Morphologic and Biochemical Changes in Apoptosis

Slide 1 · Morphologic and biochemical

changes in apoptosis

A pathology teaching lecture

Morphology • Biochemical execution • Efferocytosis

Dr Abu Suraih Sakhri

MBBS, MD (Pathology)

www.abusuraihsakhri.com

Slide 2 · Learning objectives

Recognize the four cardinal morphologic features of apoptotic cells.

Relate caspase-dependent biochemical events to cellular morphology.

Explain apoptotic-body removal and the limited inflammatory response.

Distinguish apoptotic changes from necrotic injury.

Slide 3 · Reading the phenotype of apoptosis

Apoptosis affects cells individually and produces an orderly, recognizable sequence.

Morphology and biochemistry describe different aspects of the same process.

Cells can disappear rapidly, so a single tissue section may underestimate apoptosis.

Viable

Condensed

Blebbing

Bodies

Schematic sequence; Stages may overlap

Schematic

Slide 4 · Four defining morphologic findings

Cell shrinkage and increased cytoplasmic density.

Peripheral chromatin condensation, often with nuclear fragmentation.

Membrane blebs followed by membrane-bound apoptotic bodies.

Prompt ingestion and degradation by phagocytes.

Shrinkage

Chromatin

Bodies

Removal

Schematic

Slide 5 · The phenotype evolves, rather than appearing all at once

Early: The cell contracts and chromatin becomes condensed.

Intermediate: Surface blebs emerge, and the nucleus may fragment.

Late: Apoptotic bodies are engulfed and degraded.

The steps overlap; Not every snapshot displays all features.

Viable

Condensed

Blebbing

Bodies

Schematic sequence; Stages may overlap

Schematic

Slide 6 · Cell shrinkage is a cardinal early change

The apoptotic cell becomes smaller than its neighbors.

Loss of volume makes cellular constituents more concentrated.

This is opposite to the early swelling characteristic of necrosis.

Viable cell

Apoptotic cell

Schematic

Slide 7 · Cytoplasm becomes dense and eosinophilic

Cytoplasmic compaction intensifies eosin staining in H&E sections.

A round or oval, strongly pink cell profile may stand out from adjacent cells.

Eosinophilia is a clue, not diagnostic alone.

Viable cell

Apoptotic cell

Schematic

Slide 8 · Organelles are tightly packed but relatively intact

Organelles as relatively normal during cell shrinkage.

The cytoplasmic volume contracts around those organelles.

Tightly packed organelles can become enclosed within apoptotic bodies.

Viable cell

Apoptotic cell

Schematic

Slide 9 · Shrinkage versus swelling is diagnostically useful

Apoptosis: Reduced cell size and dense cytoplasm.

Necrosis: Early cell and organelle swelling is typical.

Interpret size together with nuclear changes and membrane fate.

Viable cell

Apoptotic cell

Opposing volume responses: Apoptosis ≠ necrosis

Schematic

Slide 10 · Chromatin condensation is the most characteristic feature

Chromatin coalesces into strikingly dense aggregates.

These aggregates are much more compact than normal chromatin.

Peripheral location beneath the nuclear envelope is particularly characteristic.

Dispersed chromatin

Peripheral compaction

Schematic

Slide 11 · Chromatin shifts toward the nuclear periphery

Condensed chromatin often accumulates immediately below the nuclear membrane.

Under electron microscopy this can form a peripheral rim.

The distribution adds specificity to the observation of a dark nucleus.

Dispersed chromatin

Peripheral compaction

Schematic

Slide 12 · Peripheral crescents are a classic ultrastructural clue

Compacted chromatin may form dense crescent-shaped masses.

The masses differ in size and shape among affected cells.

Robbins Fig. 2.15 describes these nuclear patterns by electron microscopy.

Dispersed chromatin

Peripheral compaction

Schematic

Slide 13 · Some apoptotic nuclei become uniformly dense

Peripheral chromatin crescents are not the only endpoint.

The nuclear profile can appear almost uniformly electron-dense.

Nuclear appearance varies with the stage of apoptosis.

Dispersed chromatin

Uniformly dense

Schematic

Slide 14 · The nucleus may fragment into multiple pieces

Apoptosis may divide one condensed nucleus into two or more fragments.

