Alcohol isn't in the mouth for very long, so the enzymes that begin to break it down don't have much time to do their work. While a little is digested, most of your drink passes on to the stomach.

Mouth

Alcohol is broken down by two classes of enzymes. The first is more prevalent in the stomach and converts ethanol, the alcohol we drink, into acetaldehyde. Acetaldehyde is toxic, so the second step of metabolism, which occurs in the liver, happens very quickly in most people.

Alcohol will pass more slowly through the stomach if you've eaten recently, allowing for more of it to be broken down before it reaches the liver, so eating before or while drinking really does slow down your buzz. And that's a good thing! Alcohol irritates the lining of the stomach, which can bring on nausea or vomiting.

Famished? That drink is also tricking your stomach to think it's receiving fuel, as alcohol is high in calories but doesn't provide any real food, which might explain why some people feel compelled to eat while intoxicated, or are especially hungry the next day.

Stomach

The liver is responsible for breaking down most of the alcohol (now in the form of acetaldehyde) in the second stage of metabolism. Here, the second class of enzymes converts the toxic acetaldehyde into harmless acetate, which is close in chemical makeup to vinegar.

The liver can only metabolize a certain amount of alcohol per hour, no matter how much you've actually had. So why does it seem like some people can drink more than others? This rate varies between individuals, and is also affected by gender and how much you've had to eat that day. Plus, certain groups of people seem to have particularly low-functioning enzymes or lack the enzymes altogether, inhibiting the completion of this second phase of alcohol metabolism (this is commonly seen in the Asian population). When this happens, acetaldehyde accumulates, causing symptoms like rapid pulse, sweating, flushing, nausea and vomiting.

Liver

After a couple of drinks, some may experience a rapid or irregular heartbeat. Researchers aren't entirely sure as to why this happens, but alcohol seems to directly affect our internal timekeeper. People who don't drink regularly are more susceptible to this kind of reaction.

Heart

Hot around the collar? Alcohol is what's called a vasodilator, meaning it naturally enlarges the blood vessels, which can make your cheeks rosy and give you that warm and toasty "beer blanket" feeling.

Circulatory System

The immune system has two parts: One works to ward off sickness and the other fights off germs once they are already present. Because alcohol suppresses both, you are left not only more susceptible to illness, but also less able to fight it. This effect lingers for about 24 hours after throwing a few back.

Immune System

The body normally releases a hormone called vasopressin, which, when alcohol is not present, sends water back into the body. But alcohol suppresses this hormone, and sends that water to the bladder instead, which, in turn, sends you to the bathroom line!

Kidneys

In addition to the redirected water coming to the bladder from the kidneys, alcohol is also a natural diuretic, meaning it causes cells to shrink, thereby pushing water out from each cell. To manage that extra fluid, the organs secrete it to the bladder, which gives you the urge to go to the bathroom.

Although many people feel like after that first trip to the bathroom, the need to go only increases -- a phenomenon often referred to as "breaking the seal" -- this sensation is mostly an illusion. That "seal" is really just a threshold -- after a number of drinks you can't hold it any more. As you continue drinking, you're taking in more fluids and suppressing the release of more vasopressin, leading to more frequent trips to the bathroom.

Bladder

Because of the suppression happening in the frontal lobes, some people may find themselves feeling more in the mood for sex after a few drinks. But heavy drinking dulls sensation all over the body, making arousal and orgasm more difficult.

In addition, because alcohol naturally dilates the blood vessels, men may experience difficulty maintaining an erection at blood alcohol levels of about .08 to .10 and above. Blood still flows into the penis normally, but the dilated vessels allow it to flow out just as easily. While certain brain mechanisms might also affect this process, experts say there is little evidential proof.

Libido

Wake up the morning after with aches and pains? Alcohol impairs metabolism of a specific protein that can lead to increased production of uric acid, which is a waste product from normal body processes that, in high amounts, can cause a type of arthritis called gout. Some people may experience mild joint pain because of these increased levels after drinking.

Joints

Chemicals called neurotransmitters communicate messages all throughout the brain. One common neurotransmitter, which is used for slowing things down in the brain, is called Gamma-aminobutyric acid, or GABA. In certain receptors, alcohol enhances the effects of GABA, thereby further slowing down messages throughout the brain.

