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Difficulty: HardCellular Injury and Adaptation

A 54-year-old man with a history of severe alcohol use disorder is brought to the emergency department due to the sudden onset of excruciating, band-like epigastric pain radiating to his back. He reports multiple episodes of nonbilious vomiting over the past 12 hours. On arrival, his temperature is 38.4°C (101.1°F), blood pressure is 92/58 mmHg, and heart rate is 122/min. Physical examination reveals scleral icterus and significant epigastric tenderness with involuntary guarding. Ecchymoses are noted around the umbilicus. Laboratory studies are as follows:

White blood cell count: 19,500/mm³
Total bilirubin: 3.2 mg/dL
Aspartate aminotransferase (AST): 310 U/L
Alanine aminotransferase (ALT): 145 U/L
Alkaline phosphatase: 210 U/L
Lipase: 4,800 U/L (normal: 10-140 U/L)
Total calcium: 6.8 mg/dL (normal: 8.4-10.2 mg/dL)
Albumin: 3.4 g/dL (normal: 3.5-5.0 g/dL)
Prothrombin time: 15 seconds (normal: 11-13 seconds)

An abdominal CT scan demonstrates diffuse pancreatic enlargement with indistinct margins and extensive peripancreatic fluid collections. Which of the following pathophysiological mechanisms is the primary cause of this patient's hypocalcemia?

  1. A
    Widespread activation of the coagulation cascade leading to microvascular thrombosis and secondary calcium consumption
  2. B
    Decrease in the inactive, protein-bound fraction of serum calcium secondary to acute-phase hypoalbuminemia
  3. C
    Massive intracellular calcium influx secondary to failure of ATP-dependent pumps in ischemically injured acinar cells
  4. Enzymatic degradation of triglycerides by released lipases and subsequent precipitation of free fatty acids with calciumAnswer
  5. E
    Rapid induction of parathyroid gland apoptosis mediated by massive systemic release of inflammatory cytokines

Answer

Enzymatic degradation of triglycerides by released lipases and subsequent precipitation of free fatty acids with calcium
The correct answer accurately describes enzymatic fat necrosis, a hallmark of acute pancreatitis. Pancreatic lipases released from damaged acinar cells degrade triglycerides in peripancreatic adipose tissue into free fatty acids. These negatively charged free fatty acids bind to positively charged calcium ions in the serum, forming insoluble calcium soaps in a process known as saponification. This massive sequestration of calcium in the retroperitoneum leads to true, profound systemic hypocalcemia, which is a marker of severe disease and poor prognosis.

Step-by-Step Solution

1
Diagnose the patient's primary condition based on the clinical presentation and laboratory findings.
The patient has severe acute pancreatitis, evidenced by severe epigastric pain, highly elevated lipase, and periumbilical ecchymosis (Cullen sign).
Establishing the primary diagnosis is necessary to understand the subsequent systemic complications.
2
Identify the specific type of cellular injury associated with acute pancreatitis.
Acute pancreatitis is characterized by enzymatic fat necrosis of the peripancreatic adipose tissue.
Pancreatic acinar cell injury releases active lipases and proteases into the surrounding tissue.
3
Determine the biochemical consequence of enzymatic fat necrosis.
Lipases cleave triglycerides into free fatty acids, which then undergo saponification by binding to circulating calcium ions.
This precipitation of calcium into insoluble soaps physically removes calcium from the serum, explaining the profound true hypocalcemia (6.8 mg/dL) seen in this patient.

Key Concept

Saponification in Enzymatic Fat Necrosis
Estimated Time:1m 30s
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Topics

Cellular Injury and Adaptation

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