Reversible Cell Injury

Slide 1 · Reversible cell injury

Mechanisms, hydropic change, organelle alterations, and fatty change

Mild / early injury

ATP deficit

Cellular swelling

Potential recovery

Dr Abu Suraih Sakhri

MBBS, MD (Pathology)

www.abusuraihsakhri.com

Slide 2 · Learning outcomes

Define reversible injury in terms of cellular viability and repair.

Trace ATP depletion to ionic imbalance and cellular swelling.

Recognize plasma-membrane, mitochondrial, ER and nuclear alterations.

Explain hydropic change and fatty change in the appropriate tissue context.

Discriminate reversible injury from morphological evidence of necrosis.

Slide 3 · Reversible injury: Definition

Early or mild functional and structural alterations that can be corrected when the harmful stimulus is removed.

Viability is preserved during the potentially reversible phase.

Injury is not synonymous with cell death.

Recovery requires restoration of cellular homeostasis.

Slide 4 · Three conditions frame reversibility

Insult burden

Magnitude, duration, and biological target of the injury.

Repair competence

Residual organelle function and the capacity to restore homeostasis.

Timely removal

Cessation of the stressor before irreparable damage develops.

Slide 5 · Two dominant patterns

Cellular swelling

Intracellular water accumulation caused by disturbed ATP-dependent ion transport.

Fatty change

Cytoplasmic accumulation of triglycerides after disturbance of lipid metabolism, especially in the liver.

Slide 6 · Reversibility and normal appearance are different

Morphologically abnormal

Functionally recoverable

Swelling and organelle distortion may be conspicuous.

Cells may still retain viability.

Routine H&E cannot directly measure future recovery.

Damaging stimulus must cease.

Energy-dependent systems must recover.

Return toward a stable cell volume is possible.

Slide 7 · Etiologic routes into reversible injury

Oxygen deficiency

Hypoxia reduces ATP generation by mitochondrial oxidative phosphorylation.

Ischemia

Reduced perfusion can impose both oxygen and metabolic substrate deficits.

Radiation / toxins

Mitochondrial injury can disturb ATP availability.

Toxic metabolic effects

Perturbations in hepatic lipid handling can create fatty change.

Slide 8 · The core swelling mechanism

Oxygen deficiency / mitochondrial injury

Oxidative phosphorylation impaired

ATP deficit

Less energy for ion pumps

Na⁺/K⁺ ATPase dysfunction

Intracellular Na⁺ rises

Water influx

Cell and organelles swell

Swelling initially reflects transport failure, not necessarily membrane rupture.

Slide 9 · ATP supply couples organelles to membranes

Mitochondria

Oxidative phosphorylation normally supplies ATP.

Membrane pumps

Energy-dependent ion gradients maintain volume and polarity.

Osmotic balance

Impaired ion transport favors intracellular water accumulation.

Morphology

Cell size and multiple organelles become enlarged.

Slide 10 · Normal versus impaired ion regulation

ATP-dependent ion transport

Water follows the net solute disturbance

Extracellular

Intracellular

Na⁺/K⁺

Uninjured cell

ATP available

Na⁺ outward

K⁺ inward

Extracellular

Intracellular

Na⁺/K⁺

Reversibly injured cell

ATP depleted

Na⁺ retained

H₂O influx

Slide 11 · Why ATP depletion produces swelling

Reduced ATP does not directly create water; It disrupts ionic homeostasis.

Less ATP compromises the Na⁺/K⁺ pump.

Intracellular sodium accumulation alters osmotic driving forces.

Water redistributes into the cell and membrane-bound compartments.

Cytoplasmic volume and organelle volume increase.

Slide 12 · Swelling can involve several compartments

Baseline

Normal cell volume and organelle dimensions.

Reversible swelling

Cell volume increases; Membranes remain potentially repairable.

Slide 13 · A cell-wide view of early injury

Original cellular schematic — not an electron micrograph

Membrane bleb

Swollen mitochondria

Dilated rough ER

Chromatin clumping

Membrane-derived myelin figure

Slide 14 · Plasma membrane: Early blebbing

What is a bleb?