These pieces can remain within the apoptotic cell or enter apoptotic bodies.

The fragments retain dense chromatin.

Dispersed chromatin

Nuclear pieces

Schematic

Slide 15 · Condensation and fragmentation are related but distinct

Condensation describes how chromatin is packed.

Fragmentation describes physical separation of the nucleus.

A cell can show condensed chromatin before fragmentation is visible.

Dispersed chromatin

Fragmented nucleus

Schematic

Slide 16 · Plasma membrane blebbing precedes body formation

The cell surface develops multiple outward membrane protrusions.

Extensive blebbing precedes fragmentation into apoptotic bodies.

Blebbing does not by itself imply lysis of the cell membrane.

Smooth membrane

Membrane blebs

Schematic

Slide 17 · Blebs are membrane-enclosed protrusions

A bleb is continuous with the plasma membrane of the parent cell.

It is not the same as membrane rupture with release of contents.

Apoptotic blebbing can be recognized with phase-contrast imaging.

Smooth membrane

Membrane blebs

Schematic

Slide 18 · Apoptotic bodies are discrete cellular fragments

The parent cell separates into small membrane-bound pieces.

Each fragment can be readily handled by a phagocyte.

This packaging minimizes extracellular release of cellular contents.

Blebbing cell

Membrane-bound bodies

Schematic

Slide 19 · Apoptotic bodies contain packed cell material

Bodies may contain cytoplasm and closely packed organelles.

Some also contain fragments of nuclear chromatin.

A nuclear fragment is not required in every apoptotic body.

Blebbing cell

Membrane-bound bodies

Schematic

Slide 20 · Nuclear material varies among apoptotic bodies

Some fragments carry prominent condensed DNA-containing nuclear pieces.

Others contain cytoplasm and organelles without visible nuclear fragments.

Avoid equating every pink globule with a nuclear fragment.

Blebbing cell

Membrane-bound bodies

Schematic

Slide 21 · A structural sequence links all four findings

Cell contraction → chromatin compaction → membrane blebs → apoptotic bodies.

Phagocytes remove the fragments before extensive membrane breakdown.

The progression is a teaching model, not a rigid time scale.

Viable

Condensed

Blebbing

Bodies

Schematic sequence; Stages may overlap

Schematic

Slide 22 · H&E microscopy: The typical apoptotic profile

Round or oval intensely eosinophilic cytoplasmic mass.

Small condensed nuclear material, sometimes fragmented.

Frequently surrounded by viable-appearing adjacent cells.

H&E-like tissue schematic — not a photomicrograph

Slide 23 · H&E microscopy: Looking for a single dying cell

Scan for isolated small bright-pink bodies among larger cells.

Compare nuclear staining intensity and fragmentation.

Examine the immediate surroundings for an inflammatory reaction.

H&E-like tissue schematic — not a photomicrograph

Slide 24 · Cytoplasmic and nuclear clues work together

Intense eosinophilia alone is nonspecific.

Highly condensed chromatin alone is also insufficient.

A reduced cellular profile with both changes strongly supports apoptosis.

H&E-like tissue schematic — not a photomicrograph

Slide 25 · Nuclear fragments may be inconspicuous in H&E

Some apoptotic profiles show several small dense basophilic pieces.

Other profiles lack a recognizable nucleus in the plane of section.

Sectioning geometry limits what can be observed in any one cell.

H&E-like tissue schematic — not a photomicrograph

Slide 26 · Apoptosis often occurs in scattered cells

Affected cells may be separated by morphologically preserved neighbors.

The pattern contrasts with confluent destruction common in many necrotic lesions.

Spatial pattern supports—but does not establish—the mechanism.

H&E-like tissue schematic — not a photomicrograph

Slide 27 · Tissue can appear relatively preserved

Rapid removal of single apoptotic cells may leave little visible residue.

The surrounding tissue need not show broad areas of cytoplasmic leakage.

A focal snapshot can underestimate cumulative cellular loss.

H&E-like tissue schematic — not a photomicrograph

Slide 28 · Phagocytic uptake is part of the morphologic phenotype

Apoptotic cells and bodies are typically engulfed by phagocytes.

