MICROCIRCULATION OF THE EXTRAHEPATIC BILIARY TREE - A SCANNING ELECTRON-MICROSCOPY STUDY OF CORROSION CASTS

The microvascular arrangement of the extrahepatic biliary tree of the rat was studied by light microscopy (LM) and scanning electron microsc opy (SEM) of vascular corrosion casts. The plexus that encircles the l umen of the common bile duct, observed by LM, showed a network of vess els of different diameter situated under the epithelium in the lamina propria. Parallel SEM observations of the same structure demonstrated the presence of 2 main vascular layers: an outer arterial and venous l ayer, corresponding to the larger vessels seen by LM, and a richer inn er capillary layer just under the epithelium. On the luminal part of t he corrosion casts, there were many round avascular empty pits that co rresponded to the presence of small acinar glands distributed along th e epithelium of the common bile duct. The rich subepithelial capillary network present in the rat, an animal without a gallbladder, may play an important role in the reabsorption of water and solutes from bile. Moreover, in pathological conditions (e.g. portal hypertension), live r blood flow may take a preferential collateral route through the intr ahepatic peribiliary plexus into the relatively large diameter vessels of the extrahepatic peribiliary plexus because of the continuity of t he 2 plexi.