HOW ALCOHOL MOVES THROUGH THE
BODY
The amount of alcohol a
person consumes at any given time will influence how it moves through the body, but it's important to standardize the amount that we're talking about first, because
beer, wine, and spirits contain significantly different concentrations of
ethanol. A standard drink is often
classified as the amount of alcohol consumed in one twelve-ounce beer, one four-ounce glass of wine, or a mixed
drink containing one ounce of hard
liquor.
GETTING IN
Ethanol is a relatively
small molecule that is easily and quickly absorbed into the body. Once a drink is swallowed, it enters
the stomach and small intestine, where
a high concentration of small blood vessels gives the alcohol ready access to the blood. About 20
percent of a given dose of alcohol is
absorbed through the stomach, most of the remaining 80 percent is absorbed through the small intestine.
Once they enter the bloodstream, the
alcohol molecules are carried throughout the body and into direct contact with the cells of virtually all
the organs.
Often a person who goes out for a drink in the
early evening before dinner reports,
"The alcohol went straight to my head." Actually, the alcohol went very rapidly throughout the whole body,
and shortly after it was absorbed it became fairly evenly distributed. This
process is called equilibration. But
because a substantial proportion of the blood that the heart pumps at any given
time goes to the brain, and because the fatty material of the brain absorbs alcohol (which dissolves in
both fat and water) very well, that
is where the effects are first and predominantly felt. In fact, before equilibration, alcohol's concentration in
the brain is actually higher than its
concentration in the blood. Since it is alcohol's effects on the brain that lead to intoxication, soon after
drinking a person may be more impaired
than her blood alcohol level would indicate. So, there is some truth in the statement, "That drink went
right to my head."
Indeed, the presence or absence of food in the
stomach is perhaps the most powerful
influence on the absorption of alcohol. When someone drinks on an empty stomach, the blood absorbs the
alcohol very rapidly, reaching a peak
concentration in about one hour. By contrast, the same amount of alcohol consumed with a meal would not
be completely absorbed for nearly two
hours. The food dilutes the alcohol and slows the
emptying of the stomach into the small intestine,
where alcohol is very rapidly absorbed. Peak blood alcohol concentration could
be as much as three times greater in someone
with an empty stomach than in someone who
has just eaten a large meal.
The concentration of
alcohol in the beverage consumed also significantly influences its absorption—in general, the higher the
concentration, the faster it will be
absorbed. So, relatively diluted solutions of alcohol, such as beer, enter the bloodstream more slowly
than more highly concentrated
solutions, such as mixed drinks or shots. More rapid absorption usually means
higher peak blood alcohol concentrations, so a person who drinks shots might have a higher blood alcohol
level than a person who drinks the
same amount of alcohol in the form of beer or wine. While you can prove this
principle in tightly controlled scientific studies using subjects who have completely empty stomachs when they
ingest only the dose of alcohol they
receive from the researcher, this effect is pretty minimal when people are drinking recreationally, perhaps two to three drinks an hour. Furthermore, people rarely drink under such
carefully controlled conditions, and
so the safest assumption is that the most important determinant of what your blood alcohol concentration is
going to be is the amount of alcohol
you consume in an hour and whether you have just eaten—not the type of alcohol you consume.
The rapid absorption of high concentrations of
alcohol can suppress the centers of
the brain that control breathing and cause a person to pass out or even die. People who get into this kind of
extreme medical emergency sometimes do
so by accepting a challenge to drink a certain amount of alcohol in a short period of time, by playing
drinking games that result in the
rapid consumption of multiple drinks, or by taking something like Jell-O shots, which get a lot of highly
concentrated alcohol into the body in a
short time. Often, young people who cannot legally buy alcohol "drink up" before going out to a mall or to a school
dance. Some people do a lot of drinking
before leaving for an event where alcohol is not permitted. (College students, most of whom are underage and must
therefore conceal their drinking,
refer to this as "pregaming.") Given the rapid accumulation of alcohol in the brain, under these circumstances
the drinker may be very impaired in terms of her ability to drive or think
clearly, though her blood alcohol
level would not suggest this degree of impairment.
