7. Expose the duodenum and pancreas and define their parts.
Dissection of Duodenum, Pancreas, and Biliary Tract
In order to study the pancreas and duodenum it is necessary to cut the greater omentum off the greater curvature of the stomach as indicated. As you do this, be careful not to cut the middle colic vessels lying in the remnant of the transverse mesocolon. Once you have severed the great omentum, the pancreas and duodenum lie in the bed of the stomach. The duodenum continues beyond the pyloric portion of the stomach. The pyloric sphincter, shown here, is between the two. The first part of the duodenum is thin walled and somewhat dilated. It has no folds on its interior surface. It lies in front of the gastroduodenal artery and is overlaying by the gall bladder. It is suspended by the hepatoduodenal ligament and is the only portion of the duodenum that has a mesentery. The first part passes upward and to the right. The duodenum then takes a sharp bend downward and descends. This is the second part of the duodenum. The remained of the duodenum is best visualized by reflecting the stomach and transverse colon upward. Recall that the duodenum, other than the first part, is retroperitoneal. The second part of the duodenum continues after the first. It descends along the right side of the vertebral column. It embraces the head of the pancreas and receives the common bile duct and the pancreatic ducts. The duodenum continues transversely as the third portion. This passes behind the superior mesenteric vessels and runs transversely. This duodenum has a small diverticulum at the junction of the second and third parts. This is abnormal. The fourth part of the duodenum continues upward from the third. It ascends to the duodenal-jejunal junction. At the junction there is a sharp downward bend once again as the small intestine gains a mesentery. The junction is due to a ligament attaching the duodenal-jejunal junction to the posterior body wall. This is the suspensory ligament of the duodenum. Notice that the third part of the duodenum is crossed by the superior mesenteric artery and veins. The artery tends to lie anterior in this specimen. The intestinal vessels off the superior mesenteric artery pass into the mesentery and supply the small intestine. The position of the duodenum covers three vertebral levels. The first part is at L1, the second part at the body of L2, the third part at the body of L3, and the fourth part at the body of L2 again. The duodenum then is C-shaped extending from the stomach to the duodenal-jejunal junction at the suspensory ligament. Next observe the duodenal-jejunal junction. As you reflect the intestine to the right you will notice the suspensory ligament. It is responsible for the duodenal-jejunal junction being turned downward. The suspensory ligament attaches to the junction and from there up to the root of the celiac artery and the crus of the diaphragm. There is a fossa, behind the fourth part of the duodenal, the retro-duodenal fossa. To the left of this fossa, there is usually a prominent fold, made by the inferior mesenteric vein. This is the paraduodenal fold.
The Pancreas
The pancreas runs obliquely across the posterior body wall behind the stomach. It is divisible into several portions. The first portion is a remnant of the old ventral pancreas embryologically. This is the uncinate process. It projects behind the superior mesenteric vessels. To the right of the uncinate process, in the curve of the duodenum, is the head. This is followed by the neck and then the body of the pancreas, which crosses the aorta and vena cava. Pancreas ends in the hilum of the spleen as a tail.