General pathology · Hemodynamic disorders
Watershed areas and the organs most sensitive to ischemia !
- Topic
When pressure falls, neurons suffer first, along with the zones at the far end of two arterial territories, called watershed areas.
Updated 2026-11-01
What it is
Not all tissues tolerate lack of oxygen equally. Neurons die after a few minutes of complete anoxia; myocardium in under an hour; fibroblasts survive for hours. In global hypotension, the watershed zones suffer most: regions at the end of two arterial territories, such as the parasagittal strip between the anterior and middle cerebral arteries, the splenic flexure of the colon, or the subendocardium. Knowing these zones explains the pattern of damage after cardiac arrest or shock.
Step by step
- Perfusion pressure falls throughout the body (cardiac arrest, shock).
- Zones at the far end of two arterial territories are left with the lowest pressure.
- Cells with high energy demand run out of ATP first.
- In neurons, released glutamate opens channels and lets calcium in (excitotoxicity).
- Calcium switches on enzymes that destroy membranes and proteins: selective necrosis.
- When flow returns, free radicals can add to the damage (reperfusion injury).
Where global ischemia strikes first
| Organ | Most vulnerable zone | Resulting lesion |
|---|---|---|
| Brain | Watershed zones; hippocampal CA1, Purkinje cells, cortical layers | Watershed infarct, laminar necrosis, amnesia |
| Heart | Subendocardium | Subendocardial infarct |
| Kidney | Straight proximal tubule and thick ascending limb | Acute tubular necrosis |
| Colon | Splenic flexure and rectosigmoid junction | Ischemic colitis |
| Liver | Zone 3 (around the central vein) | Centrilobular necrosis, ischemic hepatitis |
| Newborn brain | Periventricular white matter (preterm); basal ganglia, thalamus and watershed zones (term) | Periventricular leukomalacia, hypoxic-ischemic encephalopathy |
Clinical notes
- After a survived cardiac arrest, amnesia may remain from hippocampal injury.
- Ischemic colitis in older adults often appears at the splenic flexure after a fall in blood pressure.
- In newborns, perinatal asphyxia causes hypoxic-ischemic encephalopathy; in preterm babies, periventricular leukomalacia is linked to cerebral palsy.
Test yourself
Think of the answer, then tap the question to see it.
Where does the most typical cerebral watershed infarct occur?
In the parasagittal strip over the convexity, between the territories of the anterior and middle cerebral arteries.
Which hippocampal neurons are most sensitive to ischemia?
The pyramidal neurons of the CA1 region (Sommer’s sector).
Why is the subendocardium the most vulnerable layer of the heart?
Because it is the last to receive coronary blood and bears the highest pressure within the wall during systole.
In which segments of the colon is ischemic colitis most common?
At the splenic flexure and the rectosigmoid junction, watershed zones between arterial territories.
Related
- Infarction: red vs white, and what decides the damage
- Shock: types, stages and the organs it damages
- Hypoxia, ischemia and reperfusion injury
- Mechanisms of cell injury: ATP, mitochondria, calcium, membranes and DNA
Related conditions
- Ischaemic stroke
- Perinatal asphyxia and hypoxic-ischaemic encephalopathy
- Ischaemic colitis
- Acute kidney injury
- Myocardial Infarction (Heart Attack)
- Cardiogenic shock
- Hypovolaemic shock
- Acute liver failure
- Cerebral palsy
Elsewhere in DurgiPedia
- Cerebral blood flow, brain metabolism and intracranial pressure
- Coronary circulation and myocardial ischemia
- Renal blood flow, autoregulation and tubuloglomerular feedback
Educational content on the mechanisms of disease; not a diagnostic or treatment guide and no substitute for a health professional's advice. No doses are given.
Sources: Ischemic Stroke (StatPearls (NCBI Bookshelf), 2026); Acute Mesenteric Ischemia (StatPearls (NCBI Bookshelf), 2026); Stroke: MedlinePlus Medical Encyclopedia (MedlinePlus, US National Library of Medicine, 2025).
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Representative model, for educational purposes only.