Localized protrusion of the cell surface caused by altered membrane–cytoskeletal relationships.

Why it matters

Indicates cellular injury but does not, by itself, establish membrane rupture or irreversible death.

Slide 15 · Blebs are not equivalent to lysis

Early reversible alteration

Necrotic membrane damage

Plasma membrane remains largely continuous.

Small surface blebs can form.

Normal membrane architecture may be restored.

Profound permeability defects or disruption.

Contents may leak from the cell.

Associated with loss of cellular viability.

Slide 16 · Microvilli: Loss of specialized surface

Blunting or disappearance of microvilli is an ultrastructural feature of reversible injury.

Brush borders support epithelial functional surface area.

In kidney proximal tubules, apical membrane changes may precede unequivocal necrosis.

The observed structural severity depends on injury and sampling stage.

Slide 17 · Mitochondria respond to mild injury

Swelling

Mitochondria may enlarge with altered ionic and water balance.

Amorphous densities

Small amorphous densities are included among reversible ultrastructural changes.

Functional consequence

Lower ATP availability may amplify membrane-pump failure.

Important boundary

Marked, sustained damage with dense deposits occurs in more advanced injury.

Slide 18 · Endoplasmic reticulum: Dilation

ER dilation is part of the reversible subcellular response.

Swelling of ER cisternae may appear as clear cytoplasmic vacuoles on H&E.

Some vacuoles represent distended, pinched-off ER segments.

Dilation can coexist with detachment of ribosomes.

Slide 19 · Ribosome detachment and protein synthesis

Early injury

Cell energy homeostasis disturbed

Rough ER change

ER cisternae dilate

Polysomes detach

Fewer ribosomes on ER

Protein production altered

Transient functional compromise

Slide 20 · Chromatin alterations can be reversible

Reversible nuclear response

Destructive nuclear changes

Clumping of nuclear chromatin.

Disaggregation of granular and fibrillar nuclear elements.

Not sufficient to establish necrosis.

Pyknosis: Dense shrunken nucleus.

Karyorrhexis: Nuclear fragmentation.

Karyolysis: Progressive nuclear dissolution.

Slide 21 · Myelin figures reflect membrane phospholipids

Material

Concentric phospholipid-rich membrane-derived structures.

Origin

Derived from membranes injured during cellular stress.

Interpretation

An ultrastructural injury feature; Isolated presence does not prove death.

Slide 22 · Five ultrastructural alterations at a glance

Compartment

Reversible ultrastructural finding

Plasma membrane

Blebs; Blunted or absent microvilli

Mitochondria

Swelling; Small amorphous densities

Cytosol

Phospholipid-rich myelin figures

Endoplasmic reticulum

Dilation with detached polysomes

Nucleus

Changes in chromatin and nuclear ultrastructure

Slide 23 · Light microscopy: Hydropic change

Cellular swelling is the earliest morphologic expression of many injuries.

Enlarged cells may develop small clear intracytoplasmic vacuoles.

The terms hydropic change and vacuolar degeneration describe this nonlethal pattern.

Affected cells can remain viable despite obvious cytoplasmic changes.

Slide 24 · Clear vacuoles: What they represent

ATP loss

Transport failure

Water uptake

Swelling of membrane compartments

ER dilation

Cisternae expand / pinch off

H&E appearance

Small optically clear vacuoles

Slide 25 · Hydropic change versus fatty change

Hydropic vacuoles

Water-related dilated ER segments

Lipid vacuoles

Triglyceride accumulation; H&E clear spaces

Slide 26 · Cell swelling and fatty change are not synonyms

Feature

Cellular swelling

Fatty change

Stored substance

Water

Triglycerides

Immediate context

ATP-dependent ion pump failure

Lipid metabolic pathway disruption

H&E feature

Fine clear cytoplasmic vacuoles

Often clear lipid vacuoles

Typical setting

Many injured cell types

Lipid-handling organs, notably liver

Teaching pitfall

Not automatically necrosis

Not necessarily identical to edema

Slide 27 · Why swollen cytoplasm can appear eosinophilic

RNA normally contributes to cytoplasmic basophilia on H&E.

