Lab Manual - Peritoneal Cavity & Intestines

Learning Objectives:

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

  1. Describe the basic organization of the peritoneum and peritoneal cavity, including subdivions, mesenteries, and ligaments. (explanation)
  2. Describe the organization of the digestive tract and its parts. (explanation)
  3. Describe the basic anatomy of the large and small intestines, including blood supply and internal structure. (explanation)

Readings and Modules:

Procedure:

1. Review the bony landmarks of the abdominal cavity. (View images: N 157, 248, 268, 486A, 486B, TG 1-08, 3-04, 3-05, 5-01, 5-03)

On the skeleton identify the boundaries of the abdominopelvic cavity. Define the plane of the pelvic inlet: sacral promontory, ala of the sacrum, iliopectineal line (same as arcuate plus pectineal lines), pubic body, pubic symphysis. Note specifically the lumbar vertebrae, their characteristics and relations to the abdominal cavity.

Bony structures of the abdomen

The relationships of the intestines and other abdominal organs are best understood in relation to their embryonic development. This should be reviewed in the learning module or by looking at the animation available online.

2. Expose the abdominal organs by making a midline vertical incision. (Play movie; View images: N 247, 260, TG 5-01, 5-06B, 5-06C)

Make a midline vertical incision from the xiphoid process toward the umbilicus, skirting just to the left side of the subject's umbilicus and continuing down through the rest of upper abdominal wall flap created in the previous dissections. Review the layers of the anterior abdominal wall, paying special attention to the peritoneum, extraperitoneal connective tissue, and transversalis fascia. Find the falciform ligament passing from the deep surface of the anterior abdominal wall to the right onto the liver.

3. Examine the abdominal contents, identifying organs, mesenteries, and their relationships. (Play movie; View images: N 269A, 269B, 270A, 270B, 271, 273, 274, 280A, 280B, 281A, 281C, 284, 310, 306, 331, 348, 349, TG 5-12A, 5-12B, 5-13, 5-14, 5-15, 5-16B, 5-16C, 5-29, 5-31, 5-42, 5-43)

Examine the abdominal cavity and its lining peritoneum. Define parietal and visceral layers, mesentery, peritoneal and retroperitoneal structures. Differentiate between abdominal and peritoneal cavities. Locate the liver, stomach, gastrocolic ligament, gastrosplenic ligament, splenorenal ligament,omental apron, small and large intestine.

Abdominal organs

Now consider the peritoneal relationships of the lower abdominal viscera. Examine the small intestine (jejunoileum), exploring its whole length. Locate the duodenojejunal flexure, at L1-L2. Identify the retroduodenal fossa and paraduodenal fold (containing the inferior mesenteric vein). Locate the ileocecal junction (level? ). Differentiate between jejunum and ileum. Examine "THE" mesentery (of jejunum and ileum), noting its body wall attachment. How long is this attachment? Read about the structures that are crossed by this line of attachment. Review the development of "the" mesentery from the primitive dorsal mesentery. What is the location of the small intestine in the peritoneal cavity?

Small intestine Jejunum and ileum Abdominal CT

Examine the large intestine; define cecum, appendix, ascending colon, right colic (hepatic) flexure, transverse colon, left colic (splenic) flexure, descending colon, sigmoid colon. Note the characteristics that define and distinguish the large intestine: teniae coli, haustra (sacculations), and omental (epiploic) appendages. What parts of the large intestine are peritoneal; what parts retroperitoneal? Demonstrate the anterior cecal fold (vascular), ileocecal fold, mesentery of the appendix (mesoappendix), transverse mesocolon, sigmoid mesocolon. Consider the derivation of these mesenteries and the rotation of the gut in development. Why are some parts peritoneal or retroperitoneal? What happens to the primitive mesentery of the retroperitoneal part of the large intestine? Define fusion fascia. What is its significance?

Barium enema of sigmoid colon Abdominal CT Abdominal CT

4. Remove the peritoneum from the right side of the mesentery to expose and identify the superior mesenteric artery and vein and their branches. (Play movie; View images: N 264, 280A, 280B, 281, 310, 311, 312, 306, 307, TG 5-13, 5-14, 5-15, 5-16B, 5-16C, 5-28, 5-34)

Pull the small intestine to the left side of the peritoneal cavity. Beginning at the root of the mesentery, use your fingers to strip the peritoneum from the right side of the mesentery. Expose and explore intestinal arteries (jejunal & ileal), arcades, arteriae rectae. Note differences throughout length of small intestine. Expose the superior mesenteric artery at the root of the mesentery. Where does it terminate? What is the relation of the superior mesenteric vein and its branches?

CT of superior mesenteric artery

Strip away the posterior body wall peritoneum, exposing the vessels to the cecum, appendix and ascending colon: ileocolic artery (anterior cecal, appendicular, ileal, and colic branches), right colic artery (ascending and descending branches, anastomoses). Find the middle colic artery and its branches in the transverse mesocolon.

5. Remove the posterior body wall peritoneum to expose the inferior mesenteric vessels. (Play movie; View images: N 266, 306, 307, 308, 310, 311, 312, 316, 317, TG 5-13, 5-14A, 5-14B, 5-28, 5-36A, 5-36B, 5-37)

Carefully strip away just the posterior body wall peritoneum leading to the descending colon and the right peritoneal layer of the sigmoid mesocolon. Expose the inferior mesenteric artery, left colic artery (ascending and descending branch), and sigmoid arteries. Identify the superior rectal artery but do not trace. Is there a separate ascending branch of the left colic artery accompanying the inferior mesenteric vein? Examine the arteriae rectae of the large intestine. How do they differ from those of the small intestine? What constitutes the marginal artery?

CT of inferior mesenteric artery

Examine the superior and inferior mesenteric veins. Note differences in course of drainage.

Look for lymph nodes in the mesentery and along the vessels of the large intestine. Organize groupings and drainage. Identify lymph channels, if possible.

6. Examine the jejunum, large bowel, cecum, and ileocecal valve and examine their interiors on plastinated specimens. (Play movie; View images: N 280, 282A, 282B, 284, TG 5-15, 5-16)

Using the plastinated jejunum specimens provided, examine circular folds. Examine the plastinated segment of the transverse colon, and note semilunar folds of the large intestine.

Also using plastinated specimens, examine the ileocecal junction of the large intestine to examine labia of the ileocecal valve.

 

Updated: 04 January 2012