Which hormone lowers blood glucose levels?

• A. Adrenaline
• B. Thyroxine
• C. Glucagon
• D. Insulin

Answer: (D)

Insulin lowers blood glucose by promoting uptake of glucose into insulin-responsive tissues, especially skeletal muscle and adipose tissue, and by encouraging the liver to store glucose as glycogen. After a meal, rising blood glucose triggers release of insulin from the pancreatic beta cells. In the liver, insulin activates glycogen synthase to form glycogen and inhibits enzymes that generate glucose, reducing hepatic glucose output. In muscle and fat, insulin causes insertion of GLUT4 transporters into the cell membranes, increasing glucose entry from the blood.

Other hormones push blood glucose upward. Adrenaline (epinephrine) stimulates glycogenolysis and gluconeogenesis to raise glucose during stress. Glucagon also promotes hepatic glucose production. Thyroxine increases metabolic rate and can alter glucose turnover, but it does not directly lower blood glucose the way insulin does.

So, the hormone that lowers blood glucose levels is insulin.