Alcohol and the body
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What the body does to alcohol
Alcohol absorption, distribution and elimination
occur simultaneously and start with consumption.
Absorption is the passage of alcohol into the
blood. Distribution is the temporary placement
of alcohol into body tissue. Elimination is the removal of alcohol
from the body. Diffusion is the method of passage of alcohol through
cell membranes, and is governed by concentration differences on
either side of the cell wall.
Blood alcohol concentration
A blood alcohol concentration (BAC) or
blood alcohol level (BAL) reflects the amount of alcohol
in the body. Food, kind and quantity of beverage, weight, sex,
and rate of elimination determine BAC after the consumption of
alcohol. BAC is a measure of the difference between the rates
of absorption and elimination. The change in BAC with time may
be described graphically as a blood alcohol curve, where the absorption
phase is represented by a rising limb and the elimination phase
by a falling limb.
Alcohol absorption
Alcohol is absorbed from the stomach and small
intestine by diffusion. Most absorption occurs from the small
intestine due to its larger surface area and rich blood supply.
The rate of absorption varies with the emptying time of the stomach.
Generally, the higher the alcohol concentration of the beverage,
the faster the absorption. However, above a certain concentration,
the rate of absorption may decrease due to delayed passage of
alcohol from the stomach into the small intestine.
The maximum absorption rate is obtained with
the consumption of an alcoholic beverage containing approximately
20-25% (by volume or v/v) alcohol on an empty stomach. The absorption
may be slower when alcohol is consumed with food or when 40% (v/v)
alcohol is consumed on an empty stomach. The rate may also slow
when high fluid volume/low alcohol content beverages, such as
beer, are consumed.
Normal social drinking
For normal social drinking, the highest BAC
is usually achieved within 30 minutes of completion of consumption,
though it could take up to 60 minutes. When large amounts of alcohol
are consumed over a short time, or when a large quantity of food
is eaten with the alcohol, the absorption may continue for up
to two hours after last consumption.
Two-hour BAC plateau
In other situations, a person may develop a plateau
where the blood alcohol level does not change for up to two hours.
This occurs because the rate of absorption is equal to the rate
of elimination. After two hours, the rate of elimination will
exceed the rate of absorption and the blood alcohol level will
begin to decrease.
Once in the blood, alcohol is carried throughout
the body. The alcohol diffuses into tissues and fluids according
to their water content (the more the water, the higher the alcohol
level). During absorption, the BAC of arterial blood is greater
than the BAC of venous blood. Arteries carry blood to a tissue,
veins remove it. At equilibrium, when body fluids and tissue have
absorbed a proportionate quantity of alcohol, the BAC of arterial
blood is equal to the BAC of venous blood.
Weight and sex affect BAC
A person's weight and sex determine the total
volume of body water and consequently the BAC obtained upon consumption
of a particular quantity of alcohol. Generally, the more a person
weighs, the larger the volume of body water and the lower the
BAC obtained from the consumption of a given amount of alcohol.
A female may have more fat tissue than a male
of the same weight and therefore a smaller volume of body water.
As a result, a female may obtain a slightly higher BAC upon consumption
of the same quantity of alcohol as a male, all other factors being
equal.
As BAC decreases, alcohol diffuses from the tissues
back into the blood.
Elimination of alcohol
Alcohol is eliminated from the body by excretion
and metabolism. Most alcohol is metabolized, or burned, in a manner
similar to food, yielding carbon dioxide and water. A small portion
of alcohol is excreted, such as through the breath, leaving the
body unchanged as alcohol. It is excretion which allows for breath
alcohol testing.
Average rate of elimination
Elimination occurs at a constant rate for a given
individual. The median rate of decrease in BAC is considered to
be 15 milligrams per cent (mg%) per hour. In a normal population,
the range of decrease in BAC is 10-20 mg% per hour. Most people
eliminate between 13 and 18 mg% per hour. Of this group, most
eliminate at the higher end. Few people eliminate at a rate of
10 mg% per hour.
Disclaimer: The material on this site is not intended as legal advice. It merely conveys general information on legal issues commonly encountered by persons facing criminal charges in Canada. If you are charged with an offence, you should contact a criminal lawyer.
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