• Cerebral circulation
• Arterial supply
• 70% via the ICA
• 30% via the vertebrobasilar system
• Venous drainage
• Superficial cerebral veins drain into the rural sinuses which drain into the jugular bulbs
• The pressure in the cerebral veins is 2-4mmHg higher than the ICP.
• CSF
• Produced mainly by Na⁺/K⁺-ATPase and CA from the choroid plexus in the lateral and third ventricles at a rate of 0.4ml/min
• BBB
• Prevents free diffusion of blood-borne substances into the brain parenchymal space
• Due to endothelial cells being tightly linked with junctional complexes that eliminate gaps
• Endothelial cells play a critical role in performing the transport of micro & macro nutrients
• CBF is usually 50ml/100g tissue
• Blood rheoloy
• Reducing Hct to 30% increases CBF but doesn't improve oxygen delivery
• CBF controlled by 4 mechanisms
• Autoregulation
• Keeps CBF constant with MAP ~ 60-150 due to a combination of myogenic (most effective at high CPP) and metabolic (most effective at low CPP). There is also some neurogenic control of autoregulation
• Can be impaired by disease processes
• Chemical control
• Under the influence of pCO₂ & pO₂. CBF increases 30%/kPa up to pCO₂ of 10.6 and little reduction below 3.5kPa. The CBF increases markedly with pO₂ <7.5
• Metabolic
• Changes in CMR will cause changes in CBF eg pyrexia, convulsions, analeptics.
• Neurogenic
• Sympathetic fibres cause vasoconstriction, and originate in the superior cervical ganglion. Parasympathetic fibres cause vasodilatation originate from the sphenopalatine ganglion.
• SNS protects the CBF and bbb during hypertension and hypoxaemia.
• CEACCP
  Link:ceaccp.oxfordjournals.org/content/1/3/67.full.pdf