Lab Manual - Peritoneal Cavity & Intestines

Assignments:

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 subdivisions, mesenteries, and ligaments.
  2. Describe the basic anatomy of the large and small intestines, including neurovascular supply and lymphatic drainage.
  3. Know the pattern of diaphragmatic musculature and its fasciae, and its functional significance in respiration.
  4. Know the three major passageways through the diaphragm and the structures traversing them.
  5. Describe the position and vertebral level for all branches of the abdominal aorta and the inferior vena cava, and the reason for the difference in their patterns.
  6. Identify the thoracic and lumbar splanchnic nerves and the collateral ganglia or regional subdivisions of the preaortic plexus to which each functionally relates.
  7. Recall the concept of perivascular plexuses, their position, nomenclature, and nerve fiber components.
  8. Describe the parasympathetic innervation of the GI tract.
  9. Identify the cisterna chyli and describe the general pattern of lymphatic drainage to the thoracic duct.
  10. Identify and demonstrate the abdominal attachments of the two major posterior abdominal wall muscles and know the action of these muscles upon the vertebral column.
  11. Locate the lumbar sympathetic trunk and white and gray rami communicantes; explain the reason for the inferior limit of the white rami.
  12. Describe the four common locations of porto-caval anastomosis.

Procedure:

1. Review the bony landmarks of the abdominal cavity. (Play movie; 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 entitled Peritoneal Cavity Development.

2. 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, 301, 306, 336, 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

3. 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, 300, 301, 302, 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.

4. 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.

5. Examine the jejunum, large bowel, cecum, and ileocecal valve and examine their interiors on plastinated specimens. (Play movie; View images: N 272, 282A, 282B, 284, TG 5-15, 5-16)

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

Also using the specimen provided, examine the ileocecal junction of the large intestine to examine labia of the ileocecal valve.

5. Clean and examine the diaphragm, its parts, apertures and the nerves, vessels and other structures passing through or behind it. (Play movie; View images: N 193, 194, 195, 253, 263, 267, 270, TG 5-07, 5-33, 5-38)

Review the thoracic and abdominal relations of the diaphragm. Consider its shape and attachments. Strip the peritoneum from its abdominal surface. Examine the fascia (transversalis) lining it. Trace to the posterior wall and identify the median, medial, and lateral arcuate ligaments. Note their relationship to the aorta, psoas major and minor, and quadratus lumborum muscles. How are these ligaments formed? Verify their bony attachments. Now strip the fascia from the diaphragm determining muscle fibers of sternal, costal and lumbar origins (medial and lateral arcuate ligaments). Clear and identify the central tendon. Elevate the kidney with its renal vessels and fat; now trace the crura of the diaphragm from the lumbar vertebrae to the central tendon, noting formation of the aortic hiatus (T12) and the esophageal hiatus (T10). Note the degree to which fibers of the two crura contribute to their formation. What is the lumbocostal trigone? Significance? Trace the phrenic nerves through the diaphragm and examine their distribution on the inferior surface. Are there other innervations? Examine the caval hiatus (T8). What are the differences in the formation and the structures transmitted by each diaphragmatic hiatus? What are the average vertebral levels of each?

Diaphragm
Left and right crura of the diaphragm

6. Examine the preaortic autonomic nerve plexuses of the abdomen and the branches of the abdominal aorta. (Play movie; View images: N 195, 209, 266, 267, 318, 319, 322, 323, 344, TG 5-34, 5-37, 5-38, 5-39, 8-16, 8-17)

Examine the pre-aortic autonomic plexuses of the abdomen, beginning with the celiac ganglia and celiac plexus. Define each and note arrangement around the celiac trunk. Trace the greater thoracic splanchnic nerve through the crus of the diaphragm to the celiac ganglion. Also locate the celiac branches of the posterior vagal trunk as they join the plexus. Significance? These structures are easier to see if the kidney is reflected medially with any fat remaining around it. Define the aorticorenal ganglion. Trace the lesser thoracic splanchnic nerve to its termination. Trace the celiac plexus to the superior mesenteric artery. Is there a superior mesenteric ganglion here? Now trace the intermesenteric plexus on the aorta to the inferior mesenteric artery. Is there an inferior mesenteric plexus here? Ganglia? Define and trace the superior hypogastric plexus. Complete the dissection of the thoracic splanchnic nerves by cutting through the diaphragm on the left side to each of the nerves and exposing their complete course (thoracic and abdominal). With the left crus of the diaphragm fragmented or removed, trace the thoracic sympathetic trunk into the abdomen noting change in location. How does it get into the abdomen? Trace the lumbar sympathetic trunk until it disappears behind the common iliac artery. Locate and identify the lumbar ganglia and the lumbar splanchnic nerves. How many splanchnic nerves are there? What part of the preaortic plexus do they join? At this time organize the autonomic distribution to the abdominal viscera. How is this distribution completed from the structures you have seen today?

Examine the abdominal aorta completely, locating place and level of entrance to abdomen, point and level of bifurcation, course, relations, branches, and vertebral levels of each. Now locate an example of the lumbar segmental arteries and the median sacral artery. How do these compare with the thoracic segmental vessels? Slit open the aorta and examine its posterior wall noting the manner in which the segmental vessels leave the aorta.

Trace the inferior vena cava from its formation from the union of the common iliac veins, noting course and relations to the aorta and viscera throughout the abdomen. Review tributaries throughout, including the right gonadal, renal, and right suprarenal veins. Now identify an example of the lumbar segmental veins. Do all terminate in the vena cava?

Note the lumbar lymph nodes located to the left of the abdominal aorta and around the inferior vena cava. What is the source of the afferent drainage of the lumbar lymph trunks and the intestinal lymph trunk? Examine the origin of the thoracic duct at the right of the aorta in the aortic hiatus. What is the cisterna chyli? Organize the parietal and visceral lymph drainage of the abdomen.

7. Fragment and remove the left psoas major (and minor if present) and examine the lumbar plexus of nerves and white and gray rami of the lumbar sympathetic trunk. (Play movie; View images: N 160, 263, 264, 265, 267, 491, 497, 498, 538, TG 5-33, 5-38, 5-38, 5-40, 5-41, 5-38, 3-25, 5-38, 5-38, 5-38, 5-38, 5-38, 5-33, 5-33, 3-13, 5-38, 3-63, 5-34, 5-34, 5-08, 5-37)

Clean the psoas major muscle and psoas minor, if you have one, as far as the inguinal ligament. Now fragment the left psoas muscle and remove, identifying the rami communicantes between the lumbar sympathetic trunk and the lumbar segmental nerves. How do you distinguish between the white and gray rami? How many white rami are there? Why?

With the left psoas muscle fragmented and removed, identify the lumbar segmental nerves and the resulting lumbar plexus of nerves. These nerves all have specific relationships to the psoas major and iliacus muscles, making them easier to identify. Identify and note course and relations of the subcostal, iliohypogastric, ilioinguinal, genitofemoral, lateral femoral cutaneous, femoral and obturator nerves. Trace only as far as the inguinal ligament. Clean the quadratus lumborum and iliacus muscles and note their relationships.

Psoas muscle

Identify the iliacus muscle in the iliac fossa and trace it along with the remains of psoas major to the inguinal ligament. Follow them into the thigh as the iliopsoas, noting its insertion and innervation. To what group of muscles does it belong? What are the actions of these muscles?

Identify the external iliac vessels as they pass beneath the inguinal ligament. Medial to the external iliac vein is the femoral ring. What ligaments surround it on three sides? Do you find a deep inguinal node within the femoral ring? Recall that the femoral ring is the abdominal opening of the femoral canal.