Macrophages as frequent phagocytic cells.

Removal follows fragmentation and may occur very quickly.

Apoptotic bodies

Phagocyte

Schematic

Slide 29 · Apoptotic material is degraded inside phagocytes

Engulfed bodies enter the phagocytic compartment.

Lysosomal enzymes break down the ingested cellular material.

Intracellular disposal limits exposure of neighboring tissue to cell contents.

Apoptotic bodies

Phagocyte

Schematic

Slide 30 · Clearance changes what the pathologist sees

An apoptotic cell may be visible only transiently.

Extensive apoptosis need not produce many visible apoptotic figures.

Morphologic counts represent a dynamic balance of formation and removal.

Apoptotic bodies

Phagocyte

Schematic

Slide 31 · Why a routine biopsy may miss active apoptosis

Shrinkage, fragmentation, and clearance occur rapidly.

Apoptotic bodies are easily overlooked in crowded tissue.

Lack of accompanying inflammation removes a conspicuous contextual clue.

H&E-like tissue schematic — not a photomicrograph

Slide 32 · Minimal inflammation is a distinguishing feature

Apoptotic cells generally do not provoke substantial inflammation.

Membrane-bounded fragments are removed before their contents spill.

Phagocytes that ingest apoptotic cells also reduce proinflammatory signaling.

Limited inflammatory signaling

Schematic

Slide 33 · Electron microscopy reveals chromatin topography

Peripheral crescents of dense chromatin are best appreciated ultrastructurally.

Other cells may show fully dense or fragmented nuclei.

Electron microscopy clarifies structure but is not usually needed for routine diagnosis.

Peripheral crescent

Fragmented nucleus

Ultrastructural nuclear patterns — schematic

Schematic

Slide 34 · Electron microscopy: Preserved packaging

Shrinkage compacts relatively preserved organelles.

Cell surfaces can form blebs and discrete bounded pieces.

Ultrastructure can separate bounded fragmentation from uncontained breakdown.

Peripheral crescent

Fragmented nucleus

Ultrastructural nuclear patterns — schematic

Schematic

Slide 35 · Phase-contrast microscopy demonstrates blebbing

Live-cell imaging can show irregular surface protrusions.

Blebs can progress to detached apoptotic bodies.

Time-resolved observation captures events missed by fixed tissue sections.

Smooth membrane

Membrane blebs

Schematic

Slide 36 · DNA stains demonstrate nuclear fragmentation

DNA-directed stains can reveal separated nuclear masses.

Interpret nuclear fragmentation alongside the cell outline and membrane changes.

A nuclear stain alone does not establish that the cell underwent apoptosis.

Dispersed chromatin

Separated DNA signals

Schematic

Slide 37 · Active caspase-3 marks biochemical execution

Robbins Fig. 2.15 illustrates immunofluorescence for active caspase-3.

Enzyme activation is a molecular readout complementary to morphology.

Positive staining should be interpreted in assay and tissue context.

Conceptual immunofluorescence — not acquired microscopy

Slide 38 · Microscopy modalities answer different questions

H&E: Location, cell shrinkage, cytoplasmic eosinophilia.

EM: Peripheral condensed chromatin and ultrastructural packaging.

Phase contrast / DNA stain / active caspase-3: Dynamic, nuclear, and enzyme-level evidence.

H&E

Cell & tissue

EM

Nuclear topology

Biomarkers

Enzyme/DNA

Schematic

Slide 39 · Caspases are the core apoptotic proteases

Caspases are cysteine proteases that cleave proteins after aspartate residues.

They exist as inactive precursors that require activation.

Activated caspases drive the biochemical execution of apoptosis.

Caspases

Execution

Structural targets

Proteolysis

Cell components

Fragments

Schematic

Slide 40 · Activation is controlled by proteolytic processing

Inactive procaspases are converted into catalytically active enzymes.

Sequential caspase activation amplifies the death program.

Detection of active enzymes is more informative than total protein abundance.

Procaspase

Inactive

Cleavage

Proteolysis

Caspase

Active enzyme

Schematic

Slide 41 · Initiation and execution are separable biochemical phases

Initiator caspases activate downstream proteases.

