Pathophysiology of Ischaemia and Infarction

Question 1

Define ischaemia and hypoxia

Answer 1

Relative lack of blood supply (ischaemia) leading to inadequate O2 supply to meet needs of tissue/organ. (hypoxia)

Question 2

Describe the four abnormal states that cause hypoxia

Answer 2

1. Hypoxic:
   a) Low inspired O2 level
   b) Normal inspired O2 but low PaO2
2. Anaemic: abnormal blood
3. Stagnant: abnormal delivery
   a) local e.g. occlusion
   b) systemic e.g. shock
4. Cytotoxic: abnormal tissue

Question 3

Define infarction

Answer 3

Ischaemic necrosis within a tissue/organ of a living body due to occlusion of either the arterial supply or venous drainage.

Question 4

Describe the process of infarction

Answer 4

Coronary arterial obstruction –> decrease in blood flow to region of myocardium –> ischaemia, rapid myocardial dysfunction –> (anaerobic metabolism –> cell death –> liberation of enzymes –> breakdown of cells –>) myocyte death

Question 5

Understand the difference between subendocardial and transmural MI and their clinical significance

Answer 5

• Subendocardial: ischaemic necrosis mostly limited to a zone of myocardium under the endocardial lining of the heart
• Transmural: ischaemic necrosis affects full thickness of the myocardium

Question 6

List the effects of infarction

Answer 6

• Site dependent: within body and organ
• Size of infarct
• Death, dysfunction (pain)
• Contribution of previous disease/infarction

Question 7

Know the detailed reparative process involved in MU

Answer 7

4-12 hours;

• Early ongoing necrosis
• Oedema
• Haemorrhage

12-24 hours;

• Ongoing coagulation necrosis
• Myocyte changes
• Early neutrophilic infiltrate

1-3 days;

• Coagulation necrosis
• Loss of nuclei and striations
• Brisk neutrophilic infiltrate

3-7 days;

• Disintegration of dead myofibres
• Dying neutrophils
• Early phagocytosis

7-10 days;

• Well-developed phagocytosis
• Granulation tissue at margins

10-14 days;
- Well established granulation tissue with new blood vessels and collagen deposition

2-8 weeks;

• Increased collagen deposition
• Decreased cellularity

> 2 months;
- Dense collagenous scar

Question 8

Know the quick reparative process involved in MU

Answer 8

• Cell death
• Acute inflammation
• Macrophage phagocytosis of dead cells
• Granulation tissue
• Collagen deposition (fibrosis)
• Scar formation