canals of Hering

**Anatomy / Bile flow pathway:** Hepatocyte canaliculi → canals of Hering (terminal bile ductules) → interlobular (portal) bile ducts → left/right hepatic ducts → common hepatic duct → common bile duct. Canaliculi are formed by the apical (canalicular) membranes of adjacent hepatocytes and lack their own wall; the canals of Hering are the first segment with a partial cholangiocyte lining. They are located at the periphery of the lobule, at the interface of the parenchyma and the portal tract (limiting plate/periportal region, near zone 1).

**Histology:** Canals of Hering are lined partly by hepatocytes and partly by cuboidal cholangiocytes (biliary epithelium). They are the transition between hepatocyte-lined canaliculi and cholangiocyte-lined bile ducts.

**Stem cell niche:** The canals of Hering are considered the niche of hepatic progenitor cells (HPCs, "oval cells" in rodents). When hepatocyte replication is inhibited or overwhelmed (e.g., chronic liver injury, massive necrosis, fulminant hepatitis, chronic hepatitis, cirrhosis), HPCs activate and can differentiate into hepatocytes or cholangiocytes. This produces a "ductular reaction" on biopsy, seen as proliferating small bile ductules at the portal tract–parenchyma interface.

**Clinical significance:** - **Ductular reaction:** Seen in biliary obstruction, primary biliary cholangitis (PBC), primary sclerosing cholangitis (PSC), chronic hepatitis, and regeneration after massive necrosis. - **Primary biliary cholangitis:** Autoimmune destruction of small intrahepatic bile ducts (interlobular ducts; florid duct lesion). Anti-mitochondrial antibodies (AMA), elevated ALP, and middle-aged women are classic. - **Liver regeneration:** Normally, regeneration occurs by hepatocyte proliferation (after partial hepatectomy). The progenitor cell compartment in the canals of Hering is a backup mechanism. - **Hepatocellular carcinoma / cholangiocarcinoma:** Some combined hepatocellular-cholangiocarcinomas are hypothesized to arise from progenitor cells.

**Board pearls:** - Canals of Hering = connection between bile canaliculi and bile ducts, and a stem cell niche in the liver. - Do not confuse with the **canals of Schlemm** (eye, aqueous humor drainage), **canal of Nuck** (female analogue of the processus vaginalis), or **canal of Lambert** (accessory bronchioalveolar communication). - The **portal triad** consists of the hepatic artery branch, portal vein branch, and bile duct. - Bile flows in the direction opposite to blood flow (from central vein area toward the portal tract), whereas blood flows from the portal tract to the central vein. - Zone 1 (periportal) is the most oxygenated and the most resistant to ischemia but the most susceptible to viral hepatitis and toxins like yellow phosphorus. Zone 3 (centrilobular) is the most susceptible to ischemia and acetaminophen toxicity (high CYP450 content).