How alcohol affects us
Alcohol doesn’t only disrupt the proper operation of the reward system it also has a detrimental effect on many other parts of the body; the gastric system, liver, kidneys and brain are all adversely affected by prolonged and regular contact with alcohol. Alcohol is carried to the organs in the bloodstream in this sequence: It is absorbed into the bloodstream in the stomach and intestines. From there it is carried to the liver, the heart and lungs, and then to the brain and muscles. Then some passes through the liver (again), some through the stomach (again) and some through the kidneys. After passing through all the organs and muscles the blood flows back to the lungs and heart where it gets re-oxygenated and re-circulated.
The alcohol trail begins in the stomach and intestines where it is absorbed into the bloodstream and carried to the liver. The liver’s principal function is to clean the blood that comes from the stomach and also the depleted parts of blood after they’ve been through the muscles and organs. It is also responsible for some other important functions including making the glucose that our body uses for energy, and breaking down unwanted chemicals that were absorbed into the blood in the stomach during digestion. The liver recognises alcohol as an unwanted toxin and it attempts to remove it, but it can’t be removed by filtering, it has to be broken down chemically. Enzymes are biological molecules which change chemicals from one form to another and they have many roles in the body including digestion and waste removal. There are many different types, each performing a specific chemical change, and it takes three different enzymes to completely break down alcohol. One enzyme changes alcohol into acetaldehyde, another changes acetaldehyde into acetic acid and a third changes acetic acid into carbon dioxide and water. But the body isn’t evolved to deal with large amounts of alcohol. It isn’t something that occurs in large volumes in nature and we only have a limited quantity of the enzymes that work to remove it. So when we drink we ingest alcohol far more quickly than these enzymes can break it down and only a little of the alcohol is converted to acetaldehyde on its first pass through the liver. The remaining alcohol and acetaldehyde are carried in the blood until it passes through the liver again. Alcohol and acetaldehyde are only slowly removed, so if we keep drinking then the amount of both alcohol and acetaldehyde in our bloodstream rises. But acetaldehyde is toxic, and it is the build-up of acetaldehyde in our blood that makes us feel sick and gives us a headache.
If we drink routinely and heavily then our liver adapts to this regular demand by increasing the amount of the enzymes it produces to work on the alcohol and acetaldehyde. But it never produces enough of these to break down all of the alcohol and acetaldehyde immediately and the blood has to pass through the liver many times before they are removed completely. So as we drink the concentrations of alcohol and acetaldehyde in our blood rise and they only subside after we greatly slow down our drinking or stop. But alcohol must first be turned into the toxic acetaldehyde before it can be reduced to the less toxic acetic acid which means that acetaldehyde removal always lags behind alcohol removal. When we stop drinking our blood/alcohol level will start to fall, but the acetaldehyde concentration will still continue to rise, and this is why we get hangovers after drinking, not during.
The increased quantity of the enzymes that break down alcohol allows the liver to process it away more quickly and this is beneficial to the body, but this causes two changes to our drinking behaviour. Faster removal of alcohol means we are able to drink more before becoming ill, but because alcohol is being removed from our blood more quickly we need to drink faster and we need to drink more in order to feel the same effect as we first did, and this is precisely what we do; we drink faster than we first did at first and we drink more.
Blood carrying alcohol and acetaldehyde first leaves the liver passing through the heart, lungs, brain and muscles before returning. But this time the blood is divided between three paths. Some blood goes to the liver where more alcohol and acetaldehyde are processed away, some goes to the stomach where the blood takes on more dissolved foodstuffs, and some goes to the kidneys where waste products are removed and the water content of the blood is regulated. But alcohol interferes with how this happens.
