Most of the gastrointestinal (G.I.) tract from the esophagus to the anus can be examined by endoscopy (endo, inside; scope, see; to see inside the body). The endoscope is a long and flexible tube and contains a light source, lens system for focusing and fiber optics to conduct light into the bowel. A picture of the bowel wall is sent back to a video camera and displayed on a monitor. The tube also contains a working channel through which small instruments can be passed for various uses.

ERCP is a specialized technique similar to panendoscopy (see Panendoscopy) that is used for diagnosing many diseases of the pancreas and biliary (bile) ducts. The biliary ducts (channels) drain the liver. ERCP involves the passage of a tube by mouth through the esophagus into the stomach and into the duodenum. It allows the physician to study the ducts of the gallbladder, pancreas and liver by inserting a catheter (thin tube) through the working channel of the endoscope into the ducts and injecting a dye that can be seen on an X-ray monitor.

Anatomy and Physiology

• The duodenum connects the stomach to the jejunum (the second part of the small bowel) (Figure 1) (See Surgery of the Duodenum)
  
• It is 20 cm (8 inches) in length and divided into four parts
  
• The duodenum is retroperitoneal (has peritoneum, the thin layer of tissue that lines the abdominal cavity) only on the anterior (front) side; fixed in location; wraps around the head, neck and body of the pancreas; and the superior mesenteric artery and vein (major blood vessels for the bowel) pass anterior to the 3rd portion.
  
• The ampulla of Vater (entrance site into duodenum of joined common bile duct and pancreatic duct) enters the medial (towards the midline) side of the 2nd portion of the duodenum.
  
• The accessory pancreatic duct enters slightly higher in the medial wall of the duodenum
  
• The ligament of Treitz (a supporting band of peritoneum and muscle fibers) marks the point between the fourth part of the duodenum and jejunum
  
• The duodenum produces many hormones that help regulate digestion. Liver bile and pancreatic secretions are added to the bowel through the ampulla of Vater. The actual passage and presence of food in the duodenum triggers the flow of hormones, bile and pancreatic secretions. By the time food leaves the duodenum most of the ingredients necessary for digestion have been added. Little digestion and absorption (passage of nutrients from the bowel into the blood) take place in the duodenum