Which of the following is least dependent on insulin to move glucose into the cells?

• A. Brain
• B. Skeletal muscle
• C. Liver
• D. Adipose tissue

Answer: (A)

Glucose entry into cells depends on the type of glucose transporter a tissue uses. Skeletal muscle and adipose tissue rely on GLUT4, which moves to the cell surface in response to insulin, so their glucose uptake markedly increases with insulin and decreases when insulin is low. The liver uses GLUT2, and glucose moves into liver cells based mainly on blood glucose concentration rather than insulin signaling, so it doesn’t depend on insulin for uptake in the same way as muscle or fat. The brain uses GLUT1 and GLUT3 transporters, which have high affinity for glucose and function largely independently of insulin, ensuring neurons receive glucose even when insulin levels are low. Therefore, the brain is least dependent on insulin to move glucose into its cells.