Hypertrophy

Slide 1 · Hypertrophy

Cellular adaptation • functional demand • clinical consequences

Normal cell

Hypertrophied cell

Dr Abu Suraih Sakhri

MBBS, MD (Pathology)

www.abusuraihsakhri.com

Slide 2 · Learning objectives

Define hypertrophy and distinguish it from increased cell number.

Relate workload and hormonal stimuli to increased cellular protein.

Explain physiologic examples and maladaptive cardiac hypertrophy.

Interpret core mechanisms and apply the concepts to short cases.

Slide 3 · Adaptation changes cellular phenotype and function

Responses to environmental change can alter cell size, cell number, phenotype, metabolism, or function.

Adaptations are potentially reversible while the precipitating conditions change.

Hypertrophy represents the cell-size component of this response.

Before stimulus

After stimulus

Same number of cells

Larger individual cells

Slide 4 · Hypertrophy is an increase in cell size

Individual cells enlarge.

The affected organ may consequently become larger.

The defining change is cell size—not cell proliferation.

Before stimulus

After stimulus

Same number of cells

Larger individual cells

Slide 5 · Enlargement does not require new cells

A hypertrophied organ contains enlarged pre-existing cells.

Cell number is not the defining contributor to hypertrophy.

Determine whether a tissue has larger cells, more cells, or both.

Before stimulus

After stimulus

Same number of cells

Larger individual cells

Slide 6 · New intracellular structure drives enlargement

Synthesis increases cellular protein content.

→

New structural components are assembled inside the cell.

→

Enlargement is an organized biosynthetic response.

Slide 7 · Cell-level change explains organ-level enlargement

Greater size of each participating cell raises tissue mass.

Tissue-level enlargement does not by itself identify the cellular mechanism.

Morphologic interpretation must consider both size and number.

Before stimulus

After stimulus

Same number of cells

Larger individual cells

Slide 8 · Division capacity shapes the adaptive response

Dividing cells

Cells capable of proliferation can undergo hypertrophy and hyperplasia.

Cells with limited division

Cardiomyocytes enlarge mainly by hypertrophy because their division is limited.

Slide 9 · Hypertrophy and hyperplasia may coexist

More cells and larger cells can contribute simultaneously to organ enlargement.

The contributions are biologically distinct despite a shared gross endpoint.

Pregnancy-related organ growth can include both processes.

Before stimulus

After stimulus

Same number of cells

Larger individual cells

Slide 10 · Hypertrophy is classified by context

Category

Predominant context

Physiologic

Appropriate increased demand or hormonal stimulation

Pathologic

Disease-related persistent mechanical or trophic stress

Slide 11 · Increased workload is a central stimulus

Myocytes respond when greater work is required.

Mechanical demand promotes the synthesis of cellular components.

The adaptive result is increased contractile machinery.

Normal muscle fiber

Hypertrophied muscle fiber

Schematic: Greater myofilament content per fiber

Slide 12 · Hormonal stimulation can enlarge cells

Hormones act through cellular receptors and biosynthetic responses.

The gravid uterus is the major Robbins example.

Hormonal hypertrophy is not synonymous with pathologic growth.

Nonpregnant uterus

Smooth-muscle cell size baseline

During pregnancy

Smooth-muscle cell size increased

Slide 13 · Growth factors participate in hypertrophy

Growth-factor signals can promote cellular protein synthesis.

Hormonal, mechanical, and growth-factor inputs may converge.

Specific intracellular pathways are illustrated in cardiac muscle.

Workload / hormones

↓

Cellular sensors and receptors

↓

Intracellular signals

↓

Protein synthesis

Slide 14 · Physiologic and pathologic do not mean different definitions

Physiologic hypertrophy

Appropriate workload or hormone signals increase structural cell mass.

Pathologic hypertrophy

Abnormal persistent demand may progress from adaptation to injury.

Slide 15 · Striated muscle is adapted by cell enlargement

Cardiac and skeletal muscle fibers have limited division potential.

