Gastrointestinal Tract

Atlas References

• Netter: 273–299, 301–305

• McMinn: 234–252

• Gray's Atlas: 157–182

In most cadavers, the liver occupies a significant portion of the peritoneal cavity. The gallbladder may be difficult to see at this point, but look for its fundus.

Dissection Steps

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  With a scalpel, make a horizontal incision at the lower edge of the liver, removing 3 to 4 cm ( inches) of liver parenchyma ( Fig. 12.1 ).

  

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  Pull the stomach downward and fully expose the gallbladder and the hepatoduodenal ligament ( Figs. 12.2 and 12.3 ).

  
  

Dissection Tip

Stripping away the hepatoduodenal ligament, you will see several nerves running along the bile duct and proper hepatic artery. These nerves are part of the autonomic nervous system and are primarily sympathetic fibers ( Fig. 12.4 ).

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  With scissors or a probe, carefully strip away the hepatoduodenal ligament and expose the bile duct, proper hepatic artery, and hepatic portal vein (see Figs. 12.4 and 12.5 ).

  

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  Note the relationships among these three structures: within the hepatoduodenal ligament, the portal vein is located posteriorly, deep to the bile duct and proper hepatic artery ( Fig. 12.6 ).

  

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  Clean the proper hepatic artery toward the liver, and identify the right and left hepatic arteries.

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  Look for the cystic artery supplying the gallbladder.

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  The cystic artery usually arises from the right hepatic artery or the proper hepatic artery.

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  Dissect out the cystic duct from the gallbladder toward its junction with the common hepatic duct to form the bile duct ( Fig. 12.7 ).

  

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  Once these structures are cleaned and identified, observe the hepatocystic triangle formed by the common hepatic duct, the cystic duct, and the liver.

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  In most cases, the cystic artery is identified within this triangular region ( Plate 12.1 ).

  

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  To expose the celiac trunk and its branches, with blunt dissection, release the transverse and the descending colon from the gastrocolic ligament ( Figs. 12.8 and 12.9 ).

  
  

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  With scissors, cut the gastrocolic ligament at the superior border of the transverse colon and release it from the stomach ( Fig. 12.10 ).

  

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  To expose the splenic artery and spleen, cut the inferior edge of the costal cartilages with a saw to expose fully the area anterior to the spleen. Place paper towels underneath the costal cartilages ( Fig. 12.11 ).

  

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  Identify the inferior border of the spleen, hidden by the gastrosplenic and splenorenal ligaments and, usually, abundant fat ( Fig. 12.12 ).

  

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  Clean the fat and the gastrosplenic and splenorenal ligaments, and expose the splenic pedicle receiving the splenic artery and vein ( Fig. 12.13 ).

  

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  Continue the exposure of the splenic artery and vein and identify the splenic hilum ( Fig. 12.14 ).

  

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  Identify the short gastric arteries, which pass to the greater curvature of the stomach.

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  Note the relationship of the spleen with the stomach and the pancreas.

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  Identify the left gastroepiploic artery, which typically derives from the most inferior splenic artery hilar branch ( Fig. 12.15 ).

  

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  Pull the stomach upward and expose the tail of the pancreas (see Fig. 12.15 ).

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  Continue the dissection of the splenic artery and vein from the hilum of the spleen toward the celiac trunk.

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  The splenic artery is tortuous and lies hidden at the upper border of the tail and body of the pancreas ( Fig. 12.16 ).

  

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  Lift the stomach upward and expose the body and tail of the pancreas ( Fig. 12.17 ).

  

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  Clean out the splenic artery and vein from the adjacent pancreas ( Fig. 12.18 ).

  

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  Do not pull the splenic artery away from the pancreas, because most of its branches are short and can be injured easily.

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  To visualize the area of the celiac trunk, it is necessary to lift the stomach upward and expose the pancreas. Palpate the upper border of the pancreas, and with your fingers, feel the celiac artery as a prominent bulge covered by the overlying peritoneum ( Plate 12.2 ).

  

Identification of Different Parts of the Stomach

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  Return to the exposed proper hepatic artery, and dissect backward toward its origin from the common hepatic artery ( Figs. 12.19 and 12.20 ).

  
  

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  Identify and expose the other branch of the common hepatic artery, the gastroduodenal artery (see Fig. 12.20 ).

