Innervation of Liver and Biliary Tract

Afferent fibers from the liver and biliary tract are conveyed through the hepatic and celiac plexuses to the thoracic splanchnic nerves or to branches of the vagus nerves. The sympathetic afferents reach the seventh to twelfth thoracic spinal cord segments through the corresponding posterior spinal nerve roots, whereas the vagal afferents are carried upward to the brainstem. The right, and possibly the left, phrenic nerve also conveys afferents from receptors in the peritoneal lining over the liver and biliary tract, which can be stimulated by stretching—as by acute hepatic enlargement or distention of the gallbladder. The resultant pain in the right shoulder region associated with liver and biliary tract disorders is an example of referred pain.

Liver. The hepatic plexuses lie in the right free margin of the lesser omentum anterior to the epiploic (omental) foramen. They are formed mainly by offshoots from the celiac plexus, which contain sympathetic and parasympathetic efferent and afferent fibers, supplemented by direct contributions from the anterior vagal trunk and by indirect contributions from the right phrenic nerve. They are arranged in two interconnected groups, one of which lies along the anterior and lateral sides of the hepatic artery, and the other, posterior to the common bile duct and portal vein.

Subsidiary plexuses surround and accompany the branches of the hepatic artery, portal vein, and right and left hepatic ducts as they enter and ramify within the liver; their offshoots penetrate between the cells of the liver lobules to form a widespread parenchymal plexus. Histochemical studies reveal that the nerve fibers in relation to the hepatocytes and sinusoids are parasympathetic, whereas sympathetic fibers remain mainly or entirely associated with vessels in the interlobular spaces. Direct contacts between the terminations of nerve fibers and liver cells have been observed in electron micrographs.

Gallbladder. The gallbladder is supplied by perivascular nerve fibers accompanying the right hepatic and cystic arteries from the anterior hepatic plexus and by other nerve fibers extending along the cystic duct from the posterior hepatic plexus. The common bile duct (choledochal duct) is supplied by twigs from both anterior and posterior hepatic plexuses and by offshoots from the plexus around the gastroduodenal artery and its retroduodenal branches. The arrangement of the nerves within the walls of these structures resembles that in the enteric plexuses.

Both the sphincter ampullae and the sphincter of the choledochal duct are supplied by sympathetic and parasympathetic fibers. The former normally cause contraction of the sphincters and dilation of the gallbladder, while the latter produce the opposite effects.

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