An increased workload is therefore met mainly by hypertrophy.

Myofilament content increases within existing muscle cells.

Normal muscle fiber

Hypertrophied muscle fiber

Schematic: Greater myofilament content per fiber

Slide 16 · Higher demand leads to more muscle proteins

Increased work

→

Cellular signaling

→

More contractile protein

→

Larger muscle cell

Slide 17 · Myofilament accumulation is functionally relevant

Myofilaments provide the contractile apparatus.

Additional myofilaments permit increased force generation.

The tissue may initially achieve higher work capacity.

Normal muscle fiber

Hypertrophied muscle fiber

Schematic: Greater myofilament content per fiber

Slide 18 · Hypertrophy enhances force per myocyte

More contractile elements

→

Greater potential force generation

→

Greater collective muscle capacity

Slide 19 · The contractile apparatus—not water—is emphasized

Hypertrophy to increased protein production.

Its characteristic change is structural enlargement, not simple swelling.

Link morphology to the stimulus and cellular composition.

Before stimulus

After stimulus

Same number of cells

Larger individual cells

Slide 20 · Cardiac hypertrophy is a classic pathologic example

Increased cardiac workload is a common initiating stimulus.

Pressure overload is associated with enlarged myocardial cells.

The process begins as adaptation but may progress to disease.

Increased load

Adaptation

More contractile machinery

Limit

Persisting hemodynamic burden

Failure

Loss of contractile elements

Slide 21 · Systemic hypertension can impose pressure overload

High pressure burden

→

Increased myocardial work

→

Hypertrophic myocyte response

→

Larger heart muscle mass

Slide 22 · Valvular disease can trigger the same response

Relevant valvular abnormalities may increase pressure load.

Cardiac cells respond by increasing contractile protein synthesis.

The initiating disease matters when interpreting hypertrophy.

Increased load

Adaptation

More contractile machinery

Limit

Persisting hemodynamic burden

Failure

Loss of contractile elements

Slide 23 · Early cardiac enlargement can preserve performance

An increased number of myofilaments supports contractile force.

The heart may initially meet an elevated workload.

Compensation is useful but does not remove the original stress.

Increased load

Adaptation

More contractile machinery

Limit

Persisting hemodynamic burden

Failure

Loss of contractile elements

Slide 24 · The compensatory response has a finite limit

Persisting demand can outstrip increased muscle mass.

Enlargement alone cannot indefinitely maintain function.

The adaptive response may become maladaptive.

Cell enlargement

Compensatory increase in work

Regressive change

Myofibrillar elements degrade

Cell injury

Possible myocyte death

Slide 25 · Loss of myofibrils marks regressive change

Hypertrophied myocardial fibers can lose contractile elements.

Myofibrillar degradation undermines previously increased capacity.

The same tissue may exhibit adaptation and progressive injury.

Cell enlargement

Compensatory increase in work

Regressive change

Myofibrillar elements degrade

Cell injury

Possible myocyte death

Slide 26 · Severe overload may progress to cell death

When compensation fails, injury can become severe.

Extreme cases may include myocyte death.

Cardiac failure is a possible downstream result.

Cell enlargement

Compensatory increase in work

Regressive change

Myofibrillar elements degrade

Cell injury

Possible myocyte death

Slide 27 · Cardiac hypertrophy: Adaptation-to-failure sequence

Increased demand

More protein synthesis

→

Early compensation

Greater work capacity

→

Persistent stress

Capacity eventually exceeded

→

Late consequences

Myofibril loss; Failure

Sustained demand initiates growth. Early compensation raises work capacity. Later injury diminishes contractile capability.

Slide 28 · Cardiac enlargement cannot be interpreted in isolation

Organ size reflects a response, not necessarily physiologic success.

Identify the hemodynamic cause and functional status.

Hypertrophy may coexist with late-stage cellular injury.

