A 52-year-old man with a 10-year history of alcohol-related cirrhosis presents with hematemesis and melena. Upper endoscopy confirms bleeding esophageal varices. The gastroenterologist notes that the patient has a prominent caput medusae and ascites. Laboratory values show INR 2.8, albumin 2.1 g/dL, and platelet count 68,000/μL. The patient is started on variceal banding and octreotide. Which of the following anatomical pathways is responsible for the formation of these esophageal varices in portal hypertension?