17. Ischaemia and Infarction Flashcards
What are vessels lined by
endothelial cells
Definition of ischaemia
Reduced blood supply and/or increased tissue requirements BUT no necrosis
How is ischaemia characterized
- insufficiency of O2
- lack of nutrient substrates (blood not getting in)
- inadequate removal of metabolites (blood not getting out)
Susceptibility of tissues to ischaemia
- poor blood supply
- atheromatous blood supply - absence of collateral circulation
- cannot compensate for reduced perfusion - high tissue metabolism
- organs w high metabolic rate and anaerobic metabolism - vulnerable tissues
- watershed areas especially during shock/hypotension
- one main supplying artery
What is acute ischaemia
- also known as acute limb ischaemia
- caused by embolism or thrombosis; thrombosis caused by peripheral vascular disease
- may cause intermittent claudication, angina, acute mesenteric ischaemia
Symptoms of acute limb ischaemia
The 6 ‘P’s
- Pain
- Pallor (pale appearance of the limb)
- Paresthesias (abnormal sensations in the limb)
- Perishingly cold
- Pulselessness
- Paralysis
What is chronic ischaemia
- also known as chronic limb threatening ischaemia
- advanced stage of peripheral artery disease
- may cause ischaemic colitis
What is reperfusion injury
restoration of blood flow after ischaemia causing a paradoxical increase in cell injury
Why does reperfusion injury occur
- formation of free radicals following the restoration of O2 supplied to cells
- failure of calcium-ATP pumps to control level of cytosolic calcium and accumulation in mitochondria
- calcium excess cause loss of cell integrity and cell death
Treatment of reperfusion injury
calcium channel blockers
-slow re-entry of calcium into cells
What is infarction
Area of ischaemic necrosis caused by occlusion of arterial supply or venous drainage
Define necrosis
Cell death in living tissue, caused by loss of membrane integrity, intracellular organ swelling and ATP depletion leading to an influx of calcium.
-always pathological
Common clinical illness due to infarction
- myocardial infarction
- cerebrovascular infarction
- pulmonary infarction
- bowel infarction
- ischaemic necrosis of the extremities
Causes of ischaemia and infarction reduced blood supply
- Shock
-hypotension
-septic
-cardiogenic
[check Yr1Sem1 lecture] - Obstruction of blood vessel
-atherosclerosis
-thrombosis
-embolus
Why myocardial ischaemia can develop into myocardial infarction
myocardial ischemia happens if blood supply to the myocardium does not meet the demand. If this imbalance persists, it triggers a cascade of cellular, inflammatory and biochemical events, leading eventually to the irreversible death of heart muscle cells, resulting in MI
Definition of thrombosis
Solid mass in flowing blood
Definition of emboli
Solid, liquid or gaseous mass that moves from one part of the circulation to another
Causes of thrombi
Virchow’s Triad
- Endothelial damage
- Stasis
- Hypercoagulability
Macroscopic appearances of infarct
- Wedge-shaped
- Early
- poorly defined, irregular
- narrow rim of hyperaemia at the edge due to inflammation/repair - Late
- solid organ: white; few RBC lysed-some haemosiderin pigment; pale and sharply defined
- e.g. Spleen, Heart, Kidney
- spongy organ: red; haemorrhagic-lots of haemosiderin pigment; firm and brown
- e.g. Vein occlusion, Dual blood supply, Testis, Lungs
Microscopic appearances of infarct
May be little in the first 12-18 hours, only haemorrhage
-necrotic tissue stimulates inflammatory response at the edge for 1-2 days
-phagocytosis of cellular debris and dead tissue
-reparative phase with scar formation
N.B. Brain exception - liquidified necrosis
