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Once in the blood stream, alcohol is distributed throughout the body in simple diffusion. Its small and relatively simple molecular structure allows it to pass right through cell membranes and mix in the entire water content of the body. The brain, liver, heart, pancreas, lungs, kidneys, and every other organ and tissue system are infiltrated by alcohol within minutes after it passes into the bloodstream.
Alcohol's immediate effect on the brain is most unusual. The brain is usually protected from chemicals and drugs by an electrical-chemical filter system known as "the blood/brain barrier," which makes sure that only very simple molecules such as those of oxygen and water can pass through. The simple molecular structure of alcohol allows it to penetrate this selective screen and gain easy access to the brain and its extension, the spinal cord.
Consequently, alcohol has immediate and profound effects on behavior. At low doses, alcohol stimulates the brain cells, and the drinker feels happy, talkative, energetic, and euphoric. After one or two drinks, the normal drinker may experience some improvement in thought and performance. As the BAL rises, however, the amount of alcohol in the brain also rises, and alcohol begins to disrupt the brain's electrical and chemical circuitry, causing complicated behavior changes.
With large amounts of alcohol surging through the brain's labyrinthine passageways, the central nervous system cells can no longer function normally. The brain malfunctions, and the major visible effect is a change in the drinker's psychological and emotional state. After several drinks, the normal drinker may begin to show signs of intoxication. He may become emotionally demonstrative, expressing great joy, sadness, or anger. He may also begin to show signs of motor incoordination, staggering slightly when he walks, knocking his drink over as he leaves the table, or slurring his words. If he continues to drink, his vision may blur, and his emotions, thoughts and judgement may become noticeably disordered.
When blood alcohol concentrations reach very high levels, the brain's control over the respiratory system may actually be paralyzed. A .30 BAL is the minimum level at which death can occur; at .40 the drinker may lapse into a coma. At .50 BAL, respiratory functions and heartbeat slow drastically, and at .60 most drinkers are dead.