Causes of Apoptosis

Slide 1 · Causes of Apoptosis

Physiologic cell removal and pathologic cell loss

Pathology lecture

Dr Abu Suraih Sakhri

MBBS, MD (Pathology)

www.abusuraihsakhri.com

Slide 2 · Learning objectives

Classify the major physiologic and pathologic triggers of apoptosis.

Explain why survival-signal withdrawal and injurious stimuli produce selective cell loss.

Link representative diseases and normal processes to their apoptotic causes.

Distinguish apoptosis from necrotic cell death in clinicopathologic interpretation.

Aetiology → cellular decision → tissue consequence

Slide 3 · Apoptosis is regulated cellular self-destruction

Cell receives a death-inducing signal

Intracellular enzymes degrade vital components

Membrane-bound apoptotic fragments form

Phagocytes remove fragments

Cell contents are contained during clearance, minimizing inflammation.

Slide 4 · Apoptosis and necrosis differ in their consequences

Apoptosis

Regulated intracellular degradation

Membrane-bound cellular fragments

Rapid phagocytic clearance

Typically little or no inflammation

Necrosis

Loss of membrane integrity

Leakage of cellular constituents

Inflammatory reaction

Often prominent after severe tissue injury

Slide 5 · Two broad contexts initiate apoptosis

Physiologic

Removes unnecessary cells

Sculpts developing tissues

Balances cell production

Terminates selected immune responses

Pathologic

Eliminates irreparably injured cells

Limits persistence of DNA-damaged cells

Can remove infected cells

May cause loss of parenchymal cells

Slide 6 · The trigger matters more than cell appearance

Different physiologic or injurious stimuli

A cell-death decision

Common apoptotic machinery

Clearance by phagocytes

The same cellular outcome can support development, tissue homeostasis, or disease.

Slide 7 · Efficient clearance limits bystander injury

Apoptotic cell fragments

Membrane integrity is maintained

Phagocytic recognition and ingestion

Little leakage or local inflammation

This contrasts with the inflammatory response that follows necrotic membrane disruption.

Slide 8 · A common physiologic mechanism: Survival-signal withdrawal

Cell needs growth or matrix signals

Required survival input decreases

Pro-apoptotic balance increases

Unneeded cell is eliminated

External signals determine whether a cell remains viable in its tissue niche.

Slide 9 · Physiologic apoptosis removes surplus cells

During development, more cells or structures may form than the mature organ requires.

Cells in excess of the needed number are eliminated selectively.

The result is controlled tissue remodeling rather than accidental injury.

Development → selective elimination → mature architecture

Slide 10 · Developmental remodeling is a selective process

Early developmental structure

Cells become unnecessary

Apoptosis of selected cells

Reshaped mature tissue

Apoptosis is a mechanism of developmental involution and remodeling.

Slide 11 · Involution of primordial structures

Some early developmental structures are temporary.

Their removal requires targeted loss of cells rather than generalized tissue destruction.

Apoptotic clearance permits neighboring tissue to remain relatively undisturbed.

Temporary structure → apoptosis → involution

Slide 12 · Tissue maturation requires removal as well as growth

Addition

Cell proliferation increases cell numbers.

Differentiation establishes specialized properties.

Removal

Apoptosis eliminates surplus cells.

Selective loss refines tissue form and cellular composition.

Slide 13 · “Programmed cell death” terminology

Apoptosis describes the characteristic pattern of cell death across many settings.

“programmed cell death” specifically for developmentally regulated apoptosis.

The terms should not be treated as identical in every source or research field.

Textbook terminology is explicitly contextual.

Slide 14 · Hormone withdrawal can initiate involution

Hormone-dependent tissue

Withdrawal of trophic stimulus

Increased apoptotic cell loss

Tissue regression

Physiologic regression follows a change in hormonal support.

Slide 15 · Endometrial breakdown during the menstrual cycle

The endometrium responds to cyclic hormonal cues.

Loss of hormonal support contributes to programmed removal of endometrial cells.

Apoptosis is one cellular component of menstrual endometrial breakdown.

Hormonal withdrawal → endometrial cell loss

Slide 16 · Ovarian follicular atresia

Ovarian follicles require appropriate hormonal and local survival support.