The kidneys perform a filtering action on blood, separating the wanted from the unwanted. Blood enters the kidney and the water in it is separated from everything else. Blood is then filtered to separate it from waste and if water is needed to replenish the water content of the blood then it is re-absorbed into the clean blood. The other water is jettisoned as urine, taking the waste from the filters as it exits. Whether or not the kidney puts water back into the blood is determined by the presence of the hormone “vasopressin” which is released by the pituitary gland in the brain. When the kidney detects vasopressin then it absorbs water back into the bloodstream, but when there is no vasopressin present then all water is removed and passed as urine. But alcohol slows the brain down and this slowing down causes the pituitary gland to release less vasopressin. This in turn reduces the amount of water being put back into the bloodstream, and this is why we become dehydrated when we drink. Drinking water will not fix this shortfall, this is a myth. The kidneys will not re-absorb water into the blood while the pituitary gland does not release vasopressin, and the pituitary gland will not release vasopressin while there is still a significant amount of alcohol in the brain. Any extra water that we drink will be passed as urine while we still have a significant amount of alcohol in our bloodstream.
While the effects of alcohol on our liver and kidneys are significant, it is what it does in our brain that causes most trouble. Alcohol disturbs how the brain works at the most basic of levels; it prevents proper performance of neurotransmitters at the synapses. Glutamate and GABA (short for GammaAminoButyric Acid) are neurotransmitters that control the speed of mental function, and alcohol interferes with how both of these work. Glutamate and GABA work in the brain in a similar way that the accelerator pedal (the gas pedal to North American readers) and the brake pedal work in a car. Glutamate makes certain neurons pass signals more quickly and is like the accelerator pedal, while GABA makes certain neurons pass signals more slowly and acts like a brake pedal. But alcohol disrupts the normal detection of both of these neurotransmitters at the neuron on the receiving side of a synapse. Alcohol molecules clog up the point on the neuron that detects glutamate and this prevents a glutamate molecule from ever reaching it. This makes the receiving neuron unable to detect when glutamate is present. Even if glutamate is released from the transmitting neuron it doesn’t get detected on the receiving side, so the effectiveness of glutamate is reduced. But while alcohol makes glutamate less potent it increases the apparent effect of GABA. The alcohol molecule is small and is what allows it to pass through the blood-brain barrier and reach the brain. But this small size and its shape also allows it to fit into the socket meant for detecting the GABA molecule on the receiving neuron. When this happens then the neuron incorrectly signals that GABA has been detected. The receiving neuron correctly identifies GABA when it is passed but it also thinks GABA has been passed when an alcohol molecule lodges there instead. These two actions combine to trick neurons into believing that glutamate has not been passed at synapses but that GABA has. In the car analogy this is like lifting your foot from the accelerator pedal while also pressing down on the brake; the speeding up of the brain is decreased and the slowing down of the brain is increased. The result of this is that the whole brain slows down, and the more we drink the more it slows down. When we drink a lot then this slowing down of mental function becomes so pronounced that it begins to have serious yet familiar consequences.
The cerebellum is the part of the brain that controls our muscle movements and if we drink a lot then the whole brain slows down, including the cerebellum. This means that it takes a fraction longer for our brain to make a single muscle contract or expand, but when a lot of things all have to happen together, or as a precise sequence in close succession, then they can fail to happen when they are needed. This is what causes slurred speech; there is so much to coordinate in a short time span that the cerebellum is no longer fast enough to do it correctly. Nor can it coordinate all the muscles required to keep us balanced steadily upright. While these two things can be seen by anyone watching us there is a third consequence that is only apparent to ourselves. A slowing down of processing in this part of the brain causes two of the most obvious signs of intoxication; slurred speech, and loss of balance but the muscles in the eye are also controlled through the cerebellum. Proper operation of the eyes requires coordinating moving the direction that each eye faces and also adjusting the focus of each to suit the distance to the object they’re looking at. But it also involves another step. Our brain is constantly searching for the most significant items in the current scene and then directing our sight to them. This is an enormously complex task of identification and selection but it needs to coordinate this action with moving the eyes and focusing them. These three things have to occur in very close succession; deciding what to look at, turning each eye to directly look at it, and then focusing each eye. When the brain slows down then the coordination and synchronisation of these three tasks starts to fail. Our focusing fails to keep up with the continual eye movement and if we drink enough then our brain also fails to direct both eyes simultaneously to the precise direction, and this is what causes double vision.