Executioner caspases modify nuclear and cytoplasmic substrates.

The present topic focuses on those downstream structural effects.

Initiator

Activates

Executioner

Cleaves targets

Morphology

Cell breakdown

Schematic

Slide 42 · Executioner caspases produce the final phenotype

Caspase-3 and caspase-6 are examples given by Robbins.

They act on multiple cellular structural proteins and regulatory substrates.

The coordinated biochemical changes culminate in fragmentation.

Caspases

Execution

Structural targets

Proteolysis

Cell components

Fragments

Schematic

Slide 43 · Caspases activate a DNA-degrading nuclease

An executioner caspase cleaves an inhibitory protein bound to a DNase.

Removing the inhibitor allows the DNase to degrade DNA.

This explains an important biochemical component of nuclear destruction.

Caspase-3

Execution

DNase inhibitor

Cleaved

DNase

Active → DNA loss

Schematic

Slide 44 · DNA degradation contributes to nuclear dismantling

Active DNase cleaves cellular DNA.

Structural nuclear changes are also needed for visible nuclear fragmentation.

Fragmented DNA and fragmented nuclei are related but different endpoints.

Caspase-3

Execution

DNase inhibitor

Cleaved

DNase

Active → DNA loss

Schematic

Slide 45 · Nuclear matrix proteins are caspase substrates

Executioner caspases proteolyze structural components of the nuclear matrix.

Loss of scaffold integrity favors disassembly of nuclear architecture.

This contributes to physical nuclear fragmentation.

Executioner

Caspases

Proteolysis

Nuclear scaffold

Degraded

Nucleus

Fragmentation

Schematic

Slide 46 · Proteolysis alters cell architecture

Caspases also act on components of the cytoskeleton.

Structural breakdown is associated with the reorganization of dying cells.

Some details of bleb and body formation remain unresolved.

Caspases

Execution

Structural targets

Proteolysis

Cell components

Fragments

Schematic

Slide 47 · Cell shape reflects coordinated biochemical events

Nuclear substrate cleavage contributes to chromatin/nuclear breakdown.

Cytoplasmic substrate cleavage contributes to structural remodeling.

The observable phenotype is produced by many targets, not a single reaction.

Caspases

Execution

Structural targets

Proteolysis

Cell components

Fragments

Schematic

Slide 48 · Mechanism and morphology should not be conflated

Condensation and blebbing are observational features.

Caspase activation and DNase activation are biochemical processes.

An assay for one feature does not automatically prove all others occurred.

Caspases

Execution

Structural targets

Proteolysis

Cell components

Fragments

Schematic

Slide 49 · Membrane integrity supports noninflammatory removal

Apoptotic bodies retain delimiting membranes during early clearance.

Phagocytes engulf material before widespread release of contents.

Membrane integrity is time-dependent; Late uncleared apoptotic cells may deteriorate.

Limited inflammatory signaling

Schematic

Slide 50 · Phosphatidylserine is normally on the inner leaflet

In viable cells, phosphatidylserine is concentrated on the cytoplasmic face.

This asymmetric distribution changes in dying apoptotic cells.

The topologic switch supplies a recognition signal.

Extracellular space

Cytoplasm

Red headgroups: Phosphatidylserine

Schematic

Slide 51 · Apoptosis exposes phosphatidylserine at the surface

Phosphatidylserine becomes displayed on the outer membrane leaflet.

External phosphatidylserine is an “eat-me” cue for phagocytes.

The lipid signal is a biochemical change with a direct disposal function.

Extracellular space

Cytoplasm

Red headgroups: Phosphatidylserine

Schematic

Slide 52 · Phagocytes recognize exposed surface cues

Macrophage receptors bind apoptotic surface ligands directly or indirectly.

Surface changes distinguish dying cells from healthy neighbors.

Recognition initiates engulfment rather than extracellular disintegration.

Apoptotic bodies

Phagocyte

Schematic

Slide 53 · Soluble factors help recruit phagocytes

Dying cells may release signals that attract phagocytes.

These cues bring scavenger cells near apoptotic targets.

The exact molecules are not specified in the assigned Robbins passage.

