Those who are acquainted with the classic (but nonetheless good) BBC television series 'The Goodies' might expect a description of the sphincter of Oddi to be not only misspelled but also an invasion of the privacy of a distinguished comedian. Have no fear: the sphincter at issue is not that of which the late great John Peel was thinking when he briefly christened himself 'Neddie Sphincter' at the height of the Punk Explosion, nor was Ruggero Oddi ever known to have ridden a trandem, although it might have been better for his career and his health if he had.
Many organs in the body have more than one function. This is especially true of the liver and to a lesser extent the pancreas. One function shared by both of these organs is the production of fluids to assist the process of digestion. The liver produces bile, while the pancreas produces pancreatic juice. These fluids are both introduced into the lower part of the duodenum by way of a converging system of tubes that form the pancreaticobiliary tract: the right hepatic duct and the left hepatic duct drain bile from the right and left lobes of the liver and then join together to form the common hepatic duct, which leaves the liver and makes its way across to the inside curve of the duodenum, where it is joined by the pancreatic duct, also known as the duct of Wirsung. The two of them merge into a short structure called the ampulla of Vater, which promptly leads into the duodenum, the join forming a structure called the major duodenal papilla. The sphincter of Oddi is located at the end of the ducts and around around the ampulla of Vater, for which reason it is also known as the sphincter of ampulla. (But only as long as nothing goes wrong with it. Possibly because Oddi was a junkie. Let that be a lesson to us all.)
The Sphincter of Oddi has three functions: it regulates the flow of bile and pancreatic juice into the duodenum, it diverts bile into the gallbladder when it is not currently required for digestion, and it stops the contents of the duodenum getting into the pancreaticobiliary tract. Simplifying things somewhat: when you eat it relaxes to let the juices into your guts and when you stop eating it closes to stop anything going the wrong way. What actually happens in detail involves varying pressures along the distal end of the pancreaticobiliary tract working in in combination with contraction or relaxation of the gall bladder to precisely regulate the flow of vital fluids, and is a glory of nature hidden just beneath your ribcage. The presence of Cholecystokinin (CCK) and nitrates appear to have a relaxing effect on the muscle, but many other substances appear to affect it as well. More research is necessary (as usual) to establish all of the factors involved. It is composed of three 'mini sphincters': the sphincter pancreaticus and sphincter choledochus around the two ducts and the sphincter papillae around the ampulla.
The two main types of sphincter of Oddi dysfunction (it is not referred to as sphincter of ampulla dysfunction) are stenosis and dyskinesia. Stenosis is the condition of the sphincter failing to open sufficiently because of chronic inflammation and fibrosis, tumors in the ampulla or papillary opening, or other chunks of superfluous tissue too numerous to mention. In dyskinesia the muscle fails to relax sufficiently to allow the fluids to flow enough. Unsurprisingly, the results of either are suboptimal: people with s. of O. dysf. tend to experience sharp pain in the upper right of their abdomen after meals, and may feel nauseous and/or vomit. The pain can last for several hours, and may spread to the back or shoulder blades. Sometimes people may become fevered, have chills, or get jaundice. Recurrent acute Pancreatitis may occur. A definitive diagnosis may be provided by expensive modern scanning equipment (machines that go beep) or expensive modern endoscopy (a tube stuck a long way down your throat).
You might expect the appropriate treatment for sphincter of Oddi dysfunction to depend on which kind it is. And some patients with dyskinesia do show an improvement with muscle relaxant therapy such as calcium channel blockers and long-acting nitrates. But not all of them do so, and these medications can have unpleasant side effects. So the therapy usually involves cutting chunks off the sphincter to make for a bigger opening. One option is surgical sphincteroplasty, which involves making an incision in the wall of the duodenum in order to get to the sphincter and carve pieces off it. But the modern method of choice is a endoscopic sphincterotomy, which involves nibbling bits off the sphincter with a device inserted down a long tube which has been pushed down the patient's throat, across their stomach, and into their duodenum. It was reading a patent for a device of that nature that awakened my interest in this wondrous little bundle of muscle, of whose existence I had until that moment been blissfully ignorant.
If you become painfully aware of your sphincter of Oddi you are quite likely to be a woman between 30 and 50 years old who has had her gall bladder removed. The prognosis with treatment is unimpressive but not gloomy: long term relief of pain, it says here, may be demonstrated in up to 70% of patients. Whatever that 'may be' and 'up to' are meant to mean (probably "don't sue us"), the risk of sphincter of Oddi dysfunction killing you seems to be low.