Another familiar consequence of drinking too much is memory loss. Everything that comes in through the senses is stored in short term memory for a few seconds. The hippocampus (the part of the brain responsible for memory formation) examines all this information and compares it with everything that is already known. It rejects the information that is either unimportant or already known, and it commits the new, significant or potentially useful information to long term memory. But this is a huge processing task and when the hippocampus is slowed down by too much alcohol then it is no longer able to process this information quickly enough to keep up with the incoming content… but the incoming content keeps coming. When the hippocampus gets significantly slowed then it fails to reach a conclusion on whether or not information is interesting before it has to move on to the next piece. This means it misses some new information that should be committed to long term memory, and this is not remembered at all. We are still upright, conscious and functioning when this occurs, but our memory of what is happening around us is incomplete or even missing completely.
The slowing down of the brain has other consequences too; it decreases inhibition, increases the pain threshold, and decreases sexual performance. It also slows down our conscious thinking which severely slows decision-making and impairs sound judgement. But alcohol causes one more particularly adverse change in the brain; it alters how ready we are to respond to danger.
We are evolved to be able to react extremely quickly when confronted by something threatening. The mechanism controlling this is known as the “fight-or-flight response” and it detects the presence of danger and then prepares the brain and body to perform to their maximum potential. To do this the body shuts down non-essential activities as well as operations that can be deferred for a while and it concentrates all resources on being able to run or fight at a moments’ notice. Three agents prepare this readiness. A neurotransmitter called noradrenaline (also called norepinephrine) is activated throughout the brain and central nervous system. Noradrenaline increases alertness, promotes vigilance, invigorates the formation and retrieval of memory, and focuses attention; it also increases restlessness and anxiety. At the same time the pituitary gland in the brain directs the adrenal gland to release two hormones; cortisol and adrenaline (also called epinephrine). Cortisol is carried in the blood to receptors in most cells in the body, so it has wide reaching effects, but significantly in this context it wakes us from sleep. The other hormone, adrenaline, increases heart rate and stroke volume, dilates the pupils, constricts the blood vessels close to the skin, and dilates the blood vessels in the major muscles. These three act together to prepare us for rapid response, but the release of all three of these agents is controlled by the flight-or-fight response, and when the brain slows then so does the flight-or-fight response. The amount of cortisol, adrenaline and noradrenaline are all reduced and this brings a very significant reduction in our physical and mental capability; less cortisol means we become sleepy, less noradrenaline makes us mentally dull, and less adrenaline makes us lethargic.
When we stop drinking and our blood/alcohol level starts to fall then the flight-or-fight response becomes more active again. Cortisol and adrenaline return to their normal levels but noradrenaline does not, it rises to abnormal levels. Acetaldehyde is created as alcohol is broken down, but it is also a releasing agent for noradrenaline. So noradrenaline activity rises as the flight-or-fight response wakes up and then it far exceeds what is normal in response to the acetaldehyde. This over-excites parts of our nervous system causing the trembling that we call ‘the shakes’. Another unwanted outcome from the flight-or-fight response is that sometimes it wakes us in the middle of the night. On these occasions the falling blood/alcohol level reactivates the flight-or-fight response sufficiently for it to release enough cortisol to wake us up. Then the other stimulants (noradrenaline and adrenaline) keep us awake by making us alert and overheated by a racing heart.
These are the bad effects of alcohol, but alcohol does of course have its up-sides otherwise we would never be interested in it at all. The slowing effect of alcohol in the brain has many unwanted effects but it also causes some that we enjoy. Glutamate and GABA have been described as respectively speeding up and slowing down the brain, but this also strongly influences how we feel. Glutamate speeds up the brain which makes us more agitated or anxious while GABA slows the brain making us calmer; so our anxiety fades as our brain starts to slow down. But the slowing down also makes the brain release more of two mood altering neurotransmitters; serotonin and dopamine. Dopamine has many functions in the brain, and its role in triggers, motivation and memory has already been discussed. But another is that when it is released it gives us a sensation of pleasure. Depending on how much dopamine is active we can range from feeling contented to euphoric. Alcohol also causes extra serotonin to be released, and serotonin too has many functions. Among them are; maintaining a balanced mood, boosting self-confidence, and decreasing worries and concerns. When we drink alcohol it makes us happier, we worry less, and our social confidence and social engagement increases. If we drink enough we will, for example, be quite convinced that we are excellent dancers and dance on a table so that everyone can see how good we are. These mood lifting changes are the positive aspects of alcohol, and until we drink regularly and heavily then these are the effects we will experience; drinking makes us happy, care-free, and socially outgoing.
