USA Biology Olympiad (USABO) Practice Exam

What physiological effect does insulin have on the liver?

1. It promotes glycogenolysis

2. It enhances gluconeogenesis

3. It increases glycogen synthesis

4. It decreases lipid metabolism

The correct answer is: It increases glycogen synthesis

Insulin plays a critical role in glucose metabolism, particularly in the liver. One of its primary functions is to promote glycogen synthesis, which is the process of converting glucose into glycogen for storage. When blood glucose levels are high, such as after a meal, insulin is secreted by the pancreas and stimulates liver cells to take up glucose and convert it into glycogen. This process is crucial for regulating blood sugar levels and ensuring that energy is stored for future use. The increased glycogen synthesis by the liver helps lower blood glucose levels back toward a normal range, which is essential for maintaining homeostasis. Additionally, insulin has broader metabolic effects, including the inhibition of gluconeogenesis (the generation of glucose from non-carbohydrate sources) and glycogenolysis (the breakdown of glycogen into glucose). By promoting glycogen synthesis instead of these processes, insulin ensures that excess glucose in the bloodstream is effectively stored rather than released back into circulation. This is why the physiological effect of insulin on the liver primarily includes increasing glycogen synthesis.