What is ethanol?
Ethanol (CH3CH2OH) is a ferment‑derived alcohol that is ingestible and produces acute physiological effects; other alcohols like methanol are toxic and can cause blindness or death.
Where is it absorbed?
- Ethanol is highly water soluble with some lipid solubility.
- It is absorbed primarily by passive diffusion (20% stomach, 80% small intestine), and its absorption rate depends on concentration, gastric emptying, and surface area
- Food in the stomach slows absorption and lowers peak BAC.
What determines BAC levels?
Peak BAC is determined by amount consumed, concentration of drink, rate of absorption, stomach contents, body water distribution (males generally have more total body water than females), and factors like age and body composition.
Describe why alcohol has a bigger impact on females than on males.
Alcohol is highly soluble in water. Females have less water than males (higher fat content, smaller stature, lower muscle mass) hence for the same amount of alcohol consumed, females have a higher BAC than in males. Even if height were normalised, females have lower water content due to higher fat content.
What effects does alcohol have on the CNS?
Ethanol depresses brain activity by enhancing GABAA inhibition and suppressing glutamate excitation, producing euphoria, impaired coordination, memory changes, and at high doses respiratory depression, coma, or death; tolerance and withdrawal occur with chronic use.
How is alcohol metabolised in the body?
About 90% of ethanol is metabolized in the liver via ADH to acetaldehyde and ALDH to acetate using NAD+ as cofactor; a minor amount is metabolized in the stomach and <10% is eliminated unchanged in breath, urine, and sweat.
As alcohol is not released into the alveoli via the pulmonary circulation, how does it get there to be registered in breathalizers?
Expired ethanol in breath reflects airway exchange driven by bronchial circulation and airway surface liquid rather than alveolar pulmonary exchange, because ethanol is highly water soluble and exchanges throughout the bronchial tree.
Why is the brain susceptible to the effects of ethanol?
Rapid access: ethanol is small, water- and lipid‑soluble so it crosses the blood–brain barrier quickly and equilibrates with brain water.
High brain water content: the brain’s large intracellular water fraction concentrates ethanol relative to fatty tissues.
No protein binding: ethanol remains free in blood and is immediately available to cross into the CNS.
Fast rise, slow clearance: rapid intestinal absorption can produce quick spikes in blood ethanol while hepatic metabolism is rate‑limited, prolonging brain exposure.
What effects do alcohol have on the brain?
Receptor effects: ethanol shifts neural balance toward inhibition by enhancing GABA(A) and suppressing glutamate transmission, producing strong functional effects (euphoria, impaired coordination, memory changes, sedation, respiratory depression) at moderate concentrations.
NB: At very high concentrations, respiratory depression may lead to coma or death
Why do chronic drinkers tolerate alcohol’s effects better than someone who rarely drinks?
Chronic exposure produces adaptation and dependence. Receptor and circuit changes reduce sensitivity to ethanol and create withdrawal syndromes when ethanol is removed.
