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

After an 11-hour fast (dinner at 8 pm, test at 7 am), the body has exhausted most hepatic glycogen. Hepatic glycogen supports blood glucose for roughly 8--12 hours; beyond that window, $\text{gluconeogenesis}$ takes over as the dominant source.

Gluconeogenesis uses substrates such as lactate (via Cori cycle), alanine (via glucose-alanine cycle), glycerol (released from adipose lipolysis), and amino acids. The key regulatory enzymes -- $\text{PEPCK}$, fructose-1,6-bisphosphatase, and glucose-6-phosphatase -- are upregulated by glucagon and cortisol during fasting.

Glycogenolysis (option 1) was the primary pathway in the first 6--8 hours but is largely exhausted by 11 hours. Dietary glucose absorption (option 3) is zero at this stage. Lipolysis (option 4) provides glycerol as a gluconeogenic precursor and free fatty acids that spare peripheral glucose use, but it does not directly release glucose into blood.

\[\boxed{\text{Gluconeogenesis}}\]