Follicles that do not persist can undergo atresia with apoptotic cell loss.

Follicular atresia, including in menopause, among physiologic examples.

Loss of support → follicular cell apoptosis

Slide 17 · Breast regression after weaning

Lactating mammary gland

Weaning

Withdrawal of lactational maintenance signals

Apoptosis and glandular involution

Regression of the lactating breast is a classic physiologic setting.

Slide 18 · Three hormone-dependent examples

Tissue

Physiologic transition

Apoptotic context

Endometrium

Menstrual hormonal changes

Endometrial cell breakdown

Ovarian follicle

Loss or alteration of follicular support

Follicular atresia

Lactating breast

Weaning

Regression of the gland

Slide 19 · Apoptosis maintains cell-number homeostasis

Continuous cell production

Mature cells perform function

Cells become unnecessary

Apoptosis balances production

A stable tissue population requires both cell generation and cell removal.

Slide 20 · The intestinal crypt is a turnover example

Intestinal epithelium is a proliferating cell population.

Homeostatic replacement requires coordinated production and loss.

Intestinal crypt epithelium as a setting in which apoptosis maintains cell numbers.

Cell renewal and cell elimination are linked.

Slide 21 · Cell number reflects opposing rates

Cell addition

Proliferation introduces new cells.

Supports epithelial replacement and renewal.

Cell removal

Apoptosis disposes of unwanted cells.

Prevents unchecked accumulation in normal tissues.

Slide 22 · Why high turnover does not imply tissue enlargement

Many new cells are produced

Equivalent cells are removed

Net cell number remains relatively stable

Tissue homeostasis is preserved

This is a conceptual balance, not a claim that all tissues turn over at identical rates.

Slide 23 · Immune-cell development includes quality control

Immature lymphocyte

Antigen-receptor assessment

Unsuitable cell fails selection

Apoptotic elimination

Lymphocytes lacking useful receptors need not persist.

Slide 24 · Bone marrow removes unsuitable immature lymphocytes

Immature lymphocytes develop and are selected in primary lymphoid tissues.

Cells that fail to generate useful antigen-receptor functions can be eliminated.

The outcome is a better-selected lymphocyte population.

Receptor inadequacy → apoptosis

Slide 25 · Thymic selection involves apoptotic cell loss

Developing T lymphocytes pass through selection checkpoints.

Cells that fail selection do not need to survive indefinitely.

Apoptotic removal contributes to the composition of the mature T-cell pool.

Selection failure → cellular deletion

Slide 26 · Germinal-center B-cell selection

B cells in germinal centers undergo functional selection.

Cells failing to produce suitable antigen-receptor function may be eliminated.

Apoptosis removes B cells that do not meet survival-selection requirements.

Functional B-cell selection → apoptosis

Slide 27 · Selection converts diversity into a functional pool

Many immature lymphocytes

Variable receptor properties

Selection of useful cells

Apoptosis of unsuccessful cells

The final repertoire reflects both successful survival and selective death.

Slide 28 · Self-reactive lymphocytes must be controlled

Lymphocyte recognizes self antigen

Potential for tissue-directed immunity

Deletion of harmful self-reactive cell

Reduced risk of autoimmunity

Apoptosis is an important route to immunologic tolerance.

Slide 29 · Deletion of autoreactive cells preserves tolerance

Recognition of the body’s own antigens can make certain lymphocytes dangerous.

Apoptotic elimination reduces survival of potentially self-reactive clones.

Loss of this regulatory function can permit unwanted immune responses.

Self-reactivity → deletion → tolerance

Slide 30 · Lymphocyte selection has two distinct purposes

Functional competence

Eliminate cells with nonfunctional receptors.

Improve the quality of the mature repertoire.

Self-tolerance

Eliminate potentially harmful autoreactive cells.

Limit immune reactions against host tissues.

Slide 31 · Apoptosis contributes to inflammation resolution

Acute inflammatory challenge

Neutrophils carry out effector function

Neutrophils are no longer required

Apoptosis and phagocytic removal

Removal of spent neutrophils helps end an acute inflammatory response.

Slide 32 · Neutrophils are removed after useful service

Neutrophils are short-lived participants in acute inflammation.

Persisting effector cells are unnecessary after the initiating threat subsides.

