During fasting, which organ predominantly conducts glycogenolysis in the body?

• A. Muscle
• B. Brain
• C. Adipose
• D. Liver

Answer: (D)

During fasting, maintaining blood glucose relies on liver glycogenolysis. The liver uniquely can convert glycogen to free glucose and release it into the bloodstream because it contains glucose-6-phosphatase, which dephosphorylates glucose-6-phosphate to glucose. Muscles also break down glycogen, but the glucose they produce is used locally for muscle contraction and cannot be released into the blood because muscle tissue lacks glucose-6-phosphatase. Adipose tissue relies on lipolysis, not glycogen breakdown, for energy. The brain uses glucose from the blood (and later ketones), but it does not supply glucose to the body. Therefore, the liver is the predominant organ conducting glycogenolysis during fasting.