Effects of Alcohol

Slide 1 · Effects of Alcohol

Metabolism, toxic injury, morphology, and multisystem consequences

A pathology lecture

Dr Abu Suraih Sakhri

MBBS, MD (Pathology)

www.abusuraihsakhri.com

Slide 2 · Learning objectives

Trace absorption and hepatic oxidation of ethanol through ADH, CYP2E1, catalase, and ALDH.

Explain how acetaldehyde, excess NADH, reactive oxygen species, and inflammation cause tissue damage.

Recognize acute toxicity and the organ-specific effects of chronic exposure.

Connect characteristic liver morphology to clinical consequences and carcinogenesis.

Slide 3 · Alcohol exposure is not risk-free

Toxicity depends on the amount and frequency of ethanol consumption.

Excess intake causes both physical and psychological injury.

The textbook cautions that even low levels of consumption may carry serious health risks.

Risk assessment depends on the exposure pattern and the susceptible host.

Slide 4 · Alcohol use disorder is a relapsing condition

Alcohol use disorder (AUD) means impaired ability to stop or control drinking.

Alcohol consumption continues despite adverse social, occupational, or health consequences.

Repeated exposure creates cumulative organ injury in addition to episodic intoxication.

AUD describes impaired control and consequences—not simply an isolated high blood level.

Slide 5 · Magnitude of alcohol exposure in the United States

Adults, 2021 survey

52% reported alcohol use in the preceding month.

28.6 million (11.3%) had AUD.

Adolescents, 2021 survey

7% reported alcohol use in the preceding month.

Nearly 900,000 (3.4%) had AUD.

Historical U.S. Estimates reported in the source; Not current surveillance figures.

Slide 6 · Alcohol contributes substantially to mortality

United States

More than 140,000 alcohol-attributable deaths per year (source estimate).

Over 13,000 deaths in alcohol-impaired driving in 2022.

Worldwide

Approximately 3 million deaths annually in the source estimate.

Estimated 5.3% of all deaths globally.

Numbers reflect the textbook’s cited observation periods, not an updated 2026 estimate.

Slide 7 · Two temporal patterns of toxicity

Acute exposure

Central nervous system depression

Gastritis or mucosal injury

Reversible hepatic steatosis

Chronic excessive exposure

Progressive liver fibrosis and cirrhosis

Neurologic and cardiovascular injury

Pancreatitis, malignancy, malnutrition, fetal injury

Timing helps predict dominant mechanisms, but acute and chronic processes can coexist.

Slide 8 · Ethanol is absorbed without chemical alteration

Ingestion

Stomach + small intestine

Systemic blood

Tissue distribution

Ethanol is absorbed unchanged from the upper gastrointestinal tract.

Distributed body levels track blood ethanol concentration.

Slide 9 · Only a small fraction is excreted unchanged

Blood ethanol

Primarily hepatic metabolism

Acetaldehyde → acetate

Less than 10% is eliminated unchanged through urine, sweat, and exhaled air.

Metabolic clearance therefore determines most of the duration of exposure.

Slide 10 · The basis of breath alcohol testing

Blood ethanol

Equilibration with exhaled air

Breath alcohol measurement

Ethanol in exhaled air is proportional to the blood concentration.

Breath testing estimates exposure; Legal thresholds depend on jurisdiction.

Slide 11 · Blood alcohol and acute clinical effects

Blood ethanol

Textbook-described effect

Interpretation

80 mg/dL (0.08%)

Legal impairment threshold in many U.S. states

Not a universal safety threshold

~200 mg/dL

Drowsiness

Marked CNS depression

~300 mg/dL

Stupor

Severe intoxication

Higher concentrations

Coma; potential respiratory arrest

Life-threatening toxicity

These are source-described approximate effects; Individual responses vary.

Slide 12 · Tolerance changes the concentration–effect relationship

Less tolerant individual

A given intake tends to produce a higher peak blood level.

Clinical depression becomes apparent at lower prior exposures.

Person with chronic AUD

Metabolic adaptation can increase alcohol clearance.

A similar intake may produce a lower peak blood concentration.

Tolerance does not protect against cumulative organ toxicity.

