4. Tissue Injury & Repair Flashcards Preview

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Flashcards in 4. Tissue Injury & Repair Deck (13)
1

Introduction

Homeostasis
Injury
Excessive physiologic stresses or adverse pathologic stimuli 
Adaptation
Reversible injury
Irreversible injury + cell death

2

Cellular Adaptation (1)

Increased demand/stimulation = hypertrophy, hyperplasia

3

Cellular Adaptation (2)

Decreased nutrients/stimulation = atrophy

4

Cellular Adaptation (3)

Chronic irritation = metaplasia

5

Cellular Injury

Acute and transient stimuli
e.g. hypoxia, chemical injury, microbial infection
 Reversible injury
 Irreversible injury  cell death
Apoptosis
Necrosis

6

Causes of Cellular Injury

Hypoxia
Physical agents
Chemical agents
Infectious agents
Immunologic reactions
Genetic derangements
Nutritional imbalances

7

Mechanisms of Cellular Injury

ATP depletion
Mitochondrial damage
Increased intracellular Ca2+
Oxidative stress
Membrane damage
DNA and protein damage

8

Tissue Regeneration & Repair

Regeneration: complete reconstitution
Tissues with high proliferative capacity
Requires viable stem cells and intact connective tissue scaffolding
Repair: combination of regeneration and scar formation
Relative contribution of two processes depends on capacity to regenerate, extent of injury, and extent of scarring/fibrosis

9

Mechanisms of Regeneration

Amphibians versus Mammals

Limited examples of true regeneration
Epithelium following superficial skin injury
Bone following fracture

Mostly compensatory
Hypertrophy (e.g. nephrons following nephrectomy)
Hyperplasia (e.g. hepatocytes following partial hepatectomy)

10

Healing by Repair, Scarring, Fibrosis

Severe tissue injury with damage to parenchyma and stroma

Fibro-proliferative response
Deposition of collagen and ECM components (scar)
“Patches” tissue

Persistent damage  chronic inflammation  fibrosis

11

Sequence of Healing

Inflammation
Angiogenesis/Neovascularization
Migration and proliferation of parenchymal cells and fibroblasts
Scar formation
Connective tissue remodeling

12

Factors Affecting Wound Healing

Local Factors
Size
Location (i.e. how well vascularised)
Type (infectious/necrotic/traumatic)
Infections, mechanical forces, foreign bodies delay healing

Systemic Factors
Nutritional status
Metabolic status (e.g. diabetes mellitus)
Circulatory/vascular status
Hormones (e.g. glucocorticoids)

13

Complications of Repair

Deficient scar formation
Excessive repair
Excessive granulation tissue (proud flesh)
Excessive collagen accumulation  hypertrophic scar
Keloid
Formation of contractures