Absorption and Distribution of Alcohol

The basic principles of alcohol absorption from the gastrointestinal (GI) tract and subsequent distribution are well understood. Beverages containing etha-nol pass down the oesophagus into the stomach. The endogenous flora of the GI tract can also transform food into a mixture of alcohols including ethanol. This is particularly important if there are anatomical variations in the upper GI tract (e.g., diverticulae).

Alcohol continues down the GI tract until absorbed. The ethanol concentration therefore

Table 2 Geographical variation in the amount of ethanol in one unita

Country

Amount of alcohol (g)

Japan

14

United States

12

Australia and New Zealand

10

United Kingdom

S

aThe unit system does not permit international comparisons.

aThe unit system does not permit international comparisons.

Table 3 Guidelines for the consumption of alcohol3

Men (units)

Women (units)

Weeklyb

Dailyc

Weekly0 Dailyc

Low risk

G-21

3-4

0-14 2-3

Hazardous

22-5G

>4

15-35 >3

Harmful

>5G

>35 >1-2d

aGuidelines regarding the consumption of alcohol are designed to reduce harm. The Royal Colleges' (1995) guidelines are for weekly consumption rates, and the Department of Health's (1995) guidelines are for daily consumption. ^Recommendations of the Working Group of the Royal Colleges of Physicians, Psychiatrists and General Practitioners (UK). cRecommendations of the Department of Health (UK). dWhen pregnant or about to become pregnant, consumption of more than 1 or 2 units of alcohol, one or two times per week, is harmful.

aGuidelines regarding the consumption of alcohol are designed to reduce harm. The Royal Colleges' (1995) guidelines are for weekly consumption rates, and the Department of Health's (1995) guidelines are for daily consumption. ^Recommendations of the Working Group of the Royal Colleges of Physicians, Psychiatrists and General Practitioners (UK). cRecommendations of the Department of Health (UK). dWhen pregnant or about to become pregnant, consumption of more than 1 or 2 units of alcohol, one or two times per week, is harmful.

Polar hydroxyl group

Non-polar carbon backbone Figure 1 Chemical structure of ethanol.

decreases down the GI tract. There is also a concentration gradient of ethanol from the lumen to the blood. The concentration of ethanol is much higher in the lumen of the upper small intestine than in plasma (Table 4). Alcohol diffuses passively across the cell membranes of the mucosal surface into the submucosal space and then the submucosal capillaries.

Absorption occurs across all of the GI mucosa but is fastest in the duodenum and jejunum. The rate of

Table 4 Approximate ethanol concentrations in the gastrointestinal tract and in the blood after a dose of ethanola

Site

Ethanol

concentration

g/dl

mmol/l

Stomach

B

174G

Jejunum

4

B7G

Ileum

G.1-G.2

22-43

Blood (15-120 minutes after dosage)

G.1-G.2

22-43

aEthanol appears in the blood as quickly as 5 minutes after ingestion and is rapidly distributed around the body. A dose of 0.8 g ethanol/kg body weight (56 g ethanol (7 units) consumed by a 70 kg male) should result in a blood ethanol concentration of 100-200 mg/dl (22-43 mmol/l) between 15 and 120 minutes after dosage. Highest concentrations occur after 30-90 minutes.

aEthanol appears in the blood as quickly as 5 minutes after ingestion and is rapidly distributed around the body. A dose of 0.8 g ethanol/kg body weight (56 g ethanol (7 units) consumed by a 70 kg male) should result in a blood ethanol concentration of 100-200 mg/dl (22-43 mmol/l) between 15 and 120 minutes after dosage. Highest concentrations occur after 30-90 minutes.

gastric emptying is the main determinant of absorption because most ethanol is absorbed after leaving the stomach through the pylorus.

Alcohol diffuses from the blood into tissues across capillary walls. Ethanol concentration equilibrates between blood and the extracellular fluid within a single pass. However, equilibration between blood water and total tissue water may take several hours, depending on the cross-sectional area of the capillary bed and tissue blood flow.

Ethanol enters most tissues but its solubility in bone and fat is negligible. Therefore, in the postabsorption phase, the volume of distribution of ethanol reflects total body water. Thus, for a given dose, BEC will reflect lean body mass.

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