Which hormone lowers blood glucose by promoting glucose uptake into tissues?

• A. Insulin
• B. Glucagon
• C. Melatonin
• D. Aldosterone

Answer: (A)

Insulin lowers blood glucose by promoting uptake of glucose into tissues. When blood glucose rises after a meal, pancreatic beta cells release insulin. It binds to receptors on muscle and adipose cells, triggering a signaling cascade that moves GLUT4 glucose transporters to the cell surface, increasing glucose entry into these cells. In the liver and muscle, insulin also stimulates glycogen synthesis (glycogenesis) and inhibits glycogen breakdown and new glucose production (gluconeogenesis), helping to reduce circulating glucose levels.

The other hormones don’t produce this uptake effect. Glucagon raises blood glucose by stimulating liver glycogenolysis and gluconeogenesis when glucose is low. Melatonin mainly regulates sleep–wake cycles and isn’t a major player in glucose uptake. Aldosterone controls electrolyte and fluid balance rather than glucose utilization.