Increased load

Adaptation

More contractile machinery

Limit

Persisting hemodynamic burden

Failure

Loss of contractile elements

Slide 29 · Cellular morphology: Larger contractile cells

Before stimulus

After stimulus

Same number of cells

Larger individual cells

Myocardial myocytes become enlarged. • Additional protein and myofilaments account for increased volume.

Slide 30 · A tissue-level schematic shows larger myocytes

Before stimulus

After stimulus

Same number of cells

Larger individual cells

Compare like-for-like cellular outlines. • Preserve cell count in a hypertrophy-only depiction.

Slide 31 · Pregnancy is a physiologic organ-enlargement example

The uterus enlarges markedly during pregnancy.

Hypertrophy of uterine smooth-muscle cells is a major contributor.

The relevant stimulus is endocrine rather than pathologic pressure.

Nonpregnant uterus

Smooth-muscle cell size baseline

During pregnancy

Smooth-muscle cell size increased

Slide 32 · Estrogen signaling stimulates uterine hypertrophy

Estrogenic hormone signal

→

Estrogen receptor activation

→

Synthesis of smooth-muscle proteins

→

Increased cell size

Slide 33 · Uterine growth requires protein synthesis

Estrogen receptor signaling changes cellular protein production.

New smooth-muscle proteins accumulate in the cells.

The result is enlargement of pre-existing smooth-muscle fibers.

Nonpregnant uterus

Smooth-muscle cell size baseline

During pregnancy

Smooth-muscle cell size increased

Slide 34 · The gravid myocyte is larger than the baseline myocyte

Nonpregnant uterus

Smooth-muscle cell size baseline

During pregnancy

Smooth-muscle cell size increased

Cells shift from small spindle-shaped forms to enlarged, plumper cells. • The comparative appearance is Fig. 2.25.

Slide 35 · Hormone-driven hypertrophy has a clear causal chain

Hormonal change is the stimulus.

Receptor-dependent biosynthesis is the cellular mechanism.

Smooth-muscle enlargement is the morphologic result.

Nonpregnant uterus

Smooth-muscle cell size baseline

During pregnancy

Smooth-muscle cell size increased

Slide 36 · Skeletal muscle responds to resistance loading

Resistance exercise raises functional demand.

Individual muscle fibers enlarge.

The increase in muscle bulk primarily reflects fiber hypertrophy.

Normal muscle fiber

Hypertrophied muscle fiber

Schematic: Greater myofilament content per fiber

Slide 37 · Muscle bulk and muscle fiber number are different

Larger fiber cross-sectional size explains the classic training adaptation.

Greater visible muscle mass does not itself prove fiber proliferation.

This distinction parallels organ-level interpretation of hypertrophy.

Normal muscle fiber

Hypertrophied muscle fiber

Schematic: Greater myofilament content per fiber

Slide 38 · Skeletal and cardiac hypertrophy share a cell response

Feature

Resistance-trained skeletal muscle

Pressure-overloaded heart

Stimulus

Increased exercise demand

Increased cardiac pressure workload

Cellular change

More myofilaments; Larger fibers

More myofilaments; Larger myocytes

Clinical frame

Physiologic adaptation

Can become pathologic

Slide 39 · Uterine and skeletal examples differ by stimulus

Characteristic

Gravid uterine smooth muscle

Resistance-trained skeletal muscle

Major initiating stimulus

Estrogen signaling

Mechanical workload

Common response

Additional cellular protein

Additional contractile protein

Tissue-level outcome

Uterine enlargement

Skeletal muscle bulk

Slide 40 · The same morphologic term spans several tissues

Cardiac myocyte enlargement accompanies elevated workload.

Skeletal fiber enlargement accompanies resistance exercise.

Uterine smooth-muscle enlargement accompanies gestational hormone signals.

Slide 41 · Mechanical sensors detect increased load

Cellular sensors respond to mechanical stretch.

The signal activates pathways that raise biosynthetic activity.

Mechanosensing is a key part of the myocardial response.

