Which statement best describes the primary action of insulin on blood glucose?

• A. Increasing hepatic glucose production
• B. Inhibiting glucose transport into cells
• C. Increasing glucose excretion by kidneys
• D. Lowering blood glucose by promoting cellular uptake of glucose

Answer: (D)

Insulin’s main effect on blood glucose is to lower it by promoting the movement of glucose from the bloodstream into cells, especially muscle and adipose tissue. When insulin binds its receptor, it triggers the translocation of GLUT4 transporters to the cell membrane, allowing glucose to enter cells from the blood. Within the liver, insulin also encourages glycogen synthesis and suppresses glucose production, but the immediate, primary action that reduces circulating glucose is this cellular uptake. The other ideas don’t fit because increasing hepatic glucose production would raise blood sugar, blocking glucose entry would prevent uptake and raise glucose levels, and increasing renal glucose excretion isn’t how insulin exerts its glucose-lowering effect.