A 52-year-old woman presents to the emergency department with acute onset severe epigastric pain radiating to the back, associated with nausea and vomiting. Serum lipase is 420 U/L (normal <30 U/L). Abdominal ultrasound shows the finding marked **A** in the diagram. Which of the following best explains the pathophysiological mechanism by which this finding leads to acute pancreatitis?