Workload / hormones

↓

Cellular sensors and receptors

↓

Intracellular signals

↓

Protein synthesis

Slide 42 · Signaling connects extracellular load to protein synthesis

Mechanical and chemical stimuli

→

Intracellular signaling pathways

→

Transcriptional reprogramming

→

Increased structural proteins

Slide 43 · PI3K–AKT is linked to physiologic hypertrophy

Phosphoinositide 3-kinase and AKT participate in growth signaling.

This pathway as particularly important in exercise-associated hypertrophy.

Relative pathway dominance is a model, not an absolute separation.

Mechanical load

↓

PI3K–AKT / GPCR-related signaling

↓

Transcription factors

↓

Contractile proteins

Slide 44 · GPCR pathways are prominent in pathologic contexts

G-protein–coupled receptor signaling integrates agonist stimulation.

Vasoactive agents and growth factors can activate associated pathways.

Greater proposed importance in pathologic hypertrophy.

Mechanical load

↓

PI3K–AKT / GPCR-related signaling

↓

Transcription factors

↓

Contractile proteins

Slide 45 · Growth-factor mediators amplify the cellular response

Examples named by Robbins include IGF-1, TGF-β, and fibroblast growth factor.

These mediators can participate in growth-promoting feedback.

They belong to the signaling network—not an independent cell-number increase.

Workload / hormones

↓

Cellular sensors and receptors

↓

Intracellular signals

↓

Protein synthesis

Slide 46 · Vasoactive agonists contribute to cardiac signaling

Examples include α-adrenergic agonists, endothelin-1, and angiotensin II.

Such mediators link physiological stress and receptor pathways.

Multiple upstream inputs can converge on growth-related gene expression.

Workload / hormones

↓

Cellular sensors and receptors

↓

Intracellular signals

↓

Protein synthesis

Slide 47 · Transcription factors implement the growth program

GATA4 • NFAT • MEF2

↓

Expression of contractile-protein genes

↓

Increase in cellular protein

↓

Myocyte enlargement

GATA4 NFAT MEF2 Contractile-protein gene expression

Slide 48 · More gene expression produces more contractile proteins

Growth-related signaling activates selected transcription factors.

Their targets include genes encoding contractile components.

Additional protein yields greater structural cell mass.

Persistent load

↓

Reprogrammed cardiac genes

↓

Fetal isoforms and stress-response proteins

↓

Altered muscle phenotype

Slide 49 · Cardiac hypertrophy includes fetal gene re-expression

Hypertrophic cardiac cells may shift their contractile-protein isoforms.

Embryonic or fetal expression programs can reappear.

Gene-expression changes accompany, but do not define, hypertrophy.

Persistent load

↓

Reprogrammed cardiac genes

↓

Fetal isoforms and stress-response proteins

↓

Altered muscle phenotype

Slide 50 · Myosin heavy-chain isoforms illustrate the switch

A shift from α- to β-myosin heavy-chain isoforms.

β-myosin heavy chain supports slower, energetically economical contraction.

The example illustrates functional consequences of altered gene expression.

Persistent load

↓

Reprogrammed cardiac genes

↓

Fetal isoforms and stress-response proteins

↓

Altered muscle phenotype

Slide 51 · Atrial natriuretic factor is a stress-response product

Cardiac hypertrophy can increase atrial natriuretic factor gene expression.

This peptide contributes to renal salt excretion.

The resulting fall in volume and pressure tends to reduce hemodynamic load.

Persistent load

↓

Reprogrammed cardiac genes

↓

Fetal isoforms and stress-response proteins

↓

Altered muscle phenotype

Slide 52 · Signaling pathways are overlapping, not exclusive

Mechanistic theme

Physiologic example

Pathologic example

Illustrative upstream input

Exercise-related stretch

Vasoactive/receptor stimuli

Textbook emphasis

PI3K–AKT signaling

GPCR-associated signaling

Shared endpoint

Increased cellular protein

Increased cellular protein

Slide 53 · Hypertrophy and hyperplasia: The diagnostic distinction

Feature

Hypertrophy

Hyperplasia

Defining cellular change

Increased cell size

Increased cell number

Pre-existing cells

Enlarge

Proliferate

May coexist?