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  Dissect out the right side of the lesser curvature of the stomach and identify the right gastric artery, a branch of the proper hepatic artery.

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  Next to the right gastric artery, identify the right gastric vein and its connection to the right gastroepiploic vein via the prepyloric vein of Mayo.

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  On the left side of the lesser curvature of the stomach, identify and clean the left gastric artery; then trace it back from its origin from the celiac trunk ( Fig. 12.21 ).

  

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  Note the esophageal arterial branches of the left gastric artery ascending toward the esophagus.

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  The left gastric artery is accompanied by the left gastric vein. Trace out any esophageal tributaries to the left gastric vein.

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  In the area between the greater curvature of the stomach and the pylorus, dissect out the fat within the gastrocolic ligament and greater omentum, and identify the right gastroepiploic artery (also known as right gastro-omental artery) ( Figs. 12.22 and 12.23 ).

  
  

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  Similarly, dissect between the left side of the greater curvature of the stomach and spleen and identify the left gastroepiploic artery.

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  After identifying the right and left gastroepiploic arteries, with scissors, cut along the line marking the junction between the body of the stomach and the pyloric antrum, 4 to 5 cm (~2 inches) proximal to the pylorus ( Fig. 12.24 ).

  

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  Retract the two parts of the transected stomach laterally and expose the celiac trunk and pancreas ( Fig. 12.25 ).

  

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  Lift the splenic artery from the upper border of the pancreas and dissect it out ( Fig. 12.26 ).

  

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  Once the splenic artery is fully exposed, notice its tortuosity ( Fig. 12.27 ).

  

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  Place the left side of the stomach in such a position that you can visualize all the branches of the celiac trunk and identify the origins and distributions of these branches ( Figs. 12.28 and 12.29 ).

  
  

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  On the right side of the cadaver, dissect out the branches of the gastroduodenal artery anteriorly.

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  Around the head of the pancreas, look for the origin of the two terminal branches of the gastroduodenal artery, the right gastroepiploic and superior pancreaticoduodenal arteries ( Fig. 12.30 ).

  

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  The right gastroepiploic artery is typically found around the right side of the greater curvature of the stomach. Identify it.

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  The superior pancreaticoduodenal artery divides into the posterior superior and anterior superior pancreaticoduodenal arteries supplying the head of the pancreas (see Fig. 12.30 ). Identify it.

Dissection Tip

To expose the arterial branches, as well as the course of the bile duct down to the duodenum, reflect the stomach and duodenum to the left. Use your fingers to dissect the area underneath the duodenum and inferior vena cava; this is an avascular plane that is easily reflected to the left. This is called the Kocher maneuver, or “kocherizing” ( Fig. 12.31 ).

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  Follow the gastroduodenal artery posteriorly toward the 1st part of the duodenum and expose the origin of the PSPD artery ( Figs. 12.32 and 12.33 ).

  
  

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  Trace the course of the anterior superior pancreaticoduodenal artery (see Figs. 12.33 and 12.34 ), and expose its anastomosis with the inferior pancreaticoduodenal artery, a branch of the superior mesenteric artery.

  

Optional Dissection of Branches of Splenic Artery

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  Lift the splenic artery up and look for the origin of several branches. The following landmarks help identify these branches:

  • 1.

    Lift the pancreas and look for the point where the portal vein crosses the pancreas posteriorly (neck of the pancreas). At this point, look for a branch from the splenic artery, the dorsal pancreatic artery.

  • 2.

    The splenic artery often gives off small branches at the superior border of the body and the tail of the pancreas, the short pancreatic branches.

  • 3.

    The largest of these short pancreatic branches is the great pancreatic artery , which often is found at the distal one-third of the pancreas near its tail.

  • 4.

    At the same point of the great pancreatic artery, look for a branch of the splenic artery traveling to the posterior part of the stomach supplying the gastric fundus, the posterior gastric artery.

  • 5.

    Look 1 to 2 cm superior to the inferior border of the pancreas; embedded in its substance is the transverse pancreatic artery.

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  Make a horizontal incision at the pyloric antrum, pylorus, and duodenum and observe the inner surface of these structures ( Fig. 12.35 ).

  

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  Appreciate the gastric folds at the inner surface of the pyloric antrum and the circular muscle of the pyloric sphincter ( Fig. 12.36 ).

