Factors That Influence Tissue Repair

Slide 1 · Factors That Influence Tissue Repair

Mechanisms, impaired healing, and clinicopathologic correlations

Inflammation • perfusion • matrix synthesis • mechanical integrity

Dr Abu Suraih Sakhri

MBBS, MD (Pathology)

www.abusuraihsakhri.com

Slide 2 · Learning objectives

Classify systemic, local, extrinsic, and tissue-intrinsic influences on repair.

Explain why infection, impaired perfusion, malnutrition, and mechanical stress delay healing.

Relate repair defects to chronic ulcers and wound dehiscence.

Distinguish resolution, organization, and scar formation in tissue spaces.

Slide 3 · Two possible outcomes after tissue injury

Regeneration

Lost cells are replaced by viable tissue cells.

Requires proliferative capacity and an adequate matrix scaffold.

May restore architecture and function.

Scar formation

Connective tissue replaces tissue that cannot regenerate adequately.

Predominates after severe framework injury or in nondividing tissue.

Restores continuity, not the original architecture.

Slide 4 · Wound repair is a coordinated sequence

Hemostatic clot

Inflammation

Granulation tissue

Collagen deposition

ECM remodeling

Interference at any stage can compromise the final scar or delay wound closure.

Slide 5 · Macrophages coordinate inflammatory resolution and repair

Macrophages remove microbes and necrotic material

They produce cytokines and growth factors

Fibroblasts, epithelial cells, and vascular cells participate in tissue repair

Slide 6 · Granulation tissue and mature scar are distinct

Granulation tissue

New capillary network and proliferating fibroblasts.

Loose extracellular matrix with inflammatory cells.

Typical of actively repairing defects.

Mature scar

Increased dense collagen deposition.

Progressive vascular regression.

Fewer proliferating fibroblasts and vessels.

Slide 7 · Connective-tissue deposition requires two linked activities

Fibroblast migration

Fibroblast proliferation

ECM synthesis

Collagen accumulation

PDGF, FGF-2, and TGF-β participate in fibroblast recruitment and matrix deposition.

Slide 8 · TGF-β favors connective-tissue accumulation

Growth factor signaling, notably TGF-β

Fibroblast activation + collagen and fibronectin synthesis

Greater extracellular matrix deposition

Slide 9 · Scar remodeling depends on opposing processes

Matrix formation

Fibroblast activity

Collagen and fibronectin synthesis

Supported by profibrogenic signals

Matrix degradation

Matrix metalloproteinases digest ECM.

Proteases activate MMP precursors.

TIMPs restrain active MMPs.

Slide 10 · Healing by primary versus secondary intention

Feature

Primary intention

Secondary intention

Wound margins

Well apposed; small gap

Larger defect; irregular edges

Inflammation

Relatively limited

More extensive

Granulation tissue

Less abundant

More abundant

Contraction

Less pronounced

Significant

Outcome

Neat linear scar

Contracted, irregular scar

Slide 11 · Skin wound healing follows an ordered timeline

Immediate

Clot

24 h

Neutrophils

24–48 h

Epithelium bridges edges

Day 3

Macrophages; Early granulation

Day 5

Marked new vessel formation

Days 14–30

Collagen-rich scar

Representative sequence for uncomplicated cutaneous healing Table 3.11.

Slide 12 · When tissue repair becomes abnormal

Inadequate repair

Persistent defect, chronic ulcer, or wound separation

Excessive repair

Excess collagen or exuberant granulation

Exaggerated contraction

Contracture and distortion of adjacent tissue

Slide 13 · Factors act at different biological levels

Systemic milieu

Diabetes, nutrition, age, glucocorticoids

Local wound conditions

Infection, perfusion, pressure, foreign material

Intrinsic tissue properties

Cell proliferation and supporting architecture

Slide 14 · Several modifiers converge on four failure mechanisms

Inflammation persists

Microbes and foreign bodies

Blood supply is inadequate

Arterial, venous, or pressure-related impairment

Collagen deposition is reduced

Protein or vitamin C deficiency; Steroids

Wound edges do not remain apposed

Mobility, tension, pressure, or torsion

Slide 15 · Infection is a major cause of delayed wound healing

Infection in an injured site

Prolonged inflammation + possible additional tissue injury

Delayed progression to effective repair

Slide 16 · Why sustained inflammation impedes repair

Persistent agent

Continued inflammatory reaction

Further local tissue damage

Delayed closure

The wound remains exposed to the cause of injury rather than advancing through uncomplicated repair.

