Hepatopancreatic ampulla and sphincter of Oddi

Ampulla hepatopancreatica; musculus sphincter ampullae

Also known as: ampulla of Vater, sphincter of Oddi, major duodenal papilla, papilla of Vater

The hepatopancreatic ampulla is the short dilated common channel formed when the bile duct and main pancreatic duct unite in the duodenal wall. It opens on the major duodenal papilla, and the smooth-muscle sphincter of Oddi controls its outflow.

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Overview

Within the posteromedial wall of the descending (2nd) part of the duodenum, the bile duct and main pancreatic duct usually join to form a short common channel, the ampulla. In some people the two ducts open separately or side by side on the papilla. The ampulla opens at the summit of the major duodenal papilla. This lies at the junction of foregut and midgut, which is why the duodenum above and below receives coeliac and SMA blood respectively.

The sphincter of Oddi is a complex of smooth muscle with three components: the sphincter of the bile duct (choledochal sphincter, the most important functionally), the sphincter of the pancreatic duct, and the sphincter of the ampulla. Between meals its tone is high, so bile is diverted into the gallbladder and duodenal reflux into the ducts is prevented. CCK relaxes it and contracts the gallbladder at the same time. Opioids contract it, and nitrates and glucagon relax it.

Location: Posteromedial wall of the 2nd part of the duodenum, at the major duodenal papilla. The minor papilla (accessory pancreatic duct) lies about 2 cm proximal.

Parts & subdivisions

Major duodenal papilla
Mucosal elevation at the opening of the ampulla, often hooded by a fold; the target for ERCP cannulation.
Sphincter of the bile duct
Choledochal sphincter; controls bile flow and gallbladder filling.
Sphincter of the pancreatic duct
Prevents bile from refluxing into the pancreatic duct.

Function

Common outlet for bile and pancreatic juice.
Regulates their delivery to the duodenum.
Prevents duodenal reflux.

Regulation: Relaxed by CCK, VIP, NO, nitrates and glucagon. Contracted by opioids and cholinergic stimulation.

Clinical significance

Gallstone pancreatitis

A stone impacted at the ampulla blocks both ducts. The common-channel theory holds that bile refluxes into the pancreatic duct and raised ductal pressure triggers acinar injury. The result is acute pancreatitis together with obstructive jaundice.

Periampullary carcinoma

Tumours of the ampulla, distal bile duct, duodenum or pancreatic head cause early painless jaundice. Ampullary tumours may also bleed intermittently. They are more often resectable (Whipple procedure) than other pancreatic cancers.

ERCP and sphincterotomy

Endoscopic retrograde cholangiopancreatography cannulates the papilla to extract stones or place stents. Sphincterotomy cuts the biliary sphincter. Post-ERCP pancreatitis is the commonest complication.

Test yourself

The major duodenal papilla is found on the:

Anterior wall of the superior (1st) part
Posteromedial wall of the descending (2nd) part
Inferior wall of the horizontal (3rd) part
Lateral wall of the ascending (4th) part

Answer: Posteromedial wall of the descending (2nd) part

The hepatopancreatic ampulla opens on the major papilla on the posteromedial wall of the descending part of the duodenum. The minor papilla (accessory duct) lies about 2 cm proximal. The foregut–midgut junction lies just distal to the major papilla.

The superior mesenteric artery supplies the gut from:

The lower oesophagus to the major duodenal papilla
The major duodenal papilla to the proximal two-thirds of the transverse colon
The distal third of the transverse colon to the pectinate line
The jejunum to the sigmoid colon

Answer: The major duodenal papilla to the proximal two-thirds of the transverse colon

The SMA (L1) supplies the midgut, from just distal to the major papilla to the proximal two-thirds of the transverse colon. The coeliac trunk supplies the foregut, and the IMA supplies the hindgut down to the pectinate line.

Gallbladder contraction and relaxation of the sphincter of Oddi after a fatty meal are mainly caused by:

Secretin
Gastrin
Cholecystokinin
Somatostatin

Answer: Cholecystokinin

Fatty acids and amino acids in the duodenum release CCK from I cells. CCK contracts the gallbladder, relaxes the sphincter of Oddi and stimulates pancreatic enzyme secretion. Somatostatin inhibits gallbladder emptying.