Slide 13 · Three routes oxidize ethanol

Ethanol

Acetaldehyde

Acetate

ADH (major) · CYP2E1 (inducible) · catalase (minor)

Cytosolic alcohol dehydrogenase (ADH) is the dominant route.

Microsomal CYP2E1 becomes important with heavy exposure; Catalase contributes minimally.

Slide 14 · Alcohol dehydrogenase is the major pathway

Ethanol

ADH · cytosol

Acetaldehyde

Located predominantly in the cytosol of hepatocytes.

Oxidation reduces NAD⁺ to NADH, linking detoxification to redox injury.

Slide 15 · CYP2E1 is a microsomal oxidation pathway

High ethanol exposure

CYP2E1 · smooth ER

Acetaldehyde + ROS

CYP2E1 belongs to the hepatic cytochrome P-450 system.

Its induction amplifies potential oxidative injury and drug interactions.

Slide 16 · Catalase has a minor quantitative role

Ethanol

Catalase · peroxisomes

Acetaldehyde

Catalase uses hydrogen peroxide in ethanol oxidation.

The source attributes approximately 5% of ethanol oxidation to this pathway.

Slide 17 · Aldehyde dehydrogenase clears acetaldehyde

Acetaldehyde

ALDH · mitochondria

Acetate

Acetate can enter mitochondrial energy metabolism or lipid synthesis.

Low ALDH activity permits acetaldehyde accumulation and toxicity.

Slide 18 · Metabolic compartmentation explains toxicity

First oxidation

ADH: Hepatocyte cytosol

CYP2E1: Smooth endoplasmic reticulum

Catalase: Peroxisome

Second oxidation

ALDH: Mitochondria

Acetaldehyde → acetate

Enzyme genotype influences acetaldehyde clearance

Compartment localization is critical to redox stress and ROS production.

Slide 19 · Excess NADH shifts hepatic redox balance

Ethanol oxidation by ADH

NAD⁺ consumed · NADH rises

NADH/NAD⁺ ratio increases

The raised reduced/oxidized cofactor ratio changes many metabolic reactions.

The liver becomes less capable of oxidizing fatty acids and handling lactate.

Slide 20 · Redox imbalance drives hepatic steatosis

Higher NADH/NAD⁺

Reduced fatty-acid oxidation

Lipid retained in hepatocytes

Fatty liver

Early hepatic fat accumulation can occur even with moderate intake.

In source-described early disease, steatosis is usually reversible after abstinence.

Slide 21 · The same redox shift increases lactate

NAD⁺ availability decreases

Lactate → pyruvate impaired

Lactate accumulates

Lactic acidosis

Lactate dehydrogenase reactions depend on available redox cofactors.

Metabolic acidosis is a mechanistic consequence of ethanol oxidation.

Slide 22 · Acetaldehyde is directly injurious

Acetaldehyde is the immediate oxidative product of ethanol.

It is responsible for some acute toxic effects and can form damaging protein adducts.

Inefficient detoxification increases exposure to reactive acetaldehyde.

Toxicity can persist downstream of the parent ethanol molecule.

Slide 23 · ALDH2 genotype influences alcohol responses

Reduced ALDH2 activity

Acetaldehyde retained

Flushing · nausea · tachycardia

The ALDH2*2 variant has very low activity.

The source describes a dominant-negative effect even with one ALDH2*2 allele.

Slide 24 · Homozygous ALDH2*2 causes marked intolerance

ALDH2*1 (usual allele)

More effective conversion of acetaldehyde to acetate.

Lower acetaldehyde exposure at a matched intake.

ALDH2*2 homozygote

Severely impaired acetaldehyde oxidation.

Flushing, nausea, tachycardia, and hyperventilation after alcohol.

Genetic prevalence and effects vary among populations; Avoid stereotyping individuals.

Slide 25 · CYP2E1 produces reactive oxygen species

Repeated high alcohol exposure

CYP2E1 induction

Reactive oxygen species

Hepatocyte damage

ROS generation occurs during microsomal ethanol oxidation.

Oxidative stress particularly affects membranes, proteins, and mitochondria.

Slide 26 · ROS trigger lipid peroxidation

Reactive oxygen species

Membrane lipid peroxidation

Membrane dysfunction

Hepatocyte injury

This mechanism complements acetaldehyde toxicity and redox imbalance.

