Dissector Answers - Stomach & Spleen

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.

Learning Objectives and Explanations:

1. Identify the parts of the stomach and describe its spatial relationships to surrounding organs and mesenteries. (W&B 448-450, N 260,264,265,267 or TG 5-01,5-18A, 5-18B)

Parts:

Curvatures:

Orientation and relationships:

The plane of the stomach is oblique, running from the fundus to the pylorus inferiorly, ventrally, and to the right. It has, then, effectively an anterior and a posterior surface. The left anterior surface contacts the diaphragm and the abdominal wall, while on the right side the anterior surface lies against the liver. The posterior surface of the stomach forms the anterior wall of the omental bursa. The stomach is almost entirely covered in peritoneum, except where vessels run along the curvatures and where the peritoneum reflects to form ligaments, or attachments to other viscera. These include the hepatogastric ligament from the lesser omentum, and the gastrophrenic, gastrosplenic, and gastrocolic ligaments from the greater omentum.

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. (W&B 451-456, N 258,290,291,292,304,307 or TG 5-19,5-27,5-35A,5-35B, TG5-37)

There are three branches of the celiac trunk:

Looking at things the other way around, the stomach is supplied by:

The lymphatic drainage of the stomach is a bit complex. Lymph from the stomach goes towards one or the other of the curvatures, draining to four main areas:

Towards lesser curvature:

  • left gastric nodes: afferents to these drain a large portion of the stomach. Efferents from here follow the left gastric blood vessels and go to the celiac nodes.
  • right gastric nodes: drain a small portion of the pylorus. Efferents go to hepatic nodes, eventually dumping into celiac nodes.
Towards greater curvature:

  • pancreaticosplenic nodes: drain the spleen, pancreas, and the left fundus and body of the stomach. They send lymph to the celiac nodes.
  • right gastro-omental nodes: drain the body and pyloric portion of the stomach. Efferents go from here to the pyloric nodes, then the hepatic nodes, and finally the celiac nodes.

In a nutshell, lymph goes toward one of the curvatures and eventually ends up in the celiac nodes. There are no "left gastro-omental nodes".

3. Describe the anatomy of the foregut peritoneal ligaments, omenta, and omental bursa. Describe their development from the embryological ventral and dorsal mesogastria. (W&B 436-443, N 261,264,267,279 or TG 5-12,5-18A,5-18B,5-21, Learning Module)

It is logical here to consider the development first. Initially the entire primordial gut tube is suspended in the center of the abdominal cavity by a "dorsal common mesentery", which is attached to the midline of the posterior body wall. As development progresses, a portion of the tube begins to enlarge into a stomach. From this point on, the attachments of the stomach to the body wall are called the ventral mesogastrium (ventral mesentery) and the dorsal mesogastrium (dorsal mesentery). The spleen and dorsal pancreas develop in the dorsal mesogastrium. Therefore, structures involving the spleen and the posterior part of the developing stomach (which becomes left and inferior), are derived from the dorsal mesogastrium. These include:

The liver begins to develop in the ventral mesogastrium, so structures involving the liver and its attachment to both the stomach and the body wall come from the ventral mesogastrium. These include:

Now we can think about the anatomy. (Come on... I know you want to!) As you've probably figured out by now, the relationships of the abdominal viscera can be very confusing as a result of that whole umbilical herniation and 270-degree rotation during development. Remember the descriptions of how things started, with the gut tube attached to the gut wall via the primitive mesentery. From there, the final relationships are only a gut rotation away.

Greater omentum: This started as a connection between the posterior stomach and the posterior abdominal wall. The stomach rotates such that what was the posterior surface becomes more left and inferior. Part of this original connection remains as the gastrophrenic ligament. Furthermore, by now the colon has done all of its business and the transverse colon is sitting there, right underneath the stomach, and has its own attachment to the posterior abdominal wall. The greater omentum grows a great deal, becoming the big "abdominal policeman" (omental apron) that we all know and love. "But, how does the stomach end up connected to the transverse colon via the gastrocolic ligament?" you ask. The greater omentum ends up draped over the transverse colon and the transverse mesocolon, and ends up fusing with both. This fusion effectively creates the gastrocolic ligament by connecting the stomach to the transverse colon. (See #5 below.) The spleen develops within the dorsal mesogastrium, between the stomach and the body wall. The tissue between the stomach and the spleen remains as the gastrosplenic ligament.

Lesser omentum: It started as the connection between the anterior stomach and the anterior body wall. As the stomach rotates, what was anterior becomes right and superior. At the same time, the liver is developing between the stomach and the body wall, within this ventral section of peritoneum. The liver ends up being huge, so when all is said and done, all of the former connection between the stomach and the ventral body wall is connection between the stomach (including part of the duodenum) and the liver, the hepatogastric and hepatoduodenal ligaments. All of the rest of the tissue, that is, what was between the liver and the body wall, ends up as the ligaments of the liver: the falciform, coronary, right triangular, and left triangular ligaments.

