Alcohol that is being consumed enters through the mouth and the esophagus into the stomach. A small amount is converted there. The rest comes pure, and thus undigested, into the blood stream and is spread throughout the body. Presence of food in the stomach at the moment of drinking delays the absorption of alcohol in the blood. That's why an alcoholic beverage has a quicker effect when the stomach is empty than when the drink is taken during or after a meal. Drinks that have an alcohol level of more than 20% stay longer in the stomach than drinks with a lower alcohol level. The quantity of alcohol in the blood is expressed in per mill. A per mill of 0.5 means that 1 milliliter (cc) of blood contains half a milligram of pure alcohol. Someone who weighs a lot has more body fluids than someone who weighs less. So a lighter person notices more of the same number of glasses of alcohol than a heavier person. There is also a difference between men and women. The body of a woman contains on average less body fluids per kilo than a man. So a woman will get a higher blood alcohol level faster than a man. Also, women digest a smaller part of the alcohol in the body.
The liver finally breaks down the alcohol, after which it is eliminated through urine.