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Difficulty: MediumCellular Injury and Adaptation

An 81-year-old male with persistent atrial fibrillation and nonadherence to anticoagulation therapy arrives at the emergency department. He reports severe, generalized abdominal pain that began abruptly two hours ago. On physical examination, the patient exhibits minimal abdominal tenderness despite his severe subjective pain. His pulse is 115/min and irregularly irregular. A CT angiogram demonstrates a large thromboembolus occluding the proximal superior mesenteric artery. The patient is prepped for emergency laparotomy to resect the affected bowel segment. Arrange the following subcellular biochemical events in the correct chronological order, representing the progressive ischemic injury occurring within the affected intestinal epithelial cells.

  1. 1Depletion of intracellular adenosine triphosphate (ATP) stores
  2. 2Dysfunction of the sodium-potassium ATPase pump
  3. 3Osmotic influx of water and rough endoplasmic reticulum dilation
  4. 4Severe disruption of plasma and lysosomal membranes
  5. 5Enzymatic degradation of cellular components by activated hydrolases

Answer

The sequence begins with ATP depletion due to anoxia, followed by failure of the Na+/K+ pump. This failure causes an osmotic influx of water and subsequent organelle swelling. Continued ischemia leads to irreversible membrane damage, and finally, enzymatic degradation of the cell by liberated lysosomal enzymes.
The correct sequence begins with the immediate consequence of hypoxia (ATP depletion), leading to the failure of energy-dependent ion pumps. This allows sodium and water to enter the cell, causing reversible cellular swelling. Prolonged ischemia eventually causes irreversible membrane damage, followed by necrosis and enzymatic degradation.

Step-by-Step Solution

1
Identify the initiating biochemical consequence of the vascular occlusion.
Loss of oxygen leads to cessation of oxidative phosphorylation and rapid depletion of intracellular ATP.
Tissues reliant on aerobic metabolism cannot produce sufficient ATP when deprived of a blood supply.
2
Determine the immediate downstream effect of ATP loss.
Failure of the ATP-dependent membrane pumps, primarily the sodium-potassium ATPase.
The Na+/K+ ATPase requires constant ATP hydrolysis to maintain the electrochemical gradient across the cell membrane.
3
Trace the osmotic consequences of pump failure.
Intracellular accumulation of sodium causes an osmotic influx of water, leading to cellular swelling and rough endoplasmic reticulum dilation.
Water passively follows the abnormal accumulation of intracellular sodium ions.
4
Identify the transition point from reversible to irreversible cellular injury.
Severe disruption of the plasma and lysosomal membranes.
Prolonged energy failure and massive calcium influx destroy membrane integrity, which is the defining hallmark of irreversible cell death.
5
Determine the final stage of cellular necrosis.
Enzymatic degradation of cellular components.
Ruptured lysosomes release acid hydrolases into the cytosol, digesting the dead cell in the process of coagulative necrosis.

Key Concept

The chronological progression of ischemic cellular injury transitions from reversible ATP depletion and cellular swelling to irreversible membrane damage and subsequent enzymatic degradation.
Estimated Time:1m 30s
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Topics

Cellular Injury and Adaptation

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