Final answer:
The liver metabolizes between 85% to 98% of alcohol, mostly via the alcohol dehydrogenase system and the microsomal ethanol oxidizing system, which are upregulated during heavy drinking.
Step-by-step explanation:
The liver metabolizes a significant percentage of alcohol, specifically between 85% to 98% of ethanol. This process involves an intricate system of enzymes that manage the breakdown of alcohol into non-toxic substances. Mainly the alcohol dehydrogenase system, which processes 80% to 90% of ethanol, catalyzes the oxidation of ethanol to acetaldehyde, which then must be further metabolized due to its toxicity.
Acetaldehyde dehydrogenase (ALDH) is crucial in this second step, converting acetaldehyde into acetate, a non-toxic molecule. Moreover, the microsomal ethanol oxidizing system (MEOS) takes care of about 10% to 20% of ethanol during moderate drinking, but this percentage can increase during periods of heavy drinking when the MEOS system's enzymes are upregulated to clear ethanol more efficiently from the body.