Apoptotic death helps clear these cells without releasing their contents.

Resolution of acute inflammation

Slide 33 · Expanded lymphocyte populations contract

Antigen-driven immune response

Expansion of responding lymphocytes

Immune response subsides

Excess effector lymphocytes undergo apoptosis

Cell death restores a smaller post-response lymphocyte population.

Slide 34 · The end of an immune response requires cell loss

Immune activation increases the number of responding cells.

After the response, much of that expanded population is no longer needed.

Apoptosis contributes to termination and population contraction.

Response → expansion → contraction

Slide 35 · Physiologic triggers can be grouped by function

Function

Example

Reason for apoptosis

Development

Surplus cells

Refine organ architecture

Endocrine adaptation

Breast after weaning

Tissue involution

Homeostasis

Intestinal epithelium

Balance renewal

Immune selection

Unsuitable lymphocytes

Quality control

Immune tolerance

Self-reactive lymphocytes

Avoid self-injury

Immune resolution

Neutrophils, lymphocytes

End effector activity

Slide 36 · Pathologic apoptosis removes irreparably injured cells

Potentially harmful cellular injury

Repair cannot restore viability

Apoptotic program is triggered

Damaged cell is eliminated

Apoptosis can protect surrounding tissue by preventing persistence of injured cells.

Slide 37 · Apoptotic death has a protective boundary

Protective role

Remove cells with unrepaired damage.

Reduce persistence of mutant or infected cells.

Limit leakage of inflammatory contents.

Pathologic cost

Loss of functional parenchymal cells.

Infection-related or immune-mediated tissue damage.

Organ atrophy in selected settings.

Slide 38 · DNA damage is a major pathologic trigger

Genotoxic exposure

Damage to cellular DNA

Damage is not adequately repaired

Intrinsic apoptosis eliminates the cell

Robbins specifically lists radiation and cytotoxic anticancer drugs.

Slide 39 · Radiation can produce apoptotic DNA injury

Radiation may damage DNA directly.

Radiation-associated free radicals may also damage nucleic acids.

When the injury cannot be repaired, apoptosis prevents continued survival of the damaged cell.

Radiation → irreparable DNA damage → apoptosis

Slide 40 · Cytotoxic anticancer drugs can trigger apoptosis

Many cytotoxic anticancer treatments injure DNA.

Persistent injury activates the cell’s death response.

Apoptosis is one mechanism by which susceptible tumor cells are eliminated.

Drug-induced DNA injury → cellular elimination

Slide 41 · Free radicals amplify DNA injury

Radiation or other DNA-damaging insult

Free-radical formation

DNA lesions

Possible apoptosis if repair fails

Free radicals are a route to damage, not a separate universal requirement for apoptosis.

Slide 42 · Repair capacity determines the response to DNA injury

Damage can be repaired

Cellular damage-response mechanisms act.

Survival remains possible.

Damage cannot be repaired

Pro-apoptotic mechanisms predominate.

The cell is removed before mutations persist.

Slide 43 · Removing DNA-damaged cells reduces cancer risk

Persistent DNA damage

Potential mutation transmission

Apoptotic elimination of damaged cell

Reduced survival of potentially transformed cells

Apoptosis as a protection against malignant transformation.

Slide 44 · Misfolded proteins can elicit apoptosis

Misfolded intracellular proteins accumulate

Endoplasmic-reticulum stress develops

Stress is excessive or unresolved

Apoptotic cell death

Protein quality-control failure can become a pathologic cell-death signal.

Slide 45 · Unresolved ER stress links protein injury to death

The endoplasmic reticulum normally handles protein folding.

Accumulation of improperly folded proteins produces ER stress.

When adaptive responses are insufficient, apoptotic cell loss may follow.

Protein misfolding → ER stress → apoptosis

Slide 46 · Infections may initiate apoptosis by two routes

Virus-associated injury

Some viral infections can directly induce apoptosis.

Adenovirus and HIV as examples.

Host immune response

Cytotoxic T lymphocytes recognize infected cells.

Killing the infected cell can damage tissue.

Slide 47 · Certain viruses can directly induce cell apoptosis

Viral infection may provide the initiating injury or death signal.