Slide 17 · Diabetes compromises healing by multiple mechanisms

Vascular disease

Perfusion can be impaired.

Neuropathy

Contributes to diabetic lower-extremity ulcers.

Secondary infection

Adds further injury and inflammation.

Tissue necrosis

Sustains nonhealing ulceration.

Slide 18 · Vascular disease is central to diabetic wound failure

Diabetes-associated vascular disease

Ischemia and injury to lower-extremity tissues

Necrosis and failure of ulcers to heal

Slide 19 · Neuropathy contributes to diabetic foot ulcers

Diabetic neuropathy

Combined with vascular disease and secondary infections

Ulceration and persistent tissue injury

Slide 20 · Secondary infection worsens diabetic ulceration

Diabetic ulcer

Secondary infection

More inflammation

Persistent tissue damage

This schematic represents a possible exacerbating mechanism, not an inevitable sequence in all diabetic ulcers.

Slide 21 · What a diabetic ulcer shows histologically

Schematic

Epithelial ulceration

Underlying granulation tissue

Chronic inflammatory infiltrate

Original editable schematic; Not a photomicrograph. Findings are described.

Slide 22 · Nutritional status directly affects collagen synthesis

Adequate substrates

Collagen synthesis

Matrix deposition

Wound strength

Protein and vitamin C deficiencies interrupt efficient collagen production and delay repair.

Slide 23 · Protein deficiency retards tissue repair

Deficient protein nutrition

Reduced capacity for collagen synthesis

Slower and less effective wound repair

Slide 24 · Vitamin C deficiency impairs collagen synthesis

Vitamin C deficiency

Impaired collagen synthesis

Delayed tissue repair

Slide 25 · Aging is a modifier, not a wound diagnosis

Healing capacity decreases with increasing age.

Age-related impairment may coexist with diabetes, malnutrition, vascular disease, and reduced mobility.

Assess the actual contributing mechanisms rather than attributing every nonhealing wound to age alone.

The last two points are clinical reasoning based on the coexisting factors.

Slide 26 · Glucocorticoids affect inflammation and scar strength

Anti-inflammatory action

Suppress inflammatory responses.

May be clinically useful when scarring itself threatens function.

Potential adverse effect on repair

Decrease TGF-β production.

Diminish fibrosis.

Can lead to weaker scars.

Slide 27 · How steroids can weaken a scar

Glucocorticoid exposure

Less TGF-β production

Reduced fibrosis

Weaker scar

A mechanistic example of systemic therapy modifying connective-tissue deposition.

Slide 28 · The effect of suppressing fibrosis depends on context

Cutaneous incision

A mechanically competent collagen scar is desirable.

Reduced fibrosis can weaken wound repair.

Corneal infection

Opacity from excessive scarring may impair transparency.

Selected use of steroids alongside antibiotics.

Slide 29 · Mechanical stress can prevent wound apposition

Schematic

Apposed wound edges

Excess movement / tension

Edges pull apart

Original native-shape schematic. Mechanical strain compromises continued contact between wound margins.

Slide 30 · Excessive mobility disrupts healing

Movement across an injured site

Failure of stable apposition of wound edges

Risk of impaired closure

Slide 31 · Pressure and torsion can separate wound margins

Local pressure / torsion

Mechanical stress at margins

Wound edges pull apart

Delayed closure

Mechanical integrity is a distinct requirement from adequate nutrition and perfusion.

Slide 32 · Poor perfusion is a major local impediment

Arterial inflow impaired

Peripheral arterial disease / atherosclerosis.

Reduced delivery to injured tissue.

Ischemia may culminate in necrosis.

Venous drainage obstructed

Varicose veins and other venous disorders.

Venous hypertension impairs healing.

Venous ulceration may follow.

Slide 33 · Arterial insufficiency causes ischemic injury

Atherosclerosis of peripheral arteries

Local ischemia, tissue atrophy, and necrosis

Painful arterial ulceration can develop

Slide 34 · Obstructed venous drainage also impairs repair

Chronic venous hypertension

Poor effective oxygen delivery in the ulcer bed

Persistent venous leg ulcer

Slide 35 · Sustained pressure causes ischemic tissue damage

Schematic

Prolonged compression

Reduced local perfusion

Necrosis / pressure sore

Original editable schematic showing compression of tissue against bone, not a clinical photograph.

