Final answer:
The hepatopancreatic sphincter, also known as the sphincter of Oddi, is made of smooth muscle and regulates the flow of bile and pancreatic juice into the duodenum.
Step-by-step explanation:
The hepatopancreatic sphincter or sphincter of Oddi is made up of smooth muscle. This anatomical sphincter surrounds the lumen of a vessel or hollow organ and can restrict flow when contracted. It plays an essential role in regulating the flow of bile and pancreatic juice into the duodenum, thereby controlling the entry of these digestive fluids from the liver and pancreas into the small intestine. The Oddi or hepatopancreatic sphincter is made up of smooth muscle.