Necrosis

Slide 1 · Necrosis

Irreversible injury, membrane breakdown, inflammation, and morphologic evidence

Severe insult

Irreversible damage

Cellular leakage

Inflammation

Dr Abu Suraih Sakhri

MBBS, MD (Pathology)

www.abusuraihsakhri.com

Slide 2 · Learning outcomes

Define necrosis and identify the injuries that cause it.

Connect irreversible mitochondrial and membrane dysfunction to cell lysis.

Explain damage-associated molecular patterns and the inflammatory response.

Recognize necrotic cytoplasmic, nuclear, and ultrastructural changes.

Interpret leakage biomarkers in their tissue and clinical context.

Slide 3 · Necrosis is a consequence of severe injury

Necrosis is a pathologic process resulting from lethal cellular injury.

Severe damage becomes irreparable across multiple essential cell components.

Loss of membrane integrity allows cellular constituents to escape.

Enzymatic degradation and local inflammation accompany the process.

Slide 4 · The four interlocking features

Protein denaturation

Cellular proteins lose their native structure and function.

Loss of membrane integrity

Intracellular components escape through damaged membranes.

Inflammatory reaction

Extracellular injury signals activate resident and recruited immune cells.

Enzymatic digestion

Lysosomal and leukocyte enzymes help dismantle dead cells.

Slide 5 · Sources of severe injury

Loss of oxygen supply

Ischemia compromises mitochondrial energy generation and cellular homeostasis.

Microbial toxins

Infectious agents can produce severe cell damage by toxic mechanisms.

Physical / chemical injury

Burns and damaging chemicals can overwhelm cellular repair.

Protease-mediated injury

Active proteases escaping cells may damage surrounding tissue, as in pancreatitis.

Slide 6 · Ischemia: Oxygen loss initiates injury

Reduced blood supply

Oxygen delivery falls

Mitochondrial stress

Oxidative phosphorylation fails

Severe ATP deficit

Multiple cellular systems impaired

Irreversible injury

Membrane failure and necrosis

Slide 7 · Microbial toxins can precipitate necrosis

Initial insult

Necrotic outcome

Toxic products from microorganisms injure susceptible cells.

Multiple organelles or cell structures may be affected.

Severity and persistence influence outcome.

Cell membrane barrier collapses.

Cytoplasmic proteins and enzymes escape.

Local inflammatory response develops.

Slide 8 · Chemical and physical injury

Chemicals

Potential direct toxicity to cellular proteins, membranes, or organelles.

Burns

Severe physical damage causes irreversible cellular dysfunction.

Common endpoint

Multiple pathways can converge on membrane loss and tissue destruction.

Slide 9 · Pancreatitis: A protease-centered example

Enzyme activation / escape

Proteases become damaging

Extracellular tissue injury

Proteolytic damage extends locally

Cellular destruction

Injured cells undergo necrosis

Inflammatory reaction

Debris drives local response

Slide 10 · Different triggers converge on one phenotype

Ischemia

Failure of oxygen supply and energy production.

Toxic stress

Irreparable disruption of key proteins or membranes.

Physical injury

Severe destruction of cellular architecture.

Proteases

Enzymatic injury of cells and local tissue.

Slide 11 · Progression from viable to dead cells

Viable

Integrity retained.

Potentially reversible

Early swelling and dysfunction.

Necrotic

Membrane rupture and digestion.

The boundary is not a universal fixed duration; Injury burden and cell type matter.

Slide 12 · Severe injury is not merely severe swelling

Reversible cellular injury

Necrosis

Cell and organelle swelling may occur.

Plasma membrane can exhibit blebs.

Recovery remains possible if stimulus abates.

Critical membrane integrity is lost.

Injury cannot be reversed by removing the stimulus alone.

Digestion, leakage, and inflammation follow.

Slide 13 · The “point of no return” is not sharply defined

The precise threshold for irreversibility as largely undefined.

A single marker does not universally identify that transition.

Severe dysfunction involves more than one linked cellular compartment.

Persistent mitochondrial failure and major membrane derangement are consistent hallmarks.

Slide 14 · Two consistent hallmarks of irreversibility

Nonrecovering mitochondria

Oxidative phosphorylation and ATP generation fail to recover even if the original injury is relieved.

Profound membrane disturbance

Loss of essential membrane functions allows gradients, contents, and enzymes to escape.

