26. Ischaemia and infarction

Question 1

Define ischaemia and infarction

Answer 1

Ischaemia: inadequate local blood supply to a tissue- inadequate transfer of metabolic substances in and out of tissues.
Infarction: necrosis of a tissue due to ischaemia.

Question 2

What are the possible causes of ischaemia

Answer 2

external occlusion, tumours, internal occlusion: artherosclerosis
Spasm of vessel: frost bite
Capillary blockage, 
Shock : circulatory failure with low map
Increased demand and venous obstruction.

Question 3

Describe the effects of ischaemia at the levels of individual cells

Answer 3

Ischaemia which is not sufficiently severe to kill can change the biology of the cell, reduces the ATP - less oxd phosph, activate signalling cascades, less protein/dna synthesis and repair, cell swelling,

Question 4

Describe the effects of ischaemia at the level of tissue - relative to damage level

Answer 4

1. There is some functional defects due to sub optimal tissue perfusion- renal , heart dysrhythmia 2. insufficiency, adaption, atrophy or shutdown,
2. apoptosis of isolated cells, then 4. infarction : necrosis

Question 5

What are the two different types of infarctions

Answer 5

Red (haemorrhagic) in tissues with dual blood supply- or tissues where blood flow is re-established

White (anaemic) in solid tissues supplied by a single artery

Question 6

What is the timing of a typical infarction- after survival starts with inflammation.

Answer 6

Within 24hrs acute inflammation starts with neutrophils, including. 1-3 days, macrophages and lymphocytes join.
Fibroblasts and endothelial cells are then recruited to form granulation tissue. Then the damage is organised replaced to make a fibrous scar (or regeneration)

Question 7

What are the treatments for myocardial infarction

Answer 7

Thrombolitic agents: eg, streptokinase/ plasminogen activator
- Mechanical re-expansion of oclulded vessel: angioplasty and stenting

Question 8

What is re-perfusion injury? (additional damage to cells due to restoration of blood flow after a LONG period of ischaemia/cell injury not short).

Answer 8

When blood flow is reintroduced damaging Reactive oxygen species are produced in cells and cause oxidative stress.
-they damage unsat fat, aa side chains for enzymes and thymine chains for DNA.

Question 9

What is the complication of myocardial infarction

Answer 9

Heart failure: dead cells reduce contractility
Mural thrombus : injury increases coagulant factors, more turbulence due to uncoordinated, injured endothelial cells leading to embolism via aorta to brain, gut, spleen
Dysrhythmia: uncoordinated contraction