Yes

Yes

Slide 54 · Cell proliferative capacity limits hyperplasia

Hyperplasia requires cells capable of division.

Striated-muscle hypertrophy is prominent because proliferative reserve is limited.

Do not equate every large organ with hyperplasia.

Before stimulus

After stimulus

Same number of cells

Larger individual cells

Slide 55 · Mixed growth must be assessed as mixed growth

Some organs enlarge through both increased cell size and number.

The contribution of each process varies by tissue and stimulus.

Descriptions should explicitly distinguish these components.

Before stimulus

After stimulus

Same number of cells

Larger individual cells

Slide 56 · Case: Cardiac pressure overload

A patient with long-standing systemic hypertension is found to have an enlarged heart.

Reason through the stimulus, cell population, and expected adaptation.

Which adaptation is expected in myocardial cells?

Why might this initially preserve function?

What cellular changes may eventually precede cardiac failure?

Slide 57 · Cardiac case: Mechanism-based resolution

The persistent pressure burden increases myocardial workload.

Myocytes synthesize additional contractile proteins and enlarge.

Progressive myofibril loss and injury can limit contractility.

Increased load

Adaptation

More contractile machinery

Limit

Persisting hemodynamic burden

Failure

Loss of contractile elements

Slide 58 · Case: Pregnancy-related uterine growth

An otherwise healthy pregnant patient has marked uterine enlargement.

Reason through the stimulus, cell population, and expected adaptation.

Which smooth-muscle cellular adaptation contributes to the change?

What endocrine signal is emphasized?

Is this example classified as physiologic or pathologic?

Slide 59 · Uterine case: Mechanism-based resolution

Uterine smooth-muscle cells enlarge substantially.

Estrogen receptor signaling promotes cellular protein synthesis.

The growth illustrates physiologic hormone-associated hypertrophy.

Nonpregnant uterus

Smooth-muscle cell size baseline

During pregnancy

Smooth-muscle cell size increased

Slide 60 · Case: Resistance training

After a prolonged period of resistance training, skeletal muscle bulk increases.

Reason through the stimulus, cell population, and expected adaptation.

What happens to individual muscle fibers?

What structural content explains greater contractile capacity?

How does this differ from cellular proliferation?

Slide 61 · Skeletal case: Mechanism-based resolution

Greater workload stimulates new contractile protein production.

Individual fibers enlarge through additional myofilaments.

The primary described adaptation is hypertrophy, not hyperplasia.

Normal muscle fiber

Hypertrophied muscle fiber

Schematic: Greater myofilament content per fiber

Slide 62 · Integrate stimulus, cellular response, and outcome

Setting

Stimulus

Cell response

Outcome

Heart

Pressure overload

Myocyte hypertrophy

Initial compensation; Potential failure

Uterus

Estrogen signaling

Smooth-muscle hypertrophy

Physiologic organ growth

Skeletal muscle

Resistance demand

Fiber hypertrophy

Greater muscle bulk

Slide 63 · Essential principles of hypertrophy

Cell enlargement reflects additional intracellular structural components.

Workload, hormones, and growth factors are important initiating inputs.

Physiologic growth and maladaptive growth share protein synthesis.

The cardiac response may eventually become injurious.

Slide 64 · References and source limitations

Robbins, Cotran & Kumar: Pathologic Basis of Disease. 11th edition (2026). Chapter 2: Cell Injury, Cell Death, and Adaptations, pp. 52–53.

Primary sections: Hypertrophy; Mechanisms of Hypertrophy. Comparison context: Hyperplasia.

Conceptual drawings are original native PowerPoint schematics; no simulated histopathology is shown.

Original chapter PDF and licensed tissue images were not available for direct figure verification.