Stroke Flashcards
What is a stroke?
A neurological deficit, of sudden onset, lasting more than 24 hours of vascular origin
What is a Transient ischaemic attack?
Same stroke symptoms but only lasts less than 24 hours
What are the causes of stroke
- Blockage with thrombus or clot
- Disease of vessel wall
- Disturbance of normal properties of blood
- Rupture of vessel wall (haemorrhage)
How many strokes are due to infarction and how many are due to haemorrhage?
85-90% due to infarction
10-15% due to haemorrhage
Describe the difference between a hemorrhagic stroke and an ischaemic stroke
Haemorrhage - blood leaks into brain tissue
Ischaemic - Clot stops blood supply to an area of the brain
What is the most common cause of large artery disease?
Carotid stenosis
What is the most common cause of cardioembolic stroke?
Atrial fibrilation commonest cause
Describe the aetiology of haemorrhagic strokes
60-70% due to hypertension
15-20% due to amyloid
Excess alcohol
Hypocholesterolaemia
Haemorrhagic transformation
Describe the ischaemic cascade in a stroke
- Without adequate blood supply and thus lack of oxygen and glucose, brain cells lose their ability to produce energy (ATP)
- Cells in the affected area switch to anaerobic metabolism which leads to a lesser production of ATP but releases lactic acid
- Lactic acid is an irritant which has the potential to destroy cells by disruption of the normal acid-base balance in the brain
- ATP reliant ion transport pumps fail
- Membrane becomes depolarised
- Influx of calcium and efflux of potassium
What is the effect in the ischaemic cascade in a stroke of the influx of calcium and the efflux of pottasium
- Intracellular calcium levels become too high and trigger the release of glutamate (excitory amino acid neurotransmitter)
- Glutamate stimulates AMPA receptor and calcium permeable NMDA receptors which leads to even more calciumm influx into cells
- Excess calcium entry overexcites cells and activates proteases (enzymes which digest cell proteins), lipases (enzymes which digest cell membranes) and free radicals formed as a result of the ischaemic cascade in a process called excitotoxicity
What is the effect of cell membranes being broken down by phospholipases within a stroke?
- It becomes more permeable and more ions and harmful chemicals enter the cell
- Mitochondria break down, releasing toxins and apoptotic factors into the cell
- Cell undergoes apoptosis
What is the effect of a cell dying via necrosis?
- It releases glutamate and toxic chemicals into the environment around it
- Toxins poison nearby neurons and glutamate can overexcite them
What is the effect of the loss of vascular structural integrity caused by a stroke?
- Breakdown in the protective blood brain barrier
- Contributes to cerebral oedema which can cause secondary prevention of the brain injury
Define ‘ penumbra’
Penumbra” is the term used for the reversibly injured brain tissue around ischemic core
What can prolonged hypoxia cause?
Hypoxia can turn to anoxia (no oxygen)
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