Cerebral Ischaemia and stroke Flashcards

1
Q

describe the brain blood supply

A

two pairs of arteries supply blood to the brain : vertebral arteries (back) and carotid arteries (front) to form the ring of arteries - circle of willis

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2
Q

which part of the brain does basilar artery supplies

A

both spinal cord and brain stem

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3
Q

which part of the brain does anterior cerebral artery supplies

A

medial surface of frontal and parietal lobes

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4
Q

which part of the brain does middle cerebral artery supplies

A

supplies most of the lateral surface of the brain as well as deep structures, such as the basal ganglia and the internal capsule.

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5
Q

which part of the brain does posterior cerebral artery supplies

A

supply the medial surfaces of the occipital (medial wall) and temporal (inferior) lobes as well as the thalamus deep in the forebrain.

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6
Q

what does stroke leads to

A

hemiplegia (paralysis on one side), balance problems, loss of sensations, loss of visual field, language

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7
Q

what are the two types of stroke

A

ischemic and haemorrhagic

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8
Q

what are the two types of ischemic stroke

A

focal ischemia which is confined to a specific region and global ischemia which encompasses the whole brain tissue which is normally caused by cardiac arrest

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9
Q

what does focal brain ischemia degree of damage depends on

A

the extent and duration of occlusion and blood supply from other vessels

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10
Q

what causes focal brain ischemia

A

thrombosis forming a platelet plug and embolism which is a blood clot

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11
Q

what is the core in ischemia

A

the part of tissue that undergoes irreversible damage

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12
Q

what is the infarct in ischemia

A

dead tissues, made from neuron and glial cells suffered from necrotic cell death

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13
Q

what is the penumbra in ischemia

A

area around the dead tissue, not severe enough to cause irreversible damage as collateral arteries supply it with oxygen and glucose

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14
Q

What do doctors target therapeutic interventions for ischemia?

A

target penumbra to preserve tissue from cell death

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15
Q

what might cause transient ischaemic attack

A

high blood pressure, cigarette, heart disease, diabetes

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16
Q

what are the two types of haemorrhagic stroke

A

intracerebral and subarachnoid

17
Q

what is the difference between intracerebral and subarachnoid ischaemia

A

intracerebral burst inside the brain and leaks into surrounding brain tissue while subarachnoid bleeds between the brain and tissue covering the brain known as subarachnoid space

18
Q

what causes intracerebral and subarachnoid ischaemia

A

intracerebral is caused by aneurysm (sac-like malformation protruding from vessel wall) and subarachnoid is caused by high blood pressure and aging blood vessels

19
Q

what may subarachnoid further cause

A

lack of blood, plus compression by the blood leaked out into the tissue
§ forming a solid clot, which also causes secondary inflammation and toxicity

20
Q

what happens when stroke occurred in anterior cerebral artery

A
  • Paralysis of contralateral leg, arm, face
  • Disturbance of intellect, executive function and judgement; diminished motivation (abulia)
  • Loss of appropriate social behaviour
21
Q

what happens when stroke occurred in middle cerebral artery

A
  • “Classic stroke”: it is the most common site of occlusion.
  • Contralateral hemiplegia (i.e. paralysis of one side of the body): arm > leg
  • Contralateral sensory deficits
  • Hemianopia (i.e. blindness over half the field of vision)
  • Aphasia (i.e. impairment of language)
22
Q

what happens when stroke occurred in posterior cerebral artery

A

Visual deficits
• homonymous hemianopia (i.e. visual field loss on the left or right side of the vertical midline).
• visual agnosia (i.e. a condition in which a person can see but cannot recognize or interpret visual information).

23
Q

which neurons are vulnerable to global ischaemia

A
  • The pyramidal cells of the area CA1 of the hippocampus
    * The pyramidal neurons of the neocortex (layers 3, 5 and 6)
    * The Purkinje cells of the cerebellum
    * The neurons in the striatum
24
Q

Why does the brain require energy ?

A

to maintain transmembrane ion gradients and to restore them after each action potential

25
Q

why do we need continuous glucose supply

A

brain cannot store, synthesize or utilize any other source of energy

26
Q

what happens to to reduced glucose delivery to brain

A

individuals sugar levels drop and individual appears disorientated, slurred speech or impaired motor function

27
Q

what happen when there is a reduction supply of oxygen

A

anoxia - completely starved of oxygen and ischaemia

28
Q

how do cells die

A

necrosis (passive) in ischaemic core and apoptosis delayed death in penumbra

29
Q

Describe the necrosis mechanism

A
  1. Ischaemia causes the fall of ATP levels below the levels needed for the Na+-K+-ATPase to maintain ion gradients.
  2. Depolarisation causes opening of Ca2+channels.
  3. Increased intracellular Ca2+causes glutamate release from synaptic vesicles and extracellularly.
  4. Activation of glutamate receptors - NMDA and AMPA allows influx of calcium in the postsynaptic neuron.
  5. Excessive calcium accumulation in mitochondria causes dysfunction.
  6. Damaged mitochondria produce free oxygen radicals which damage cell structures. Free radicals are generated also by the inflammatory process.
  7. Calcium activates a number of enzymes (lipases, proteases) that contribute to the breakdown of the cell components.
30
Q

what is the difference between extrinsic and intrinsic apoptosis

A

extrinsic is initiated by binding of a death ligand to cell surface receptor while intrinsic started by stress within the cell

31
Q

Similarity between two apoptosis pathway

A

both requires activation of a sequence of signals, including caspases which induce release of further protein eg. cytochrome c

32
Q

what changes does apoptotic cell undergo

A

cell shrinkage, chromatin condensation, breakdown of nucleus, cleavage of DNA and blebbing of plasma memrbane and fragmentation of cell into small vesicles

33
Q

how are dead cells engulfed by microglia

A
  • lipid phosphatidylserine on the inner leaflet surface of the plasma membrane
    * redistributed during apoptosis to the extracellular surface, and acts as a “eat me” signal for microglia
34
Q

Treatment for stroke

A

thrombolytic agent -tPA to dissolve the clot and restore blood flow but only small fraction of patients are eligible, remove clot surgically, preventions

35
Q

Explain key differences between focal and global ischemic stroke

A
  • Focal ischemia occurs when a blood clot or other material (embolus) has occluded a cerebral vessel
    • Global brain ischemia occurs when blood flow to the whole brain is halted or drastically reduced. This is commonly caused by cardiac arrest
    • Focal brain ischemia reduces blood flow to a specific brain region, causing cell death. It can be caused by either a platelet plug that forms in the vessel itself (thrombosis), or by a blood clot or other material (such as a fat globule or an air bubble) originated elsewhere (embolism).
    • The part of the tissue that undergoes irreversible damage during an ischemic stroke is termed the ischemic core.
    • The area around it, termed penumbra (“almost shadow” in Latin) still suffers a reduction in blood flow but not severe enough to cause irreversible damage, thanks to sufficient flow from surrounding vessels (“collateral flow”) to keep it alive for some time