To get a good idea of what is going on with all of the "twisting around", check out the several gut rotation movies in Animations.

4. Describe the pattern of parasympathetic innervation of the GI tract. (W&B 456-457 (stomach), 465-466 (duodenum), 482 (SI), 488 (LI), N 228,309,310,311,314B or TG 8-17, TG8-21)

Parasympathetic innervation to most of the GI tract, from the stomach to the splenic flexure of the colon, is originally from the vagus nerves (CN X). Along the way they will form various plexuses and then reorganize into nerves, but it is all vagus derived. (For example, after the esophageal plexus, fibers come back together to form the anterior and posterior vagal trunks, which supply the stomach and other viscera.) For the portions of the colon distal to the splenic flexure, the parasympathetic innervation is from S2-S4, via the pelvic splanchnic nerves and the inferior hypogastric plexus. (Recall that arterial blood supply to the colon also had a "transition" at the splenic flexure.)

Cultural enrichment: Check out these sections from the 1918 version of Gray's Anatomy of the Human Body! Some of the terms are (of course) out-of-date, but the illustrations are timeless.

The Stomach - The Spleen - The Abdominal Aorta - Surface Anatomy of the Abdomen -Surface Markings of the Abdomen

Questions and Answers:

5. Examine how the greater omentum has combined with and assists in the formation of the transverse mesocolon. (N 261,263,264, TG 5-12,5-18)

"The layers [of the omental apron] returning from the fold to the body wall lie against the transverse colon and the superior layer of its mesocolon, and these opposed parts fuse. Thus, the inferior extension of the greater omentum becomes the gastrocolic ligament and helps form the transverse mesocolon."

6. Define the omental bursa (lesser sac). How does it develop? What is its entrance? What are its boundaries? (N 264,265,335,336, TG 5-18,5-42)

The omental bursa is a space that exists between the stomach and the posterior wall of the abdominal cavity. It gives the stomach room to expand after a meal. It is created by the rotation of the stomach during development so that the greater curvature faces left (and inferiorly) and the lesser curvature faces right (and superiorly). The growth of the liver helps to define the borders of the omental bursa. Your fingers can be stuck into the space through the omental foramen. The boundaries of the omental bursa are as follows:

7. 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? (N 290, TG 5-19)

Yes, the right gastric anastomoses with the left.

8. Does the left gastro-omental artery anastomose with the right? (N 290, TG 5-19)

You bet.

9. How does the splenic artery reach the spleen? How do its branches reach the stomach? (Note relations to stomach, kidney and left colic (splenic) flexure.) (N 291, TG 5-19)

The course of the splenic artery from the celiac trunk to the spleen is very tortuous. Along the way, it is partially embedded in the superior part of the pancreas, and therefore more or less runs in the floor of the omental bursa. It passes through the splenorenal ligament, dividing into several branches to supply the spleen. Near its end, the splenic artery gives off the left gastro-omental artery, which supplies the greater curvature of the stomach and anastomoses with the right gastro-omental artery. It also gives off four or five short gastric branches, which supply some blood to the fundus of the stomach. They anastomose with both the left gastric and the left gastro-omental arteries.

10. What is the coronary vein? (N 299, 302, TG 5-19, 5-28)

The coronary vein is the circular venous structure formed by the anastomoses of the right and left gastric veins. Its circular course along the lesser curvature is said to crown the stomach, hence its name.

11. Organize the lymph drainage of the stomach and spleen. (N 258, 304, 307, TG 5-37, 5-35, 5-35)

See #2 above.

12. Look for a hepatic branch of the anterior vagal trunk 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? (N 309, 310)

The anterior vagal trunk sends branches to the stomach and liver, usually with an extension of this hepatic branch going down to the duodenum. The posterior vagal trunk also branches to stomach, but has no hepatic branch. It also branches to the celiac ganglion.

13. Consider distribution and function of the vagus nerve. (N 228, 309, 310, 311, TG 4-37)

See #4 above.

14. How do sympathetic branches distribute to the stomach? (N 205, 310, 311, TG 4-38)

Well, if you stumble across a ferocious bear, your stomach should take a break. This allows energy and oxygen to be used for that panic-induced sprint you are about to undertake. So, sympathetic innervation is essential. It is provided from T5-T9 via the greater thoracic splanchnic nerve, to the celiac ganglion and plexus.

15. Organize the mesenteries of the stomach, considering their contents and functional importance to the stomach. (N 261, 264, 267, TG 5-12, 5-18, 5-18)

See #3 above.