Final answer:
The liver is the main site of alcohol metabolism, primarily through the alcohol dehydrogenase system, which converts ethanol to acetaldehyde and then acetate. The microsomal ethanol oxidizing system also plays a role, especially during heavy drinking.
Step-by-step explanation:
The principal site where the majority of alcohol metabolism takes place is in the liver. Approximately 85% to 98% of ethanol in the bloodstream is metabolized by the liver. This high level of metabolism is paramount to ensuring that toxic compounds are converted into less harmful substances as swiftly as possible.
The main pathway involves the alcohol dehydrogenase system, where 80 to 90% of ethanol is processed into acetaldehyde, NADH, and H+ ion. Subsequently, acetaldehyde, which is toxic to liver cells, is quickly converted into acetate, a non-toxic molecule, by acetaldehyde dehydrogenase (ALDH). In situations of heavy alcohol consumption, the microsomal ethanol oxidizing system (MEOS) becomes more active, handling 10 to 20% of ethanol metabolism and most of the excess ethanol during periods of heavy drinking.
In addition to alcohol metabolism, the liver is also involved in protein metabolism, drug metabolism, and the breakdown of various other substances which are not directly removed from the body but transformed to safer compounds.