Several pathways contribute simultaneously to alcohol-associated liver injury.

Slide 27 · Gut-derived endotoxin drives hepatic inflammation

Alcohol exposure

Greater gut endotoxin entry

Kupffer-cell activation

TNF + cytokines

Bacterial lipopolysaccharide from the intestinal microbiota reaches the liver.

Inflammatory signaling recruits additional injury beyond direct ethanol metabolism.

Slide 28 · Alcohol injury involves several convergent mechanisms

Hepatocyte injury

Metabolic

NADH excess

Chemical

Acetaldehyde adducts

Oxidative

CYP2E1-derived ROS

Inflammatory

LPS → Kupffer cells

Cellular

Mitochondrial injury

Tissue

Inflammation / fibrosis

Convergence explains why a single metabolic pathway cannot account for the full phenotype.

Slide 29 · Chronic drinking changes drug metabolism

Repeated ethanol exposure

CYP2E1 induction

Altered xenobiotic metabolism

Acetaminophen, cocaine, anesthetics, carcinogens, and solvents as relevant substrates.

Induced oxidation may increase formation of toxic metabolites for some drugs.

Slide 30 · Acute ethanol can compete for CYP2E1

During high ethanol concentrations

Ethanol competes with other CYP2E1 substrates.

Catabolism of other compounds may be delayed.

With chronic enzyme induction

Enzyme capacity is increased.

Metabolism of some xenobiotics can produce more reactive intermediates.

Acute competition and chronic induction are distinct phenomena.

Slide 31 · The CNS is the main target of acute toxicity

Ethanol is a central nervous system depressant.

Early effects disturb regulatory circuits that normally constrain cortical behavior.

Progression causes increasingly direct suppression of cortical and brainstem activity.

Apparent early excitation does not mean ethanol is a primary CNS stimulant.

Slide 32 · Early intoxication causes disinhibition

Subcortical regulatory depression

Reduced cortical restraint

Disordered behavior + judgment

Impaired regulatory activity can resemble stimulation.

Motor coordination and intellectual performance become abnormal.

Slide 33 · With rising exposure, cerebral function fails

Behavioral dysregulation

Cortical suppression

Drowsiness

Stupor

Severity generally increases with blood ethanol concentration.

Clinical observation must consider individual tolerance and co-exposures.

Slide 34 · Medullary suppression is the life-threatening endpoint

Very high blood ethanol

Lower brainstem depression

Respiratory-center failure

Respiratory arrest

Coma at high exposure may progress to fatal respiratory failure.

The mechanism is central respiratory depression, not merely intoxicated behavior.

Slide 35 · Acute alcohol can induce fatty change

Lipid droplets may appear in hepatocyte cytoplasm even with moderate ethanol exposure.

High NADH suppresses fatty-acid oxidation and promotes lipid accumulation.

Abstinence can reverse this early metabolic injury.

Steatosis reflects disturbed intracellular lipid handling rather than inevitable cirrhosis.

Slide 36 · Ethanol can acutely injure gastric mucosa

Gastric inflammation

Acute gastritis accompanies excessive alcohol exposure.

Mucosal damage can contribute to pain or bleeding.

Ulceration

Ethanol-associated ulceration may develop.

Bleeding can be serious, particularly with concurrent liver disease.

Acute gastric injury and portal-hypertensive variceal bleeding have different mechanisms.

Slide 37 · Acute and chronic toxicities interact

Acute mechanisms

CNS depression

Gastric mucosal damage

Metabolic redox shifts

Chronic consequences

Cumulative inflammation / fibrosis

Neurologic degeneration or deficiency

Cardiac, pancreatic, and neoplastic disease

A patient with cirrhosis can also present with acute intoxication or acute gastritis.

Slide 38 · Chronic exposure damages multiple organs

Chronic alcohol toxicity

Liver

Steatohepatitis, cirrhosis

GI tract

Gastritis, hemorrhage

CNS

Atrophy, nutritional injury

Heart

Dilated cardiomyopathy

Pancreas

Acute or chronic pancreatitis

Fetus / cancer

Developmental and oncologic harm

Many of these effects reflect both direct toxicity and nutritional or secondary mechanisms.

