Lab Manual - Stomach, Spleen, Duodenum, & Pancreas

Assignments:

Learning Objectives:

Upon completion of this session, the student will be able to:

  1. Identify the parts of the stomach and describe its spatial relationships to surrounding organs and mesenteries.
  2. Describe the blood supply of the abdominal foregut via branches of the celiac artery, and the basic pattern of lymphatic drainage in this region.
  3. Describe the anatomy of the foregut peritoneal ligaments, omenta and omental bursa, and their development from the embryological ventral and dorsal mesogastria.
  4. Describe the pattern of parasympathetic innervation of the GI tract.
  5. Identify and describe the parts and peritoneal relationships of the duodenum and pancreas.
  6. Describe the pattern of common vasculature of the duodenum and pancreas.
  7. Trace the potential collateral blood flow between celiac and superior mesenteric arterial territories, and between superior and inferior mesenteric arterial territories.
  8. Trace the pathway of common entry of the bile ducts and pancreatic ducts into the 2nd part of the duodenum.

Procedure:

1. Remove the costal arch from the anterior aspect of the diaphragm. (Play movie; View images: N 266, 268, TG 5-01, 5-18)

Because the rigid lower ribs (except 11 and 12) overlap the liver and other foregut structures anterolaterally, it is advisable to cut and remove them before attempting detailed inspection of this region. Along the same vertical line of incision used to cut through the upper 6 ribs, now cut through ribs 7-10. Remove them completely, being careful not to damage the diaphragm as you detach it from the deep surface of the rib cage.

2. Examine the omental bursa and the derivatives of the dorsal and ventral mesogastria. (Play movie; View images: N 263, 269, 272, 273, 275, 336, 348, TG 5-12A, 5-12B, 5-18A, 5-18B, 5-42)

Study the development of the peritoneum of the upper abdominal viscera. The adult derivative of the ventral mesogastrium is the lesser omentum, composed of hepatogastric and hepatoduodenal ligaments. Note the right free border of the hepatoduodenal ligament, and locate the omental (epiploic) foramen behind it. Put your finger in the omental (epiploic) foramen and explore.

The adult derivative of the dorsal mesogastrium is the greater omentum, composed of the gastrosplenic ligament, gastrocolic ligament, omental apron and splenorenal ligament. Examine how the greater omentum has combined with and assists in the formation of the transverse mesocolon.

Define the omental bursa (lesser sac). How does it develop? What is its entrance? Boundaries? Lift up the transverse colon and cut through the remaining layer of peritoneum of the transverse mesocolon and explore the omental bursa from below, locating the stomach, spleen, pancreas, and posterior body wall peritoneum. In subsequent dissections add to this list of boundaries as you expose other areas.

3. Identify the parts of the stomach and expose the celiac artery. (Play movie; View images: N 232, 264, 274, 275, 276, 277 TG 4-37, 5-18, 5-19, 5-26, 5-34)

Stomach. Examine and define parts: cardia, fundus, body, pyloric antrum, pylorus. On plastinated specimens, observe its ventral wall and observe the mucosa and gastric rugae. On your cadaver, cut through the pylorus and examine arrangement of the pyloric sphincter. Define the lesser and greater curvatures and the mesenteric attachments. Note the abdominal esophagus passing through the diaphragm and the peritoneum reflecting from the diaphragm onto the esophagus and stomach. Also note the pyloroduodenal junction and its peritoneal relations.

Esophagus Stomach with barium
3D images of esophagus Pyloric ulcer
Pylorus    

4. Expose the branches of the celiac artery and define its branches to the stomach and spleen. (Play movie; View images: N 272, 275, 291, 300, 301, 309, 312, 319, 348, TG 5-18A, 5-18B, 5-19, 5-27, 5-28)

Cut through the central (hepatogastric) part of the lesser omentum and spread open with your fingers, exposing the cavity of the omental bursa (do not mobilize the right side of the stomach). Identify the left gastric artery within the left gastropancreatic fold. Trace the artery upward to the cardia of the stomach and identify esophageal, gastric, and possibly hepatic branches. Trace as far along the lesser curvature as you can, noting distribution to stomach. Preserve the accompanying left gastric vein. Be careful to preserve the superior portion of the hepatogastric ligament, which contains the hepatic branch of the anterior vagal trunk. Now trace the artery back to its source, the celiac trunk. Locate but do not try to expose completely. In the posterior body wall peritoneum locate the right gastropancreatic fold, open and trace the common hepatic artery to the pyloroduodenal junction. As it divides identify the proper hepatic artery and the gastroduodenal artery. Follow along the proper hepatic artery into the hepatoduodenal ligament until you locate the right gastric artery. Trace it to the lesser curvature of the stomach. Does it anastomose with the left gastric artery? Consider how both of these vessels have entered the lesser omentum from a source (celiac trunk) behind the posterior body wall peritoneum.