Loss of cytoplasmic RNA reduces hematoxylin binding.

Injured-cell cytoplasm may therefore look relatively more pink/red.

Greater eosinophilia during progression toward necrosis is not a stand-alone indicator of irreversibility.

Slide 28 · H&E eosinophilia requires context

Hematoxylin

Highlights nucleic-acid-rich structures, particularly chromatin and ribosomal RNA.

Eosin

Highlights many proteins in cytoplasm and extracellular matrix.

Relative staining shift

Loss of RNA and altered proteins shift injured cytoplasm toward pink.

Key diagnostic consideration:

Eosinophilia alone is not an assay of membrane integrity or cell viability.

Slide 29 · Nuclear preservation is informative—but limited

An intact nucleus supports the possibility of reversible injury; It does not prove recovery.

Early injury may exhibit chromatin changes without frank nuclear loss.

Nuclear fragmentation and disappearance favor necrosis in the appropriate context.

A static biopsy cannot establish the subsequent fate of every cell.

Slide 30 · Macroscopic changes from widespread swelling

Pallor

Affected tissue may become paler.

Increased turgor

The organ may feel more tense or firm.

Increased organ weight

Aggregate water accumulation enlarges tissue mass.

Slide 31 · Microscopic versus gross examination

Light-microscopic scale

Organ scale

Swollen epithelial or parenchymal cells.

Small clear vacuoles in cytoplasm.

Variable eosinophilic change.

Gross appearance requires a sufficient extent of injury.

Pallor and turgor may change.

Organ weight may increase.

Slide 32 · Renal tubule: Architectural example

Intact tubular epithelium

Luminal microvilli and intact epithelial nuclei

Swollen tubular epithelium

Less regular brush border; Cytoplasmic vacuoles

Schematic of epithelial organization; Real sections vary by tubule segment

Slide 33 · Kidney injury: What can be reversible?

Surface blebs

Early surface distortion of viable tubular epithelial cells.

Brush-border loss

Altered microvilli may precede irreversible injury.

Cellular swelling

Water influx enlarges the cytoplasm and organelles.

Intact nuclei

More consistent with non-necrotic injury than total nuclear loss.

Slide 34 · Reading a hypothetical renal H&E field

A renal biopsy after a short ischemic episode shows enlarged tubule epithelial cells with fine cytoplasmic vacuoles; Many nuclei remain identifiable and the tissue is not extensively fragmented.

Which description best fits the morphology?

Hydropic / vacuolar cell injury.

Established confluent tubular necrosis.

Slide 35 · Renal H&E case: Interpretation

Cell swelling with vacuoles supports hydropic change.

Water-related ER dilation is a plausible basis for the clear vacuoles.

Preserved nuclei are compatible with reversible injury.

A biopsy cannot by itself prove future recovery; Evaluate extent, context, and time.

Slide 36 · The reversible injury phenotype is dynamic

Insult begins

Transport / metabolism affected

Early biochemical change

ATP and ion balance altered

Visible swelling

Cells / organelles enlarge

Insult removed

Repair and recovery possible

A conceptual sequence only; No universal duration or fixed recovery interval is implied.

Slide 37 · Why morphology may lag function

Biochemistry

ATP generation and membrane transport may decline first.

Function

Active secretion, absorption, or contractility may be compromised.

Ultrastructure

Blebs, swollen mitochondria and dilated ER become detectable.

Routine microscopy

Cell swelling and vacuolation become recognizable.

Slide 38 · The threshold to irreversibility

Early injury

Swollen, metabolically disturbed cell.

Resolution

Restoration of homeostasis.

Persistent severe injury

Membrane breakdown; Necrosis may follow.

Potential recovery and progression are distinct outcomes; Exact thresholds vary.

