Most vital organ

Containing center for circulation ,

respiration and most other bodily

functions

Needs continues blood supply

Highly sensitive to hypoxia

Uses glucose as main fuel

Metabolic requirements are fairly

constant irrespective of needs

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

BBB allows selective permeability of

substances

Not well developed in infants

Narrow tight junctions

Thick basement membrane

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

Anterior cerebral arteries

Middle cerebral arteries

Posterior cerebral arteries

Deep veins

Dural venous sinuses

Draining into internal jugular vein

750ml per min

Wt of brain is 1400g

54ml/100g tissue /min

3.3ml of O2/100g/min

Kety method

By using radioactive subs

› Single photon emission tomography (SPECT)

› Positron emission tomography (PET)

Mri

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

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

Perfusion pressure determines CBF

MAP at the level of head – JVP

Metabolic

Autoregulation

Role of intracranial pressure

Nervous regulation

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

Hypoxia – vasodialtion

Hyperbaric oxygen

K+ ions causes vaodilatation

BP of 60 – 140 mm/hg

Monro-kellie doctrine – brain tissue , csf ,

blood in vessels are in equilibrium inside

rigid cranial cavity

Positive G , Negative G

Raised ICP

Vasocontriction

Bradycardia

Inceased BP

Fainting or transient LOC due to

temporary loss of blood supply to brain

Cardiogenic

Non- cardiogenic