  

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  Continue the incision at the 1st, 2nd, and 3rd parts of the duodenum, and note the circular folds of Kerckring ( Figs. 12.37 and 12.38 ).

  
  

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  Cut the gastroduodenal artery and expose the course of the bile duct toward the duodenum ( Fig. 12.39 ).

  

Anatomy Note

The bile duct is divided into supraduodenal (above duodenum), retroduodenal (behind duodenum), and pancreatic parts (terminal part) ( Fig. 12.40 ).

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  Open up the descending part of the duodenum and identify the intraduodenal portion of the bile duct; find its connection with the main pancreatic duct (of Wirsung), forming the hepatopancreatic ampulla (of Vater).

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  Identify the duodenal papilla, which contains the hepatopancreatic ampulla.

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  Expose the main pancreatic duct into the substance of the pancreas by removing pancreatic tissue with your forceps (see Fig. 12.40 ).

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  Look for an accessory pancreatic duct (of Santorini), if present.

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  With your forceps, lift the pancreas and identify the splenic vein ( Fig. 12.41 ).

  

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  Expose the splenic vein along its entire length, and trace out its junction with the superior mesenteric vein to form the portal vein ( Figs. 12.42 and 12.43 ).

  
  

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  Next to the superior mesenteric vein, look for the inferior mesenteric vein, usually draining into the splenic vein ( Plate 12.3 ).

  

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  Continue exposing the tributaries of the superior mesenteric vein.

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  Next to its tributaries, expose the arterial branches of the superior mesenteric artery ( Fig. 12.44 ).

  

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  Lift the transverse colon and observe the transverse mesocolon ( Fig. 12.45 ).

  

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  With your fingertips, penetrate the transverse mesocolon and expose the underlying superior mesenteric artery and vein ( Fig. 12.46 ).

  

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  Continue cleaning the branches of the superior mesenteric artery and the tributaries of the superior mesenteric vein from fat and nerve tissue ( Fig. 12.47 ).

  

Dissection Tip

The ileocolic artery is fairly constant and provides a good landmark for this dissection ( Fig. 12.48 ).

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  Identify the ileocolic artery and trace it to the ileocecal junction, between the ileum and the cecum.

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  Identify the middle and right colic arteries that supply the transverse and the ascending colon, respectively (see Fig. 12.48 ).

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  Look for a branch of the middle colic artery, the marginal artery (of Drummond), that supplies the ascending, transverse, and descending colon, and anastomose with the left colic artery, a branch of the inferior mesenteric artery (see Fig. 12.52 ).

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  Once the main three arterial branches of the superior mesenteric artery (middle colic, right colic and ileocolic) are identified, expose the ileal and jejunal arteries from their origin from the superior mesenteric artery to the margin of the ileum and jejunum.

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  Dissect out the vascular arcades, appreciating their greater number in the ileum than in the jejunum ( Fig. 12.49 ).

  

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  Similarly, the vasa recti are shorter and more numerous in the ileum ( Figs. 12.50 and 12.51 ).

  
  

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  Once the dissection of the superior mesenteric vessels is concluded, lift the transverse colon and review all dissected structures dissected out ( Figs. 12.52 and 12.53 ).

  
  

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  Retract the small intestine to the right and expose the transverse, descending, and sigmoid colon ( Fig. 12.54 ).

  

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  With scissors, continue the exposure of the inferior mesenteric vein ( Fig. 12.55 ) toward the margins of the colon.

  

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  To the right or medial to the inferior mesenteric vein, identify the inferior mesenteric artery ( Plate 12.4 ).

  

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  Identify the branches of the inferior mesenteric artery, the left colic artery and the sigmoid arteries and fully expose them ( Fig. 12.56 ).

  

If Time Permits

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  Tie two strings close together around the proximal segment of the jejunum, and cut between them.

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  Perform the same technique along a distal portion of the ileum.

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  Clean the two segments and observe their internal morphology.

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  Note the increased number of plicae circulares and villi, as well as increased wall thickness in the jejunum compared to the ileum.

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  Similarly, place a ligature at the ileocecal junction and another ligature at the midportion of the ascending colon.

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  Remove this segment and examine its internal morphology.

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  Identify the ileocecal valve and the plicae semilunares coli.

Laboratory Identification Checklist