Learning Objective
Understand the causes of ischemia and identify the organs and specific regions most vulnerable to hypoxic-ischemic injury.
Ischemia
Ischemia refers to an inadequate blood supply that fails to meet the tissue’s metabolic demands.
Major mechanisms include:
- ↓ Arterial perfusion (eg, atherosclerosis)
- ↓ Venous drainage (eg, testicular torsion, Budd–Chiari syndrome)
- Systemic hypoperfusion (shock)
Ischemia leads to hypoxia, tissue injury, and—if prolonged—infarction.
Regions Most Vulnerable to Ischemia
| Organ | Susceptible Region | Notes |
|---|---|---|
| Brain | ACA/MCA/PCA watershed zones
Specific neurons: Purkinje cells (cerebellum), pyramidal cells (hippocampus, neocortex layers 3, 5, 6) |
Highly vulnerable during systemic hypoperfusion (watershed infarcts)
Most sensitive to hypoxic-ischemic injury |
| Heart | Subendocardium of the left ventricle | Area with the highest oxygen demand; first to infarct |
| Kidney | The straight segment of the proximal tubule (medulla) and the thick ascending limb | High metabolic activity, low oxygen reserve |
| Liver | Zone III (around the central vein) | Farthest from the hepatic artery and portal vein, most hypoxia-prone |
| Colon | Splenic flexure (Griffith point) and rectosigmoid junction (Sudeck point) | Classic watershed areas |
Activity
Key Concepts
- Watershed areas are located at the most distal branches of two arterial supplies.
They have limited collateral circulation and are highly susceptible to ischemia during hypotension or shock. - Neuronal vulnerability:
The brain’s Purkinje cells and hippocampal pyramidal cells are among the most oxygen-sensitive cells in the body.