Slide 15 · Mitochondrial failure cannot be rescued

Severe injury

Mitochondrial structures impaired

Oxidative phosphorylation fails

ATP production compromised

Insult ends

Original cause may be removed

No energy recovery

Irreversibility persists

Slide 16 · Plasma membrane breakdown

Schematic — not a photomicrograph

Intact cellular boundary

Nucleus and organelles retained

Irreversible membrane injury

Fragments leak; Debris is cleared

Slide 17 · Lysosomal membranes: A destructive breach

Lysosome injured

Membrane no longer confines enzymes

Enzyme escape

Hydrolytic enzymes reach cytosol

Intracellular digestion

Proteins and organelles degrade

Cell clearance

Remnants become debris

Slide 18 · Three cellular compartments in irreversible injury

Mitochondria

Persistent impairment of oxidative phosphorylation and ATP production

Plasma membrane

Loss of ion barrier and escape of cytosolic constituents

Lysosomal membrane

Enzyme escape and digestion of cellular structures

Slide 19 · Protein denaturation is a defining feature

Necrotic injury disrupts the structure of numerous cellular proteins.

Denaturation changes the native conformation of protein targets.

Enzyme activity and structural integrity may be lost together.

Morphologic consequences become apparent in the staining of necrotic cytoplasm.

Slide 20 · Denaturation and digestion are distinct

Denaturation

Digestion

Native protein conformation is disturbed.

Protein function becomes impaired.

Cell structure may temporarily be recognizable.

Hydrolases cleave cellular constituents.

Organelles and cells are dismantled.

Debris is removed by phagocytes.

Slide 21 · Lysosomal enzymes dismantle dead cells

Source inside the cell

Lysosomal leakage delivers enzymes to damaged cytoplasm.

Extracellular response

Leukocytes can release additional degradative enzymes.

Fate of remnants

Enzymatic breakdown and phagocytosis remove necrotic debris.

Slide 22 · Membrane failure enables two downstream effects

Plasma membrane breach

Intracellular compartment exposed

Contents escape

Proteins and DAMPs are released

Local sensing

Inflammatory response initiated

Circulating biomarkers

Organ-associated analytes measurable

Slide 23 · Necrosis is a coupled cascade

Irreversible injury

Mitochondria and membranes

Protein denaturation

Structural / enzymatic dysfunction

Cellular digestion

Lysosomal and inflammatory enzymes

Inflammation & debris clearance

Immune sensing and phagocytosis

Slide 24 · Why necrosis provokes inflammation

Schematic: Leakage leads to sterile inflammatory signaling

ATP · uric acid · other DAMPs

Sensing cell (e.g., macrophage)

Recognition → cytokines → phagocytosis and leukocyte recruitment

Slide 25 · Damage-associated molecular patterns (DAMPs)

DAMPs are endogenous molecules whose abnormal extracellular presence signals cell damage.

Normally confined or regulated within healthy cells.

Released in substantial injury when compartments lose integrity.

Recognized by immune or tissue cells and can stimulate local inflammatory responses.

Slide 26 · Two DAMP examples

ATP

Released in the context of damaged mitochondria and other injured cellular compartments.

Uric acid

A breakdown product of cellular DNA that can participate in danger signaling.

Slide 27 · DAMPs are not microbial toxins

DAMPs

Microbial triggers

Endogenous molecules associated with host-cell damage.

May be exposed in sterile necrosis.

Signal disrupted tissue homeostasis.

Exogenous products associated with microorganisms.

Can act as initiating injuries.

Infection and tissue necrosis can coexist.

Slide 28 · Cellular recognition of leaked injury signals

DAMP release

Necrotic material outside cells

Recognition

Receptors on macrophages / other cells

Cytokine production

Local inflammatory mediators

Response

Phagocytosis and recruited leukocytes

Slide 29 · Macrophages: Sensing and removal

Recognition

Respond to molecules released from damaged cells.

Mediator release

Produce cytokines that contribute to inflammatory recruitment.

Phagocytosis

Engulf cellular fragments and participate in cleanup.

Slide 30 · Inflammation assists clearance

Dead cell debris

Extracellular and tissue fragments

Inflammatory cell arrival

Leukocyte accumulation

Proteolytic enzymes

Further breakdown of debris

Phagocytic removal

Digested remnants cleared

Slide 31 · A reciprocal relationship: Injury and inflammation

Necrosis → inflammation

Leakage of DAMPs and cell proteins activates local innate responses.

Inflammation → clearance

Recruited inflammatory cells provide proteases and phagocytic activity.

Inflammation can amplify damage

Leukocyte enzymes can affect additional nearby constituents.

