Blood Supply to the Brain

The Brain's Vascular Network

The brain is one of the most energy-demanding organs in our body, requiring a constant and rich supply of oxygen and nutrients. Let's dive into how this remarkable system works!

Major Arteries

1. Internal Carotid Arteries
   • Two main vessels that supply the front and middle portions of the brain
   • Carry about 80% of the brain's blood supply
   • Branch into smaller arteries that feed different brain regions
2. Vertebral Arteries
   • Run through the vertebrae in the neck
   • Join to form the basilar artery
   • Supply the brain stem and back of the brain

The brain receives about 15-20% of the body's total blood supply, despite making up only 2% of body weight!

The Circle of Willis

The Circle of Willis is nature's backup system for brain blood supply. It's a circular connection of arteries that ensures if one blood vessel gets blocked, others can compensate.

Key components include:

• Anterior cerebral arteries
• Middle cerebral arteries
• Posterior cerebral arteries
• Communicating arteries that connect them

Think of the Circle of Willis as a traffic roundabout system - if one road is blocked, traffic can still flow through alternative routes!

Blood-Brain Barrier

While discussing brain blood supply, we can't ignore the blood-brain barrier:

• Acts as a selective filter
• Protects brain tissue from harmful substances
• Allows essential nutrients to pass through

Don't confuse the blood-brain barrier with regular capillary walls - it's much more selective and complex!

Regulation of Blood Flow

The brain has impressive mechanisms to maintain constant blood flow:

1. Autoregulation
   • Maintains steady blood flow despite changes in blood pressure
   • Works between blood pressures of 60-150 mmHg
2. Local Control
   • Blood vessels dilate or constrict based on:
     • Carbon dioxide levels
     • Oxygen levels
     • pH changes

When studying brain blood supply, focus on understanding both the structural components (arteries) and regulatory mechanisms!

Clinical Significance

Understanding brain blood supply is crucial because:

• Interruptions can lead to strokes
• Proper blood flow is essential for cognitive function
• Many neurological conditions involve vascular components
• The carbohydrate storage in the brain is small so glucose must be supplied continuously

If the middle cerebral artery becomes blocked, it can affect:

• Speech
• Movement on one side of the body
• Sensation This demonstrates why multiple blood supply routes are so important!