Question

A patient had dinner at 8 pm. He then did a blood sugar test at 7 am the next morning. A major source of blood glucose at the time of this test would be:

• A. Glycogenolysis
• B. Gluconeogenesis
• C. Dietary glucose absorption
• D. Lipolysis

Hint:

Consider how many hours have elapsed since the last meal and which metabolic pathway predominates after glycogen stores are depleted.

Answer 1

The Correct Option is B

Step 1: Identify the time gap. The patient ate dinner at 8 pm and the blood glucose test was performed at 7 am -- an 11-hour overnight fast.

Step 2: Glycogen stores and their depletion timeline. Hepatic glycogen is the first responder to falling blood glucose. Hepatic glycogen stores support blood glucose for approximately 8--12 hours of fasting. By 11 hours, hepatic glycogen stores are largely depleted.

Step 3: Role of gluconeogenesis in prolonged fasting. After glycogen is exhausted, gluconeogenesis becomes the dominant pathway. The liver synthesizes glucose de novo from substrates such as lactate (Cori cycle), alanine (glucose-alanine cycle), glycerol (from lipolysis), and oxaloacetate. Gluconeogenesis is actively upregulated by glucagon and cortisol during the overnight fasted state.

Step 4: Why not glycogenolysis? Glycogenolysis would have been the major source in the first 4--6 hours after the meal; by 11 hours it is no longer the primary pathway. Dietary glucose absorption is irrelevant at 11 hours post-meal. Lipolysis provides free fatty acids (which spare glucose use) and glycerol as a gluconeogenic substrate, but is not itself a direct glucose source in blood.

Conclusion: At 11 hours of fasting (7 am after an 8 pm dinner), gluconeogenesis is the major source of blood glucose.