insulin to help tissues take up glucose. Insulin promotes glucose uptake into skeletal muscle and adipose tissue (via GLUT4) and suppresses glucose production by the liver, lowering blood sugar.

The secretion mechanism is tied to glucose metabolism: glucose entering the beta cell increases the ATP/ADP ratio, which closes KATP channels, causing cell depolarization. This opens voltage-gated calcium channels, allowing calcium influx that triggers exocytosis of insulin-containing granules.

Other islet cells have different roles: alpha cells secrete glucagon to raise blood glucose, delta cells secrete somatostatin which slows the release of other hormones and gastrointestinal processes, and acinar cells are part of the exocrine pancreas, producing digestive enzymes.