Slide 36 · Foreign bodies perpetuate inflammation

Retained foreign material

Ongoing chronic inflammatory reaction

Impaired or delayed tissue healing

Slide 37 · The tissue type limits regenerative capacity

Cell population

Examples

Implication for repair

Labile

Surface epithelia; hematopoietic cells

Continuously renewed; regeneration possible

Stable

Most parenchymal tissues

Proliferation possible when stimulated

Permanent

Neurons; cardiac and skeletal muscle

Limited cell replacement; injury often scars

Slide 38 · An intact extracellular scaffold matters

Scaffold preserved

Regenerating cells retain a structural framework.

More complete tissue restoration can occur.

Scaffold destroyed

Normal tissue organization cannot be reconstituted readily.

Repair shifts toward connective-tissue replacement.

Slide 39 · Extent of tissue injury affects the outcome

Schematic

Small, aligned incision

Large tissue defect

Greater need for scar formation

Editable schematic contrasts injury geometry; It does not claim a quantitative threshold.

Slide 40 · Anatomic location changes the repair pathway

Cutaneous defect

Closure, granulation, epithelialization, and scar

Pleural cavity

Exudate may undergo resolution or organization

Peritoneal cavity

Large exudates may organize

Synovial cavity

Repair also depends on exudate clearance

Slide 41 · Resolution removes inflammatory exudate

Inflammatory exudate

Proteolytic digestion

Resorption

Restored architecture

Typically possible in the absence of cell necrosis when the exudate can be cleared.

Slide 42 · Organization converts retained exudate into scar

Large exudate

Granulation tissue ingrowth

Fibrous deposition

Organization

The reparative pathway changes when an exudate is not effectively resolved.

Slide 43 · Resolution and organization differ fundamentally

Resolution

Leukocyte enzymes liquefy exudate.

Resorption removes inflammatory material.

Architecture generally returns if necrosis is absent.

Organization

Granulation tissue grows into retained exudate.

Connective tissue replaces the material.

A fibrous scar remains.

Slide 44 · Chronic wound patterns illustrate failed repair

Venous leg ulcer

Venous hypertension

Arterial ulcer

Ischemia due to arterial disease

Diabetic foot ulcer

Ischemia, neuropathy, and infection

Pressure sore

Pressure-related local ischemia

Slide 45 · Venous leg ulcers reflect venous hypertension

Severe varicose veins or congestive heart failure

Chronic venous hypertension and poor oxygen delivery

Chronic nonhealing leg ulcer

Slide 46 · Why hemosiderin may accompany venous ulcers

Red-cell breakdown

Iron pigment deposition

Hemosiderin

Chronic venous ulcer bed

Hemosiderin and chronic inflammation are described accompanying findings, not diagnostic requirements.

Slide 47 · Arterial ulcers develop from tissue ischemia

Peripheral atherosclerosis

Reduced arterial perfusion

Atrophy and necrosis

Arterial ulcer

That these lesions can be quite painful.

Slide 48 · Diabetic ulcers are multifactorial

Perfusion

Vascular disease causes ischemia

Neural contribution

Neuropathy contributes to ulceration

Microbiology

Secondary infections aggravate the lesion

Morphology

Epithelial ulcer and underlying granulation tissue

Slide 49 · Pressure sores begin with sustained compression

Immobility / pressure

Compressed tissue over bone

Local ischemia

Ulceration and necrosis

This example links mechanical stress to an insufficiency of tissue perfusion.

Slide 50 · Four common chronic ulcers: Causal comparison

Type

Dominant mechanism

Distinctive accompanying feature

Venous

Chronic venous hypertension

Hemosiderin / chronic inflammation

Arterial

Atherosclerotic ischemia

Atrophy, necrosis; often painful

Diabetic

Ischemia + neuropathy + infection

Ulcer with granulation tissue

Pressure

Prolonged compression

Necrosis over bony prominence

Slide 51 · Wound dehiscence is reopening of an incision

Insufficient wound strength and/or stress across incision

Failure of mechanical integrity

Internal or external surgical wound reopening

Slide 52 · Factors increasing dehiscence risk

Nutrition

Malnutrition

Local biology

Infection and vascular insufficiency

Body factors

Obesity

Mechanical loading

Excessive strain or poor apposition

Slide 53 · Coughing and vomiting can trigger abdominal dehiscence

Fresh abdominal incision

Sudden mechanical stress

Wound edge separation

Dehiscence

Robbins specifically names coughing and vomiting as possible precipitating events.

