Question 54

Question:

A prisoner goes on a hunger strike to protest the conditions of his detainment. After several days, his blood glucose level is significantly reduced. In order to keep a constant supply of energy to his brain and muscle, which of the following molecules is his liver releasing?

Correct Answer: A.  Beta-hydroxybutyrate

The liver’s role during starvation is to release both glucose (via gluconeogenesis) and ketone bodies into the blood.

Adipose tissue provides fatty acids both for muscle and liver. Muscle oxidizes the fatty acids completely to CO2 and water for energy. The liver converts about half of the fatty acids it takes up into ketone bodies (acetoacetate and b-hydroxybutyrate), which it releases into the blood. The other half is oxidized to provide energy for the liver.

Glycogen reserves are gone after 30 hours, but even when present, glycogen is never released into the blood as a polymer. It is broken down into G1P, which is then converted to G6P, which is then hydrolyzed to free glucose. Only free glucose can exit the cell.