Glutamate is a neurotransmitter with the opposite effect; it gets things going in the brain. But because alcohol can block the effects of glutamate at certain receptors, messages are further slowed in the brain.

Brain

At blood alcohol levels of around .05, this area of the brain begins to show signs of disruption. This part of the brain is involved in decision-making and impulse control, so you begin to make poorer choices and may have more trouble controlling your urges.

As you move into a more moderate dose of alcohol consumption, you begin to only see the near future, called alcohol myopia, and the search for immediate gratification takes over. This is what causes you to eat a whole bunch of bar snacks when you're on a diet, or kiss a cute stranger when someone special is waiting at home.

Ever told all your secrets while drinking? The more you throw back, the more you suppress the frontal lobes, until you eventually lose control over your emotional expression. The problem is, alcohol isn't exactly a truth serum so your drunken confessions may not be what you really think.

Frontal Lobe

This part of the brain warns you when you're in danger. It makes you feel anxious and afraid when faced with a threat. With low doses of alcohol, the amygdala is slightly suppressed, so you begin to ignore the consequences of your actions (and you're already making poorer choices because the frontal lobes are also suppressed).

As you move into a more moderate dose of alcohol, you can't recognize when you're in danger. This may account for risky sexual scenarios and any number of bar fights. It's also what leads people to believe it's a good idea to, say, jump off a roof into a swimming pool or other "Jackass"-style stunts.

Amygdala

This part of the brain is important for memory, but is particularly involved in learning and executing patterns of movement. The more you drink, the more the cerebellum is disrupted, leading to balance problems, slower reaction time and slurred speech.

Cerebellum

Feel like having just one more? Our brains naturally make us feel good when we're eating, having sex or engaging in other primal urges that are key to survival and reproduction to ensure that we repeat those behaviors. Because of its euphoric effects, alcohol tricks the brain into thinking that drinking is essential to our existence and we must continue, but the truth is it's not.

Some people may be able to ignore this desire to raise another glass. Others, including possibly those who may be predisposed to alcohol dependence or abuse, might have an insatiable thirst for this euphoria and may be more inclined to continue drinking in order to hold onto it.

But that good feeling will only increase to a certain point. In fact, from the first sip of alcohol, the brain is working to return to homeostasis from its alcohol-altered state. If you've ever felt anxious or depressed as you begin to sober up it might be a type of rebound effect. You might feel worse the next day simply because you felt so great while getting buzzed and returning to normal can temporarily feel like a letdown.

Reward System

As you drink more, some impairment happens to the hippocampus, a part of the brain associated with memory. When you reach a blood alcohol level of about .15, the low end of the range considered a high dose of alcohol, you can start experiencing problems recording autobiographical memories, meaning you may not remember where you went or what you did. With a blood alcohol level of .2 or above, some research suggests there's a 50 percent chance of experiencing this hole in memory, commonly referred to as a blackout. And when you wake up the next morning and a friend fills in the details, it's not often good news, thanks to the suppressed frontal lobe and amygdala.

It can be difficult even for trained law enforcement to tell when someone has been drinking -- or is experiencing a blackout -- up until this .15 level. Drinking a higher dose results in a "sloppier" drunk; although it may still be difficult to tell if someone is experiencing a blackout, the physical impairments -- like stumbling and slurred speech -- will be obvious.

While many drinkers assume blacking out is a consequence of drinking too much, research suggests it's more likely a result of how fast you drink, although experts are not exactly sure why.

Hippocampus

Deep down in the brain stem are a number of small circuits called the vital reflex centers. This is where sneezing, coughing, gagging, breathing and other involuntary reactions that keep us alive are controlled. If your blood alcohol level reaches .35 or higher, it's possible to shut down these circuits completely. This is how alcohol overdose causes death, either directly, or, as is more common, by causing someone who vomits to inhale the vomit and drown.

Note: Certain prescription medications can affect the brain stem in a similar way, amplifying the risk of overdose. This is one of the reasons why many medications are not to be mixed with alcohol.

Brain Stem