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.
| Location | Middle layer of the gallbladder wall, beneath the mucosa and surrounded by connective tissue |
|---|---|
| Parts |
|
| Nerve Supply | Coeliac plexus fibres; Vagus nerve (parasympathetic, promotes contraction) |
| Blood Supply | Cystic artery |
Contracts mainly in response to the hormone cholecystokinin after a fatty meal, pushing stored bile into the bile duct. Poor contraction contributes to biliary pain.
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.
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