A 42-year-old fisherman from the shores of Lake Victoria, Uganda, presents with portal hypertension manifested by ascites and oesophageal varices. Liver biopsy shows periportal (Symmers pipestem) fibrosis with granulomata. Rectal biopsy reveals eggs with lateral spines. His hepatocellular function is relatively preserved with normal albumin and near-normal transaminases. Why is hepatocellular function typically preserved in hepatosplenic schistosomiasis?