Not every inflammatory focus is infected

Necrotic sterile tissues can be inflammatory in the absence of microorganisms.

Slide 32 · Sterile necrosis still triggers immunity

An infectious organism is not required for inflammation around necrotic cells.

Injured host cells can release DAMPs without microbial invasion.

Resident macrophages and other cells detect damage.

The resulting response participates in the removal of necrotic material.

Slide 33 · Inflammation is part of the tissue response

Trigger

Severe injury disrupts membranes and releases DAMPs.

Recognition

Macrophages and other receptor-bearing cells respond.

Effector phase

Cytokines and leukocytes support local inflammation.

Resolution of debris

Proteolysis and phagocytosis clear dead cells.

Slide 34 · Cytoplasmic eosinophilia in necrosis

Intact nuclei; Cytoplasmic baseline

Hypereosinophilia; Nuclear loss

Slide 35 · Why necrotic cytoplasm becomes more pink

Loss of cytoplasmic RNA

Less baseline basophilia

Denatured proteins increase

Eosin-binding substrate

Shift in staining

More eosinophilic cytoplasm

H&E recognition

Intensely pink necrotic cells

Slide 36 · Glassy cytoplasm: A second appearance

Observation

Necrotic cytoplasm may become relatively smooth and homogeneous.

Pathologic correlate

This appearance largely with loss of cytoplasmic glycogen particles.

Slide 37 · When organelles are digested, vacuoles appear

Lethal injury

Organelle integrity compromised

Hydrolytic action

Enzymes digest organelles

Irregular clear spaces

Cytoplasmic vacuolation

Moth-eaten appearance

Advanced cytoplasmic breakdown

Slide 38 · Myelin figures originate from damaged membranes

Source material

Injured phospholipid-rich cellular membranes.

Appearance

Whorled membrane-derived phospholipid precipitates.

Subsequent fate

Phagocytosis or breakdown into fatty acids; Residues may calcify.

Slide 39 · Ultrastructural features of necrosis

Compartment

Electron microscopy appearance

Cell membrane

Discontinuities or frank breaks

Organelle membranes

Discontinuities and severe injury

Mitochondria

Marked dilation, including large amorphous densities

Cytoplasm

Myelin figures and amorphous debris

Proteins

Fluffy aggregates of denatured material

Slide 40 · Light microscopy and electron microscopy

Light microscopy (H&E)

Electron microscopy

Marked cytoplasmic eosinophilia.

Variable vacuolation and a homogeneous appearance.

Nuclear pyknosis, fragmentation, or loss.

Plasma and organelle membrane breaks.

Severely altered mitochondria.

Myelin figures and electron-dense cellular debris.

Slide 41 · The three principal nuclear changes

Intact nucleus

Distinct nuclear chromatin

Pyknosis

Small, hyperchromatic nucleus

Karyorrhexis

Nuclear fragmentation

Karyolysis

Progressive nuclear fading

Schematic nuclear appearances; All three nuclear endpoints need not be present simultaneously.

Slide 42 · Pyknosis: Dense nuclear shrinkage

Pyknosis is nuclear shrinkage with conspicuous chromatin condensation and basophilia.

Nuclear volume decreases.

Chromatin forms a small, dark, condensed mass.

Pyknosis is not unique to necrosis; It may also occur in apoptosis.

Slide 43 · Karyorrhexis: Fragmented nucleus

Karyorrhexis denotes fragmentation of a pyknotic nucleus.

The condensed chromatin separates into fragments.

Intact nuclear continuity is lost.

The finding supports cell death when read in the correct morphologic context.

Slide 44 · Karyolysis: Loss of nuclear staining

Karyolysis is progressive fading of nuclear basophilia during DNA degradation.

Endonuclease-mediated breakdown reduces stainable nuclear DNA.

The nucleus can become difficult to identify.

Ultimately, nuclear material may disappear from the necrotic cell.

Slide 45 · Nuclear disappearance is a temporal process

Cell injury

Chromatin organization disturbed

Pyknosis

Condensation and shrinkage

Karyorrhexis

Fragmentation may develop

Karyolysis / loss

Nuclear staining fades

Nuclei of necrotic cells can disappear over roughly 1–2 days; Patterns are not a rigid universal sequence.

Slide 46 · Avoid overinterpreting a single nuclear sign

Pyknosis alone

Not exclusive to necrosis; Apoptotic cells may also show chromatin condensation.

Karyorrhexis

Supports nuclear breakdown, but interpret alongside the surrounding cell and tissue.

Karyolysis

Fading nuclear staining usually indicates substantial DNA degradation.

