LEARNING MODULE Blood Alcohol Concentration: Alcohol's Story

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When we talk about 1 standard drink, we mean.... 12 oz of beer, 5 ounces of wine, 1.5 oz of

liquor. Alcohol has effects on the nervous system, the function of which is to gather

information and initiate behaviours. Alcohol interferes with pathways of communication

in the brain. The brain operates by sending out and receiving signals from both the body

and other brain regions. Molecules called neurotransmitters influence this process by

either increasing or decreasing the likelihood that a message will be sent out from a brain

cell. When alcohol is in the brain, it acts by both

preventing excitatory neurotransmitters from working and by facilitating the operations

of the inhibitory neurotransmitters. This dual effect makes it even more difficult for

the brain to carry out its functions.

To measure someone's intoxication level, their Blood Alcohol Concentration or BAC is calculated.

The BAC tells you how much alcohol is present in the blood, in terms of percentage by volume.

So a BAC of .10, means that 0.1% of a person's blood is made of alcohol. BAC is most often

measured using a breathalyzer. Why? 5% of the alcohol in your blood is removed through

your lungs when you exhale. Therefore, the concentration of alcohol in the air you exhale

is a reliable indicator of the alcohol concentration in your blood.

Of the remaining 95%, 5% of the alcohol leaves your body through your urine and the remaining

90% is metabolized by your liver. On average, is metabolized at a rate of one drink per


Effects seen at various BAC "BAC = 0.02 -- 0.03"

0.02-.03 The effects at this level are pretty mild.

Along with a slight buzz in your head, you might feel more at ease and happier than normal.

Alcohol is already acting on your brain's reward and pleasure centres, which explains

why you're experiencing these pleasant effects.

BAC = .04-.06 Euphoria, relaxation and sociability are still

on the rise. At this stage, your inner daredevil comes out to play, and your normally impeccable

memory isn't quite up to its usual standards. This is mainly thanks to alcohol's effect

on the cerebral cortex, a brain region that is involved in everything including sensory

perception, motor activity, attention, impulse control and memory.

BAC = .07-.09 Vision, hearing, reaction time, speech and

coordination become noticeably impaired. You might notice that pushing the tiny buttons

on your cellphone is strangely challenging and that you're talking a little louder than

usual. You'll still feel okay though, as the booze will boost your confidence in everything...including

your own sobriety. What's more, your ability to make and execute plans, think rationally,

and use good judgment, are being compromised thanks to the pre-frontal cortex slowly becoming

more and more inhibited.

It's probably a good time to mention that at .08, you are no longer legally allowed

to drive: not a car, not a truck and no, not even a bicycle.

BAC = .10-.15 Alcohol is now making an appreciable impact

on these areas of the brain: The limbic system regulates emotional responses,

it essentially helps us inhibit ourselves.... Most of the time, we know when to keep our

mouths shut or when to back down from a confrontation. Alcohol can slowly bring this regulatory mechanism

to a standstill, resulting in highly emotional or unusually aggressive responses becoming

more common.

The Hypothalamus and Pituitary Gland play a role in the physical aspects of sexual arousal.

While alcohol can decrease psychological inhibitions and increase the desire for sex, it can simultaneously

suppress physiological functions resulting in temporary erectile dysfunction or low vaginal


The cerebellum plays an important role in motor control, affecting the accuracy of movement,

precision and coordination. With alcohol present, these all become compromised. Fine motor movements

such as touching your finger to your nose become difficult and shaky. Balance is impaired

and reflexes are slower to respond.

BAC = .16-.19 A good percentage of people experience intense

nausea at this level because of the acidic environment alcohol has created in the stomach.

All the effects we've previously mentioned, from unchecked emotions and impaired judgment

to balance problems and delayed reflexes are now becoming even stronger.

BAC = .20-.25 Dazed, confused and generally disoriented,

standing and walking seem impossible. This puts you at increased risk of serious physical

injury with the added danger that pain signals are now inhibited, making it more likely that

you will fail to notice an injury until the effects of alcohol wear off.

At this stage, nausea and vomiting are typical effects. Memory blackouts are also common.

BAC = .30 At this point, the effects that alcohol is

having on your medulla are a serious cause for concern. The medulla controls autonomic

functions you normally don't need to think about.... Breathing, heart rate, blood pressure

and lastly, vomiting is the result of the stomach being irritated by the toxicity of

the alcohol. The medulla is what triggers the gag reflex that allows you to clear vomit

from your body. With a high enough dose of alcohol, this reflex is inhibited and if you're

unconscious, choking on your own vomit is a huge risk. Such cases often result in fatalities.

Bladder function is impaired so loss of bladder control is not out of the question.

BAC = .40 The alcohol has turned off all communication

pathways in your brain. The onset of a coma and possible death due to respiratory arrest

are both possible outcomes.