Prolonged Starvation Glucose Maintenance: Correct Answer Revealed

In prolonged starvation, the body sustains minimum blood glucose levels for the brain and RBCs primarily through gluconeogenesis in the liver and kidney.

Correct Answer

2. Gluconeogenesis in liver and kidney
This process synthesizes glucose from non-carbohydrate precursors like amino acids, lactate, and glycerol, becoming dominant after glycogen stores deplete (around 24 hours). In extended starvation (e.g., 5-6 weeks), the liver provides ~50% of glucose, with kidneys contributing the rest via cortical gluconeogenesis.

Option Explanations

1. Glycogenolysis in Liver

Glycogenolysis breaks down liver glycogen to glucose-6-phosphate, then free glucose for blood release. It maintains glucose in early fasting (4-16 hours) but depletes after ~24 hours, insufficient for prolonged starvation.​​

2. Gluconeogenesis in Liver and Kidney (Correct)

Key in prolonged starvation; liver uses alanine/glutamine from muscle, glycerol from fat. Kidneys ramp up after days, handling ~50% using glutamine, supporting blood glucose despite low rates (~86g/day total).

3. Glycogenolysis in Muscle

Muscle glycogen breaks down to glucose-6-phosphate for local glycolysis (no glucose-6-phosphatase), fueling muscle ATP. It does not release glucose to blood, irrelevant for brain/RBC supply.​

4. Gluconeogenesis in Muscle and Liver

Muscle lacks glucose-6-phosphatase, preventing free glucose release; it supplies substrates (e.g., alanine) to liver instead. Only liver/kidney export glucose systemically.