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Biliary Tract : Intrahepatic & Extrahepatic Biliary Architecture,…
Biliary Tract : Intrahepatic & Extrahepatic Biliary Architecture
Intrahepatic Biliary Tree (Canaliculi ➔ Hering ➔ Interlobular)
Intrahepatic Biliary System
Interlobular Bile Ducts
Peripheral transition zone lined partly by hepatocytes and partly by simple cuboidal cholangiocytes, harboring hepatic progenitor/oval cells
Canals of Hering (Cholangioles)
Situated within portal triads (ensheathed by Glisson’s capsule); epithelium transitions from simple cuboidal to simple columnar as duct caliber increases
Bile Canaliculi
Virtual intralobular channels formed by the apical membranes of adjacent hepatocytes; sealed by tight junctions (zonula occludens)
Extrahepatic System & Gallbladder Microanatomy
Principal Ducts (Common Hepatic & Common Bile Duct / Choledochus)
Lined by simple columnar epithelium
Lamina propria contains occasional mucous glands
Encased by a fibromuscular layer; terminates at the Ampulla of Vater wrapped by the Sphincter of Oddi
Gallbladder Wall Architecture
Serosa vs. Adventitia
Unattached inferior surface is covered by serosa (visceral peritoneum); attached hepatic surface is covered by adventitia
Mucosa
High, complex folds lined by simple columnar clear cells with apical microvilli specialized for water/electrolyte absorption
Crypts form characteristic pseudoglands (Luschka's crypts)
Muscularis
Smooth muscle fibers oriented in an irregular, plexiform network (contracts under CCK stimulation)
Absence of Submucosa
The gallbladder uniquely lacks a submucosa (the lamina propria sits directly on the muscularis)
Hierarchical Biliary Flow Path
Bile Canaliculi [Intralobular,no epithelium]
Canals of Hering [Low cuboidal + oval stem cells]
[Interlobular Bile Ducts [Simple cuboidal to tall columnar]
Extrahepatic Ducts [Simple columnar + fibromuscular layer]
Gallbladder [Simple columnar + absorptive microvilli]
Biliary Segments
Gallbladder
Simple Columnar (Absorptive)
Mucosa + Muscularis + Serosa/Adventitia (No Submucosa!)
Pseudoglands of Luschka; prominent mucosa folds
Bile Canaliculi
None (Apical hepatocyte membranes)
No wall; membrane bounded
Microvilli, tight junction seals
Interlobular Ducts
Simple Cuboidal to Columnar
Ensheathed in portal connective tissue
Runs alongside hepatic arteriole & portal venule
Common Bile Duct
Simple Columnar
Mucosa + Lamina Propria + Fibromuscular layer
Sphincter of Oddi smooth muscle thickening
Canals of Hering
Low Cuboidal
Minimal basement membrane
Oval/Stem cell niche
Cellular Mechanics of Concentration
Capillaries of Lamina Propria
Absorptive venules and capillaries rapidly remove the hypertonic fluid, leaving bile acids, cholesterol, and bilirubin concentrated 5- to 10-fold in the lumen
Basolateral Na⁺/K⁺-ATPase Pumps
Actively transport Na⁺ out of epithelial cytoplasm into the lateral intercellular spaces
Osmotic Water Drag
Water follows the osmotic gradient from the lumen through water channels (aquaporins) and leaky tight junctions into the intercellular spaces
Epithelial Lining
Wall Layering Features
Distinctive Histological Signatures
Epithelial Lining
Wall Layering Features
Distinctive Histological Signatures