Stroke

1. 1

   System

   the whole body at work

   • The brain is a high-demand metabolic engine that consumes 20% of your body's oxygen despite being only 2% of its weight.
   • Constant perfusion is maintained by the Circle of Willis, a redundant plumbing system that ensures if one pipe clogs, others can pick up the slack.
   • Autoregulation keeps blood flow steady across a wide range of pressures, ensuring that sodium-potassium pumps have the ATP they need to keep neurons quiet and ready.
2. 2

   Organ

   the healthy sequence, step by step

   • Constant glucose and oxygen delivery via carotid and vertebral arteries
   • Autoregulation of cerebral blood flow via myogenic response
   • ATP-dependent ion pumps maintain cellular resting potential
   • Collateral circulation via the Circle of Willis provides redundancy
3. 3

   Tissue & mechanism

   where and why it breaks

   • The ischemic cascade is the central pathway where a focal occlusion creates two zones: the dead 'core' and the 'penumbra'—tissue that is stunned but not yet dead.
   • Reperfusion is the only way to stop this cascade before the penumbra is swallowed by the core.
   • This is why every intervention is timed to the 'last known well'—we are racing against the exhaustion of cellular energy reserves.
4. 4

   Cell & molecule

   the break at its smallest scale

   • Vessel occlusion (thrombus or embolus) stops downstream flow
   • Ionic gradient collapse leads to massive depolarization
   • Calcium influx triggers proteases and lipases that digest the cell
   • Microvascular inflammation further restricts collateral flow
5. 5

   The result

   what the break produces

   • Abrupt cessation of focal blood flow leading to ATP depletion
   • Failure of Na/K-ATPase pumps causing intracellular sodium accumulation
   • Cytotoxic edema as water follows sodium into the neurons
   • Glutamate excitotoxicity causing neighboring cell death

• The brain is a high-demand metabolic engine that consumes 20% of your body's oxygen despite being only 2% of its weight.
• Constant perfusion is maintained by the Circle of Willis, a redundant plumbing system that ensures if one pipe clogs, others can pick up the slack.
• Autoregulation keeps blood flow steady across a wide range of pressures, ensuring that sodium-potassium pumps have the ATP they need to keep neurons quiet and ready.

• The ischemic cascade is the central pathway where a focal occlusion creates two zones: the dead 'core' and the 'penumbra'—tissue that is stunned but not yet dead.
• Reperfusion is the only way to stop this cascade before the penumbra is swallowed by the core.
• This is why every intervention is timed to the 'last known well'—we are racing against the exhaustion of cellular energy reserves.

• Everything breaks when a vessel is either plugged by a clot or blown open by pressure.
• The first break is the immediate cessation of nutrient delivery, which forces cells into anaerobic metabolism.
• Without ATP, the pumps fail, sodium stays inside the cell, and water follows it, leading to cytotoxic edema and a toxic release of glutamate.

The chain that produces them

1. 1Failure of Na/K-ATPase pumps causing intracellular sodium accumulation
2. 2Cytotoxic edema as water follows sodium into the neurons
3. 3Glutamate excitotoxicity causing neighboring cell death
4. 4Expansion of the ischemic core into the salvageable penumbra

• We aren't drawing labs to diagnose the stroke—the physical exam does that—we draw them to rule out mimics and check if it's safe to intervene.

Uncertainty: The exact 'tissue window' varies by individual collateral circulation, making bedside decision-making for late-window thrombectomy highly patient-specific.