Why Does the Brain Need Blood?
Consumes 15-20% of the body’s total energy needs, (and receives 15%
of Cardiac Output), despite being only 2% of total body mass.
Neurons require high ATP to:
Maintain Ion Gradients across Plasma Membrane
Regulate Neurotransmitter synthesis/re-uptake.
...
,Why Does the Brain Need Blood?
Consumes 15-20% of the body’s total energy needs, (and receives 15%
of Cardiac Output), despite being only 2% of total body mass.
Neurons require high ATP to:
Maintain Ion Gradients across Plasma Membrane
Regulate Neurotransmitter synthesis/re-uptake.
Neurons have NO ANAEROBIC CAPACITY → Therefore the brain
absolutely depends on Oxygenated Blood.
Hence, any deficit in blood supply is detrimental (≈30+sec
lack of blood/O2 to brain → unconscious
Blood Supply to the Brain is an ANASTOMOSIS:
Anastomosis: Where Multiple Arteries Supply the Same
Region of Tissue. Ie: A Dual Blood-Supply.
The Advantage: If one of the arteries becomes
blocked/damaged, the other artery will compensate for it
Arterial Supply of the Brain:
Brain is Supplied by 2 Arterial Systems:
2x Vertebral Arteries → 1x Basilar Artery → Circle of
Willis
2x Internal Carotid Arteries → Circle of Willis
, ‘Circle of Willis’, The Anastomosis of the Brain:
(The ‘Roundabout’ of Arteries on the underside of the Brain with
multiple ‘Roads’ coming off it)
(Encircles the Optic Chiasma, The Pituitary Gland & the
Mammillary Bodies.)
The ‘Roads’: (Anterior → Posterior)
2x Anterior Cerebral Arteries
1x Anterior Communicating Artery
2x Internal Carotid Arteries
2x Middle Cerebral Arteries
2x Posterior Communicating Arteries
2x Posterior Cerebral Arteries
1x Basilar Artery
Note: Communicating Arteries are always patent, but generally not functional
(no blood flow) when blood flow from both Carotids & Basilar Arteries is
normal. However, if blood flow from one of the major arteries is impeded, blood
is shunted through the Communicating Arteries to compensate
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