Apoptotic bodies

Phagocyte

Recruitment cues

Schematic

Slide 54 · Opsonins can further promote engulfment

Natural antibodies and complement proteins can coat apoptotic fragments.

The complement component C1q.

Coated targets become recognizable to appropriate phagocytic receptors.

Apoptotic bodies

Phagocyte

Antibodies • C1q

Schematic

Slide 55 · Efferocytosis is removal of apoptotic cells

Efferocytosis denotes phagocytic clearance of apoptotic cells and fragments.

Membrane changes, recruitment cues, and opsonic signals work together.

The process is efficient enough for dead cells to vanish without a trace.

Apoptotic bodies

Phagocyte

Schematic

Slide 56 · Efferocytosis suppresses inflammatory signaling

Macrophages that ingest apoptotic material reduce proinflammatory cytokine production.

Rapid containment and clearance limit local inflammatory injury.

This biochemical behavior helps explain the quiet histologic picture.

Limited inflammatory signaling

Schematic

Slide 57 · Apoptosis and necrosis differ at the cell surface

Apoptosis: Shrinkage, bounded blebs/bodies, prompt removal.

Necrosis: Swelling followed by membrane damage and leakage.

These are typical patterns; Tissue context and timing still matter.

Apoptosis

Necrosis

Schematic

Slide 58 · Nuclear and inflammatory distinctions aid interpretation

Apoptosis favors chromatin compaction and controlled fragmentation.

Necrosis can show nuclear loss during cellular disintegration.

Prominent inflammation favors necrotic injury but is not absolute.

Apoptosis

Necrosis

Schematic

Slide 59 · Diagnostic synthesis: Use convergent findings

Seek small eosinophilic cells with dense, often fragmented chromatin.

Look for bounded apoptotic bodies and phagocytic clearance.

Use biochemical markers selectively as supporting evidence.

H&E

Cell & tissue

EM

Nuclear topology

Biomarkers

Enzyme/DNA

Schematic

Slide 60 · Application: Identify the mechanism

A biopsy contains scattered contracted intensely pink cells with multiple dark nuclear fragments. Adjacent tissue is preserved.

Question: Which form of cell death best explains this combined phenotype?

H&E-like tissue schematic — not a photomicrograph

Slide 61 · Application: Interpretation

Apoptosis is the best morphologic interpretation.

Supporting findings: Shrinkage, eosinophilia, fragmented condensed chromatin, isolated distribution.

Confirm that there is not prominent membrane rupture with widespread inflammation.

H&E-like tissue schematic — not a photomicrograph

Slide 62 · Application: Connect biochemistry to disposal

A dying cell displays phosphatidylserine on its external membrane and is rapidly engulfed by a macrophage.

Question: Which clearance process is occurring, and why is inflammation limited?

Extracellular space

Cytoplasm

Red headgroups: Phosphatidylserine

Schematic

Slide 63 · Application: Mechanism and consequence

The process is efferocytosis: Phagocytes recognize eat-me signals and engulf cell bodies.

Rapid clearance prevents leakage; Engulfing macrophages reduce proinflammatory cytokine output.

Thus a large amount of apoptosis can remain histologically subtle.

Extracellular space

Cytoplasm

Red headgroups: Phosphatidylserine

Schematic

Slide 64 · Integrated picture of apoptotic cell death

Morphology: Shrinkage → chromatin condensation → blebs/bodies.

Biochemistry: Executioner-caspase effects on DNase and structural targets.

Resolution: Phosphatidylserine recognition → efferocytosis → limited inflammation.

Viable

Condensed

Blebbing

Bodies

Schematic sequence; Stages may overlap

Schematic

Slide 65 · Sources and illustration status

Robbins, Cotran & Kumar, Pathologic Basis of Disease, 11th ed. (2026), Chapter 2, pp. 41–44.

Assigned section: “Morphologic and Biochemical Changes in Apoptosis,” p. 41 onward.

Biochemical execution and removal details are drawn from adjacent “Mechanisms of Apoptosis,” pp. 42–44.

All cell/tissue drawings in this deck are original schematic PowerPoint shapes, not photomicrographs.

Illustrations are labeled as schematic; genuine diagnostic micrographs were not available for embedding.