Slide 39 · Reversible swelling versus necrosis

Attribute

Reversible injury

Necrosis

Cell size

Often enlarged

Often enlarged; Cellular disruption

Plasma membrane

Blebbing; Substantial integrity retained

Disrupted with leakage

Nucleus

Chromatin alterations, generally retained

Pyknosis, karyorrhexis, karyolysis

Cytoplasm

Hydropic vacuoles possible

Digestive breakdown and cell debris

Recovery

Possible if insult removed

Not possible for dead cells

Slide 40 · Fatty change: Definition

Accumulation of intracellular triglyceride droplets in cells with disrupted lipid metabolism.

Organs involved in lipid processing—especially the liver.

Toxic injury is one described route to the altered metabolic pathways.

Fatty change is a morphologic response, not a specific etiologic diagnosis.

Slide 41 · Why hepatocytes show fatty change

Metabolic role

Hepatocytes ordinarily handle large lipid fluxes.

Toxic disturbance

Disrupted metabolic pathways alter triglyceride handling.

Cell phenotype

Lipid accumulates in cytoplasmic droplets.

Slide 42 · Fat accumulation: A qualitative pathway

Toxic / metabolic insult

Pathways disrupted

Imbalance in lipid handling

Input, use or export affected

Triglyceride retention

Droplets accumulate

Fatty change

Clear spaces in routine H&E

Slide 43 · Fatty change: An original cell schematic

Normal hepatocyte

No conspicuous fat

Multiple lipid droplets

Small clear spaces

Large lipid vacuole

Nuclear displacement may occur

Schematic only; Not a histologic classification of clinical steatosis

Slide 44 · What a lipid droplet looks like in H&E

Routine tissue processing can dissolve neutral lipid, leaving optically empty spaces.

Droplet size and number may vary between affected hepatocytes.

Large vacuoles may shift the nucleus toward the cell periphery.

Histologic appearance does not uniquely identify the cause of steatosis.

Slide 45 · Do not confuse water, lipid, and clearing artifacts

Clear cytoplasmic spaces on H&E

Small hydropic vacuoles

Lipid / other mimics

Correlate cell type, architecture, and insult history.

Use additional stains or preparations only when indicated.

Do not assign reversibility from a single image alone.

Slide 46 · When vacuoles have different origins

Potential explanation

Interpretive clue / limitation

Water-related swelling

Small clear vacuoles may reflect distended ER

Triglyceride accumulation

Lipid droplets are conspicuous in metabolically stressed hepatocytes

Glycogen accumulation

Clear cytoplasm may require periodic acid–Schiff correlation

Processing / fixation artifact

Distribution and technical context help interpretation

Slide 47 · Fatty change is not synonymous with necrosis

Fatty change

Necrosis

Triglycerides accumulate in cytoplasm.

Many affected cells may remain viable.

Morphology by itself does not prove death.

Irreversible loss of cellular viability.

Nuclear and membrane destruction develops.

Often produces tissue inflammation.

Slide 48 · Cell swelling and steatosis can coexist

Distinct substances

Water accumulation and triglyceride deposition reflect different immediate processes.

Shared context

A severe systemic or toxic insult can perturb several pathways at once.

Morphologic heterogeneity

A single tissue may contain cells at different degrees or types of injury.

Reporting discipline

Describe what is observed without assuming one mechanism explains all vacuoles.

Slide 49 · Cellular phenotype depends on tissue role

Renal tubular epithelium

Hepatocytes

ATP-dependent transport is crucial.

Cell swelling may affect apical microvilli.

Hydropic and ultrastructural changes are demonstrable.

Extensive intermediary lipid metabolism.

Triglyceride imbalance manifests as fatty change.

Clear lipid vacuoles can be prominent.

Slide 50 · What a routine H&E section cannot prove

Whether the cell will eventually recover after the insult ends.

The precise ATP concentration in a particular cell.

The number or composition of small ultrastructural membrane lesions.

Whether all pale vacuoles contain the same substance.

Slide 51 · How electron microscopy adds information

Routine H&E

Ultrastructure (electron microscopy)

Swollen epithelial cells

Plasma-membrane blebbing and altered microvilli

Pale vacuolated cytoplasm

ER dilation / altered cisternae

Subtle early injury

Mitochondrial swelling and small densities

Limited organelle localization

Detached polysomes and myelin figures

Slide 52 · Five cautionary statements

Swelling ≠ death

Enlarged volume is compatible with reversible injury.

