When a person drinks alcohol, it passes into the stomach. There, some of it is absorbed into the bloodstream. The rest is absorbed in the small intestines. Once it is in the bloodstream, alcohol circulates to all parts of the body. The liver begins to break down the alcohol into other substances. The liver can process about 10 ml of alcohol an hour. If more than that amount is taken in, the alcohol builds up in the blood, and the person becomes drunk.
Alcohol acts on the brain and nervous system. The effects depend mainly on how much alcohol is in the blood. If the amount is small, the person feels happy, warm, and relaxed. As the concentration of alcohol in the blood builds up, the person becomes less co-ordinated. The hands may shake and memory and alertness are decreased. Thus, drinkers sometimes do things that would be embarrassing to them if they were sober. Some people argue or fight, others just act silly. If more alcohol is drunk, the drinker’s ability to walk and talk properly will be affected. At this point, continued drinking could cause unconsciousness or even death.
As the effects wear off, the drinker feels “hung over.” Some symptoms of a hangover are an upset stomach, unusual thirst, and a headache.
Text taken from http://www.col.org/what-alcohol-does-in-your-body.html