By Edwin T. Scallon, Copyright © 1990, 1995, 2008, 2020 All Rights Reserved
ACCIDENT RECONSTRUCTION AND BAC CALCULATION PROGRAMS
PHYSIOLOGY and ALCOHOL
The human body is divided into systems. There is the circulatory system, nervous system, hepatic portal system, adipose system, alimentary system, cerebrospinal system, glandular system, hermaphroditic system, respiratory system, urogenital system to name a few.
Each system has a specific job of keeping the body in a state of homeostasis (balance). We will see that the ingestion of food or alcohol will affect these systems differently and eventually the ethanol will reach the cerebrospinal and autonomic nervous system. When that occurs, the person will be affected. The amount of the substance introduced (in this case alcohol) will proportionately affect the systems which at high volume will render the system nonfunctioning.
Ethyl (beverage alcohol) distributes in the body in proportion to the water content in the particular tissue. Ethyl alcohol crosses with water into the blood stream, therefore the process of distribution of alcohol is rapid. The more one drinks, the more alcohol would be in the blood.
Since ethyl alcohol mixes freely with water it would be expected that within the blood, alcohol distribution would parallel the distribution of water in the blood. Since plasma and serum have approximately the same water content (92%), whereas whole blood has bout 80% water, it would be expected that the ration of ethyl alcohol content in plasma or serum to alcohol content in whole blood would be equal to the ration of water in plasma to the water in whole blood. This is what was found in the ratio which is approximately 1.12 for both (92%/80%=1.15). Since water diffuses easily across cell membranes through aqueous channels, including vascular endothelium it is expected that ethyl alcohol would do the same. Further, it is expected that the ethyl alcohol concentration in the tissues would rapidly reach equilibrium with the ethyl alcohol in the blood. This has certainty been found to be true.
ALCOHOL METABOLISM: (Editorial note: You will learn that alcohol does not get metabolized, as such, it gets catabolized, and is never digested, but the bio-chem pundits insist on using the word metabolism, so for continuity sake, we will use metabolism of alcohol interchangeably with my term catabolism of alcohol).
More than 90% of the ethyl alcohol that enters the body is completely oxidized to acetic acid. This process occurs primarily in the liver. The remainder of the alcohol is not metabolized and is excreted either in the sweat, urine or given off in one's breath. There are several routes of metabolism of ethyl alcohol in the body. The major pathways involve the liver and in particular the oxidation of ethyl alcohol by alcohol dehydrogenase (ADH).
As mentioned above perhaps the major route of metabolism of ethyl alcohol is its oxidation in the liver catalyzed by the cytosolic enzyme alcohol dehdrogenase (ADH).
This reaction produces acetaldehyde, a highly toxic substance. (Ed. note: I have proffered and many agree the "alcohol breath of an intoxicated person" is nothing more than the smell of the persons acetaldehyde, since alcohol is colorless and odorless.)
The second step of ethanol metabolism is catalyzed by acetaldehyde dehydrogenase. This enzyme converts acetaldehyde to acetic acid, which is a normal metabolite in humans and hence is non toxic.
Another system in the liver which oxidizes ethanol via the enzyme cytochrome P450IIE1 (CYP2E1) is called the MEOS system. Though of minor significance in comparison to SDH metabolism of ethanol it is present. It is not surprising that there are variations in the P450E1 enzyme which lead to differences in the rate of ethanol metabolism. This may have implications for tissue damage from ethanol, particular in the liver.
No matter how you ingest alcohol, which will be discussed in the ingestion portion of this web page, alcohol rich blood is first taken by the portal vein from the stomach to the liver. The liver eliminates approximately 20% of the alcohol per hour. The inferior vena Cava transport still heavily saturated blood to the pulmonary vein. The alcohol is then transported by the arterial circulation to the entire body. When the arterial blood alcohol reached the muscle, the alcohol rapidly distributes among the muscle cells; and thus, less alcohol is available to circulate in the blood and influence the brain centers. The rapid decrease in blood alcohol concentration allows the liver to more efficiently remove alcohol at slightly faster rate than one bottle of beer per hour. [.02% per hour]. This phenomenon is called alcohol plunge and is best seen when alcohol is administered intravenously, but is also seen in fasting individuals.
Normally, the liquid passes from the mouth through the pharynx and esophagus, into the stomach, and then into the small intestine, just beyond the stomach. The alcohol in the stomach and small intestines passes through the walls of these organs and enter the blood vessels within these walls. This alcohol is in its original form as undigested alcohol and is said to have been absorbed into the blood.
Brain tissue and liver tissue contain about the same fraction of alcohol as does blood. Urine, saliva and spinal fluid contain more water than is present in blood; thus they contain more absorbed alcohol.
The breath in the lungs absorbs alcohol from the blood vessels in the walls of the lungs and thus takes up its share of the circulating alcohol. The effect of alcohol is produced by alcohol stored in the brain, measurement of intoxication are expressed in terms of alcohol content of blood (Blood-Alcohol) because the first chemical determinations of alcohol in the body were made by analyzing blood. There is no normal alcohol in the body; that is, the body does not contain any detectable amount of alcohol other than that ingested so that, when alcohol is determined in any body fluid, or in the breath, we are sure that the alcohol was introduced into the body from some outside source.
Alcohol is oxidized, whether the body needs energy or not. It is never stored for future use. Not all persons burn alcohol at the same rate, with some persons burning up the alcohol faster than the average, and others burning it slower. However, for most individuals, the rate of destruction (denigration of alcohol) is partially constant, regardless of the percent of alcohol stored in the body.
It has been found that on the average, a healthy person will metabolize and eliminate about 1/3 fluid ounce (10cc) of alcohol per hour.
When death occurs, alcohol burning stops immediately, thus making it possible to determine the alcohol level in the body at the time of death, even if blood or urine samples are taken several hours after death.
For us the living, here is what happens to your brain on EtOH.
In order to keep the brain functioning normally, the brain attempts to chemically counteract whatever ethanol is doing to disrupt its action. A simple illustration is the reaction of the body if someone starts pushing it. The natural reaction is to compensate by correcting the balance and attempting to counteract the pressure of the push until the push is gone and the body returns to normal. Interestingly, neuroadaptiona also sometimes results in an increased response to the drug (sensitization). Whether there is a diminished response or an enhanced response depends upon a variety of factors including the amount of compound taken in and the timing of the intake. The development of sensitization may be more likely with intermittent exposure than with continuous exposure. Ethanol is first facilitated by the action of the major depressant neurotransmitter in the brain (GABA) and then inhibits the action of the major excitatory neurotransmitter in the brain (gltamate).
Ethanol acts at specific sites on a specific subset of GABA and glutamate receptors (protein molecule upon which the neurotramsmitters act). By influencing the action of these receptors, ethanol "slows down" the function of the nervous system. Thus, ethanol is called a central nervous system (CNS) depressant.
With neuroadaptation, the brain attempts to counteract this depressant effect by increasing the activity of the glutamate system and decreasing the activity of the GABA system. This in part can be accomplished by altering the number or function of the receptors.
GABA and glutamate receptors are only two of a number of key players in the transmission of information from one cell to the next. Activation of receptors is the occasion for intercellular signaling, meaning that a series of events within the cell take place when neurotransmitter binds to the receptor. Thus, neuroadaptation can also take place at other locations within the cascade of events that takes place in the brain.