Which hormone lowers blood glucose by promoting cellular uptake of glucose into cells?

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

Answer: (B)

Insulin is the hormone that lowers blood glucose by promoting the uptake of glucose into cells. When blood glucose rises after a meal, pancreatic beta cells release insulin into the bloodstream. Insulin binds to receptors on muscle and adipose cells, triggering a signaling cascade that causes GLUT4 glucose transporters to move to the cell surface. With GLUT4 present on the membrane, glucose can enter the cells more readily, reducing circulating blood glucose. This uptake in muscle and fat tissues is a major way insulin lowers blood glucose and also supports storage of excess glucose as glycogen in liver and muscle and fat synthesis in adipose tissue. In the liver, glucose uptake uses GLUT2 and is regulated by insulin’s effects on enzymes, promoting glycogen synthesis and inhibiting glucose production. By contrast, glucagon raises blood glucose by promoting glycogenolysis and gluconeogenesis, while ADH and melatonin regulate water balance and circadian rhythms, respectively, and do not directly drive glucose uptake into cells.