Slide 39 · Alcohol-associated liver disease is a spectrum

Steatosis

Steatohepatitis

Fibrosis

Cirrhosis

The histologic categories overlap rather than representing an obligatory linear sequence.

A subset of patients first presents with established cirrhosis.

Slide 40 · Risk of advanced liver disease is heterogeneous

Not all patients with alcohol use disorder develop cirrhosis.

Biologic sex, inherited susceptibility, and other liver diseases influence progression.

Daily ethanol dose and duration matter, but alone do not determine individual outcome.

Avoid predicting an individual’s pathology solely from reported intake.

Slide 41 · Other liver insults amplify alcohol-associated injury

Coexisting conditions

Iron overload

Hepatitis B or hepatitis C infection

Metabolic dysfunction–associated steatohepatitis

Why this matters

Multiple insults can act synergistically.

Steatosis alone is not diagnostic of alcohol as its cause.

Clinical context is needed to assign etiology.

Coexisting etiologies need assessment before assigning the liver injury to ethanol.

Slide 42 · Hepatic steatosis has recognizable morphology

Schematic — not a histologic specimen

Large clear lipid vacuoles displace nuclei

Macrovesicular steatosis is the dominant pattern in alcohol-associated liver disease.

Intracellular fat vacuoles enlarge and displace the nucleus.

Grossly the liver may become enlarged, yellow, soft, and greasy.

Slide 43 · Alcoholic injury often begins near central veins

Zone 3 · centrilobular injury

Progressive hepatocyte change

Extension toward portal areas

Characteristic early injury begins near centrilobular zone 3.

Greater injury extends away from central veins toward portal tracts.

Slide 44 · Ballooning represents hepatocyte damage

Schematic — not a histologic specimen

Selected hepatocytes are expanded and pale

Ballooned hepatocytes are swollen with pale, cleared-out cytoplasm.

Cytoskeletal dysfunction accompanies the cell injury.

Ballooning is important in steatohepatitis but is not specific for alcohol.

Slide 45 · Mallory hyaline marks cytoskeletal injury

Hepatocyte injury

Keratin 8/18 disruption

Ubiquitinated intermediate filaments

Mallory hyaline

Mallory hyaline consists of abnormal cytoplasmic intermediate filament aggregates.

It can also be encountered in nonalcohol-associated liver disorders.

Slide 46 · Neutrophils are conspicuous in alcohol-associated hepatitis

Schematic — not a histologic specimen

Inflammatory cells cluster near hepatocytes

Neutrophils may cluster around injured, ballooned hepatocytes.

Lobular lymphocytes and macrophages can also be present.

Focal hepatocyte necrosis or apoptosis accompanies the inflammatory process.

Slide 47 · Pericellular fibrosis has a chicken-wire pattern

Schematic — not a histologic specimen

Pericellular network represents progressive collagen

Fibrosis commonly starts around sinusoids in acinar zone 3.

Pericellular / perisinusoidal collagen surrounds hepatocytes in a network.

The pattern can precede bridging fibrosis and cirrhosis.

Slide 48 · Persistent injury reshapes liver architecture

Pericellular scarring

Portal / periportal fibrosis

Bridging fibrosis

Cirrhosis

Fibrosis progressively remodels parenchyma and vascular channels.

Micronodular cirrhosis is commonly described, although morphology can evolve.

Slide 49 · Cirrhosis produces portal hypertension

Architectural distortion

Increased portal resistance

Portal hypertension

Varices / complications

Cirrhotic vascular dysfunction can create life-threatening esophageal varices.

Cirrhosis also increases hepatocellular carcinoma risk.

Slide 50 · Alcohol-associated hepatitis has clinical correlates

Clinical features

Malaise, anorexia, weight loss

Upper abdominal discomfort

Tender hepatomegaly

Laboratory changes

Hyperbilirubinemia

Aminotransferase elevation

Neutrophilic leukocytosis may occur

These findings support context but are not individually specific for alcohol-related injury.

Slide 51 · AST predominance is a useful clue—not proof

AST commonly exceeds ALT in alcohol-associated liver disease.

A ratio of AST:ALT of 2:1 or greater can raise suspicion.