Adenovirus and HIV infection are examples listed.

Direct virus-associated injury is distinct from cytotoxic lymphocyte killing.

Infected host cell → apoptotic response

Slide 48 · Cytotoxic T cells eliminate virus-infected cells

Viral proteins expressed by host cell

Virus-specific CTL recognition

Induction of target-cell apoptosis

Loss of infected cellular reservoir

Immune cytotoxicity protects the host by removing infected cells.

Slide 49 · Viral hepatitis illustrates immune-related tissue injury

Viral infection of hepatocytes

CTL recognition of viral antigens

Apoptosis of target hepatocytes

Tissue damage despite an antiviral goal

The immune response can be protective and injurious simultaneously.

Slide 50 · Antiviral killing has two competing consequences

Benefit

Eliminates infected cells.

Limits reservoirs of infection.

Cost

Destroys host cells.

May cause clinically significant tissue injury.

Slide 51 · CTL cytotoxicity also removes tumor cells

Tumor-associated target cell

Immune recognition by CTLs

Target-cell apoptosis

Elimination of malignant cells

CTL-mediated apoptosis with anti-tumor cytotoxicity.

Slide 52 · Cellular transplant rejection involves apoptosis

Transplanted tissue carries target antigens

Recipient CTLs attack graft cells

Apoptosis of targeted cells

Graft cellular injury

The same effector mechanism that defends against viruses can injure allografts.

Slide 53 · Graft-versus-host disease involves target-cell loss

Donor immune cells recognize recipient tissues

Cytotoxic cellular attack

Apoptosis of host target cells

Tissue injury

Apoptotic killing is a mechanism contributing to graft-versus-host disease.

Slide 54 · A shared CTL effector mechanism spans diseases

Setting

Cell targeted

Functional consequence

Viral infection

Infected host cell

Helps clear infection

Tumor immunity

Tumor cell

Eliminates neoplastic targets

Transplant rejection

Allograft cell

Graft injury

Graft-versus-host disease

Recipient tissue cell

Host tissue injury

Slide 55 · Duct obstruction can lead to pathologic atrophy

Duct outflow is obstructed

Parenchymal tissue is affected

Apoptotic cell loss contributes

Organ parenchyma atrophies

Pancreas, parotid gland, and kidney.

Slide 56 · Pancreatic duct obstruction and cell loss

Duct obstruction may affect pancreatic parenchyma.

Loss of parenchymal cells contributes to atrophy.

Apoptosis is one mechanism implicated in this form of pathologic regression.

Obstruction → parenchymal apoptosis → atrophy

Slide 57 · Parotid gland atrophy after obstruction

The parotid gland is a second example of obstructive parenchymal atrophy.

Sustained obstruction can be associated with apoptotic cell loss.

The tissue consequence is loss of glandular substance.

Obstruction-associated loss of salivary parenchyma

Slide 58 · Renal parenchymal atrophy and obstruction

The kidney among organs that can atrophy after duct obstruction.

Cellular loss can include apoptosis.

The initiating problem is obstructed drainage, not a normal physiologic need for involution.

Obstruction-associated renal parenchymal loss

Slide 59 · One trigger can have several organ outcomes

Organ

Pathologic context

Result

Pancreas

Duct obstruction

Parenchymal atrophy

Parotid gland

Duct obstruction

Parenchymal atrophy

Kidney

Urinary outflow obstruction

Parenchymal atrophy

Slide 60 · Physiologic and pathologic causes converge

Initiating condition

Representative setting

Biologic purpose or consequence

Survival-signal withdrawal

Tissue involution

Remove unneeded cells

Failed lymphocyte selection

Immune development

Improve repertoire

DNA damage

Radiation, cytotoxic therapy

Remove severely damaged cells

ER stress

Misfolded protein accumulation

Eliminate injured cell

CTL-mediated recognition

Infection, transplant

Target-cell killing

Obstruction

Pancreas, parotid, kidney

Parenchymal atrophy

Slide 61 · Most triggers engage intrinsic death machinery

Survival signals decline or intracellular injury develops

Balance shifts toward pro-apoptotic BCL2 family activity

Mitochondrial proteins are released

Caspase activation and cell death

Mechanistic bridge from the adjacent Robbins section; Not an exhaustive pathway map.

