Flashcards in Infarction, Shock Deck (62)
What is meant by hypoxia, and what are the 2 types?
Any state of reduced oxygen availability
Generalised - whole body eg. altitude or anaemia
Localised - specific tissue affected
What is meant by ischaemia?
Pathological reduction in blood flow to tissues, ischaemia results in tissue hypoxia
What is the most common cause of ischaemia?
Usually as a result of obstruction to arterial flow commonly as a result of thrombosis/embolism
What are the consequences of limited compared to prolonged ischaemia?
Limited - cell injury is reversible
Prolonged - irreversible cell damage
-Cell death occurs by necrosis
When would therapeutic tissue reperfusion be used?
Only if the ischaemia is reversible
Why is therapeutic reperfusion not used in infarcted tissues?
Reperfusion of infarcted tissues will have no effect
Why could reperfusion of ischaemic non infarcted tissues be harmful?
Whilst the tissue is hypoxic inflammatory cells produce reactive oxygen species
When the tissue is reperfused these reactive oxygen species can travel around the body and cause damage
What is meant by infarction?
Ischaemic necrosis caused by occlusion of the arterial supply or venous drainage
What is infarct?
An area of infarction in tissues
Other than thrombosis and embolism, name 7 other causes of infarction?
2) Atheroma expansion
3) Extrinsic compression eg. tumour
4) Twisting of vessel roots eg. volvulus
5) Rupture of vascular supply eg. AAA
How can infarction be classified by colour?
White infarction (anaemic)
Single blood supply hence totally cut off
Dual blood supply/venous infarction
Loss of one blood supply, tissue starts to undergo necrosis, damages blood vessels of other supply and blood leaks into tissues
What shape are most infarcts and why?
Obstruction usually occurs at an upstream point, the entire down-stream area will therefore be affected
Infarction is normally what type of necrosis?
Normally coagulative necrosis - maintains tissue structure
Colliquative necrosis occurs in the brain
If a person died suddenly of an MI what would be seen in the tissues?
Nothing as there is no time to develop haemorrhage or inflammatory response
What 4 factors influence the degree of ischaemic damage?
1) Nature of blood supply
2) Rate of occlusion
3) Tissue vulnerability to hypoxia
4) Blood oxygen content
How does the nature of the blood supply influence the degree of ischaemic damage?
- An alternative blood supply will mean less damage hence severe ischeamia is required for infarction
- Tissues with a single blood supply are more vulnerable to infarction
eg. kidneys, spleen, testis
Name 3 tissues with dual blood supply (and those supplies) which are thus less vulnerable to infarction?
1) Lungs (pulmonary and bronchial arteries)
2) Liver (hepatic artery and portal vein)
3) Hand (radial and ulnar artery)`
Why are slow developing occlusions less likely to lead to infarction?
Allows time for the development of alternative collateral perfusion pathways
How does rate of occlusion affect coronary arteries?
- Small anastamoses connect major branches and have minimal flow
- If a coronary arterial branch is slowly occluded flow can be directed through these channels
- Infarction can therefore be avoided even if the main arterial branch is totally occluded
Why is the brain typically very vulnerable to hypoxia?
If a neurone is deprived of O2 irreversible cell damage occurs in 3-4 mins
Brain is 1-2% of total body weight but requires 15% of cardiac output
Therefore very vulnerable to injury
Why is the heart less vulnerable to hypoxia than the brain?
The heart is more resistant with cardiac myocyte death taking 20-30 minutes
How does blood oxygen content affect infarction?
Reduced oxygen supply in the blood (anaemia etc.) increases the chances of infarction
Why does congestive heart failure make people more vulnerable to infarction?
-Poor cardiac output and impaired pulmonary ventilation
-May develop an infarct with a normally inconsequential narrowing of vessels
Name 4 clinical manifestations of infarction?
1) Ischaemic heart disease
2) Cerebrovascular disease
3) Ischaemic bowel
4) Peripheral vascular disease/ gangrene
What is the leading cause of deaths in the west?
Ischaemic heart disease
What are 90% of cases of cardiac ischaemia due to?
Impaired coronary artery flow following complications of atherosclerotic disease
What is the 3rd leading cause of death in the west?
What does cerebrovascular disease refer to?
Any abnormality of the brain caused by a pathological process involving the blood vessels
Includes thrombosis and embolism (ischaemic)
and Bleeding (haemorrhagic)
What is a cerebrovascular accident?