The sphincter of Oddi is a complex smooth muscle valve at the ampulla of Vater regulating bile and pancreatic juice flow into the duodenum. It has three components: the choledochal sphincter (around CBD terminal), the pancreatic sphincter, and the ampullary sphincter. Its resting pressure (10-20 mmHg above duodenal pressure) maintains biliary and pancreatic duct patency against duodenal pressure fluctuations.
| Origin | Circular smooth muscle surrounding the terminal common bile duct, the terminal pancreatic duct, and the hepatopancreatic ampulla (ampulla of Vater) within the wall of the second part of the duodenum |
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| Insertion | Continuous with the duodenal muscularis propria; the sphincter complex surrounds the distal 6-10 mm of the CBD, 2-3 mm of the pancreatic duct, and the ampulla |
| Nerve Supply | Vagus nerve (CN X) parasympathetic — promotes relaxation and bile flow; sympathetic via coeliac plexus — promotes contraction; cholecystokinin (CCK) — the primary hormonal trigger for sphincter relaxation following fat ingestion |
| Blood Supply | Inferior pancreaticoduodenal artery; superior pancreaticoduodenal artery |
| Actions | Maintains tonic contraction of the biliary and pancreatic ducts during the fasting state, preventing bile and pancreatic juice from entering the duodenum; relaxes in response to CCK (released from duodenal I-cells after fat ingestion) to allow bile and pancreatic juice into the duodenum for digestion; prevents duodenal content from refluxing into the bile and pancreatic ducts |
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Sphincter of Oddi dysfunction (SOD) produces recurrent biliary or pancreatic pain from abnormal sphincter function. Type 1 SOD (elevated LFTs, dilated CBD, delayed drainage) is treated by biliary sphincterotomy at ERCP with excellent results. Type 2-3 SOD is more complex and sphincterotomy results are variable. Sphincter manometry at ERCP (basal pressure greater than 40 mmHg defines hypertension) guides treatment decisions. In chronic pancreatitis, pancreatic sphincter hypertension is treated by minor papilla sphincterotomy or surgical sphincteroplasty.
Elevated liver enzymes with dilated common bile duct and delayed biliary drainage after cholecystectomy indicates Type 1 sphincter of Oddi dysfunction from biliary sphincter hypertension; biliary sphincterotomy at ERCP divides the choledochal sphincter, providing relief in approximately 90% of Type 1 cases.
