The Brain Part 2: Blood Brain Supply & CVA Flashcards
what does the common carotid artery divide into
- internal carotid arteries
- external carotid arteries
what does the internal carotid arteries divide into
- anterior cerebral artery
- middle cerebral artery
- posterior cerebral artery
describe the vertebral artery + what it divides into
ascends in the neck through openings of cervical vertebrae
divides into:
- cerebellar arteries
- posterior cerebral arteries
Describe the circle of willis
Branches of internal carotid arteries + basilar artery join to form the circle
blood is then distributed around the brain
describe venous drainage
venous sinuses in the dura mater
- sinuses converge at back of skull
- sigmoid sinus on each side - to the internal jugular vein
list the substances that move freely through the blood brain barrier
- blood
- gases
- water
- alcohol
- anaesthetics
list the substances that do not move freely through the blood brain barrier
- antibiotics
- other drugs
- glucose
- amino acids (these 2 require carrier proteins to move across)
describe the anatomy of the blood brain barrier
lipid nature = water soluble to molecules acting as barrier
- tight junctions seal the pathway
- efflux pumps extrude fat soluble molecules
list the components of intracranial pressure within the skull
Brain - 80%
Blood - 12%
CSF - 8%
how is cerebral blood flow maintained
- arterioles dilate to increase flow if BP drops
- arterioles constrict if BP constrict
what happens when there is > co2 in cerebral Blood flow
= vasodilation to > flow + carry it away
cerebrovascular accident
CVA
tissue which has died because blood supply has failed = infarct
Describe the features of Transient Ischaemic Attack (TIA)
- mini stroke
- spontaneous blood restore before cell death
- symptoms disappear completely within 24 hours
- increases risk of stroke
define thrombosis
obstruction of blood vessel by a clot
define embolism
obstruction due to clot from elsewhere in the body
how does an occlusive “ischaemic” stroke occur
- thrombosis
or - embolism
describe the process petechial bleeding
when blood flows through damaged vessels
- depolarisation of neurone
- influx of calcium
- release of neurotransmitters
- further depolarisation + calcium influx
what are the 2 major zones of injury within ischaemic tissue
- Core Ischaemic tissue
2. Ischaemic penumbra
Define Ischaemic Penumbra
a rim of mild to moderate ischaemic tissue between tissue that is normally perfused + an area of severe ischaemia. Brain cells remain viable for 7 hours.
describe penumbral blood supply
collateral arteries connecting with branches of occluded vessels
- this is where pharmacological interventions are most likely to work
define necrosis
severe ischaemia where neurones + glial cells die
- tissues replaced by CSF
List the 2 different types of Oedema
- Cytotoxic (cellular)
2. Vasogenic Oedema
describe cytotoxic oedema
- swelling of all cellular elements of the affected area
- cells sweep within minutes
describe vasogenic oedema
an increase in ISF due to increased permeability which is a local inflammatory response following damage which takes between hours and days
define herniation
when an increase in pressure inside the skull causes a displace of brain tissue
where does herniation occur through
occipital foramen or within skull
how does herniation cause death
due to compression of blood vessels + structures such as respiratory centres of the brain stem
where does bleeding occur within the hemorrhagic stroke
bleeding may occur
- within brain
- within surrounding meningeal spaces
describe the presenting features of a hemorrhagic stroke
- nausea
- vomitting
- headache
if haematoma absorbs; surrounding tissue regains most function
where does an intracerebral haemorrhage occur
- basal ganglia
- thalamus
- cerebellum
- pons
- brainstem
(deep structures)
factors which contribute to intracerebral haemorrhage
- compression
- increase in ICP = herniation
- blood in subarachnoid space
describe subarachnoid haemorrhage
“berry” aneurysm ruptures + blood goes into subarachnoid space
list the presentation of acute stroke
- alteration in consciousness
- headache
- aphasia
- facial weakness
- paralysis
- ataxia (poor balance)
- visual loss
- vertigo, double vision, vomitting
list the 3 mechanisms of head injury
- primary
- secondary
- tertiary
describe a primary head injury
caused by impact
describe what causes a secondary head injury
- cerebral oedema
- haematoma
- infection
- increased ICP
describe what causes a tertiary head injury
- hypotension
- respiratory + cardiovascular effects of primary and secondary injuries
list the effects of increasing ICP and what part of the brain means is affected
- consciousness = brainstem/cerebral cortex
- headache = meninges
- vomiting = pressure on emetic centre in medulla
list the clinical management of head injuries
- induced coma
- oxygen
- steroids
- diuretics
post traumatic amnesia scale
< 5 minutes = very mild 5-60 min = mild injury 1-24 hours = moderate 1-7 days = severe > 7 days = very severe
