Question
A man is trapped in a tunnel for 5 consecutive days without access to food but survives. What is the primary source of energy for his brain during this period?
| A. |
Gluconeogenesis
|
| B. |
Glycogenolysis
|
| C. |
Ketosis
|
| D. |
Lipolysis
|
Show Answer
|
Correct Answer � C
Explanation
|
|
In prolonged fasting (>72 hours), glycogen stores deplete. Gluconeogenesis alone can’t meet energy demands.
The liver ↑ ketone body production (ketosis) via fatty acid oxidation.
Ketone bodies – acetoacetate & β-hydroxybutyrate – become the brain’s primary energy source, ↓ glucose reliance.
This shift spares muscle protein from excessive gluconeogenesis breakdown.
Incorrect Options:
– A: Gluconeogenesis is not the primary brain fuel.
– B: Glycogenolysis is exhausted within 24 hours.
– D: Lipolysis provides fatty acids; brain uses only derived ketones.
