The gallbladder muscularis is the smooth muscle coat that enables gallbladder contraction to expel bile. Unlike the intestinal muscularis propria, the gallbladder smooth muscle lacks a strict inner circular and outer longitudinal arrangement, instead having interlacing bundles that allow the entire organ to contract uniformly. Gallbladder smooth muscle is the functional unit responsible for biliary dynamics.
| Origin | Interlacing smooth muscle bundles in the gallbladder wall, arranged in oblique, longitudinal, and circular layers without the strict layering of the GI tract |
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| Insertion | Continuous throughout the gallbladder wall from the fundus to the infundibulum and cystic duct junction |
| Nerve Supply | Vagus nerve (CN X) parasympathetic — triggers contraction; Sympathetic via coeliac plexus — inhibits contraction; Cholecystokinin (CCK, from duodenal I-cells after fat ingestion) — the principal hormonal trigger for gallbladder smooth muscle contraction |
| Blood Supply | Cystic artery (from right hepatic artery) |
| Actions | Contracts in response to CCK to expel bile through the cystic duct into the common bile duct and duodenum after a fatty meal; tonic low-level contraction maintains bile concentration by preventing stasis; the gallbladder contracts by approximately 70-80% of its fasting volume in response to a fatty meal |
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Biliary dyskinesia (functional gallbladder disorder) is characterised by impaired gallbladder smooth muscle contraction — a low ejection fraction (less than 40%) on cholecystokinin-stimulated cholescintigraphy — producing biliary colic without gallstones. Laparoscopic cholecystectomy is curative. Acute cholecystitis involves smooth muscle inflammation and spasm contributing to the severe colicky pain. Porcelain gallbladder (dystrophic calcification of the gallbladder wall) reduces smooth muscle compliance. Acalculous cholecystitis in critically ill patients results from impaired CCK response and bile stasis.
Impaired gallbladder smooth muscle contraction producing an ejection fraction below 40% on CCK-stimulated HIDA scan causes right upper quadrant biliary colic without gallstones; laparoscopic cholecystectomy removes the dysfunctional smooth muscle organ and relieves symptoms in approximately 85% of carefully selected patients.
