4. Tissue Injury & Repair

Question 1

Introduction

Answer 1

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

Question 2

Cellular Adaptation (1)

Answer 2

Increased demand/stimulation = hypertrophy, hyperplasia

Question 3

Cellular Adaptation (2)

Answer 3

Decreased nutrients/stimulation = atrophy

Question 4

Cellular Adaptation (3)

Answer 4

Chronic irritation = metaplasia

Question 5

Cellular Injury

Answer 5

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

Question 6

Causes of Cellular Injury

Answer 6

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

Question 7

Mechanisms of Cellular Injury

Answer 7

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

Question 8

Tissue Regeneration & Repair

Answer 8

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

Question 9

Mechanisms of Regeneration

Answer 9

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)

Question 10

Healing by Repair, Scarring, Fibrosis

Answer 10

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

Question 11

Sequence of Healing

Answer 11

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

Question 12

Factors Affecting Wound Healing

Answer 12

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)

Question 13

Complications of Repair

Answer 13

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