Integrative diagnosis

Combine nuclear, cytoplasmic, membrane, and tissue-inflammatory features.

Slide 47 · Necrosis compared with reversible injury

Feature

Potentially reversible injury

Necrosis

Cell boundary

Blebbing may occur; Integrity can persist

Major barrier failure; Contents escape

Energy system

Mitochondrial dysfunction may recover

Severe failure does not recover

Cytoplasm

Swelling and vacuolation

Denaturation and enzymatic digestion

Nucleus

May remain identifiable

Pyknosis, fragmentation, or fading

Inflammation

Not intrinsic to every early injured cell

Common local response to DAMP release

Slide 48 · Necrosis contrasted with apoptosis

Characteristic

Necrosis

Apoptosis

Typical context

Severe pathologic injury

Regulated death pathway

Cell membrane

Disrupted, with leakage

Initially intact; Apoptotic bodies enclosed

Cell contents

Leak into surroundings

Packaged for phagocytic removal

Inflammation

Frequently prominent

Usually minimal / absent

Tissue response

Proteolysis and inflammatory cleanup

Rapid phagocytosis of bodies

Slide 49 · Tissue injury becomes a blood-test signal

Three linked spaces

Intracellular compartment

Proteins normally retained

Extracellular tissue

Escape follows membrane disruption

Circulating blood

Detectable tissue-associated analytes

Biomarker detection relies on membrane leakage and access of the analyte to circulation.

Slide 50 · Biomarkers track different cellular origins

Cardiomyocytes

Cardiac-specific troponin

Myocardial cell injury

Hepatocytes

Transaminases

Hepatocellular injury

Bile duct epithelium

Specific alkaline phosphatase isoform

Biliary epithelial injury

Specificity varies: A circulating analyte is interpreted with clinical context, not in isolation.

Slide 51 · Cardiac-specific troponins

Cell of origin

Cardiac myocytes express cardiac-specific variants of the contractile protein troponin.

Clinical implication

Released troponins are sensitive markers used in serial testing for myocardial cell injury.

Slide 52 · Hepatocyte transaminases

Source tissue

Hepatocytes contain the transaminases used as serum indicators of hepatocellular injury.

Interpretive limitation

Elevated transaminases indicate hepatocellular injury, not a unique cause or stand-alone proof of necrosis.

Slide 53 · Biliary alkaline phosphatase isoforms

Relevant tissue

Bile duct epithelial cells express a characteristic alkaline phosphatase isoform.

Clinical use

Increased circulating activity may indicate biliary injury; Other ALP sources must be considered.

Slide 54 · Serum markers: What can be inferred?

Observed finding

Supported implication

Not established by marker alone

Cardiac troponin rise

Myocardial cellular injury

Specific mechanism without clinical data

Transaminase elevation

Hepatocyte damage

Etiology or tissue histologic pattern

ALP elevation

Potential hepatobiliary source

Exclusive bile duct provenance

Serial change over time

Dynamic injury information

Exact morphologic timing of every cell

Slide 55 · Biochemistry can precede visible necrosis

Injury begins

Biochemical dysfunction starts

Membrane injury

Cellular proteins escape

Serum detection

Circulating analytes become measurable

Visible histology

Routine morphologic changes develop later

The timing is conceptual; The exact interval depends on organ, insult, and test sensitivity.

Slide 56 · Myocardial troponin may rise before histology

That cardiac-specific troponins may be detectable as early as 2 hours after myocardial cell necrosis.

Biochemical evidence can predate unmistakable light-microscopic changes.

Serial serum troponin testing has a central role in myocardial infarction assessment.

Absolute timing varies with assay, clinical course, and sampling.

Slide 57 · Membrane leakage does not specify a single etiology

What a marker can support

What else must be integrated

Presence of tissue-associated intracellular protein in circulation.

A biologically plausible cell-injury process.

Change over time with repeated testing.

Symptoms and relevant clinical findings.

Organ-specific physiological assessment.

Alternative sources and assay-related limitations.

Slide 58 · From dead cells to tissue-level necrosis

Multiple cells die

Loss of individual cellular viability

Necrotic tissue develops

Larger region affected

Architecture is altered

Pattern depends on mechanism/site

Clinicopathologic effect

Organ dysfunction and inflammation

Slide 59 · Tissue patterns are a separate classification

Coagulative pattern

Typical of ischemic necrosis in many solid organs; Preserved outlines may remain transiently.

Liquefactive pattern

Digestion predominates; Classic settings include brain infarcts and certain infections.

