Which gland secretes insulin to lower blood glucose levels?

• A. Glucagon
• B. Insulin
• C. Cortisol
• D. Epinephrine

Answer: (B)

Insulin is the hormone that lowers blood glucose levels. It’s produced by the beta cells of the pancreas and released when blood sugar is high after a meal. Once in the bloodstream, insulin signals liver, muscle, and fat tissues to take up glucose. In muscle and fat, this happens mainly by promoting the movement of GLUT4 transporters to the cell surface, increasing glucose uptake. In the liver, insulin encourages glycogen synthesis and suppresses glucose production. Through these actions, circulating glucose falls back toward normal.

The other substances listed raise blood glucose: glucagon increases glucose by promoting glycogen breakdown and gluconeogenesis; cortisol stimulates glucose production during stress; epinephrine also drives glucose release during fight-or-flight. So insulin uniquely lowers blood glucose, and it is produced by the pancreas.