A person's body type also determines alcohol
distribution. A particularly
muscular or obese person may seem to be "really holding his booze" because he has more fat and muscle to absorb the
alcohol. A heavy person
would register a lower alcohol level in the blood
than a lean individual
after
an identical dose. However, the extra weight also slows the elimination of
alcohol, so he would retain it longer.
In pregnant women,
alcohol is freely distributed to the fetus. In fact, because of the large blood supply to the uterus
and developing fetus, sonic studies
actually indicate that the tissues of the fetus may achieve a higher alcohol concentration than those of the mother.
Later in this chapter, we will discuss
the effects of alcohol on the fetus, and the lasting effects that prenatal exposure has on the child later in life.
For now, it is important to recognize
that when alcohol is distributed in the body, it does not discriminate between
the tissues of the mother and those of the fetus.
GETTING OUT
The roadside
Breathalyzer test is actually an excellent way of estimating the amount of alcohol consumed, even though 95
percent of the alcohol a person
drinks is metabolized before the body excretes it. Only about 5 percent of the absorbed alcohol is eliminated
unchanged, in the urine or through
the lungs, but it is enough to result in "alcohol breath"—and the proportion exhaled stays constant enough to give a
very accurate estimate of how much
alcohol is in the blood.
Most
alcohol is metabolized by the liver, where an enzyme called alcohol dehydrogenase, or ADH, breaks ethanol down into
acetaldehyde, which in turn is broken
down by another enzyme called acetaldehyde dehydrogenase into acetate, which
then becomes part of the energy cycle of the cell. The intermediate product,
acetaldehyde, is a toxic chemical that can make a person feel sick. Although under normal conditions
acetaldehyde is broken down quite
rapidly, if it accumulates in the body, intense feelings of nausea and illness result. One early drug therapy for
alcoholism was a drug called disulfiram (or Antabuse), which allows the
concentration of acetaldehyde to accumulate,
making a person feel quite ill after drinking and less likely to drink again. While this strategy appeared promising
initially, it has not resulted in
consistent positive clinical outcomes with alcohol-dependent patients.
The rate at which alcohol is metabolized and
eliminated from the body is critical
for understanding how long a person can expect to be affected by drinking. The rate of alcohol metabolism is
constant across time. In general, an
adult metabolizes the alcohol from one ounce of whiskey (which is about 40 percent alcohol) in about one hour. The
liver handles this rate of
metabolism efficiently. If the drinker consumes
more than this amount the system
becomes saturated and the additional alcohol simply accumulates in the blood and body tissues and waits its
turn for metabolism. The results are
higher blood alcohol concentrations and more intoxication.
In addition, continued
drinking increases the enzymes that metabolize alcohol. The increased level of these enzymes promotes metabolism of some
other drugs and medications, harming the drinker in a variety of ways. For example, some medications used to prevent blood
clotting and to treat diabetes are
metabolized more rapidly in chronic drinkers and are thus less effective.
Similarly, these enzymes increase the breakdown of the painkiller acetaminophen (found in Tylenol) into substances
that can be toxic to the liver.
Finally, metabolic tolerance to alcohol results in similar tolerance to other sedative drugs, such as barbiturates, even
if the individual has never taken
barbiturates. This is called cross tolerance and may place the drinker at greater risk for the use or abuse of such drugs.
TYPES OF "ALCOHOLS"
The alcohol that is used in beverages is called
ethanol. It is actually only
one of many different types. The
alcohol a nurse rubs on the skin as a dis‑
infectant before giving an injection or
drawing a blood sample is not the
same—it is isopropyl alcohol. The chemical
structures of most alcohols
make them quite toxic to the human
body. Ethanol is the only one that
should ever be consumed, but people regularly
poison themselves with
other alcohols. For example, methanol, produced in
home-distilling oper‑
ations, can cause blindness. A case of methanol poisoning requires immediate
medical attention. Therefore, home-distilled liquor, or "moonshine," should always be avoided.
Wilkie Wilson
