USMLE (United States Medical Licensing Examination) Step 1 Practice Exam

How do opioids contribute to biliary colic?

1. Inducing bile duct dilation

2. Reducing gallbladder contractility

3. Constricting the sphincter of Oddi

4. Increasing pancreatic enzyme secretion

The correct answer is: Constricting the sphincter of Oddi

Opioids can contribute to biliary colic primarily by constricting the sphincter of Oddi. This mechanism is significant because the sphincter of Oddi regulates the flow of bile and pancreatic juices into the duodenum. When opioids are administered, they bind to opioid receptors leading to increased tone and spasm of the sphincter. This can impede the normal flow of bile, causing a backup of bile within the biliary tree, which may lead to increased pressure and pain typically associated with biliary colic. The other choices involve processes that are not directly related to the mechanism of biliary colic in the context of opioid use. Inducing bile duct dilation would typically alleviate biliary colic rather than contribute to it. Reducing gallbladder contractility can lead to slower emptying, but it is the increased tone of the sphincter of Oddi that primarily leads to the symptoms. Increasing pancreatic enzyme secretion is not a mechanism typically associated with opioids and does not explain the development of biliary colic. Therefore, the role of opioids in constricting the sphincter of Oddi crucially contributes to the pathophysiology of biliary colic.