Slide 54 · Healing defects and excessive scarring are opposites

Deficient repair

Chronic ulcers

Weak scar

Dehiscence

Excessive repair

Hypertrophic scar or keloid

Exuberant granulation

Contracture

Excessive scarring is treated briefly here because it is a separate adjacent Robbins teaching topic.

Slide 55 · Case 1 — A pressure-related ulcer

An older immobile patient develops ulceration and necrosis of skin over a bony prominence.

Reason through the mechanisms

What immediate physical factor caused the injury?

What is the key vascular consequence?

Which injury pattern best fits the description?

Slide 56 · Case 1 — Mechanism and answer

Prolonged pressure

Compression against bone

Local ischemia

Pressure sore

Pressure is a mechanical factor; Tissue necrosis is mediated through insufficient local blood flow.

Slide 57 · Case 2 — A persistent diabetic foot ulcer

A patient with diabetes has a chronic foot ulcer with tissue necrosis and signs of secondary infection.

Reason through the mechanisms

List the three major mechanisms emphasized.

Which factor directly reduces oxygen delivery?

Why can inflammation remain prolonged?

Slide 58 · Case 2 — Converging reasons for poor healing

Vascular disease

Ischemia → tissue injury

Neuropathy

Contributes to foot ulceration

Secondary infection

Sustains inflammation and injury

Slide 59 · Case 3 — An incision reopens

After abdominal surgery, a malnourished patient with wound infection develops incision separation after repeated coughing.

Reason through the mechanisms

Name this complication.

Identify the systemic, local, and mechanical risk factors.

Which factors can compromise collagen formation or scar strength?

Slide 60 · Case 3 — Dehiscence has combined causes

Malnutrition + infection

Weakened healing process

Cough-related stress

Wound dehiscence

The clinical outcome depends on both repair biology and mechanical load.

Slide 61 · Case 4 — An inflammatory cavity exudate

Two pleural inflammatory exudates evolve differently: One disappears without residual architectural damage; The other is replaced by fibrous connective tissue.

Reason through the mechanisms

What is the first outcome called?

What is the second outcome called?

What role does the size/persistence of the exudate play?

Slide 62 · Case 4 — Resolution versus organization

Exudate cleared

Proteolytic digestion and resorption

Resolution

Architecture generally restored if no necrosis

Exudate retained

Granulation tissue grows into material

Organization

Fibrous scar forms

Slide 63 · Pattern recognition: Connect factor to mechanism

Finding / exposure

Immediate concern

Repair consequence

Infected wound

Persistent inflammation

Delayed healing

Reduced arterial flow

Ischemic tissue injury

Nonhealing ulcer

Protein / vitamin C deficiency

Reduced collagen synthesis

Delayed repair

Steroid exposure

Reduced TGF-β / fibrosis

Weak scar

Excessive motion

Loss of edge apposition

Separation / dehiscence

Slide 64 · Synthesis: Successful healing needs several conditions

Offending agent controlled

The inflammatory stimulus must abate

Functional perfusion

Tissue must receive adequate blood flow

Capacity to lay down matrix

Nutrition and fibroblast signaling are sufficient

Stable wound geometry

Margins stay apposed without excessive pressure

Slide 65 · Clinical interpretation begins with mechanisms

A chronic wound may reflect more than one modifying factor.

Identify whether the principal problem is inflammation, perfusion, matrix synthesis, or mechanics.

Consider the injury depth, intrinsic regenerative potential, and anatomic site.

Different causal combinations can produce the same outcome: Delayed healing.

Slide 66 · References and scope

Robbins, Cotran & Kumar: Pathologic Basis of Disease. 11th edition (2026). Chapter 3: Inflammation and Repair; pp. 94–99.

Primary topic: Factors That Influence Tissue Repair (pp. 97–98).

Context used: Repair by Scarring, Healing of Skin Wounds, and Defects in Healing: Chronic Wounds (pp. 94–99).

All illustrations in this lecture are editable conceptual schematics, not actual histologic or clinical specimens.