CT of celiac artery

Now trace the gastroduodenal artery behind the pyloroduodenal junction, noting that the posterior superior pancreaticoduodenal artery arises from it near its origin. As the gastroduodenal artery emerges from below the duodenum, it divides into anterior superior pancreaticoduodenal and right gastro-omental arteries. Trace the right gastro-omental artery through the gastrocolic ligament, noting omental and gastric branches.

Return to the celiac trunk. Note its relation to the superior border of the pancreas. Locate the splenic artery. Lift the stomach and observe the artery lying along the superior border of the pancreas, but do not remove at this time. Note the artery entering the splenorenal ligament and passing to the hilum of the spleen. Return to the stomach and identify the gastrosplenic ligament. As this ligament attaches to the hilum of the spleen locate the splenic artery and its splenic branches, short gastric arteries and the left gastro-omental artery. Trace each of these vessels. Does the left gastro-omental artery anastomose with the right? Locate gastric and omental branches.

5. Examine the spleen, its mesenteric relations and the origin of the portal vein. (Play movie; View images: N 266, 268, 272, 275, 288, 291, 300, 309, 312, 314, 315, TG 5-01, 5-18A, 5-18B, 5-19, 5-24, 5-27, 5-28, 5-35A, 5-35B, 5-37)

Mobilize the spleen, note shape, size, relation to ribs and diaphragm. Review gastrosplenic and splenorenal ligaments. How does the splenic artery reach the spleen and its branches reach the stomach? Note relations to stomach, kidney and left colic flexure.

Locate the right gastric vein and trace to the portal vein. In the hepatoduodenal ligament (free border of the lesser omentum), locate the bile duct, the portal vein and the proper hepatic artery. Note their relationship to each other and to the omental foramen. Locate the left gastric vein and trace as far as possible (usually to the portal vein). What is the coronary vein?

Lymphatics. Organize the lymph drainage of the stomach and spleen. Look for paracardial, left gastric, celiac, pyloric, gastroomental, hepatic, and pancreaticosplenic node groups.

6. Expose the branches of the vagal trunks to liver, stomach, and celiac ganglion. (Play movie; View images: N 126, 209, 240, 269, 272, 273, 275, 319, 320, 321, 336, 348, TG 4-45, 5-12, 5-18A, 5-18B, 5-42, 7-92, 8-16, 8-17)

Return to the lesser curvature of the stomach and the left gastric artery. Locate gastric branches of the anterior vagal trunk along the anterior part of the lesser curvature. Trace them back to the esophagus and note relation to esophagus. Look for a hepatic branch passing within the lesser omentum to the liver and then to the duodenum. Do you have an accompanying hepatic branch of the left gastric artery?

On the posterior border of the lesser curvature locate gastric branches of the posterior vagal trunk. Trace to the esophagus, noting relationships. Locate the celiac branch and trace to the celiac plexus. Consider distribution and function of the vagus nerve. How do sympathetic branches distribute to the stomach?

Organize the mesenteries of the stomach, considering their contents and functional importance to the stomach.

7. Expose the duodenum and pancreas and define their parts. (Play movie; View images: N 268, 270A, 270B, 272, 273, 274, 278, 298, 300, 301, 302, 304, 305, 329, TG 5-14, 5-18, 5-19, 5-26A, 5-26B, 5-26C, 5-27B, 5-27C)

Review the development of the duodenum and pancreas. Determine the manner in which they become secondarily retroperitoneal and fixed by the attachments of the transverse mesocolon and the mesentery.

Review, with the aid of your atlas, the structures that are retroperitoneal and overlain by the pancreas and duodenum (aorta, inferior vena cava, kidneys, ureters, portal vein, etc.).

If not done previously, cut through the attachment of the gastrocolic ligament to the transverse colon (preserving the gastro-omental arteries along the greater curavture of the stomach) and turn the stomach up, exposing the posterior wall of the omental bursa. Trace the attachment of the transverse mesocolon across the duodenum and pancreas. Note which parts of the pancreas and duodenum constitute boundaries of the omental bursa and which parts are below or outside. Locate the tail of the pancreas and note that it and the splenic artery and vein are within the splenorenal (lienorenal) ligament. Note the manner in which the mesentery attaches to the fourth (ascending) part of the duodenum. Observe how this placement allows the superior mesenteric artery and vein to enter the root of the mesentery after crossing the third part of the duodenum.

Remove these mesenteric attachments and clear the surface of the duodenum and pancreas.

Duodenum. Observe the 4 subdivisions of the duodenum, their vertebral levels, the peritoneal and visceral relations of each. Is the first part peritoneal or retroperitoneal? Why? What is the suspensory muscle of the duodenum (ligament of Treitz)? Identify the retroduodenal fossa and paraduodenal fold. Find the inferior mesenteric vein within the paraduodenal fold. What is the relation of the horizontal (3rd) part of the duodenum to the superior and inferior mesenteric arteries?

