The brain is the most vital organ that requires constant blood supply to function. It has high metabolic needs but maintains constant circulation irrespective of activity. Blood flows to the brain through arteries and drains through veins and sinuses. The blood brain barrier selectively regulates substance permeability and protects the brain microenvironment. Cerebral blood flow is tightly regulated by factors like blood pressure, carbon dioxide levels, oxygen levels and intracranial pressure to maintain homeostasis.

2.  Most vital organ
 Containing center for circulation ,
respiration and most other bodily
functions
 Needs continues blood supply

3.  Highly sensitive to hypoxia
 Uses glucose as main fuel
 Metabolic requirements are fairly
constant irrespective of needs

4.  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

6.  BBB allows selective permeability of
substances
 Not well developed in infants
 Narrow tight junctions
 Thick basement membrane

7.  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

8.  Anterior cerebral arteries
 Middle cerebral arteries
 Posterior cerebral arteries

17.  Deep veins
 Dural venous sinuses
 Draining into internal jugular vein

18.  750ml per min
 Wt of brain is 1400g
 54ml/100g tissue /min
 3.3ml of O2/100g/min

19.  Kety method
 By using radioactive subs
› Single photon emission tomography (SPECT)
› Positron emission tomography (PET)
 Mri

20.  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

21.  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

22.  Perfusion pressure determines CBF
 MAP at the level of head – JVP
 Metabolic
 Autoregulation
 Role of intracranial pressure
 Nervous regulation

23.  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

24.  Hypoxia – vasodialtion
 Hyperbaric oxygen
 K+ ions causes vaodilatation

25.  BP of 60 – 140 mm/hg

26.  Monro-kellie doctrine – brain tissue , csf ,
blood in vessels are in equilibrium inside
rigid cranial cavity
 Positive G , Negative G

27.  Raised ICP
 Vasocontriction
 Bradycardia
 Inceased BP

29.  Fainting or transient LOC due to
temporary loss of blood supply to brain
 Cardiogenic
 Non- cardiogenic