Physiology and Effects of Alcohol on Brain

Alcohol can be regarded as a drug as it can cause physiologic addiction in all who consume it and may result in intoxication, tolerance or withdrawal.

Absorption and Elimination of alcohol:
  1. 20% in stomach and 80% in small intestine
  2. Can be detected in blood within 2-3 minutes of swallowing a few sips of whisky or beer
  3. A single bolus of alcohol taken into an empty stomach will be completely absorbed into portal bloodstream within 30-90 minutes
  4. As soon as alcohol enters the bloodstream, liver and kidneys will begin to eliminate
  5. 90% is eliminated by liver and 10% by kidneys, sweat and breath
  6. Chronic alcoholics with induced liver Cyt. P450 (until their liver fails) can metabolize alcohol at an abnormally high rate
  7. Normal rate of elimination for non-alcoholic: 10 to 25 mg/100ml/hr

Blood Alcohol Concentration (BAC): BAC expressed as mg/dl or mg% is the most useful measurement of alcohol, because the rapid equilibrtion of alcohol across Blood brain barrier (BBB) means that BAC reflects the concentration of alcohol currently affecting the brain.

Mathematically, BAC = Total amount of alcohol in body/ Total amount of body water

The factors increasing BAC are:

1. Decreased body water
  • Low body weight
  • Appreciable adiposity
  • Female gender
2. Faster absorption
  • Rapid drinking
  • Empty stomach
  • Food physically obstructs the contact of alcohol molecules with gastric mucosa
  • Food delays emptying through the pylorus
  • Optimum concentration of alcohol (around 20%)
  • Week drinks like beer have poor absorption
  • Strong spirits (>40% concentration) irritate gastric mucosa resulting in excess secretion of mucus (barrier), cause pyloric spasm and reduce gastric motility
  • Gastrectomy, Gastrojejunostomy
Effects of Alcohol on Brain:

Alcohol depresses the nervous system and any apparent initial excitant effect is due to suppression of inhibition by the cerebral cortex. It begins to act at lowest concentration upon the higher centers and it affect the lower centers of CNS only when BAC becomes higher. The correlation of BAC and physiologic effects have been correlated below:
  • 0 to 50 mg%: No significant effect or mild euphoria
  • 50 to 100 mg% (Cerebral cortex): Talkativeness, More self confidence, Reduced social inhibitions, Slight sensory disturbance, Poor judgement
  • 100 to 150 mg% (Limbic system): Exaggerated emotions and memory loss
  • 150 to 300 mg% (Cerebellum): Incoordination, unsteadiness, slurred speech, ataxia (Obvious drunkenness)
  • 300 to 400 mg+ % (Hypothalamus and Medulla): Stupor, Increased BP, Decreased temperature, Bradycardia, Respiratory depression, Coma, Death 
A person is likely to appear more uninhibited in a student party than in a very formal function given the same level of alcohol.

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