14 Ischaemia infarction and shock

Question 1

Differentiate between hypoxia and ischaemia.

Answer 1

Hypoxia: any state of reduced tissue oxygen availability.
Ischaemia: pathological reduction in blood flow to tissues.

Question 2

Why is reperfusion of non-infarcted but ischaemic tissues sometimes bad?

Answer 2

May cause repercussion injury. Inflammatory cells generate reactive oxygen species causing further cell damage.

Question 3

What causes infarction?

Answer 3

Thrombosis, embolus.
Vasospasm, extrinsic compression, vessel root twisting, vascular supply rupture.
Venous occlusion.

Question 4

Differentiate between red and white infarction.

Answer 4

Red: dual blood supply (lungs).
White: single blood supply (heart).

Question 5

What shape are infarcts?

Answer 5

Wedge shaped.

Question 6

What are the histological features of infarction?

Answer 6

Coagulative necrosis.

If brain = colliquative.

Question 7

What factors influence the degree of ischaemic damage?

Answer 7

Nature of blood supply.
Rate of occlusion - collaterals.
Tissue vulnerability to hypoxia (brain:4mins, heart:30mins).
Blood oxygen content.

Question 8

Which organs are particularly vulnerable to ischaemic damage?

Answer 8

Single supply: kidney, spleen, testis.

Question 9

What causes gas gangrene?

Answer 9

A gas producing organism e.g. clostridium perfringens.

Question 10

What are the cellular effects of shock?

Answer 10

Membrane ion pump dysfunction.
Intracellular swelling.
Intracellular content leakage.
pH dysregulation.
Lactic acid production.

Question 11

What are the systemic effects of shock?

Answer 11

Serum pH changes.
Vascular leakage.
Stimulation of inflammatory cascades.
End-organ damage.

Question 12

What are the classifications of shock?

Answer 12

Hypovolaemic.
Cardiogenic.
Distributive: anaphylactic, septic, TSS, neurogenic.

Question 13

What are the causes of hypovolaemic shock?

Answer 13

Haemorrhage.

Non-hemorrhagic: D+V, heat stroke, burns, third spacing (acute loss of fluid into internal body cavities).

Question 14

What are the categories of cardiogenic shock?

Answer 14

Myopathic (heart muscle failure).
Arrhythmia-related.
Mechanical (valvular/septal defects).
Extra-cardiac (obstruction to blood outflow).

Question 15

What are the causes of extra-cardiac cardiogenic shock?

Answer 15

Massive PE.
Tension pneumothorax.
Severe constrictive pericarditis.
Pericardial tamponade.

Question 16

How does septic shock occur?

Answer 16

Increased cytokines/mediators cause vasodilation.

DIC causes ischaemia.

Question 17

How does neurogenic shock occur?

Answer 17

Spinal injury/ anaesthetic accidents causing loss of sympathetic vascular tone and systemic vasodilation.

Question 18

What is toxic shock syndrome?

Answer 18

S. aureus / S. pyogenies produce exotoxins which do not require processing by antigen presenting cells. 
Non specific binding of class II MHC to T cell receptors. 
20% T cells activated with massive cytokine release.