Slide 62 · Death-receptor signals provide another entry

Death ligand binds a receptor such as Fas

Adaptor proteins recruit initiator caspases

Caspase activation proceeds

Apoptosis of target cell

Death-receptor initiation is another route described in the adjacent section.

Slide 63 · Different triggers share common apoptotic execution

Intrinsic or extrinsic initiation

Caspase cascade

Controlled degradation of cell components

Apoptotic bodies and phagocytosis

The common endpoint explains similar morphology despite different causes.

Slide 64 · Morphology confirms the process—not its cause

Morphologic recognition

Cell shrinkage

Chromatin condensation

Membrane-bound apoptotic bodies

Rapid phagocytosis

Etiologic attribution

Requires knowledge of tissue context.

Physiologic turnover and disease can look similar.

Cell death alone does not identify the initiator.

Slide 65 · Apoptosis can be sparse in a tissue section

Individual cells shrink and fragment.

Apoptotic bodies are rapidly removed by phagocytes.

A substantial rate of apoptosis may be difficult to appreciate in a single H&E section.

A single static section is a limited temporal sample.

Slide 66 · Application: The breast after weaning

After cessation of breastfeeding, a previously lactating mammary gland decreases in functional glandular mass.

What apoptotic trigger best explains this change?

Discuss the initiating condition and its biological purpose or consequence.

Slide 67 · Application: Interpreting breast involution

Why is this not necessarily pathologic atrophy?

The initiating event is a normal physiologic transition—cessation of lactation.

Selective cell loss helps return the tissue from a lactational state.

The cellular mode of death is apoptosis, but the context is physiologic.

Slide 68 · Application: Hepatocyte apoptosis in viral hepatitis

Liver tissue from a patient with viral hepatitis contains scattered apoptotic hepatocytes in a background of an antiviral cellular immune response.

Which mechanism is most directly implicated?

Discuss the initiating condition and its biological purpose or consequence.

Slide 69 · Application: Antiviral defense versus injury

Why can effective immunity damage an organ?

CTL-mediated killing removes infected target cells.

The target cell is also a functional component of host tissue.

Cumulative apoptotic death can contribute to organ injury.

Slide 70 · Application: Apoptosis during anticancer therapy

Tumor cells exposed to a DNA-damaging cytotoxic agent accumulate injury that cannot be adequately repaired.

Why might these cells undergo apoptosis?

Discuss the initiating condition and its biological purpose or consequence.

Slide 71 · Application: DNA damage and cell-fate selection

What is the protective significance?

Persistently damaged DNA creates a risk of mutation.

Apoptotic clearance removes cells with irreparable injury.

In a tumor, the same mechanism contributes to the intended cytotoxic effect.

Slide 72 · Discriminate causes, mechanisms, and consequences

Cause

Proximal cellular signal

Contextual consequence

Weaning

Withdrawal of tissue-maintenance signals

Physiologic involution

Unsuccessful immune selection

Inadequate receptor/survival cues

Repertoire quality control

Radiation

DNA injury that cannot be repaired

Elimination of damaged cells

Viral hepatitis

CTL-mediated attack

Infected-cell loss and tissue injury

Duct obstruction

Stress and loss of parenchymal cells

Pathologic atrophy

Slide 73 · Core synthesis: The biologic context defines the cause

Physiologic apoptosis removes surplus, obsolete, or potentially harmful cells.

Pathologic apoptosis follows irreparable injury, infection-related killing, or selected obstructive disease.

Both are regulated processes with rapid clearance and relatively little inflammatory leakage.

Identify the initiating condition before assigning the significance of apoptotic morphology.

Same cell-death process; Different biological meanings.

Slide 74 · Reference and scope

Robbins, Cotran & Kumar. Pathologic Basis of Disease. 11th ed. (2026). Chapter 2, “Causes of Apoptosis,” printed pp. 39–41.

Adjacent textbook context: “Apoptosis,” pp. 39; “Morphologic and Biochemical Changes in Apoptosis,” pp. 41–42; “Mechanisms of Apoptosis,” pp. 42–43.

The source supplied for this deck is a Markdown extraction. Original chapter PDF pages were not available for comparison. No textbook figures are reproduced.