The effects of alcohol on the body and brain are significant and wide-ranging, but they don’t all happen at once; there is a sequence they pass through. When we take the first drink, then if this drink is in response to a drinking trigger we will get an immediate surge of ease and comfort wash through us as we experience the dopamine released by the reward system. The alcohol is carried to the stomach where it is absorbed into the bloodstream and passes to our liver which starts to break it down, but it can’t all be removed immediately. Alcohol that isn’t reduced to acetaldehyde circulates in the blood, and as we drink more the blood/alcohol level begins to rise and soon the toxic acetaldehyde level starts rising too. But the rising blood/alcohol level also begins to change the recognition of GABA and glutamate and our brain starts to slow down. This slowing causes dopamine and serotonin to be released which makes us feel like we are having a good time. As our brain slows down the pituitary gland stops producing the hormone AHD and this makes our kidneys stop re-absorbing water back into the bloodstream. We begin to become de-hydrated but we don’t care; we’re having a good time. As we continue to drink then the brain further increases the amount of dopamine and serotonin released making us more cheerful, relaxed, care-free and socially confident, but the mental slowing also begins to significantly affect our alertness and mental function. As we continue to drink everything escalates. We become happier, more care free, and excessively self-confident. Unfortunately though, while we feel wonderful, the adverse consequences are escalating too. Increasing blood/alcohol levels slows the brain even further and reduces activation of the flight-or-fight response. This results in reduced alertness, increased drowsiness, slowed heart rate, surface blood vessels dilate (we get a flushed appearance and perspire), and we start to lose the ability to focus attention. Eventually complex tasks like balancing and speech can’t be performed quickly enough to be successful, so we begin to slur our words and struggle to maintain balance. Our eyes begin to lose focus and if we drink enough they will fail to operate as a coordinated pair and we’ll develop double-vision. Proper transfer of useful information from short-term to long-term memory begins to fail, and if we drink enough then we prevent the brain being from being able to form new memories completely. We struggle to stay awake, but if we continue to drink then our brain will slow down to the point that we lose consciousness.
At the point we stop consuming alcohol then the blood/alcohol level stops increasing, but blood toxicity continues to climb as the alcohol still circulating is steadily converted to more and more acetaldehyde. When we wake we are dehydrated, but most of the alcohol has by now been converted to acetaldehyde. Lower blood/alcohol levels allow serotonin and dopamine to return to their normal states and we are no longer overly happy or confident; but we are now suffering the effects of dehydration and being poisoned by the acetaldehyde: we have a hangover. The high acetaldehyde concentration causes noradrenaline to be released throughout the nervous system at abnormally high rates which makes us tremble. Our liver continues to work at breaking down acetaldehyde and eventually our blood/alcohol level drops sufficiently for the brain to speed up again and the pituitary gland finally instructs our kidneys to resume absorbing water back into the bloodstream. Our hangover fades as the toxic acetaldehyde is removed and our body slowly rehydrates.
This is what happens when we drink heavily, and this is the universal experience; it happens to everyone that drinks a lot. Our body’s principal reactions to alcohol are identified here, but these bodily functions are not entirely fixed; we evolved to be able to adapt to changing circumstances. If we begin to drink regularly and heavily then though we enjoy the experience a significant proportion of our day is spent bodily and mentally compromised because of alcohol. Our brain and body begin to adjust in an attempt to counter this regular impairment. But the changes that occur, though their aim is to maintain optimal performance, are ultimately the changes that lock our addiction in place.