When an alcoholic beverage is consumed, approximately 20% of the alcohol is absorbed in the stomach and 80% is absorbed in the small intestine (Freudenrich, 2001).  After absorption, alcohol enters the bloodstream and dissolves in the water of the blood where it is quickly distributed to body tissues.  When alcohol reaches the brain, it affects the cerebral cortex first, followed by the limbic system (hippocampus and septal area), cerebellum, hypothalamus, pituitary gland, and lastly, the medulla, or brain stem.  When BAC is near toxic levels, lower order brain regions are affected, which is often followed by sleepiness, lack of consciousness, coma, or death.

Source: Laberge, Jason C., Nicholas J. Ward., "Research Note: Cannabis and Driving - Research Needs and Issues for Transportation Policy," Journal of Drug Issues, Dec. 2004, pp. 973.