What function does insulin serve in glucose metabolism?

Insulin plays a critical role in glucose metabolism by facilitating glucose uptake into cells. When blood glucose levels rise after a meal, insulin is released from the pancreas. The presence of insulin signals cells throughout the body, particularly in muscle and adipose (fat) tissues, to increase their permeability to glucose. This occurs through the promotion of glucose transporter proteins, such as GLUT4, which capture glucose from the bloodstream and transport it into the cells for energy production or storage. By enhancing glucose uptake, insulin effectively lowers blood glucose levels, ensuring that the body's energy needs are met and maintaining metabolic homeostasis.

In contrast, the other functions listed are not accurate representations of insulin's role. Insulin does not trigger glucose production in the liver; instead, it inhibits gluconeogenesis (the production of glucose) when blood sugar is high. While it does play a role in fat metabolism, particularly in the synthesis of fatty acids, insulin does not directly break down stored fats; that process is typically stimulated by hormones like glucagon during fasting states. Finally, insulin functions to decrease blood sugar levels, not increase them, making it a key regulatory hormone in preventing hyperglycemia.