Duodenum

Pancreas. Identify uncinate process, head, neck, body and tail, and review position and visceral relations. Specifically note relations to celiac trunk, superior mesenteric artery and vein, splenic artery and vein, and the bile duct.

Pancreatic cancer

The vasculature of the pancreas and duodenum is so arranged that it may be considered common to both. Arteries are derived from the celiac trunk, the superior mesenteric artery, and arcades formed between. The vessels are delicate. Dissect with care. Locate and trace the gastroduodenal artery. Continue tracing to its branching into the right gastro-omental and the anterior superior pancreaticoduodenal artery. Note that it lies between the duodenum and pancreas. Passing deep to a part of the head of the pancreas it becomes continuous with the anterior inferior pancreaticoduodenal artery. Trace the latter to the common stem, the inferior pancreaticoduodenal from the superior mesenteric artery. This completes the anterior arcade. Examine the arteriae rectae off the arcade.

8. Incise the peritoneum at the right border of the duodenum and reflect it medially. Identify the arterial supply to the pancreas and duodenum. (Play movie; View images: N 295, 301, 302, 304A, 304B, 305, 309, 311, 312, TG 5-24, 5-26, 5-27B, 5-27C, 5-28)

Now incise the peritoneum along the right border of the second part of the duodenum. Reflect the duodenum and pancreas toward the mid-line in the plane of the fusion fascia (explain). Carefully trace the bile duct as it courses behind the first part of the duodenum and the head of the pancreas to the medial wall of the second part of the duodenum. Does an artery cross it? This artery is usually the first branch from the gastroduodenal artery and is the posterior superior pancreaticoduodenal. Trace to its source and then across the bile duct and head of the pancreas to become continuous with the posterior inferior pancreaticoduodenal. Trace to its source. How does this posterior arcade differ from the anterior?

Locate the splenic artery as it leaves the celiac trunk. Trace along the pancreas, noting multiple small pancreatic and, in the region of the tail, small caudal pancreatic branches. A large branch near the beginning of the splenic artery, the dorsal pancreatic artery, passes dorsal to the pancreas, continues to the inferior border of the pancreas and divides into 1) a left branch (the inferior pancreatic artery) and 2) a right branch (which crosses ventral to the head to unite with a left branch of the anterior superior pancreaticoduodenal artery as the prepancreatic arcade). Do you find veins with the arteries?

9. Trace the splenic vein to its junction with the superior mesenteric vein and the formation of the portal vein. (Play movie; View images: N 266, 311, 312, 313, 314, 317, TG 5-27, 5-28, 5-35A, 5-35B, 5-37)

Trace the splenic vein; note relations to splenic artery and pancreas. Does it receive the inferior mesenteric vein? Note junction with superior mesenteric vein and the point of formation of the portal vein.

CT of pancreas Portal venous system

Look for lymph nodes: pyloric, pancreaticosplenic, celiac and hepatic and consider lymph drainage. Organize with the lymph drainage of the stomach.

10. Incise the duodenum and examine its interior including the papillae and folds. (Play movie; View images: N 276, 279, 279, 281, 290, 295, 297, 300, 304, 317, 319, 320, 322, 346, TG 5-19A, 5-19B, 5-24B, 5-24C, 5-26, 5-27, 5-35, 5-42)

Cut open the duodenum in its first and second parts. Observe the pyloric sphincter, the smooth first part, and the circular folds of the second. Locate the greater duodenal papilla, a visible protrusion of the mucosa on the posteromedial wall of the descending part of the duodenum. Do you find a lesser duodenal papilla? Differences?

Lift the first and second parts of the duodenum and associated pancreas to the left and trace the bile duct caudally to the dorsal side of the pancreas and to its termination in the duodenum (which part? ). Explore the termination of the bile duct and the main pancreatic duct in the greater duodenal papilla. These two ducts may open independently on the papilla, but they often unite within the duodenal wall to form a dilation called the hepatopancreatic ampulla (of Vater) (within the papilla). Note nerve plexus and lymph nodes along the structures of the hepatoduodenal ligament. Examine the portal vein and epiploic foramen. Where is the inferior vena cava?

11. Expose pancreatic ducts on the posterior aspect of the pancreas. (Play movie; View images: N 278, 279, 294, 298, 301, 302, 304A, 304B, TG 5-24, 5-26, 5-27B, 5-27C)

On the posterior aspect of the head of the pancreas, follow the bile duct to the wall of the duodenum. From this point, dissect away pancreatic tissue to find the main pancreatic duct and follow it into the body of the pancreas. Note that it lies closer to the dorsal than to the ventral surface of the pancreas. Do you have an accessory pancreatic duct? A large pancreatic artery that arises from the splenic artery and enters the pancreas, accompanying the pancreatic duct, is the great pancreatic artery.