Clinical exposure history and exclusion of alternative causes remain necessary.

Do not use one aminotransferase ratio as a stand-alone etiologic diagnosis.

Slide 52 · Early injury has greater reversibility

Steatosis

Often completely reversible with abstinence.

Cellular lipid accumulation can resolve without major architectural damage.

Established cirrhosis

Dense scarring and vascular distortion limit full recovery.

Complete regression is reported but uncommon.

Fibrosis at earlier stages can regress after removal of the injury.

Slide 53 · Gastrointestinal bleeding has distinct sources

Primary mucosal injury

Gastritis

Gastric ulceration

Mucosal bleeding

Secondary portal-hypertensive injury

Cirrhosis increases portal venous pressure.

Esophageal varices may rupture.

Massive hemorrhage may be fatal.

Not all bleeding in a patient with AUD comes directly from gastric mucosa.

Slide 54 · Thiamine deficiency contributes to neurologic injury

Chronic AUD

Nutritional deficiency

Thiamine (vitamin B₁) depletion

Neurologic syndromes

The source specifically links thiamine deficiency to neuropathy and Wernicke–Korsakoff syndrome.

This mechanism differs from direct acute ethanol-induced CNS depression.

Slide 55 · Cerebellar degeneration affects coordination

Chronic excessive alcohol use

Anterior vermis neuron loss

Impaired cerebellar coordination

Cerebellar degeneration is a described structural neurologic complication.

Chronic cerebral atrophy and optic neuropathy can also occur.

Slide 56 · Peripheral neuropathy is another chronic effect

Peripheral nerve damage is recognized in chronic AUD.

The textbook associates thiamine deficiency with peripheral neuropathies.

Neurologic deficits may coexist with cerebellar disease or Wernicke–Korsakoff syndrome.

Separate a nutritional neuropathy mechanism from the direct sedative effect of ethanol.

Slide 57 · Alcohol can cause dilated cardiomyopathy

Long-term excessive exposure

Myocardial injury

Cardiac dilation

Congestive dysfunction

Alcoholic cardiomyopathy as a chronic cardiovascular effect.

The damaged heart develops a dilated, poorly functioning phenotype.

Slide 58 · Cardiovascular effects extend beyond cardiomyopathy

Recognized adverse effects

Increased frequency of hypertension

Myocardial injury and congestive cardiomyopathy

Interpreting lipid associations

Severe liver injury may lower HDL cholesterol.

Reported favorable associations with modest intake are not proof of benefit.

Cardiovascular risk cannot be inferred from HDL changes alone.

Slide 59 · Excess alcohol increases pancreatitis risk

Acute pancreatitis

Can occur with excessive intake.

Represents pancreatic inflammatory injury.

Chronic pancreatitis

Associated with repeated or prolonged heavy intake.

Can contribute to lasting pancreatic dysfunction.

Both forms are recognized as important consequences of excessive intake.

Slide 60 · Prenatal exposure may cause fetal alcohol syndrome

Fetal alcohol syndrome

Growth

Growth retardation

Head

Microcephaly

Face

Facial abnormalities

Development

Reduced later mental function

The source stresses first-trimester vulnerability and uncertainty regarding a safe exposure threshold.

Slide 61 · Chronic alcohol intake is carcinogenic

Alcohol-linked cancer risk

Oral cavity

Increased risk

Esophagus

Increased risk

Liver

Increased risk

Larynx

Acetaldehyde implicated

Breast

Risk can rise even at low–moderate intake

The source explicitly cautions that even light-to-moderate drinking can increase cancer risk.

Slide 62 · Acetaldehyde can damage genomic DNA

Ethanol

Acetaldehyde exposure

DNA adduct formation

Carcinogenic potential

Acetaldehyde–DNA adducts have been detected in certain upper aerodigestive tract tumors.

The source implicates acetaldehyde in laryngeal and esophageal carcinogenesis.

Slide 63 · ALDH2 deficiency modifies esophageal cancer risk

ALDH2*2 allele + drinking

Slower acetaldehyde clearance

Greater acetaldehyde exposure

Higher esophageal cancer risk

The source highlights increased esophageal cancer risk in drinkers carrying one ALDH2*2 allele.

Acute flushing therefore must not be interpreted as protection from cancer.

