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Once ethanol is in the circulation, the reaches all tissues in the body, including the brain, wherein it causes intoxication. Our bodies room designed to terminate the action of drugs, including alcohol, so the the intoxication doesn’t persist once a person stops drinking. In fact, the human body starts eliminating ethanol prior to it also gets right into the general circulation!

Ethanol moves from the GI street to the liver

When a human being consumes alcohol, the an initial place that the alcohol walk after it pipeline the GI tract is the liver (Figure 1.10). As soon as it start the capillaries neighboring the stomach and little intestines, the capillaries cause the portal vein, which enters the liver and also branches out when again right into capillaries. Ethanol diffuses from the capillaries (with the concentration gradient) right into the surrounding hepatic cell (the significant cells that the liver). In the hepatic (liver) cells, few of the ethanol is converted, or detoxified by enzymes to inactive products. This procedure is dubbed metabolism, and the commodities are called metabolites.

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Figure 1.10 Alcohol move from the GI tract with the portal vein to the liver. The diffuses right into hepatic cells of the liver whereby it is metabolized.

Alcohol is metabolized in 2 stages

Metabolism of drugs by liver enzymes serves 2 purposes. First, line is a means of “turning off” the activity of a drug. In general, metabolites have actually less biological task relative come the parent compound, back there are some exceptions to this rule, as we will certainly see through ethanol.

Second, metabolism helps to convert the drug right into a more polar (water-soluble) kind so it have the right to be brought in the bloodstream to the kidneys, where it is excreted in the to pee (water-based). During metabolism, the enzymes actually help speed increase the reactions; however, the rate is various for various people.

Review enzymes together catalysts.

Stage 1: Ethanol come acetaldehyde

Although part alcohol is metabolized in the stomach, the main site of management is in the liver. The cytoplasm the liver cells contain an enzyme called alcohol dehydrogenase (ADH) the catalyzes the oxidation that ethanol to acetaldehyde (Figure 1.11). The oxidation occurs once ethanol binding to a site on the ADH enzyme and also loses some electrons in the type of H atoms. Actually ethanol offers up 2 H atoms to an additional molecule that likewise binds to ADH. In this case, the recipient molecule that the electron is called a coenzyme. There is no the coenzyme, the ADH enzyme won’t work.


The liver is the major site of oxidation of alcohol, some alcohol is oxidized the in the stomach, too.

The main metabolite the ethanol oxidation, is acetaldehyde. This compound is reasonably toxic, and also it is responsible for alcohol-related flushing, headaches, nausea, and increased heart rate. These toxic impacts of acetaldehyde contribute to the alcohol “hang-over” the persists for a far-ranging time after drinking.

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Figure 1.11 Ethanol is oxidized by ADH to acetaldehyde in the cytoplasm, and then the acetaldehyde is oxidized by ALDH in the mitochondria to acetic acid.

Stage 2: Acetaldehyde to acetic acid

The body has actually a natural method to “get rid” the the acetaldehyde—a 2nd liver enzyme, present in the mitochondria, is acetaldehyde dehydrogenase (ALDH). This enzyme metabolizes acetaldehyde come acetic mountain (Figure 1. 11), i m sorry is inactive. The acetic acid is ultimately converted in the cell right into carbon dioxide and also water. Some world do not have actually the capacity to metabolize acetaldehyde an extremely well. When they drink alcohol, acetaldehyde accumulates in the blood and makes them feel sick. They have facial flushing, headaches, nausea, vomiting, and also a quick heart rate. The factor that some world can’t metabolize acetaldehyde really well is since they have actually a form of ALDH that has a mutation in the gene the codes for it. The alternative form of ALDH is really inefficient in ~ metabolizing acetaldehyde. Human being with this hereditary mutation execute not like to drink alcohol.To learn more about various forms the ALDH and also ADH in assorted populations, see Module 2I.


Alcohol is metabolized by an oxidation reaction to acetaldehyde, a toxic metabolite. The acetaldehyde is climate oxidized come acetic acid, one inert metabolite.

Learn more about oxidation.

Overwhelming the alcohol metabolizing enzymes

There is sufficient ADH present in a person’s liver to metabolize every the alcohol molecule from one drink quite efficiently within an hour or two. The rate of management remains consistent during continued drinking. Why is this important? as the intake of alcohol boosts there just aren’t enough ADH molecule (in the liver or the stomach) to metabolize the extra alcohol efficiently. So, alcohol begins to accumulate in the bloodstream, giving an boosted blood alcohol concentration (BAC) (Figure 1.12) that leads to intoxication. In other words, once the line of ethanol is restricted by the variety of ADH enzyme molecules present, it proceeds independent of the quantity of alcohol in the bloodstream.

Figure 1.12 The number of ADH enzyme molecules in the liver is limited. With an ext than one drink that alcohol, the enzymes become saturated with ethanol molecules. Some ethanol is metabolized in the liver, yet the remainder of the ethanol pipeline the liver and also accumulates in the bloodstream.


With more than one drink the alcohol, management proceeds in ~ a consistent rate due to the fact that ADH molecules are fully saturated through alcohol. This causes alcohol to accumulate in the bloodstream.

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Alcohol the is not metabolized top top its very first passage v the liver continues to circulate transparent the body together an energetic drug. Ultimately, just a small portion of the ingested alcohol escapes metabolism. This tiny amount that alcohol (5-10%) is removed unchanged in the breath together vapor or in the urine.