Download - Cerebral circulation
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Most vital organ
Containing center for circulation ,
respiration and most other bodily
functions
Needs continues blood supply
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Highly sensitive to hypoxia
Uses glucose as main fuel
Metabolic requirements are fairly
constant irrespective of needs
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Cerebral arteries are end arteries
Volume of blood , ecf , csf remains fairly
constant
Capillaries in brain are mostly non-
fenestrated
Capillaries are surrounded by foot
process of astrocytes
Forming blood brain barrier
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BBB allows selective permeability of
substances
Not well developed in infants
Narrow tight junctions
Thick basement membrane
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Receives blood from two major sources
1. Vertebro-basilar system
2. Internal carotid arteries
Both systems unite to form circle of willis
Which give rise to three pairs of major
vessels
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Anterior cerebral arteries
Middle cerebral arteries
Posterior cerebral arteries
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Deep veins
Dural venous sinuses
Draining into internal jugular vein
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750ml per min
Wt of brain is 1400g
54ml/100g tissue /min
3.3ml of O2/100g/min
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Kety method
By using radioactive subs
› Single photon emission tomography (SPECT)
› Positron emission tomography (PET)
Mri
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Uses ficks principle
Subject is made to brath 15% mix of N2O
and air for 10 min
Blood samples are taken every min from
IJV and peripheral artery
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CBF = N2o taken by brain tissue /min
AV diff of N2o concentration
Disadvantages › Average value and no information about
regional circulation
› Cannot be used in changing BP
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Perfusion pressure determines CBF
MAP at the level of head – JVP
Metabolic
Autoregulation
Role of intracranial pressure
Nervous regulation
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Carbon dioxide – most potent
vasodialator
I mm raise in Pco2 raises CBF by 3ml/100g
tissue
1 mm decrease will reduce CBF by 1.5 ml
Effect of pco2 is mediated by H+ ions in
csf
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Hypoxia – vasodialtion
Hyperbaric oxygen
K+ ions causes vaodilatation
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BP of 60 – 140 mm/hg
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Monro-kellie doctrine – brain tissue , csf ,
blood in vessels are in equilibrium inside
rigid cranial cavity
Positive G , Negative G
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Raised ICP
Vasocontriction
Bradycardia
Inceased BP
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Fainting or transient LOC due to
temporary loss of blood supply to brain
Cardiogenic
Non- cardiogenic
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