Other patterns

Distinctive settings include gangrene, caseous, fat, and fibrinoid change; Developed in Topic 22.

Slide 60 · Case: Ischemic myocardial injury

A patient with a coronary occlusion has elevated serial cardiac troponin concentrations, but an early myocardial sample does not yet show unmistakable cell death by routine light microscopy.

Is this temporal combination compatible with myocardial necrosis?

Yes — a circulating marker can precede clear H&E findings.

No — histologic necrosis must always appear first.

Slide 61 · Myocardial case: Interpretation

Yes. Biochemical and histologic manifestations have different delays.

Cellular proteins can escape into blood after membrane injury.

Necrotic morphology requires additional time to develop at light-microscopic scale.

Correlate serial troponins with symptoms, ECG, and other clinical evidence.

Slide 62 · Case: Acute proteolytic pancreatic injury

Severe pancreatic injury is accompanied by escape of active proteases into local tissue. Surrounding cells become irreversibly damaged and recruit inflammatory cells.

What feature makes this an example of necrosis?

Protease-associated cell destruction with leakage and inflammation.

Intracellular triglyceride accumulation alone.

Slide 63 · Pancreatic case: Interpretation

Uncontrolled proteolytic injury can contribute to cell destruction and necrosis.

Protease escape in pancreatitis as an illustrative necrotic trigger.

Membrane disruption releases tissue contents and inflammatory signals.

This mechanism should not be generalized to every necrotic disease.

Slide 64 · Knowledge check: The irreversibility boundary

Which pair most strongly characterizes the irreversible transition?

(A) Persistent mitochondrial failure and profound membrane dysfunction.

(B) Mild cell swelling and ribosomal detachment alone.

(C) Reduced intracellular triglyceride and normal ATP.

(D) Intact membranes with rapid apoptotic body clearance.

Slide 65 · Irreversibility check: Answer

Persistent mitochondrial failure + severe membrane disturbance.

The threshold is not defined by one exact time or one isolated lesion.

Severe loss of oxidative phosphorylation and membrane homeostasis are consistent features.

Lysosomal membrane injury contributes to enzymatic dissolution.

Slide 66 · Knowledge check: Nuclear morphology

Which term describes the fading of nuclear basophilia caused by DNA breakdown?

(A) Pyknosis.

(B) Karyorrhexis.

(C) Karyolysis.

(D) Hydropic change.

Slide 67 · Nuclear change check: Answer

Karyolysis describes nuclear fading.

Pyknosis denotes condensation and shrinkage.

Karyorrhexis denotes fragmentation.

Karyolysis reflects loss of stainable DNA and may precede nuclear disappearance.

Slide 68 · Knowledge check: Inflammatory trigger

Why can necrotic tissue produce an inflammatory response without microbes?

(A) DAMP release activates resident and recruited host cells.

(B) Apoptotic bodies must invariably rupture before being cleared.

(C) Every necrosis focus is caused by bacteria.

(D) The plasma membrane remains fully intact indefinitely.

Slide 69 · DAMP check: Answer

Released endogenous danger signals can activate innate immune sensing.

ATP and uric acid are examples named.

Macrophages and other host cells recognize damaging extracellular signals.

Cytokines, proteolysis, and phagocytosis support the subsequent response.

Slide 70 · Integrated necrosis mechanism

Lethal insult

Ischemic / toxic / physical / proteolytic

Irreversibility

Mitochondria and membranes

Cell disintegration

Denaturation, digestion, leakage

Tissue response

DAMPs, inflammation, clearance

Slide 71 · Necrosis: Five durable conclusions

Necrosis follows severe pathologic injury with irreparable cellular damage.

Persistent mitochondrial dysfunction and profound membrane damage mark irreversibility.

Cellular proteins denature; Lysosomal and inflammatory enzymes digest dead cells.

DAMP leakage stimulates inflammation, while intracellular proteins may become serum biomarkers.

Necrotic cytoplasm and nuclei show characteristic H&E and ultrastructural alterations.

Slide 72 · Primary source and figure provenance

Robbins, Cotran & Kumar: Pathologic Basis of Disease. 11th ed. (2026), Chapter 2, “Necrosis,” p. 38.

Adjacent textual context: “Progression of Cell Injury and Death,” p. 35.

Adjacent morphology: “Patterns of Tissue Necrosis—Morphology,” pp. 38–39.

All mechanism and morphology graphics are original native editable PowerPoint schematics.

No source photomicrograph is reproduced; schematics are not clinical or histologic specimens.