Blood Supply

Question 1

What are the two main pairs of arteries that supply the brain?

Answer 1

• 1- Internal Carotid - ANTERIOR
  
  • Gives rise to ACA and MCA
• 2- Vertebral or Vertebrobasilar - POSTERIOR
  
  • Gives rise to PCA, SCA, AICA, PICA
  • 2 vertebral arteries join to become basilar artery

Question 2

Circle of Willis

Answer 2

• Anastomotic ring - helps equalize blood flow
• Composed of 5 pairs of arteries
  
  • ACAs, MCAs, PCAs, anterior communicating arteries and posterior communicating arteries

Question 3

What arteries supply the cerebellum?

Answer 3

• All 3 cerebellar arteries
  
  • SCA- anterior cerebellum
  • AICA - middle strip of inferior cerebellum
  • PICA- most of the posterior cerebellum

Question 4

What arteries supply ea part of the brainstem?

Answer 4

• Midbrain - basilar supplies medial wedge; PCA supplies ventrolateral portion; SCA/PCA supply dorsolateral region
• Pons - basilar supplies medial wedge and some lateral pons; SCA supplies dorsal-most part; AICA also supplies lateral pons
• Medulla - PICA and posterior spinal supply lateral area; vertebral and anterior spinal supply medial medulla and olives (including pyramids and 4th ventricle)

Question 5

What 3 arteries supply the cortex? Where does each supply specifically?

Answer 5

• ACA - forms a nose-shaped bend and moves medially —> b/n hemispheres (inter hemispheric fissure) —> emerges on lateral surface and supplies a strip there (medial 2/3 cortex)
• MCA- forms defining loops; moves lateral and passes through Sylvian fissure —> lateral 2/3 cortex (outside)
  
  • If superior L MCA stroke… R arm weakness, R facial weakness (spare forehead b/c upper), Broca’s aphasia (prob w/ speech production)
• PCA- ventral temporal lobe, inferior and middle occipital lobe, medial regions on posterior parietal

Question 6

Watershed Areas

Answer 6

• “Arterial Border Zones”
• ACA-MCA watershed and MCA-PCA watershed
• Anastomoses - so if one blood supply is cut off they may be spared by second blood supply BUT very distal so if systemic/global ischemia to brain then they are the last to get blood so likely die)

Question 7

What arteries supply the basal ganglia?

Answer 7

• ACA - anterior ganglia and anterior internal capsule
• MCA- middle portion of basal ganglia
• PCA- most of the thalamus
• Anterior Choroid Artery - supplies choroid plexus (w/in ventricles)
• Lenticulostriates - come off MCA; small so prone to narrowing w/ hypertension —> small lacunar strokes

Question 8

4 Cellular Components of BBB

Answer 8

• Endothelial Cells - these capillaries lack fenestra (windows); cont sheets of tight junctions
• Astrocytes - wrap around outside of capillaries; cover a large part of capillary surface; maintain integrity and regulate water permeability
• Pericytes -contractile cells (for vasoconstriction); also secrete cytokines, NO, MMPs to affect capillaries and affect tightness of junctions
• Basal lamina - basement membrane - anchor and maintains tight junctions

Question 9

What components can and cannot cross BBB?

Answer 9

• Block polar molecules
• O2, CO2, anesthetic gases and alcohol readily diffuse
• Molecular transporters for glucose, AA and other large molecules