Slide 64 · Alcohol and tobacco act synergistically

Alcohol exposure

Combined carcinogenic exposures

Greater upper aerodigestive cancer risk

Synergy for several cancers involving tobacco and alcohol.

Joint exposure is more hazardous than considering each exposure in isolation.

Slide 65 · Ethanol calories do not prevent malnutrition

Substantial alcohol calories

Poor nutrient adequacy

Vitamin deficiencies

Systemic consequences

The source characterizes ethanol as a source of “empty calories.”

Severe chronic AUD is associated with malnutrition, particularly B-vitamin deficiency.

Slide 66 · Claims of moderate drinking benefit need caution

Reported observational associations

Some studies found reduced cardiovascular mortality with moderate consumption.

Proposed factors include HDL, platelet effects, and fibrinogen.

Why causality is uncertain

Socioeconomic status, diet, and lifestyle can confound results.

The textbook does not establish alcohol consumption as a safe intervention.

Association is not proof of cardioprotection or a recommendation to consume ethanol.

Slide 67 · Alcohol and metabolic fatty liver may overlap

Alcohol-associated steatotic injury

Exposure to ethanol and toxic metabolites

Steatosis ± ballooning, inflammation, fibrosis

Metabolic dysfunction-associated disease

Associated with cardiometabolic risk factors

Many microscopic features overlap with alcohol-associated injury

Neither steatosis nor ballooning alone establishes the etiologic diagnosis.

Slide 68 · Case 1: Progressive intoxication

Clinical stem

A person with marked ethanol exposure develops unsteady behavior, then drowsiness, and finally reduced responsiveness with poor respiratory effort.

Which sequence best explains the change in neurologic manifestations?

Early depression of regulatory subcortical circuitry causes apparent disinhibition.

Higher concentrations suppress cortical neurons and then medullary respiratory centers.

Respiratory compromise is the critical life-threatening progression.

Slide 69 · Case 2: Injured fatty liver

Clinical stem

A patient with sustained excessive ethanol consumption has hepatomegaly and abnormal aminotransferases. Biopsy shows steatosis, ballooned hepatocytes, neutrophils, and zone-3 pericellular fibrosis.

Which tissue mechanisms and stage of injury are suggested?

NADH-driven steatosis plus oxidative and inflammatory hepatocyte injury.

Ballooning and neutrophils support steatohepatitis; Zone-3 fibrosis signifies chronic injury.

Steatosis may regress; Scarring may progress if exposure continues.

Slide 70 · Case 3: Flushing and cancer susceptibility

Clinical stem

A person experiences facial flushing and tachycardia after ethanol intake but continues to drink. Genotyping identifies an ALDH2*2 allele.

How can acute intolerance coexist with longer-term cancer risk?

Low ALDH2 activity prolongs acetaldehyde exposure.

Acetaldehyde causes acute symptoms and can form DNA adducts.

The source links ALDH2*2 in drinkers to increased esophageal cancer risk.

Slide 71 · Mechanisms connect exposure to organ injury

Ethanol exposure

Brain

Dose-related depression

Liver

Redox + ROS + LPS

Stomach

Gastritis / ulceration

Heart

Myocardial damage

Pancreas

Inflammatory injury

Cancer / fetus

DNA damage / teratogenicity

Acute intoxication is only one component of total alcohol-associated pathology.

Slide 72 · Core points for clinical pathology

ADH, CYP2E1, and catalase form acetaldehyde; Mitochondrial ALDH converts it to acetate.

NADH excess, acetaldehyde injury, ROS, and Kupffer-cell inflammation drive hepatotoxicity.

The chronic liver spectrum includes steatosis, steatohepatitis, fibrosis, and cirrhosis.

Alcohol affects brain, gut, cardiovascular system, pancreas, fetal development, and cancer risk.

Interpret findings by integrating exposure, metabolism, morphology, and organ effects.

Slide 73 · Selected reference

Robbins, Cotran & Kumar. Pathologic Basis of Disease. 11th edition (2026).

Primary textbook section: “Effects of Alcohol” (Environmental and Nutritional Diseases).

Additional textbook section: “Alcohol-Associated Liver Disease” (Liver and Gallbladder).