Blebbing ≠ lysis

Early membrane distortions can occur before rupture.

Steatosis ≠ necrosis

Intracellular fat alone does not establish cell loss.

Eosinophilia ≠ irreversible injury

Relative pink staining needs morphologic context.

Normal H&E ≠ normal function

Biochemical disturbance can precede routine visible changes.

Slide 53 · Application: Hypoxia and renal cells

In an experiment, renal epithelial cells briefly experience low oxygen tension. Electron microscopy shows moderate mitochondrial swelling and membrane blebs, but severe membrane rupture is not seen.

What is the most accurate classification?

Compatible with early potentially reversible injury.

Proof that all cells are necrotic.

Slide 54 · Hypoxia case: Interpretation

This constellation is compatible with reversible injury.

The insult can lower mitochondrial ATP production.

Blebbing and moderate mitochondrial swelling are among reversible changes.

Cell survival still depends on injury severity, duration, and recovery.

Slide 55 · Application: Liver with vacuolated hepatocytes

A liver biopsy shows hepatocytes containing optically empty rounded vacuoles; Several large vacuoles displace nuclei. The patient has a relevant toxic or metabolic exposure.

Which reversible pattern should be considered?

Fatty change from triglyceride accumulation.

Mandatory liquefactive necrosis.

Slide 56 · Hepatic case: Interpretation

Fatty change is a strong morphologic consideration.

Lipid metabolism disturbance can produce cytoplasmic triglyceride droplets.

Routine H&E may show empty vacuoles after lipid extraction.

A specific cause requires clinicopathologic context; Fat alone is not death.

Slide 57 · Knowledge check: First visible change

What is the characteristic early morphologic expression of many reversible injuries?

(A) Generalized cellular swelling.

(B) Confluent karyolysis in every cell.

(C) Extensive tissue fibrosis.

(D) Complete cell-membrane rupture.

Slide 58 · Knowledge check: Mechanisms

Which sequence most directly accounts for reversible hypoxic cell swelling?

(A) ATP rises → Na⁺ pump accelerates → water enters.

(B) ATP falls → Na⁺/K⁺ pump fails → intracellular water rises.

(C) Triglycerides disappear → mitochondria shrink → water exits.

(D) Ribosomes detach → the plasma membrane must rupture.

Slide 59 · Knowledge check: Ultrastructure

Which change belongs to the reversible ultrastructural injury spectrum?

(A) Distended ER with detached polysomes.

(B) Universal absence of all nuclei.

(C) Complete dissolution of cytoplasmic membranes.

(D) Replacement of cells by dense collagen.

Slide 60 · Knowledge check: Fatty change

What best defines the fatty-change pattern?

(A) Edema in the interstitium only.

(B) Triglyceride-rich intracellular lipid vacuoles.

(C) Accumulation of extracellular amyloid.

(D) Irreversible rupture of lysosomal membranes.

Slide 61 · Integrated summary

Reversible injury is early or mild injury with potential restoration after removal of the stimulus.

Cell swelling follows disturbed ATP-dependent ion transport and water redistribution.

Ultrastructural findings include blebs, microvillus loss, mitochondrial/ER swelling, myelin figures, and nuclear alterations.

Hydropic change produces fine clear vacuoles; Fatty change reflects triglyceride accumulation, often in liver.

Morphologic injury alone does not establish irreversibility; Membrane and nuclear destruction favor necrosis.

Slide 62 · Primary references and figure provenance

Robbins, Cotran & Kumar. Pathologic Basis of Disease. 11th ed. (2026), Chapter 2, “Reversible Cell Injury,” pp. 35–36.

Adjacent interpretive context: “Progression of Cell Injury and Death,” p. 35; “Cell Death / Necrosis,” pp. 36–38.

Morphology source: Fig. 2.8 caption; reversible ultrastructural description and Fig. 2.9 caption.

All illustrations are new native, editable PowerPoint schematics, not textbook figures or microscopy.

No external diagnostic tissue micrograph was embedded; authentic source imagery can be added where redistribution rights permit.